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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
29 - Key access filesystem
30
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
116
117====================
118KEY SERVICE OVERVIEW
119====================
120
121The key service provides a number of features besides keys:
122
123 (*) The key service defines two special key types:
124
125 (+) "keyring"
126
127 Keyrings are special keys that contain a list of other keys. Keyring
128 lists can be modified using various system calls. Keyrings should not
129 be given a payload when created.
130
131 (+) "user"
132
133 A key of this type has a description and a payload that are arbitrary
134 blobs of data. These can be created, updated and read by userspace,
135 and aren't intended for use by kernel services.
136
137 (*) Each process subscribes to three keyrings: a thread-specific keyring, a
138 process-specific keyring, and a session-specific keyring.
139
140 The thread-specific keyring is discarded from the child when any sort of
141 clone, fork, vfork or execve occurs. A new keyring is created only when
142 required.
143
David Howells76d8aea2005-06-23 22:00:49 -0700144 The process-specific keyring is replaced with an empty one in the child on
145 clone, fork, vfork unless CLONE_THREAD is supplied, in which case it is
146 shared. execve also discards the process's process keyring and creates a
147 new one.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148
149 The session-specific keyring is persistent across clone, fork, vfork and
150 execve, even when the latter executes a set-UID or set-GID binary. A
151 process can, however, replace its current session keyring with a new one
152 by using PR_JOIN_SESSION_KEYRING. It is permitted to request an anonymous
153 new one, or to attempt to create or join one of a specific name.
154
155 The ownership of the thread keyring changes when the real UID and GID of
156 the thread changes.
157
158 (*) Each user ID resident in the system holds two special keyrings: a user
159 specific keyring and a default user session keyring. The default session
160 keyring is initialised with a link to the user-specific keyring.
161
162 When a process changes its real UID, if it used to have no session key, it
163 will be subscribed to the default session key for the new UID.
164
165 If a process attempts to access its session key when it doesn't have one,
166 it will be subscribed to the default for its current UID.
167
168 (*) Each user has two quotas against which the keys they own are tracked. One
169 limits the total number of keys and keyrings, the other limits the total
170 amount of description and payload space that can be consumed.
171
172 The user can view information on this and other statistics through procfs
David Howells0b77f5b2008-04-29 01:01:32 -0700173 files. The root user may also alter the quota limits through sysctl files
174 (see the section "New procfs files").
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175
176 Process-specific and thread-specific keyrings are not counted towards a
177 user's quota.
178
179 If a system call that modifies a key or keyring in some way would put the
180 user over quota, the operation is refused and error EDQUOT is returned.
181
David Howells76d8aea2005-06-23 22:00:49 -0700182 (*) There's a system call interface by which userspace programs can create and
183 manipulate keys and keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700184
David Howells76d8aea2005-06-23 22:00:49 -0700185 (*) There's a kernel interface by which services can register types and search
186 for keys.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187
188 (*) There's a way for the a search done from the kernel to call back to
189 userspace to request a key that can't be found in a process's keyrings.
190
191 (*) An optional filesystem is available through which the key database can be
192 viewed and manipulated.
193
194
195======================
196KEY ACCESS PERMISSIONS
197======================
198
David Howells76d8aea2005-06-23 22:00:49 -0700199Keys have an owner user ID, a group access ID, and a permissions mask. The mask
David Howells664cceb2005-09-28 17:03:15 +0100200has up to eight bits each for possessor, user, group and other access. Only
David Howells29db9192005-10-30 15:02:44 -0800201six of each set of eight bits are defined. These permissions granted are:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700202
203 (*) View
204
205 This permits a key or keyring's attributes to be viewed - including key
206 type and description.
207
208 (*) Read
209
210 This permits a key's payload to be viewed or a keyring's list of linked
211 keys.
212
213 (*) Write
214
David Howells76d8aea2005-06-23 22:00:49 -0700215 This permits a key's payload to be instantiated or updated, or it allows a
216 link to be added to or removed from a keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700217
218 (*) Search
219
220 This permits keyrings to be searched and keys to be found. Searches can
221 only recurse into nested keyrings that have search permission set.
222
223 (*) Link
224
225 This permits a key or keyring to be linked to. To create a link from a
226 keyring to a key, a process must have Write permission on the keyring and
227 Link permission on the key.
228
David Howells29db9192005-10-30 15:02:44 -0800229 (*) Set Attribute
230
231 This permits a key's UID, GID and permissions mask to be changed.
232
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233For changing the ownership, group ID or permissions mask, being the owner of
234the key or having the sysadmin capability is sufficient.
235
236
Michael LeMayd7200242006-06-22 14:47:17 -0700237===============
238SELINUX SUPPORT
239===============
240
241The security class "key" has been added to SELinux so that mandatory access
242controls can be applied to keys created within various contexts. This support
243is preliminary, and is likely to change quite significantly in the near future.
244Currently, all of the basic permissions explained above are provided in SELinux
Michael LeMay4eb582c2006-06-26 00:24:57 -0700245as well; SELinux is simply invoked after all basic permission checks have been
Michael LeMayd7200242006-06-22 14:47:17 -0700246performed.
247
Michael LeMay4eb582c2006-06-26 00:24:57 -0700248The value of the file /proc/self/attr/keycreate influences the labeling of
249newly-created keys. If the contents of that file correspond to an SELinux
250security context, then the key will be assigned that context. Otherwise, the
251key will be assigned the current context of the task that invoked the key
252creation request. Tasks must be granted explicit permission to assign a
253particular context to newly-created keys, using the "create" permission in the
254key security class.
Michael LeMayd7200242006-06-22 14:47:17 -0700255
Michael LeMay4eb582c2006-06-26 00:24:57 -0700256The default keyrings associated with users will be labeled with the default
257context of the user if and only if the login programs have been instrumented to
258properly initialize keycreate during the login process. Otherwise, they will
259be labeled with the context of the login program itself.
Michael LeMayd7200242006-06-22 14:47:17 -0700260
261Note, however, that the default keyrings associated with the root user are
262labeled with the default kernel context, since they are created early in the
263boot process, before root has a chance to log in.
264
Michael LeMay4eb582c2006-06-26 00:24:57 -0700265The keyrings associated with new threads are each labeled with the context of
266their associated thread, and both session and process keyrings are handled
267similarly.
268
Michael LeMayd7200242006-06-22 14:47:17 -0700269
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270================
271NEW PROCFS FILES
272================
273
274Two files have been added to procfs by which an administrator can find out
275about the status of the key service:
276
277 (*) /proc/keys
278
Michael LeMay06ec7be2006-06-26 00:24:56 -0700279 This lists the keys that are currently viewable by the task reading the
280 file, giving information about their type, description and permissions.
281 It is not possible to view the payload of the key this way, though some
282 information about it may be given.
283
284 The only keys included in the list are those that grant View permission to
285 the reading process whether or not it possesses them. Note that LSM
286 security checks are still performed, and may further filter out keys that
287 the current process is not authorised to view.
288
289 The contents of the file look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700290
David Howells664cceb2005-09-28 17:03:15 +0100291 SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
David Howells29db9192005-10-30 15:02:44 -0800292 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4
293 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty
294 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty
295 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty
296 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4
297 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty
David Howells664cceb2005-09-28 17:03:15 +0100298 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0
David Howells29db9192005-10-30 15:02:44 -0800299 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0
300 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301
302 The flags are:
303
304 I Instantiated
305 R Revoked
306 D Dead
307 Q Contributes to user's quota
Matt LaPlante5d3f0832006-11-30 05:21:10 +0100308 U Under construction by callback to userspace
Linus Torvalds1da177e2005-04-16 15:20:36 -0700309 N Negative key
310
311 This file must be enabled at kernel configuration time as it allows anyone
312 to list the keys database.
313
314 (*) /proc/key-users
315
316 This file lists the tracking data for each user that has at least one key
Michael LeMay06ec7be2006-06-26 00:24:56 -0700317 on the system. Such data includes quota information and statistics:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700318
319 [root@andromeda root]# cat /proc/key-users
320 0: 46 45/45 1/100 13/10000
321 29: 2 2/2 2/100 40/10000
322 32: 2 2/2 2/100 40/10000
323 38: 2 2/2 2/100 40/10000
324
325 The format of each line is
326 <UID>: User ID to which this applies
327 <usage> Structure refcount
328 <inst>/<keys> Total number of keys and number instantiated
329 <keys>/<max> Key count quota
330 <bytes>/<max> Key size quota
331
332
David Howells0b77f5b2008-04-29 01:01:32 -0700333Four new sysctl files have been added also for the purpose of controlling the
334quota limits on keys:
335
336 (*) /proc/sys/kernel/keys/root_maxkeys
337 /proc/sys/kernel/keys/root_maxbytes
338
339 These files hold the maximum number of keys that root may have and the
340 maximum total number of bytes of data that root may have stored in those
341 keys.
342
343 (*) /proc/sys/kernel/keys/maxkeys
344 /proc/sys/kernel/keys/maxbytes
345
346 These files hold the maximum number of keys that each non-root user may
347 have and the maximum total number of bytes of data that each of those
348 users may have stored in their keys.
349
350Root may alter these by writing each new limit as a decimal number string to
351the appropriate file.
352
353
Linus Torvalds1da177e2005-04-16 15:20:36 -0700354===============================
355USERSPACE SYSTEM CALL INTERFACE
356===============================
357
358Userspace can manipulate keys directly through three new syscalls: add_key,
359request_key and keyctl. The latter provides a number of functions for
360manipulating keys.
361
362When referring to a key directly, userspace programs should use the key's
363serial number (a positive 32-bit integer). However, there are some special
364values available for referring to special keys and keyrings that relate to the
365process making the call:
366
367 CONSTANT VALUE KEY REFERENCED
368 ============================== ====== ===========================
369 KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring
370 KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring
371 KEY_SPEC_SESSION_KEYRING -3 session-specific keyring
372 KEY_SPEC_USER_KEYRING -4 UID-specific keyring
373 KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring
374 KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring
David Howellsb5f545c2006-01-08 01:02:47 -0800375 KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key()
376 authorisation key
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377
378
379The main syscalls are:
380
381 (*) Create a new key of given type, description and payload and add it to the
382 nominated keyring:
383
384 key_serial_t add_key(const char *type, const char *desc,
385 const void *payload, size_t plen,
386 key_serial_t keyring);
387
388 If a key of the same type and description as that proposed already exists
389 in the keyring, this will try to update it with the given payload, or it
390 will return error EEXIST if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700391 type. The process must also have permission to write to the key to be able
392 to update it. The new key will have all user permissions granted and no
393 group or third party permissions.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700394
David Howells76d8aea2005-06-23 22:00:49 -0700395 Otherwise, this will attempt to create a new key of the specified type and
396 description, and to instantiate it with the supplied payload and attach it
397 to the keyring. In this case, an error will be generated if the process
398 does not have permission to write to the keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700399
400 The payload is optional, and the pointer can be NULL if not required by
401 the type. The payload is plen in size, and plen can be zero for an empty
402 payload.
403
David Howells76d8aea2005-06-23 22:00:49 -0700404 A new keyring can be generated by setting type "keyring", the keyring name
405 as the description (or NULL) and setting the payload to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700406
407 User defined keys can be created by specifying type "user". It is
408 recommended that a user defined key's description by prefixed with a type
409 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting
410 ticket.
411
412 Any other type must have been registered with the kernel in advance by a
413 kernel service such as a filesystem.
414
415 The ID of the new or updated key is returned if successful.
416
417
418 (*) Search the process's keyrings for a key, potentially calling out to
419 userspace to create it.
420
421 key_serial_t request_key(const char *type, const char *description,
422 const char *callout_info,
423 key_serial_t dest_keyring);
424
425 This function searches all the process's keyrings in the order thread,
426 process, session for a matching key. This works very much like
427 KEYCTL_SEARCH, including the optional attachment of the discovered key to
428 a keyring.
429
430 If a key cannot be found, and if callout_info is not NULL, then
431 /sbin/request-key will be invoked in an attempt to obtain a key. The
432 callout_info string will be passed as an argument to the program.
433
David Howellsf1a9bad2005-10-07 15:04:52 +0100434 See also Documentation/keys-request-key.txt.
435
Linus Torvalds1da177e2005-04-16 15:20:36 -0700436
437The keyctl syscall functions are:
438
439 (*) Map a special key ID to a real key ID for this process:
440
441 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id,
442 int create);
443
David Howells76d8aea2005-06-23 22:00:49 -0700444 The special key specified by "id" is looked up (with the key being created
445 if necessary) and the ID of the key or keyring thus found is returned if
446 it exists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700447
448 If the key does not yet exist, the key will be created if "create" is
449 non-zero; and the error ENOKEY will be returned if "create" is zero.
450
451
452 (*) Replace the session keyring this process subscribes to with a new one:
453
454 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name);
455
456 If name is NULL, an anonymous keyring is created attached to the process
457 as its session keyring, displacing the old session keyring.
458
459 If name is not NULL, if a keyring of that name exists, the process
460 attempts to attach it as the session keyring, returning an error if that
461 is not permitted; otherwise a new keyring of that name is created and
462 attached as the session keyring.
463
464 To attach to a named keyring, the keyring must have search permission for
465 the process's ownership.
466
467 The ID of the new session keyring is returned if successful.
468
469
470 (*) Update the specified key:
471
472 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload,
473 size_t plen);
474
475 This will try to update the specified key with the given payload, or it
476 will return error EOPNOTSUPP if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700477 type. The process must also have permission to write to the key to be able
478 to update it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700479
480 The payload is of length plen, and may be absent or empty as for
481 add_key().
482
483
484 (*) Revoke a key:
485
486 long keyctl(KEYCTL_REVOKE, key_serial_t key);
487
488 This makes a key unavailable for further operations. Further attempts to
489 use the key will be met with error EKEYREVOKED, and the key will no longer
490 be findable.
491
492
493 (*) Change the ownership of a key:
494
495 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid);
496
David Howells76d8aea2005-06-23 22:00:49 -0700497 This function permits a key's owner and group ID to be changed. Either one
498 of uid or gid can be set to -1 to suppress that change.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700499
500 Only the superuser can change a key's owner to something other than the
501 key's current owner. Similarly, only the superuser can change a key's
502 group ID to something other than the calling process's group ID or one of
503 its group list members.
504
505
506 (*) Change the permissions mask on a key:
507
508 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm);
509
510 This function permits the owner of a key or the superuser to change the
511 permissions mask on a key.
512
513 Only bits the available bits are permitted; if any other bits are set,
514 error EINVAL will be returned.
515
516
517 (*) Describe a key:
518
519 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer,
520 size_t buflen);
521
522 This function returns a summary of the key's attributes (but not its
523 payload data) as a string in the buffer provided.
524
525 Unless there's an error, it always returns the amount of data it could
526 produce, even if that's too big for the buffer, but it won't copy more
527 than requested to userspace. If the buffer pointer is NULL then no copy
528 will take place.
529
530 A process must have view permission on the key for this function to be
531 successful.
532
533 If successful, a string is placed in the buffer in the following format:
534
535 <type>;<uid>;<gid>;<perm>;<description>
536
537 Where type and description are strings, uid and gid are decimal, and perm
538 is hexadecimal. A NUL character is included at the end of the string if
539 the buffer is sufficiently big.
540
541 This can be parsed with
542
543 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc);
544
545
546 (*) Clear out a keyring:
547
548 long keyctl(KEYCTL_CLEAR, key_serial_t keyring);
549
550 This function clears the list of keys attached to a keyring. The calling
551 process must have write permission on the keyring, and it must be a
552 keyring (or else error ENOTDIR will result).
553
554
555 (*) Link a key into a keyring:
556
557 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key);
558
David Howells76d8aea2005-06-23 22:00:49 -0700559 This function creates a link from the keyring to the key. The process must
560 have write permission on the keyring and must have link permission on the
561 key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700562
David Howells76d8aea2005-06-23 22:00:49 -0700563 Should the keyring not be a keyring, error ENOTDIR will result; and if the
564 keyring is full, error ENFILE will result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700565
566 The link procedure checks the nesting of the keyrings, returning ELOOP if
David Howells017679c2006-01-08 01:02:43 -0800567 it appears too deep or EDEADLK if the link would introduce a cycle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700568
David Howellscab8eb52006-01-08 01:02:45 -0800569 Any links within the keyring to keys that match the new key in terms of
570 type and description will be discarded from the keyring as the new one is
571 added.
572
Linus Torvalds1da177e2005-04-16 15:20:36 -0700573
574 (*) Unlink a key or keyring from another keyring:
575
576 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
577
578 This function looks through the keyring for the first link to the
579 specified key, and removes it if found. Subsequent links to that key are
580 ignored. The process must have write permission on the keyring.
581
David Howells76d8aea2005-06-23 22:00:49 -0700582 If the keyring is not a keyring, error ENOTDIR will result; and if the key
583 is not present, error ENOENT will be the result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700584
585
586 (*) Search a keyring tree for a key:
587
588 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring,
589 const char *type, const char *description,
590 key_serial_t dest_keyring);
591
David Howells76d8aea2005-06-23 22:00:49 -0700592 This searches the keyring tree headed by the specified keyring until a key
593 is found that matches the type and description criteria. Each keyring is
594 checked for keys before recursion into its children occurs.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700595
596 The process must have search permission on the top level keyring, or else
597 error EACCES will result. Only keyrings that the process has search
598 permission on will be recursed into, and only keys and keyrings for which
599 a process has search permission can be matched. If the specified keyring
600 is not a keyring, ENOTDIR will result.
601
602 If the search succeeds, the function will attempt to link the found key
603 into the destination keyring if one is supplied (non-zero ID). All the
604 constraints applicable to KEYCTL_LINK apply in this case too.
605
606 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search
607 fails. On success, the resulting key ID will be returned.
608
609
610 (*) Read the payload data from a key:
611
David Howellsf1a9bad2005-10-07 15:04:52 +0100612 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
613 size_t buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700614
615 This function attempts to read the payload data from the specified key
616 into the buffer. The process must have read permission on the key to
617 succeed.
618
619 The returned data will be processed for presentation by the key type. For
620 instance, a keyring will return an array of key_serial_t entries
621 representing the IDs of all the keys to which it is subscribed. The user
622 defined key type will return its data as is. If a key type does not
623 implement this function, error EOPNOTSUPP will result.
624
625 As much of the data as can be fitted into the buffer will be copied to
626 userspace if the buffer pointer is not NULL.
627
David Howells76d8aea2005-06-23 22:00:49 -0700628 On a successful return, the function will always return the amount of data
629 available rather than the amount copied.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700630
631
632 (*) Instantiate a partially constructed key.
633
David Howellsf1a9bad2005-10-07 15:04:52 +0100634 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
635 const void *payload, size_t plen,
636 key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700637
638 If the kernel calls back to userspace to complete the instantiation of a
639 key, userspace should use this call to supply data for the key before the
640 invoked process returns, or else the key will be marked negative
641 automatically.
642
643 The process must have write access on the key to be able to instantiate
644 it, and the key must be uninstantiated.
645
646 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700647 that keyring, however all the constraints applying in KEYCTL_LINK apply in
648 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700649
650 The payload and plen arguments describe the payload data as for add_key().
651
652
653 (*) Negatively instantiate a partially constructed key.
654
David Howellsf1a9bad2005-10-07 15:04:52 +0100655 long keyctl(KEYCTL_NEGATE, key_serial_t key,
656 unsigned timeout, key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700657
658 If the kernel calls back to userspace to complete the instantiation of a
659 key, userspace should use this call mark the key as negative before the
660 invoked process returns if it is unable to fulfil the request.
661
662 The process must have write access on the key to be able to instantiate
663 it, and the key must be uninstantiated.
664
665 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700666 that keyring, however all the constraints applying in KEYCTL_LINK apply in
667 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700668
669
David Howells3e301482005-06-23 22:00:56 -0700670 (*) Set the default request-key destination keyring.
671
672 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl);
673
674 This sets the default keyring to which implicitly requested keys will be
675 attached for this thread. reqkey_defl should be one of these constants:
676
677 CONSTANT VALUE NEW DEFAULT KEYRING
678 ====================================== ====== =======================
679 KEY_REQKEY_DEFL_NO_CHANGE -1 No change
680 KEY_REQKEY_DEFL_DEFAULT 0 Default[1]
681 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring
682 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring
683 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring
684 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring
685 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring
686 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring
687
688 The old default will be returned if successful and error EINVAL will be
689 returned if reqkey_defl is not one of the above values.
690
691 The default keyring can be overridden by the keyring indicated to the
692 request_key() system call.
693
694 Note that this setting is inherited across fork/exec.
695
Paolo Ornati670e9f32006-10-03 22:57:56 +0200696 [1] The default is: the thread keyring if there is one, otherwise
David Howells3e301482005-06-23 22:00:56 -0700697 the process keyring if there is one, otherwise the session keyring if
698 there is one, otherwise the user default session keyring.
699
700
David Howells017679c2006-01-08 01:02:43 -0800701 (*) Set the timeout on a key.
702
703 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
704
705 This sets or clears the timeout on a key. The timeout can be 0 to clear
706 the timeout or a number of seconds to set the expiry time that far into
707 the future.
708
709 The process must have attribute modification access on a key to set its
710 timeout. Timeouts may not be set with this function on negative, revoked
711 or expired keys.
712
713
David Howellsb5f545c2006-01-08 01:02:47 -0800714 (*) Assume the authority granted to instantiate a key
715
716 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
717
718 This assumes or divests the authority required to instantiate the
719 specified key. Authority can only be assumed if the thread has the
720 authorisation key associated with the specified key in its keyrings
721 somewhere.
722
723 Once authority is assumed, searches for keys will also search the
724 requester's keyrings using the requester's security label, UID, GID and
725 groups.
726
727 If the requested authority is unavailable, error EPERM will be returned,
728 likewise if the authority has been revoked because the target key is
729 already instantiated.
730
731 If the specified key is 0, then any assumed authority will be divested.
732
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200733 The assumed authoritative key is inherited across fork and exec.
David Howellsb5f545c2006-01-08 01:02:47 -0800734
735
David Howells70a5bb72008-04-29 01:01:26 -0700736 (*) Get the LSM security context attached to a key.
737
738 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
739 size_t buflen)
740
741 This function returns a string that represents the LSM security context
742 attached to a key in the buffer provided.
743
744 Unless there's an error, it always returns the amount of data it could
745 produce, even if that's too big for the buffer, but it won't copy more
746 than requested to userspace. If the buffer pointer is NULL then no copy
747 will take place.
748
749 A NUL character is included at the end of the string if the buffer is
750 sufficiently big. This is included in the returned count. If no LSM is
751 in force then an empty string will be returned.
752
753 A process must have view permission on the key for this function to be
754 successful.
755
756
Linus Torvalds1da177e2005-04-16 15:20:36 -0700757===============
758KERNEL SERVICES
759===============
760
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200761The kernel services for key management are fairly simple to deal with. They can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700762be broken down into two areas: keys and key types.
763
764Dealing with keys is fairly straightforward. Firstly, the kernel service
765registers its type, then it searches for a key of that type. It should retain
766the key as long as it has need of it, and then it should release it. For a
David Howells76d8aea2005-06-23 22:00:49 -0700767filesystem or device file, a search would probably be performed during the open
768call, and the key released upon close. How to deal with conflicting keys due to
769two different users opening the same file is left to the filesystem author to
770solve.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700771
David Howells76181c12007-10-16 23:29:46 -0700772To access the key manager, the following header must be #included:
773
774 <linux/key.h>
775
776Specific key types should have a header file under include/keys/ that should be
777used to access that type. For keys of type "user", for example, that would be:
778
779 <keys/user-type.h>
780
David Howells664cceb2005-09-28 17:03:15 +0100781Note that there are two different types of pointers to keys that may be
782encountered:
783
784 (*) struct key *
785
786 This simply points to the key structure itself. Key structures will be at
787 least four-byte aligned.
788
789 (*) key_ref_t
790
791 This is equivalent to a struct key *, but the least significant bit is set
792 if the caller "possesses" the key. By "possession" it is meant that the
793 calling processes has a searchable link to the key from one of its
794 keyrings. There are three functions for dealing with these:
795
796 key_ref_t make_key_ref(const struct key *key,
797 unsigned long possession);
798
799 struct key *key_ref_to_ptr(const key_ref_t key_ref);
800
801 unsigned long is_key_possessed(const key_ref_t key_ref);
802
803 The first function constructs a key reference from a key pointer and
804 possession information (which must be 0 or 1 and not any other value).
805
806 The second function retrieves the key pointer from a reference and the
807 third retrieves the possession flag.
808
David Howells76d8aea2005-06-23 22:00:49 -0700809When accessing a key's payload contents, certain precautions must be taken to
810prevent access vs modification races. See the section "Notes on accessing
811payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700812
813(*) To search for a key, call:
814
815 struct key *request_key(const struct key_type *type,
816 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700817 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700818
819 This is used to request a key or keyring with a description that matches
820 the description specified according to the key type's match function. This
821 permits approximate matching to occur. If callout_string is not NULL, then
822 /sbin/request-key will be invoked in an attempt to obtain the key from
823 userspace. In that case, callout_string will be passed as an argument to
824 the program.
825
826 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
827 returned.
828
David Howells3e301482005-06-23 22:00:56 -0700829 If successful, the key will have been attached to the default keyring for
830 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
831
David Howellsf1a9bad2005-10-07 15:04:52 +0100832 See also Documentation/keys-request-key.txt.
833
Linus Torvalds1da177e2005-04-16 15:20:36 -0700834
David Howells4e54f082006-06-29 02:24:28 -0700835(*) To search for a key, passing auxiliary data to the upcaller, call:
836
837 struct key *request_key_with_auxdata(const struct key_type *type,
838 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700839 const void *callout_info,
840 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700841 void *aux);
842
843 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700844 passed to the key_type->request_key() op if it exists, and the callout_info
845 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700846
847
David Howells76181c12007-10-16 23:29:46 -0700848(*) A key can be requested asynchronously by calling one of:
849
850 struct key *request_key_async(const struct key_type *type,
851 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700852 const void *callout_info,
853 size_t callout_len);
David Howells76181c12007-10-16 23:29:46 -0700854
855 or:
856
857 struct key *request_key_async_with_auxdata(const struct key_type *type,
858 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700859 const char *callout_info,
860 size_t callout_len,
David Howells76181c12007-10-16 23:29:46 -0700861 void *aux);
862
863 which are asynchronous equivalents of request_key() and
864 request_key_with_auxdata() respectively.
865
866 These two functions return with the key potentially still under
867 construction. To wait for contruction completion, the following should be
868 called:
869
870 int wait_for_key_construction(struct key *key, bool intr);
871
872 The function will wait for the key to finish being constructed and then
873 invokes key_validate() to return an appropriate value to indicate the state
874 of the key (0 indicates the key is usable).
875
876 If intr is true, then the wait can be interrupted by a signal, in which
877 case error ERESTARTSYS will be returned.
878
879
Linus Torvalds1da177e2005-04-16 15:20:36 -0700880(*) When it is no longer required, the key should be released using:
881
882 void key_put(struct key *key);
883
David Howells664cceb2005-09-28 17:03:15 +0100884 Or:
885
886 void key_ref_put(key_ref_t key_ref);
887
888 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700889 the argument will not be parsed.
890
891
892(*) Extra references can be made to a key by calling the following function:
893
894 struct key *key_get(struct key *key);
895
896 These need to be disposed of by calling key_put() when they've been
897 finished with. The key pointer passed in will be returned. If the pointer
898 is NULL or CONFIG_KEYS is not set then the key will not be dereferenced and
899 no increment will take place.
900
901
902(*) A key's serial number can be obtained by calling:
903
904 key_serial_t key_serial(struct key *key);
905
906 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
907 latter case without parsing the argument).
908
909
910(*) If a keyring was found in the search, this can be further searched by:
911
David Howells664cceb2005-09-28 17:03:15 +0100912 key_ref_t keyring_search(key_ref_t keyring_ref,
913 const struct key_type *type,
914 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700915
916 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +0100917 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
918 the returned key will need to be released.
919
920 The possession attribute from the keyring reference is used to control
921 access through the permissions mask and is propagated to the returned key
922 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700923
924
925(*) To check the validity of a key, this function can be called:
926
927 int validate_key(struct key *key);
928
929 This checks that the key in question hasn't expired or and hasn't been
930 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
931 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
932 returned (in the latter case without parsing the argument).
933
934
935(*) To register a key type, the following function should be called:
936
937 int register_key_type(struct key_type *type);
938
939 This will return error EEXIST if a type of the same name is already
940 present.
941
942
943(*) To unregister a key type, call:
944
945 void unregister_key_type(struct key_type *type);
946
947
Satyam Sharma7eacbbd2007-07-31 00:38:17 -0700948Under some circumstances, it may be desirable to deal with a bundle of keys.
949The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -0700950
951 struct key_type key_type_keyring;
952
953This can be used with a function such as request_key() to find a specific
954keyring in a process's keyrings. A keyring thus found can then be searched
955with keyring_search(). Note that it is not possible to use request_key() to
956search a specific keyring, so using keyrings in this way is of limited utility.
957
958
David Howells76d8aea2005-06-23 22:00:49 -0700959===================================
960NOTES ON ACCESSING PAYLOAD CONTENTS
961===================================
962
963The simplest payload is just a number in key->payload.value. In this case,
964there's no need to indulge in RCU or locking when accessing the payload.
965
966More complex payload contents must be allocated and a pointer to them set in
967key->payload.data. One of the following ways must be selected to access the
968data:
969
David Howells664cceb2005-09-28 17:03:15 +0100970 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -0700971
972 If the key type does not have a modify method, then the key's payload can
973 be accessed without any form of locking, provided that it's known to be
974 instantiated (uninstantiated keys cannot be "found").
975
976 (2) The key's semaphore.
977
978 The semaphore could be used to govern access to the payload and to control
979 the payload pointer. It must be write-locked for modifications and would
980 have to be read-locked for general access. The disadvantage of doing this
981 is that the accessor may be required to sleep.
982
983 (3) RCU.
984
985 RCU must be used when the semaphore isn't already held; if the semaphore
986 is held then the contents can't change under you unexpectedly as the
987 semaphore must still be used to serialise modifications to the key. The
988 key management code takes care of this for the key type.
989
990 However, this means using:
991
992 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
993
994 to read the pointer, and:
995
996 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
997
998 to set the pointer and dispose of the old contents after a grace period.
999 Note that only the key type should ever modify a key's payload.
1000
1001 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1002 use of call_rcu() and, if the payload is of variable size, the length of
1003 the payload. key->datalen cannot be relied upon to be consistent with the
1004 payload just dereferenced if the key's semaphore is not held.
1005
1006
Linus Torvalds1da177e2005-04-16 15:20:36 -07001007===================
1008DEFINING A KEY TYPE
1009===================
1010
1011A kernel service may want to define its own key type. For instance, an AFS
1012filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c12007-10-16 23:29:46 -07001013author fills in a key_type struct and registers it with the system.
1014
1015Source files that implement key types should include the following header file:
1016
1017 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001018
1019The structure has a number of fields, some of which are mandatory:
1020
1021 (*) const char *name
1022
1023 The name of the key type. This is used to translate a key type name
1024 supplied by userspace into a pointer to the structure.
1025
1026
1027 (*) size_t def_datalen
1028
1029 This is optional - it supplies the default payload data length as
1030 contributed to the quota. If the key type's payload is always or almost
1031 always the same size, then this is a more efficient way to do things.
1032
1033 The data length (and quota) on a particular key can always be changed
1034 during instantiation or update by calling:
1035
1036 int key_payload_reserve(struct key *key, size_t datalen);
1037
David Howells76d8aea2005-06-23 22:00:49 -07001038 With the revised data length. Error EDQUOT will be returned if this is not
1039 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001040
1041
1042 (*) int (*instantiate)(struct key *key, const void *data, size_t datalen);
1043
1044 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001045 The payload attached need not bear any relation to the data passed to this
1046 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001047
1048 If the amount of data attached to the key differs from the size in
1049 keytype->def_datalen, then key_payload_reserve() should be called.
1050
1051 This method does not have to lock the key in order to attach a payload.
1052 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1053 anything else from gaining access to the key.
1054
David Howells76d8aea2005-06-23 22:00:49 -07001055 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001056
1057
Linus Torvalds1da177e2005-04-16 15:20:36 -07001058 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1059
David Howells76d8aea2005-06-23 22:00:49 -07001060 If this type of key can be updated, then this method should be provided.
1061 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001062
1063 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001064 before any changes are actually made. Note that if this succeeds, the type
1065 is committed to changing the key because it's already been altered, so all
1066 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001067
David Howells76d8aea2005-06-23 22:00:49 -07001068 The key will have its semaphore write-locked before this method is called,
1069 but this only deters other writers; any changes to the key's payload must
1070 be made under RCU conditions, and call_rcu() must be used to dispose of
1071 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001072
David Howells76d8aea2005-06-23 22:00:49 -07001073 key_payload_reserve() should be called before the changes are made, but
1074 after all allocations and other potentially failing function calls are
1075 made.
1076
1077 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001078
1079
1080 (*) int (*match)(const struct key *key, const void *desc);
1081
1082 This method is called to match a key against a description. It should
1083 return non-zero if the two match, zero if they don't.
1084
1085 This method should not need to lock the key in any way. The type and
1086 description can be considered invariant, and the payload should not be
1087 accessed (the key may not yet be instantiated).
1088
1089 It is not safe to sleep in this method; the caller may hold spinlocks.
1090
1091
David Howells04c567d2006-06-22 14:47:18 -07001092 (*) void (*revoke)(struct key *key);
1093
1094 This method is optional. It is called to discard part of the payload
1095 data upon a key being revoked. The caller will have the key semaphore
1096 write-locked.
1097
1098 It is safe to sleep in this method, though care should be taken to avoid
1099 a deadlock against the key semaphore.
1100
1101
Linus Torvalds1da177e2005-04-16 15:20:36 -07001102 (*) void (*destroy)(struct key *key);
1103
David Howells76d8aea2005-06-23 22:00:49 -07001104 This method is optional. It is called to discard the payload data on a key
1105 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001106
David Howells76d8aea2005-06-23 22:00:49 -07001107 This method does not need to lock the key to access the payload; it can
1108 consider the key as being inaccessible at this time. Note that the key's
1109 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001110
1111 It is not safe to sleep in this method; the caller may hold spinlocks.
1112
1113
1114 (*) void (*describe)(const struct key *key, struct seq_file *p);
1115
1116 This method is optional. It is called during /proc/keys reading to
1117 summarise a key's description and payload in text form.
1118
David Howells76d8aea2005-06-23 22:00:49 -07001119 This method will be called with the RCU read lock held. rcu_dereference()
1120 should be used to read the payload pointer if the payload is to be
1121 accessed. key->datalen cannot be trusted to stay consistent with the
1122 contents of the payload.
1123
1124 The description will not change, though the key's state may.
1125
1126 It is not safe to sleep in this method; the RCU read lock is held by the
1127 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001128
1129
1130 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1131
1132 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001133 key's payload into something a blob of data for userspace to deal with.
1134 Ideally, the blob should be in the same format as that passed in to the
1135 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001136
1137 If successful, the blob size that could be produced should be returned
1138 rather than the size copied.
1139
David Howells76d8aea2005-06-23 22:00:49 -07001140 This method will be called with the key's semaphore read-locked. This will
1141 prevent the key's payload changing. It is not necessary to use RCU locking
1142 when accessing the key's payload. It is safe to sleep in this method, such
1143 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001144
1145
David Howells76181c12007-10-16 23:29:46 -07001146 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001147 void *aux);
1148
David Howells76181c12007-10-16 23:29:46 -07001149 This method is optional. If provided, request_key() and friends will
1150 invoke this function rather than upcalling to /sbin/request-key to operate
1151 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001152
David Howells76181c12007-10-16 23:29:46 -07001153 The aux parameter is as passed to request_key_async_with_auxdata() and
1154 similar or is NULL otherwise. Also passed are the construction record for
1155 the key to be operated upon and the operation type (currently only
1156 "create").
David Howells4e54f082006-06-29 02:24:28 -07001157
David Howells76181c12007-10-16 23:29:46 -07001158 This method is permitted to return before the upcall is complete, but the
1159 following function must be called under all circumstances to complete the
1160 instantiation process, whether or not it succeeds, whether or not there's
1161 an error:
1162
1163 void complete_request_key(struct key_construction *cons, int error);
1164
1165 The error parameter should be 0 on success, -ve on error. The
1166 construction record is destroyed by this action and the authorisation key
1167 will be revoked. If an error is indicated, the key under construction
1168 will be negatively instantiated if it wasn't already instantiated.
1169
1170 If this method returns an error, that error will be returned to the
1171 caller of request_key*(). complete_request_key() must be called prior to
1172 returning.
1173
1174 The key under construction and the authorisation key can be found in the
1175 key_construction struct pointed to by cons:
1176
1177 (*) struct key *key;
1178
1179 The key under construction.
1180
1181 (*) struct key *authkey;
1182
1183 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001184
1185
Linus Torvalds1da177e2005-04-16 15:20:36 -07001186============================
1187REQUEST-KEY CALLBACK SERVICE
1188============================
1189
1190To create a new key, the kernel will attempt to execute the following command
1191line:
1192
1193 /sbin/request-key create <key> <uid> <gid> \
1194 <threadring> <processring> <sessionring> <callout_info>
1195
1196<key> is the key being constructed, and the three keyrings are the process
1197keyrings from the process that caused the search to be issued. These are
1198included for two reasons:
1199
1200 (1) There may be an authentication token in one of the keyrings that is
1201 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1202
1203 (2) The new key should probably be cached in one of these rings.
1204
1205This program should set it UID and GID to those specified before attempting to
1206access any more keys. It may then look around for a user specific process to
1207hand the request off to (perhaps a path held in placed in another key by, for
1208example, the KDE desktop manager).
1209
1210The program (or whatever it calls) should finish construction of the key by
1211calling KEYCTL_INSTANTIATE, which also permits it to cache the key in one of
1212the keyrings (probably the session ring) before returning. Alternatively, the
1213key can be marked as negative with KEYCTL_NEGATE; this also permits the key to
1214be cached in one of the keyrings.
1215
1216If it returns with the key remaining in the unconstructed state, the key will
1217be marked as being negative, it will be added to the session keyring, and an
1218error will be returned to the key requestor.
1219
David Howells76d8aea2005-06-23 22:00:49 -07001220Supplementary information may be provided from whoever or whatever invoked this
1221service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001222information was made available, then "-" will be passed as this parameter
1223instead.
1224
1225
1226Similarly, the kernel may attempt to update an expired or a soon to expire key
1227by executing:
1228
1229 /sbin/request-key update <key> <uid> <gid> \
1230 <threadring> <processring> <sessionring>
1231
1232In this case, the program isn't required to actually attach the key to a ring;
1233the rings are provided for reference.