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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
415 The payload is optional, and the pointer can be NULL if not required by
416 the type. The payload is plen in size, and plen can be zero for an empty
417 payload.
418
David Howells76d8aea2005-06-23 22:00:49 -0700419 A new keyring can be generated by setting type "keyring", the keyring name
420 as the description (or NULL) and setting the payload to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700421
422 User defined keys can be created by specifying type "user". It is
423 recommended that a user defined key's description by prefixed with a type
424 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting
425 ticket.
426
427 Any other type must have been registered with the kernel in advance by a
428 kernel service such as a filesystem.
429
430 The ID of the new or updated key is returned if successful.
431
432
433 (*) Search the process's keyrings for a key, potentially calling out to
434 userspace to create it.
435
436 key_serial_t request_key(const char *type, const char *description,
437 const char *callout_info,
438 key_serial_t dest_keyring);
439
440 This function searches all the process's keyrings in the order thread,
441 process, session for a matching key. This works very much like
442 KEYCTL_SEARCH, including the optional attachment of the discovered key to
443 a keyring.
444
445 If a key cannot be found, and if callout_info is not NULL, then
446 /sbin/request-key will be invoked in an attempt to obtain a key. The
447 callout_info string will be passed as an argument to the program.
448
Randy Dunlapd410fa42011-05-19 15:59:38 -0700449 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100450
Linus Torvalds1da177e2005-04-16 15:20:36 -0700451
452The keyctl syscall functions are:
453
454 (*) Map a special key ID to a real key ID for this process:
455
456 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id,
457 int create);
458
David Howells76d8aea2005-06-23 22:00:49 -0700459 The special key specified by "id" is looked up (with the key being created
460 if necessary) and the ID of the key or keyring thus found is returned if
461 it exists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700462
463 If the key does not yet exist, the key will be created if "create" is
464 non-zero; and the error ENOKEY will be returned if "create" is zero.
465
466
467 (*) Replace the session keyring this process subscribes to with a new one:
468
469 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name);
470
471 If name is NULL, an anonymous keyring is created attached to the process
472 as its session keyring, displacing the old session keyring.
473
474 If name is not NULL, if a keyring of that name exists, the process
475 attempts to attach it as the session keyring, returning an error if that
476 is not permitted; otherwise a new keyring of that name is created and
477 attached as the session keyring.
478
479 To attach to a named keyring, the keyring must have search permission for
480 the process's ownership.
481
482 The ID of the new session keyring is returned if successful.
483
484
485 (*) Update the specified key:
486
487 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload,
488 size_t plen);
489
490 This will try to update the specified key with the given payload, or it
491 will return error EOPNOTSUPP if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700492 type. The process must also have permission to write to the key to be able
493 to update it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700494
495 The payload is of length plen, and may be absent or empty as for
496 add_key().
497
498
499 (*) Revoke a key:
500
501 long keyctl(KEYCTL_REVOKE, key_serial_t key);
502
503 This makes a key unavailable for further operations. Further attempts to
504 use the key will be met with error EKEYREVOKED, and the key will no longer
505 be findable.
506
507
508 (*) Change the ownership of a key:
509
510 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid);
511
David Howells76d8aea2005-06-23 22:00:49 -0700512 This function permits a key's owner and group ID to be changed. Either one
513 of uid or gid can be set to -1 to suppress that change.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700514
515 Only the superuser can change a key's owner to something other than the
516 key's current owner. Similarly, only the superuser can change a key's
517 group ID to something other than the calling process's group ID or one of
518 its group list members.
519
520
521 (*) Change the permissions mask on a key:
522
523 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm);
524
525 This function permits the owner of a key or the superuser to change the
526 permissions mask on a key.
527
528 Only bits the available bits are permitted; if any other bits are set,
529 error EINVAL will be returned.
530
531
532 (*) Describe a key:
533
534 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer,
535 size_t buflen);
536
537 This function returns a summary of the key's attributes (but not its
538 payload data) as a string in the buffer provided.
539
540 Unless there's an error, it always returns the amount of data it could
541 produce, even if that's too big for the buffer, but it won't copy more
542 than requested to userspace. If the buffer pointer is NULL then no copy
543 will take place.
544
545 A process must have view permission on the key for this function to be
546 successful.
547
548 If successful, a string is placed in the buffer in the following format:
549
550 <type>;<uid>;<gid>;<perm>;<description>
551
552 Where type and description are strings, uid and gid are decimal, and perm
553 is hexadecimal. A NUL character is included at the end of the string if
554 the buffer is sufficiently big.
555
556 This can be parsed with
557
558 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc);
559
560
561 (*) Clear out a keyring:
562
563 long keyctl(KEYCTL_CLEAR, key_serial_t keyring);
564
565 This function clears the list of keys attached to a keyring. The calling
566 process must have write permission on the keyring, and it must be a
567 keyring (or else error ENOTDIR will result).
568
David Howells700920e2012-01-18 15:31:45 +0000569 This function can also be used to clear special kernel keyrings if they
570 are appropriately marked if the user has CAP_SYS_ADMIN capability. The
571 DNS resolver cache keyring is an example of this.
572
Linus Torvalds1da177e2005-04-16 15:20:36 -0700573
574 (*) Link a key into a keyring:
575
576 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key);
577
David Howells76d8aea2005-06-23 22:00:49 -0700578 This function creates a link from the keyring to the key. The process must
579 have write permission on the keyring and must have link permission on the
580 key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700581
David Howells76d8aea2005-06-23 22:00:49 -0700582 Should the keyring not be a keyring, error ENOTDIR will result; and if the
583 keyring is full, error ENFILE will result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700584
585 The link procedure checks the nesting of the keyrings, returning ELOOP if
David Howells017679c2006-01-08 01:02:43 -0800586 it appears too deep or EDEADLK if the link would introduce a cycle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700587
David Howellscab8eb52006-01-08 01:02:45 -0800588 Any links within the keyring to keys that match the new key in terms of
589 type and description will be discarded from the keyring as the new one is
590 added.
591
Linus Torvalds1da177e2005-04-16 15:20:36 -0700592
593 (*) Unlink a key or keyring from another keyring:
594
595 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
596
597 This function looks through the keyring for the first link to the
598 specified key, and removes it if found. Subsequent links to that key are
599 ignored. The process must have write permission on the keyring.
600
David Howells76d8aea2005-06-23 22:00:49 -0700601 If the keyring is not a keyring, error ENOTDIR will result; and if the key
602 is not present, error ENOENT will be the result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700603
604
605 (*) Search a keyring tree for a key:
606
607 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring,
608 const char *type, const char *description,
609 key_serial_t dest_keyring);
610
David Howells76d8aea2005-06-23 22:00:49 -0700611 This searches the keyring tree headed by the specified keyring until a key
612 is found that matches the type and description criteria. Each keyring is
613 checked for keys before recursion into its children occurs.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700614
615 The process must have search permission on the top level keyring, or else
616 error EACCES will result. Only keyrings that the process has search
617 permission on will be recursed into, and only keys and keyrings for which
618 a process has search permission can be matched. If the specified keyring
619 is not a keyring, ENOTDIR will result.
620
621 If the search succeeds, the function will attempt to link the found key
622 into the destination keyring if one is supplied (non-zero ID). All the
623 constraints applicable to KEYCTL_LINK apply in this case too.
624
625 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search
626 fails. On success, the resulting key ID will be returned.
627
628
629 (*) Read the payload data from a key:
630
David Howellsf1a9bad2005-10-07 15:04:52 +0100631 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
632 size_t buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700633
634 This function attempts to read the payload data from the specified key
635 into the buffer. The process must have read permission on the key to
636 succeed.
637
638 The returned data will be processed for presentation by the key type. For
639 instance, a keyring will return an array of key_serial_t entries
640 representing the IDs of all the keys to which it is subscribed. The user
641 defined key type will return its data as is. If a key type does not
642 implement this function, error EOPNOTSUPP will result.
643
644 As much of the data as can be fitted into the buffer will be copied to
645 userspace if the buffer pointer is not NULL.
646
David Howells76d8aea2005-06-23 22:00:49 -0700647 On a successful return, the function will always return the amount of data
648 available rather than the amount copied.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700649
650
651 (*) Instantiate a partially constructed key.
652
David Howellsf1a9bad2005-10-07 15:04:52 +0100653 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
654 const void *payload, size_t plen,
655 key_serial_t keyring);
David Howellsee009e42011-03-07 15:06:20 +0000656 long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key,
657 const struct iovec *payload_iov, unsigned ioc,
658 key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700659
660 If the kernel calls back to userspace to complete the instantiation of a
661 key, userspace should use this call to supply data for the key before the
662 invoked process returns, or else the key will be marked negative
663 automatically.
664
665 The process must have write access on the key to be able to instantiate
666 it, and the key must be uninstantiated.
667
668 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700669 that keyring, however all the constraints applying in KEYCTL_LINK apply in
670 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700671
672 The payload and plen arguments describe the payload data as for add_key().
673
David Howellsee009e42011-03-07 15:06:20 +0000674 The payload_iov and ioc arguments describe the payload data in an iovec
675 array instead of a single buffer.
676
Linus Torvalds1da177e2005-04-16 15:20:36 -0700677
678 (*) Negatively instantiate a partially constructed key.
679
David Howellsf1a9bad2005-10-07 15:04:52 +0100680 long keyctl(KEYCTL_NEGATE, key_serial_t key,
681 unsigned timeout, key_serial_t keyring);
David Howellsfdd1b942011-03-07 15:06:09 +0000682 long keyctl(KEYCTL_REJECT, key_serial_t key,
683 unsigned timeout, unsigned error, key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700684
685 If the kernel calls back to userspace to complete the instantiation of a
686 key, userspace should use this call mark the key as negative before the
Masanari Iida40e47122012-03-04 23:16:11 +0900687 invoked process returns if it is unable to fulfill the request.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700688
689 The process must have write access on the key to be able to instantiate
690 it, and the key must be uninstantiated.
691
692 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700693 that keyring, however all the constraints applying in KEYCTL_LINK apply in
694 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700695
David Howellsfdd1b942011-03-07 15:06:09 +0000696 If the key is rejected, future searches for it will return the specified
697 error code until the rejected key expires. Negating the key is the same
698 as rejecting the key with ENOKEY as the error code.
699
Linus Torvalds1da177e2005-04-16 15:20:36 -0700700
David Howells3e301482005-06-23 22:00:56 -0700701 (*) Set the default request-key destination keyring.
702
703 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl);
704
705 This sets the default keyring to which implicitly requested keys will be
706 attached for this thread. reqkey_defl should be one of these constants:
707
708 CONSTANT VALUE NEW DEFAULT KEYRING
709 ====================================== ====== =======================
710 KEY_REQKEY_DEFL_NO_CHANGE -1 No change
711 KEY_REQKEY_DEFL_DEFAULT 0 Default[1]
712 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring
713 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring
714 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring
715 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring
716 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring
717 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring
718
719 The old default will be returned if successful and error EINVAL will be
720 returned if reqkey_defl is not one of the above values.
721
722 The default keyring can be overridden by the keyring indicated to the
723 request_key() system call.
724
725 Note that this setting is inherited across fork/exec.
726
Paolo Ornati670e9f32006-10-03 22:57:56 +0200727 [1] The default is: the thread keyring if there is one, otherwise
David Howells3e301482005-06-23 22:00:56 -0700728 the process keyring if there is one, otherwise the session keyring if
729 there is one, otherwise the user default session keyring.
730
731
David Howells017679c2006-01-08 01:02:43 -0800732 (*) Set the timeout on a key.
733
734 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
735
736 This sets or clears the timeout on a key. The timeout can be 0 to clear
737 the timeout or a number of seconds to set the expiry time that far into
738 the future.
739
740 The process must have attribute modification access on a key to set its
741 timeout. Timeouts may not be set with this function on negative, revoked
742 or expired keys.
743
744
David Howellsb5f545c2006-01-08 01:02:47 -0800745 (*) Assume the authority granted to instantiate a key
746
747 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
748
749 This assumes or divests the authority required to instantiate the
750 specified key. Authority can only be assumed if the thread has the
751 authorisation key associated with the specified key in its keyrings
752 somewhere.
753
754 Once authority is assumed, searches for keys will also search the
755 requester's keyrings using the requester's security label, UID, GID and
756 groups.
757
758 If the requested authority is unavailable, error EPERM will be returned,
759 likewise if the authority has been revoked because the target key is
760 already instantiated.
761
762 If the specified key is 0, then any assumed authority will be divested.
763
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200764 The assumed authoritative key is inherited across fork and exec.
David Howellsb5f545c2006-01-08 01:02:47 -0800765
766
David Howells70a5bb72008-04-29 01:01:26 -0700767 (*) Get the LSM security context attached to a key.
768
769 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
770 size_t buflen)
771
772 This function returns a string that represents the LSM security context
773 attached to a key in the buffer provided.
774
775 Unless there's an error, it always returns the amount of data it could
776 produce, even if that's too big for the buffer, but it won't copy more
777 than requested to userspace. If the buffer pointer is NULL then no copy
778 will take place.
779
780 A NUL character is included at the end of the string if the buffer is
781 sufficiently big. This is included in the returned count. If no LSM is
782 in force then an empty string will be returned.
783
784 A process must have view permission on the key for this function to be
785 successful.
786
787
David Howellsee18d642009-09-02 09:14:21 +0100788 (*) Install the calling process's session keyring on its parent.
789
790 long keyctl(KEYCTL_SESSION_TO_PARENT);
791
792 This functions attempts to install the calling process's session keyring
793 on to the calling process's parent, replacing the parent's current session
794 keyring.
795
796 The calling process must have the same ownership as its parent, the
797 keyring must have the same ownership as the calling process, the calling
798 process must have LINK permission on the keyring and the active LSM module
799 mustn't deny permission, otherwise error EPERM will be returned.
800
801 Error ENOMEM will be returned if there was insufficient memory to complete
802 the operation, otherwise 0 will be returned to indicate success.
803
804 The keyring will be replaced next time the parent process leaves the
805 kernel and resumes executing userspace.
806
807
Linus Torvalds1da177e2005-04-16 15:20:36 -0700808===============
809KERNEL SERVICES
810===============
811
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200812The kernel services for key management are fairly simple to deal with. They can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700813be broken down into two areas: keys and key types.
814
815Dealing with keys is fairly straightforward. Firstly, the kernel service
816registers its type, then it searches for a key of that type. It should retain
817the key as long as it has need of it, and then it should release it. For a
David Howells76d8aea2005-06-23 22:00:49 -0700818filesystem or device file, a search would probably be performed during the open
819call, and the key released upon close. How to deal with conflicting keys due to
820two different users opening the same file is left to the filesystem author to
821solve.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700822
David Howells76181c12007-10-16 23:29:46 -0700823To access the key manager, the following header must be #included:
824
825 <linux/key.h>
826
827Specific key types should have a header file under include/keys/ that should be
828used to access that type. For keys of type "user", for example, that would be:
829
830 <keys/user-type.h>
831
David Howells664cceb2005-09-28 17:03:15 +0100832Note that there are two different types of pointers to keys that may be
833encountered:
834
835 (*) struct key *
836
837 This simply points to the key structure itself. Key structures will be at
838 least four-byte aligned.
839
840 (*) key_ref_t
841
842 This is equivalent to a struct key *, but the least significant bit is set
843 if the caller "possesses" the key. By "possession" it is meant that the
844 calling processes has a searchable link to the key from one of its
845 keyrings. There are three functions for dealing with these:
846
847 key_ref_t make_key_ref(const struct key *key,
848 unsigned long possession);
849
850 struct key *key_ref_to_ptr(const key_ref_t key_ref);
851
852 unsigned long is_key_possessed(const key_ref_t key_ref);
853
854 The first function constructs a key reference from a key pointer and
855 possession information (which must be 0 or 1 and not any other value).
856
857 The second function retrieves the key pointer from a reference and the
858 third retrieves the possession flag.
859
David Howells76d8aea2005-06-23 22:00:49 -0700860When accessing a key's payload contents, certain precautions must be taken to
861prevent access vs modification races. See the section "Notes on accessing
862payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700863
864(*) To search for a key, call:
865
866 struct key *request_key(const struct key_type *type,
867 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700868 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700869
870 This is used to request a key or keyring with a description that matches
871 the description specified according to the key type's match function. This
872 permits approximate matching to occur. If callout_string is not NULL, then
873 /sbin/request-key will be invoked in an attempt to obtain the key from
874 userspace. In that case, callout_string will be passed as an argument to
875 the program.
876
877 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
878 returned.
879
David Howells3e301482005-06-23 22:00:56 -0700880 If successful, the key will have been attached to the default keyring for
881 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
882
Randy Dunlapd410fa42011-05-19 15:59:38 -0700883 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100884
Linus Torvalds1da177e2005-04-16 15:20:36 -0700885
David Howells4e54f082006-06-29 02:24:28 -0700886(*) To search for a key, passing auxiliary data to the upcaller, call:
887
888 struct key *request_key_with_auxdata(const struct key_type *type,
889 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700890 const void *callout_info,
891 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700892 void *aux);
893
894 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700895 passed to the key_type->request_key() op if it exists, and the callout_info
896 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700897
898
David Howells76181c12007-10-16 23:29:46 -0700899(*) A key can be requested asynchronously by calling one of:
900
901 struct key *request_key_async(const struct key_type *type,
902 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700903 const void *callout_info,
904 size_t callout_len);
David Howells76181c12007-10-16 23:29:46 -0700905
906 or:
907
908 struct key *request_key_async_with_auxdata(const struct key_type *type,
909 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700910 const char *callout_info,
911 size_t callout_len,
David Howells76181c12007-10-16 23:29:46 -0700912 void *aux);
913
914 which are asynchronous equivalents of request_key() and
915 request_key_with_auxdata() respectively.
916
917 These two functions return with the key potentially still under
Matt LaPlanted9195882008-07-25 19:45:33 -0700918 construction. To wait for construction completion, the following should be
David Howells76181c12007-10-16 23:29:46 -0700919 called:
920
921 int wait_for_key_construction(struct key *key, bool intr);
922
923 The function will wait for the key to finish being constructed and then
924 invokes key_validate() to return an appropriate value to indicate the state
925 of the key (0 indicates the key is usable).
926
927 If intr is true, then the wait can be interrupted by a signal, in which
928 case error ERESTARTSYS will be returned.
929
930
Linus Torvalds1da177e2005-04-16 15:20:36 -0700931(*) When it is no longer required, the key should be released using:
932
933 void key_put(struct key *key);
934
David Howells664cceb2005-09-28 17:03:15 +0100935 Or:
936
937 void key_ref_put(key_ref_t key_ref);
938
939 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700940 the argument will not be parsed.
941
942
943(*) Extra references can be made to a key by calling the following function:
944
945 struct key *key_get(struct key *key);
946
947 These need to be disposed of by calling key_put() when they've been
948 finished with. The key pointer passed in will be returned. If the pointer
949 is NULL or CONFIG_KEYS is not set then the key will not be dereferenced and
950 no increment will take place.
951
952
953(*) A key's serial number can be obtained by calling:
954
955 key_serial_t key_serial(struct key *key);
956
957 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
958 latter case without parsing the argument).
959
960
961(*) If a keyring was found in the search, this can be further searched by:
962
David Howells664cceb2005-09-28 17:03:15 +0100963 key_ref_t keyring_search(key_ref_t keyring_ref,
964 const struct key_type *type,
965 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700966
967 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +0100968 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
969 the returned key will need to be released.
970
971 The possession attribute from the keyring reference is used to control
972 access through the permissions mask and is propagated to the returned key
973 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700974
975
976(*) To check the validity of a key, this function can be called:
977
978 int validate_key(struct key *key);
979
980 This checks that the key in question hasn't expired or and hasn't been
981 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
982 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
983 returned (in the latter case without parsing the argument).
984
985
986(*) To register a key type, the following function should be called:
987
988 int register_key_type(struct key_type *type);
989
990 This will return error EEXIST if a type of the same name is already
991 present.
992
993
994(*) To unregister a key type, call:
995
996 void unregister_key_type(struct key_type *type);
997
998
Satyam Sharma7eacbbd2007-07-31 00:38:17 -0700999Under some circumstances, it may be desirable to deal with a bundle of keys.
1000The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -07001001
1002 struct key_type key_type_keyring;
1003
1004This can be used with a function such as request_key() to find a specific
1005keyring in a process's keyrings. A keyring thus found can then be searched
1006with keyring_search(). Note that it is not possible to use request_key() to
1007search a specific keyring, so using keyrings in this way is of limited utility.
1008
1009
David Howells76d8aea2005-06-23 22:00:49 -07001010===================================
1011NOTES ON ACCESSING PAYLOAD CONTENTS
1012===================================
1013
1014The simplest payload is just a number in key->payload.value. In this case,
1015there's no need to indulge in RCU or locking when accessing the payload.
1016
1017More complex payload contents must be allocated and a pointer to them set in
1018key->payload.data. One of the following ways must be selected to access the
1019data:
1020
David Howells664cceb2005-09-28 17:03:15 +01001021 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -07001022
1023 If the key type does not have a modify method, then the key's payload can
1024 be accessed without any form of locking, provided that it's known to be
1025 instantiated (uninstantiated keys cannot be "found").
1026
1027 (2) The key's semaphore.
1028
1029 The semaphore could be used to govern access to the payload and to control
1030 the payload pointer. It must be write-locked for modifications and would
1031 have to be read-locked for general access. The disadvantage of doing this
1032 is that the accessor may be required to sleep.
1033
1034 (3) RCU.
1035
1036 RCU must be used when the semaphore isn't already held; if the semaphore
1037 is held then the contents can't change under you unexpectedly as the
1038 semaphore must still be used to serialise modifications to the key. The
1039 key management code takes care of this for the key type.
1040
1041 However, this means using:
1042
1043 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
1044
1045 to read the pointer, and:
1046
1047 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
1048
1049 to set the pointer and dispose of the old contents after a grace period.
1050 Note that only the key type should ever modify a key's payload.
1051
1052 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1053 use of call_rcu() and, if the payload is of variable size, the length of
1054 the payload. key->datalen cannot be relied upon to be consistent with the
1055 payload just dereferenced if the key's semaphore is not held.
1056
1057
Linus Torvalds1da177e2005-04-16 15:20:36 -07001058===================
1059DEFINING A KEY TYPE
1060===================
1061
1062A kernel service may want to define its own key type. For instance, an AFS
1063filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c12007-10-16 23:29:46 -07001064author fills in a key_type struct and registers it with the system.
1065
1066Source files that implement key types should include the following header file:
1067
1068 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001069
1070The structure has a number of fields, some of which are mandatory:
1071
1072 (*) const char *name
1073
1074 The name of the key type. This is used to translate a key type name
1075 supplied by userspace into a pointer to the structure.
1076
1077
1078 (*) size_t def_datalen
1079
1080 This is optional - it supplies the default payload data length as
1081 contributed to the quota. If the key type's payload is always or almost
1082 always the same size, then this is a more efficient way to do things.
1083
1084 The data length (and quota) on a particular key can always be changed
1085 during instantiation or update by calling:
1086
1087 int key_payload_reserve(struct key *key, size_t datalen);
1088
David Howells76d8aea2005-06-23 22:00:49 -07001089 With the revised data length. Error EDQUOT will be returned if this is not
1090 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001091
1092
David Howellsb9fffa32011-03-07 15:05:59 +00001093 (*) int (*vet_description)(const char *description);
1094
1095 This optional method is called to vet a key description. If the key type
1096 doesn't approve of the key description, it may return an error, otherwise
1097 it should return 0.
1098
1099
Linus Torvalds1da177e2005-04-16 15:20:36 -07001100 (*) int (*instantiate)(struct key *key, const void *data, size_t datalen);
1101
1102 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001103 The payload attached need not bear any relation to the data passed to this
1104 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001105
1106 If the amount of data attached to the key differs from the size in
1107 keytype->def_datalen, then key_payload_reserve() should be called.
1108
1109 This method does not have to lock the key in order to attach a payload.
1110 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1111 anything else from gaining access to the key.
1112
David Howells76d8aea2005-06-23 22:00:49 -07001113 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001114
1115
Linus Torvalds1da177e2005-04-16 15:20:36 -07001116 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1117
David Howells76d8aea2005-06-23 22:00:49 -07001118 If this type of key can be updated, then this method should be provided.
1119 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001120
1121 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001122 before any changes are actually made. Note that if this succeeds, the type
1123 is committed to changing the key because it's already been altered, so all
1124 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001125
David Howells76d8aea2005-06-23 22:00:49 -07001126 The key will have its semaphore write-locked before this method is called,
1127 but this only deters other writers; any changes to the key's payload must
1128 be made under RCU conditions, and call_rcu() must be used to dispose of
1129 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001130
David Howells76d8aea2005-06-23 22:00:49 -07001131 key_payload_reserve() should be called before the changes are made, but
1132 after all allocations and other potentially failing function calls are
1133 made.
1134
1135 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001136
1137
1138 (*) int (*match)(const struct key *key, const void *desc);
1139
1140 This method is called to match a key against a description. It should
1141 return non-zero if the two match, zero if they don't.
1142
1143 This method should not need to lock the key in any way. The type and
1144 description can be considered invariant, and the payload should not be
1145 accessed (the key may not yet be instantiated).
1146
1147 It is not safe to sleep in this method; the caller may hold spinlocks.
1148
1149
David Howells04c567d2006-06-22 14:47:18 -07001150 (*) void (*revoke)(struct key *key);
1151
1152 This method is optional. It is called to discard part of the payload
1153 data upon a key being revoked. The caller will have the key semaphore
1154 write-locked.
1155
1156 It is safe to sleep in this method, though care should be taken to avoid
1157 a deadlock against the key semaphore.
1158
1159
Linus Torvalds1da177e2005-04-16 15:20:36 -07001160 (*) void (*destroy)(struct key *key);
1161
David Howells76d8aea2005-06-23 22:00:49 -07001162 This method is optional. It is called to discard the payload data on a key
1163 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001164
David Howells76d8aea2005-06-23 22:00:49 -07001165 This method does not need to lock the key to access the payload; it can
1166 consider the key as being inaccessible at this time. Note that the key's
1167 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001168
1169 It is not safe to sleep in this method; the caller may hold spinlocks.
1170
1171
1172 (*) void (*describe)(const struct key *key, struct seq_file *p);
1173
1174 This method is optional. It is called during /proc/keys reading to
1175 summarise a key's description and payload in text form.
1176
David Howells76d8aea2005-06-23 22:00:49 -07001177 This method will be called with the RCU read lock held. rcu_dereference()
1178 should be used to read the payload pointer if the payload is to be
1179 accessed. key->datalen cannot be trusted to stay consistent with the
1180 contents of the payload.
1181
1182 The description will not change, though the key's state may.
1183
1184 It is not safe to sleep in this method; the RCU read lock is held by the
1185 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001186
1187
1188 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1189
1190 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001191 key's payload into something a blob of data for userspace to deal with.
1192 Ideally, the blob should be in the same format as that passed in to the
1193 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001194
1195 If successful, the blob size that could be produced should be returned
1196 rather than the size copied.
1197
David Howells76d8aea2005-06-23 22:00:49 -07001198 This method will be called with the key's semaphore read-locked. This will
1199 prevent the key's payload changing. It is not necessary to use RCU locking
1200 when accessing the key's payload. It is safe to sleep in this method, such
1201 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001202
1203
David Howells76181c12007-10-16 23:29:46 -07001204 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001205 void *aux);
1206
David Howells76181c12007-10-16 23:29:46 -07001207 This method is optional. If provided, request_key() and friends will
1208 invoke this function rather than upcalling to /sbin/request-key to operate
1209 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001210
David Howells76181c12007-10-16 23:29:46 -07001211 The aux parameter is as passed to request_key_async_with_auxdata() and
1212 similar or is NULL otherwise. Also passed are the construction record for
1213 the key to be operated upon and the operation type (currently only
1214 "create").
David Howells4e54f082006-06-29 02:24:28 -07001215
David Howells76181c12007-10-16 23:29:46 -07001216 This method is permitted to return before the upcall is complete, but the
1217 following function must be called under all circumstances to complete the
1218 instantiation process, whether or not it succeeds, whether or not there's
1219 an error:
1220
1221 void complete_request_key(struct key_construction *cons, int error);
1222
1223 The error parameter should be 0 on success, -ve on error. The
1224 construction record is destroyed by this action and the authorisation key
1225 will be revoked. If an error is indicated, the key under construction
1226 will be negatively instantiated if it wasn't already instantiated.
1227
1228 If this method returns an error, that error will be returned to the
1229 caller of request_key*(). complete_request_key() must be called prior to
1230 returning.
1231
1232 The key under construction and the authorisation key can be found in the
1233 key_construction struct pointed to by cons:
1234
1235 (*) struct key *key;
1236
1237 The key under construction.
1238
1239 (*) struct key *authkey;
1240
1241 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001242
1243
Linus Torvalds1da177e2005-04-16 15:20:36 -07001244============================
1245REQUEST-KEY CALLBACK SERVICE
1246============================
1247
1248To create a new key, the kernel will attempt to execute the following command
1249line:
1250
1251 /sbin/request-key create <key> <uid> <gid> \
1252 <threadring> <processring> <sessionring> <callout_info>
1253
1254<key> is the key being constructed, and the three keyrings are the process
1255keyrings from the process that caused the search to be issued. These are
1256included for two reasons:
1257
1258 (1) There may be an authentication token in one of the keyrings that is
1259 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1260
1261 (2) The new key should probably be cached in one of these rings.
1262
1263This program should set it UID and GID to those specified before attempting to
1264access any more keys. It may then look around for a user specific process to
1265hand the request off to (perhaps a path held in placed in another key by, for
1266example, the KDE desktop manager).
1267
1268The program (or whatever it calls) should finish construction of the key by
David Howellsee009e42011-03-07 15:06:20 +00001269calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to
1270cache the key in one of the keyrings (probably the session ring) before
1271returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE
1272or KEYCTL_REJECT; this also permits the key to be cached in one of the
1273keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001274
1275If it returns with the key remaining in the unconstructed state, the key will
1276be marked as being negative, it will be added to the session keyring, and an
1277error will be returned to the key requestor.
1278
David Howells76d8aea2005-06-23 22:00:49 -07001279Supplementary information may be provided from whoever or whatever invoked this
1280service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001281information was made available, then "-" will be passed as this parameter
1282instead.
1283
1284
1285Similarly, the kernel may attempt to update an expired or a soon to expire key
1286by executing:
1287
1288 /sbin/request-key update <key> <uid> <gid> \
1289 <threadring> <processring> <sessionring>
1290
1291In this case, the program isn't required to actually attach the key to a ring;
1292the rings are provided for reference.
David Howells5d135442009-09-02 09:14:00 +01001293
1294
1295==================
1296GARBAGE COLLECTION
1297==================
1298
1299Dead keys (for which the type has been removed) will be automatically unlinked
1300from those keyrings that point to them and deleted as soon as possible by a
1301background garbage collector.
1302
1303Similarly, revoked and expired keys will be garbage collected, but only after a
1304certain amount of time has passed. This time is set as a number of seconds in:
1305
1306 /proc/sys/kernel/keys/gc_delay