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1da177e4 LT |
1 | ============================ |
2 | KERNEL KEY RETENTION SERVICE | |
3 | ============================ | |
4 | ||
5 | This service allows cryptographic keys, authentication tokens, cross-domain | |
6 | user mappings, and similar to be cached in the kernel for the use of | |
76181c13 | 7 | filesystems and other kernel services. |
1da177e4 LT |
8 | |
9 | Keyrings are permitted; these are a special type of key that can hold links to | |
10 | other keys. Processes each have three standard keyring subscriptions that a | |
11 | kernel service can search for relevant keys. | |
12 | ||
13 | The key service can be configured on by enabling: | |
14 | ||
15 | "Security options"/"Enable access key retention support" (CONFIG_KEYS) | |
16 | ||
17 | This document has the following sections: | |
18 | ||
19 | - Key overview | |
20 | - Key service overview | |
21 | - Key access permissions | |
d720024e | 22 | - SELinux support |
1da177e4 LT |
23 | - New procfs files |
24 | - Userspace system call interface | |
25 | - Kernel services | |
76d8aeab | 26 | - Notes on accessing payload contents |
1da177e4 LT |
27 | - Defining a key type |
28 | - Request-key callback service | |
5d135440 | 29 | - Garbage collection |
1da177e4 LT |
30 | |
31 | ||
32 | ============ | |
33 | KEY OVERVIEW | |
34 | ============ | |
35 | ||
36 | In this context, keys represent units of cryptographic data, authentication | |
37 | tokens, keyrings, etc.. These are represented in the kernel by struct key. | |
38 | ||
39 | Each 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 | ||
76d8aeab DH |
50 | (*) 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. | |
1da177e4 LT |
53 | |
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 | |
76d8aeab DH |
58 | 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. | |
1da177e4 | 60 | |
76d8aeab DH |
61 | 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. | |
1da177e4 LT |
63 | |
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 | |
76d8aeab DH |
68 | type provides an operation to perform a match between the description on a |
69 | key and a criterion string. | |
1da177e4 LT |
70 | |
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 | ||
76d8aeab DH |
78 | (*) 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. | |
1da177e4 LT |
82 | |
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 | ||
76d8aeab DH |
96 | (*) Uninstantiated. The key exists, but does not have any data attached. |
97 | Keys being requested from userspace will be in this state. | |
1da177e4 LT |
98 | |
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 | ||
5d135440 DH |
116 | Keys in the last three states are subject to garbage collection. See the |
117 | section on "Garbage collection". | |
118 | ||
1da177e4 LT |
119 | |
120 | ==================== | |
121 | KEY SERVICE OVERVIEW | |
122 | ==================== | |
123 | ||
124 | The 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 | ||
76d8aeab DH |
147 | 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. | |
1da177e4 LT |
151 | |
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 | |
0b77f5bf DH |
176 | files. The root user may also alter the quota limits through sysctl files |
177 | (see the section "New procfs files"). | |
1da177e4 LT |
178 | |
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 | ||
76d8aeab DH |
185 | (*) There's a system call interface by which userspace programs can create and |
186 | manipulate keys and keyrings. | |
1da177e4 | 187 | |
76d8aeab DH |
188 | (*) There's a kernel interface by which services can register types and search |
189 | for keys. | |
1da177e4 LT |
190 | |
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 | ====================== | |
199 | KEY ACCESS PERMISSIONS | |
200 | ====================== | |
201 | ||
76d8aeab | 202 | Keys have an owner user ID, a group access ID, and a permissions mask. The mask |
664cceb0 | 203 | has up to eight bits each for possessor, user, group and other access. Only |
29db9190 | 204 | six of each set of eight bits are defined. These permissions granted are: |
1da177e4 LT |
205 | |
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 | ||
76d8aeab DH |
218 | 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. | |
1da177e4 LT |
220 | |
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 | ||
29db9190 DH |
232 | (*) Set Attribute |
233 | ||
234 | This permits a key's UID, GID and permissions mask to be changed. | |
235 | ||
1da177e4 LT |
236 | For changing the ownership, group ID or permissions mask, being the owner of |
237 | the key or having the sysadmin capability is sufficient. | |
238 | ||
239 | ||
d720024e ML |
240 | =============== |
241 | SELINUX SUPPORT | |
242 | =============== | |
243 | ||
244 | The security class "key" has been added to SELinux so that mandatory access | |
245 | controls can be applied to keys created within various contexts. This support | |
246 | is preliminary, and is likely to change quite significantly in the near future. | |
247 | Currently, all of the basic permissions explained above are provided in SELinux | |
4eb582cf | 248 | as well; SELinux is simply invoked after all basic permission checks have been |
d720024e ML |
249 | performed. |
250 | ||
4eb582cf ML |
251 | The value of the file /proc/self/attr/keycreate influences the labeling of |
252 | newly-created keys. If the contents of that file correspond to an SELinux | |
253 | security context, then the key will be assigned that context. Otherwise, the | |
254 | key will be assigned the current context of the task that invoked the key | |
255 | creation request. Tasks must be granted explicit permission to assign a | |
256 | particular context to newly-created keys, using the "create" permission in the | |
257 | key security class. | |
d720024e | 258 | |
4eb582cf ML |
259 | The default keyrings associated with users will be labeled with the default |
260 | context of the user if and only if the login programs have been instrumented to | |
261 | properly initialize keycreate during the login process. Otherwise, they will | |
262 | be labeled with the context of the login program itself. | |
d720024e ML |
263 | |
264 | Note, however, that the default keyrings associated with the root user are | |
265 | labeled with the default kernel context, since they are created early in the | |
266 | boot process, before root has a chance to log in. | |
267 | ||
4eb582cf ML |
268 | The keyrings associated with new threads are each labeled with the context of |
269 | their associated thread, and both session and process keyrings are handled | |
270 | similarly. | |
271 | ||
d720024e | 272 | |
1da177e4 LT |
273 | ================ |
274 | NEW PROCFS FILES | |
275 | ================ | |
276 | ||
277 | Two files have been added to procfs by which an administrator can find out | |
278 | about the status of the key service: | |
279 | ||
280 | (*) /proc/keys | |
281 | ||
06ec7be5 ML |
282 | 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: | |
1da177e4 | 293 | |
664cceb0 | 294 | SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY |
29db9190 DH |
295 | 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 | |
664cceb0 | 301 | 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0 |
29db9190 DH |
302 | 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 | |
1da177e4 LT |
304 | |
305 | The flags are: | |
306 | ||
307 | I Instantiated | |
308 | R Revoked | |
309 | D Dead | |
310 | Q Contributes to user's quota | |
5d3f083d | 311 | U Under construction by callback to userspace |
1da177e4 LT |
312 | 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 | |
06ec7be5 | 320 | on the system. Such data includes quota information and statistics: |
1da177e4 LT |
321 | |
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 | ||
0b77f5bf DH |
336 | Four new sysctl files have been added also for the purpose of controlling the |
337 | quota 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 | ||
353 | Root may alter these by writing each new limit as a decimal number string to | |
354 | the appropriate file. | |
355 | ||
356 | ||
1da177e4 LT |
357 | =============================== |
358 | USERSPACE SYSTEM CALL INTERFACE | |
359 | =============================== | |
360 | ||
361 | Userspace can manipulate keys directly through three new syscalls: add_key, | |
362 | request_key and keyctl. The latter provides a number of functions for | |
363 | manipulating keys. | |
364 | ||
365 | When referring to a key directly, userspace programs should use the key's | |
366 | serial number (a positive 32-bit integer). However, there are some special | |
367 | values available for referring to special keys and keyrings that relate to the | |
368 | process 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 | |
b5f545c8 DH |
378 | KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key() |
379 | authorisation key | |
1da177e4 LT |
380 | |
381 | ||
382 | The 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 | |
76d8aeab DH |
394 | 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. | |
1da177e4 | 397 | |
76d8aeab DH |
398 | 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. | |
1da177e4 LT |
402 | |
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 | ||
76d8aeab DH |
407 | 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. | |
1da177e4 LT |
409 | |
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 | ||
d410fa4e | 437 | See also Documentation/security/keys-request-key.txt. |
f1a9badc | 438 | |
1da177e4 LT |
439 | |
440 | The 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 | ||
76d8aeab DH |
447 | 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. | |
1da177e4 LT |
450 | |
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 | |
76d8aeab DH |
480 | type. The process must also have permission to write to the key to be able |
481 | to update it. | |
1da177e4 LT |
482 | |
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 | ||
76d8aeab DH |
500 | 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. | |
1da177e4 LT |
502 | |
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 | ||
700920eb DH |
557 | This function can also be used to clear special kernel keyrings if they |
558 | are appropriately marked if the user has CAP_SYS_ADMIN capability. The | |
559 | DNS resolver cache keyring is an example of this. | |
560 | ||
1da177e4 LT |
561 | |
562 | (*) Link a key into a keyring: | |
563 | ||
564 | long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key); | |
565 | ||
76d8aeab DH |
566 | This function creates a link from the keyring to the key. The process must |
567 | have write permission on the keyring and must have link permission on the | |
568 | key. | |
1da177e4 | 569 | |
76d8aeab DH |
570 | Should the keyring not be a keyring, error ENOTDIR will result; and if the |
571 | keyring is full, error ENFILE will result. | |
1da177e4 LT |
572 | |
573 | The link procedure checks the nesting of the keyrings, returning ELOOP if | |
017679c4 | 574 | it appears too deep or EDEADLK if the link would introduce a cycle. |
1da177e4 | 575 | |
cab8eb59 DH |
576 | Any links within the keyring to keys that match the new key in terms of |
577 | type and description will be discarded from the keyring as the new one is | |
578 | added. | |
579 | ||
1da177e4 LT |
580 | |
581 | (*) Unlink a key or keyring from another keyring: | |
582 | ||
583 | long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key); | |
584 | ||
585 | This function looks through the keyring for the first link to the | |
586 | specified key, and removes it if found. Subsequent links to that key are | |
587 | ignored. The process must have write permission on the keyring. | |
588 | ||
76d8aeab DH |
589 | If the keyring is not a keyring, error ENOTDIR will result; and if the key |
590 | is not present, error ENOENT will be the result. | |
1da177e4 LT |
591 | |
592 | ||
593 | (*) Search a keyring tree for a key: | |
594 | ||
595 | key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring, | |
596 | const char *type, const char *description, | |
597 | key_serial_t dest_keyring); | |
598 | ||
76d8aeab DH |
599 | This searches the keyring tree headed by the specified keyring until a key |
600 | is found that matches the type and description criteria. Each keyring is | |
601 | checked for keys before recursion into its children occurs. | |
1da177e4 LT |
602 | |
603 | The process must have search permission on the top level keyring, or else | |
604 | error EACCES will result. Only keyrings that the process has search | |
605 | permission on will be recursed into, and only keys and keyrings for which | |
606 | a process has search permission can be matched. If the specified keyring | |
607 | is not a keyring, ENOTDIR will result. | |
608 | ||
609 | If the search succeeds, the function will attempt to link the found key | |
610 | into the destination keyring if one is supplied (non-zero ID). All the | |
611 | constraints applicable to KEYCTL_LINK apply in this case too. | |
612 | ||
613 | Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search | |
614 | fails. On success, the resulting key ID will be returned. | |
615 | ||
616 | ||
617 | (*) Read the payload data from a key: | |
618 | ||
f1a9badc DH |
619 | long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer, |
620 | size_t buflen); | |
1da177e4 LT |
621 | |
622 | This function attempts to read the payload data from the specified key | |
623 | into the buffer. The process must have read permission on the key to | |
624 | succeed. | |
625 | ||
626 | The returned data will be processed for presentation by the key type. For | |
627 | instance, a keyring will return an array of key_serial_t entries | |
628 | representing the IDs of all the keys to which it is subscribed. The user | |
629 | defined key type will return its data as is. If a key type does not | |
630 | implement this function, error EOPNOTSUPP will result. | |
631 | ||
632 | As much of the data as can be fitted into the buffer will be copied to | |
633 | userspace if the buffer pointer is not NULL. | |
634 | ||
76d8aeab DH |
635 | On a successful return, the function will always return the amount of data |
636 | available rather than the amount copied. | |
1da177e4 LT |
637 | |
638 | ||
639 | (*) Instantiate a partially constructed key. | |
640 | ||
f1a9badc DH |
641 | long keyctl(KEYCTL_INSTANTIATE, key_serial_t key, |
642 | const void *payload, size_t plen, | |
643 | key_serial_t keyring); | |
ee009e4a DH |
644 | long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key, |
645 | const struct iovec *payload_iov, unsigned ioc, | |
646 | key_serial_t keyring); | |
1da177e4 LT |
647 | |
648 | If the kernel calls back to userspace to complete the instantiation of a | |
649 | key, userspace should use this call to supply data for the key before the | |
650 | invoked process returns, or else the key will be marked negative | |
651 | automatically. | |
652 | ||
653 | The process must have write access on the key to be able to instantiate | |
654 | it, and the key must be uninstantiated. | |
655 | ||
656 | If a keyring is specified (non-zero), the key will also be linked into | |
76d8aeab DH |
657 | that keyring, however all the constraints applying in KEYCTL_LINK apply in |
658 | this case too. | |
1da177e4 LT |
659 | |
660 | The payload and plen arguments describe the payload data as for add_key(). | |
661 | ||
ee009e4a DH |
662 | The payload_iov and ioc arguments describe the payload data in an iovec |
663 | array instead of a single buffer. | |
664 | ||
1da177e4 LT |
665 | |
666 | (*) Negatively instantiate a partially constructed key. | |
667 | ||
f1a9badc DH |
668 | long keyctl(KEYCTL_NEGATE, key_serial_t key, |
669 | unsigned timeout, key_serial_t keyring); | |
fdd1b945 DH |
670 | long keyctl(KEYCTL_REJECT, key_serial_t key, |
671 | unsigned timeout, unsigned error, key_serial_t keyring); | |
1da177e4 LT |
672 | |
673 | If the kernel calls back to userspace to complete the instantiation of a | |
674 | key, userspace should use this call mark the key as negative before the | |
40e47125 | 675 | invoked process returns if it is unable to fulfill the request. |
1da177e4 LT |
676 | |
677 | The process must have write access on the key to be able to instantiate | |
678 | it, and the key must be uninstantiated. | |
679 | ||
680 | If a keyring is specified (non-zero), the key will also be linked into | |
76d8aeab DH |
681 | that keyring, however all the constraints applying in KEYCTL_LINK apply in |
682 | this case too. | |
1da177e4 | 683 | |
fdd1b945 DH |
684 | If the key is rejected, future searches for it will return the specified |
685 | error code until the rejected key expires. Negating the key is the same | |
686 | as rejecting the key with ENOKEY as the error code. | |
687 | ||
1da177e4 | 688 | |
3e30148c DH |
689 | (*) Set the default request-key destination keyring. |
690 | ||
691 | long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl); | |
692 | ||
693 | This sets the default keyring to which implicitly requested keys will be | |
694 | attached for this thread. reqkey_defl should be one of these constants: | |
695 | ||
696 | CONSTANT VALUE NEW DEFAULT KEYRING | |
697 | ====================================== ====== ======================= | |
698 | KEY_REQKEY_DEFL_NO_CHANGE -1 No change | |
699 | KEY_REQKEY_DEFL_DEFAULT 0 Default[1] | |
700 | KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring | |
701 | KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring | |
702 | KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring | |
703 | KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring | |
704 | KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring | |
705 | KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring | |
706 | ||
707 | The old default will be returned if successful and error EINVAL will be | |
708 | returned if reqkey_defl is not one of the above values. | |
709 | ||
710 | The default keyring can be overridden by the keyring indicated to the | |
711 | request_key() system call. | |
712 | ||
713 | Note that this setting is inherited across fork/exec. | |
714 | ||
670e9f34 | 715 | [1] The default is: the thread keyring if there is one, otherwise |
3e30148c DH |
716 | the process keyring if there is one, otherwise the session keyring if |
717 | there is one, otherwise the user default session keyring. | |
718 | ||
719 | ||
017679c4 DH |
720 | (*) Set the timeout on a key. |
721 | ||
722 | long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout); | |
723 | ||
724 | This sets or clears the timeout on a key. The timeout can be 0 to clear | |
725 | the timeout or a number of seconds to set the expiry time that far into | |
726 | the future. | |
727 | ||
728 | The process must have attribute modification access on a key to set its | |
729 | timeout. Timeouts may not be set with this function on negative, revoked | |
730 | or expired keys. | |
731 | ||
732 | ||
b5f545c8 DH |
733 | (*) Assume the authority granted to instantiate a key |
734 | ||
735 | long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key); | |
736 | ||
737 | This assumes or divests the authority required to instantiate the | |
738 | specified key. Authority can only be assumed if the thread has the | |
739 | authorisation key associated with the specified key in its keyrings | |
740 | somewhere. | |
741 | ||
742 | Once authority is assumed, searches for keys will also search the | |
743 | requester's keyrings using the requester's security label, UID, GID and | |
744 | groups. | |
745 | ||
746 | If the requested authority is unavailable, error EPERM will be returned, | |
747 | likewise if the authority has been revoked because the target key is | |
748 | already instantiated. | |
749 | ||
750 | If the specified key is 0, then any assumed authority will be divested. | |
751 | ||
3f6dee9b | 752 | The assumed authoritative key is inherited across fork and exec. |
b5f545c8 DH |
753 | |
754 | ||
70a5bb72 DH |
755 | (*) Get the LSM security context attached to a key. |
756 | ||
757 | long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer, | |
758 | size_t buflen) | |
759 | ||
760 | This function returns a string that represents the LSM security context | |
761 | attached to a key in the buffer provided. | |
762 | ||
763 | Unless there's an error, it always returns the amount of data it could | |
764 | produce, even if that's too big for the buffer, but it won't copy more | |
765 | than requested to userspace. If the buffer pointer is NULL then no copy | |
766 | will take place. | |
767 | ||
768 | A NUL character is included at the end of the string if the buffer is | |
769 | sufficiently big. This is included in the returned count. If no LSM is | |
770 | in force then an empty string will be returned. | |
771 | ||
772 | A process must have view permission on the key for this function to be | |
773 | successful. | |
774 | ||
775 | ||
ee18d64c DH |
776 | (*) Install the calling process's session keyring on its parent. |
777 | ||
778 | long keyctl(KEYCTL_SESSION_TO_PARENT); | |
779 | ||
780 | This functions attempts to install the calling process's session keyring | |
781 | on to the calling process's parent, replacing the parent's current session | |
782 | keyring. | |
783 | ||
784 | The calling process must have the same ownership as its parent, the | |
785 | keyring must have the same ownership as the calling process, the calling | |
786 | process must have LINK permission on the keyring and the active LSM module | |
787 | mustn't deny permission, otherwise error EPERM will be returned. | |
788 | ||
789 | Error ENOMEM will be returned if there was insufficient memory to complete | |
790 | the operation, otherwise 0 will be returned to indicate success. | |
791 | ||
792 | The keyring will be replaced next time the parent process leaves the | |
793 | kernel and resumes executing userspace. | |
794 | ||
795 | ||
1da177e4 LT |
796 | =============== |
797 | KERNEL SERVICES | |
798 | =============== | |
799 | ||
2fe0ae78 | 800 | The kernel services for key management are fairly simple to deal with. They can |
1da177e4 LT |
801 | be broken down into two areas: keys and key types. |
802 | ||
803 | Dealing with keys is fairly straightforward. Firstly, the kernel service | |
804 | registers its type, then it searches for a key of that type. It should retain | |
805 | the key as long as it has need of it, and then it should release it. For a | |
76d8aeab DH |
806 | filesystem or device file, a search would probably be performed during the open |
807 | call, and the key released upon close. How to deal with conflicting keys due to | |
808 | two different users opening the same file is left to the filesystem author to | |
809 | solve. | |
810 | ||
76181c13 DH |
811 | To access the key manager, the following header must be #included: |
812 | ||
813 | <linux/key.h> | |
814 | ||
815 | Specific key types should have a header file under include/keys/ that should be | |
816 | used to access that type. For keys of type "user", for example, that would be: | |
817 | ||
818 | <keys/user-type.h> | |
819 | ||
664cceb0 DH |
820 | Note that there are two different types of pointers to keys that may be |
821 | encountered: | |
822 | ||
823 | (*) struct key * | |
824 | ||
825 | This simply points to the key structure itself. Key structures will be at | |
826 | least four-byte aligned. | |
827 | ||
828 | (*) key_ref_t | |
829 | ||
830 | This is equivalent to a struct key *, but the least significant bit is set | |
831 | if the caller "possesses" the key. By "possession" it is meant that the | |
832 | calling processes has a searchable link to the key from one of its | |
833 | keyrings. There are three functions for dealing with these: | |
834 | ||
835 | key_ref_t make_key_ref(const struct key *key, | |
836 | unsigned long possession); | |
837 | ||
838 | struct key *key_ref_to_ptr(const key_ref_t key_ref); | |
839 | ||
840 | unsigned long is_key_possessed(const key_ref_t key_ref); | |
841 | ||
842 | The first function constructs a key reference from a key pointer and | |
843 | possession information (which must be 0 or 1 and not any other value). | |
844 | ||
845 | The second function retrieves the key pointer from a reference and the | |
846 | third retrieves the possession flag. | |
847 | ||
76d8aeab DH |
848 | When accessing a key's payload contents, certain precautions must be taken to |
849 | prevent access vs modification races. See the section "Notes on accessing | |
850 | payload contents" for more information. | |
1da177e4 LT |
851 | |
852 | (*) To search for a key, call: | |
853 | ||
854 | struct key *request_key(const struct key_type *type, | |
855 | const char *description, | |
4a38e122 | 856 | const char *callout_info); |
1da177e4 LT |
857 | |
858 | This is used to request a key or keyring with a description that matches | |
859 | the description specified according to the key type's match function. This | |
860 | permits approximate matching to occur. If callout_string is not NULL, then | |
861 | /sbin/request-key will be invoked in an attempt to obtain the key from | |
862 | userspace. In that case, callout_string will be passed as an argument to | |
863 | the program. | |
864 | ||
865 | Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be | |
866 | returned. | |
867 | ||
3e30148c DH |
868 | If successful, the key will have been attached to the default keyring for |
869 | implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING. | |
870 | ||
d410fa4e | 871 | See also Documentation/security/keys-request-key.txt. |
f1a9badc | 872 | |
1da177e4 | 873 | |
4e54f085 DH |
874 | (*) To search for a key, passing auxiliary data to the upcaller, call: |
875 | ||
876 | struct key *request_key_with_auxdata(const struct key_type *type, | |
877 | const char *description, | |
4a38e122 DH |
878 | const void *callout_info, |
879 | size_t callout_len, | |
4e54f085 DH |
880 | void *aux); |
881 | ||
882 | This is identical to request_key(), except that the auxiliary data is | |
4a38e122 DH |
883 | passed to the key_type->request_key() op if it exists, and the callout_info |
884 | is a blob of length callout_len, if given (the length may be 0). | |
4e54f085 DH |
885 | |
886 | ||
76181c13 DH |
887 | (*) A key can be requested asynchronously by calling one of: |
888 | ||
889 | struct key *request_key_async(const struct key_type *type, | |
890 | const char *description, | |
4a38e122 DH |
891 | const void *callout_info, |
892 | size_t callout_len); | |
76181c13 DH |
893 | |
894 | or: | |
895 | ||
896 | struct key *request_key_async_with_auxdata(const struct key_type *type, | |
897 | const char *description, | |
4a38e122 DH |
898 | const char *callout_info, |
899 | size_t callout_len, | |
76181c13 DH |
900 | void *aux); |
901 | ||
902 | which are asynchronous equivalents of request_key() and | |
903 | request_key_with_auxdata() respectively. | |
904 | ||
905 | These two functions return with the key potentially still under | |
d9195881 | 906 | construction. To wait for construction completion, the following should be |
76181c13 DH |
907 | called: |
908 | ||
909 | int wait_for_key_construction(struct key *key, bool intr); | |
910 | ||
911 | The function will wait for the key to finish being constructed and then | |
912 | invokes key_validate() to return an appropriate value to indicate the state | |
913 | of the key (0 indicates the key is usable). | |
914 | ||
915 | If intr is true, then the wait can be interrupted by a signal, in which | |
916 | case error ERESTARTSYS will be returned. | |
917 | ||
918 | ||
1da177e4 LT |
919 | (*) When it is no longer required, the key should be released using: |
920 | ||
921 | void key_put(struct key *key); | |
922 | ||
664cceb0 DH |
923 | Or: |
924 | ||
925 | void key_ref_put(key_ref_t key_ref); | |
926 | ||
927 | These can be called from interrupt context. If CONFIG_KEYS is not set then | |
1da177e4 LT |
928 | the argument will not be parsed. |
929 | ||
930 | ||
931 | (*) Extra references can be made to a key by calling the following function: | |
932 | ||
933 | struct key *key_get(struct key *key); | |
934 | ||
935 | These need to be disposed of by calling key_put() when they've been | |
936 | finished with. The key pointer passed in will be returned. If the pointer | |
937 | is NULL or CONFIG_KEYS is not set then the key will not be dereferenced and | |
938 | no increment will take place. | |
939 | ||
940 | ||
941 | (*) A key's serial number can be obtained by calling: | |
942 | ||
943 | key_serial_t key_serial(struct key *key); | |
944 | ||
945 | If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the | |
946 | latter case without parsing the argument). | |
947 | ||
948 | ||
949 | (*) If a keyring was found in the search, this can be further searched by: | |
950 | ||
664cceb0 DH |
951 | key_ref_t keyring_search(key_ref_t keyring_ref, |
952 | const struct key_type *type, | |
953 | const char *description) | |
1da177e4 LT |
954 | |
955 | This searches the keyring tree specified for a matching key. Error ENOKEY | |
664cceb0 DH |
956 | is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful, |
957 | the returned key will need to be released. | |
958 | ||
959 | The possession attribute from the keyring reference is used to control | |
960 | access through the permissions mask and is propagated to the returned key | |
961 | reference pointer if successful. | |
1da177e4 LT |
962 | |
963 | ||
964 | (*) To check the validity of a key, this function can be called: | |
965 | ||
966 | int validate_key(struct key *key); | |
967 | ||
968 | This checks that the key in question hasn't expired or and hasn't been | |
969 | revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will | |
970 | be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be | |
971 | returned (in the latter case without parsing the argument). | |
972 | ||
973 | ||
974 | (*) To register a key type, the following function should be called: | |
975 | ||
976 | int register_key_type(struct key_type *type); | |
977 | ||
978 | This will return error EEXIST if a type of the same name is already | |
979 | present. | |
980 | ||
981 | ||
982 | (*) To unregister a key type, call: | |
983 | ||
984 | void unregister_key_type(struct key_type *type); | |
985 | ||
986 | ||
7eacbbd3 SS |
987 | Under some circumstances, it may be desirable to deal with a bundle of keys. |
988 | The facility provides access to the keyring type for managing such a bundle: | |
7318226e DH |
989 | |
990 | struct key_type key_type_keyring; | |
991 | ||
992 | This can be used with a function such as request_key() to find a specific | |
993 | keyring in a process's keyrings. A keyring thus found can then be searched | |
994 | with keyring_search(). Note that it is not possible to use request_key() to | |
995 | search a specific keyring, so using keyrings in this way is of limited utility. | |
996 | ||
997 | ||
76d8aeab DH |
998 | =================================== |
999 | NOTES ON ACCESSING PAYLOAD CONTENTS | |
1000 | =================================== | |
1001 | ||
1002 | The simplest payload is just a number in key->payload.value. In this case, | |
1003 | there's no need to indulge in RCU or locking when accessing the payload. | |
1004 | ||
1005 | More complex payload contents must be allocated and a pointer to them set in | |
1006 | key->payload.data. One of the following ways must be selected to access the | |
1007 | data: | |
1008 | ||
664cceb0 | 1009 | (1) Unmodifiable key type. |
76d8aeab DH |
1010 | |
1011 | If the key type does not have a modify method, then the key's payload can | |
1012 | be accessed without any form of locking, provided that it's known to be | |
1013 | instantiated (uninstantiated keys cannot be "found"). | |
1014 | ||
1015 | (2) The key's semaphore. | |
1016 | ||
1017 | The semaphore could be used to govern access to the payload and to control | |
1018 | the payload pointer. It must be write-locked for modifications and would | |
1019 | have to be read-locked for general access. The disadvantage of doing this | |
1020 | is that the accessor may be required to sleep. | |
1021 | ||
1022 | (3) RCU. | |
1023 | ||
1024 | RCU must be used when the semaphore isn't already held; if the semaphore | |
1025 | is held then the contents can't change under you unexpectedly as the | |
1026 | semaphore must still be used to serialise modifications to the key. The | |
1027 | key management code takes care of this for the key type. | |
1028 | ||
1029 | However, this means using: | |
1030 | ||
1031 | rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock() | |
1032 | ||
1033 | to read the pointer, and: | |
1034 | ||
1035 | rcu_dereference() ... rcu_assign_pointer() ... call_rcu() | |
1036 | ||
1037 | to set the pointer and dispose of the old contents after a grace period. | |
1038 | Note that only the key type should ever modify a key's payload. | |
1039 | ||
1040 | Furthermore, an RCU controlled payload must hold a struct rcu_head for the | |
1041 | use of call_rcu() and, if the payload is of variable size, the length of | |
1042 | the payload. key->datalen cannot be relied upon to be consistent with the | |
1043 | payload just dereferenced if the key's semaphore is not held. | |
1044 | ||
1045 | ||
1da177e4 LT |
1046 | =================== |
1047 | DEFINING A KEY TYPE | |
1048 | =================== | |
1049 | ||
1050 | A kernel service may want to define its own key type. For instance, an AFS | |
1051 | filesystem might want to define a Kerberos 5 ticket key type. To do this, it | |
76181c13 DH |
1052 | author fills in a key_type struct and registers it with the system. |
1053 | ||
1054 | Source files that implement key types should include the following header file: | |
1055 | ||
1056 | <linux/key-type.h> | |
1da177e4 LT |
1057 | |
1058 | The structure has a number of fields, some of which are mandatory: | |
1059 | ||
1060 | (*) const char *name | |
1061 | ||
1062 | The name of the key type. This is used to translate a key type name | |
1063 | supplied by userspace into a pointer to the structure. | |
1064 | ||
1065 | ||
1066 | (*) size_t def_datalen | |
1067 | ||
1068 | This is optional - it supplies the default payload data length as | |
1069 | contributed to the quota. If the key type's payload is always or almost | |
1070 | always the same size, then this is a more efficient way to do things. | |
1071 | ||
1072 | The data length (and quota) on a particular key can always be changed | |
1073 | during instantiation or update by calling: | |
1074 | ||
1075 | int key_payload_reserve(struct key *key, size_t datalen); | |
1076 | ||
76d8aeab DH |
1077 | With the revised data length. Error EDQUOT will be returned if this is not |
1078 | viable. | |
1da177e4 LT |
1079 | |
1080 | ||
b9fffa38 DH |
1081 | (*) int (*vet_description)(const char *description); |
1082 | ||
1083 | This optional method is called to vet a key description. If the key type | |
1084 | doesn't approve of the key description, it may return an error, otherwise | |
1085 | it should return 0. | |
1086 | ||
1087 | ||
1da177e4 LT |
1088 | (*) int (*instantiate)(struct key *key, const void *data, size_t datalen); |
1089 | ||
1090 | This method is called to attach a payload to a key during construction. | |
76d8aeab DH |
1091 | The payload attached need not bear any relation to the data passed to this |
1092 | function. | |
1da177e4 LT |
1093 | |
1094 | If the amount of data attached to the key differs from the size in | |
1095 | keytype->def_datalen, then key_payload_reserve() should be called. | |
1096 | ||
1097 | This method does not have to lock the key in order to attach a payload. | |
1098 | The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents | |
1099 | anything else from gaining access to the key. | |
1100 | ||
76d8aeab | 1101 | It is safe to sleep in this method. |
1da177e4 LT |
1102 | |
1103 | ||
1da177e4 LT |
1104 | (*) int (*update)(struct key *key, const void *data, size_t datalen); |
1105 | ||
76d8aeab DH |
1106 | If this type of key can be updated, then this method should be provided. |
1107 | It is called to update a key's payload from the blob of data provided. | |
1da177e4 LT |
1108 | |
1109 | key_payload_reserve() should be called if the data length might change | |
76d8aeab DH |
1110 | before any changes are actually made. Note that if this succeeds, the type |
1111 | is committed to changing the key because it's already been altered, so all | |
1112 | memory allocation must be done first. | |
1113 | ||
1114 | The key will have its semaphore write-locked before this method is called, | |
1115 | but this only deters other writers; any changes to the key's payload must | |
1116 | be made under RCU conditions, and call_rcu() must be used to dispose of | |
1117 | the old payload. | |
1da177e4 | 1118 | |
76d8aeab DH |
1119 | key_payload_reserve() should be called before the changes are made, but |
1120 | after all allocations and other potentially failing function calls are | |
1121 | made. | |
1da177e4 | 1122 | |
76d8aeab | 1123 | It is safe to sleep in this method. |
1da177e4 LT |
1124 | |
1125 | ||
1126 | (*) int (*match)(const struct key *key, const void *desc); | |
1127 | ||
1128 | This method is called to match a key against a description. It should | |
1129 | return non-zero if the two match, zero if they don't. | |
1130 | ||
1131 | This method should not need to lock the key in any way. The type and | |
1132 | description can be considered invariant, and the payload should not be | |
1133 | accessed (the key may not yet be instantiated). | |
1134 | ||
1135 | It is not safe to sleep in this method; the caller may hold spinlocks. | |
1136 | ||
1137 | ||
04c567d9 DH |
1138 | (*) void (*revoke)(struct key *key); |
1139 | ||
1140 | This method is optional. It is called to discard part of the payload | |
1141 | data upon a key being revoked. The caller will have the key semaphore | |
1142 | write-locked. | |
1143 | ||
1144 | It is safe to sleep in this method, though care should be taken to avoid | |
1145 | a deadlock against the key semaphore. | |
1146 | ||
1147 | ||
1da177e4 LT |
1148 | (*) void (*destroy)(struct key *key); |
1149 | ||
76d8aeab DH |
1150 | This method is optional. It is called to discard the payload data on a key |
1151 | when it is being destroyed. | |
1da177e4 | 1152 | |
76d8aeab DH |
1153 | This method does not need to lock the key to access the payload; it can |
1154 | consider the key as being inaccessible at this time. Note that the key's | |
1155 | type may have been changed before this function is called. | |
1da177e4 LT |
1156 | |
1157 | It is not safe to sleep in this method; the caller may hold spinlocks. | |
1158 | ||
1159 | ||
1160 | (*) void (*describe)(const struct key *key, struct seq_file *p); | |
1161 | ||
1162 | This method is optional. It is called during /proc/keys reading to | |
1163 | summarise a key's description and payload in text form. | |
1164 | ||
76d8aeab DH |
1165 | This method will be called with the RCU read lock held. rcu_dereference() |
1166 | should be used to read the payload pointer if the payload is to be | |
1167 | accessed. key->datalen cannot be trusted to stay consistent with the | |
1168 | contents of the payload. | |
1169 | ||
1170 | The description will not change, though the key's state may. | |
1171 | ||
1172 | It is not safe to sleep in this method; the RCU read lock is held by the | |
1173 | caller. | |
1da177e4 LT |
1174 | |
1175 | ||
1176 | (*) long (*read)(const struct key *key, char __user *buffer, size_t buflen); | |
1177 | ||
1178 | This method is optional. It is called by KEYCTL_READ to translate the | |
76d8aeab DH |
1179 | key's payload into something a blob of data for userspace to deal with. |
1180 | Ideally, the blob should be in the same format as that passed in to the | |
1181 | instantiate and update methods. | |
1da177e4 LT |
1182 | |
1183 | If successful, the blob size that could be produced should be returned | |
1184 | rather than the size copied. | |
1185 | ||
76d8aeab DH |
1186 | This method will be called with the key's semaphore read-locked. This will |
1187 | prevent the key's payload changing. It is not necessary to use RCU locking | |
1188 | when accessing the key's payload. It is safe to sleep in this method, such | |
1189 | as might happen when the userspace buffer is accessed. | |
1da177e4 LT |
1190 | |
1191 | ||
76181c13 | 1192 | (*) int (*request_key)(struct key_construction *cons, const char *op, |
4e54f085 DH |
1193 | void *aux); |
1194 | ||
76181c13 DH |
1195 | This method is optional. If provided, request_key() and friends will |
1196 | invoke this function rather than upcalling to /sbin/request-key to operate | |
1197 | upon a key of this type. | |
1198 | ||
1199 | The aux parameter is as passed to request_key_async_with_auxdata() and | |
1200 | similar or is NULL otherwise. Also passed are the construction record for | |
1201 | the key to be operated upon and the operation type (currently only | |
1202 | "create"). | |
1203 | ||
1204 | This method is permitted to return before the upcall is complete, but the | |
1205 | following function must be called under all circumstances to complete the | |
1206 | instantiation process, whether or not it succeeds, whether or not there's | |
1207 | an error: | |
1208 | ||
1209 | void complete_request_key(struct key_construction *cons, int error); | |
1210 | ||
1211 | The error parameter should be 0 on success, -ve on error. The | |
1212 | construction record is destroyed by this action and the authorisation key | |
1213 | will be revoked. If an error is indicated, the key under construction | |
1214 | will be negatively instantiated if it wasn't already instantiated. | |
1215 | ||
1216 | If this method returns an error, that error will be returned to the | |
1217 | caller of request_key*(). complete_request_key() must be called prior to | |
1218 | returning. | |
1219 | ||
1220 | The key under construction and the authorisation key can be found in the | |
1221 | key_construction struct pointed to by cons: | |
1222 | ||
1223 | (*) struct key *key; | |
1224 | ||
1225 | The key under construction. | |
4e54f085 | 1226 | |
76181c13 | 1227 | (*) struct key *authkey; |
4e54f085 | 1228 | |
76181c13 | 1229 | The authorisation key. |
4e54f085 DH |
1230 | |
1231 | ||
1da177e4 LT |
1232 | ============================ |
1233 | REQUEST-KEY CALLBACK SERVICE | |
1234 | ============================ | |
1235 | ||
1236 | To create a new key, the kernel will attempt to execute the following command | |
1237 | line: | |
1238 | ||
1239 | /sbin/request-key create <key> <uid> <gid> \ | |
1240 | <threadring> <processring> <sessionring> <callout_info> | |
1241 | ||
1242 | <key> is the key being constructed, and the three keyrings are the process | |
1243 | keyrings from the process that caused the search to be issued. These are | |
1244 | included for two reasons: | |
1245 | ||
1246 | (1) There may be an authentication token in one of the keyrings that is | |
1247 | required to obtain the key, eg: a Kerberos Ticket-Granting Ticket. | |
1248 | ||
1249 | (2) The new key should probably be cached in one of these rings. | |
1250 | ||
1251 | This program should set it UID and GID to those specified before attempting to | |
1252 | access any more keys. It may then look around for a user specific process to | |
1253 | hand the request off to (perhaps a path held in placed in another key by, for | |
1254 | example, the KDE desktop manager). | |
1255 | ||
1256 | The program (or whatever it calls) should finish construction of the key by | |
ee009e4a DH |
1257 | calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to |
1258 | cache the key in one of the keyrings (probably the session ring) before | |
1259 | returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE | |
1260 | or KEYCTL_REJECT; this also permits the key to be cached in one of the | |
1261 | keyrings. | |
1da177e4 LT |
1262 | |
1263 | If it returns with the key remaining in the unconstructed state, the key will | |
1264 | be marked as being negative, it will be added to the session keyring, and an | |
1265 | error will be returned to the key requestor. | |
1266 | ||
76d8aeab DH |
1267 | Supplementary information may be provided from whoever or whatever invoked this |
1268 | service. This will be passed as the <callout_info> parameter. If no such | |
1da177e4 LT |
1269 | information was made available, then "-" will be passed as this parameter |
1270 | instead. | |
1271 | ||
1272 | ||
1273 | Similarly, the kernel may attempt to update an expired or a soon to expire key | |
1274 | by executing: | |
1275 | ||
1276 | /sbin/request-key update <key> <uid> <gid> \ | |
1277 | <threadring> <processring> <sessionring> | |
1278 | ||
1279 | In this case, the program isn't required to actually attach the key to a ring; | |
1280 | the rings are provided for reference. | |
5d135440 DH |
1281 | |
1282 | ||
1283 | ================== | |
1284 | GARBAGE COLLECTION | |
1285 | ================== | |
1286 | ||
1287 | Dead keys (for which the type has been removed) will be automatically unlinked | |
1288 | from those keyrings that point to them and deleted as soon as possible by a | |
1289 | background garbage collector. | |
1290 | ||
1291 | Similarly, revoked and expired keys will be garbage collected, but only after a | |
1292 | certain amount of time has passed. This time is set as a number of seconds in: | |
1293 | ||
1294 | /proc/sys/kernel/keys/gc_delay |