Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1 | ============================ |
| 2 | Kernel Key Retention Service |
| 3 | ============================ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 4 | |
| 5 | This service allows cryptographic keys, authentication tokens, cross-domain |
| 6 | user mappings, and similar to be cached in the kernel for the use of |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 7 | filesystems and other kernel services. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 8 | |
| 9 | Keyrings are permitted; these are a special type of key that can hold links to |
| 10 | other keys. Processes each have three standard keyring subscriptions that a |
| 11 | kernel service can search for relevant keys. |
| 12 | |
| 13 | The key service can be configured on by enabling: |
| 14 | |
| 15 | "Security options"/"Enable access key retention support" (CONFIG_KEYS) |
| 16 | |
| 17 | This document has the following sections: |
| 18 | |
| 19 | - Key overview |
| 20 | - Key service overview |
| 21 | - Key access permissions |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 22 | - SELinux support |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 23 | - New procfs files |
| 24 | - Userspace system call interface |
| 25 | - Kernel services |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 26 | - Notes on accessing payload contents |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 27 | - Defining a key type |
| 28 | - Request-key callback service |
David Howells | 5d13544 | 2009-09-02 09:14:00 +0100 | [diff] [blame] | 29 | - Garbage collection |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 30 | |
| 31 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 32 | Key Overview |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 33 | ============ |
| 34 | |
| 35 | In this context, keys represent units of cryptographic data, authentication |
| 36 | tokens, keyrings, etc.. These are represented in the kernel by struct key. |
| 37 | |
| 38 | Each key has a number of attributes: |
| 39 | |
| 40 | - A serial number. |
| 41 | - A type. |
| 42 | - A description (for matching a key in a search). |
| 43 | - Access control information. |
| 44 | - An expiry time. |
| 45 | - A payload. |
| 46 | - State. |
| 47 | |
| 48 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 49 | * Each key is issued a serial number of type key_serial_t that is unique for |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 50 | the lifetime of that key. All serial numbers are positive non-zero 32-bit |
| 51 | integers. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 52 | |
| 53 | Userspace programs can use a key's serial numbers as a way to gain access |
| 54 | to it, subject to permission checking. |
| 55 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 56 | * Each key is of a defined "type". Types must be registered inside the |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 57 | kernel by a kernel service (such as a filesystem) before keys of that type |
| 58 | can be added or used. Userspace programs cannot define new types directly. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 59 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 60 | Key types are represented in the kernel by struct key_type. This defines a |
| 61 | number of operations that can be performed on a key of that type. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 62 | |
| 63 | Should a type be removed from the system, all the keys of that type will |
| 64 | be invalidated. |
| 65 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 66 | * Each key has a description. This should be a printable string. The key |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 67 | type provides an operation to perform a match between the description on a |
| 68 | key and a criterion string. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 69 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 70 | * Each key has an owner user ID, a group ID and a permissions mask. These |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 71 | are used to control what a process may do to a key from userspace, and |
| 72 | whether a kernel service will be able to find the key. |
| 73 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 74 | * Each key can be set to expire at a specific time by the key type's |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 75 | instantiation function. Keys can also be immortal. |
| 76 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 77 | * Each key can have a payload. This is a quantity of data that represent the |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 78 | actual "key". In the case of a keyring, this is a list of keys to which |
| 79 | the keyring links; in the case of a user-defined key, it's an arbitrary |
| 80 | blob of data. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 81 | |
| 82 | Having a payload is not required; and the payload can, in fact, just be a |
| 83 | value stored in the struct key itself. |
| 84 | |
| 85 | When a key is instantiated, the key type's instantiation function is |
| 86 | called with a blob of data, and that then creates the key's payload in |
| 87 | some way. |
| 88 | |
| 89 | Similarly, when userspace wants to read back the contents of the key, if |
| 90 | permitted, another key type operation will be called to convert the key's |
| 91 | attached payload back into a blob of data. |
| 92 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 93 | * Each key can be in one of a number of basic states: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 94 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 95 | * Uninstantiated. The key exists, but does not have any data attached. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 96 | Keys being requested from userspace will be in this state. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 97 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 98 | * Instantiated. This is the normal state. The key is fully formed, and |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 99 | has data attached. |
| 100 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 101 | * Negative. This is a relatively short-lived state. The key acts as a |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 102 | note saying that a previous call out to userspace failed, and acts as |
| 103 | a throttle on key lookups. A negative key can be updated to a normal |
| 104 | state. |
| 105 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 106 | * Expired. Keys can have lifetimes set. If their lifetime is exceeded, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 107 | they traverse to this state. An expired key can be updated back to a |
| 108 | normal state. |
| 109 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 110 | * Revoked. A key is put in this state by userspace action. It can't be |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 111 | found or operated upon (apart from by unlinking it). |
| 112 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 113 | * Dead. The key's type was unregistered, and so the key is now useless. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 114 | |
David Howells | 5d13544 | 2009-09-02 09:14:00 +0100 | [diff] [blame] | 115 | Keys in the last three states are subject to garbage collection. See the |
| 116 | section on "Garbage collection". |
| 117 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 118 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 119 | Key Service Overview |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 120 | ==================== |
| 121 | |
| 122 | The key service provides a number of features besides keys: |
| 123 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 124 | * The key service defines three special key types: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 125 | |
| 126 | (+) "keyring" |
| 127 | |
| 128 | Keyrings are special keys that contain a list of other keys. Keyring |
| 129 | lists can be modified using various system calls. Keyrings should not |
| 130 | be given a payload when created. |
| 131 | |
| 132 | (+) "user" |
| 133 | |
| 134 | A key of this type has a description and a payload that are arbitrary |
| 135 | blobs of data. These can be created, updated and read by userspace, |
| 136 | and aren't intended for use by kernel services. |
| 137 | |
Jeff Layton | a05a483 | 2012-04-25 12:46:50 -0400 | [diff] [blame] | 138 | (+) "logon" |
| 139 | |
| 140 | Like a "user" key, a "logon" key has a payload that is an arbitrary |
| 141 | blob of data. It is intended as a place to store secrets which are |
| 142 | accessible to the kernel but not to userspace programs. |
| 143 | |
| 144 | The description can be arbitrary, but must be prefixed with a non-zero |
| 145 | length string that describes the key "subclass". The subclass is |
| 146 | separated from the rest of the description by a ':'. "logon" keys can |
| 147 | be created and updated from userspace, but the payload is only |
| 148 | readable from kernel space. |
| 149 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 150 | * Each process subscribes to three keyrings: a thread-specific keyring, a |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 151 | process-specific keyring, and a session-specific keyring. |
| 152 | |
| 153 | The thread-specific keyring is discarded from the child when any sort of |
| 154 | clone, fork, vfork or execve occurs. A new keyring is created only when |
| 155 | required. |
| 156 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 157 | The process-specific keyring is replaced with an empty one in the child on |
| 158 | clone, fork, vfork unless CLONE_THREAD is supplied, in which case it is |
| 159 | shared. execve also discards the process's process keyring and creates a |
| 160 | new one. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 161 | |
| 162 | The session-specific keyring is persistent across clone, fork, vfork and |
| 163 | execve, even when the latter executes a set-UID or set-GID binary. A |
| 164 | process can, however, replace its current session keyring with a new one |
| 165 | by using PR_JOIN_SESSION_KEYRING. It is permitted to request an anonymous |
| 166 | new one, or to attempt to create or join one of a specific name. |
| 167 | |
| 168 | The ownership of the thread keyring changes when the real UID and GID of |
| 169 | the thread changes. |
| 170 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 171 | * Each user ID resident in the system holds two special keyrings: a user |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 172 | specific keyring and a default user session keyring. The default session |
| 173 | keyring is initialised with a link to the user-specific keyring. |
| 174 | |
| 175 | When a process changes its real UID, if it used to have no session key, it |
| 176 | will be subscribed to the default session key for the new UID. |
| 177 | |
| 178 | If a process attempts to access its session key when it doesn't have one, |
| 179 | it will be subscribed to the default for its current UID. |
| 180 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 181 | * Each user has two quotas against which the keys they own are tracked. One |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 182 | limits the total number of keys and keyrings, the other limits the total |
| 183 | amount of description and payload space that can be consumed. |
| 184 | |
| 185 | The user can view information on this and other statistics through procfs |
David Howells | 0b77f5b | 2008-04-29 01:01:32 -0700 | [diff] [blame] | 186 | files. The root user may also alter the quota limits through sysctl files |
| 187 | (see the section "New procfs files"). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 188 | |
| 189 | Process-specific and thread-specific keyrings are not counted towards a |
| 190 | user's quota. |
| 191 | |
| 192 | If a system call that modifies a key or keyring in some way would put the |
| 193 | user over quota, the operation is refused and error EDQUOT is returned. |
| 194 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 195 | * There's a system call interface by which userspace programs can create and |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 196 | manipulate keys and keyrings. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 197 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 198 | * There's a kernel interface by which services can register types and search |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 199 | for keys. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 200 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 201 | * There's a way for the a search done from the kernel to call back to |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 202 | userspace to request a key that can't be found in a process's keyrings. |
| 203 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 204 | * An optional filesystem is available through which the key database can be |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 205 | viewed and manipulated. |
| 206 | |
| 207 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 208 | Key Access Permissions |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 209 | ====================== |
| 210 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 211 | Keys have an owner user ID, a group access ID, and a permissions mask. The mask |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 212 | has up to eight bits each for possessor, user, group and other access. Only |
David Howells | 29db919 | 2005-10-30 15:02:44 -0800 | [diff] [blame] | 213 | six of each set of eight bits are defined. These permissions granted are: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 214 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 215 | * View |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 216 | |
| 217 | This permits a key or keyring's attributes to be viewed - including key |
| 218 | type and description. |
| 219 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 220 | * Read |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 221 | |
| 222 | This permits a key's payload to be viewed or a keyring's list of linked |
| 223 | keys. |
| 224 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 225 | * Write |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 226 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 227 | This permits a key's payload to be instantiated or updated, or it allows a |
| 228 | link to be added to or removed from a keyring. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 229 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 230 | * Search |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 231 | |
| 232 | This permits keyrings to be searched and keys to be found. Searches can |
| 233 | only recurse into nested keyrings that have search permission set. |
| 234 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 235 | * Link |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 236 | |
| 237 | This permits a key or keyring to be linked to. To create a link from a |
| 238 | keyring to a key, a process must have Write permission on the keyring and |
| 239 | Link permission on the key. |
| 240 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 241 | * Set Attribute |
David Howells | 29db919 | 2005-10-30 15:02:44 -0800 | [diff] [blame] | 242 | |
| 243 | This permits a key's UID, GID and permissions mask to be changed. |
| 244 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 245 | For changing the ownership, group ID or permissions mask, being the owner of |
| 246 | the key or having the sysadmin capability is sufficient. |
| 247 | |
| 248 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 249 | SELinux Support |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 250 | =============== |
| 251 | |
| 252 | The security class "key" has been added to SELinux so that mandatory access |
| 253 | controls can be applied to keys created within various contexts. This support |
| 254 | is preliminary, and is likely to change quite significantly in the near future. |
| 255 | Currently, all of the basic permissions explained above are provided in SELinux |
Michael LeMay | 4eb582c | 2006-06-26 00:24:57 -0700 | [diff] [blame] | 256 | as well; SELinux is simply invoked after all basic permission checks have been |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 257 | performed. |
| 258 | |
Michael LeMay | 4eb582c | 2006-06-26 00:24:57 -0700 | [diff] [blame] | 259 | The value of the file /proc/self/attr/keycreate influences the labeling of |
| 260 | newly-created keys. If the contents of that file correspond to an SELinux |
| 261 | security context, then the key will be assigned that context. Otherwise, the |
| 262 | key will be assigned the current context of the task that invoked the key |
| 263 | creation request. Tasks must be granted explicit permission to assign a |
| 264 | particular context to newly-created keys, using the "create" permission in the |
| 265 | key security class. |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 266 | |
Michael LeMay | 4eb582c | 2006-06-26 00:24:57 -0700 | [diff] [blame] | 267 | The default keyrings associated with users will be labeled with the default |
| 268 | context of the user if and only if the login programs have been instrumented to |
| 269 | properly initialize keycreate during the login process. Otherwise, they will |
| 270 | be labeled with the context of the login program itself. |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 271 | |
| 272 | Note, however, that the default keyrings associated with the root user are |
| 273 | labeled with the default kernel context, since they are created early in the |
| 274 | boot process, before root has a chance to log in. |
| 275 | |
Michael LeMay | 4eb582c | 2006-06-26 00:24:57 -0700 | [diff] [blame] | 276 | The keyrings associated with new threads are each labeled with the context of |
| 277 | their associated thread, and both session and process keyrings are handled |
| 278 | similarly. |
| 279 | |
Michael LeMay | d720024 | 2006-06-22 14:47:17 -0700 | [diff] [blame] | 280 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 281 | New ProcFS Files |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 282 | ================ |
| 283 | |
| 284 | Two files have been added to procfs by which an administrator can find out |
| 285 | about the status of the key service: |
| 286 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 287 | * /proc/keys |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 288 | |
Michael LeMay | 06ec7be | 2006-06-26 00:24:56 -0700 | [diff] [blame] | 289 | This lists the keys that are currently viewable by the task reading the |
| 290 | file, giving information about their type, description and permissions. |
| 291 | It is not possible to view the payload of the key this way, though some |
| 292 | information about it may be given. |
| 293 | |
| 294 | The only keys included in the list are those that grant View permission to |
| 295 | the reading process whether or not it possesses them. Note that LSM |
| 296 | security checks are still performed, and may further filter out keys that |
| 297 | the current process is not authorised to view. |
| 298 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 299 | The contents of the file look like this:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 300 | |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 301 | SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY |
David Howells | 29db919 | 2005-10-30 15:02:44 -0800 | [diff] [blame] | 302 | 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4 |
| 303 | 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty |
| 304 | 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty |
| 305 | 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty |
| 306 | 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4 |
| 307 | 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 308 | 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0 |
David Howells | 29db919 | 2005-10-30 15:02:44 -0800 | [diff] [blame] | 309 | 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0 |
| 310 | 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 311 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 312 | The flags are:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 313 | |
| 314 | I Instantiated |
| 315 | R Revoked |
| 316 | D Dead |
| 317 | Q Contributes to user's quota |
Matt LaPlante | 5d3f083 | 2006-11-30 05:21:10 +0100 | [diff] [blame] | 318 | U Under construction by callback to userspace |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 319 | N Negative key |
| 320 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 321 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 322 | * /proc/key-users |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 323 | |
| 324 | This file lists the tracking data for each user that has at least one key |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 325 | on the system. Such data includes quota information and statistics:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 326 | |
| 327 | [root@andromeda root]# cat /proc/key-users |
| 328 | 0: 46 45/45 1/100 13/10000 |
| 329 | 29: 2 2/2 2/100 40/10000 |
| 330 | 32: 2 2/2 2/100 40/10000 |
| 331 | 38: 2 2/2 2/100 40/10000 |
| 332 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 333 | The format of each line is:: |
| 334 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 335 | <UID>: User ID to which this applies |
| 336 | <usage> Structure refcount |
| 337 | <inst>/<keys> Total number of keys and number instantiated |
| 338 | <keys>/<max> Key count quota |
| 339 | <bytes>/<max> Key size quota |
| 340 | |
| 341 | |
David Howells | 0b77f5b | 2008-04-29 01:01:32 -0700 | [diff] [blame] | 342 | Four new sysctl files have been added also for the purpose of controlling the |
| 343 | quota limits on keys: |
| 344 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 345 | * /proc/sys/kernel/keys/root_maxkeys |
David Howells | 0b77f5b | 2008-04-29 01:01:32 -0700 | [diff] [blame] | 346 | /proc/sys/kernel/keys/root_maxbytes |
| 347 | |
| 348 | These files hold the maximum number of keys that root may have and the |
| 349 | maximum total number of bytes of data that root may have stored in those |
| 350 | keys. |
| 351 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 352 | * /proc/sys/kernel/keys/maxkeys |
David Howells | 0b77f5b | 2008-04-29 01:01:32 -0700 | [diff] [blame] | 353 | /proc/sys/kernel/keys/maxbytes |
| 354 | |
| 355 | These files hold the maximum number of keys that each non-root user may |
| 356 | have and the maximum total number of bytes of data that each of those |
| 357 | users may have stored in their keys. |
| 358 | |
| 359 | Root may alter these by writing each new limit as a decimal number string to |
| 360 | the appropriate file. |
| 361 | |
| 362 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 363 | Userspace System Call Interface |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 364 | =============================== |
| 365 | |
| 366 | Userspace can manipulate keys directly through three new syscalls: add_key, |
| 367 | request_key and keyctl. The latter provides a number of functions for |
| 368 | manipulating keys. |
| 369 | |
| 370 | When referring to a key directly, userspace programs should use the key's |
| 371 | serial number (a positive 32-bit integer). However, there are some special |
| 372 | values available for referring to special keys and keyrings that relate to the |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 373 | process making the call:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 374 | |
| 375 | CONSTANT VALUE KEY REFERENCED |
| 376 | ============================== ====== =========================== |
| 377 | KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring |
| 378 | KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring |
| 379 | KEY_SPEC_SESSION_KEYRING -3 session-specific keyring |
| 380 | KEY_SPEC_USER_KEYRING -4 UID-specific keyring |
| 381 | KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring |
| 382 | KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring |
David Howells | b5f545c | 2006-01-08 01:02:47 -0800 | [diff] [blame] | 383 | KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key() |
| 384 | authorisation key |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 385 | |
| 386 | |
| 387 | The main syscalls are: |
| 388 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 389 | * Create a new key of given type, description and payload and add it to the |
| 390 | nominated keyring:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 391 | |
| 392 | key_serial_t add_key(const char *type, const char *desc, |
| 393 | const void *payload, size_t plen, |
| 394 | key_serial_t keyring); |
| 395 | |
| 396 | If a key of the same type and description as that proposed already exists |
| 397 | in the keyring, this will try to update it with the given payload, or it |
| 398 | will return error EEXIST if that function is not supported by the key |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 399 | type. The process must also have permission to write to the key to be able |
| 400 | to update it. The new key will have all user permissions granted and no |
| 401 | group or third party permissions. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 402 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 403 | Otherwise, this will attempt to create a new key of the specified type and |
| 404 | description, and to instantiate it with the supplied payload and attach it |
| 405 | to the keyring. In this case, an error will be generated if the process |
| 406 | does not have permission to write to the keyring. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 407 | |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 408 | If the key type supports it, if the description is NULL or an empty |
| 409 | string, the key type will try and generate a description from the content |
| 410 | of the payload. |
| 411 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 412 | The payload is optional, and the pointer can be NULL if not required by |
| 413 | the type. The payload is plen in size, and plen can be zero for an empty |
| 414 | payload. |
| 415 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 416 | A new keyring can be generated by setting type "keyring", the keyring name |
| 417 | as the description (or NULL) and setting the payload to NULL. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 418 | |
| 419 | User defined keys can be created by specifying type "user". It is |
| 420 | recommended that a user defined key's description by prefixed with a type |
| 421 | ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting |
| 422 | ticket. |
| 423 | |
| 424 | Any other type must have been registered with the kernel in advance by a |
| 425 | kernel service such as a filesystem. |
| 426 | |
| 427 | The ID of the new or updated key is returned if successful. |
| 428 | |
| 429 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 430 | * Search the process's keyrings for a key, potentially calling out to |
| 431 | userspace to create it:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 432 | |
| 433 | key_serial_t request_key(const char *type, const char *description, |
| 434 | const char *callout_info, |
| 435 | key_serial_t dest_keyring); |
| 436 | |
| 437 | This function searches all the process's keyrings in the order thread, |
| 438 | process, session for a matching key. This works very much like |
| 439 | KEYCTL_SEARCH, including the optional attachment of the discovered key to |
| 440 | a keyring. |
| 441 | |
| 442 | If a key cannot be found, and if callout_info is not NULL, then |
| 443 | /sbin/request-key will be invoked in an attempt to obtain a key. The |
| 444 | callout_info string will be passed as an argument to the program. |
| 445 | |
Randy Dunlap | d410fa4 | 2011-05-19 15:59:38 -0700 | [diff] [blame] | 446 | See also Documentation/security/keys-request-key.txt. |
David Howells | f1a9bad | 2005-10-07 15:04:52 +0100 | [diff] [blame] | 447 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 448 | |
| 449 | The keyctl syscall functions are: |
| 450 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 451 | * Map a special key ID to a real key ID for this process:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 452 | |
| 453 | key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id, |
| 454 | int create); |
| 455 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 456 | The special key specified by "id" is looked up (with the key being created |
| 457 | if necessary) and the ID of the key or keyring thus found is returned if |
| 458 | it exists. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 459 | |
| 460 | If the key does not yet exist, the key will be created if "create" is |
| 461 | non-zero; and the error ENOKEY will be returned if "create" is zero. |
| 462 | |
| 463 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 464 | * Replace the session keyring this process subscribes to with a new one:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 465 | |
| 466 | key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name); |
| 467 | |
| 468 | If name is NULL, an anonymous keyring is created attached to the process |
| 469 | as its session keyring, displacing the old session keyring. |
| 470 | |
| 471 | If name is not NULL, if a keyring of that name exists, the process |
| 472 | attempts to attach it as the session keyring, returning an error if that |
| 473 | is not permitted; otherwise a new keyring of that name is created and |
| 474 | attached as the session keyring. |
| 475 | |
| 476 | To attach to a named keyring, the keyring must have search permission for |
| 477 | the process's ownership. |
| 478 | |
| 479 | The ID of the new session keyring is returned if successful. |
| 480 | |
| 481 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 482 | * Update the specified key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 483 | |
| 484 | long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload, |
| 485 | size_t plen); |
| 486 | |
| 487 | This will try to update the specified key with the given payload, or it |
| 488 | will return error EOPNOTSUPP if that function is not supported by the key |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 489 | type. The process must also have permission to write to the key to be able |
| 490 | to update it. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 491 | |
| 492 | The payload is of length plen, and may be absent or empty as for |
| 493 | add_key(). |
| 494 | |
| 495 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 496 | * Revoke a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 497 | |
| 498 | long keyctl(KEYCTL_REVOKE, key_serial_t key); |
| 499 | |
| 500 | This makes a key unavailable for further operations. Further attempts to |
| 501 | use the key will be met with error EKEYREVOKED, and the key will no longer |
| 502 | be findable. |
| 503 | |
| 504 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 505 | * Change the ownership of a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 506 | |
| 507 | long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid); |
| 508 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 509 | This function permits a key's owner and group ID to be changed. Either one |
| 510 | of uid or gid can be set to -1 to suppress that change. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 511 | |
| 512 | Only the superuser can change a key's owner to something other than the |
| 513 | key's current owner. Similarly, only the superuser can change a key's |
| 514 | group ID to something other than the calling process's group ID or one of |
| 515 | its group list members. |
| 516 | |
| 517 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 518 | * Change the permissions mask on a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 519 | |
| 520 | long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm); |
| 521 | |
| 522 | This function permits the owner of a key or the superuser to change the |
| 523 | permissions mask on a key. |
| 524 | |
| 525 | Only bits the available bits are permitted; if any other bits are set, |
| 526 | error EINVAL will be returned. |
| 527 | |
| 528 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 529 | * Describe a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 530 | |
| 531 | long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer, |
| 532 | size_t buflen); |
| 533 | |
| 534 | This function returns a summary of the key's attributes (but not its |
| 535 | payload data) as a string in the buffer provided. |
| 536 | |
| 537 | Unless there's an error, it always returns the amount of data it could |
| 538 | produce, even if that's too big for the buffer, but it won't copy more |
| 539 | than requested to userspace. If the buffer pointer is NULL then no copy |
| 540 | will take place. |
| 541 | |
| 542 | A process must have view permission on the key for this function to be |
| 543 | successful. |
| 544 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 545 | If successful, a string is placed in the buffer in the following format:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 546 | |
| 547 | <type>;<uid>;<gid>;<perm>;<description> |
| 548 | |
| 549 | Where type and description are strings, uid and gid are decimal, and perm |
| 550 | is hexadecimal. A NUL character is included at the end of the string if |
| 551 | the buffer is sufficiently big. |
| 552 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 553 | This can be parsed with:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 554 | |
| 555 | sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc); |
| 556 | |
| 557 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 558 | * Clear out a keyring:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 559 | |
| 560 | long keyctl(KEYCTL_CLEAR, key_serial_t keyring); |
| 561 | |
| 562 | This function clears the list of keys attached to a keyring. The calling |
| 563 | process must have write permission on the keyring, and it must be a |
| 564 | keyring (or else error ENOTDIR will result). |
| 565 | |
David Howells | 700920e | 2012-01-18 15:31:45 +0000 | [diff] [blame] | 566 | This function can also be used to clear special kernel keyrings if they |
| 567 | are appropriately marked if the user has CAP_SYS_ADMIN capability. The |
| 568 | DNS resolver cache keyring is an example of this. |
| 569 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 570 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 571 | * Link a key into a keyring:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 572 | |
| 573 | long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key); |
| 574 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 575 | This function creates a link from the keyring to the key. The process must |
| 576 | have write permission on the keyring and must have link permission on the |
| 577 | key. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 578 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 579 | Should the keyring not be a keyring, error ENOTDIR will result; and if the |
| 580 | keyring is full, error ENFILE will result. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 581 | |
| 582 | The link procedure checks the nesting of the keyrings, returning ELOOP if |
David Howells | 017679c | 2006-01-08 01:02:43 -0800 | [diff] [blame] | 583 | it appears too deep or EDEADLK if the link would introduce a cycle. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 584 | |
David Howells | cab8eb5 | 2006-01-08 01:02:45 -0800 | [diff] [blame] | 585 | Any links within the keyring to keys that match the new key in terms of |
| 586 | type and description will be discarded from the keyring as the new one is |
| 587 | added. |
| 588 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 589 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 590 | * Unlink a key or keyring from another keyring:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 591 | |
| 592 | long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key); |
| 593 | |
| 594 | This function looks through the keyring for the first link to the |
| 595 | specified key, and removes it if found. Subsequent links to that key are |
| 596 | ignored. The process must have write permission on the keyring. |
| 597 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 598 | If the keyring is not a keyring, error ENOTDIR will result; and if the key |
| 599 | is not present, error ENOENT will be the result. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 600 | |
| 601 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 602 | * Search a keyring tree for a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 603 | |
| 604 | key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring, |
| 605 | const char *type, const char *description, |
| 606 | key_serial_t dest_keyring); |
| 607 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 608 | This searches the keyring tree headed by the specified keyring until a key |
| 609 | is found that matches the type and description criteria. Each keyring is |
| 610 | checked for keys before recursion into its children occurs. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 611 | |
| 612 | The process must have search permission on the top level keyring, or else |
| 613 | error EACCES will result. Only keyrings that the process has search |
| 614 | permission on will be recursed into, and only keys and keyrings for which |
| 615 | a process has search permission can be matched. If the specified keyring |
| 616 | is not a keyring, ENOTDIR will result. |
| 617 | |
| 618 | If the search succeeds, the function will attempt to link the found key |
| 619 | into the destination keyring if one is supplied (non-zero ID). All the |
| 620 | constraints applicable to KEYCTL_LINK apply in this case too. |
| 621 | |
| 622 | Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search |
| 623 | fails. On success, the resulting key ID will be returned. |
| 624 | |
| 625 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 626 | * Read the payload data from a key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 627 | |
David Howells | f1a9bad | 2005-10-07 15:04:52 +0100 | [diff] [blame] | 628 | long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer, |
| 629 | size_t buflen); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 630 | |
| 631 | This function attempts to read the payload data from the specified key |
| 632 | into the buffer. The process must have read permission on the key to |
| 633 | succeed. |
| 634 | |
| 635 | The returned data will be processed for presentation by the key type. For |
| 636 | instance, a keyring will return an array of key_serial_t entries |
| 637 | representing the IDs of all the keys to which it is subscribed. The user |
| 638 | defined key type will return its data as is. If a key type does not |
| 639 | implement this function, error EOPNOTSUPP will result. |
| 640 | |
| 641 | As much of the data as can be fitted into the buffer will be copied to |
| 642 | userspace if the buffer pointer is not NULL. |
| 643 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 644 | On a successful return, the function will always return the amount of data |
| 645 | available rather than the amount copied. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 646 | |
| 647 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 648 | * Instantiate a partially constructed key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 649 | |
David Howells | f1a9bad | 2005-10-07 15:04:52 +0100 | [diff] [blame] | 650 | long keyctl(KEYCTL_INSTANTIATE, key_serial_t key, |
| 651 | const void *payload, size_t plen, |
| 652 | key_serial_t keyring); |
David Howells | ee009e4a0 | 2011-03-07 15:06:20 +0000 | [diff] [blame] | 653 | long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key, |
| 654 | const struct iovec *payload_iov, unsigned ioc, |
| 655 | key_serial_t keyring); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 656 | |
| 657 | If the kernel calls back to userspace to complete the instantiation of a |
| 658 | key, userspace should use this call to supply data for the key before the |
| 659 | invoked process returns, or else the key will be marked negative |
| 660 | automatically. |
| 661 | |
| 662 | The process must have write access on the key to be able to instantiate |
| 663 | it, and the key must be uninstantiated. |
| 664 | |
| 665 | If a keyring is specified (non-zero), the key will also be linked into |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 666 | that keyring, however all the constraints applying in KEYCTL_LINK apply in |
| 667 | this case too. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 668 | |
| 669 | The payload and plen arguments describe the payload data as for add_key(). |
| 670 | |
David Howells | ee009e4a0 | 2011-03-07 15:06:20 +0000 | [diff] [blame] | 671 | The payload_iov and ioc arguments describe the payload data in an iovec |
| 672 | array instead of a single buffer. |
| 673 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 674 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 675 | * Negatively instantiate a partially constructed key:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 676 | |
David Howells | f1a9bad | 2005-10-07 15:04:52 +0100 | [diff] [blame] | 677 | long keyctl(KEYCTL_NEGATE, key_serial_t key, |
| 678 | unsigned timeout, key_serial_t keyring); |
David Howells | fdd1b94 | 2011-03-07 15:06:09 +0000 | [diff] [blame] | 679 | long keyctl(KEYCTL_REJECT, key_serial_t key, |
| 680 | unsigned timeout, unsigned error, key_serial_t keyring); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 681 | |
| 682 | If the kernel calls back to userspace to complete the instantiation of a |
| 683 | key, userspace should use this call mark the key as negative before the |
Masanari Iida | 40e4712 | 2012-03-04 23:16:11 +0900 | [diff] [blame] | 684 | invoked process returns if it is unable to fulfill the request. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 685 | |
| 686 | The process must have write access on the key to be able to instantiate |
| 687 | it, and the key must be uninstantiated. |
| 688 | |
| 689 | If a keyring is specified (non-zero), the key will also be linked into |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 690 | that keyring, however all the constraints applying in KEYCTL_LINK apply in |
| 691 | this case too. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 692 | |
David Howells | fdd1b94 | 2011-03-07 15:06:09 +0000 | [diff] [blame] | 693 | If the key is rejected, future searches for it will return the specified |
| 694 | error code until the rejected key expires. Negating the key is the same |
| 695 | as rejecting the key with ENOKEY as the error code. |
| 696 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 697 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 698 | * Set the default request-key destination keyring:: |
David Howells | 3e30148 | 2005-06-23 22:00:56 -0700 | [diff] [blame] | 699 | |
| 700 | long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl); |
| 701 | |
| 702 | This sets the default keyring to which implicitly requested keys will be |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 703 | attached for this thread. reqkey_defl should be one of these constants:: |
David Howells | 3e30148 | 2005-06-23 22:00:56 -0700 | [diff] [blame] | 704 | |
| 705 | CONSTANT VALUE NEW DEFAULT KEYRING |
| 706 | ====================================== ====== ======================= |
| 707 | KEY_REQKEY_DEFL_NO_CHANGE -1 No change |
| 708 | KEY_REQKEY_DEFL_DEFAULT 0 Default[1] |
| 709 | KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring |
| 710 | KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring |
| 711 | KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring |
| 712 | KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring |
| 713 | KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring |
| 714 | KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring |
| 715 | |
| 716 | The old default will be returned if successful and error EINVAL will be |
| 717 | returned if reqkey_defl is not one of the above values. |
| 718 | |
| 719 | The default keyring can be overridden by the keyring indicated to the |
| 720 | request_key() system call. |
| 721 | |
| 722 | Note that this setting is inherited across fork/exec. |
| 723 | |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 724 | [1] The default is: the thread keyring if there is one, otherwise |
David Howells | 3e30148 | 2005-06-23 22:00:56 -0700 | [diff] [blame] | 725 | the process keyring if there is one, otherwise the session keyring if |
| 726 | there is one, otherwise the user default session keyring. |
| 727 | |
| 728 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 729 | * Set the timeout on a key:: |
David Howells | 017679c | 2006-01-08 01:02:43 -0800 | [diff] [blame] | 730 | |
| 731 | long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout); |
| 732 | |
| 733 | This sets or clears the timeout on a key. The timeout can be 0 to clear |
| 734 | the timeout or a number of seconds to set the expiry time that far into |
| 735 | the future. |
| 736 | |
| 737 | The process must have attribute modification access on a key to set its |
| 738 | timeout. Timeouts may not be set with this function on negative, revoked |
| 739 | or expired keys. |
| 740 | |
| 741 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 742 | * Assume the authority granted to instantiate a key:: |
David Howells | b5f545c | 2006-01-08 01:02:47 -0800 | [diff] [blame] | 743 | |
| 744 | long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key); |
| 745 | |
| 746 | This assumes or divests the authority required to instantiate the |
| 747 | specified key. Authority can only be assumed if the thread has the |
| 748 | authorisation key associated with the specified key in its keyrings |
| 749 | somewhere. |
| 750 | |
| 751 | Once authority is assumed, searches for keys will also search the |
| 752 | requester's keyrings using the requester's security label, UID, GID and |
| 753 | groups. |
| 754 | |
| 755 | If the requested authority is unavailable, error EPERM will be returned, |
| 756 | likewise if the authority has been revoked because the target key is |
| 757 | already instantiated. |
| 758 | |
| 759 | If the specified key is 0, then any assumed authority will be divested. |
| 760 | |
Matt LaPlante | 3f6dee9 | 2006-10-03 22:45:33 +0200 | [diff] [blame] | 761 | The assumed authoritative key is inherited across fork and exec. |
David Howells | b5f545c | 2006-01-08 01:02:47 -0800 | [diff] [blame] | 762 | |
| 763 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 764 | * Get the LSM security context attached to a key:: |
David Howells | 70a5bb7 | 2008-04-29 01:01:26 -0700 | [diff] [blame] | 765 | |
| 766 | long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer, |
| 767 | size_t buflen) |
| 768 | |
| 769 | This function returns a string that represents the LSM security context |
| 770 | attached to a key in the buffer provided. |
| 771 | |
| 772 | Unless there's an error, it always returns the amount of data it could |
| 773 | produce, even if that's too big for the buffer, but it won't copy more |
| 774 | than requested to userspace. If the buffer pointer is NULL then no copy |
| 775 | will take place. |
| 776 | |
| 777 | A NUL character is included at the end of the string if the buffer is |
| 778 | sufficiently big. This is included in the returned count. If no LSM is |
| 779 | in force then an empty string will be returned. |
| 780 | |
| 781 | A process must have view permission on the key for this function to be |
| 782 | successful. |
| 783 | |
| 784 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 785 | * Install the calling process's session keyring on its parent:: |
David Howells | ee18d64 | 2009-09-02 09:14:21 +0100 | [diff] [blame] | 786 | |
| 787 | long keyctl(KEYCTL_SESSION_TO_PARENT); |
| 788 | |
| 789 | This functions attempts to install the calling process's session keyring |
| 790 | on to the calling process's parent, replacing the parent's current session |
| 791 | keyring. |
| 792 | |
| 793 | The calling process must have the same ownership as its parent, the |
| 794 | keyring must have the same ownership as the calling process, the calling |
| 795 | process must have LINK permission on the keyring and the active LSM module |
| 796 | mustn't deny permission, otherwise error EPERM will be returned. |
| 797 | |
| 798 | Error ENOMEM will be returned if there was insufficient memory to complete |
| 799 | the operation, otherwise 0 will be returned to indicate success. |
| 800 | |
| 801 | The keyring will be replaced next time the parent process leaves the |
| 802 | kernel and resumes executing userspace. |
| 803 | |
| 804 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 805 | * Invalidate a key:: |
David Howells | fd75815 | 2012-05-11 10:56:56 +0100 | [diff] [blame] | 806 | |
| 807 | long keyctl(KEYCTL_INVALIDATE, key_serial_t key); |
| 808 | |
| 809 | This function marks a key as being invalidated and then wakes up the |
| 810 | garbage collector. The garbage collector immediately removes invalidated |
| 811 | keys from all keyrings and deletes the key when its reference count |
| 812 | reaches zero. |
| 813 | |
| 814 | Keys that are marked invalidated become invisible to normal key operations |
| 815 | immediately, though they are still visible in /proc/keys until deleted |
| 816 | (they're marked with an 'i' flag). |
| 817 | |
| 818 | A process must have search permission on the key for this function to be |
| 819 | successful. |
| 820 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 821 | * Compute a Diffie-Hellman shared secret or public key:: |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 822 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 823 | long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params, |
| 824 | char *buffer, size_t buflen, struct keyctl_kdf_params *kdf); |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 825 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 826 | The params struct contains serial numbers for three keys:: |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 827 | |
| 828 | - The prime, p, known to both parties |
| 829 | - The local private key |
| 830 | - The base integer, which is either a shared generator or the |
| 831 | remote public key |
| 832 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 833 | The value computed is:: |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 834 | |
| 835 | result = base ^ private (mod prime) |
| 836 | |
| 837 | If the base is the shared generator, the result is the local |
| 838 | public key. If the base is the remote public key, the result is |
| 839 | the shared secret. |
| 840 | |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 841 | If the parameter kdf is NULL, the following applies: |
Stephan Mueller | 4693fc7 | 2016-05-26 23:38:12 +0200 | [diff] [blame] | 842 | |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 843 | - The buffer length must be at least the length of the prime, or zero. |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 844 | |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 845 | - If the buffer length is nonzero, the length of the result is |
| 846 | returned when it is successfully calculated and copied in to the |
| 847 | buffer. When the buffer length is zero, the minimum required |
| 848 | buffer length is returned. |
| 849 | |
| 850 | The kdf parameter allows the caller to apply a key derivation function |
| 851 | (KDF) on the Diffie-Hellman computation where only the result |
| 852 | of the KDF is returned to the caller. The KDF is characterized with |
| 853 | struct keyctl_kdf_params as follows: |
| 854 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 855 | - ``char *hashname`` specifies the NUL terminated string identifying |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 856 | the hash used from the kernel crypto API and applied for the KDF |
| 857 | operation. The KDF implemenation complies with SP800-56A as well |
| 858 | as with SP800-108 (the counter KDF). |
| 859 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 860 | - ``char *otherinfo`` specifies the OtherInfo data as documented in |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 861 | SP800-56A section 5.8.1.2. The length of the buffer is given with |
| 862 | otherinfolen. The format of OtherInfo is defined by the caller. |
| 863 | The otherinfo pointer may be NULL if no OtherInfo shall be used. |
Mat Martineau | ddbb411 | 2016-04-12 19:54:58 +0100 | [diff] [blame] | 864 | |
| 865 | This function will return error EOPNOTSUPP if the key type is not |
| 866 | supported, error ENOKEY if the key could not be found, or error |
Stephan Mueller | f1c316a | 2016-08-19 20:39:09 +0200 | [diff] [blame] | 867 | EACCES if the key is not readable by the caller. In addition, the |
| 868 | function will return EMSGSIZE when the parameter kdf is non-NULL |
| 869 | and either the buffer length or the OtherInfo length exceeds the |
| 870 | allowed length. |
David Howells | fd75815 | 2012-05-11 10:56:56 +0100 | [diff] [blame] | 871 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 872 | * Restrict keyring linkage:: |
Mat Martineau | 6563c91 | 2017-03-01 16:44:09 -0800 | [diff] [blame] | 873 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 874 | long keyctl(KEYCTL_RESTRICT_KEYRING, key_serial_t keyring, |
| 875 | const char *type, const char *restriction); |
Mat Martineau | 6563c91 | 2017-03-01 16:44:09 -0800 | [diff] [blame] | 876 | |
| 877 | An existing keyring can restrict linkage of additional keys by evaluating |
| 878 | the contents of the key according to a restriction scheme. |
| 879 | |
| 880 | "keyring" is the key ID for an existing keyring to apply a restriction |
| 881 | to. It may be empty or may already have keys linked. Existing linked keys |
| 882 | will remain in the keyring even if the new restriction would reject them. |
| 883 | |
| 884 | "type" is a registered key type. |
| 885 | |
| 886 | "restriction" is a string describing how key linkage is to be restricted. |
| 887 | The format varies depending on the key type, and the string is passed to |
| 888 | the lookup_restriction() function for the requested type. It may specify |
| 889 | a method and relevant data for the restriction such as signature |
| 890 | verification or constraints on key payload. If the requested key type is |
| 891 | later unregistered, no keys may be added to the keyring after the key type |
| 892 | is removed. |
| 893 | |
| 894 | To apply a keyring restriction the process must have Set Attribute |
| 895 | permission and the keyring must not be previously restricted. |
| 896 | |
Mat Martineau | 7228b66 | 2017-07-13 13:17:03 +0100 | [diff] [blame] | 897 | One application of restricted keyrings is to verify X.509 certificate |
| 898 | chains or individual certificate signatures using the asymmetric key type. |
| 899 | See Documentation/crypto/asymmetric-keys.txt for specific restrictions |
| 900 | applicable to the asymmetric key type. |
| 901 | |
| 902 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 903 | Kernel Services |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 904 | =============== |
| 905 | |
Matt LaPlante | 2fe0ae7 | 2006-10-03 22:50:39 +0200 | [diff] [blame] | 906 | The kernel services for key management are fairly simple to deal with. They can |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 907 | be broken down into two areas: keys and key types. |
| 908 | |
| 909 | Dealing with keys is fairly straightforward. Firstly, the kernel service |
| 910 | registers its type, then it searches for a key of that type. It should retain |
| 911 | the key as long as it has need of it, and then it should release it. For a |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 912 | filesystem or device file, a search would probably be performed during the open |
| 913 | call, and the key released upon close. How to deal with conflicting keys due to |
| 914 | two different users opening the same file is left to the filesystem author to |
| 915 | solve. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 916 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 917 | To access the key manager, the following header must be #included:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 918 | |
| 919 | <linux/key.h> |
| 920 | |
| 921 | Specific key types should have a header file under include/keys/ that should be |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 922 | used to access that type. For keys of type "user", for example, that would be:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 923 | |
| 924 | <keys/user-type.h> |
| 925 | |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 926 | Note that there are two different types of pointers to keys that may be |
| 927 | encountered: |
| 928 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 929 | * struct key * |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 930 | |
| 931 | This simply points to the key structure itself. Key structures will be at |
| 932 | least four-byte aligned. |
| 933 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 934 | * key_ref_t |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 935 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 936 | This is equivalent to a ``struct key *``, but the least significant bit is set |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 937 | if the caller "possesses" the key. By "possession" it is meant that the |
| 938 | calling processes has a searchable link to the key from one of its |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 939 | keyrings. There are three functions for dealing with these:: |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 940 | |
David Howells | a5b4bd2 | 2013-09-24 10:35:14 +0100 | [diff] [blame] | 941 | key_ref_t make_key_ref(const struct key *key, bool possession); |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 942 | |
| 943 | struct key *key_ref_to_ptr(const key_ref_t key_ref); |
| 944 | |
David Howells | a5b4bd2 | 2013-09-24 10:35:14 +0100 | [diff] [blame] | 945 | bool is_key_possessed(const key_ref_t key_ref); |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 946 | |
| 947 | The first function constructs a key reference from a key pointer and |
David Howells | a5b4bd2 | 2013-09-24 10:35:14 +0100 | [diff] [blame] | 948 | possession information (which must be true or false). |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 949 | |
| 950 | The second function retrieves the key pointer from a reference and the |
| 951 | third retrieves the possession flag. |
| 952 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 953 | When accessing a key's payload contents, certain precautions must be taken to |
| 954 | prevent access vs modification races. See the section "Notes on accessing |
| 955 | payload contents" for more information. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 956 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 957 | * To search for a key, call:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 958 | |
| 959 | struct key *request_key(const struct key_type *type, |
| 960 | const char *description, |
David Howells | 4a38e12 | 2008-04-29 01:01:24 -0700 | [diff] [blame] | 961 | const char *callout_info); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 962 | |
| 963 | This is used to request a key or keyring with a description that matches |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 964 | the description specified according to the key type's match_preparse() |
| 965 | method. This permits approximate matching to occur. If callout_string is |
| 966 | not NULL, then /sbin/request-key will be invoked in an attempt to obtain |
| 967 | the key from userspace. In that case, callout_string will be passed as an |
| 968 | argument to the program. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 969 | |
| 970 | Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be |
| 971 | returned. |
| 972 | |
David Howells | 3e30148 | 2005-06-23 22:00:56 -0700 | [diff] [blame] | 973 | If successful, the key will have been attached to the default keyring for |
| 974 | implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING. |
| 975 | |
Randy Dunlap | d410fa4 | 2011-05-19 15:59:38 -0700 | [diff] [blame] | 976 | See also Documentation/security/keys-request-key.txt. |
David Howells | f1a9bad | 2005-10-07 15:04:52 +0100 | [diff] [blame] | 977 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 978 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 979 | * To search for a key, passing auxiliary data to the upcaller, call:: |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 980 | |
| 981 | struct key *request_key_with_auxdata(const struct key_type *type, |
| 982 | const char *description, |
David Howells | 4a38e12 | 2008-04-29 01:01:24 -0700 | [diff] [blame] | 983 | const void *callout_info, |
| 984 | size_t callout_len, |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 985 | void *aux); |
| 986 | |
| 987 | This is identical to request_key(), except that the auxiliary data is |
David Howells | 4a38e12 | 2008-04-29 01:01:24 -0700 | [diff] [blame] | 988 | passed to the key_type->request_key() op if it exists, and the callout_info |
| 989 | is a blob of length callout_len, if given (the length may be 0). |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 990 | |
| 991 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 992 | * A key can be requested asynchronously by calling one of:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 993 | |
| 994 | struct key *request_key_async(const struct key_type *type, |
| 995 | const char *description, |
David Howells | 4a38e12 | 2008-04-29 01:01:24 -0700 | [diff] [blame] | 996 | const void *callout_info, |
| 997 | size_t callout_len); |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 998 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 999 | or:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1000 | |
| 1001 | struct key *request_key_async_with_auxdata(const struct key_type *type, |
| 1002 | const char *description, |
David Howells | 4a38e12 | 2008-04-29 01:01:24 -0700 | [diff] [blame] | 1003 | const char *callout_info, |
| 1004 | size_t callout_len, |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1005 | void *aux); |
| 1006 | |
| 1007 | which are asynchronous equivalents of request_key() and |
| 1008 | request_key_with_auxdata() respectively. |
| 1009 | |
| 1010 | These two functions return with the key potentially still under |
Matt LaPlante | d919588 | 2008-07-25 19:45:33 -0700 | [diff] [blame] | 1011 | construction. To wait for construction completion, the following should be |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1012 | called:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1013 | |
| 1014 | int wait_for_key_construction(struct key *key, bool intr); |
| 1015 | |
| 1016 | The function will wait for the key to finish being constructed and then |
| 1017 | invokes key_validate() to return an appropriate value to indicate the state |
| 1018 | of the key (0 indicates the key is usable). |
| 1019 | |
| 1020 | If intr is true, then the wait can be interrupted by a signal, in which |
| 1021 | case error ERESTARTSYS will be returned. |
| 1022 | |
| 1023 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1024 | * When it is no longer required, the key should be released using:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1025 | |
| 1026 | void key_put(struct key *key); |
| 1027 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1028 | Or:: |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 1029 | |
| 1030 | void key_ref_put(key_ref_t key_ref); |
| 1031 | |
| 1032 | These can be called from interrupt context. If CONFIG_KEYS is not set then |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1033 | the argument will not be parsed. |
| 1034 | |
| 1035 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1036 | * Extra references can be made to a key by calling one of the following |
| 1037 | functions:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1038 | |
David Howells | ccc3e6d | 2013-09-24 10:35:16 +0100 | [diff] [blame] | 1039 | struct key *__key_get(struct key *key); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1040 | struct key *key_get(struct key *key); |
| 1041 | |
David Howells | ccc3e6d | 2013-09-24 10:35:16 +0100 | [diff] [blame] | 1042 | Keys so references will need to be disposed of by calling key_put() when |
| 1043 | they've been finished with. The key pointer passed in will be returned. |
| 1044 | |
| 1045 | In the case of key_get(), if the pointer is NULL or CONFIG_KEYS is not set |
| 1046 | then the key will not be dereferenced and no increment will take place. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1047 | |
| 1048 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1049 | * A key's serial number can be obtained by calling:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1050 | |
| 1051 | key_serial_t key_serial(struct key *key); |
| 1052 | |
| 1053 | If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the |
| 1054 | latter case without parsing the argument). |
| 1055 | |
| 1056 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1057 | * If a keyring was found in the search, this can be further searched by:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1058 | |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 1059 | key_ref_t keyring_search(key_ref_t keyring_ref, |
| 1060 | const struct key_type *type, |
| 1061 | const char *description) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1062 | |
| 1063 | This searches the keyring tree specified for a matching key. Error ENOKEY |
David Howells | 664cceb | 2005-09-28 17:03:15 +0100 | [diff] [blame] | 1064 | is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful, |
| 1065 | the returned key will need to be released. |
| 1066 | |
| 1067 | The possession attribute from the keyring reference is used to control |
| 1068 | access through the permissions mask and is propagated to the returned key |
| 1069 | reference pointer if successful. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1070 | |
| 1071 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1072 | * A keyring can be created by:: |
David Howells | f8aa23a | 2012-10-02 19:24:56 +0100 | [diff] [blame] | 1073 | |
| 1074 | struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid, |
| 1075 | const struct cred *cred, |
| 1076 | key_perm_t perm, |
Mat Martineau | 2b6aa41 | 2016-08-31 16:05:43 -0700 | [diff] [blame] | 1077 | struct key_restriction *restrict_link, |
David Howells | f8aa23a | 2012-10-02 19:24:56 +0100 | [diff] [blame] | 1078 | unsigned long flags, |
| 1079 | struct key *dest); |
| 1080 | |
| 1081 | This creates a keyring with the given attributes and returns it. If dest |
| 1082 | is not NULL, the new keyring will be linked into the keyring to which it |
| 1083 | points. No permission checks are made upon the destination keyring. |
| 1084 | |
| 1085 | Error EDQUOT can be returned if the keyring would overload the quota (pass |
| 1086 | KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted |
| 1087 | towards the user's quota). Error ENOMEM can also be returned. |
| 1088 | |
Mat Martineau | 2b6aa41 | 2016-08-31 16:05:43 -0700 | [diff] [blame] | 1089 | If restrict_link is not NULL, it should point to a structure that contains |
| 1090 | the function that will be called each time an attempt is made to link a |
| 1091 | key into the new keyring. The structure may also contain a key pointer |
| 1092 | and an associated key type. The function is called to check whether a key |
| 1093 | may be added into the keyring or not. The key type is used by the garbage |
| 1094 | collector to clean up function or data pointers in this structure if the |
| 1095 | given key type is unregistered. Callers of key_create_or_update() within |
| 1096 | the kernel can pass KEY_ALLOC_BYPASS_RESTRICTION to suppress the check. |
| 1097 | An example of using this is to manage rings of cryptographic keys that are |
| 1098 | set up when the kernel boots where userspace is also permitted to add keys |
| 1099 | - provided they can be verified by a key the kernel already has. |
David Howells | 5ac7eac | 2016-04-06 16:14:24 +0100 | [diff] [blame] | 1100 | |
| 1101 | When called, the restriction function will be passed the keyring being |
Mat Martineau | aaf66c8 | 2016-08-30 11:33:13 -0700 | [diff] [blame] | 1102 | added to, the key type, the payload of the key being added, and data to be |
| 1103 | used in the restriction check. Note that when a new key is being created, |
| 1104 | this is called between payload preparsing and actual key creation. The |
| 1105 | function should return 0 to allow the link or an error to reject it. |
David Howells | 5ac7eac | 2016-04-06 16:14:24 +0100 | [diff] [blame] | 1106 | |
| 1107 | A convenience function, restrict_link_reject, exists to always return |
| 1108 | -EPERM to in this case. |
| 1109 | |
David Howells | f8aa23a | 2012-10-02 19:24:56 +0100 | [diff] [blame] | 1110 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1111 | * To check the validity of a key, this function can be called:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1112 | |
| 1113 | int validate_key(struct key *key); |
| 1114 | |
| 1115 | This checks that the key in question hasn't expired or and hasn't been |
| 1116 | revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will |
| 1117 | be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be |
| 1118 | returned (in the latter case without parsing the argument). |
| 1119 | |
| 1120 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1121 | * To register a key type, the following function should be called:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1122 | |
| 1123 | int register_key_type(struct key_type *type); |
| 1124 | |
| 1125 | This will return error EEXIST if a type of the same name is already |
| 1126 | present. |
| 1127 | |
| 1128 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1129 | * To unregister a key type, call:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1130 | |
| 1131 | void unregister_key_type(struct key_type *type); |
| 1132 | |
| 1133 | |
Satyam Sharma | 7eacbbd | 2007-07-31 00:38:17 -0700 | [diff] [blame] | 1134 | Under some circumstances, it may be desirable to deal with a bundle of keys. |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1135 | The facility provides access to the keyring type for managing such a bundle:: |
David Howells | 7318226 | 2007-04-26 15:46:23 -0700 | [diff] [blame] | 1136 | |
| 1137 | struct key_type key_type_keyring; |
| 1138 | |
| 1139 | This can be used with a function such as request_key() to find a specific |
| 1140 | keyring in a process's keyrings. A keyring thus found can then be searched |
| 1141 | with keyring_search(). Note that it is not possible to use request_key() to |
| 1142 | search a specific keyring, so using keyrings in this way is of limited utility. |
| 1143 | |
| 1144 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1145 | Notes On Accessing Payload Contents |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1146 | =================================== |
| 1147 | |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1148 | The simplest payload is just data stored in key->payload directly. In this |
| 1149 | case, there's no need to indulge in RCU or locking when accessing the payload. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1150 | |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1151 | More complex payload contents must be allocated and pointers to them set in the |
| 1152 | key->payload.data[] array. One of the following ways must be selected to |
| 1153 | access the data: |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1154 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1155 | 1) Unmodifiable key type. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1156 | |
| 1157 | If the key type does not have a modify method, then the key's payload can |
| 1158 | be accessed without any form of locking, provided that it's known to be |
| 1159 | instantiated (uninstantiated keys cannot be "found"). |
| 1160 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1161 | 2) The key's semaphore. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1162 | |
| 1163 | The semaphore could be used to govern access to the payload and to control |
| 1164 | the payload pointer. It must be write-locked for modifications and would |
| 1165 | have to be read-locked for general access. The disadvantage of doing this |
| 1166 | is that the accessor may be required to sleep. |
| 1167 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1168 | 3) RCU. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1169 | |
| 1170 | RCU must be used when the semaphore isn't already held; if the semaphore |
| 1171 | is held then the contents can't change under you unexpectedly as the |
| 1172 | semaphore must still be used to serialise modifications to the key. The |
| 1173 | key management code takes care of this for the key type. |
| 1174 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1175 | However, this means using:: |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1176 | |
| 1177 | rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock() |
| 1178 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1179 | to read the pointer, and:: |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1180 | |
| 1181 | rcu_dereference() ... rcu_assign_pointer() ... call_rcu() |
| 1182 | |
| 1183 | to set the pointer and dispose of the old contents after a grace period. |
| 1184 | Note that only the key type should ever modify a key's payload. |
| 1185 | |
| 1186 | Furthermore, an RCU controlled payload must hold a struct rcu_head for the |
| 1187 | use of call_rcu() and, if the payload is of variable size, the length of |
| 1188 | the payload. key->datalen cannot be relied upon to be consistent with the |
| 1189 | payload just dereferenced if the key's semaphore is not held. |
| 1190 | |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1191 | Note that key->payload.data[0] has a shadow that is marked for __rcu |
| 1192 | usage. This is called key->payload.rcu_data0. The following accessors |
| 1193 | wrap the RCU calls to this element: |
| 1194 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1195 | a) Set or change the first payload pointer:: |
David Howells | 0837e49 | 2017-03-01 15:11:23 +0000 | [diff] [blame] | 1196 | |
| 1197 | rcu_assign_keypointer(struct key *key, void *data); |
| 1198 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1199 | b) Read the first payload pointer with the key semaphore held:: |
David Howells | 0837e49 | 2017-03-01 15:11:23 +0000 | [diff] [blame] | 1200 | |
| 1201 | [const] void *dereference_key_locked([const] struct key *key); |
| 1202 | |
| 1203 | Note that the return value will inherit its constness from the key |
| 1204 | parameter. Static analysis will give an error if it things the lock |
| 1205 | isn't held. |
| 1206 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1207 | c) Read the first payload pointer with the RCU read lock held:: |
David Howells | 0837e49 | 2017-03-01 15:11:23 +0000 | [diff] [blame] | 1208 | |
| 1209 | const void *dereference_key_rcu(const struct key *key); |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1210 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1211 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1212 | Defining a Key Type |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1213 | =================== |
| 1214 | |
| 1215 | A kernel service may want to define its own key type. For instance, an AFS |
| 1216 | filesystem might want to define a Kerberos 5 ticket key type. To do this, it |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1217 | author fills in a key_type struct and registers it with the system. |
| 1218 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1219 | Source files that implement key types should include the following header file:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1220 | |
| 1221 | <linux/key-type.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1222 | |
| 1223 | The structure has a number of fields, some of which are mandatory: |
| 1224 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1225 | * ``const char *name`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1226 | |
| 1227 | The name of the key type. This is used to translate a key type name |
| 1228 | supplied by userspace into a pointer to the structure. |
| 1229 | |
| 1230 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1231 | * ``size_t def_datalen`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1232 | |
| 1233 | This is optional - it supplies the default payload data length as |
| 1234 | contributed to the quota. If the key type's payload is always or almost |
| 1235 | always the same size, then this is a more efficient way to do things. |
| 1236 | |
| 1237 | The data length (and quota) on a particular key can always be changed |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1238 | during instantiation or update by calling:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1239 | |
| 1240 | int key_payload_reserve(struct key *key, size_t datalen); |
| 1241 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1242 | With the revised data length. Error EDQUOT will be returned if this is not |
| 1243 | viable. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1244 | |
| 1245 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1246 | * ``int (*vet_description)(const char *description);`` |
David Howells | b9fffa3 | 2011-03-07 15:05:59 +0000 | [diff] [blame] | 1247 | |
| 1248 | This optional method is called to vet a key description. If the key type |
| 1249 | doesn't approve of the key description, it may return an error, otherwise |
| 1250 | it should return 0. |
| 1251 | |
| 1252 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1253 | * ``int (*preparse)(struct key_preparsed_payload *prep);`` |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1254 | |
| 1255 | This optional method permits the key type to attempt to parse payload |
| 1256 | before a key is created (add key) or the key semaphore is taken (update or |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1257 | instantiate key). The structure pointed to by prep looks like:: |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1258 | |
| 1259 | struct key_preparsed_payload { |
| 1260 | char *description; |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1261 | union key_payload payload; |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1262 | const void *data; |
| 1263 | size_t datalen; |
| 1264 | size_t quotalen; |
David Howells | 7dfa0ca | 2014-07-18 18:56:34 +0100 | [diff] [blame] | 1265 | time_t expiry; |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1266 | }; |
| 1267 | |
| 1268 | Before calling the method, the caller will fill in data and datalen with |
| 1269 | the payload blob parameters; quotalen will be filled in with the default |
David Howells | 7dfa0ca | 2014-07-18 18:56:34 +0100 | [diff] [blame] | 1270 | quota size from the key type; expiry will be set to TIME_T_MAX and the |
| 1271 | rest will be cleared. |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1272 | |
| 1273 | If a description can be proposed from the payload contents, that should be |
| 1274 | attached as a string to the description field. This will be used for the |
| 1275 | key description if the caller of add_key() passes NULL or "". |
| 1276 | |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1277 | The method can attach anything it likes to payload. This is merely passed |
| 1278 | along to the instantiate() or update() operations. If set, the expiry |
| 1279 | time will be applied to the key if it is instantiated from this data. |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1280 | |
David Howells | 7dfa0ca | 2014-07-18 18:56:34 +0100 | [diff] [blame] | 1281 | The method should return 0 if successful or a negative error code |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1282 | otherwise. |
| 1283 | |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1284 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1285 | * ``void (*free_preparse)(struct key_preparsed_payload *prep);`` |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1286 | |
| 1287 | This method is only required if the preparse() method is provided, |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1288 | otherwise it is unused. It cleans up anything attached to the description |
| 1289 | and payload fields of the key_preparsed_payload struct as filled in by the |
| 1290 | preparse() method. It will always be called after preparse() returns |
| 1291 | successfully, even if instantiate() or update() succeed. |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1292 | |
| 1293 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1294 | * ``int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1295 | |
| 1296 | This method is called to attach a payload to a key during construction. |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1297 | The payload attached need not bear any relation to the data passed to this |
| 1298 | function. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1299 | |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1300 | The prep->data and prep->datalen fields will define the original payload |
| 1301 | blob. If preparse() was supplied then other fields may be filled in also. |
| 1302 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1303 | If the amount of data attached to the key differs from the size in |
| 1304 | keytype->def_datalen, then key_payload_reserve() should be called. |
| 1305 | |
| 1306 | This method does not have to lock the key in order to attach a payload. |
| 1307 | The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents |
| 1308 | anything else from gaining access to the key. |
| 1309 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1310 | It is safe to sleep in this method. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1311 | |
David Howells | 146aa8b | 2015-10-21 14:04:48 +0100 | [diff] [blame] | 1312 | generic_key_instantiate() is provided to simply copy the data from |
| 1313 | prep->payload.data[] to key->payload.data[], with RCU-safe assignment on |
| 1314 | the first element. It will then clear prep->payload.data[] so that the |
| 1315 | free_preparse method doesn't release the data. |
| 1316 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1317 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1318 | * ``int (*update)(struct key *key, const void *data, size_t datalen);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1319 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1320 | If this type of key can be updated, then this method should be provided. |
| 1321 | It is called to update a key's payload from the blob of data provided. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1322 | |
David Howells | d4f65b5 | 2012-09-13 13:06:29 +0100 | [diff] [blame] | 1323 | The prep->data and prep->datalen fields will define the original payload |
| 1324 | blob. If preparse() was supplied then other fields may be filled in also. |
| 1325 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1326 | key_payload_reserve() should be called if the data length might change |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1327 | before any changes are actually made. Note that if this succeeds, the type |
| 1328 | is committed to changing the key because it's already been altered, so all |
| 1329 | memory allocation must be done first. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1330 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1331 | The key will have its semaphore write-locked before this method is called, |
| 1332 | but this only deters other writers; any changes to the key's payload must |
| 1333 | be made under RCU conditions, and call_rcu() must be used to dispose of |
| 1334 | the old payload. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1335 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1336 | key_payload_reserve() should be called before the changes are made, but |
| 1337 | after all allocations and other potentially failing function calls are |
| 1338 | made. |
| 1339 | |
| 1340 | It is safe to sleep in this method. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1341 | |
| 1342 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1343 | * ``int (*match_preparse)(struct key_match_data *match_data);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1344 | |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1345 | This method is optional. It is called when a key search is about to be |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1346 | performed. It is given the following structure:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1347 | |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1348 | struct key_match_data { |
| 1349 | bool (*cmp)(const struct key *key, |
| 1350 | const struct key_match_data *match_data); |
| 1351 | const void *raw_data; |
| 1352 | void *preparsed; |
| 1353 | unsigned lookup_type; |
| 1354 | }; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1355 | |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1356 | On entry, raw_data will be pointing to the criteria to be used in matching |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1357 | a key by the caller and should not be modified. ``(*cmp)()`` will be pointing |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1358 | to the default matcher function (which does an exact description match |
| 1359 | against raw_data) and lookup_type will be set to indicate a direct lookup. |
| 1360 | |
| 1361 | The following lookup_type values are available: |
| 1362 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1363 | * KEYRING_SEARCH_LOOKUP_DIRECT - A direct lookup hashes the type and |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1364 | description to narrow down the search to a small number of keys. |
| 1365 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1366 | * KEYRING_SEARCH_LOOKUP_ITERATE - An iterative lookup walks all the |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1367 | keys in the keyring until one is matched. This must be used for any |
| 1368 | search that's not doing a simple direct match on the key description. |
| 1369 | |
| 1370 | The method may set cmp to point to a function of its choice that does some |
| 1371 | other form of match, may set lookup_type to KEYRING_SEARCH_LOOKUP_ITERATE |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1372 | and may attach something to the preparsed pointer for use by ``(*cmp)()``. |
| 1373 | ``(*cmp)()`` should return true if a key matches and false otherwise. |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1374 | |
| 1375 | If preparsed is set, it may be necessary to use the match_free() method to |
| 1376 | clean it up. |
| 1377 | |
| 1378 | The method should return 0 if successful or a negative error code |
| 1379 | otherwise. |
| 1380 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1381 | It is permitted to sleep in this method, but ``(*cmp)()`` may not sleep as |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1382 | locks will be held over it. |
| 1383 | |
| 1384 | If match_preparse() is not provided, keys of this type will be matched |
| 1385 | exactly by their description. |
| 1386 | |
| 1387 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1388 | * ``void (*match_free)(struct key_match_data *match_data);`` |
David Howells | f93b3cc | 2014-09-16 17:36:09 +0100 | [diff] [blame] | 1389 | |
| 1390 | This method is optional. If given, it called to clean up |
| 1391 | match_data->preparsed after a successful call to match_preparse(). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1392 | |
| 1393 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1394 | * ``void (*revoke)(struct key *key);`` |
David Howells | 04c567d | 2006-06-22 14:47:18 -0700 | [diff] [blame] | 1395 | |
| 1396 | This method is optional. It is called to discard part of the payload |
| 1397 | data upon a key being revoked. The caller will have the key semaphore |
| 1398 | write-locked. |
| 1399 | |
| 1400 | It is safe to sleep in this method, though care should be taken to avoid |
| 1401 | a deadlock against the key semaphore. |
| 1402 | |
| 1403 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1404 | * ``void (*destroy)(struct key *key);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1405 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1406 | This method is optional. It is called to discard the payload data on a key |
| 1407 | when it is being destroyed. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1408 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1409 | This method does not need to lock the key to access the payload; it can |
| 1410 | consider the key as being inaccessible at this time. Note that the key's |
| 1411 | type may have been changed before this function is called. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1412 | |
| 1413 | It is not safe to sleep in this method; the caller may hold spinlocks. |
| 1414 | |
| 1415 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1416 | * ``void (*describe)(const struct key *key, struct seq_file *p);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1417 | |
| 1418 | This method is optional. It is called during /proc/keys reading to |
| 1419 | summarise a key's description and payload in text form. |
| 1420 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1421 | This method will be called with the RCU read lock held. rcu_dereference() |
| 1422 | should be used to read the payload pointer if the payload is to be |
| 1423 | accessed. key->datalen cannot be trusted to stay consistent with the |
| 1424 | contents of the payload. |
| 1425 | |
| 1426 | The description will not change, though the key's state may. |
| 1427 | |
| 1428 | It is not safe to sleep in this method; the RCU read lock is held by the |
| 1429 | caller. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1430 | |
| 1431 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1432 | * ``long (*read)(const struct key *key, char __user *buffer, size_t buflen);`` |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1433 | |
| 1434 | This method is optional. It is called by KEYCTL_READ to translate the |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1435 | key's payload into something a blob of data for userspace to deal with. |
| 1436 | Ideally, the blob should be in the same format as that passed in to the |
| 1437 | instantiate and update methods. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1438 | |
| 1439 | If successful, the blob size that could be produced should be returned |
| 1440 | rather than the size copied. |
| 1441 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1442 | This method will be called with the key's semaphore read-locked. This will |
| 1443 | prevent the key's payload changing. It is not necessary to use RCU locking |
| 1444 | when accessing the key's payload. It is safe to sleep in this method, such |
| 1445 | as might happen when the userspace buffer is accessed. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1446 | |
| 1447 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1448 | * ``int (*request_key)(struct key_construction *cons, const char *op, void *aux);`` |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 1449 | |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1450 | This method is optional. If provided, request_key() and friends will |
| 1451 | invoke this function rather than upcalling to /sbin/request-key to operate |
| 1452 | upon a key of this type. |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 1453 | |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1454 | The aux parameter is as passed to request_key_async_with_auxdata() and |
| 1455 | similar or is NULL otherwise. Also passed are the construction record for |
| 1456 | the key to be operated upon and the operation type (currently only |
| 1457 | "create"). |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 1458 | |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1459 | This method is permitted to return before the upcall is complete, but the |
| 1460 | following function must be called under all circumstances to complete the |
| 1461 | instantiation process, whether or not it succeeds, whether or not there's |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1462 | an error:: |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1463 | |
| 1464 | void complete_request_key(struct key_construction *cons, int error); |
| 1465 | |
| 1466 | The error parameter should be 0 on success, -ve on error. The |
| 1467 | construction record is destroyed by this action and the authorisation key |
| 1468 | will be revoked. If an error is indicated, the key under construction |
| 1469 | will be negatively instantiated if it wasn't already instantiated. |
| 1470 | |
| 1471 | If this method returns an error, that error will be returned to the |
| 1472 | caller of request_key*(). complete_request_key() must be called prior to |
| 1473 | returning. |
| 1474 | |
| 1475 | The key under construction and the authorisation key can be found in the |
| 1476 | key_construction struct pointed to by cons: |
| 1477 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1478 | * ``struct key *key;`` |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1479 | |
| 1480 | The key under construction. |
| 1481 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1482 | * ``struct key *authkey;`` |
David Howells | 76181c1 | 2007-10-16 23:29:46 -0700 | [diff] [blame] | 1483 | |
| 1484 | The authorisation key. |
David Howells | 4e54f08 | 2006-06-29 02:24:28 -0700 | [diff] [blame] | 1485 | |
| 1486 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1487 | * ``struct key_restriction *(*lookup_restriction)(const char *params);`` |
Mat Martineau | efba797 | 2016-05-06 15:38:17 -0700 | [diff] [blame] | 1488 | |
| 1489 | This optional method is used to enable userspace configuration of keyring |
| 1490 | restrictions. The restriction parameter string (not including the key type |
| 1491 | name) is passed in, and this method returns a pointer to a key_restriction |
| 1492 | structure containing the relevant functions and data to evaluate each |
| 1493 | attempted key link operation. If there is no match, -EINVAL is returned. |
| 1494 | |
| 1495 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1496 | Request-Key Callback Service |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1497 | ============================ |
| 1498 | |
| 1499 | To create a new key, the kernel will attempt to execute the following command |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1500 | line:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1501 | |
| 1502 | /sbin/request-key create <key> <uid> <gid> \ |
| 1503 | <threadring> <processring> <sessionring> <callout_info> |
| 1504 | |
| 1505 | <key> is the key being constructed, and the three keyrings are the process |
| 1506 | keyrings from the process that caused the search to be issued. These are |
| 1507 | included for two reasons: |
| 1508 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1509 | 1 There may be an authentication token in one of the keyrings that is |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1510 | required to obtain the key, eg: a Kerberos Ticket-Granting Ticket. |
| 1511 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1512 | 2 The new key should probably be cached in one of these rings. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1513 | |
| 1514 | This program should set it UID and GID to those specified before attempting to |
| 1515 | access any more keys. It may then look around for a user specific process to |
| 1516 | hand the request off to (perhaps a path held in placed in another key by, for |
| 1517 | example, the KDE desktop manager). |
| 1518 | |
| 1519 | The program (or whatever it calls) should finish construction of the key by |
David Howells | ee009e4a0 | 2011-03-07 15:06:20 +0000 | [diff] [blame] | 1520 | calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to |
| 1521 | cache the key in one of the keyrings (probably the session ring) before |
| 1522 | returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE |
| 1523 | or KEYCTL_REJECT; this also permits the key to be cached in one of the |
| 1524 | keyrings. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1525 | |
| 1526 | If it returns with the key remaining in the unconstructed state, the key will |
| 1527 | be marked as being negative, it will be added to the session keyring, and an |
| 1528 | error will be returned to the key requestor. |
| 1529 | |
David Howells | 76d8aea | 2005-06-23 22:00:49 -0700 | [diff] [blame] | 1530 | Supplementary information may be provided from whoever or whatever invoked this |
| 1531 | service. This will be passed as the <callout_info> parameter. If no such |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1532 | information was made available, then "-" will be passed as this parameter |
| 1533 | instead. |
| 1534 | |
| 1535 | |
| 1536 | Similarly, the kernel may attempt to update an expired or a soon to expire key |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1537 | by executing:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1538 | |
| 1539 | /sbin/request-key update <key> <uid> <gid> \ |
| 1540 | <threadring> <processring> <sessionring> |
| 1541 | |
| 1542 | In this case, the program isn't required to actually attach the key to a ring; |
| 1543 | the rings are provided for reference. |
David Howells | 5d13544 | 2009-09-02 09:14:00 +0100 | [diff] [blame] | 1544 | |
| 1545 | |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1546 | Garbage Collection |
David Howells | 5d13544 | 2009-09-02 09:14:00 +0100 | [diff] [blame] | 1547 | ================== |
| 1548 | |
| 1549 | Dead keys (for which the type has been removed) will be automatically unlinked |
| 1550 | from those keyrings that point to them and deleted as soon as possible by a |
| 1551 | background garbage collector. |
| 1552 | |
| 1553 | Similarly, revoked and expired keys will be garbage collected, but only after a |
Kees Cook | b68101a | 2017-05-13 04:51:50 -0700 | [diff] [blame] | 1554 | certain amount of time has passed. This time is set as a number of seconds in:: |
David Howells | 5d13544 | 2009-09-02 09:14:00 +0100 | [diff] [blame] | 1555 | |
| 1556 | /proc/sys/kernel/keys/gc_delay |