1============================ 2Kernel 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 7filesystems and other kernel services. 8 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.. contents:: :local: 20 21 22Key Overview 23============ 24 25In this context, keys represent units of cryptographic data, authentication 26tokens, keyrings, etc.. These are represented in the kernel by struct key. 27 28Each key has a number of attributes: 29 30 - A serial number. 31 - A type. 32 - A description (for matching a key in a search). 33 - Access control information. 34 - An expiry time. 35 - A payload. 36 - State. 37 38 39 * Each key is issued a serial number of type key_serial_t that is unique for 40 the lifetime of that key. All serial numbers are positive non-zero 32-bit 41 integers. 42 43 Userspace programs can use a key's serial numbers as a way to gain access 44 to it, subject to permission checking. 45 46 * Each key is of a defined "type". Types must be registered inside the 47 kernel by a kernel service (such as a filesystem) before keys of that type 48 can be added or used. Userspace programs cannot define new types directly. 49 50 Key types are represented in the kernel by struct key_type. This defines a 51 number of operations that can be performed on a key of that type. 52 53 Should a type be removed from the system, all the keys of that type will 54 be invalidated. 55 56 * Each key has a description. This should be a printable string. The key 57 type provides an operation to perform a match between the description on a 58 key and a criterion string. 59 60 * Each key has an owner user ID, a group ID and a permissions mask. These 61 are used to control what a process may do to a key from userspace, and 62 whether a kernel service will be able to find the key. 63 64 * Each key can be set to expire at a specific time by the key type's 65 instantiation function. Keys can also be immortal. 66 67 * Each key can have a payload. This is a quantity of data that represent the 68 actual "key". In the case of a keyring, this is a list of keys to which 69 the keyring links; in the case of a user-defined key, it's an arbitrary 70 blob of data. 71 72 Having a payload is not required; and the payload can, in fact, just be a 73 value stored in the struct key itself. 74 75 When a key is instantiated, the key type's instantiation function is 76 called with a blob of data, and that then creates the key's payload in 77 some way. 78 79 Similarly, when userspace wants to read back the contents of the key, if 80 permitted, another key type operation will be called to convert the key's 81 attached payload back into a blob of data. 82 83 * Each key can be in one of a number of basic states: 84 85 * Uninstantiated. The key exists, but does not have any data attached. 86 Keys being requested from userspace will be in this state. 87 88 * Instantiated. This is the normal state. The key is fully formed, and 89 has data attached. 90 91 * Negative. This is a relatively short-lived state. The key acts as a 92 note saying that a previous call out to userspace failed, and acts as 93 a throttle on key lookups. A negative key can be updated to a normal 94 state. 95 96 * Expired. Keys can have lifetimes set. If their lifetime is exceeded, 97 they traverse to this state. An expired key can be updated back to a 98 normal state. 99 100 * Revoked. A key is put in this state by userspace action. It can't be 101 found or operated upon (apart from by unlinking it). 102 103 * Dead. The key's type was unregistered, and so the key is now useless. 104 105Keys in the last three states are subject to garbage collection. See the 106section on "Garbage collection". 107 108 109Key Service Overview 110==================== 111 112The key service provides a number of features besides keys: 113 114 * The key service defines three special key types: 115 116 (+) "keyring" 117 118 Keyrings are special keys that contain a list of other keys. Keyring 119 lists can be modified using various system calls. Keyrings should not 120 be given a payload when created. 121 122 (+) "user" 123 124 A key of this type has a description and a payload that are arbitrary 125 blobs of data. These can be created, updated and read by userspace, 126 and aren't intended for use by kernel services. 127 128 (+) "logon" 129 130 Like a "user" key, a "logon" key has a payload that is an arbitrary 131 blob of data. It is intended as a place to store secrets which are 132 accessible to the kernel but not to userspace programs. 133 134 The description can be arbitrary, but must be prefixed with a non-zero 135 length string that describes the key "subclass". The subclass is 136 separated from the rest of the description by a ':'. "logon" keys can 137 be created and updated from userspace, but the payload is only 138 readable from kernel space. 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. 146 147 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. 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 176 files. The root user may also alter the quota limits through sysctl files 177 (see the section "New procfs files"). 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. 184 185 * There's a system call interface by which userspace programs can create and 186 manipulate keys and keyrings. 187 188 * There's a kernel interface by which services can register types and search 189 for keys. 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 198Key Access Permissions 199====================== 200 201Keys have an owner user ID, a group access ID, and a permissions mask. The mask 202has up to eight bits each for possessor, user, group and other access. Only 203six of each set of eight bits are defined. These permissions granted are: 204 205 * View 206 207 This permits a key or keyring's attributes to be viewed - including key 208 type and description. 209 210 * Read 211 212 This permits a key's payload to be viewed or a keyring's list of linked 213 keys. 214 215 * Write 216 217 This permits a key's payload to be instantiated or updated, or it allows a 218 link to be added to or removed from a keyring. 219 220 * Search 221 222 This permits keyrings to be searched and keys to be found. Searches can 223 only recurse into nested keyrings that have search permission set. 224 225 * Link 226 227 This permits a key or keyring to be linked to. To create a link from a 228 keyring to a key, a process must have Write permission on the keyring and 229 Link permission on the key. 230 231 * Set Attribute 232 233 This permits a key's UID, GID and permissions mask to be changed. 234 235For changing the ownership, group ID or permissions mask, being the owner of 236the key or having the sysadmin capability is sufficient. 237 238 239SELinux Support 240=============== 241 242The security class "key" has been added to SELinux so that mandatory access 243controls can be applied to keys created within various contexts. This support 244is preliminary, and is likely to change quite significantly in the near future. 245Currently, all of the basic permissions explained above are provided in SELinux 246as well; SELinux is simply invoked after all basic permission checks have been 247performed. 248 249The value of the file /proc/self/attr/keycreate influences the labeling of 250newly-created keys. If the contents of that file correspond to an SELinux 251security context, then the key will be assigned that context. Otherwise, the 252key will be assigned the current context of the task that invoked the key 253creation request. Tasks must be granted explicit permission to assign a 254particular context to newly-created keys, using the "create" permission in the 255key security class. 256 257The default keyrings associated with users will be labeled with the default 258context of the user if and only if the login programs have been instrumented to 259properly initialize keycreate during the login process. Otherwise, they will 260be labeled with the context of the login program itself. 261 262Note, however, that the default keyrings associated with the root user are 263labeled with the default kernel context, since they are created early in the 264boot process, before root has a chance to log in. 265 266The keyrings associated with new threads are each labeled with the context of 267their associated thread, and both session and process keyrings are handled 268similarly. 269 270 271New ProcFS Files 272================ 273 274Two files have been added to procfs by which an administrator can find out 275about the status of the key service: 276 277 * /proc/keys 278 279 This lists the keys that are currently viewable by the task reading the 280 file, giving information about their type, description and permissions. 281 It is not possible to view the payload of the key this way, though some 282 information about it may be given. 283 284 The only keys included in the list are those that grant View permission to 285 the reading process whether or not it possesses them. Note that LSM 286 security checks are still performed, and may further filter out keys that 287 the current process is not authorised to view. 288 289 The contents of the file look like this:: 290 291 SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY 292 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4 293 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty 294 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty 295 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty 296 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4 297 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty 298 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0 299 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0 300 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0 301 302 The flags are:: 303 304 I Instantiated 305 R Revoked 306 D Dead 307 Q Contributes to user's quota 308 U Under construction by callback to userspace 309 N Negative key 310 311 312 * /proc/key-users 313 314 This file lists the tracking data for each user that has at least one key 315 on the system. Such data includes quota information and statistics:: 316 317 [root@andromeda root]# cat /proc/key-users 318 0: 46 45/45 1/100 13/10000 319 29: 2 2/2 2/100 40/10000 320 32: 2 2/2 2/100 40/10000 321 38: 2 2/2 2/100 40/10000 322 323 The format of each line is:: 324 325 <UID>: User ID to which this applies 326 <usage> Structure refcount 327 <inst>/<keys> Total number of keys and number instantiated 328 <keys>/<max> Key count quota 329 <bytes>/<max> Key size quota 330 331 332Four new sysctl files have been added also for the purpose of controlling the 333quota limits on keys: 334 335 * /proc/sys/kernel/keys/root_maxkeys 336 /proc/sys/kernel/keys/root_maxbytes 337 338 These files hold the maximum number of keys that root may have and the 339 maximum total number of bytes of data that root may have stored in those 340 keys. 341 342 * /proc/sys/kernel/keys/maxkeys 343 /proc/sys/kernel/keys/maxbytes 344 345 These files hold the maximum number of keys that each non-root user may 346 have and the maximum total number of bytes of data that each of those 347 users may have stored in their keys. 348 349Root may alter these by writing each new limit as a decimal number string to 350the appropriate file. 351 352 353Userspace System Call Interface 354=============================== 355 356Userspace can manipulate keys directly through three new syscalls: add_key, 357request_key and keyctl. The latter provides a number of functions for 358manipulating keys. 359 360When referring to a key directly, userspace programs should use the key's 361serial number (a positive 32-bit integer). However, there are some special 362values available for referring to special keys and keyrings that relate to the 363process making the call:: 364 365 CONSTANT VALUE KEY REFERENCED 366 ============================== ====== =========================== 367 KEY_SPEC_THREAD_KEYRING -1 thread-specific keyring 368 KEY_SPEC_PROCESS_KEYRING -2 process-specific keyring 369 KEY_SPEC_SESSION_KEYRING -3 session-specific keyring 370 KEY_SPEC_USER_KEYRING -4 UID-specific keyring 371 KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring 372 KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring 373 KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key() 374 authorisation key 375 376 377The main syscalls are: 378 379 * Create a new key of given type, description and payload and add it to the 380 nominated keyring:: 381 382 key_serial_t add_key(const char *type, const char *desc, 383 const void *payload, size_t plen, 384 key_serial_t keyring); 385 386 If a key of the same type and description as that proposed already exists 387 in the keyring, this will try to update it with the given payload, or it 388 will return error EEXIST if that function is not supported by the key 389 type. The process must also have permission to write to the key to be able 390 to update it. The new key will have all user permissions granted and no 391 group or third party permissions. 392 393 Otherwise, this will attempt to create a new key of the specified type and 394 description, and to instantiate it with the supplied payload and attach it 395 to the keyring. In this case, an error will be generated if the process 396 does not have permission to write to the keyring. 397 398 If the key type supports it, if the description is NULL or an empty 399 string, the key type will try and generate a description from the content 400 of the payload. 401 402 The payload is optional, and the pointer can be NULL if not required by 403 the type. The payload is plen in size, and plen can be zero for an empty 404 payload. 405 406 A new keyring can be generated by setting type "keyring", the keyring name 407 as the description (or NULL) and setting the payload to NULL. 408 409 User defined keys can be created by specifying type "user". It is 410 recommended that a user defined key's description by prefixed with a type 411 ID and a colon, such as "krb5tgt:" for a Kerberos 5 ticket granting 412 ticket. 413 414 Any other type must have been registered with the kernel in advance by a 415 kernel service such as a filesystem. 416 417 The ID of the new or updated key is returned if successful. 418 419 420 * Search the process's keyrings for a key, potentially calling out to 421 userspace to create it:: 422 423 key_serial_t request_key(const char *type, const char *description, 424 const char *callout_info, 425 key_serial_t dest_keyring); 426 427 This function searches all the process's keyrings in the order thread, 428 process, session for a matching key. This works very much like 429 KEYCTL_SEARCH, including the optional attachment of the discovered key to 430 a keyring. 431 432 If a key cannot be found, and if callout_info is not NULL, then 433 /sbin/request-key will be invoked in an attempt to obtain a key. The 434 callout_info string will be passed as an argument to the program. 435 436 See also Documentation/security/keys/request-key.rst. 437 438 439The keyctl syscall functions are: 440 441 * Map a special key ID to a real key ID for this process:: 442 443 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id, 444 int create); 445 446 The special key specified by "id" is looked up (with the key being created 447 if necessary) and the ID of the key or keyring thus found is returned if 448 it exists. 449 450 If the key does not yet exist, the key will be created if "create" is 451 non-zero; and the error ENOKEY will be returned if "create" is zero. 452 453 454 * Replace the session keyring this process subscribes to with a new one:: 455 456 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name); 457 458 If name is NULL, an anonymous keyring is created attached to the process 459 as its session keyring, displacing the old session keyring. 460 461 If name is not NULL, if a keyring of that name exists, the process 462 attempts to attach it as the session keyring, returning an error if that 463 is not permitted; otherwise a new keyring of that name is created and 464 attached as the session keyring. 465 466 To attach to a named keyring, the keyring must have search permission for 467 the process's ownership. 468 469 The ID of the new session keyring is returned if successful. 470 471 472 * Update the specified key:: 473 474 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload, 475 size_t plen); 476 477 This will try to update the specified key with the given payload, or it 478 will return error EOPNOTSUPP if that function is not supported by the key 479 type. The process must also have permission to write to the key to be able 480 to update it. 481 482 The payload is of length plen, and may be absent or empty as for 483 add_key(). 484 485 486 * Revoke a key:: 487 488 long keyctl(KEYCTL_REVOKE, key_serial_t key); 489 490 This makes a key unavailable for further operations. Further attempts to 491 use the key will be met with error EKEYREVOKED, and the key will no longer 492 be findable. 493 494 495 * Change the ownership of a key:: 496 497 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid); 498 499 This function permits a key's owner and group ID to be changed. Either one 500 of uid or gid can be set to -1 to suppress that change. 501 502 Only the superuser can change a key's owner to something other than the 503 key's current owner. Similarly, only the superuser can change a key's 504 group ID to something other than the calling process's group ID or one of 505 its group list members. 506 507 508 * Change the permissions mask on a key:: 509 510 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm); 511 512 This function permits the owner of a key or the superuser to change the 513 permissions mask on a key. 514 515 Only bits the available bits are permitted; if any other bits are set, 516 error EINVAL will be returned. 517 518 519 * Describe a key:: 520 521 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer, 522 size_t buflen); 523 524 This function returns a summary of the key's attributes (but not its 525 payload data) as a string in the buffer provided. 526 527 Unless there's an error, it always returns the amount of data it could 528 produce, even if that's too big for the buffer, but it won't copy more 529 than requested to userspace. If the buffer pointer is NULL then no copy 530 will take place. 531 532 A process must have view permission on the key for this function to be 533 successful. 534 535 If successful, a string is placed in the buffer in the following format:: 536 537 <type>;<uid>;<gid>;<perm>;<description> 538 539 Where type and description are strings, uid and gid are decimal, and perm 540 is hexadecimal. A NUL character is included at the end of the string if 541 the buffer is sufficiently big. 542 543 This can be parsed with:: 544 545 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc); 546 547 548 * Clear out a keyring:: 549 550 long keyctl(KEYCTL_CLEAR, key_serial_t keyring); 551 552 This function clears the list of keys attached to a keyring. The calling 553 process must have write permission on the keyring, and it must be a 554 keyring (or else error ENOTDIR will result). 555 556 This function can also be used to clear special kernel keyrings if they 557 are appropriately marked if the user has CAP_SYS_ADMIN capability. The 558 DNS resolver cache keyring is an example of this. 559 560 561 * Link a key into a keyring:: 562 563 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key); 564 565 This function creates a link from the keyring to the key. The process must 566 have write permission on the keyring and must have link permission on the 567 key. 568 569 Should the keyring not be a keyring, error ENOTDIR will result; and if the 570 keyring is full, error ENFILE will result. 571 572 The link procedure checks the nesting of the keyrings, returning ELOOP if 573 it appears too deep or EDEADLK if the link would introduce a cycle. 574 575 Any links within the keyring to keys that match the new key in terms of 576 type and description will be discarded from the keyring as the new one is 577 added. 578 579 580 * Move a key from one keyring to another:: 581 582 long keyctl(KEYCTL_MOVE, 583 key_serial_t id, 584 key_serial_t from_ring_id, 585 key_serial_t to_ring_id, 586 unsigned int flags); 587 588 Move the key specified by "id" from the keyring specified by 589 "from_ring_id" to the keyring specified by "to_ring_id". If the two 590 keyrings are the same, nothing is done. 591 592 "flags" can have KEYCTL_MOVE_EXCL set in it to cause the operation to fail 593 with EEXIST if a matching key exists in the destination keyring, otherwise 594 such a key will be replaced. 595 596 A process must have link permission on the key for this function to be 597 successful and write permission on both keyrings. Any errors that can 598 occur from KEYCTL_LINK also apply on the destination keyring here. 599 600 601 * Unlink a key or keyring from another keyring:: 602 603 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key); 604 605 This function looks through the keyring for the first link to the 606 specified key, and removes it if found. Subsequent links to that key are 607 ignored. The process must have write permission on the keyring. 608 609 If the keyring is not a keyring, error ENOTDIR will result; and if the key 610 is not present, error ENOENT will be the result. 611 612 613 * Search a keyring tree for a key:: 614 615 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring, 616 const char *type, const char *description, 617 key_serial_t dest_keyring); 618 619 This searches the keyring tree headed by the specified keyring until a key 620 is found that matches the type and description criteria. Each keyring is 621 checked for keys before recursion into its children occurs. 622 623 The process must have search permission on the top level keyring, or else 624 error EACCES will result. Only keyrings that the process has search 625 permission on will be recursed into, and only keys and keyrings for which 626 a process has search permission can be matched. If the specified keyring 627 is not a keyring, ENOTDIR will result. 628 629 If the search succeeds, the function will attempt to link the found key 630 into the destination keyring if one is supplied (non-zero ID). All the 631 constraints applicable to KEYCTL_LINK apply in this case too. 632 633 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search 634 fails. On success, the resulting key ID will be returned. 635 636 637 * Read the payload data from a key:: 638 639 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer, 640 size_t buflen); 641 642 This function attempts to read the payload data from the specified key 643 into the buffer. The process must have read permission on the key to 644 succeed. 645 646 The returned data will be processed for presentation by the key type. For 647 instance, a keyring will return an array of key_serial_t entries 648 representing the IDs of all the keys to which it is subscribed. The user 649 defined key type will return its data as is. If a key type does not 650 implement this function, error EOPNOTSUPP will result. 651 652 If the specified buffer is too small, then the size of the buffer required 653 will be returned. Note that in this case, the contents of the buffer may 654 have been overwritten in some undefined way. 655 656 Otherwise, on success, the function will return the amount of data copied 657 into the buffer. 658 659 * Instantiate a partially constructed key:: 660 661 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key, 662 const void *payload, size_t plen, 663 key_serial_t keyring); 664 long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key, 665 const struct iovec *payload_iov, unsigned ioc, 666 key_serial_t keyring); 667 668 If the kernel calls back to userspace to complete the instantiation of a 669 key, userspace should use this call to supply data for the key before the 670 invoked process returns, or else the key will be marked negative 671 automatically. 672 673 The process must have write access on the key to be able to instantiate 674 it, and the key must be uninstantiated. 675 676 If a keyring is specified (non-zero), the key will also be linked into 677 that keyring, however all the constraints applying in KEYCTL_LINK apply in 678 this case too. 679 680 The payload and plen arguments describe the payload data as for add_key(). 681 682 The payload_iov and ioc arguments describe the payload data in an iovec 683 array instead of a single buffer. 684 685 686 * Negatively instantiate a partially constructed key:: 687 688 long keyctl(KEYCTL_NEGATE, key_serial_t key, 689 unsigned timeout, key_serial_t keyring); 690 long keyctl(KEYCTL_REJECT, key_serial_t key, 691 unsigned timeout, unsigned error, key_serial_t keyring); 692 693 If the kernel calls back to userspace to complete the instantiation of a 694 key, userspace should use this call mark the key as negative before the 695 invoked process returns if it is unable to fulfill the request. 696 697 The process must have write access on the key to be able to instantiate 698 it, and the key must be uninstantiated. 699 700 If a keyring is specified (non-zero), the key will also be linked into 701 that keyring, however all the constraints applying in KEYCTL_LINK apply in 702 this case too. 703 704 If the key is rejected, future searches for it will return the specified 705 error code until the rejected key expires. Negating the key is the same 706 as rejecting the key with ENOKEY as the error code. 707 708 709 * Set the default request-key destination keyring:: 710 711 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl); 712 713 This sets the default keyring to which implicitly requested keys will be 714 attached for this thread. reqkey_defl should be one of these constants:: 715 716 CONSTANT VALUE NEW DEFAULT KEYRING 717 ====================================== ====== ======================= 718 KEY_REQKEY_DEFL_NO_CHANGE -1 No change 719 KEY_REQKEY_DEFL_DEFAULT 0 Default[1] 720 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring 721 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring 722 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring 723 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring 724 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring 725 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring 726 727 The old default will be returned if successful and error EINVAL will be 728 returned if reqkey_defl is not one of the above values. 729 730 The default keyring can be overridden by the keyring indicated to the 731 request_key() system call. 732 733 Note that this setting is inherited across fork/exec. 734 735 [1] The default is: the thread keyring if there is one, otherwise 736 the process keyring if there is one, otherwise the session keyring if 737 there is one, otherwise the user default session keyring. 738 739 740 * Set the timeout on a key:: 741 742 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout); 743 744 This sets or clears the timeout on a key. The timeout can be 0 to clear 745 the timeout or a number of seconds to set the expiry time that far into 746 the future. 747 748 The process must have attribute modification access on a key to set its 749 timeout. Timeouts may not be set with this function on negative, revoked 750 or expired keys. 751 752 753 * Assume the authority granted to instantiate a key:: 754 755 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key); 756 757 This assumes or divests the authority required to instantiate the 758 specified key. Authority can only be assumed if the thread has the 759 authorisation key associated with the specified key in its keyrings 760 somewhere. 761 762 Once authority is assumed, searches for keys will also search the 763 requester's keyrings using the requester's security label, UID, GID and 764 groups. 765 766 If the requested authority is unavailable, error EPERM will be returned, 767 likewise if the authority has been revoked because the target key is 768 already instantiated. 769 770 If the specified key is 0, then any assumed authority will be divested. 771 772 The assumed authoritative key is inherited across fork and exec. 773 774 775 * Get the LSM security context attached to a key:: 776 777 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer, 778 size_t buflen) 779 780 This function returns a string that represents the LSM security context 781 attached to a key in the buffer provided. 782 783 Unless there's an error, it always returns the amount of data it could 784 produce, even if that's too big for the buffer, but it won't copy more 785 than requested to userspace. If the buffer pointer is NULL then no copy 786 will take place. 787 788 A NUL character is included at the end of the string if the buffer is 789 sufficiently big. This is included in the returned count. If no LSM is 790 in force then an empty string will be returned. 791 792 A process must have view permission on the key for this function to be 793 successful. 794 795 796 * Install the calling process's session keyring on its parent:: 797 798 long keyctl(KEYCTL_SESSION_TO_PARENT); 799 800 This functions attempts to install the calling process's session keyring 801 on to the calling process's parent, replacing the parent's current session 802 keyring. 803 804 The calling process must have the same ownership as its parent, the 805 keyring must have the same ownership as the calling process, the calling 806 process must have LINK permission on the keyring and the active LSM module 807 mustn't deny permission, otherwise error EPERM will be returned. 808 809 Error ENOMEM will be returned if there was insufficient memory to complete 810 the operation, otherwise 0 will be returned to indicate success. 811 812 The keyring will be replaced next time the parent process leaves the 813 kernel and resumes executing userspace. 814 815 816 * Invalidate a key:: 817 818 long keyctl(KEYCTL_INVALIDATE, key_serial_t key); 819 820 This function marks a key as being invalidated and then wakes up the 821 garbage collector. The garbage collector immediately removes invalidated 822 keys from all keyrings and deletes the key when its reference count 823 reaches zero. 824 825 Keys that are marked invalidated become invisible to normal key operations 826 immediately, though they are still visible in /proc/keys until deleted 827 (they're marked with an 'i' flag). 828 829 A process must have search permission on the key for this function to be 830 successful. 831 832 * Compute a Diffie-Hellman shared secret or public key:: 833 834 long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params, 835 char *buffer, size_t buflen, struct keyctl_kdf_params *kdf); 836 837 The params struct contains serial numbers for three keys:: 838 839 - The prime, p, known to both parties 840 - The local private key 841 - The base integer, which is either a shared generator or the 842 remote public key 843 844 The value computed is:: 845 846 result = base ^ private (mod prime) 847 848 If the base is the shared generator, the result is the local 849 public key. If the base is the remote public key, the result is 850 the shared secret. 851 852 If the parameter kdf is NULL, the following applies: 853 854 - The buffer length must be at least the length of the prime, or zero. 855 856 - If the buffer length is nonzero, the length of the result is 857 returned when it is successfully calculated and copied in to the 858 buffer. When the buffer length is zero, the minimum required 859 buffer length is returned. 860 861 The kdf parameter allows the caller to apply a key derivation function 862 (KDF) on the Diffie-Hellman computation where only the result 863 of the KDF is returned to the caller. The KDF is characterized with 864 struct keyctl_kdf_params as follows: 865 866 - ``char *hashname`` specifies the NUL terminated string identifying 867 the hash used from the kernel crypto API and applied for the KDF 868 operation. The KDF implemenation complies with SP800-56A as well 869 as with SP800-108 (the counter KDF). 870 871 - ``char *otherinfo`` specifies the OtherInfo data as documented in 872 SP800-56A section 5.8.1.2. The length of the buffer is given with 873 otherinfolen. The format of OtherInfo is defined by the caller. 874 The otherinfo pointer may be NULL if no OtherInfo shall be used. 875 876 This function will return error EOPNOTSUPP if the key type is not 877 supported, error ENOKEY if the key could not be found, or error 878 EACCES if the key is not readable by the caller. In addition, the 879 function will return EMSGSIZE when the parameter kdf is non-NULL 880 and either the buffer length or the OtherInfo length exceeds the 881 allowed length. 882 883 884 * Restrict keyring linkage:: 885 886 long keyctl(KEYCTL_RESTRICT_KEYRING, key_serial_t keyring, 887 const char *type, const char *restriction); 888 889 An existing keyring can restrict linkage of additional keys by evaluating 890 the contents of the key according to a restriction scheme. 891 892 "keyring" is the key ID for an existing keyring to apply a restriction 893 to. It may be empty or may already have keys linked. Existing linked keys 894 will remain in the keyring even if the new restriction would reject them. 895 896 "type" is a registered key type. 897 898 "restriction" is a string describing how key linkage is to be restricted. 899 The format varies depending on the key type, and the string is passed to 900 the lookup_restriction() function for the requested type. It may specify 901 a method and relevant data for the restriction such as signature 902 verification or constraints on key payload. If the requested key type is 903 later unregistered, no keys may be added to the keyring after the key type 904 is removed. 905 906 To apply a keyring restriction the process must have Set Attribute 907 permission and the keyring must not be previously restricted. 908 909 One application of restricted keyrings is to verify X.509 certificate 910 chains or individual certificate signatures using the asymmetric key type. 911 See Documentation/crypto/asymmetric-keys.txt for specific restrictions 912 applicable to the asymmetric key type. 913 914 915 * Query an asymmetric key:: 916 917 long keyctl(KEYCTL_PKEY_QUERY, 918 key_serial_t key_id, unsigned long reserved, 919 struct keyctl_pkey_query *info); 920 921 Get information about an asymmetric key. The information is returned in 922 the keyctl_pkey_query struct:: 923 924 __u32 supported_ops; 925 __u32 key_size; 926 __u16 max_data_size; 927 __u16 max_sig_size; 928 __u16 max_enc_size; 929 __u16 max_dec_size; 930 __u32 __spare[10]; 931 932 ``supported_ops`` contains a bit mask of flags indicating which ops are 933 supported. This is constructed from a bitwise-OR of:: 934 935 KEYCTL_SUPPORTS_{ENCRYPT,DECRYPT,SIGN,VERIFY} 936 937 ``key_size`` indicated the size of the key in bits. 938 939 ``max_*_size`` indicate the maximum sizes in bytes of a blob of data to be 940 signed, a signature blob, a blob to be encrypted and a blob to be 941 decrypted. 942 943 ``__spare[]`` must be set to 0. This is intended for future use to hand 944 over one or more passphrases needed unlock a key. 945 946 If successful, 0 is returned. If the key is not an asymmetric key, 947 EOPNOTSUPP is returned. 948 949 950 * Encrypt, decrypt, sign or verify a blob using an asymmetric key:: 951 952 long keyctl(KEYCTL_PKEY_ENCRYPT, 953 const struct keyctl_pkey_params *params, 954 const char *info, 955 const void *in, 956 void *out); 957 958 long keyctl(KEYCTL_PKEY_DECRYPT, 959 const struct keyctl_pkey_params *params, 960 const char *info, 961 const void *in, 962 void *out); 963 964 long keyctl(KEYCTL_PKEY_SIGN, 965 const struct keyctl_pkey_params *params, 966 const char *info, 967 const void *in, 968 void *out); 969 970 long keyctl(KEYCTL_PKEY_VERIFY, 971 const struct keyctl_pkey_params *params, 972 const char *info, 973 const void *in, 974 const void *in2); 975 976 Use an asymmetric key to perform a public-key cryptographic operation a 977 blob of data. For encryption and verification, the asymmetric key may 978 only need the public parts to be available, but for decryption and signing 979 the private parts are required also. 980 981 The parameter block pointed to by params contains a number of integer 982 values:: 983 984 __s32 key_id; 985 __u32 in_len; 986 __u32 out_len; 987 __u32 in2_len; 988 989 ``key_id`` is the ID of the asymmetric key to be used. ``in_len`` and 990 ``in2_len`` indicate the amount of data in the in and in2 buffers and 991 ``out_len`` indicates the size of the out buffer as appropriate for the 992 above operations. 993 994 For a given operation, the in and out buffers are used as follows:: 995 996 Operation ID in,in_len out,out_len in2,in2_len 997 ======================= =============== =============== =============== 998 KEYCTL_PKEY_ENCRYPT Raw data Encrypted data - 999 KEYCTL_PKEY_DECRYPT Encrypted data Raw data - 1000 KEYCTL_PKEY_SIGN Raw data Signature - 1001 KEYCTL_PKEY_VERIFY Raw data - Signature 1002 1003 ``info`` is a string of key=value pairs that supply supplementary 1004 information. These include: 1005 1006 ``enc=<encoding>`` The encoding of the encrypted/signature blob. This 1007 can be "pkcs1" for RSASSA-PKCS1-v1.5 or 1008 RSAES-PKCS1-v1.5; "pss" for "RSASSA-PSS"; "oaep" for 1009 "RSAES-OAEP". If omitted or is "raw", the raw output 1010 of the encryption function is specified. 1011 1012 ``hash=<algo>`` If the data buffer contains the output of a hash 1013 function and the encoding includes some indication of 1014 which hash function was used, the hash function can be 1015 specified with this, eg. "hash=sha256". 1016 1017 The ``__spare[]`` space in the parameter block must be set to 0. This is 1018 intended, amongst other things, to allow the passing of passphrases 1019 required to unlock a key. 1020 1021 If successful, encrypt, decrypt and sign all return the amount of data 1022 written into the output buffer. Verification returns 0 on success. 1023 1024 1025Kernel Services 1026=============== 1027 1028The kernel services for key management are fairly simple to deal with. They can 1029be broken down into two areas: keys and key types. 1030 1031Dealing with keys is fairly straightforward. Firstly, the kernel service 1032registers its type, then it searches for a key of that type. It should retain 1033the key as long as it has need of it, and then it should release it. For a 1034filesystem or device file, a search would probably be performed during the open 1035call, and the key released upon close. How to deal with conflicting keys due to 1036two different users opening the same file is left to the filesystem author to 1037solve. 1038 1039To access the key manager, the following header must be #included:: 1040 1041 <linux/key.h> 1042 1043Specific key types should have a header file under include/keys/ that should be 1044used to access that type. For keys of type "user", for example, that would be:: 1045 1046 <keys/user-type.h> 1047 1048Note that there are two different types of pointers to keys that may be 1049encountered: 1050 1051 * struct key * 1052 1053 This simply points to the key structure itself. Key structures will be at 1054 least four-byte aligned. 1055 1056 * key_ref_t 1057 1058 This is equivalent to a ``struct key *``, but the least significant bit is set 1059 if the caller "possesses" the key. By "possession" it is meant that the 1060 calling processes has a searchable link to the key from one of its 1061 keyrings. There are three functions for dealing with these:: 1062 1063 key_ref_t make_key_ref(const struct key *key, bool possession); 1064 1065 struct key *key_ref_to_ptr(const key_ref_t key_ref); 1066 1067 bool is_key_possessed(const key_ref_t key_ref); 1068 1069 The first function constructs a key reference from a key pointer and 1070 possession information (which must be true or false). 1071 1072 The second function retrieves the key pointer from a reference and the 1073 third retrieves the possession flag. 1074 1075When accessing a key's payload contents, certain precautions must be taken to 1076prevent access vs modification races. See the section "Notes on accessing 1077payload contents" for more information. 1078 1079 * To search for a key, call:: 1080 1081 struct key *request_key(const struct key_type *type, 1082 const char *description, 1083 const char *callout_info); 1084 1085 This is used to request a key or keyring with a description that matches 1086 the description specified according to the key type's match_preparse() 1087 method. This permits approximate matching to occur. If callout_string is 1088 not NULL, then /sbin/request-key will be invoked in an attempt to obtain 1089 the key from userspace. In that case, callout_string will be passed as an 1090 argument to the program. 1091 1092 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be 1093 returned. 1094 1095 If successful, the key will have been attached to the default keyring for 1096 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING. 1097 1098 See also Documentation/security/keys/request-key.rst. 1099 1100 1101 * To search for a key, passing auxiliary data to the upcaller, call:: 1102 1103 struct key *request_key_with_auxdata(const struct key_type *type, 1104 const char *description, 1105 const void *callout_info, 1106 size_t callout_len, 1107 void *aux); 1108 1109 This is identical to request_key(), except that the auxiliary data is 1110 passed to the key_type->request_key() op if it exists, and the callout_info 1111 is a blob of length callout_len, if given (the length may be 0). 1112 1113 1114 * A key can be requested asynchronously by calling one of:: 1115 1116 struct key *request_key_async(const struct key_type *type, 1117 const char *description, 1118 const void *callout_info, 1119 size_t callout_len); 1120 1121 or:: 1122 1123 struct key *request_key_async_with_auxdata(const struct key_type *type, 1124 const char *description, 1125 const char *callout_info, 1126 size_t callout_len, 1127 void *aux); 1128 1129 which are asynchronous equivalents of request_key() and 1130 request_key_with_auxdata() respectively. 1131 1132 These two functions return with the key potentially still under 1133 construction. To wait for construction completion, the following should be 1134 called:: 1135 1136 int wait_for_key_construction(struct key *key, bool intr); 1137 1138 The function will wait for the key to finish being constructed and then 1139 invokes key_validate() to return an appropriate value to indicate the state 1140 of the key (0 indicates the key is usable). 1141 1142 If intr is true, then the wait can be interrupted by a signal, in which 1143 case error ERESTARTSYS will be returned. 1144 1145 1146 * When it is no longer required, the key should be released using:: 1147 1148 void key_put(struct key *key); 1149 1150 Or:: 1151 1152 void key_ref_put(key_ref_t key_ref); 1153 1154 These can be called from interrupt context. If CONFIG_KEYS is not set then 1155 the argument will not be parsed. 1156 1157 1158 * Extra references can be made to a key by calling one of the following 1159 functions:: 1160 1161 struct key *__key_get(struct key *key); 1162 struct key *key_get(struct key *key); 1163 1164 Keys so references will need to be disposed of by calling key_put() when 1165 they've been finished with. The key pointer passed in will be returned. 1166 1167 In the case of key_get(), if the pointer is NULL or CONFIG_KEYS is not set 1168 then the key will not be dereferenced and no increment will take place. 1169 1170 1171 * A key's serial number can be obtained by calling:: 1172 1173 key_serial_t key_serial(struct key *key); 1174 1175 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the 1176 latter case without parsing the argument). 1177 1178 1179 * If a keyring was found in the search, this can be further searched by:: 1180 1181 key_ref_t keyring_search(key_ref_t keyring_ref, 1182 const struct key_type *type, 1183 const char *description) 1184 1185 This searches the keyring tree specified for a matching key. Error ENOKEY 1186 is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful, 1187 the returned key will need to be released. 1188 1189 The possession attribute from the keyring reference is used to control 1190 access through the permissions mask and is propagated to the returned key 1191 reference pointer if successful. 1192 1193 1194 * A keyring can be created by:: 1195 1196 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid, 1197 const struct cred *cred, 1198 key_perm_t perm, 1199 struct key_restriction *restrict_link, 1200 unsigned long flags, 1201 struct key *dest); 1202 1203 This creates a keyring with the given attributes and returns it. If dest 1204 is not NULL, the new keyring will be linked into the keyring to which it 1205 points. No permission checks are made upon the destination keyring. 1206 1207 Error EDQUOT can be returned if the keyring would overload the quota (pass 1208 KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted 1209 towards the user's quota). Error ENOMEM can also be returned. 1210 1211 If restrict_link is not NULL, it should point to a structure that contains 1212 the function that will be called each time an attempt is made to link a 1213 key into the new keyring. The structure may also contain a key pointer 1214 and an associated key type. The function is called to check whether a key 1215 may be added into the keyring or not. The key type is used by the garbage 1216 collector to clean up function or data pointers in this structure if the 1217 given key type is unregistered. Callers of key_create_or_update() within 1218 the kernel can pass KEY_ALLOC_BYPASS_RESTRICTION to suppress the check. 1219 An example of using this is to manage rings of cryptographic keys that are 1220 set up when the kernel boots where userspace is also permitted to add keys 1221 - provided they can be verified by a key the kernel already has. 1222 1223 When called, the restriction function will be passed the keyring being 1224 added to, the key type, the payload of the key being added, and data to be 1225 used in the restriction check. Note that when a new key is being created, 1226 this is called between payload preparsing and actual key creation. The 1227 function should return 0 to allow the link or an error to reject it. 1228 1229 A convenience function, restrict_link_reject, exists to always return 1230 -EPERM to in this case. 1231 1232 1233 * To check the validity of a key, this function can be called:: 1234 1235 int validate_key(struct key *key); 1236 1237 This checks that the key in question hasn't expired or and hasn't been 1238 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will 1239 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be 1240 returned (in the latter case without parsing the argument). 1241 1242 1243 * To register a key type, the following function should be called:: 1244 1245 int register_key_type(struct key_type *type); 1246 1247 This will return error EEXIST if a type of the same name is already 1248 present. 1249 1250 1251 * To unregister a key type, call:: 1252 1253 void unregister_key_type(struct key_type *type); 1254 1255 1256Under some circumstances, it may be desirable to deal with a bundle of keys. 1257The facility provides access to the keyring type for managing such a bundle:: 1258 1259 struct key_type key_type_keyring; 1260 1261This can be used with a function such as request_key() to find a specific 1262keyring in a process's keyrings. A keyring thus found can then be searched 1263with keyring_search(). Note that it is not possible to use request_key() to 1264search a specific keyring, so using keyrings in this way is of limited utility. 1265 1266 1267Notes On Accessing Payload Contents 1268=================================== 1269 1270The simplest payload is just data stored in key->payload directly. In this 1271case, there's no need to indulge in RCU or locking when accessing the payload. 1272 1273More complex payload contents must be allocated and pointers to them set in the 1274key->payload.data[] array. One of the following ways must be selected to 1275access the data: 1276 1277 1) Unmodifiable key type. 1278 1279 If the key type does not have a modify method, then the key's payload can 1280 be accessed without any form of locking, provided that it's known to be 1281 instantiated (uninstantiated keys cannot be "found"). 1282 1283 2) The key's semaphore. 1284 1285 The semaphore could be used to govern access to the payload and to control 1286 the payload pointer. It must be write-locked for modifications and would 1287 have to be read-locked for general access. The disadvantage of doing this 1288 is that the accessor may be required to sleep. 1289 1290 3) RCU. 1291 1292 RCU must be used when the semaphore isn't already held; if the semaphore 1293 is held then the contents can't change under you unexpectedly as the 1294 semaphore must still be used to serialise modifications to the key. The 1295 key management code takes care of this for the key type. 1296 1297 However, this means using:: 1298 1299 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock() 1300 1301 to read the pointer, and:: 1302 1303 rcu_dereference() ... rcu_assign_pointer() ... call_rcu() 1304 1305 to set the pointer and dispose of the old contents after a grace period. 1306 Note that only the key type should ever modify a key's payload. 1307 1308 Furthermore, an RCU controlled payload must hold a struct rcu_head for the 1309 use of call_rcu() and, if the payload is of variable size, the length of 1310 the payload. key->datalen cannot be relied upon to be consistent with the 1311 payload just dereferenced if the key's semaphore is not held. 1312 1313 Note that key->payload.data[0] has a shadow that is marked for __rcu 1314 usage. This is called key->payload.rcu_data0. The following accessors 1315 wrap the RCU calls to this element: 1316 1317 a) Set or change the first payload pointer:: 1318 1319 rcu_assign_keypointer(struct key *key, void *data); 1320 1321 b) Read the first payload pointer with the key semaphore held:: 1322 1323 [const] void *dereference_key_locked([const] struct key *key); 1324 1325 Note that the return value will inherit its constness from the key 1326 parameter. Static analysis will give an error if it things the lock 1327 isn't held. 1328 1329 c) Read the first payload pointer with the RCU read lock held:: 1330 1331 const void *dereference_key_rcu(const struct key *key); 1332 1333 1334Defining a Key Type 1335=================== 1336 1337A kernel service may want to define its own key type. For instance, an AFS 1338filesystem might want to define a Kerberos 5 ticket key type. To do this, it 1339author fills in a key_type struct and registers it with the system. 1340 1341Source files that implement key types should include the following header file:: 1342 1343 <linux/key-type.h> 1344 1345The structure has a number of fields, some of which are mandatory: 1346 1347 * ``const char *name`` 1348 1349 The name of the key type. This is used to translate a key type name 1350 supplied by userspace into a pointer to the structure. 1351 1352 1353 * ``size_t def_datalen`` 1354 1355 This is optional - it supplies the default payload data length as 1356 contributed to the quota. If the key type's payload is always or almost 1357 always the same size, then this is a more efficient way to do things. 1358 1359 The data length (and quota) on a particular key can always be changed 1360 during instantiation or update by calling:: 1361 1362 int key_payload_reserve(struct key *key, size_t datalen); 1363 1364 With the revised data length. Error EDQUOT will be returned if this is not 1365 viable. 1366 1367 1368 * ``int (*vet_description)(const char *description);`` 1369 1370 This optional method is called to vet a key description. If the key type 1371 doesn't approve of the key description, it may return an error, otherwise 1372 it should return 0. 1373 1374 1375 * ``int (*preparse)(struct key_preparsed_payload *prep);`` 1376 1377 This optional method permits the key type to attempt to parse payload 1378 before a key is created (add key) or the key semaphore is taken (update or 1379 instantiate key). The structure pointed to by prep looks like:: 1380 1381 struct key_preparsed_payload { 1382 char *description; 1383 union key_payload payload; 1384 const void *data; 1385 size_t datalen; 1386 size_t quotalen; 1387 time_t expiry; 1388 }; 1389 1390 Before calling the method, the caller will fill in data and datalen with 1391 the payload blob parameters; quotalen will be filled in with the default 1392 quota size from the key type; expiry will be set to TIME_T_MAX and the 1393 rest will be cleared. 1394 1395 If a description can be proposed from the payload contents, that should be 1396 attached as a string to the description field. This will be used for the 1397 key description if the caller of add_key() passes NULL or "". 1398 1399 The method can attach anything it likes to payload. This is merely passed 1400 along to the instantiate() or update() operations. If set, the expiry 1401 time will be applied to the key if it is instantiated from this data. 1402 1403 The method should return 0 if successful or a negative error code 1404 otherwise. 1405 1406 1407 * ``void (*free_preparse)(struct key_preparsed_payload *prep);`` 1408 1409 This method is only required if the preparse() method is provided, 1410 otherwise it is unused. It cleans up anything attached to the description 1411 and payload fields of the key_preparsed_payload struct as filled in by the 1412 preparse() method. It will always be called after preparse() returns 1413 successfully, even if instantiate() or update() succeed. 1414 1415 1416 * ``int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);`` 1417 1418 This method is called to attach a payload to a key during construction. 1419 The payload attached need not bear any relation to the data passed to this 1420 function. 1421 1422 The prep->data and prep->datalen fields will define the original payload 1423 blob. If preparse() was supplied then other fields may be filled in also. 1424 1425 If the amount of data attached to the key differs from the size in 1426 keytype->def_datalen, then key_payload_reserve() should be called. 1427 1428 This method does not have to lock the key in order to attach a payload. 1429 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents 1430 anything else from gaining access to the key. 1431 1432 It is safe to sleep in this method. 1433 1434 generic_key_instantiate() is provided to simply copy the data from 1435 prep->payload.data[] to key->payload.data[], with RCU-safe assignment on 1436 the first element. It will then clear prep->payload.data[] so that the 1437 free_preparse method doesn't release the data. 1438 1439 1440 * ``int (*update)(struct key *key, const void *data, size_t datalen);`` 1441 1442 If this type of key can be updated, then this method should be provided. 1443 It is called to update a key's payload from the blob of data provided. 1444 1445 The prep->data and prep->datalen fields will define the original payload 1446 blob. If preparse() was supplied then other fields may be filled in also. 1447 1448 key_payload_reserve() should be called if the data length might change 1449 before any changes are actually made. Note that if this succeeds, the type 1450 is committed to changing the key because it's already been altered, so all 1451 memory allocation must be done first. 1452 1453 The key will have its semaphore write-locked before this method is called, 1454 but this only deters other writers; any changes to the key's payload must 1455 be made under RCU conditions, and call_rcu() must be used to dispose of 1456 the old payload. 1457 1458 key_payload_reserve() should be called before the changes are made, but 1459 after all allocations and other potentially failing function calls are 1460 made. 1461 1462 It is safe to sleep in this method. 1463 1464 1465 * ``int (*match_preparse)(struct key_match_data *match_data);`` 1466 1467 This method is optional. It is called when a key search is about to be 1468 performed. It is given the following structure:: 1469 1470 struct key_match_data { 1471 bool (*cmp)(const struct key *key, 1472 const struct key_match_data *match_data); 1473 const void *raw_data; 1474 void *preparsed; 1475 unsigned lookup_type; 1476 }; 1477 1478 On entry, raw_data will be pointing to the criteria to be used in matching 1479 a key by the caller and should not be modified. ``(*cmp)()`` will be pointing 1480 to the default matcher function (which does an exact description match 1481 against raw_data) and lookup_type will be set to indicate a direct lookup. 1482 1483 The following lookup_type values are available: 1484 1485 * KEYRING_SEARCH_LOOKUP_DIRECT - A direct lookup hashes the type and 1486 description to narrow down the search to a small number of keys. 1487 1488 * KEYRING_SEARCH_LOOKUP_ITERATE - An iterative lookup walks all the 1489 keys in the keyring until one is matched. This must be used for any 1490 search that's not doing a simple direct match on the key description. 1491 1492 The method may set cmp to point to a function of its choice that does some 1493 other form of match, may set lookup_type to KEYRING_SEARCH_LOOKUP_ITERATE 1494 and may attach something to the preparsed pointer for use by ``(*cmp)()``. 1495 ``(*cmp)()`` should return true if a key matches and false otherwise. 1496 1497 If preparsed is set, it may be necessary to use the match_free() method to 1498 clean it up. 1499 1500 The method should return 0 if successful or a negative error code 1501 otherwise. 1502 1503 It is permitted to sleep in this method, but ``(*cmp)()`` may not sleep as 1504 locks will be held over it. 1505 1506 If match_preparse() is not provided, keys of this type will be matched 1507 exactly by their description. 1508 1509 1510 * ``void (*match_free)(struct key_match_data *match_data);`` 1511 1512 This method is optional. If given, it called to clean up 1513 match_data->preparsed after a successful call to match_preparse(). 1514 1515 1516 * ``void (*revoke)(struct key *key);`` 1517 1518 This method is optional. It is called to discard part of the payload 1519 data upon a key being revoked. The caller will have the key semaphore 1520 write-locked. 1521 1522 It is safe to sleep in this method, though care should be taken to avoid 1523 a deadlock against the key semaphore. 1524 1525 1526 * ``void (*destroy)(struct key *key);`` 1527 1528 This method is optional. It is called to discard the payload data on a key 1529 when it is being destroyed. 1530 1531 This method does not need to lock the key to access the payload; it can 1532 consider the key as being inaccessible at this time. Note that the key's 1533 type may have been changed before this function is called. 1534 1535 It is not safe to sleep in this method; the caller may hold spinlocks. 1536 1537 1538 * ``void (*describe)(const struct key *key, struct seq_file *p);`` 1539 1540 This method is optional. It is called during /proc/keys reading to 1541 summarise a key's description and payload in text form. 1542 1543 This method will be called with the RCU read lock held. rcu_dereference() 1544 should be used to read the payload pointer if the payload is to be 1545 accessed. key->datalen cannot be trusted to stay consistent with the 1546 contents of the payload. 1547 1548 The description will not change, though the key's state may. 1549 1550 It is not safe to sleep in this method; the RCU read lock is held by the 1551 caller. 1552 1553 1554 * ``long (*read)(const struct key *key, char __user *buffer, size_t buflen);`` 1555 1556 This method is optional. It is called by KEYCTL_READ to translate the 1557 key's payload into something a blob of data for userspace to deal with. 1558 Ideally, the blob should be in the same format as that passed in to the 1559 instantiate and update methods. 1560 1561 If successful, the blob size that could be produced should be returned 1562 rather than the size copied. 1563 1564 This method will be called with the key's semaphore read-locked. This will 1565 prevent the key's payload changing. It is not necessary to use RCU locking 1566 when accessing the key's payload. It is safe to sleep in this method, such 1567 as might happen when the userspace buffer is accessed. 1568 1569 1570 * ``int (*request_key)(struct key_construction *cons, const char *op, void *aux);`` 1571 1572 This method is optional. If provided, request_key() and friends will 1573 invoke this function rather than upcalling to /sbin/request-key to operate 1574 upon a key of this type. 1575 1576 The aux parameter is as passed to request_key_async_with_auxdata() and 1577 similar or is NULL otherwise. Also passed are the construction record for 1578 the key to be operated upon and the operation type (currently only 1579 "create"). 1580 1581 This method is permitted to return before the upcall is complete, but the 1582 following function must be called under all circumstances to complete the 1583 instantiation process, whether or not it succeeds, whether or not there's 1584 an error:: 1585 1586 void complete_request_key(struct key_construction *cons, int error); 1587 1588 The error parameter should be 0 on success, -ve on error. The 1589 construction record is destroyed by this action and the authorisation key 1590 will be revoked. If an error is indicated, the key under construction 1591 will be negatively instantiated if it wasn't already instantiated. 1592 1593 If this method returns an error, that error will be returned to the 1594 caller of request_key*(). complete_request_key() must be called prior to 1595 returning. 1596 1597 The key under construction and the authorisation key can be found in the 1598 key_construction struct pointed to by cons: 1599 1600 * ``struct key *key;`` 1601 1602 The key under construction. 1603 1604 * ``struct key *authkey;`` 1605 1606 The authorisation key. 1607 1608 1609 * ``struct key_restriction *(*lookup_restriction)(const char *params);`` 1610 1611 This optional method is used to enable userspace configuration of keyring 1612 restrictions. The restriction parameter string (not including the key type 1613 name) is passed in, and this method returns a pointer to a key_restriction 1614 structure containing the relevant functions and data to evaluate each 1615 attempted key link operation. If there is no match, -EINVAL is returned. 1616 1617 1618 * ``int (*asym_eds_op)(struct kernel_pkey_params *params, 1619 const void *in, void *out);`` 1620 ``int (*asym_verify_signature)(struct kernel_pkey_params *params, 1621 const void *in, const void *in2);`` 1622 1623 These methods are optional. If provided the first allows a key to be 1624 used to encrypt, decrypt or sign a blob of data, and the second allows a 1625 key to verify a signature. 1626 1627 In all cases, the following information is provided in the params block:: 1628 1629 struct kernel_pkey_params { 1630 struct key *key; 1631 const char *encoding; 1632 const char *hash_algo; 1633 char *info; 1634 __u32 in_len; 1635 union { 1636 __u32 out_len; 1637 __u32 in2_len; 1638 }; 1639 enum kernel_pkey_operation op : 8; 1640 }; 1641 1642 This includes the key to be used; a string indicating the encoding to use 1643 (for instance, "pkcs1" may be used with an RSA key to indicate 1644 RSASSA-PKCS1-v1.5 or RSAES-PKCS1-v1.5 encoding or "raw" if no encoding); 1645 the name of the hash algorithm used to generate the data for a signature 1646 (if appropriate); the sizes of the input and output (or second input) 1647 buffers; and the ID of the operation to be performed. 1648 1649 For a given operation ID, the input and output buffers are used as 1650 follows:: 1651 1652 Operation ID in,in_len out,out_len in2,in2_len 1653 ======================= =============== =============== =============== 1654 kernel_pkey_encrypt Raw data Encrypted data - 1655 kernel_pkey_decrypt Encrypted data Raw data - 1656 kernel_pkey_sign Raw data Signature - 1657 kernel_pkey_verify Raw data - Signature 1658 1659 asym_eds_op() deals with encryption, decryption and signature creation as 1660 specified by params->op. Note that params->op is also set for 1661 asym_verify_signature(). 1662 1663 Encrypting and signature creation both take raw data in the input buffer 1664 and return the encrypted result in the output buffer. Padding may have 1665 been added if an encoding was set. In the case of signature creation, 1666 depending on the encoding, the padding created may need to indicate the 1667 digest algorithm - the name of which should be supplied in hash_algo. 1668 1669 Decryption takes encrypted data in the input buffer and returns the raw 1670 data in the output buffer. Padding will get checked and stripped off if 1671 an encoding was set. 1672 1673 Verification takes raw data in the input buffer and the signature in the 1674 second input buffer and checks that the one matches the other. Padding 1675 will be validated. Depending on the encoding, the digest algorithm used 1676 to generate the raw data may need to be indicated in hash_algo. 1677 1678 If successful, asym_eds_op() should return the number of bytes written 1679 into the output buffer. asym_verify_signature() should return 0. 1680 1681 A variety of errors may be returned, including EOPNOTSUPP if the operation 1682 is not supported; EKEYREJECTED if verification fails; ENOPKG if the 1683 required crypto isn't available. 1684 1685 1686 * ``int (*asym_query)(const struct kernel_pkey_params *params, 1687 struct kernel_pkey_query *info);`` 1688 1689 This method is optional. If provided it allows information about the 1690 public or asymmetric key held in the key to be determined. 1691 1692 The parameter block is as for asym_eds_op() and co. but in_len and out_len 1693 are unused. The encoding and hash_algo fields should be used to reduce 1694 the returned buffer/data sizes as appropriate. 1695 1696 If successful, the following information is filled in:: 1697 1698 struct kernel_pkey_query { 1699 __u32 supported_ops; 1700 __u32 key_size; 1701 __u16 max_data_size; 1702 __u16 max_sig_size; 1703 __u16 max_enc_size; 1704 __u16 max_dec_size; 1705 }; 1706 1707 The supported_ops field will contain a bitmask indicating what operations 1708 are supported by the key, including encryption of a blob, decryption of a 1709 blob, signing a blob and verifying the signature on a blob. The following 1710 constants are defined for this:: 1711 1712 KEYCTL_SUPPORTS_{ENCRYPT,DECRYPT,SIGN,VERIFY} 1713 1714 The key_size field is the size of the key in bits. max_data_size and 1715 max_sig_size are the maximum raw data and signature sizes for creation and 1716 verification of a signature; max_enc_size and max_dec_size are the maximum 1717 raw data and signature sizes for encryption and decryption. The 1718 max_*_size fields are measured in bytes. 1719 1720 If successful, 0 will be returned. If the key doesn't support this, 1721 EOPNOTSUPP will be returned. 1722 1723 1724Request-Key Callback Service 1725============================ 1726 1727To create a new key, the kernel will attempt to execute the following command 1728line:: 1729 1730 /sbin/request-key create <key> <uid> <gid> \ 1731 <threadring> <processring> <sessionring> <callout_info> 1732 1733<key> is the key being constructed, and the three keyrings are the process 1734keyrings from the process that caused the search to be issued. These are 1735included for two reasons: 1736 1737 1 There may be an authentication token in one of the keyrings that is 1738 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket. 1739 1740 2 The new key should probably be cached in one of these rings. 1741 1742This program should set it UID and GID to those specified before attempting to 1743access any more keys. It may then look around for a user specific process to 1744hand the request off to (perhaps a path held in placed in another key by, for 1745example, the KDE desktop manager). 1746 1747The program (or whatever it calls) should finish construction of the key by 1748calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to 1749cache the key in one of the keyrings (probably the session ring) before 1750returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE 1751or KEYCTL_REJECT; this also permits the key to be cached in one of the 1752keyrings. 1753 1754If it returns with the key remaining in the unconstructed state, the key will 1755be marked as being negative, it will be added to the session keyring, and an 1756error will be returned to the key requestor. 1757 1758Supplementary information may be provided from whoever or whatever invoked this 1759service. This will be passed as the <callout_info> parameter. If no such 1760information was made available, then "-" will be passed as this parameter 1761instead. 1762 1763 1764Similarly, the kernel may attempt to update an expired or a soon to expire key 1765by executing:: 1766 1767 /sbin/request-key update <key> <uid> <gid> \ 1768 <threadring> <processring> <sessionring> 1769 1770In this case, the program isn't required to actually attach the key to a ring; 1771the rings are provided for reference. 1772 1773 1774Garbage Collection 1775================== 1776 1777Dead keys (for which the type has been removed) will be automatically unlinked 1778from those keyrings that point to them and deleted as soon as possible by a 1779background garbage collector. 1780 1781Similarly, revoked and expired keys will be garbage collected, but only after a 1782certain amount of time has passed. This time is set as a number of seconds in:: 1783 1784 /proc/sys/kernel/keys/gc_delay 1785