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Linus Torvalds1da177e2005-04-16 15:20:36 -07001 ============================
2 KERNEL KEY RETENTION SERVICE
3 ============================
4
5This service allows cryptographic keys, authentication tokens, cross-domain
6user mappings, and similar to be cached in the kernel for the use of
David Howells76181c12007-10-16 23:29:46 -07007filesystems and other kernel services.
Linus Torvalds1da177e2005-04-16 15:20:36 -07008
9Keyrings are permitted; these are a special type of key that can hold links to
10other keys. Processes each have three standard keyring subscriptions that a
11kernel service can search for relevant keys.
12
13The key service can be configured on by enabling:
14
15 "Security options"/"Enable access key retention support" (CONFIG_KEYS)
16
17This document has the following sections:
18
19 - Key overview
20 - Key service overview
21 - Key access permissions
Michael LeMayd7200242006-06-22 14:47:17 -070022 - SELinux support
Linus Torvalds1da177e2005-04-16 15:20:36 -070023 - New procfs files
24 - Userspace system call interface
25 - Kernel services
David Howells76d8aea2005-06-23 22:00:49 -070026 - Notes on accessing payload contents
Linus Torvalds1da177e2005-04-16 15:20:36 -070027 - Defining a key type
28 - Request-key callback service
David Howells5d135442009-09-02 09:14:00 +010029 - Garbage collection
Linus Torvalds1da177e2005-04-16 15:20:36 -070030
31
32============
33KEY OVERVIEW
34============
35
36In this context, keys represent units of cryptographic data, authentication
37tokens, keyrings, etc.. These are represented in the kernel by struct key.
38
39Each key has a number of attributes:
40
41 - A serial number.
42 - A type.
43 - A description (for matching a key in a search).
44 - Access control information.
45 - An expiry time.
46 - A payload.
47 - State.
48
49
David Howells76d8aea2005-06-23 22:00:49 -070050 (*) Each key is issued a serial number of type key_serial_t that is unique for
51 the lifetime of that key. All serial numbers are positive non-zero 32-bit
52 integers.
Linus Torvalds1da177e2005-04-16 15:20:36 -070053
54 Userspace programs can use a key's serial numbers as a way to gain access
55 to it, subject to permission checking.
56
57 (*) Each key is of a defined "type". Types must be registered inside the
David Howells76d8aea2005-06-23 22:00:49 -070058 kernel by a kernel service (such as a filesystem) before keys of that type
59 can be added or used. Userspace programs cannot define new types directly.
Linus Torvalds1da177e2005-04-16 15:20:36 -070060
David Howells76d8aea2005-06-23 22:00:49 -070061 Key types are represented in the kernel by struct key_type. This defines a
62 number of operations that can be performed on a key of that type.
Linus Torvalds1da177e2005-04-16 15:20:36 -070063
64 Should a type be removed from the system, all the keys of that type will
65 be invalidated.
66
67 (*) Each key has a description. This should be a printable string. The key
David Howells76d8aea2005-06-23 22:00:49 -070068 type provides an operation to perform a match between the description on a
69 key and a criterion string.
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
71 (*) Each key has an owner user ID, a group ID and a permissions mask. These
72 are used to control what a process may do to a key from userspace, and
73 whether a kernel service will be able to find the key.
74
75 (*) Each key can be set to expire at a specific time by the key type's
76 instantiation function. Keys can also be immortal.
77
David Howells76d8aea2005-06-23 22:00:49 -070078 (*) Each key can have a payload. This is a quantity of data that represent the
79 actual "key". In the case of a keyring, this is a list of keys to which
80 the keyring links; in the case of a user-defined key, it's an arbitrary
81 blob of data.
Linus Torvalds1da177e2005-04-16 15:20:36 -070082
83 Having a payload is not required; and the payload can, in fact, just be a
84 value stored in the struct key itself.
85
86 When a key is instantiated, the key type's instantiation function is
87 called with a blob of data, and that then creates the key's payload in
88 some way.
89
90 Similarly, when userspace wants to read back the contents of the key, if
91 permitted, another key type operation will be called to convert the key's
92 attached payload back into a blob of data.
93
94 (*) Each key can be in one of a number of basic states:
95
David Howells76d8aea2005-06-23 22:00:49 -070096 (*) Uninstantiated. The key exists, but does not have any data attached.
97 Keys being requested from userspace will be in this state.
Linus Torvalds1da177e2005-04-16 15:20:36 -070098
99 (*) Instantiated. This is the normal state. The key is fully formed, and
100 has data attached.
101
102 (*) Negative. This is a relatively short-lived state. The key acts as a
103 note saying that a previous call out to userspace failed, and acts as
104 a throttle on key lookups. A negative key can be updated to a normal
105 state.
106
107 (*) Expired. Keys can have lifetimes set. If their lifetime is exceeded,
108 they traverse to this state. An expired key can be updated back to a
109 normal state.
110
111 (*) Revoked. A key is put in this state by userspace action. It can't be
112 found or operated upon (apart from by unlinking it).
113
114 (*) Dead. The key's type was unregistered, and so the key is now useless.
115
David Howells5d135442009-09-02 09:14:00 +0100116Keys in the last three states are subject to garbage collection. See the
117section on "Garbage collection".
118
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
120====================
121KEY SERVICE OVERVIEW
122====================
123
124The key service provides a number of features besides keys:
125
126 (*) The key service defines two special key types:
127
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
140 (*) Each process subscribes to three keyrings: a thread-specific keyring, a
141 process-specific keyring, and a session-specific keyring.
142
143 The thread-specific keyring is discarded from the child when any sort of
144 clone, fork, vfork or execve occurs. A new keyring is created only when
145 required.
146
David Howells76d8aea2005-06-23 22:00:49 -0700147 The process-specific keyring is replaced with an empty one in the child on
148 clone, fork, vfork unless CLONE_THREAD is supplied, in which case it is
149 shared. execve also discards the process's process keyring and creates a
150 new one.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151
152 The session-specific keyring is persistent across clone, fork, vfork and
153 execve, even when the latter executes a set-UID or set-GID binary. A
154 process can, however, replace its current session keyring with a new one
155 by using PR_JOIN_SESSION_KEYRING. It is permitted to request an anonymous
156 new one, or to attempt to create or join one of a specific name.
157
158 The ownership of the thread keyring changes when the real UID and GID of
159 the thread changes.
160
161 (*) Each user ID resident in the system holds two special keyrings: a user
162 specific keyring and a default user session keyring. The default session
163 keyring is initialised with a link to the user-specific keyring.
164
165 When a process changes its real UID, if it used to have no session key, it
166 will be subscribed to the default session key for the new UID.
167
168 If a process attempts to access its session key when it doesn't have one,
169 it will be subscribed to the default for its current UID.
170
171 (*) Each user has two quotas against which the keys they own are tracked. One
172 limits the total number of keys and keyrings, the other limits the total
173 amount of description and payload space that can be consumed.
174
175 The user can view information on this and other statistics through procfs
David Howells0b77f5b2008-04-29 01:01:32 -0700176 files. The root user may also alter the quota limits through sysctl files
177 (see the section "New procfs files").
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178
179 Process-specific and thread-specific keyrings are not counted towards a
180 user's quota.
181
182 If a system call that modifies a key or keyring in some way would put the
183 user over quota, the operation is refused and error EDQUOT is returned.
184
David Howells76d8aea2005-06-23 22:00:49 -0700185 (*) There's a system call interface by which userspace programs can create and
186 manipulate keys and keyrings.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187
David Howells76d8aea2005-06-23 22:00:49 -0700188 (*) There's a kernel interface by which services can register types and search
189 for keys.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190
191 (*) There's a way for the a search done from the kernel to call back to
192 userspace to request a key that can't be found in a process's keyrings.
193
194 (*) An optional filesystem is available through which the key database can be
195 viewed and manipulated.
196
197
198======================
199KEY ACCESS PERMISSIONS
200======================
201
David Howells76d8aea2005-06-23 22:00:49 -0700202Keys have an owner user ID, a group access ID, and a permissions mask. The mask
David Howells664cceb2005-09-28 17:03:15 +0100203has up to eight bits each for possessor, user, group and other access. Only
David Howells29db9192005-10-30 15:02:44 -0800204six of each set of eight bits are defined. These permissions granted are:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205
206 (*) View
207
208 This permits a key or keyring's attributes to be viewed - including key
209 type and description.
210
211 (*) Read
212
213 This permits a key's payload to be viewed or a keyring's list of linked
214 keys.
215
216 (*) Write
217
David Howells76d8aea2005-06-23 22:00:49 -0700218 This permits a key's payload to be instantiated or updated, or it allows a
219 link to be added to or removed from a keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700220
221 (*) Search
222
223 This permits keyrings to be searched and keys to be found. Searches can
224 only recurse into nested keyrings that have search permission set.
225
226 (*) Link
227
228 This permits a key or keyring to be linked to. To create a link from a
229 keyring to a key, a process must have Write permission on the keyring and
230 Link permission on the key.
231
David Howells29db9192005-10-30 15:02:44 -0800232 (*) Set Attribute
233
234 This permits a key's UID, GID and permissions mask to be changed.
235
Linus Torvalds1da177e2005-04-16 15:20:36 -0700236For changing the ownership, group ID or permissions mask, being the owner of
237the key or having the sysadmin capability is sufficient.
238
239
Michael LeMayd7200242006-06-22 14:47:17 -0700240===============
241SELINUX SUPPORT
242===============
243
244The security class "key" has been added to SELinux so that mandatory access
245controls can be applied to keys created within various contexts. This support
246is preliminary, and is likely to change quite significantly in the near future.
247Currently, all of the basic permissions explained above are provided in SELinux
Michael LeMay4eb582c2006-06-26 00:24:57 -0700248as well; SELinux is simply invoked after all basic permission checks have been
Michael LeMayd7200242006-06-22 14:47:17 -0700249performed.
250
Michael LeMay4eb582c2006-06-26 00:24:57 -0700251The value of the file /proc/self/attr/keycreate influences the labeling of
252newly-created keys. If the contents of that file correspond to an SELinux
253security context, then the key will be assigned that context. Otherwise, the
254key will be assigned the current context of the task that invoked the key
255creation request. Tasks must be granted explicit permission to assign a
256particular context to newly-created keys, using the "create" permission in the
257key security class.
Michael LeMayd7200242006-06-22 14:47:17 -0700258
Michael LeMay4eb582c2006-06-26 00:24:57 -0700259The default keyrings associated with users will be labeled with the default
260context of the user if and only if the login programs have been instrumented to
261properly initialize keycreate during the login process. Otherwise, they will
262be labeled with the context of the login program itself.
Michael LeMayd7200242006-06-22 14:47:17 -0700263
264Note, however, that the default keyrings associated with the root user are
265labeled with the default kernel context, since they are created early in the
266boot process, before root has a chance to log in.
267
Michael LeMay4eb582c2006-06-26 00:24:57 -0700268The keyrings associated with new threads are each labeled with the context of
269their associated thread, and both session and process keyrings are handled
270similarly.
271
Michael LeMayd7200242006-06-22 14:47:17 -0700272
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273================
274NEW PROCFS FILES
275================
276
277Two files have been added to procfs by which an administrator can find out
278about the status of the key service:
279
280 (*) /proc/keys
281
Michael LeMay06ec7be2006-06-26 00:24:56 -0700282 This lists the keys that are currently viewable by the task reading the
283 file, giving information about their type, description and permissions.
284 It is not possible to view the payload of the key this way, though some
285 information about it may be given.
286
287 The only keys included in the list are those that grant View permission to
288 the reading process whether or not it possesses them. Note that LSM
289 security checks are still performed, and may further filter out keys that
290 the current process is not authorised to view.
291
292 The contents of the file look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700293
David Howells664cceb2005-09-28 17:03:15 +0100294 SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
David Howells29db9192005-10-30 15:02:44 -0800295 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4
296 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty
297 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty
298 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty
299 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4
300 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty
David Howells664cceb2005-09-28 17:03:15 +0100301 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0
David Howells29db9192005-10-30 15:02:44 -0800302 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0
303 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -0700304
305 The flags are:
306
307 I Instantiated
308 R Revoked
309 D Dead
310 Q Contributes to user's quota
Matt LaPlante5d3f0832006-11-30 05:21:10 +0100311 U Under construction by callback to userspace
Linus Torvalds1da177e2005-04-16 15:20:36 -0700312 N Negative key
313
314 This file must be enabled at kernel configuration time as it allows anyone
315 to list the keys database.
316
317 (*) /proc/key-users
318
319 This file lists the tracking data for each user that has at least one key
Michael LeMay06ec7be2006-06-26 00:24:56 -0700320 on the system. Such data includes quota information and statistics:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321
322 [root@andromeda root]# cat /proc/key-users
323 0: 46 45/45 1/100 13/10000
324 29: 2 2/2 2/100 40/10000
325 32: 2 2/2 2/100 40/10000
326 38: 2 2/2 2/100 40/10000
327
328 The format of each line is
329 <UID>: User ID to which this applies
330 <usage> Structure refcount
331 <inst>/<keys> Total number of keys and number instantiated
332 <keys>/<max> Key count quota
333 <bytes>/<max> Key size quota
334
335
David Howells0b77f5b2008-04-29 01:01:32 -0700336Four new sysctl files have been added also for the purpose of controlling the
337quota limits on keys:
338
339 (*) /proc/sys/kernel/keys/root_maxkeys
340 /proc/sys/kernel/keys/root_maxbytes
341
342 These files hold the maximum number of keys that root may have and the
343 maximum total number of bytes of data that root may have stored in those
344 keys.
345
346 (*) /proc/sys/kernel/keys/maxkeys
347 /proc/sys/kernel/keys/maxbytes
348
349 These files hold the maximum number of keys that each non-root user may
350 have and the maximum total number of bytes of data that each of those
351 users may have stored in their keys.
352
353Root may alter these by writing each new limit as a decimal number string to
354the appropriate file.
355
356
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357===============================
358USERSPACE SYSTEM CALL INTERFACE
359===============================
360
361Userspace can manipulate keys directly through three new syscalls: add_key,
362request_key and keyctl. The latter provides a number of functions for
363manipulating keys.
364
365When referring to a key directly, userspace programs should use the key's
366serial number (a positive 32-bit integer). However, there are some special
367values available for referring to special keys and keyrings that relate to the
368process making the call:
369
370 CONSTANT VALUE KEY REFERENCED
371 ============================== ====== ===========================
372 KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring
373 KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring
374 KEY_SPEC_SESSION_KEYRING -3 session-specific keyring
375 KEY_SPEC_USER_KEYRING -4 UID-specific keyring
376 KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring
377 KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring
David Howellsb5f545c2006-01-08 01:02:47 -0800378 KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key()
379 authorisation key
Linus Torvalds1da177e2005-04-16 15:20:36 -0700380
381
382The main syscalls are:
383
384 (*) Create a new key of given type, description and payload and add it to the
385 nominated keyring:
386
387 key_serial_t add_key(const char *type, const char *desc,
388 const void *payload, size_t plen,
389 key_serial_t keyring);
390
391 If a key of the same type and description as that proposed already exists
392 in the keyring, this will try to update it with the given payload, or it
393 will return error EEXIST if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700394 type. The process must also have permission to write to the key to be able
395 to update it. The new key will have all user permissions granted and no
396 group or third party permissions.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700397
David Howells76d8aea2005-06-23 22:00:49 -0700398 Otherwise, this will attempt to create a new key of the specified type and
399 description, and to instantiate it with the supplied payload and attach it
400 to the keyring. In this case, an error will be generated if the process
401 does not have permission to write to the keyring.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700402
403 The payload is optional, and the pointer can be NULL if not required by
404 the type. The payload is plen in size, and plen can be zero for an empty
405 payload.
406
David Howells76d8aea2005-06-23 22:00:49 -0700407 A new keyring can be generated by setting type "keyring", the keyring name
408 as the description (or NULL) and setting the payload to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700409
410 User defined keys can be created by specifying type "user". It is
411 recommended that a user defined key's description by prefixed with a type
412 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting
413 ticket.
414
415 Any other type must have been registered with the kernel in advance by a
416 kernel service such as a filesystem.
417
418 The ID of the new or updated key is returned if successful.
419
420
421 (*) Search the process's keyrings for a key, potentially calling out to
422 userspace to create it.
423
424 key_serial_t request_key(const char *type, const char *description,
425 const char *callout_info,
426 key_serial_t dest_keyring);
427
428 This function searches all the process's keyrings in the order thread,
429 process, session for a matching key. This works very much like
430 KEYCTL_SEARCH, including the optional attachment of the discovered key to
431 a keyring.
432
433 If a key cannot be found, and if callout_info is not NULL, then
434 /sbin/request-key will be invoked in an attempt to obtain a key. The
435 callout_info string will be passed as an argument to the program.
436
David Howellsf1a9bad2005-10-07 15:04:52 +0100437 See also Documentation/keys-request-key.txt.
438
Linus Torvalds1da177e2005-04-16 15:20:36 -0700439
440The keyctl syscall functions are:
441
442 (*) Map a special key ID to a real key ID for this process:
443
444 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id,
445 int create);
446
David Howells76d8aea2005-06-23 22:00:49 -0700447 The special key specified by "id" is looked up (with the key being created
448 if necessary) and the ID of the key or keyring thus found is returned if
449 it exists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700450
451 If the key does not yet exist, the key will be created if "create" is
452 non-zero; and the error ENOKEY will be returned if "create" is zero.
453
454
455 (*) Replace the session keyring this process subscribes to with a new one:
456
457 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name);
458
459 If name is NULL, an anonymous keyring is created attached to the process
460 as its session keyring, displacing the old session keyring.
461
462 If name is not NULL, if a keyring of that name exists, the process
463 attempts to attach it as the session keyring, returning an error if that
464 is not permitted; otherwise a new keyring of that name is created and
465 attached as the session keyring.
466
467 To attach to a named keyring, the keyring must have search permission for
468 the process's ownership.
469
470 The ID of the new session keyring is returned if successful.
471
472
473 (*) Update the specified key:
474
475 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload,
476 size_t plen);
477
478 This will try to update the specified key with the given payload, or it
479 will return error EOPNOTSUPP if that function is not supported by the key
David Howells76d8aea2005-06-23 22:00:49 -0700480 type. The process must also have permission to write to the key to be able
481 to update it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700482
483 The payload is of length plen, and may be absent or empty as for
484 add_key().
485
486
487 (*) Revoke a key:
488
489 long keyctl(KEYCTL_REVOKE, key_serial_t key);
490
491 This makes a key unavailable for further operations. Further attempts to
492 use the key will be met with error EKEYREVOKED, and the key will no longer
493 be findable.
494
495
496 (*) Change the ownership of a key:
497
498 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid);
499
David Howells76d8aea2005-06-23 22:00:49 -0700500 This function permits a key's owner and group ID to be changed. Either one
501 of uid or gid can be set to -1 to suppress that change.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700502
503 Only the superuser can change a key's owner to something other than the
504 key's current owner. Similarly, only the superuser can change a key's
505 group ID to something other than the calling process's group ID or one of
506 its group list members.
507
508
509 (*) Change the permissions mask on a key:
510
511 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm);
512
513 This function permits the owner of a key or the superuser to change the
514 permissions mask on a key.
515
516 Only bits the available bits are permitted; if any other bits are set,
517 error EINVAL will be returned.
518
519
520 (*) Describe a key:
521
522 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer,
523 size_t buflen);
524
525 This function returns a summary of the key's attributes (but not its
526 payload data) as a string in the buffer provided.
527
528 Unless there's an error, it always returns the amount of data it could
529 produce, even if that's too big for the buffer, but it won't copy more
530 than requested to userspace. If the buffer pointer is NULL then no copy
531 will take place.
532
533 A process must have view permission on the key for this function to be
534 successful.
535
536 If successful, a string is placed in the buffer in the following format:
537
538 <type>;<uid>;<gid>;<perm>;<description>
539
540 Where type and description are strings, uid and gid are decimal, and perm
541 is hexadecimal. A NUL character is included at the end of the string if
542 the buffer is sufficiently big.
543
544 This can be parsed with
545
546 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc);
547
548
549 (*) Clear out a keyring:
550
551 long keyctl(KEYCTL_CLEAR, key_serial_t keyring);
552
553 This function clears the list of keys attached to a keyring. The calling
554 process must have write permission on the keyring, and it must be a
555 keyring (or else error ENOTDIR will result).
556
557
558 (*) Link a key into a keyring:
559
560 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key);
561
David Howells76d8aea2005-06-23 22:00:49 -0700562 This function creates a link from the keyring to the key. The process must
563 have write permission on the keyring and must have link permission on the
564 key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700565
David Howells76d8aea2005-06-23 22:00:49 -0700566 Should the keyring not be a keyring, error ENOTDIR will result; and if the
567 keyring is full, error ENFILE will result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700568
569 The link procedure checks the nesting of the keyrings, returning ELOOP if
David Howells017679c2006-01-08 01:02:43 -0800570 it appears too deep or EDEADLK if the link would introduce a cycle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700571
David Howellscab8eb52006-01-08 01:02:45 -0800572 Any links within the keyring to keys that match the new key in terms of
573 type and description will be discarded from the keyring as the new one is
574 added.
575
Linus Torvalds1da177e2005-04-16 15:20:36 -0700576
577 (*) Unlink a key or keyring from another keyring:
578
579 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
580
581 This function looks through the keyring for the first link to the
582 specified key, and removes it if found. Subsequent links to that key are
583 ignored. The process must have write permission on the keyring.
584
David Howells76d8aea2005-06-23 22:00:49 -0700585 If the keyring is not a keyring, error ENOTDIR will result; and if the key
586 is not present, error ENOENT will be the result.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700587
588
589 (*) Search a keyring tree for a key:
590
591 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring,
592 const char *type, const char *description,
593 key_serial_t dest_keyring);
594
David Howells76d8aea2005-06-23 22:00:49 -0700595 This searches the keyring tree headed by the specified keyring until a key
596 is found that matches the type and description criteria. Each keyring is
597 checked for keys before recursion into its children occurs.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700598
599 The process must have search permission on the top level keyring, or else
600 error EACCES will result. Only keyrings that the process has search
601 permission on will be recursed into, and only keys and keyrings for which
602 a process has search permission can be matched. If the specified keyring
603 is not a keyring, ENOTDIR will result.
604
605 If the search succeeds, the function will attempt to link the found key
606 into the destination keyring if one is supplied (non-zero ID). All the
607 constraints applicable to KEYCTL_LINK apply in this case too.
608
609 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search
610 fails. On success, the resulting key ID will be returned.
611
612
613 (*) Read the payload data from a key:
614
David Howellsf1a9bad2005-10-07 15:04:52 +0100615 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
616 size_t buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700617
618 This function attempts to read the payload data from the specified key
619 into the buffer. The process must have read permission on the key to
620 succeed.
621
622 The returned data will be processed for presentation by the key type. For
623 instance, a keyring will return an array of key_serial_t entries
624 representing the IDs of all the keys to which it is subscribed. The user
625 defined key type will return its data as is. If a key type does not
626 implement this function, error EOPNOTSUPP will result.
627
628 As much of the data as can be fitted into the buffer will be copied to
629 userspace if the buffer pointer is not NULL.
630
David Howells76d8aea2005-06-23 22:00:49 -0700631 On a successful return, the function will always return the amount of data
632 available rather than the amount copied.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700633
634
635 (*) Instantiate a partially constructed key.
636
David Howellsf1a9bad2005-10-07 15:04:52 +0100637 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
638 const void *payload, size_t plen,
639 key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700640
641 If the kernel calls back to userspace to complete the instantiation of a
642 key, userspace should use this call to supply data for the key before the
643 invoked process returns, or else the key will be marked negative
644 automatically.
645
646 The process must have write access on the key to be able to instantiate
647 it, and the key must be uninstantiated.
648
649 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700650 that keyring, however all the constraints applying in KEYCTL_LINK apply in
651 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700652
653 The payload and plen arguments describe the payload data as for add_key().
654
655
656 (*) Negatively instantiate a partially constructed key.
657
David Howellsf1a9bad2005-10-07 15:04:52 +0100658 long keyctl(KEYCTL_NEGATE, key_serial_t key,
659 unsigned timeout, key_serial_t keyring);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700660
661 If the kernel calls back to userspace to complete the instantiation of a
662 key, userspace should use this call mark the key as negative before the
663 invoked process returns if it is unable to fulfil the request.
664
665 The process must have write access on the key to be able to instantiate
666 it, and the key must be uninstantiated.
667
668 If a keyring is specified (non-zero), the key will also be linked into
David Howells76d8aea2005-06-23 22:00:49 -0700669 that keyring, however all the constraints applying in KEYCTL_LINK apply in
670 this case too.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700671
672
David Howells3e301482005-06-23 22:00:56 -0700673 (*) Set the default request-key destination keyring.
674
675 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl);
676
677 This sets the default keyring to which implicitly requested keys will be
678 attached for this thread. reqkey_defl should be one of these constants:
679
680 CONSTANT VALUE NEW DEFAULT KEYRING
681 ====================================== ====== =======================
682 KEY_REQKEY_DEFL_NO_CHANGE -1 No change
683 KEY_REQKEY_DEFL_DEFAULT 0 Default[1]
684 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring
685 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring
686 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring
687 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring
688 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring
689 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring
690
691 The old default will be returned if successful and error EINVAL will be
692 returned if reqkey_defl is not one of the above values.
693
694 The default keyring can be overridden by the keyring indicated to the
695 request_key() system call.
696
697 Note that this setting is inherited across fork/exec.
698
Paolo Ornati670e9f32006-10-03 22:57:56 +0200699 [1] The default is: the thread keyring if there is one, otherwise
David Howells3e301482005-06-23 22:00:56 -0700700 the process keyring if there is one, otherwise the session keyring if
701 there is one, otherwise the user default session keyring.
702
703
David Howells017679c2006-01-08 01:02:43 -0800704 (*) Set the timeout on a key.
705
706 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
707
708 This sets or clears the timeout on a key. The timeout can be 0 to clear
709 the timeout or a number of seconds to set the expiry time that far into
710 the future.
711
712 The process must have attribute modification access on a key to set its
713 timeout. Timeouts may not be set with this function on negative, revoked
714 or expired keys.
715
716
David Howellsb5f545c2006-01-08 01:02:47 -0800717 (*) Assume the authority granted to instantiate a key
718
719 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
720
721 This assumes or divests the authority required to instantiate the
722 specified key. Authority can only be assumed if the thread has the
723 authorisation key associated with the specified key in its keyrings
724 somewhere.
725
726 Once authority is assumed, searches for keys will also search the
727 requester's keyrings using the requester's security label, UID, GID and
728 groups.
729
730 If the requested authority is unavailable, error EPERM will be returned,
731 likewise if the authority has been revoked because the target key is
732 already instantiated.
733
734 If the specified key is 0, then any assumed authority will be divested.
735
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200736 The assumed authoritative key is inherited across fork and exec.
David Howellsb5f545c2006-01-08 01:02:47 -0800737
738
David Howells70a5bb72008-04-29 01:01:26 -0700739 (*) Get the LSM security context attached to a key.
740
741 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
742 size_t buflen)
743
744 This function returns a string that represents the LSM security context
745 attached to a key in the buffer provided.
746
747 Unless there's an error, it always returns the amount of data it could
748 produce, even if that's too big for the buffer, but it won't copy more
749 than requested to userspace. If the buffer pointer is NULL then no copy
750 will take place.
751
752 A NUL character is included at the end of the string if the buffer is
753 sufficiently big. This is included in the returned count. If no LSM is
754 in force then an empty string will be returned.
755
756 A process must have view permission on the key for this function to be
757 successful.
758
759
David Howellsee18d642009-09-02 09:14:21 +0100760 (*) Install the calling process's session keyring on its parent.
761
762 long keyctl(KEYCTL_SESSION_TO_PARENT);
763
764 This functions attempts to install the calling process's session keyring
765 on to the calling process's parent, replacing the parent's current session
766 keyring.
767
768 The calling process must have the same ownership as its parent, the
769 keyring must have the same ownership as the calling process, the calling
770 process must have LINK permission on the keyring and the active LSM module
771 mustn't deny permission, otherwise error EPERM will be returned.
772
773 Error ENOMEM will be returned if there was insufficient memory to complete
774 the operation, otherwise 0 will be returned to indicate success.
775
776 The keyring will be replaced next time the parent process leaves the
777 kernel and resumes executing userspace.
778
779
Linus Torvalds1da177e2005-04-16 15:20:36 -0700780===============
781KERNEL SERVICES
782===============
783
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200784The kernel services for key management are fairly simple to deal with. They can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700785be broken down into two areas: keys and key types.
786
787Dealing with keys is fairly straightforward. Firstly, the kernel service
788registers its type, then it searches for a key of that type. It should retain
789the key as long as it has need of it, and then it should release it. For a
David Howells76d8aea2005-06-23 22:00:49 -0700790filesystem or device file, a search would probably be performed during the open
791call, and the key released upon close. How to deal with conflicting keys due to
792two different users opening the same file is left to the filesystem author to
793solve.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700794
David Howells76181c12007-10-16 23:29:46 -0700795To access the key manager, the following header must be #included:
796
797 <linux/key.h>
798
799Specific key types should have a header file under include/keys/ that should be
800used to access that type. For keys of type "user", for example, that would be:
801
802 <keys/user-type.h>
803
David Howells664cceb2005-09-28 17:03:15 +0100804Note that there are two different types of pointers to keys that may be
805encountered:
806
807 (*) struct key *
808
809 This simply points to the key structure itself. Key structures will be at
810 least four-byte aligned.
811
812 (*) key_ref_t
813
814 This is equivalent to a struct key *, but the least significant bit is set
815 if the caller "possesses" the key. By "possession" it is meant that the
816 calling processes has a searchable link to the key from one of its
817 keyrings. There are three functions for dealing with these:
818
819 key_ref_t make_key_ref(const struct key *key,
820 unsigned long possession);
821
822 struct key *key_ref_to_ptr(const key_ref_t key_ref);
823
824 unsigned long is_key_possessed(const key_ref_t key_ref);
825
826 The first function constructs a key reference from a key pointer and
827 possession information (which must be 0 or 1 and not any other value).
828
829 The second function retrieves the key pointer from a reference and the
830 third retrieves the possession flag.
831
David Howells76d8aea2005-06-23 22:00:49 -0700832When accessing a key's payload contents, certain precautions must be taken to
833prevent access vs modification races. See the section "Notes on accessing
834payload contents" for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700835
836(*) To search for a key, call:
837
838 struct key *request_key(const struct key_type *type,
839 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700840 const char *callout_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700841
842 This is used to request a key or keyring with a description that matches
843 the description specified according to the key type's match function. This
844 permits approximate matching to occur. If callout_string is not NULL, then
845 /sbin/request-key will be invoked in an attempt to obtain the key from
846 userspace. In that case, callout_string will be passed as an argument to
847 the program.
848
849 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be
850 returned.
851
David Howells3e301482005-06-23 22:00:56 -0700852 If successful, the key will have been attached to the default keyring for
853 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
854
David Howellsf1a9bad2005-10-07 15:04:52 +0100855 See also Documentation/keys-request-key.txt.
856
Linus Torvalds1da177e2005-04-16 15:20:36 -0700857
David Howells4e54f082006-06-29 02:24:28 -0700858(*) To search for a key, passing auxiliary data to the upcaller, call:
859
860 struct key *request_key_with_auxdata(const struct key_type *type,
861 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700862 const void *callout_info,
863 size_t callout_len,
David Howells4e54f082006-06-29 02:24:28 -0700864 void *aux);
865
866 This is identical to request_key(), except that the auxiliary data is
David Howells4a38e122008-04-29 01:01:24 -0700867 passed to the key_type->request_key() op if it exists, and the callout_info
868 is a blob of length callout_len, if given (the length may be 0).
David Howells4e54f082006-06-29 02:24:28 -0700869
870
David Howells76181c12007-10-16 23:29:46 -0700871(*) A key can be requested asynchronously by calling one of:
872
873 struct key *request_key_async(const struct key_type *type,
874 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700875 const void *callout_info,
876 size_t callout_len);
David Howells76181c12007-10-16 23:29:46 -0700877
878 or:
879
880 struct key *request_key_async_with_auxdata(const struct key_type *type,
881 const char *description,
David Howells4a38e122008-04-29 01:01:24 -0700882 const char *callout_info,
883 size_t callout_len,
David Howells76181c12007-10-16 23:29:46 -0700884 void *aux);
885
886 which are asynchronous equivalents of request_key() and
887 request_key_with_auxdata() respectively.
888
889 These two functions return with the key potentially still under
Matt LaPlanted9195882008-07-25 19:45:33 -0700890 construction. To wait for construction completion, the following should be
David Howells76181c12007-10-16 23:29:46 -0700891 called:
892
893 int wait_for_key_construction(struct key *key, bool intr);
894
895 The function will wait for the key to finish being constructed and then
896 invokes key_validate() to return an appropriate value to indicate the state
897 of the key (0 indicates the key is usable).
898
899 If intr is true, then the wait can be interrupted by a signal, in which
900 case error ERESTARTSYS will be returned.
901
902
Linus Torvalds1da177e2005-04-16 15:20:36 -0700903(*) When it is no longer required, the key should be released using:
904
905 void key_put(struct key *key);
906
David Howells664cceb2005-09-28 17:03:15 +0100907 Or:
908
909 void key_ref_put(key_ref_t key_ref);
910
911 These can be called from interrupt context. If CONFIG_KEYS is not set then
Linus Torvalds1da177e2005-04-16 15:20:36 -0700912 the argument will not be parsed.
913
914
915(*) Extra references can be made to a key by calling the following function:
916
917 struct key *key_get(struct key *key);
918
919 These need to be disposed of by calling key_put() when they've been
920 finished with. The key pointer passed in will be returned. If the pointer
921 is NULL or CONFIG_KEYS is not set then the key will not be dereferenced and
922 no increment will take place.
923
924
925(*) A key's serial number can be obtained by calling:
926
927 key_serial_t key_serial(struct key *key);
928
929 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the
930 latter case without parsing the argument).
931
932
933(*) If a keyring was found in the search, this can be further searched by:
934
David Howells664cceb2005-09-28 17:03:15 +0100935 key_ref_t keyring_search(key_ref_t keyring_ref,
936 const struct key_type *type,
937 const char *description)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700938
939 This searches the keyring tree specified for a matching key. Error ENOKEY
David Howells664cceb2005-09-28 17:03:15 +0100940 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
941 the returned key will need to be released.
942
943 The possession attribute from the keyring reference is used to control
944 access through the permissions mask and is propagated to the returned key
945 reference pointer if successful.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700946
947
948(*) To check the validity of a key, this function can be called:
949
950 int validate_key(struct key *key);
951
952 This checks that the key in question hasn't expired or and hasn't been
953 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will
954 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be
955 returned (in the latter case without parsing the argument).
956
957
958(*) To register a key type, the following function should be called:
959
960 int register_key_type(struct key_type *type);
961
962 This will return error EEXIST if a type of the same name is already
963 present.
964
965
966(*) To unregister a key type, call:
967
968 void unregister_key_type(struct key_type *type);
969
970
Satyam Sharma7eacbbd2007-07-31 00:38:17 -0700971Under some circumstances, it may be desirable to deal with a bundle of keys.
972The facility provides access to the keyring type for managing such a bundle:
David Howells73182262007-04-26 15:46:23 -0700973
974 struct key_type key_type_keyring;
975
976This can be used with a function such as request_key() to find a specific
977keyring in a process's keyrings. A keyring thus found can then be searched
978with keyring_search(). Note that it is not possible to use request_key() to
979search a specific keyring, so using keyrings in this way is of limited utility.
980
981
David Howells76d8aea2005-06-23 22:00:49 -0700982===================================
983NOTES ON ACCESSING PAYLOAD CONTENTS
984===================================
985
986The simplest payload is just a number in key->payload.value. In this case,
987there's no need to indulge in RCU or locking when accessing the payload.
988
989More complex payload contents must be allocated and a pointer to them set in
990key->payload.data. One of the following ways must be selected to access the
991data:
992
David Howells664cceb2005-09-28 17:03:15 +0100993 (1) Unmodifiable key type.
David Howells76d8aea2005-06-23 22:00:49 -0700994
995 If the key type does not have a modify method, then the key's payload can
996 be accessed without any form of locking, provided that it's known to be
997 instantiated (uninstantiated keys cannot be "found").
998
999 (2) The key's semaphore.
1000
1001 The semaphore could be used to govern access to the payload and to control
1002 the payload pointer. It must be write-locked for modifications and would
1003 have to be read-locked for general access. The disadvantage of doing this
1004 is that the accessor may be required to sleep.
1005
1006 (3) RCU.
1007
1008 RCU must be used when the semaphore isn't already held; if the semaphore
1009 is held then the contents can't change under you unexpectedly as the
1010 semaphore must still be used to serialise modifications to the key. The
1011 key management code takes care of this for the key type.
1012
1013 However, this means using:
1014
1015 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock()
1016
1017 to read the pointer, and:
1018
1019 rcu_dereference() ... rcu_assign_pointer() ... call_rcu()
1020
1021 to set the pointer and dispose of the old contents after a grace period.
1022 Note that only the key type should ever modify a key's payload.
1023
1024 Furthermore, an RCU controlled payload must hold a struct rcu_head for the
1025 use of call_rcu() and, if the payload is of variable size, the length of
1026 the payload. key->datalen cannot be relied upon to be consistent with the
1027 payload just dereferenced if the key's semaphore is not held.
1028
1029
Linus Torvalds1da177e2005-04-16 15:20:36 -07001030===================
1031DEFINING A KEY TYPE
1032===================
1033
1034A kernel service may want to define its own key type. For instance, an AFS
1035filesystem might want to define a Kerberos 5 ticket key type. To do this, it
David Howells76181c12007-10-16 23:29:46 -07001036author fills in a key_type struct and registers it with the system.
1037
1038Source files that implement key types should include the following header file:
1039
1040 <linux/key-type.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07001041
1042The structure has a number of fields, some of which are mandatory:
1043
1044 (*) const char *name
1045
1046 The name of the key type. This is used to translate a key type name
1047 supplied by userspace into a pointer to the structure.
1048
1049
1050 (*) size_t def_datalen
1051
1052 This is optional - it supplies the default payload data length as
1053 contributed to the quota. If the key type's payload is always or almost
1054 always the same size, then this is a more efficient way to do things.
1055
1056 The data length (and quota) on a particular key can always be changed
1057 during instantiation or update by calling:
1058
1059 int key_payload_reserve(struct key *key, size_t datalen);
1060
David Howells76d8aea2005-06-23 22:00:49 -07001061 With the revised data length. Error EDQUOT will be returned if this is not
1062 viable.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001063
1064
1065 (*) int (*instantiate)(struct key *key, const void *data, size_t datalen);
1066
1067 This method is called to attach a payload to a key during construction.
David Howells76d8aea2005-06-23 22:00:49 -07001068 The payload attached need not bear any relation to the data passed to this
1069 function.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001070
1071 If the amount of data attached to the key differs from the size in
1072 keytype->def_datalen, then key_payload_reserve() should be called.
1073
1074 This method does not have to lock the key in order to attach a payload.
1075 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents
1076 anything else from gaining access to the key.
1077
David Howells76d8aea2005-06-23 22:00:49 -07001078 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001079
1080
Linus Torvalds1da177e2005-04-16 15:20:36 -07001081 (*) int (*update)(struct key *key, const void *data, size_t datalen);
1082
David Howells76d8aea2005-06-23 22:00:49 -07001083 If this type of key can be updated, then this method should be provided.
1084 It is called to update a key's payload from the blob of data provided.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001085
1086 key_payload_reserve() should be called if the data length might change
David Howells76d8aea2005-06-23 22:00:49 -07001087 before any changes are actually made. Note that if this succeeds, the type
1088 is committed to changing the key because it's already been altered, so all
1089 memory allocation must be done first.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001090
David Howells76d8aea2005-06-23 22:00:49 -07001091 The key will have its semaphore write-locked before this method is called,
1092 but this only deters other writers; any changes to the key's payload must
1093 be made under RCU conditions, and call_rcu() must be used to dispose of
1094 the old payload.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001095
David Howells76d8aea2005-06-23 22:00:49 -07001096 key_payload_reserve() should be called before the changes are made, but
1097 after all allocations and other potentially failing function calls are
1098 made.
1099
1100 It is safe to sleep in this method.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001101
1102
1103 (*) int (*match)(const struct key *key, const void *desc);
1104
1105 This method is called to match a key against a description. It should
1106 return non-zero if the two match, zero if they don't.
1107
1108 This method should not need to lock the key in any way. The type and
1109 description can be considered invariant, and the payload should not be
1110 accessed (the key may not yet be instantiated).
1111
1112 It is not safe to sleep in this method; the caller may hold spinlocks.
1113
1114
David Howells04c567d2006-06-22 14:47:18 -07001115 (*) void (*revoke)(struct key *key);
1116
1117 This method is optional. It is called to discard part of the payload
1118 data upon a key being revoked. The caller will have the key semaphore
1119 write-locked.
1120
1121 It is safe to sleep in this method, though care should be taken to avoid
1122 a deadlock against the key semaphore.
1123
1124
Linus Torvalds1da177e2005-04-16 15:20:36 -07001125 (*) void (*destroy)(struct key *key);
1126
David Howells76d8aea2005-06-23 22:00:49 -07001127 This method is optional. It is called to discard the payload data on a key
1128 when it is being destroyed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001129
David Howells76d8aea2005-06-23 22:00:49 -07001130 This method does not need to lock the key to access the payload; it can
1131 consider the key as being inaccessible at this time. Note that the key's
1132 type may have been changed before this function is called.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001133
1134 It is not safe to sleep in this method; the caller may hold spinlocks.
1135
1136
1137 (*) void (*describe)(const struct key *key, struct seq_file *p);
1138
1139 This method is optional. It is called during /proc/keys reading to
1140 summarise a key's description and payload in text form.
1141
David Howells76d8aea2005-06-23 22:00:49 -07001142 This method will be called with the RCU read lock held. rcu_dereference()
1143 should be used to read the payload pointer if the payload is to be
1144 accessed. key->datalen cannot be trusted to stay consistent with the
1145 contents of the payload.
1146
1147 The description will not change, though the key's state may.
1148
1149 It is not safe to sleep in this method; the RCU read lock is held by the
1150 caller.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001151
1152
1153 (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen);
1154
1155 This method is optional. It is called by KEYCTL_READ to translate the
David Howells76d8aea2005-06-23 22:00:49 -07001156 key's payload into something a blob of data for userspace to deal with.
1157 Ideally, the blob should be in the same format as that passed in to the
1158 instantiate and update methods.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001159
1160 If successful, the blob size that could be produced should be returned
1161 rather than the size copied.
1162
David Howells76d8aea2005-06-23 22:00:49 -07001163 This method will be called with the key's semaphore read-locked. This will
1164 prevent the key's payload changing. It is not necessary to use RCU locking
1165 when accessing the key's payload. It is safe to sleep in this method, such
1166 as might happen when the userspace buffer is accessed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001167
1168
David Howells76181c12007-10-16 23:29:46 -07001169 (*) int (*request_key)(struct key_construction *cons, const char *op,
David Howells4e54f082006-06-29 02:24:28 -07001170 void *aux);
1171
David Howells76181c12007-10-16 23:29:46 -07001172 This method is optional. If provided, request_key() and friends will
1173 invoke this function rather than upcalling to /sbin/request-key to operate
1174 upon a key of this type.
David Howells4e54f082006-06-29 02:24:28 -07001175
David Howells76181c12007-10-16 23:29:46 -07001176 The aux parameter is as passed to request_key_async_with_auxdata() and
1177 similar or is NULL otherwise. Also passed are the construction record for
1178 the key to be operated upon and the operation type (currently only
1179 "create").
David Howells4e54f082006-06-29 02:24:28 -07001180
David Howells76181c12007-10-16 23:29:46 -07001181 This method is permitted to return before the upcall is complete, but the
1182 following function must be called under all circumstances to complete the
1183 instantiation process, whether or not it succeeds, whether or not there's
1184 an error:
1185
1186 void complete_request_key(struct key_construction *cons, int error);
1187
1188 The error parameter should be 0 on success, -ve on error. The
1189 construction record is destroyed by this action and the authorisation key
1190 will be revoked. If an error is indicated, the key under construction
1191 will be negatively instantiated if it wasn't already instantiated.
1192
1193 If this method returns an error, that error will be returned to the
1194 caller of request_key*(). complete_request_key() must be called prior to
1195 returning.
1196
1197 The key under construction and the authorisation key can be found in the
1198 key_construction struct pointed to by cons:
1199
1200 (*) struct key *key;
1201
1202 The key under construction.
1203
1204 (*) struct key *authkey;
1205
1206 The authorisation key.
David Howells4e54f082006-06-29 02:24:28 -07001207
1208
Linus Torvalds1da177e2005-04-16 15:20:36 -07001209============================
1210REQUEST-KEY CALLBACK SERVICE
1211============================
1212
1213To create a new key, the kernel will attempt to execute the following command
1214line:
1215
1216 /sbin/request-key create <key> <uid> <gid> \
1217 <threadring> <processring> <sessionring> <callout_info>
1218
1219<key> is the key being constructed, and the three keyrings are the process
1220keyrings from the process that caused the search to be issued. These are
1221included for two reasons:
1222
1223 (1) There may be an authentication token in one of the keyrings that is
1224 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket.
1225
1226 (2) The new key should probably be cached in one of these rings.
1227
1228This program should set it UID and GID to those specified before attempting to
1229access any more keys. It may then look around for a user specific process to
1230hand the request off to (perhaps a path held in placed in another key by, for
1231example, the KDE desktop manager).
1232
1233The program (or whatever it calls) should finish construction of the key by
1234calling KEYCTL_INSTANTIATE, which also permits it to cache the key in one of
1235the keyrings (probably the session ring) before returning. Alternatively, the
1236key can be marked as negative with KEYCTL_NEGATE; this also permits the key to
1237be cached in one of the keyrings.
1238
1239If it returns with the key remaining in the unconstructed state, the key will
1240be marked as being negative, it will be added to the session keyring, and an
1241error will be returned to the key requestor.
1242
David Howells76d8aea2005-06-23 22:00:49 -07001243Supplementary information may be provided from whoever or whatever invoked this
1244service. This will be passed as the <callout_info> parameter. If no such
Linus Torvalds1da177e2005-04-16 15:20:36 -07001245information was made available, then "-" will be passed as this parameter
1246instead.
1247
1248
1249Similarly, the kernel may attempt to update an expired or a soon to expire key
1250by executing:
1251
1252 /sbin/request-key update <key> <uid> <gid> \
1253 <threadring> <processring> <sessionring>
1254
1255In this case, the program isn't required to actually attach the key to a ring;
1256the rings are provided for reference.
David Howells5d135442009-09-02 09:14:00 +01001257
1258
1259==================
1260GARBAGE COLLECTION
1261==================
1262
1263Dead keys (for which the type has been removed) will be automatically unlinked
1264from those keyrings that point to them and deleted as soon as possible by a
1265background garbage collector.
1266
1267Similarly, revoked and expired keys will be garbage collected, but only after a
1268certain amount of time has passed. This time is set as a number of seconds in:
1269
1270 /proc/sys/kernel/keys/gc_delay