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Linus Torvalds1da177e2005-04-16 15:20:36 -07001 ============================
2 KERNEL KEY RETENTION SERVICE
3 ============================
4
5This service allows cryptographic keys, authentication tokens, cross-domain
6user mappings, and similar to be cached in the kernel for the use of
David Howells76181c12007-10-16 23:29:46 -07007filesystems and other kernel services.
Linus Torvalds1da177e2005-04-16 15:20:36 -07008
9Keyrings are permitted; these are a special type of key that can hold links to
10other keys. Processes each have three standard keyring subscriptions that a
11kernel service can search for relevant keys.
12
13The key service can be configured on by enabling:
14
15 "Security options"/"Enable access key retention support" (CONFIG_KEYS)
16
17This document has the following sections:
18
19 - Key overview
20 - Key service overview
21 - Key access permissions
Michael LeMayd7200242006-06-22 14:47:17 -070022 - SELinux support
Linus Torvalds1da177e2005-04-16 15:20:36 -070023 - New procfs files
24 - Userspace system call interface
25 - Kernel services
David Howells76d8aea2005-06-23 22:00:49 -070026 - Notes on accessing payload contents
Linus Torvalds1da177e2005-04-16 15:20:36 -070027 - Defining a key type
28 - Request-key callback service
David Howells5d135442009-09-02 09:14:00 +010029 - Garbage collection
Linus Torvalds1da177e2005-04-16 15:20:36 -070030
31
32============
33KEY OVERVIEW
34============
35
36In this context, keys represent units of cryptographic data, authentication
37tokens, keyrings, etc.. These are represented in the kernel by struct key.
38
39Each key has a number of attributes:
40
41 - A serial number.
42 - A type.
43 - A description (for matching a key in a search).
44 - Access control information.
45 - An expiry time.
46 - A payload.
47 - State.
48
49
David Howells76d8aea2005-06-23 22:00:49 -070050 (*) Each key is issued a serial number of type key_serial_t that is unique for
51 the lifetime of that key. All serial numbers are positive non-zero 32-bit
52 integers.
Linus Torvalds1da177e2005-04-16 15:20:36 -070053
54 Userspace programs can use a key's serial numbers as a way to gain access
55 to it, subject to permission checking.
56
57 (*) Each key is of a defined "type". Types must be registered inside the
David Howells76d8aea2005-06-23 22:00:49 -070058 kernel by a kernel service (such as a filesystem) before keys of that type
59 can be added or used. Userspace programs cannot define new types directly.
Linus Torvalds1da177e2005-04-16 15:20:36 -070060
David Howells76d8aea2005-06-23 22:00:49 -070061 Key types are represented in the kernel by struct key_type. This defines a
62 number of operations that can be performed on a key of that type.
Linus Torvalds1da177e2005-04-16 15:20:36 -070063
64 Should a type be removed from the system, all the keys of that type will
65 be invalidated.
66
67 (*) Each key has a description. This should be a printable string. The key
David Howells76d8aea2005-06-23 22:00:49 -070068 type provides an operation to perform a match between the description on a
69 key and a criterion string.
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
71 (*) Each key has an owner user ID, a group ID and a permissions mask. These
72 are used to control what a process may do to a key from userspace, and
73 whether a kernel service will be able to find the key.
74
75 (*) Each key can be set to expire at a specific time by the key type's
76 instantiation function. Keys can also be immortal.
77
David Howells76d8aea2005-06-23 22:00:49 -070078 (*) Each key can have a payload. This is a quantity of data that represent the
79 actual "key". In the case of a keyring, this is a list of keys to which
80 the keyring links; in the case of a user-defined key, it's an arbitrary
81 blob of data.
Linus Torvalds1da177e2005-04-16 15:20:36 -070082
83 Having a payload is not required; and the payload can, in fact, just be a
84 value stored in the struct key itself.
85
86 When a key is instantiated, the key type's instantiation function is
87 called with a blob of data, and that then creates the key's payload in
88 some way.
89
90 Similarly, when userspace wants to read back the contents of the key, if
91 permitted, another key type operation will be called to convert the key's
92 attached payload back into a blob of data.
93
94 (*) Each key can be in one of a number of basic states:
95
David Howells76d8aea2005-06-23 22:00:49 -070096 (*) Uninstantiated. The key exists, but does not have any data attached.
97 Keys being requested from userspace will be in this state.
Linus Torvalds1da177e2005-04-16 15:20:36 -070098
99 (*) Instantiated. This is the normal state. The key is fully formed, and
100 has data attached.
101
102 (*) Negative. This is a relatively short-lived state. The key acts as a
103 note saying that a previous call out to userspace failed, and acts as
104 a throttle on key lookups. A negative key can be updated to a normal
105 state.
106
107 (*) Expired. Keys can have lifetimes set. If their lifetime is exceeded,
108 they traverse to this state. An expired key can be updated back to a
109 normal state.
110
111 (*) Revoked. A key is put in this state by userspace action. It can't be
112 found or operated upon (apart from by unlinking it).
113
114 (*) Dead. The key's type was unregistered, and so the key is now useless.
115
David Howells5d135442009-09-02 09:14:00 +0100116Keys in the last three states are subject to garbage collection. See the
117section on "Garbage collection".
118
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
120====================
121KEY SERVICE OVERVIEW
122====================
123
124The key service provides a number of features besides keys:
125
Jeff Laytona05a4832012-04-25 12:46:50 -0400126 (*) The key service defines three special key types:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127
128 (+) "keyring"
129
130 Keyrings are special keys that contain a list of other keys. Keyring
131 lists can be modified using various system calls. Keyrings should not
132 be given a payload when created.
133
134 (+) "user"
135
136 A key of this type has a description and a payload that are arbitrary
137 blobs of data. These can be created, updated and read by userspace,
138 and aren't intended for use by kernel services.
139
Jeff Laytona05a4832012-04-25 12:46:50 -0400140 (+) "logon"
141
142 Like a "user" key, a "logon" key has a payload that is an arbitrary
143 blob of data. It is intended as a place to store secrets which are
144 accessible to the kernel but not to userspace programs.
145
146 The description can be arbitrary, but must be prefixed with a non-zero
147 length string that describes the key "subclass". The subclass is
148 separated from the rest of the description by a ':'. "logon" keys can
149 be created and updated from userspace, but the payload is only
150 readable from kernel space.
151
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152 (*) Each process subscribes to three keyrings: a thread-specific keyring, a
153 process-specific keyring, and a session-specific keyring.
154
155 The thread-specific keyring is discarded from the child when any sort of
156 clone, fork, vfork or execve occurs. A new keyring is created only when
157 required.
158
David Howells76d8aea2005-06-23 22:00:49 -0700159 The process-specific keyring is replaced with an empty one in the child on
160 clone, fork, vfork unless CLONE_THREAD is supplied, in which case it is
161 shared. execve also discards the process's process keyring and creates a
162 new one.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163
164 The session-specific keyring is persistent across clone, fork, vfork and
165 execve, even when the latter executes a set-UID or set-GID binary. A
166 process can, however, replace its current session keyring with a new one
167 by using PR_JOIN_SESSION_KEYRING. It is permitted to request an anonymous
168 new one, or to attempt to create or join one of a specific name.
169
170 The ownership of the thread keyring changes when the real UID and GID of
171 the thread changes.
172
173 (*) Each user ID resident in the system holds two special keyrings: a user
174 specific keyring and a default user session keyring. The default session
175 keyring is initialised with a link to the user-specific keyring.
176
177 When a process changes its real UID, if it used to have no session key, it
178 will be subscribed to the default session key for the new UID.
179
180 If a process attempts to access its session key when it doesn't have one,
181 it will be subscribed to the default for its current UID.
182
183 (*) Each user has two quotas against which the keys they own are tracked. One
184 limits the total number of keys and keyrings, the other limits the total
185 amount of description and payload space that can be consumed.
186
187 The user can view information on this and other statistics through procfs
David Howells0b77f5b2008-04-29 01:01:32 -0700188 files. The root user may also alter the quota limits through sysctl files
189 (see the section "New procfs files").
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190
191 Process-specific and thread-specific keyrings are not counted towards a
192 user's quota.
193
194 If a system call that modifies a key or keyring in some way would put the
195 user over quota, the operation is refused and error EDQUOT is returned.
196
David Howells76d8aea2005-06-23 22:00:49 -0700197 (*) There's a system call interface by which userspace programs can create and
198 manipulate keys and keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199
David Howells76d8aea2005-06-23 22:00:49 -0700200 (*) There's a kernel interface by which services can register types and search
201 for keys.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700202
203 (*) There's a way for the a search done from the kernel to call back to
204 userspace to request a key that can't be found in a process's keyrings.
205
206 (*) An optional filesystem is available through which the key database can be
207 viewed and manipulated.
208
209
210======================
211KEY ACCESS PERMISSIONS
212======================
213
David Howells76d8aea2005-06-23 22:00:49 -0700214Keys have an owner user ID, a group access ID, and a permissions mask. The mask
David Howells664cceb2005-09-28 17:03:15 +0100215has up to eight bits each for possessor, user, group and other access. Only
David Howells29db9192005-10-30 15:02:44 -0800216six of each set of eight bits are defined. These permissions granted are:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700217
218 (*) View
219
220 This permits a key or keyring's attributes to be viewed - including key
221 type and description.
222
223 (*) Read
224
225 This permits a key's payload to be viewed or a keyring's list of linked
226 keys.
227
228 (*) Write
229
David Howells76d8aea2005-06-23 22:00:49 -0700230 This permits a key's payload to be instantiated or updated, or it allows a
231 link to be added to or removed from a keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700232
233 (*) Search
234
235 This permits keyrings to be searched and keys to be found. Searches can
236 only recurse into nested keyrings that have search permission set.
237
238 (*) Link
239
240 This permits a key or keyring to be linked to. To create a link from a
241 keyring to a key, a process must have Write permission on the keyring and
242 Link permission on the key.
243
David Howells29db9192005-10-30 15:02:44 -0800244 (*) Set Attribute
245
246 This permits a key's UID, GID and permissions mask to be changed.
247
Linus Torvalds1da177e2005-04-16 15:20:36 -0700248For changing the ownership, group ID or permissions mask, being the owner of
249the key or having the sysadmin capability is sufficient.
250
251
Michael LeMayd7200242006-06-22 14:47:17 -0700252===============
253SELINUX SUPPORT
254===============
255
256The security class "key" has been added to SELinux so that mandatory access
257controls can be applied to keys created within various contexts. This support
258is preliminary, and is likely to change quite significantly in the near future.
259Currently, all of the basic permissions explained above are provided in SELinux
Michael LeMay4eb582c2006-06-26 00:24:57 -0700260as well; SELinux is simply invoked after all basic permission checks have been
Michael LeMayd7200242006-06-22 14:47:17 -0700261performed.
262
Michael LeMay4eb582c2006-06-26 00:24:57 -0700263The value of the file /proc/self/attr/keycreate influences the labeling of
264newly-created keys. If the contents of that file correspond to an SELinux
265security context, then the key will be assigned that context. Otherwise, the
266key will be assigned the current context of the task that invoked the key
267creation request. Tasks must be granted explicit permission to assign a
268particular context to newly-created keys, using the "create" permission in the
269key security class.
Michael LeMayd7200242006-06-22 14:47:17 -0700270
Michael LeMay4eb582c2006-06-26 00:24:57 -0700271The default keyrings associated with users will be labeled with the default
272context of the user if and only if the login programs have been instrumented to
273properly initialize keycreate during the login process. Otherwise, they will
274be labeled with the context of the login program itself.
Michael LeMayd7200242006-06-22 14:47:17 -0700275
276Note, however, that the default keyrings associated with the root user are
277labeled with the default kernel context, since they are created early in the
278boot process, before root has a chance to log in.
279
Michael LeMay4eb582c2006-06-26 00:24:57 -0700280The keyrings associated with new threads are each labeled with the context of
281their associated thread, and both session and process keyrings are handled
282similarly.
283
Michael LeMayd7200242006-06-22 14:47:17 -0700284
Linus Torvalds1da177e2005-04-16 15:20:36 -0700285================
286NEW PROCFS FILES
287================
288
289Two files have been added to procfs by which an administrator can find out
290about the status of the key service:
291
292 (*) /proc/keys
293
Michael LeMay06ec7be2006-06-26 00:24:56 -0700294 This lists the keys that are currently viewable by the task reading the
295 file, giving information about their type, description and permissions.
296 It is not possible to view the payload of the key this way, though some
297 information about it may be given.
298
299 The only keys included in the list are those that grant View permission to
300 the reading process whether or not it possesses them. Note that LSM
301 security checks are still performed, and may further filter out keys that
302 the current process is not authorised to view.
303
304 The contents of the file look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700305
David Howells664cceb2005-09-28 17:03:15 +0100306 SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
David Howells29db9192005-10-30 15:02:44 -0800307 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4
308 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty
309 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty
310 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty
311 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4
312 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty
David Howells664cceb2005-09-28 17:03:15 +0100313 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0
David Howells29db9192005-10-30 15:02:44 -0800314 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0
315 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316
317 The flags are:
318
319 I Instantiated
320 R Revoked
321 D Dead
322 Q Contributes to user's quota
Matt LaPlante5d3f0832006-11-30 05:21:10 +0100323 U Under construction by callback to userspace
Linus Torvalds1da177e2005-04-16 15:20:36 -0700324 N Negative key
325
Linus Torvalds1da177e2005-04-16 15:20:36 -0700326
327 (*) /proc/key-users
328
329 This file lists the tracking data for each user that has at least one key
Michael LeMay06ec7be2006-06-26 00:24:56 -0700330 on the system. Such data includes quota information and statistics:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700331
332 [root@andromeda root]# cat /proc/key-users
333 0: 46 45/45 1/100 13/10000
334 29: 2 2/2 2/100 40/10000
335 32: 2 2/2 2/100 40/10000
336 38: 2 2/2 2/100 40/10000
337
338 The format of each line is
339 <UID>: User ID to which this applies
340 <usage> Structure refcount
341 <inst>/<keys> Total number of keys and number instantiated
342 <keys>/<max> Key count quota
343 <bytes>/<max> Key size quota
344
345
David Howells0b77f5b2008-04-29 01:01:32 -0700346Four new sysctl files have been added also for the purpose of controlling the
347quota limits on keys:
348
349 (*) /proc/sys/kernel/keys/root_maxkeys
350 /proc/sys/kernel/keys/root_maxbytes
351
352 These files hold the maximum number of keys that root may have and the
353 maximum total number of bytes of data that root may have stored in those
354 keys.
355
356 (*) /proc/sys/kernel/keys/maxkeys
357 /proc/sys/kernel/keys/maxbytes
358
359 These files hold the maximum number of keys that each non-root user may
360 have and the maximum total number of bytes of data that each of those
361 users may have stored in their keys.
362
363Root may alter these by writing each new limit as a decimal number string to
364the appropriate file.
365
366
Linus Torvalds1da177e2005-04-16 15:20:36 -0700367===============================
368USERSPACE SYSTEM CALL INTERFACE
369===============================
370
371Userspace can manipulate keys directly through three new syscalls: add_key,
372request_key and keyctl. The latter provides a number of functions for
373manipulating keys.
374
375When referring to a key directly, userspace programs should use the key's
376serial number (a positive 32-bit integer). However, there are some special
377values available for referring to special keys and keyrings that relate to the
378process making the call:
379
380 CONSTANT VALUE KEY REFERENCED
381 ============================== ====== ===========================
382 KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring
383 KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring
384 KEY_SPEC_SESSION_KEYRING -3 session-specific keyring
385 KEY_SPEC_USER_KEYRING -4 UID-specific keyring
386 KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring
387 KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring
David Howellsb5f545c2006-01-08 01:02:47 -0800388 KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key()
389 authorisation key
Linus Torvalds1da177e2005-04-16 15:20:36 -0700390
391
392The main syscalls are:
393
394 (*) Create a new key of given type, description and payload and add it to the
395 nominated keyring:
396
397 key_serial_t add_key(const char *type, const char *desc,
398 const void *payload, size_t plen,
399 key_serial_t keyring);
400
401 If a key of the same type and description as that proposed already exists
402 in the keyring, this will try to update it with the given payload, or it
403 will return error EEXIST if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700404 type. The process must also have permission to write to the key to be able
405 to update it. The new key will have all user permissions granted and no
406 group or third party permissions.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700407
David Howells76d8aea2005-06-23 22:00:49 -0700408 Otherwise, this will attempt to create a new key of the specified type and
409 description, and to instantiate it with the supplied payload and attach it
410 to the keyring. In this case, an error will be generated if the process
411 does not have permission to write to the keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700412
David Howellsd4f65b52012-09-13 13:06:29 +0100413 If the key type supports it, if the description is NULL or an empty
414 string, the key type will try and generate a description from the content
415 of the payload.
416
Linus Torvalds1da177e2005-04-16 15:20:36 -0700417 The payload is optional, and the pointer can be NULL if not required by
418 the type. The payload is plen in size, and plen can be zero for an empty
419 payload.
420
David Howells76d8aea2005-06-23 22:00:49 -0700421 A new keyring can be generated by setting type "keyring", the keyring name
422 as the description (or NULL) and setting the payload to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700423
424 User defined keys can be created by specifying type "user". It is
425 recommended that a user defined key's description by prefixed with a type
426 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting
427 ticket.
428
429 Any other type must have been registered with the kernel in advance by a
430 kernel service such as a filesystem.
431
432 The ID of the new or updated key is returned if successful.
433
434
435 (*) Search the process's keyrings for a key, potentially calling out to
436 userspace to create it.
437
438 key_serial_t request_key(const char *type, const char *description,
439 const char *callout_info,
440 key_serial_t dest_keyring);
441
442 This function searches all the process's keyrings in the order thread,
443 process, session for a matching key. This works very much like
444 KEYCTL_SEARCH, including the optional attachment of the discovered key to
445 a keyring.
446
447 If a key cannot be found, and if callout_info is not NULL, then
448 /sbin/request-key will be invoked in an attempt to obtain a key. The
449 callout_info string will be passed as an argument to the program.
450
Randy Dunlapd410fa42011-05-19 15:59:38 -0700451 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100452
Linus Torvalds1da177e2005-04-16 15:20:36 -0700453
454The keyctl syscall functions are:
455
456 (*) Map a special key ID to a real key ID for this process:
457
458 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id,
459 int create);
460
David Howells76d8aea2005-06-23 22:00:49 -0700461 The special key specified by "id" is looked up (with the key being created
462 if necessary) and the ID of the key or keyring thus found is returned if
463 it exists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700464
465 If the key does not yet exist, the key will be created if "create" is
466 non-zero; and the error ENOKEY will be returned if "create" is zero.
467
468
469 (*) Replace the session keyring this process subscribes to with a new one:
470
471 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name);
472
473 If name is NULL, an anonymous keyring is created attached to the process
474 as its session keyring, displacing the old session keyring.
475
476 If name is not NULL, if a keyring of that name exists, the process
477 attempts to attach it as the session keyring, returning an error if that
478 is not permitted; otherwise a new keyring of that name is created and
479 attached as the session keyring.
480
481 To attach to a named keyring, the keyring must have search permission for
482 the process's ownership.
483
484 The ID of the new session keyring is returned if successful.
485
486
487 (*) Update the specified key:
488
489 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload,
490 size_t plen);
491
492 This will try to update the specified key with the given payload, or it
493 will return error EOPNOTSUPP if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700494 type. The process must also have permission to write to the key to be able
495 to update it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700496
497 The payload is of length plen, and may be absent or empty as for
498 add_key().
499
500
501 (*) Revoke a key:
502
503 long keyctl(KEYCTL_REVOKE, key_serial_t key);
504
505 This makes a key unavailable for further operations. Further attempts to
506 use the key will be met with error EKEYREVOKED, and the key will no longer
507 be findable.
508
509
510 (*) Change the ownership of a key:
511
512 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid);
513
David Howells76d8aea2005-06-23 22:00:49 -0700514 This function permits a key's owner and group ID to be changed. Either one
515 of uid or gid can be set to -1 to suppress that change.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700516
517 Only the superuser can change a key's owner to something other than the
518 key's current owner. Similarly, only the superuser can change a key's
519 group ID to something other than the calling process's group ID or one of
520 its group list members.
521
522
523 (*) Change the permissions mask on a key:
524
525 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm);
526
527 This function permits the owner of a key or the superuser to change the
528 permissions mask on a key.
529
530 Only bits the available bits are permitted; if any other bits are set,
531 error EINVAL will be returned.
532
533
534 (*) Describe a key:
535
536 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer,
537 size_t buflen);
538
539 This function returns a summary of the key's attributes (but not its
540 payload data) as a string in the buffer provided.
541
542 Unless there's an error, it always returns the amount of data it could
543 produce, even if that's too big for the buffer, but it won't copy more
544 than requested to userspace. If the buffer pointer is NULL then no copy
545 will take place.
546
547 A process must have view permission on the key for this function to be
548 successful.
549
550 If successful, a string is placed in the buffer in the following format:
551
552 <type>;<uid>;<gid>;<perm>;<description>
553
554 Where type and description are strings, uid and gid are decimal, and perm
555 is hexadecimal. A NUL character is included at the end of the string if
556 the buffer is sufficiently big.
557
558 This can be parsed with
559
560 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc);
561
562
563 (*) Clear out a keyring:
564
565 long keyctl(KEYCTL_CLEAR, key_serial_t keyring);
566
567 This function clears the list of keys attached to a keyring. The calling
568 process must have write permission on the keyring, and it must be a
569 keyring (or else error ENOTDIR will result).
570
David Howells700920e2012-01-18 15:31:45 +0000571 This function can also be used to clear special kernel keyrings if they
572 are appropriately marked if the user has CAP_SYS_ADMIN capability. The
573 DNS resolver cache keyring is an example of this.
574
Linus Torvalds1da177e2005-04-16 15:20:36 -0700575
576 (*) Link a key into a keyring:
577
578 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key);
579
David Howells76d8aea2005-06-23 22:00:49 -0700580 This function creates a link from the keyring to the key. The process must
581 have write permission on the keyring and must have link permission on the
582 key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700583
David Howells76d8aea2005-06-23 22:00:49 -0700584 Should the keyring not be a keyring, error ENOTDIR will result; and if the
585 keyring is full, error ENFILE will result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700586
587 The link procedure checks the nesting of the keyrings, returning ELOOP if
David Howells017679c2006-01-08 01:02:43 -0800588 it appears too deep or EDEADLK if the link would introduce a cycle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700589
David Howellscab8eb52006-01-08 01:02:45 -0800590 Any links within the keyring to keys that match the new key in terms of
591 type and description will be discarded from the keyring as the new one is
592 added.
593
Linus Torvalds1da177e2005-04-16 15:20:36 -0700594
595 (*) Unlink a key or keyring from another keyring:
596
597 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
598
599 This function looks through the keyring for the first link to the
600 specified key, and removes it if found. Subsequent links to that key are
601 ignored. The process must have write permission on the keyring.
602
David Howells76d8aea2005-06-23 22:00:49 -0700603 If the keyring is not a keyring, error ENOTDIR will result; and if the key
604 is not present, error ENOENT will be the result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700605
606
607 (*) Search a keyring tree for a key:
608
609 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring,
610 const char *type, const char *description,
611 key_serial_t dest_keyring);
612
David Howells76d8aea2005-06-23 22:00:49 -0700613 This searches the keyring tree headed by the specified keyring until a key
614 is found that matches the type and description criteria. Each keyring is
615 checked for keys before recursion into its children occurs.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700616
617 The process must have search permission on the top level keyring, or else
618 error EACCES will result. Only keyrings that the process has search
619 permission on will be recursed into, and only keys and keyrings for which
620 a process has search permission can be matched. If the specified keyring
621 is not a keyring, ENOTDIR will result.
622
623 If the search succeeds, the function will attempt to link the found key
624 into the destination keyring if one is supplied (non-zero ID). All the
625 constraints applicable to KEYCTL_LINK apply in this case too.
626
627 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search
628 fails. On success, the resulting key ID will be returned.
629
630
631 (*) Read the payload data from a key:
632
David Howellsf1a9bad2005-10-07 15:04:52 +0100633 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
634 size_t buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700635
636 This function attempts to read the payload data from the specified key
637 into the buffer. The process must have read permission on the key to
638 succeed.
639
640 The returned data will be processed for presentation by the key type. For
641 instance, a keyring will return an array of key_serial_t entries
642 representing the IDs of all the keys to which it is subscribed. The user
643 defined key type will return its data as is. If a key type does not
644 implement this function, error EOPNOTSUPP will result.
645
646 As much of the data as can be fitted into the buffer will be copied to
647 userspace if the buffer pointer is not NULL.
648
David Howells76d8aea2005-06-23 22:00:49 -0700649 On a successful return, the function will always return the amount of data
650 available rather than the amount copied.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700651
652
653 (*) Instantiate a partially constructed key.
654
David Howellsf1a9bad2005-10-07 15:04:52 +0100655 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
656 const void *payload, size_t plen,
657 key_serial_t keyring);
David Howellsee009e4a02011-03-07 15:06:20 +0000658 long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key,
659 const struct iovec *payload_iov, unsigned ioc,
660 key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700661
662 If the kernel calls back to userspace to complete the instantiation of a
663 key, userspace should use this call to supply data for the key before the
664 invoked process returns, or else the key will be marked negative
665 automatically.
666
667 The process must have write access on the key to be able to instantiate
668 it, and the key must be uninstantiated.
669
670 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700671 that keyring, however all the constraints applying in KEYCTL_LINK apply in
672 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700673
674 The payload and plen arguments describe the payload data as for add_key().
675
David Howellsee009e4a02011-03-07 15:06:20 +0000676 The payload_iov and ioc arguments describe the payload data in an iovec
677 array instead of a single buffer.
678
Linus Torvalds1da177e2005-04-16 15:20:36 -0700679
680 (*) Negatively instantiate a partially constructed key.
681
David Howellsf1a9bad2005-10-07 15:04:52 +0100682 long keyctl(KEYCTL_NEGATE, key_serial_t key,
683 unsigned timeout, key_serial_t keyring);
David Howellsfdd1b942011-03-07 15:06:09 +0000684 long keyctl(KEYCTL_REJECT, key_serial_t key,
685 unsigned timeout, unsigned error, key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700686
687 If the kernel calls back to userspace to complete the instantiation of a
688 key, userspace should use this call mark the key as negative before the
Masanari Iida40e47122012-03-04 23:16:11 +0900689 invoked process returns if it is unable to fulfill the request.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700690
691 The process must have write access on the key to be able to instantiate
692 it, and the key must be uninstantiated.
693
694 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700695 that keyring, however all the constraints applying in KEYCTL_LINK apply in
696 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700697
David Howellsfdd1b942011-03-07 15:06:09 +0000698 If the key is rejected, future searches for it will return the specified
699 error code until the rejected key expires. Negating the key is the same
700 as rejecting the key with ENOKEY as the error code.
701
Linus Torvalds1da177e2005-04-16 15:20:36 -0700702
David Howells3e301482005-06-23 22:00:56 -0700703 (*) Set the default request-key destination keyring.
704
705 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl);
706
707 This sets the default keyring to which implicitly requested keys will be
708 attached for this thread. reqkey_defl should be one of these constants:
709
710 CONSTANT VALUE NEW DEFAULT KEYRING
711 ====================================== ====== =======================
712 KEY_REQKEY_DEFL_NO_CHANGE -1 No change
713 KEY_REQKEY_DEFL_DEFAULT 0 Default[1]
714 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring
715 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring
716 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring
717 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring
718 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring
719 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring
720
721 The old default will be returned if successful and error EINVAL will be
722 returned if reqkey_defl is not one of the above values.
723
724 The default keyring can be overridden by the keyring indicated to the
725 request_key() system call.
726
727 Note that this setting is inherited across fork/exec.
728
Paolo Ornati670e9f32006-10-03 22:57:56 +0200729 [1] The default is: the thread keyring if there is one, otherwise
David Howells3e301482005-06-23 22:00:56 -0700730 the process keyring if there is one, otherwise the session keyring if
731 there is one, otherwise the user default session keyring.
732
733
David Howells017679c2006-01-08 01:02:43 -0800734 (*) Set the timeout on a key.
735
736 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
737
738 This sets or clears the timeout on a key. The timeout can be 0 to clear
739 the timeout or a number of seconds to set the expiry time that far into
740 the future.
741
742 The process must have attribute modification access on a key to set its
743 timeout. Timeouts may not be set with this function on negative, revoked
744 or expired keys.
745
746
David Howellsb5f545c2006-01-08 01:02:47 -0800747 (*) Assume the authority granted to instantiate a key
748
749 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
750
751 This assumes or divests the authority required to instantiate the
752 specified key. Authority can only be assumed if the thread has the
753 authorisation key associated with the specified key in its keyrings
754 somewhere.
755
756 Once authority is assumed, searches for keys will also search the
757 requester's keyrings using the requester's security label, UID, GID and
758 groups.
759
760 If the requested authority is unavailable, error EPERM will be returned,
761 likewise if the authority has been revoked because the target key is
762 already instantiated.
763
764 If the specified key is 0, then any assumed authority will be divested.
765
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200766 The assumed authoritative key is inherited across fork and exec.
David Howellsb5f545c2006-01-08 01:02:47 -0800767
768
David Howells70a5bb72008-04-29 01:01:26 -0700769 (*) Get the LSM security context attached to a key.
770
771 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
772 size_t buflen)
773
774 This function returns a string that represents the LSM security context
775 attached to a key in the buffer provided.
776
777 Unless there's an error, it always returns the amount of data it could
778 produce, even if that's too big for the buffer, but it won't copy more
779 than requested to userspace. If the buffer pointer is NULL then no copy
780 will take place.
781
782 A NUL character is included at the end of the string if the buffer is
783 sufficiently big. This is included in the returned count. If no LSM is
784 in force then an empty string will be returned.
785
786 A process must have view permission on the key for this function to be
787 successful.
788
789
David Howellsee18d642009-09-02 09:14:21 +0100790 (*) Install the calling process's session keyring on its parent.
791
792 long keyctl(KEYCTL_SESSION_TO_PARENT);
793
794 This functions attempts to install the calling process's session keyring
795 on to the calling process's parent, replacing the parent's current session
796 keyring.
797
798 The calling process must have the same ownership as its parent, the
799 keyring must have the same ownership as the calling process, the calling
800 process must have LINK permission on the keyring and the active LSM module
801 mustn't deny permission, otherwise error EPERM will be returned.
802
803 Error ENOMEM will be returned if there was insufficient memory to complete
804 the operation, otherwise 0 will be returned to indicate success.
805
806 The keyring will be replaced next time the parent process leaves the
807 kernel and resumes executing userspace.
808
809
David Howellsfd758152012-05-11 10:56:56 +0100810 (*) Invalidate a key.
811
812 long keyctl(KEYCTL_INVALIDATE, key_serial_t key);
813
814 This function marks a key as being invalidated and then wakes up the
815 garbage collector. The garbage collector immediately removes invalidated
816 keys from all keyrings and deletes the key when its reference count
817 reaches zero.
818
819 Keys that are marked invalidated become invisible to normal key operations
820 immediately, though they are still visible in /proc/keys until deleted
821 (they're marked with an 'i' flag).
822
823 A process must have search permission on the key for this function to be
824 successful.
825
Mat Martineauddbb4112016-04-12 19:54:58 +0100826 (*) Compute a Diffie-Hellman shared secret or public key
827
828 long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params,
Stephan Mueller4693fc72016-05-26 23:38:12 +0200829 char *buffer, size_t buflen,
830 void *reserved);
Mat Martineauddbb4112016-04-12 19:54:58 +0100831
832 The params struct contains serial numbers for three keys:
833
834 - The prime, p, known to both parties
835 - The local private key
836 - The base integer, which is either a shared generator or the
837 remote public key
838
839 The value computed is:
840
841 result = base ^ private (mod prime)
842
843 If the base is the shared generator, the result is the local
844 public key. If the base is the remote public key, the result is
845 the shared secret.
846
Stephan Mueller4693fc72016-05-26 23:38:12 +0200847 The reserved argument must be set to NULL.
848
Mat Martineauddbb4112016-04-12 19:54:58 +0100849 The buffer length must be at least the length of the prime, or zero.
850
851 If the buffer length is nonzero, the length of the result is
852 returned when it is successfully calculated and copied in to the
853 buffer. When the buffer length is zero, the minimum required
854 buffer length is returned.
855
856 This function will return error EOPNOTSUPP if the key type is not
857 supported, error ENOKEY if the key could not be found, or error
858 EACCES if the key is not readable by the caller.
David Howellsfd758152012-05-11 10:56:56 +0100859
Linus Torvalds1da177e2005-04-16 15:20:36 -0700860===============
861KERNEL SERVICES
862===============
863
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200864The kernel services for key management are fairly simple to deal with. They can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700865be broken down into two areas: keys and key types.
866
867Dealing with keys is fairly straightforward. Firstly, the kernel service
868registers its type, then it searches for a key of that type. It should retain
869the key as long as it has need of it, and then it should release it. For a
David Howells76d8aea2005-06-23 22:00:49 -0700870filesystem or device file, a search would probably be performed during the open
871call, and the key released upon close. How to deal with conflicting keys due to
872two different users opening the same file is left to the filesystem author to
873solve.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700874
David Howells76181c12007-10-16 23:29:46 -0700875To access the key manager, the following header must be #included:
876
877 <linux/key.h>
878
879Specific key types should have a header file under include/keys/ that should be
880used to access that type. For keys of type "user", for example, that would be:
881
882 <keys/user-type.h>
883
David Howells664cceb2005-09-28 17:03:15 +0100884Note that there are two different types of pointers to keys that may be
885encountered:
886
887 (*) struct key *
888
889 This simply points to the key structure itself. Key structures will be at
890 least four-byte aligned.
891
892 (*) key_ref_t
893
894 This is equivalent to a struct key *, but the least significant bit is set
895 if the caller "possesses" the key. By "possession" it is meant that the
896 calling processes has a searchable link to the key from one of its
897 keyrings. There are three functions for dealing with these:
898
David Howellsa5b4bd22013-09-24 10:35:14 +0100899 key_ref_t make_key_ref(const struct key *key, bool possession);
David Howells664cceb2005-09-28 17:03:15 +0100900
901 struct key *key_ref_to_ptr(const key_ref_t key_ref);
902
David Howellsa5b4bd22013-09-24 10:35:14 +0100903 bool is_key_possessed(const key_ref_t key_ref);
David Howells664cceb2005-09-28 17:03:15 +0100904
905 The first function constructs a key reference from a key pointer and
David Howellsa5b4bd22013-09-24 10:35:14 +0100906 possession information (which must be true or false).
David Howells664cceb2005-09-28 17:03:15 +0100907
908 The second function retrieves the key pointer from a reference and the
909 third retrieves the possession flag.
910
David Howells76d8aea2005-06-23 22:00:49 -0700911When accessing a key's payload contents, certain precautions must be taken to
912prevent access vs modification races. See the section "Notes on accessing
913payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700914
915(*) To search for a key, call:
916
917 struct key *request_key(const struct key_type *type,
918 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700919 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700920
921 This is used to request a key or keyring with a description that matches
David Howellsf93b3cc2014-09-16 17:36:09 +0100922 the description specified according to the key type's match_preparse()
923 method. This permits approximate matching to occur. If callout_string is
924 not NULL, then /sbin/request-key will be invoked in an attempt to obtain
925 the key from userspace. In that case, callout_string will be passed as an
926 argument to the program.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700927
928 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
929 returned.
930
David Howells3e301482005-06-23 22:00:56 -0700931 If successful, the key will have been attached to the default keyring for
932 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
933
Randy Dunlapd410fa42011-05-19 15:59:38 -0700934 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100935
Linus Torvalds1da177e2005-04-16 15:20:36 -0700936
David Howells4e54f082006-06-29 02:24:28 -0700937(*) To search for a key, passing auxiliary data to the upcaller, call:
938
939 struct key *request_key_with_auxdata(const struct key_type *type,
940 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700941 const void *callout_info,
942 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700943 void *aux);
944
945 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700946 passed to the key_type->request_key() op if it exists, and the callout_info
947 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700948
949
David Howells76181c12007-10-16 23:29:46 -0700950(*) A key can be requested asynchronously by calling one of:
951
952 struct key *request_key_async(const struct key_type *type,
953 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700954 const void *callout_info,
955 size_t callout_len);
David Howells76181c12007-10-16 23:29:46 -0700956
957 or:
958
959 struct key *request_key_async_with_auxdata(const struct key_type *type,
960 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700961 const char *callout_info,
962 size_t callout_len,
David Howells76181c12007-10-16 23:29:46 -0700963 void *aux);
964
965 which are asynchronous equivalents of request_key() and
966 request_key_with_auxdata() respectively.
967
968 These two functions return with the key potentially still under
Matt LaPlanted9195882008-07-25 19:45:33 -0700969 construction. To wait for construction completion, the following should be
David Howells76181c12007-10-16 23:29:46 -0700970 called:
971
972 int wait_for_key_construction(struct key *key, bool intr);
973
974 The function will wait for the key to finish being constructed and then
975 invokes key_validate() to return an appropriate value to indicate the state
976 of the key (0 indicates the key is usable).
977
978 If intr is true, then the wait can be interrupted by a signal, in which
979 case error ERESTARTSYS will be returned.
980
981
Linus Torvalds1da177e2005-04-16 15:20:36 -0700982(*) When it is no longer required, the key should be released using:
983
984 void key_put(struct key *key);
985
David Howells664cceb2005-09-28 17:03:15 +0100986 Or:
987
988 void key_ref_put(key_ref_t key_ref);
989
990 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700991 the argument will not be parsed.
992
993
David Howellsccc3e6d2013-09-24 10:35:16 +0100994(*) Extra references can be made to a key by calling one of the following
995 functions:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700996
David Howellsccc3e6d2013-09-24 10:35:16 +0100997 struct key *__key_get(struct key *key);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700998 struct key *key_get(struct key *key);
999
David Howellsccc3e6d2013-09-24 10:35:16 +01001000 Keys so references will need to be disposed of by calling key_put() when
1001 they've been finished with. The key pointer passed in will be returned.
1002
1003 In the case of key_get(), if the pointer is NULL or CONFIG_KEYS is not set
1004 then the key will not be dereferenced and no increment will take place.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001005
1006
1007(*) A key's serial number can be obtained by calling:
1008
1009 key_serial_t key_serial(struct key *key);
1010
1011 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
1012 latter case without parsing the argument).
1013
1014
1015(*) If a keyring was found in the search, this can be further searched by:
1016
David Howells664cceb2005-09-28 17:03:15 +01001017 key_ref_t keyring_search(key_ref_t keyring_ref,
1018 const struct key_type *type,
1019 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001020
1021 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +01001022 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
1023 the returned key will need to be released.
1024
1025 The possession attribute from the keyring reference is used to control
1026 access through the permissions mask and is propagated to the returned key
1027 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001028
1029
David Howellsf8aa23a2012-10-02 19:24:56 +01001030(*) A keyring can be created by:
1031
1032 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
1033 const struct cred *cred,
1034 key_perm_t perm,
David Howells5ac7eac2016-04-06 16:14:24 +01001035 int (*restrict_link)(struct key *,
1036 const struct key_type *,
1037 unsigned long,
1038 const union key_payload *),
David Howellsf8aa23a2012-10-02 19:24:56 +01001039 unsigned long flags,
1040 struct key *dest);
1041
1042 This creates a keyring with the given attributes and returns it. If dest
1043 is not NULL, the new keyring will be linked into the keyring to which it
1044 points. No permission checks are made upon the destination keyring.
1045
1046 Error EDQUOT can be returned if the keyring would overload the quota (pass
1047 KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted
1048 towards the user's quota). Error ENOMEM can also be returned.
1049
David Howells5ac7eac2016-04-06 16:14:24 +01001050 If restrict_link not NULL, it should point to a function that will be
1051 called each time an attempt is made to link a key into the new keyring.
1052 This function is called to check whether a key may be added into the keying
1053 or not. Callers of key_create_or_update() within the kernel can pass
1054 KEY_ALLOC_BYPASS_RESTRICTION to suppress the check. An example of using
1055 this is to manage rings of cryptographic keys that are set up when the
1056 kernel boots where userspace is also permitted to add keys - provided they
1057 can be verified by a key the kernel already has.
1058
1059 When called, the restriction function will be passed the keyring being
1060 added to, the key flags value and the type and payload of the key being
1061 added. Note that when a new key is being created, this is called between
1062 payload preparsing and actual key creation. The function should return 0
1063 to allow the link or an error to reject it.
1064
1065 A convenience function, restrict_link_reject, exists to always return
1066 -EPERM to in this case.
1067
David Howellsf8aa23a2012-10-02 19:24:56 +01001068
Linus Torvalds1da177e2005-04-16 15:20:36 -07001069(*) To check the validity of a key, this function can be called:
1070
1071 int validate_key(struct key *key);
1072
1073 This checks that the key in question hasn't expired or and hasn't been
1074 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
1075 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
1076 returned (in the latter case without parsing the argument).
1077
1078
1079(*) To register a key type, the following function should be called:
1080
1081 int register_key_type(struct key_type *type);
1082
1083 This will return error EEXIST if a type of the same name is already
1084 present.
1085
1086
1087(*) To unregister a key type, call:
1088
1089 void unregister_key_type(struct key_type *type);
1090
1091
Satyam Sharma7eacbbd2007-07-31 00:38:17 -07001092Under some circumstances, it may be desirable to deal with a bundle of keys.
1093The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -07001094
1095 struct key_type key_type_keyring;
1096
1097This can be used with a function such as request_key() to find a specific
1098keyring in a process's keyrings. A keyring thus found can then be searched
1099with keyring_search(). Note that it is not possible to use request_key() to
1100search a specific keyring, so using keyrings in this way is of limited utility.
1101
1102
David Howells76d8aea2005-06-23 22:00:49 -07001103===================================
1104NOTES ON ACCESSING PAYLOAD CONTENTS
1105===================================
1106
David Howells146aa8b2015-10-21 14:04:48 +01001107The simplest payload is just data stored in key->payload directly. In this
1108case, there's no need to indulge in RCU or locking when accessing the payload.
David Howells76d8aea2005-06-23 22:00:49 -07001109
David Howells146aa8b2015-10-21 14:04:48 +01001110More complex payload contents must be allocated and pointers to them set in the
1111key->payload.data[] array. One of the following ways must be selected to
1112access the data:
David Howells76d8aea2005-06-23 22:00:49 -07001113
David Howells664cceb2005-09-28 17:03:15 +01001114 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -07001115
1116 If the key type does not have a modify method, then the key's payload can
1117 be accessed without any form of locking, provided that it's known to be
1118 instantiated (uninstantiated keys cannot be "found").
1119
1120 (2) The key's semaphore.
1121
1122 The semaphore could be used to govern access to the payload and to control
1123 the payload pointer. It must be write-locked for modifications and would
1124 have to be read-locked for general access. The disadvantage of doing this
1125 is that the accessor may be required to sleep.
1126
1127 (3) RCU.
1128
1129 RCU must be used when the semaphore isn't already held; if the semaphore
1130 is held then the contents can't change under you unexpectedly as the
1131 semaphore must still be used to serialise modifications to the key. The
1132 key management code takes care of this for the key type.
1133
1134 However, this means using:
1135
1136 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
1137
1138 to read the pointer, and:
1139
1140 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
1141
1142 to set the pointer and dispose of the old contents after a grace period.
1143 Note that only the key type should ever modify a key's payload.
1144
1145 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1146 use of call_rcu() and, if the payload is of variable size, the length of
1147 the payload. key->datalen cannot be relied upon to be consistent with the
1148 payload just dereferenced if the key's semaphore is not held.
1149
David Howells146aa8b2015-10-21 14:04:48 +01001150 Note that key->payload.data[0] has a shadow that is marked for __rcu
1151 usage. This is called key->payload.rcu_data0. The following accessors
1152 wrap the RCU calls to this element:
1153
1154 rcu_assign_keypointer(struct key *key, void *data);
1155 void *rcu_dereference_key(struct key *key);
1156
David Howells76d8aea2005-06-23 22:00:49 -07001157
Linus Torvalds1da177e2005-04-16 15:20:36 -07001158===================
1159DEFINING A KEY TYPE
1160===================
1161
1162A kernel service may want to define its own key type. For instance, an AFS
1163filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c12007-10-16 23:29:46 -07001164author fills in a key_type struct and registers it with the system.
1165
1166Source files that implement key types should include the following header file:
1167
1168 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001169
1170The structure has a number of fields, some of which are mandatory:
1171
1172 (*) const char *name
1173
1174 The name of the key type. This is used to translate a key type name
1175 supplied by userspace into a pointer to the structure.
1176
1177
1178 (*) size_t def_datalen
1179
1180 This is optional - it supplies the default payload data length as
1181 contributed to the quota. If the key type's payload is always or almost
1182 always the same size, then this is a more efficient way to do things.
1183
1184 The data length (and quota) on a particular key can always be changed
1185 during instantiation or update by calling:
1186
1187 int key_payload_reserve(struct key *key, size_t datalen);
1188
David Howells76d8aea2005-06-23 22:00:49 -07001189 With the revised data length. Error EDQUOT will be returned if this is not
1190 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001191
1192
David Howellsb9fffa32011-03-07 15:05:59 +00001193 (*) int (*vet_description)(const char *description);
1194
1195 This optional method is called to vet a key description. If the key type
1196 doesn't approve of the key description, it may return an error, otherwise
1197 it should return 0.
1198
1199
David Howellsd4f65b52012-09-13 13:06:29 +01001200 (*) int (*preparse)(struct key_preparsed_payload *prep);
1201
1202 This optional method permits the key type to attempt to parse payload
1203 before a key is created (add key) or the key semaphore is taken (update or
1204 instantiate key). The structure pointed to by prep looks like:
1205
1206 struct key_preparsed_payload {
1207 char *description;
David Howells146aa8b2015-10-21 14:04:48 +01001208 union key_payload payload;
David Howellsd4f65b52012-09-13 13:06:29 +01001209 const void *data;
1210 size_t datalen;
1211 size_t quotalen;
David Howells7dfa0ca2014-07-18 18:56:34 +01001212 time_t expiry;
David Howellsd4f65b52012-09-13 13:06:29 +01001213 };
1214
1215 Before calling the method, the caller will fill in data and datalen with
1216 the payload blob parameters; quotalen will be filled in with the default
David Howells7dfa0ca2014-07-18 18:56:34 +01001217 quota size from the key type; expiry will be set to TIME_T_MAX and the
1218 rest will be cleared.
David Howellsd4f65b52012-09-13 13:06:29 +01001219
1220 If a description can be proposed from the payload contents, that should be
1221 attached as a string to the description field. This will be used for the
1222 key description if the caller of add_key() passes NULL or "".
1223
David Howells146aa8b2015-10-21 14:04:48 +01001224 The method can attach anything it likes to payload. This is merely passed
1225 along to the instantiate() or update() operations. If set, the expiry
1226 time will be applied to the key if it is instantiated from this data.
David Howellsd4f65b52012-09-13 13:06:29 +01001227
David Howells7dfa0ca2014-07-18 18:56:34 +01001228 The method should return 0 if successful or a negative error code
David Howellsd4f65b52012-09-13 13:06:29 +01001229 otherwise.
1230
David Howellsf93b3cc2014-09-16 17:36:09 +01001231
David Howellsd4f65b52012-09-13 13:06:29 +01001232 (*) void (*free_preparse)(struct key_preparsed_payload *prep);
1233
1234 This method is only required if the preparse() method is provided,
David Howells146aa8b2015-10-21 14:04:48 +01001235 otherwise it is unused. It cleans up anything attached to the description
1236 and payload fields of the key_preparsed_payload struct as filled in by the
1237 preparse() method. It will always be called after preparse() returns
1238 successfully, even if instantiate() or update() succeed.
David Howellsd4f65b52012-09-13 13:06:29 +01001239
1240
1241 (*) int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001242
1243 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001244 The payload attached need not bear any relation to the data passed to this
1245 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001246
David Howellsd4f65b52012-09-13 13:06:29 +01001247 The prep->data and prep->datalen fields will define the original payload
1248 blob. If preparse() was supplied then other fields may be filled in also.
1249
Linus Torvalds1da177e2005-04-16 15:20:36 -07001250 If the amount of data attached to the key differs from the size in
1251 keytype->def_datalen, then key_payload_reserve() should be called.
1252
1253 This method does not have to lock the key in order to attach a payload.
1254 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1255 anything else from gaining access to the key.
1256
David Howells76d8aea2005-06-23 22:00:49 -07001257 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001258
David Howells146aa8b2015-10-21 14:04:48 +01001259 generic_key_instantiate() is provided to simply copy the data from
1260 prep->payload.data[] to key->payload.data[], with RCU-safe assignment on
1261 the first element. It will then clear prep->payload.data[] so that the
1262 free_preparse method doesn't release the data.
1263
Linus Torvalds1da177e2005-04-16 15:20:36 -07001264
Linus Torvalds1da177e2005-04-16 15:20:36 -07001265 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1266
David Howells76d8aea2005-06-23 22:00:49 -07001267 If this type of key can be updated, then this method should be provided.
1268 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001269
David Howellsd4f65b52012-09-13 13:06:29 +01001270 The prep->data and prep->datalen fields will define the original payload
1271 blob. If preparse() was supplied then other fields may be filled in also.
1272
Linus Torvalds1da177e2005-04-16 15:20:36 -07001273 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001274 before any changes are actually made. Note that if this succeeds, the type
1275 is committed to changing the key because it's already been altered, so all
1276 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001277
David Howells76d8aea2005-06-23 22:00:49 -07001278 The key will have its semaphore write-locked before this method is called,
1279 but this only deters other writers; any changes to the key's payload must
1280 be made under RCU conditions, and call_rcu() must be used to dispose of
1281 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001282
David Howells76d8aea2005-06-23 22:00:49 -07001283 key_payload_reserve() should be called before the changes are made, but
1284 after all allocations and other potentially failing function calls are
1285 made.
1286
1287 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001288
1289
David Howellsf93b3cc2014-09-16 17:36:09 +01001290 (*) int (*match_preparse)(struct key_match_data *match_data);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001291
David Howellsf93b3cc2014-09-16 17:36:09 +01001292 This method is optional. It is called when a key search is about to be
1293 performed. It is given the following structure:
Linus Torvalds1da177e2005-04-16 15:20:36 -07001294
David Howellsf93b3cc2014-09-16 17:36:09 +01001295 struct key_match_data {
1296 bool (*cmp)(const struct key *key,
1297 const struct key_match_data *match_data);
1298 const void *raw_data;
1299 void *preparsed;
1300 unsigned lookup_type;
1301 };
Linus Torvalds1da177e2005-04-16 15:20:36 -07001302
David Howellsf93b3cc2014-09-16 17:36:09 +01001303 On entry, raw_data will be pointing to the criteria to be used in matching
1304 a key by the caller and should not be modified. (*cmp)() will be pointing
1305 to the default matcher function (which does an exact description match
1306 against raw_data) and lookup_type will be set to indicate a direct lookup.
1307
1308 The following lookup_type values are available:
1309
1310 [*] KEYRING_SEARCH_LOOKUP_DIRECT - A direct lookup hashes the type and
1311 description to narrow down the search to a small number of keys.
1312
1313 [*] KEYRING_SEARCH_LOOKUP_ITERATE - An iterative lookup walks all the
1314 keys in the keyring until one is matched. This must be used for any
1315 search that's not doing a simple direct match on the key description.
1316
1317 The method may set cmp to point to a function of its choice that does some
1318 other form of match, may set lookup_type to KEYRING_SEARCH_LOOKUP_ITERATE
1319 and may attach something to the preparsed pointer for use by (*cmp)().
1320 (*cmp)() should return true if a key matches and false otherwise.
1321
1322 If preparsed is set, it may be necessary to use the match_free() method to
1323 clean it up.
1324
1325 The method should return 0 if successful or a negative error code
1326 otherwise.
1327
1328 It is permitted to sleep in this method, but (*cmp)() may not sleep as
1329 locks will be held over it.
1330
1331 If match_preparse() is not provided, keys of this type will be matched
1332 exactly by their description.
1333
1334
1335 (*) void (*match_free)(struct key_match_data *match_data);
1336
1337 This method is optional. If given, it called to clean up
1338 match_data->preparsed after a successful call to match_preparse().
Linus Torvalds1da177e2005-04-16 15:20:36 -07001339
1340
David Howells04c567d2006-06-22 14:47:18 -07001341 (*) void (*revoke)(struct key *key);
1342
1343 This method is optional. It is called to discard part of the payload
1344 data upon a key being revoked. The caller will have the key semaphore
1345 write-locked.
1346
1347 It is safe to sleep in this method, though care should be taken to avoid
1348 a deadlock against the key semaphore.
1349
1350
Linus Torvalds1da177e2005-04-16 15:20:36 -07001351 (*) void (*destroy)(struct key *key);
1352
David Howells76d8aea2005-06-23 22:00:49 -07001353 This method is optional. It is called to discard the payload data on a key
1354 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001355
David Howells76d8aea2005-06-23 22:00:49 -07001356 This method does not need to lock the key to access the payload; it can
1357 consider the key as being inaccessible at this time. Note that the key's
1358 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001359
1360 It is not safe to sleep in this method; the caller may hold spinlocks.
1361
1362
1363 (*) void (*describe)(const struct key *key, struct seq_file *p);
1364
1365 This method is optional. It is called during /proc/keys reading to
1366 summarise a key's description and payload in text form.
1367
David Howells76d8aea2005-06-23 22:00:49 -07001368 This method will be called with the RCU read lock held. rcu_dereference()
1369 should be used to read the payload pointer if the payload is to be
1370 accessed. key->datalen cannot be trusted to stay consistent with the
1371 contents of the payload.
1372
1373 The description will not change, though the key's state may.
1374
1375 It is not safe to sleep in this method; the RCU read lock is held by the
1376 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001377
1378
1379 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1380
1381 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001382 key's payload into something a blob of data for userspace to deal with.
1383 Ideally, the blob should be in the same format as that passed in to the
1384 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001385
1386 If successful, the blob size that could be produced should be returned
1387 rather than the size copied.
1388
David Howells76d8aea2005-06-23 22:00:49 -07001389 This method will be called with the key's semaphore read-locked. This will
1390 prevent the key's payload changing. It is not necessary to use RCU locking
1391 when accessing the key's payload. It is safe to sleep in this method, such
1392 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001393
1394
David Howells76181c12007-10-16 23:29:46 -07001395 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001396 void *aux);
1397
David Howells76181c12007-10-16 23:29:46 -07001398 This method is optional. If provided, request_key() and friends will
1399 invoke this function rather than upcalling to /sbin/request-key to operate
1400 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001401
David Howells76181c12007-10-16 23:29:46 -07001402 The aux parameter is as passed to request_key_async_with_auxdata() and
1403 similar or is NULL otherwise. Also passed are the construction record for
1404 the key to be operated upon and the operation type (currently only
1405 "create").
David Howells4e54f082006-06-29 02:24:28 -07001406
David Howells76181c12007-10-16 23:29:46 -07001407 This method is permitted to return before the upcall is complete, but the
1408 following function must be called under all circumstances to complete the
1409 instantiation process, whether or not it succeeds, whether or not there's
1410 an error:
1411
1412 void complete_request_key(struct key_construction *cons, int error);
1413
1414 The error parameter should be 0 on success, -ve on error. The
1415 construction record is destroyed by this action and the authorisation key
1416 will be revoked. If an error is indicated, the key under construction
1417 will be negatively instantiated if it wasn't already instantiated.
1418
1419 If this method returns an error, that error will be returned to the
1420 caller of request_key*(). complete_request_key() must be called prior to
1421 returning.
1422
1423 The key under construction and the authorisation key can be found in the
1424 key_construction struct pointed to by cons:
1425
1426 (*) struct key *key;
1427
1428 The key under construction.
1429
1430 (*) struct key *authkey;
1431
1432 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001433
1434
Linus Torvalds1da177e2005-04-16 15:20:36 -07001435============================
1436REQUEST-KEY CALLBACK SERVICE
1437============================
1438
1439To create a new key, the kernel will attempt to execute the following command
1440line:
1441
1442 /sbin/request-key create <key> <uid> <gid> \
1443 <threadring> <processring> <sessionring> <callout_info>
1444
1445<key> is the key being constructed, and the three keyrings are the process
1446keyrings from the process that caused the search to be issued. These are
1447included for two reasons:
1448
1449 (1) There may be an authentication token in one of the keyrings that is
1450 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1451
1452 (2) The new key should probably be cached in one of these rings.
1453
1454This program should set it UID and GID to those specified before attempting to
1455access any more keys. It may then look around for a user specific process to
1456hand the request off to (perhaps a path held in placed in another key by, for
1457example, the KDE desktop manager).
1458
1459The program (or whatever it calls) should finish construction of the key by
David Howellsee009e4a02011-03-07 15:06:20 +00001460calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to
1461cache the key in one of the keyrings (probably the session ring) before
1462returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE
1463or KEYCTL_REJECT; this also permits the key to be cached in one of the
1464keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001465
1466If it returns with the key remaining in the unconstructed state, the key will
1467be marked as being negative, it will be added to the session keyring, and an
1468error will be returned to the key requestor.
1469
David Howells76d8aea2005-06-23 22:00:49 -07001470Supplementary information may be provided from whoever or whatever invoked this
1471service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001472information was made available, then "-" will be passed as this parameter
1473instead.
1474
1475
1476Similarly, the kernel may attempt to update an expired or a soon to expire key
1477by executing:
1478
1479 /sbin/request-key update <key> <uid> <gid> \
1480 <threadring> <processring> <sessionring>
1481
1482In this case, the program isn't required to actually attach the key to a ring;
1483the rings are provided for reference.
David Howells5d135442009-09-02 09:14:00 +01001484
1485
1486==================
1487GARBAGE COLLECTION
1488==================
1489
1490Dead keys (for which the type has been removed) will be automatically unlinked
1491from those keyrings that point to them and deleted as soon as possible by a
1492background garbage collector.
1493
1494Similarly, revoked and expired keys will be garbage collected, but only after a
1495certain amount of time has passed. This time is set as a number of seconds in:
1496
1497 /proc/sys/kernel/keys/gc_delay