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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 Howells76181c132007-10-16 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 Dunlapd410fa4e2011-05-19 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 Howells76181c132007-10-16 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
David Howellsa5b4bd22013-09-24 10:35:14 +0100868 key_ref_t make_key_ref(const struct key *key, bool possession);
David Howells664cceb2005-09-28 17:03:15 +0100869
870 struct key *key_ref_to_ptr(const key_ref_t key_ref);
871
David Howellsa5b4bd22013-09-24 10:35:14 +0100872 bool is_key_possessed(const key_ref_t key_ref);
David Howells664cceb2005-09-28 17:03:15 +0100873
874 The first function constructs a key reference from a key pointer and
David Howellsa5b4bd22013-09-24 10:35:14 +0100875 possession information (which must be true or false).
David Howells664cceb2005-09-28 17:03:15 +0100876
877 The second function retrieves the key pointer from a reference and the
878 third retrieves the possession flag.
879
David Howells76d8aea2005-06-23 22:00:49 -0700880When accessing a key's payload contents, certain precautions must be taken to
881prevent access vs modification races. See the section "Notes on accessing
882payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700883
884(*) To search for a key, call:
885
886 struct key *request_key(const struct key_type *type,
887 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700888 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700889
890 This is used to request a key or keyring with a description that matches
David Howellsf93b3cc2014-09-16 17:36:09 +0100891 the description specified according to the key type's match_preparse()
892 method. This permits approximate matching to occur. If callout_string is
893 not NULL, then /sbin/request-key will be invoked in an attempt to obtain
894 the key from userspace. In that case, callout_string will be passed as an
895 argument to the program.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700896
897 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
898 returned.
899
David Howells3e301482005-06-23 22:00:56 -0700900 If successful, the key will have been attached to the default keyring for
901 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
902
Randy Dunlapd410fa4e2011-05-19 15:59:38 -0700903 See also Documentation/security/keys-request-key.txt.
David Howellsf1a9bad2005-10-07 15:04:52 +0100904
Linus Torvalds1da177e2005-04-16 15:20:36 -0700905
David Howells4e54f082006-06-29 02:24:28 -0700906(*) To search for a key, passing auxiliary data to the upcaller, call:
907
908 struct key *request_key_with_auxdata(const struct key_type *type,
909 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700910 const void *callout_info,
911 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700912 void *aux);
913
914 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700915 passed to the key_type->request_key() op if it exists, and the callout_info
916 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700917
918
David Howells76181c132007-10-16 23:29:46 -0700919(*) A key can be requested asynchronously by calling one of:
920
921 struct key *request_key_async(const struct key_type *type,
922 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700923 const void *callout_info,
924 size_t callout_len);
David Howells76181c132007-10-16 23:29:46 -0700925
926 or:
927
928 struct key *request_key_async_with_auxdata(const struct key_type *type,
929 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700930 const char *callout_info,
931 size_t callout_len,
David Howells76181c132007-10-16 23:29:46 -0700932 void *aux);
933
934 which are asynchronous equivalents of request_key() and
935 request_key_with_auxdata() respectively.
936
937 These two functions return with the key potentially still under
Matt LaPlanted9195882008-07-25 19:45:33 -0700938 construction. To wait for construction completion, the following should be
David Howells76181c132007-10-16 23:29:46 -0700939 called:
940
941 int wait_for_key_construction(struct key *key, bool intr);
942
943 The function will wait for the key to finish being constructed and then
944 invokes key_validate() to return an appropriate value to indicate the state
945 of the key (0 indicates the key is usable).
946
947 If intr is true, then the wait can be interrupted by a signal, in which
948 case error ERESTARTSYS will be returned.
949
950
Linus Torvalds1da177e2005-04-16 15:20:36 -0700951(*) When it is no longer required, the key should be released using:
952
953 void key_put(struct key *key);
954
David Howells664cceb2005-09-28 17:03:15 +0100955 Or:
956
957 void key_ref_put(key_ref_t key_ref);
958
959 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700960 the argument will not be parsed.
961
962
David Howellsccc3e6d2013-09-24 10:35:16 +0100963(*) Extra references can be made to a key by calling one of the following
964 functions:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700965
David Howellsccc3e6d2013-09-24 10:35:16 +0100966 struct key *__key_get(struct key *key);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700967 struct key *key_get(struct key *key);
968
David Howellsccc3e6d2013-09-24 10:35:16 +0100969 Keys so references will need to be disposed of by calling key_put() when
970 they've been finished with. The key pointer passed in will be returned.
971
972 In the case of key_get(), if the pointer is NULL or CONFIG_KEYS is not set
973 then the key will not be dereferenced and no increment will take place.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700974
975
976(*) A key's serial number can be obtained by calling:
977
978 key_serial_t key_serial(struct key *key);
979
980 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
981 latter case without parsing the argument).
982
983
984(*) If a keyring was found in the search, this can be further searched by:
985
David Howells664cceb2005-09-28 17:03:15 +0100986 key_ref_t keyring_search(key_ref_t keyring_ref,
987 const struct key_type *type,
988 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700989
990 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +0100991 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
992 the returned key will need to be released.
993
994 The possession attribute from the keyring reference is used to control
995 access through the permissions mask and is propagated to the returned key
996 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700997
998
David Howellsf8aa23a2012-10-02 19:24:56 +0100999(*) A keyring can be created by:
1000
1001 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
1002 const struct cred *cred,
1003 key_perm_t perm,
1004 unsigned long flags,
1005 struct key *dest);
1006
1007 This creates a keyring with the given attributes and returns it. If dest
1008 is not NULL, the new keyring will be linked into the keyring to which it
1009 points. No permission checks are made upon the destination keyring.
1010
1011 Error EDQUOT can be returned if the keyring would overload the quota (pass
1012 KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted
1013 towards the user's quota). Error ENOMEM can also be returned.
1014
1015
Linus Torvalds1da177e2005-04-16 15:20:36 -07001016(*) To check the validity of a key, this function can be called:
1017
1018 int validate_key(struct key *key);
1019
1020 This checks that the key in question hasn't expired or and hasn't been
1021 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
1022 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
1023 returned (in the latter case without parsing the argument).
1024
1025
1026(*) To register a key type, the following function should be called:
1027
1028 int register_key_type(struct key_type *type);
1029
1030 This will return error EEXIST if a type of the same name is already
1031 present.
1032
1033
1034(*) To unregister a key type, call:
1035
1036 void unregister_key_type(struct key_type *type);
1037
1038
Satyam Sharma7eacbbd2007-07-31 00:38:17 -07001039Under some circumstances, it may be desirable to deal with a bundle of keys.
1040The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -07001041
1042 struct key_type key_type_keyring;
1043
1044This can be used with a function such as request_key() to find a specific
1045keyring in a process's keyrings. A keyring thus found can then be searched
1046with keyring_search(). Note that it is not possible to use request_key() to
1047search a specific keyring, so using keyrings in this way is of limited utility.
1048
1049
David Howells76d8aea2005-06-23 22:00:49 -07001050===================================
1051NOTES ON ACCESSING PAYLOAD CONTENTS
1052===================================
1053
1054The simplest payload is just a number in key->payload.value. In this case,
1055there's no need to indulge in RCU or locking when accessing the payload.
1056
1057More complex payload contents must be allocated and a pointer to them set in
1058key->payload.data. One of the following ways must be selected to access the
1059data:
1060
David Howells664cceb2005-09-28 17:03:15 +01001061 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -07001062
1063 If the key type does not have a modify method, then the key's payload can
1064 be accessed without any form of locking, provided that it's known to be
1065 instantiated (uninstantiated keys cannot be "found").
1066
1067 (2) The key's semaphore.
1068
1069 The semaphore could be used to govern access to the payload and to control
1070 the payload pointer. It must be write-locked for modifications and would
1071 have to be read-locked for general access. The disadvantage of doing this
1072 is that the accessor may be required to sleep.
1073
1074 (3) RCU.
1075
1076 RCU must be used when the semaphore isn't already held; if the semaphore
1077 is held then the contents can't change under you unexpectedly as the
1078 semaphore must still be used to serialise modifications to the key. The
1079 key management code takes care of this for the key type.
1080
1081 However, this means using:
1082
1083 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
1084
1085 to read the pointer, and:
1086
1087 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
1088
1089 to set the pointer and dispose of the old contents after a grace period.
1090 Note that only the key type should ever modify a key's payload.
1091
1092 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1093 use of call_rcu() and, if the payload is of variable size, the length of
1094 the payload. key->datalen cannot be relied upon to be consistent with the
1095 payload just dereferenced if the key's semaphore is not held.
1096
1097
Linus Torvalds1da177e2005-04-16 15:20:36 -07001098===================
1099DEFINING A KEY TYPE
1100===================
1101
1102A kernel service may want to define its own key type. For instance, an AFS
1103filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c132007-10-16 23:29:46 -07001104author fills in a key_type struct and registers it with the system.
1105
1106Source files that implement key types should include the following header file:
1107
1108 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001109
1110The structure has a number of fields, some of which are mandatory:
1111
1112 (*) const char *name
1113
1114 The name of the key type. This is used to translate a key type name
1115 supplied by userspace into a pointer to the structure.
1116
1117
1118 (*) size_t def_datalen
1119
1120 This is optional - it supplies the default payload data length as
1121 contributed to the quota. If the key type's payload is always or almost
1122 always the same size, then this is a more efficient way to do things.
1123
1124 The data length (and quota) on a particular key can always be changed
1125 during instantiation or update by calling:
1126
1127 int key_payload_reserve(struct key *key, size_t datalen);
1128
David Howells76d8aea2005-06-23 22:00:49 -07001129 With the revised data length. Error EDQUOT will be returned if this is not
1130 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001131
1132
David Howellsb9fffa32011-03-07 15:05:59 +00001133 (*) int (*vet_description)(const char *description);
1134
1135 This optional method is called to vet a key description. If the key type
1136 doesn't approve of the key description, it may return an error, otherwise
1137 it should return 0.
1138
1139
David Howellsd4f65b52012-09-13 13:06:29 +01001140 (*) int (*preparse)(struct key_preparsed_payload *prep);
1141
1142 This optional method permits the key type to attempt to parse payload
1143 before a key is created (add key) or the key semaphore is taken (update or
1144 instantiate key). The structure pointed to by prep looks like:
1145
1146 struct key_preparsed_payload {
1147 char *description;
1148 void *type_data[2];
1149 void *payload;
1150 const void *data;
1151 size_t datalen;
1152 size_t quotalen;
David Howells7dfa0ca62014-07-18 18:56:34 +01001153 time_t expiry;
David Howellsd4f65b52012-09-13 13:06:29 +01001154 };
1155
1156 Before calling the method, the caller will fill in data and datalen with
1157 the payload blob parameters; quotalen will be filled in with the default
David Howells7dfa0ca62014-07-18 18:56:34 +01001158 quota size from the key type; expiry will be set to TIME_T_MAX and the
1159 rest will be cleared.
David Howellsd4f65b52012-09-13 13:06:29 +01001160
1161 If a description can be proposed from the payload contents, that should be
1162 attached as a string to the description field. This will be used for the
1163 key description if the caller of add_key() passes NULL or "".
1164
1165 The method can attach anything it likes to type_data[] and payload. These
David Howells7dfa0ca62014-07-18 18:56:34 +01001166 are merely passed along to the instantiate() or update() operations. If
1167 set, the expiry time will be applied to the key if it is instantiated from
1168 this data.
David Howellsd4f65b52012-09-13 13:06:29 +01001169
David Howells7dfa0ca62014-07-18 18:56:34 +01001170 The method should return 0 if successful or a negative error code
David Howellsd4f65b52012-09-13 13:06:29 +01001171 otherwise.
1172
David Howellsf93b3cc2014-09-16 17:36:09 +01001173
David Howellsd4f65b52012-09-13 13:06:29 +01001174 (*) void (*free_preparse)(struct key_preparsed_payload *prep);
1175
1176 This method is only required if the preparse() method is provided,
1177 otherwise it is unused. It cleans up anything attached to the
1178 description, type_data and payload fields of the key_preparsed_payload
David Howells4d8c0252014-07-18 18:56:34 +01001179 struct as filled in by the preparse() method. It will always be called
1180 after preparse() returns successfully, even if instantiate() or update()
1181 succeed.
David Howellsd4f65b52012-09-13 13:06:29 +01001182
1183
1184 (*) int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001185
1186 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001187 The payload attached need not bear any relation to the data passed to this
1188 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001189
David Howellsd4f65b52012-09-13 13:06:29 +01001190 The prep->data and prep->datalen fields will define the original payload
1191 blob. If preparse() was supplied then other fields may be filled in also.
1192
Linus Torvalds1da177e2005-04-16 15:20:36 -07001193 If the amount of data attached to the key differs from the size in
1194 keytype->def_datalen, then key_payload_reserve() should be called.
1195
1196 This method does not have to lock the key in order to attach a payload.
1197 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1198 anything else from gaining access to the key.
1199
David Howells76d8aea2005-06-23 22:00:49 -07001200 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001201
1202
Linus Torvalds1da177e2005-04-16 15:20:36 -07001203 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1204
David Howells76d8aea2005-06-23 22:00:49 -07001205 If this type of key can be updated, then this method should be provided.
1206 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001207
David Howellsd4f65b52012-09-13 13:06:29 +01001208 The prep->data and prep->datalen fields will define the original payload
1209 blob. If preparse() was supplied then other fields may be filled in also.
1210
Linus Torvalds1da177e2005-04-16 15:20:36 -07001211 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001212 before any changes are actually made. Note that if this succeeds, the type
1213 is committed to changing the key because it's already been altered, so all
1214 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001215
David Howells76d8aea2005-06-23 22:00:49 -07001216 The key will have its semaphore write-locked before this method is called,
1217 but this only deters other writers; any changes to the key's payload must
1218 be made under RCU conditions, and call_rcu() must be used to dispose of
1219 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001220
David Howells76d8aea2005-06-23 22:00:49 -07001221 key_payload_reserve() should be called before the changes are made, but
1222 after all allocations and other potentially failing function calls are
1223 made.
1224
1225 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001226
1227
David Howellsf93b3cc2014-09-16 17:36:09 +01001228 (*) int (*match_preparse)(struct key_match_data *match_data);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001229
David Howellsf93b3cc2014-09-16 17:36:09 +01001230 This method is optional. It is called when a key search is about to be
1231 performed. It is given the following structure:
Linus Torvalds1da177e2005-04-16 15:20:36 -07001232
David Howellsf93b3cc2014-09-16 17:36:09 +01001233 struct key_match_data {
1234 bool (*cmp)(const struct key *key,
1235 const struct key_match_data *match_data);
1236 const void *raw_data;
1237 void *preparsed;
1238 unsigned lookup_type;
1239 };
Linus Torvalds1da177e2005-04-16 15:20:36 -07001240
David Howellsf93b3cc2014-09-16 17:36:09 +01001241 On entry, raw_data will be pointing to the criteria to be used in matching
1242 a key by the caller and should not be modified. (*cmp)() will be pointing
1243 to the default matcher function (which does an exact description match
1244 against raw_data) and lookup_type will be set to indicate a direct lookup.
1245
1246 The following lookup_type values are available:
1247
1248 [*] KEYRING_SEARCH_LOOKUP_DIRECT - A direct lookup hashes the type and
1249 description to narrow down the search to a small number of keys.
1250
1251 [*] KEYRING_SEARCH_LOOKUP_ITERATE - An iterative lookup walks all the
1252 keys in the keyring until one is matched. This must be used for any
1253 search that's not doing a simple direct match on the key description.
1254
1255 The method may set cmp to point to a function of its choice that does some
1256 other form of match, may set lookup_type to KEYRING_SEARCH_LOOKUP_ITERATE
1257 and may attach something to the preparsed pointer for use by (*cmp)().
1258 (*cmp)() should return true if a key matches and false otherwise.
1259
1260 If preparsed is set, it may be necessary to use the match_free() method to
1261 clean it up.
1262
1263 The method should return 0 if successful or a negative error code
1264 otherwise.
1265
1266 It is permitted to sleep in this method, but (*cmp)() may not sleep as
1267 locks will be held over it.
1268
1269 If match_preparse() is not provided, keys of this type will be matched
1270 exactly by their description.
1271
1272
1273 (*) void (*match_free)(struct key_match_data *match_data);
1274
1275 This method is optional. If given, it called to clean up
1276 match_data->preparsed after a successful call to match_preparse().
Linus Torvalds1da177e2005-04-16 15:20:36 -07001277
1278
David Howells04c567d2006-06-22 14:47:18 -07001279 (*) void (*revoke)(struct key *key);
1280
1281 This method is optional. It is called to discard part of the payload
1282 data upon a key being revoked. The caller will have the key semaphore
1283 write-locked.
1284
1285 It is safe to sleep in this method, though care should be taken to avoid
1286 a deadlock against the key semaphore.
1287
1288
Linus Torvalds1da177e2005-04-16 15:20:36 -07001289 (*) void (*destroy)(struct key *key);
1290
David Howells76d8aea2005-06-23 22:00:49 -07001291 This method is optional. It is called to discard the payload data on a key
1292 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001293
David Howells76d8aea2005-06-23 22:00:49 -07001294 This method does not need to lock the key to access the payload; it can
1295 consider the key as being inaccessible at this time. Note that the key's
1296 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001297
1298 It is not safe to sleep in this method; the caller may hold spinlocks.
1299
1300
1301 (*) void (*describe)(const struct key *key, struct seq_file *p);
1302
1303 This method is optional. It is called during /proc/keys reading to
1304 summarise a key's description and payload in text form.
1305
David Howells76d8aea2005-06-23 22:00:49 -07001306 This method will be called with the RCU read lock held. rcu_dereference()
1307 should be used to read the payload pointer if the payload is to be
1308 accessed. key->datalen cannot be trusted to stay consistent with the
1309 contents of the payload.
1310
1311 The description will not change, though the key's state may.
1312
1313 It is not safe to sleep in this method; the RCU read lock is held by the
1314 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001315
1316
1317 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1318
1319 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001320 key's payload into something a blob of data for userspace to deal with.
1321 Ideally, the blob should be in the same format as that passed in to the
1322 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001323
1324 If successful, the blob size that could be produced should be returned
1325 rather than the size copied.
1326
David Howells76d8aea2005-06-23 22:00:49 -07001327 This method will be called with the key's semaphore read-locked. This will
1328 prevent the key's payload changing. It is not necessary to use RCU locking
1329 when accessing the key's payload. It is safe to sleep in this method, such
1330 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001331
1332
David Howells76181c132007-10-16 23:29:46 -07001333 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001334 void *aux);
1335
David Howells76181c132007-10-16 23:29:46 -07001336 This method is optional. If provided, request_key() and friends will
1337 invoke this function rather than upcalling to /sbin/request-key to operate
1338 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001339
David Howells76181c132007-10-16 23:29:46 -07001340 The aux parameter is as passed to request_key_async_with_auxdata() and
1341 similar or is NULL otherwise. Also passed are the construction record for
1342 the key to be operated upon and the operation type (currently only
1343 "create").
David Howells4e54f082006-06-29 02:24:28 -07001344
David Howells76181c132007-10-16 23:29:46 -07001345 This method is permitted to return before the upcall is complete, but the
1346 following function must be called under all circumstances to complete the
1347 instantiation process, whether or not it succeeds, whether or not there's
1348 an error:
1349
1350 void complete_request_key(struct key_construction *cons, int error);
1351
1352 The error parameter should be 0 on success, -ve on error. The
1353 construction record is destroyed by this action and the authorisation key
1354 will be revoked. If an error is indicated, the key under construction
1355 will be negatively instantiated if it wasn't already instantiated.
1356
1357 If this method returns an error, that error will be returned to the
1358 caller of request_key*(). complete_request_key() must be called prior to
1359 returning.
1360
1361 The key under construction and the authorisation key can be found in the
1362 key_construction struct pointed to by cons:
1363
1364 (*) struct key *key;
1365
1366 The key under construction.
1367
1368 (*) struct key *authkey;
1369
1370 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001371
1372
Linus Torvalds1da177e2005-04-16 15:20:36 -07001373============================
1374REQUEST-KEY CALLBACK SERVICE
1375============================
1376
1377To create a new key, the kernel will attempt to execute the following command
1378line:
1379
1380 /sbin/request-key create <key> <uid> <gid> \
1381 <threadring> <processring> <sessionring> <callout_info>
1382
1383<key> is the key being constructed, and the three keyrings are the process
1384keyrings from the process that caused the search to be issued. These are
1385included for two reasons:
1386
1387 (1) There may be an authentication token in one of the keyrings that is
1388 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1389
1390 (2) The new key should probably be cached in one of these rings.
1391
1392This program should set it UID and GID to those specified before attempting to
1393access any more keys. It may then look around for a user specific process to
1394hand the request off to (perhaps a path held in placed in another key by, for
1395example, the KDE desktop manager).
1396
1397The program (or whatever it calls) should finish construction of the key by
David Howellsee009e4a02011-03-07 15:06:20 +00001398calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to
1399cache the key in one of the keyrings (probably the session ring) before
1400returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE
1401or KEYCTL_REJECT; this also permits the key to be cached in one of the
1402keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001403
1404If it returns with the key remaining in the unconstructed state, the key will
1405be marked as being negative, it will be added to the session keyring, and an
1406error will be returned to the key requestor.
1407
David Howells76d8aea2005-06-23 22:00:49 -07001408Supplementary information may be provided from whoever or whatever invoked this
1409service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001410information was made available, then "-" will be passed as this parameter
1411instead.
1412
1413
1414Similarly, the kernel may attempt to update an expired or a soon to expire key
1415by executing:
1416
1417 /sbin/request-key update <key> <uid> <gid> \
1418 <threadring> <processring> <sessionring>
1419
1420In this case, the program isn't required to actually attach the key to a ring;
1421the rings are provided for reference.
David Howells5d135442009-09-02 09:14:00 +01001422
1423
1424==================
1425GARBAGE COLLECTION
1426==================
1427
1428Dead keys (for which the type has been removed) will be automatically unlinked
1429from those keyrings that point to them and deleted as soon as possible by a
1430background garbage collector.
1431
1432Similarly, revoked and expired keys will be garbage collected, but only after a
1433certain amount of time has passed. This time is set as a number of seconds in:
1434
1435 /proc/sys/kernel/keys/gc_delay