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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
326 This file must be enabled at kernel configuration time as it allows anyone
327 to list the keys database.
328
329 (*) /proc/key-users
330
331 This file lists the tracking data for each user that has at least one key
Michael LeMay06ec7be2006-06-26 00:24:56 -0700332 on the system. Such data includes quota information and statistics:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700333
334 [root@andromeda root]# cat /proc/key-users
335 0: 46 45/45 1/100 13/10000
336 29: 2 2/2 2/100 40/10000
337 32: 2 2/2 2/100 40/10000
338 38: 2 2/2 2/100 40/10000
339
340 The format of each line is
341 <UID>: User ID to which this applies
342 <usage> Structure refcount
343 <inst>/<keys> Total number of keys and number instantiated
344 <keys>/<max> Key count quota
345 <bytes>/<max> Key size quota
346
347
David Howells0b77f5b2008-04-29 01:01:32 -0700348Four new sysctl files have been added also for the purpose of controlling the
349quota limits on keys:
350
351 (*) /proc/sys/kernel/keys/root_maxkeys
352 /proc/sys/kernel/keys/root_maxbytes
353
354 These files hold the maximum number of keys that root may have and the
355 maximum total number of bytes of data that root may have stored in those
356 keys.
357
358 (*) /proc/sys/kernel/keys/maxkeys
359 /proc/sys/kernel/keys/maxbytes
360
361 These files hold the maximum number of keys that each non-root user may
362 have and the maximum total number of bytes of data that each of those
363 users may have stored in their keys.
364
365Root may alter these by writing each new limit as a decimal number string to
366the appropriate file.
367
368
Linus Torvalds1da177e2005-04-16 15:20:36 -0700369===============================
370USERSPACE SYSTEM CALL INTERFACE
371===============================
372
373Userspace can manipulate keys directly through three new syscalls: add_key,
374request_key and keyctl. The latter provides a number of functions for
375manipulating keys.
376
377When referring to a key directly, userspace programs should use the key's
378serial number (a positive 32-bit integer). However, there are some special
379values available for referring to special keys and keyrings that relate to the
380process making the call:
381
382 CONSTANT VALUE KEY REFERENCED
383 ============================== ====== ===========================
384 KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring
385 KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring
386 KEY_SPEC_SESSION_KEYRING -3 session-specific keyring
387 KEY_SPEC_USER_KEYRING -4 UID-specific keyring
388 KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring
389 KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring
David Howellsb5f545c2006-01-08 01:02:47 -0800390 KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key()
391 authorisation key
Linus Torvalds1da177e2005-04-16 15:20:36 -0700392
393
394The main syscalls are:
395
396 (*) Create a new key of given type, description and payload and add it to the
397 nominated keyring:
398
399 key_serial_t add_key(const char *type, const char *desc,
400 const void *payload, size_t plen,
401 key_serial_t keyring);
402
403 If a key of the same type and description as that proposed already exists
404 in the keyring, this will try to update it with the given payload, or it
405 will return error EEXIST if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700406 type. The process must also have permission to write to the key to be able
407 to update it. The new key will have all user permissions granted and no
408 group or third party permissions.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700409
David Howells76d8aea2005-06-23 22:00:49 -0700410 Otherwise, this will attempt to create a new key of the specified type and
411 description, and to instantiate it with the supplied payload and attach it
412 to the keyring. In this case, an error will be generated if the process
413 does not have permission to write to the keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700414
David Howellsd4f65b52012-09-13 13:06:29 +0100415 If the key type supports it, if the description is NULL or an empty
416 string, the key type will try and generate a description from the content
417 of the payload.
418
Linus Torvalds1da177e2005-04-16 15:20:36 -0700419 The payload is optional, and the pointer can be NULL if not required by
420 the type. The payload is plen in size, and plen can be zero for an empty
421 payload.
422
David Howells76d8aea2005-06-23 22:00:49 -0700423 A new keyring can be generated by setting type "keyring", the keyring name
424 as the description (or NULL) and setting the payload to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700425
426 User defined keys can be created by specifying type "user". It is
427 recommended that a user defined key's description by prefixed with a type
428 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting
429 ticket.
430
431 Any other type must have been registered with the kernel in advance by a
432 kernel service such as a filesystem.
433
434 The ID of the new or updated key is returned if successful.
435
436
437 (*) Search the process's keyrings for a key, potentially calling out to
438 userspace to create it.
439
440 key_serial_t request_key(const char *type, const char *description,
441 const char *callout_info,
442 key_serial_t dest_keyring);
443
444 This function searches all the process's keyrings in the order thread,
445 process, session for a matching key. This works very much like
446 KEYCTL_SEARCH, including the optional attachment of the discovered key to
447 a keyring.
448
449 If a key cannot be found, and if callout_info is not NULL, then
450 /sbin/request-key will be invoked in an attempt to obtain a key. The
451 callout_info string will be passed as an argument to the program.
452
Randy Dunlapd410fa42011-05-19 15:59:38 -0700453 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100454
Linus Torvalds1da177e2005-04-16 15:20:36 -0700455
456The keyctl syscall functions are:
457
458 (*) Map a special key ID to a real key ID for this process:
459
460 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id,
461 int create);
462
David Howells76d8aea2005-06-23 22:00:49 -0700463 The special key specified by "id" is looked up (with the key being created
464 if necessary) and the ID of the key or keyring thus found is returned if
465 it exists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700466
467 If the key does not yet exist, the key will be created if "create" is
468 non-zero; and the error ENOKEY will be returned if "create" is zero.
469
470
471 (*) Replace the session keyring this process subscribes to with a new one:
472
473 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name);
474
475 If name is NULL, an anonymous keyring is created attached to the process
476 as its session keyring, displacing the old session keyring.
477
478 If name is not NULL, if a keyring of that name exists, the process
479 attempts to attach it as the session keyring, returning an error if that
480 is not permitted; otherwise a new keyring of that name is created and
481 attached as the session keyring.
482
483 To attach to a named keyring, the keyring must have search permission for
484 the process's ownership.
485
486 The ID of the new session keyring is returned if successful.
487
488
489 (*) Update the specified key:
490
491 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload,
492 size_t plen);
493
494 This will try to update the specified key with the given payload, or it
495 will return error EOPNOTSUPP if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700496 type. The process must also have permission to write to the key to be able
497 to update it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700498
499 The payload is of length plen, and may be absent or empty as for
500 add_key().
501
502
503 (*) Revoke a key:
504
505 long keyctl(KEYCTL_REVOKE, key_serial_t key);
506
507 This makes a key unavailable for further operations. Further attempts to
508 use the key will be met with error EKEYREVOKED, and the key will no longer
509 be findable.
510
511
512 (*) Change the ownership of a key:
513
514 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid);
515
David Howells76d8aea2005-06-23 22:00:49 -0700516 This function permits a key's owner and group ID to be changed. Either one
517 of uid or gid can be set to -1 to suppress that change.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700518
519 Only the superuser can change a key's owner to something other than the
520 key's current owner. Similarly, only the superuser can change a key's
521 group ID to something other than the calling process's group ID or one of
522 its group list members.
523
524
525 (*) Change the permissions mask on a key:
526
527 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm);
528
529 This function permits the owner of a key or the superuser to change the
530 permissions mask on a key.
531
532 Only bits the available bits are permitted; if any other bits are set,
533 error EINVAL will be returned.
534
535
536 (*) Describe a key:
537
538 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer,
539 size_t buflen);
540
541 This function returns a summary of the key's attributes (but not its
542 payload data) as a string in the buffer provided.
543
544 Unless there's an error, it always returns the amount of data it could
545 produce, even if that's too big for the buffer, but it won't copy more
546 than requested to userspace. If the buffer pointer is NULL then no copy
547 will take place.
548
549 A process must have view permission on the key for this function to be
550 successful.
551
552 If successful, a string is placed in the buffer in the following format:
553
554 <type>;<uid>;<gid>;<perm>;<description>
555
556 Where type and description are strings, uid and gid are decimal, and perm
557 is hexadecimal. A NUL character is included at the end of the string if
558 the buffer is sufficiently big.
559
560 This can be parsed with
561
562 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc);
563
564
565 (*) Clear out a keyring:
566
567 long keyctl(KEYCTL_CLEAR, key_serial_t keyring);
568
569 This function clears the list of keys attached to a keyring. The calling
570 process must have write permission on the keyring, and it must be a
571 keyring (or else error ENOTDIR will result).
572
David Howells700920e2012-01-18 15:31:45 +0000573 This function can also be used to clear special kernel keyrings if they
574 are appropriately marked if the user has CAP_SYS_ADMIN capability. The
575 DNS resolver cache keyring is an example of this.
576
Linus Torvalds1da177e2005-04-16 15:20:36 -0700577
578 (*) Link a key into a keyring:
579
580 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key);
581
David Howells76d8aea2005-06-23 22:00:49 -0700582 This function creates a link from the keyring to the key. The process must
583 have write permission on the keyring and must have link permission on the
584 key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700585
David Howells76d8aea2005-06-23 22:00:49 -0700586 Should the keyring not be a keyring, error ENOTDIR will result; and if the
587 keyring is full, error ENFILE will result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700588
589 The link procedure checks the nesting of the keyrings, returning ELOOP if
David Howells017679c2006-01-08 01:02:43 -0800590 it appears too deep or EDEADLK if the link would introduce a cycle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700591
David Howellscab8eb52006-01-08 01:02:45 -0800592 Any links within the keyring to keys that match the new key in terms of
593 type and description will be discarded from the keyring as the new one is
594 added.
595
Linus Torvalds1da177e2005-04-16 15:20:36 -0700596
597 (*) Unlink a key or keyring from another keyring:
598
599 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
600
601 This function looks through the keyring for the first link to the
602 specified key, and removes it if found. Subsequent links to that key are
603 ignored. The process must have write permission on the keyring.
604
David Howells76d8aea2005-06-23 22:00:49 -0700605 If the keyring is not a keyring, error ENOTDIR will result; and if the key
606 is not present, error ENOENT will be the result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700607
608
609 (*) Search a keyring tree for a key:
610
611 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring,
612 const char *type, const char *description,
613 key_serial_t dest_keyring);
614
David Howells76d8aea2005-06-23 22:00:49 -0700615 This searches the keyring tree headed by the specified keyring until a key
616 is found that matches the type and description criteria. Each keyring is
617 checked for keys before recursion into its children occurs.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700618
619 The process must have search permission on the top level keyring, or else
620 error EACCES will result. Only keyrings that the process has search
621 permission on will be recursed into, and only keys and keyrings for which
622 a process has search permission can be matched. If the specified keyring
623 is not a keyring, ENOTDIR will result.
624
625 If the search succeeds, the function will attempt to link the found key
626 into the destination keyring if one is supplied (non-zero ID). All the
627 constraints applicable to KEYCTL_LINK apply in this case too.
628
629 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search
630 fails. On success, the resulting key ID will be returned.
631
632
633 (*) Read the payload data from a key:
634
David Howellsf1a9bad2005-10-07 15:04:52 +0100635 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
636 size_t buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700637
638 This function attempts to read the payload data from the specified key
639 into the buffer. The process must have read permission on the key to
640 succeed.
641
642 The returned data will be processed for presentation by the key type. For
643 instance, a keyring will return an array of key_serial_t entries
644 representing the IDs of all the keys to which it is subscribed. The user
645 defined key type will return its data as is. If a key type does not
646 implement this function, error EOPNOTSUPP will result.
647
648 As much of the data as can be fitted into the buffer will be copied to
649 userspace if the buffer pointer is not NULL.
650
David Howells76d8aea2005-06-23 22:00:49 -0700651 On a successful return, the function will always return the amount of data
652 available rather than the amount copied.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700653
654
655 (*) Instantiate a partially constructed key.
656
David Howellsf1a9bad2005-10-07 15:04:52 +0100657 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
658 const void *payload, size_t plen,
659 key_serial_t keyring);
David Howellsee009e4a02011-03-07 15:06:20 +0000660 long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key,
661 const struct iovec *payload_iov, unsigned ioc,
662 key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700663
664 If the kernel calls back to userspace to complete the instantiation of a
665 key, userspace should use this call to supply data for the key before the
666 invoked process returns, or else the key will be marked negative
667 automatically.
668
669 The process must have write access on the key to be able to instantiate
670 it, and the key must be uninstantiated.
671
672 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700673 that keyring, however all the constraints applying in KEYCTL_LINK apply in
674 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700675
676 The payload and plen arguments describe the payload data as for add_key().
677
David Howellsee009e4a02011-03-07 15:06:20 +0000678 The payload_iov and ioc arguments describe the payload data in an iovec
679 array instead of a single buffer.
680
Linus Torvalds1da177e2005-04-16 15:20:36 -0700681
682 (*) Negatively instantiate a partially constructed key.
683
David Howellsf1a9bad2005-10-07 15:04:52 +0100684 long keyctl(KEYCTL_NEGATE, key_serial_t key,
685 unsigned timeout, key_serial_t keyring);
David Howellsfdd1b942011-03-07 15:06:09 +0000686 long keyctl(KEYCTL_REJECT, key_serial_t key,
687 unsigned timeout, unsigned error, key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700688
689 If the kernel calls back to userspace to complete the instantiation of a
690 key, userspace should use this call mark the key as negative before the
Masanari Iida40e47122012-03-04 23:16:11 +0900691 invoked process returns if it is unable to fulfill the request.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700692
693 The process must have write access on the key to be able to instantiate
694 it, and the key must be uninstantiated.
695
696 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700697 that keyring, however all the constraints applying in KEYCTL_LINK apply in
698 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700699
David Howellsfdd1b942011-03-07 15:06:09 +0000700 If the key is rejected, future searches for it will return the specified
701 error code until the rejected key expires. Negating the key is the same
702 as rejecting the key with ENOKEY as the error code.
703
Linus Torvalds1da177e2005-04-16 15:20:36 -0700704
David Howells3e301482005-06-23 22:00:56 -0700705 (*) Set the default request-key destination keyring.
706
707 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl);
708
709 This sets the default keyring to which implicitly requested keys will be
710 attached for this thread. reqkey_defl should be one of these constants:
711
712 CONSTANT VALUE NEW DEFAULT KEYRING
713 ====================================== ====== =======================
714 KEY_REQKEY_DEFL_NO_CHANGE -1 No change
715 KEY_REQKEY_DEFL_DEFAULT 0 Default[1]
716 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring
717 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring
718 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring
719 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring
720 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring
721 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring
722
723 The old default will be returned if successful and error EINVAL will be
724 returned if reqkey_defl is not one of the above values.
725
726 The default keyring can be overridden by the keyring indicated to the
727 request_key() system call.
728
729 Note that this setting is inherited across fork/exec.
730
Paolo Ornati670e9f32006-10-03 22:57:56 +0200731 [1] The default is: the thread keyring if there is one, otherwise
David Howells3e301482005-06-23 22:00:56 -0700732 the process keyring if there is one, otherwise the session keyring if
733 there is one, otherwise the user default session keyring.
734
735
David Howells017679c2006-01-08 01:02:43 -0800736 (*) Set the timeout on a key.
737
738 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
739
740 This sets or clears the timeout on a key. The timeout can be 0 to clear
741 the timeout or a number of seconds to set the expiry time that far into
742 the future.
743
744 The process must have attribute modification access on a key to set its
745 timeout. Timeouts may not be set with this function on negative, revoked
746 or expired keys.
747
748
David Howellsb5f545c2006-01-08 01:02:47 -0800749 (*) Assume the authority granted to instantiate a key
750
751 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
752
753 This assumes or divests the authority required to instantiate the
754 specified key. Authority can only be assumed if the thread has the
755 authorisation key associated with the specified key in its keyrings
756 somewhere.
757
758 Once authority is assumed, searches for keys will also search the
759 requester's keyrings using the requester's security label, UID, GID and
760 groups.
761
762 If the requested authority is unavailable, error EPERM will be returned,
763 likewise if the authority has been revoked because the target key is
764 already instantiated.
765
766 If the specified key is 0, then any assumed authority will be divested.
767
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200768 The assumed authoritative key is inherited across fork and exec.
David Howellsb5f545c2006-01-08 01:02:47 -0800769
770
David Howells70a5bb72008-04-29 01:01:26 -0700771 (*) Get the LSM security context attached to a key.
772
773 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
774 size_t buflen)
775
776 This function returns a string that represents the LSM security context
777 attached to a key in the buffer provided.
778
779 Unless there's an error, it always returns the amount of data it could
780 produce, even if that's too big for the buffer, but it won't copy more
781 than requested to userspace. If the buffer pointer is NULL then no copy
782 will take place.
783
784 A NUL character is included at the end of the string if the buffer is
785 sufficiently big. This is included in the returned count. If no LSM is
786 in force then an empty string will be returned.
787
788 A process must have view permission on the key for this function to be
789 successful.
790
791
David Howellsee18d642009-09-02 09:14:21 +0100792 (*) Install the calling process's session keyring on its parent.
793
794 long keyctl(KEYCTL_SESSION_TO_PARENT);
795
796 This functions attempts to install the calling process's session keyring
797 on to the calling process's parent, replacing the parent's current session
798 keyring.
799
800 The calling process must have the same ownership as its parent, the
801 keyring must have the same ownership as the calling process, the calling
802 process must have LINK permission on the keyring and the active LSM module
803 mustn't deny permission, otherwise error EPERM will be returned.
804
805 Error ENOMEM will be returned if there was insufficient memory to complete
806 the operation, otherwise 0 will be returned to indicate success.
807
808 The keyring will be replaced next time the parent process leaves the
809 kernel and resumes executing userspace.
810
811
David Howellsfd758152012-05-11 10:56:56 +0100812 (*) Invalidate a key.
813
814 long keyctl(KEYCTL_INVALIDATE, key_serial_t key);
815
816 This function marks a key as being invalidated and then wakes up the
817 garbage collector. The garbage collector immediately removes invalidated
818 keys from all keyrings and deletes the key when its reference count
819 reaches zero.
820
821 Keys that are marked invalidated become invisible to normal key operations
822 immediately, though they are still visible in /proc/keys until deleted
823 (they're marked with an 'i' flag).
824
825 A process must have search permission on the key for this function to be
826 successful.
827
828
Linus Torvalds1da177e2005-04-16 15:20:36 -0700829===============
830KERNEL SERVICES
831===============
832
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200833The kernel services for key management are fairly simple to deal with. They can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700834be broken down into two areas: keys and key types.
835
836Dealing with keys is fairly straightforward. Firstly, the kernel service
837registers its type, then it searches for a key of that type. It should retain
838the key as long as it has need of it, and then it should release it. For a
David Howells76d8aea2005-06-23 22:00:49 -0700839filesystem or device file, a search would probably be performed during the open
840call, and the key released upon close. How to deal with conflicting keys due to
841two different users opening the same file is left to the filesystem author to
842solve.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700843
David Howells76181c12007-10-16 23:29:46 -0700844To access the key manager, the following header must be #included:
845
846 <linux/key.h>
847
848Specific key types should have a header file under include/keys/ that should be
849used to access that type. For keys of type "user", for example, that would be:
850
851 <keys/user-type.h>
852
David Howells664cceb2005-09-28 17:03:15 +0100853Note that there are two different types of pointers to keys that may be
854encountered:
855
856 (*) struct key *
857
858 This simply points to the key structure itself. Key structures will be at
859 least four-byte aligned.
860
861 (*) key_ref_t
862
863 This is equivalent to a struct key *, but the least significant bit is set
864 if the caller "possesses" the key. By "possession" it is meant that the
865 calling processes has a searchable link to the key from one of its
866 keyrings. There are three functions for dealing with these:
867
868 key_ref_t make_key_ref(const struct key *key,
869 unsigned long possession);
870
871 struct key *key_ref_to_ptr(const key_ref_t key_ref);
872
873 unsigned long is_key_possessed(const key_ref_t key_ref);
874
875 The first function constructs a key reference from a key pointer and
876 possession information (which must be 0 or 1 and not any other value).
877
878 The second function retrieves the key pointer from a reference and the
879 third retrieves the possession flag.
880
David Howells76d8aea2005-06-23 22:00:49 -0700881When accessing a key's payload contents, certain precautions must be taken to
882prevent access vs modification races. See the section "Notes on accessing
883payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700884
885(*) To search for a key, call:
886
887 struct key *request_key(const struct key_type *type,
888 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700889 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700890
891 This is used to request a key or keyring with a description that matches
892 the description specified according to the key type's match function. This
893 permits approximate matching to occur. If callout_string is not NULL, then
894 /sbin/request-key will be invoked in an attempt to obtain the key from
895 userspace. In that case, callout_string will be passed as an argument to
896 the program.
897
898 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
899 returned.
900
David Howells3e301482005-06-23 22:00:56 -0700901 If successful, the key will have been attached to the default keyring for
902 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
903
Randy Dunlapd410fa42011-05-19 15:59:38 -0700904 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100905
Linus Torvalds1da177e2005-04-16 15:20:36 -0700906
David Howells4e54f082006-06-29 02:24:28 -0700907(*) To search for a key, passing auxiliary data to the upcaller, call:
908
909 struct key *request_key_with_auxdata(const struct key_type *type,
910 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700911 const void *callout_info,
912 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700913 void *aux);
914
915 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700916 passed to the key_type->request_key() op if it exists, and the callout_info
917 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700918
919
David Howells76181c12007-10-16 23:29:46 -0700920(*) A key can be requested asynchronously by calling one of:
921
922 struct key *request_key_async(const struct key_type *type,
923 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700924 const void *callout_info,
925 size_t callout_len);
David Howells76181c12007-10-16 23:29:46 -0700926
927 or:
928
929 struct key *request_key_async_with_auxdata(const struct key_type *type,
930 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700931 const char *callout_info,
932 size_t callout_len,
David Howells76181c12007-10-16 23:29:46 -0700933 void *aux);
934
935 which are asynchronous equivalents of request_key() and
936 request_key_with_auxdata() respectively.
937
938 These two functions return with the key potentially still under
Matt LaPlanted9195882008-07-25 19:45:33 -0700939 construction. To wait for construction completion, the following should be
David Howells76181c12007-10-16 23:29:46 -0700940 called:
941
942 int wait_for_key_construction(struct key *key, bool intr);
943
944 The function will wait for the key to finish being constructed and then
945 invokes key_validate() to return an appropriate value to indicate the state
946 of the key (0 indicates the key is usable).
947
948 If intr is true, then the wait can be interrupted by a signal, in which
949 case error ERESTARTSYS will be returned.
950
951
Linus Torvalds1da177e2005-04-16 15:20:36 -0700952(*) When it is no longer required, the key should be released using:
953
954 void key_put(struct key *key);
955
David Howells664cceb2005-09-28 17:03:15 +0100956 Or:
957
958 void key_ref_put(key_ref_t key_ref);
959
960 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700961 the argument will not be parsed.
962
963
964(*) Extra references can be made to a key by calling the following function:
965
966 struct key *key_get(struct key *key);
967
968 These need to be disposed of by calling key_put() when they've been
969 finished with. The key pointer passed in will be returned. If the pointer
970 is NULL or CONFIG_KEYS is not set then the key will not be dereferenced and
971 no increment will take place.
972
973
974(*) A key's serial number can be obtained by calling:
975
976 key_serial_t key_serial(struct key *key);
977
978 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
979 latter case without parsing the argument).
980
981
982(*) If a keyring was found in the search, this can be further searched by:
983
David Howells664cceb2005-09-28 17:03:15 +0100984 key_ref_t keyring_search(key_ref_t keyring_ref,
985 const struct key_type *type,
986 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700987
988 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +0100989 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
990 the returned key will need to be released.
991
992 The possession attribute from the keyring reference is used to control
993 access through the permissions mask and is propagated to the returned key
994 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700995
996
David Howellsf8aa23a2012-10-02 19:24:56 +0100997(*) A keyring can be created by:
998
999 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
1000 const struct cred *cred,
1001 key_perm_t perm,
1002 unsigned long flags,
1003 struct key *dest);
1004
1005 This creates a keyring with the given attributes and returns it. If dest
1006 is not NULL, the new keyring will be linked into the keyring to which it
1007 points. No permission checks are made upon the destination keyring.
1008
1009 Error EDQUOT can be returned if the keyring would overload the quota (pass
1010 KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted
1011 towards the user's quota). Error ENOMEM can also be returned.
1012
1013
Linus Torvalds1da177e2005-04-16 15:20:36 -07001014(*) To check the validity of a key, this function can be called:
1015
1016 int validate_key(struct key *key);
1017
1018 This checks that the key in question hasn't expired or and hasn't been
1019 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
1020 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
1021 returned (in the latter case without parsing the argument).
1022
1023
1024(*) To register a key type, the following function should be called:
1025
1026 int register_key_type(struct key_type *type);
1027
1028 This will return error EEXIST if a type of the same name is already
1029 present.
1030
1031
1032(*) To unregister a key type, call:
1033
1034 void unregister_key_type(struct key_type *type);
1035
1036
Satyam Sharma7eacbbd2007-07-31 00:38:17 -07001037Under some circumstances, it may be desirable to deal with a bundle of keys.
1038The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -07001039
1040 struct key_type key_type_keyring;
1041
1042This can be used with a function such as request_key() to find a specific
1043keyring in a process's keyrings. A keyring thus found can then be searched
1044with keyring_search(). Note that it is not possible to use request_key() to
1045search a specific keyring, so using keyrings in this way is of limited utility.
1046
1047
David Howells76d8aea2005-06-23 22:00:49 -07001048===================================
1049NOTES ON ACCESSING PAYLOAD CONTENTS
1050===================================
1051
1052The simplest payload is just a number in key->payload.value. In this case,
1053there's no need to indulge in RCU or locking when accessing the payload.
1054
1055More complex payload contents must be allocated and a pointer to them set in
1056key->payload.data. One of the following ways must be selected to access the
1057data:
1058
David Howells664cceb2005-09-28 17:03:15 +01001059 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -07001060
1061 If the key type does not have a modify method, then the key's payload can
1062 be accessed without any form of locking, provided that it's known to be
1063 instantiated (uninstantiated keys cannot be "found").
1064
1065 (2) The key's semaphore.
1066
1067 The semaphore could be used to govern access to the payload and to control
1068 the payload pointer. It must be write-locked for modifications and would
1069 have to be read-locked for general access. The disadvantage of doing this
1070 is that the accessor may be required to sleep.
1071
1072 (3) RCU.
1073
1074 RCU must be used when the semaphore isn't already held; if the semaphore
1075 is held then the contents can't change under you unexpectedly as the
1076 semaphore must still be used to serialise modifications to the key. The
1077 key management code takes care of this for the key type.
1078
1079 However, this means using:
1080
1081 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
1082
1083 to read the pointer, and:
1084
1085 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
1086
1087 to set the pointer and dispose of the old contents after a grace period.
1088 Note that only the key type should ever modify a key's payload.
1089
1090 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1091 use of call_rcu() and, if the payload is of variable size, the length of
1092 the payload. key->datalen cannot be relied upon to be consistent with the
1093 payload just dereferenced if the key's semaphore is not held.
1094
1095
Linus Torvalds1da177e2005-04-16 15:20:36 -07001096===================
1097DEFINING A KEY TYPE
1098===================
1099
1100A kernel service may want to define its own key type. For instance, an AFS
1101filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c12007-10-16 23:29:46 -07001102author fills in a key_type struct and registers it with the system.
1103
1104Source files that implement key types should include the following header file:
1105
1106 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001107
1108The structure has a number of fields, some of which are mandatory:
1109
1110 (*) const char *name
1111
1112 The name of the key type. This is used to translate a key type name
1113 supplied by userspace into a pointer to the structure.
1114
1115
1116 (*) size_t def_datalen
1117
1118 This is optional - it supplies the default payload data length as
1119 contributed to the quota. If the key type's payload is always or almost
1120 always the same size, then this is a more efficient way to do things.
1121
1122 The data length (and quota) on a particular key can always be changed
1123 during instantiation or update by calling:
1124
1125 int key_payload_reserve(struct key *key, size_t datalen);
1126
David Howells76d8aea2005-06-23 22:00:49 -07001127 With the revised data length. Error EDQUOT will be returned if this is not
1128 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001129
1130
David Howellsb9fffa32011-03-07 15:05:59 +00001131 (*) int (*vet_description)(const char *description);
1132
1133 This optional method is called to vet a key description. If the key type
1134 doesn't approve of the key description, it may return an error, otherwise
1135 it should return 0.
1136
1137
David Howellsd4f65b52012-09-13 13:06:29 +01001138 (*) int (*preparse)(struct key_preparsed_payload *prep);
1139
1140 This optional method permits the key type to attempt to parse payload
1141 before a key is created (add key) or the key semaphore is taken (update or
1142 instantiate key). The structure pointed to by prep looks like:
1143
1144 struct key_preparsed_payload {
1145 char *description;
1146 void *type_data[2];
1147 void *payload;
1148 const void *data;
1149 size_t datalen;
1150 size_t quotalen;
1151 };
1152
1153 Before calling the method, the caller will fill in data and datalen with
1154 the payload blob parameters; quotalen will be filled in with the default
1155 quota size from the key type and the rest will be cleared.
1156
1157 If a description can be proposed from the payload contents, that should be
1158 attached as a string to the description field. This will be used for the
1159 key description if the caller of add_key() passes NULL or "".
1160
1161 The method can attach anything it likes to type_data[] and payload. These
1162 are merely passed along to the instantiate() or update() operations.
1163
1164 The method should return 0 if success ful or a negative error code
1165 otherwise.
1166
1167
1168 (*) void (*free_preparse)(struct key_preparsed_payload *prep);
1169
1170 This method is only required if the preparse() method is provided,
1171 otherwise it is unused. It cleans up anything attached to the
1172 description, type_data and payload fields of the key_preparsed_payload
1173 struct as filled in by the preparse() method.
1174
1175
1176 (*) int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001177
1178 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001179 The payload attached need not bear any relation to the data passed to this
1180 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001181
David Howellsd4f65b52012-09-13 13:06:29 +01001182 The prep->data and prep->datalen fields will define the original payload
1183 blob. If preparse() was supplied then other fields may be filled in also.
1184
Linus Torvalds1da177e2005-04-16 15:20:36 -07001185 If the amount of data attached to the key differs from the size in
1186 keytype->def_datalen, then key_payload_reserve() should be called.
1187
1188 This method does not have to lock the key in order to attach a payload.
1189 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1190 anything else from gaining access to the key.
1191
David Howells76d8aea2005-06-23 22:00:49 -07001192 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001193
1194
Linus Torvalds1da177e2005-04-16 15:20:36 -07001195 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1196
David Howells76d8aea2005-06-23 22:00:49 -07001197 If this type of key can be updated, then this method should be provided.
1198 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001199
David Howellsd4f65b52012-09-13 13:06:29 +01001200 The prep->data and prep->datalen fields will define the original payload
1201 blob. If preparse() was supplied then other fields may be filled in also.
1202
Linus Torvalds1da177e2005-04-16 15:20:36 -07001203 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001204 before any changes are actually made. Note that if this succeeds, the type
1205 is committed to changing the key because it's already been altered, so all
1206 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001207
David Howells76d8aea2005-06-23 22:00:49 -07001208 The key will have its semaphore write-locked before this method is called,
1209 but this only deters other writers; any changes to the key's payload must
1210 be made under RCU conditions, and call_rcu() must be used to dispose of
1211 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001212
David Howells76d8aea2005-06-23 22:00:49 -07001213 key_payload_reserve() should be called before the changes are made, but
1214 after all allocations and other potentially failing function calls are
1215 made.
1216
1217 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001218
1219
1220 (*) int (*match)(const struct key *key, const void *desc);
1221
1222 This method is called to match a key against a description. It should
1223 return non-zero if the two match, zero if they don't.
1224
1225 This method should not need to lock the key in any way. The type and
1226 description can be considered invariant, and the payload should not be
1227 accessed (the key may not yet be instantiated).
1228
1229 It is not safe to sleep in this method; the caller may hold spinlocks.
1230
1231
David Howells04c567d2006-06-22 14:47:18 -07001232 (*) void (*revoke)(struct key *key);
1233
1234 This method is optional. It is called to discard part of the payload
1235 data upon a key being revoked. The caller will have the key semaphore
1236 write-locked.
1237
1238 It is safe to sleep in this method, though care should be taken to avoid
1239 a deadlock against the key semaphore.
1240
1241
Linus Torvalds1da177e2005-04-16 15:20:36 -07001242 (*) void (*destroy)(struct key *key);
1243
David Howells76d8aea2005-06-23 22:00:49 -07001244 This method is optional. It is called to discard the payload data on a key
1245 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001246
David Howells76d8aea2005-06-23 22:00:49 -07001247 This method does not need to lock the key to access the payload; it can
1248 consider the key as being inaccessible at this time. Note that the key's
1249 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001250
1251 It is not safe to sleep in this method; the caller may hold spinlocks.
1252
1253
1254 (*) void (*describe)(const struct key *key, struct seq_file *p);
1255
1256 This method is optional. It is called during /proc/keys reading to
1257 summarise a key's description and payload in text form.
1258
David Howells76d8aea2005-06-23 22:00:49 -07001259 This method will be called with the RCU read lock held. rcu_dereference()
1260 should be used to read the payload pointer if the payload is to be
1261 accessed. key->datalen cannot be trusted to stay consistent with the
1262 contents of the payload.
1263
1264 The description will not change, though the key's state may.
1265
1266 It is not safe to sleep in this method; the RCU read lock is held by the
1267 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001268
1269
1270 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1271
1272 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001273 key's payload into something a blob of data for userspace to deal with.
1274 Ideally, the blob should be in the same format as that passed in to the
1275 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001276
1277 If successful, the blob size that could be produced should be returned
1278 rather than the size copied.
1279
David Howells76d8aea2005-06-23 22:00:49 -07001280 This method will be called with the key's semaphore read-locked. This will
1281 prevent the key's payload changing. It is not necessary to use RCU locking
1282 when accessing the key's payload. It is safe to sleep in this method, such
1283 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001284
1285
David Howells76181c12007-10-16 23:29:46 -07001286 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001287 void *aux);
1288
David Howells76181c12007-10-16 23:29:46 -07001289 This method is optional. If provided, request_key() and friends will
1290 invoke this function rather than upcalling to /sbin/request-key to operate
1291 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001292
David Howells76181c12007-10-16 23:29:46 -07001293 The aux parameter is as passed to request_key_async_with_auxdata() and
1294 similar or is NULL otherwise. Also passed are the construction record for
1295 the key to be operated upon and the operation type (currently only
1296 "create").
David Howells4e54f082006-06-29 02:24:28 -07001297
David Howells76181c12007-10-16 23:29:46 -07001298 This method is permitted to return before the upcall is complete, but the
1299 following function must be called under all circumstances to complete the
1300 instantiation process, whether or not it succeeds, whether or not there's
1301 an error:
1302
1303 void complete_request_key(struct key_construction *cons, int error);
1304
1305 The error parameter should be 0 on success, -ve on error. The
1306 construction record is destroyed by this action and the authorisation key
1307 will be revoked. If an error is indicated, the key under construction
1308 will be negatively instantiated if it wasn't already instantiated.
1309
1310 If this method returns an error, that error will be returned to the
1311 caller of request_key*(). complete_request_key() must be called prior to
1312 returning.
1313
1314 The key under construction and the authorisation key can be found in the
1315 key_construction struct pointed to by cons:
1316
1317 (*) struct key *key;
1318
1319 The key under construction.
1320
1321 (*) struct key *authkey;
1322
1323 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001324
1325
Linus Torvalds1da177e2005-04-16 15:20:36 -07001326============================
1327REQUEST-KEY CALLBACK SERVICE
1328============================
1329
1330To create a new key, the kernel will attempt to execute the following command
1331line:
1332
1333 /sbin/request-key create <key> <uid> <gid> \
1334 <threadring> <processring> <sessionring> <callout_info>
1335
1336<key> is the key being constructed, and the three keyrings are the process
1337keyrings from the process that caused the search to be issued. These are
1338included for two reasons:
1339
1340 (1) There may be an authentication token in one of the keyrings that is
1341 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1342
1343 (2) The new key should probably be cached in one of these rings.
1344
1345This program should set it UID and GID to those specified before attempting to
1346access any more keys. It may then look around for a user specific process to
1347hand the request off to (perhaps a path held in placed in another key by, for
1348example, the KDE desktop manager).
1349
1350The program (or whatever it calls) should finish construction of the key by
David Howellsee009e4a02011-03-07 15:06:20 +00001351calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to
1352cache the key in one of the keyrings (probably the session ring) before
1353returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE
1354or KEYCTL_REJECT; this also permits the key to be cached in one of the
1355keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001356
1357If it returns with the key remaining in the unconstructed state, the key will
1358be marked as being negative, it will be added to the session keyring, and an
1359error will be returned to the key requestor.
1360
David Howells76d8aea2005-06-23 22:00:49 -07001361Supplementary information may be provided from whoever or whatever invoked this
1362service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001363information was made available, then "-" will be passed as this parameter
1364instead.
1365
1366
1367Similarly, the kernel may attempt to update an expired or a soon to expire key
1368by executing:
1369
1370 /sbin/request-key update <key> <uid> <gid> \
1371 <threadring> <processring> <sessionring>
1372
1373In this case, the program isn't required to actually attach the key to a ring;
1374the rings are provided for reference.
David Howells5d135442009-09-02 09:14:00 +01001375
1376
1377==================
1378GARBAGE COLLECTION
1379==================
1380
1381Dead keys (for which the type has been removed) will be automatically unlinked
1382from those keyrings that point to them and deleted as soon as possible by a
1383background garbage collector.
1384
1385Similarly, revoked and expired keys will be garbage collected, but only after a
1386certain amount of time has passed. This time is set as a number of seconds in:
1387
1388 /proc/sys/kernel/keys/gc_delay