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linux-6.19.14/Documentation/security/keys/core.rst
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 To link a key into the destination keyring the key must grant link 437 permission on the key to the caller and the keyring must grant write 438 permission. 439 440 See also Documentation/security/keys/request-key.rst. 441 442 443The keyctl syscall functions are: 444 445 * Map a special key ID to a real key ID for this process:: 446 447 key_serial_t keyctl(KEYCTL_GET_KEYRING_ID, key_serial_t id, 448 int create); 449 450 The special key specified by "id" is looked up (with the key being created 451 if necessary) and the ID of the key or keyring thus found is returned if 452 it exists. 453 454 If the key does not yet exist, the key will be created if "create" is 455 non-zero; and the error ENOKEY will be returned if "create" is zero. 456 457 458 * Replace the session keyring this process subscribes to with a new one:: 459 460 key_serial_t keyctl(KEYCTL_JOIN_SESSION_KEYRING, const char *name); 461 462 If name is NULL, an anonymous keyring is created attached to the process 463 as its session keyring, displacing the old session keyring. 464 465 If name is not NULL, if a keyring of that name exists, the process 466 attempts to attach it as the session keyring, returning an error if that 467 is not permitted; otherwise a new keyring of that name is created and 468 attached as the session keyring. 469 470 To attach to a named keyring, the keyring must have search permission for 471 the process's ownership. 472 473 The ID of the new session keyring is returned if successful. 474 475 476 * Update the specified key:: 477 478 long keyctl(KEYCTL_UPDATE, key_serial_t key, const void *payload, 479 size_t plen); 480 481 This will try to update the specified key with the given payload, or it 482 will return error EOPNOTSUPP if that function is not supported by the key 483 type. The process must also have permission to write to the key to be able 484 to update it. 485 486 The payload is of length plen, and may be absent or empty as for 487 add_key(). 488 489 490 * Revoke a key:: 491 492 long keyctl(KEYCTL_REVOKE, key_serial_t key); 493 494 This makes a key unavailable for further operations. Further attempts to 495 use the key will be met with error EKEYREVOKED, and the key will no longer 496 be findable. 497 498 499 * Change the ownership of a key:: 500 501 long keyctl(KEYCTL_CHOWN, key_serial_t key, uid_t uid, gid_t gid); 502 503 This function permits a key's owner and group ID to be changed. Either one 504 of uid or gid can be set to -1 to suppress that change. 505 506 Only the superuser can change a key's owner to something other than the 507 key's current owner. Similarly, only the superuser can change a key's 508 group ID to something other than the calling process's group ID or one of 509 its group list members. 510 511 512 * Change the permissions mask on a key:: 513 514 long keyctl(KEYCTL_SETPERM, key_serial_t key, key_perm_t perm); 515 516 This function permits the owner of a key or the superuser to change the 517 permissions mask on a key. 518 519 Only bits the available bits are permitted; if any other bits are set, 520 error EINVAL will be returned. 521 522 523 * Describe a key:: 524 525 long keyctl(KEYCTL_DESCRIBE, key_serial_t key, char *buffer, 526 size_t buflen); 527 528 This function returns a summary of the key's attributes (but not its 529 payload data) as a string in the buffer provided. 530 531 Unless there's an error, it always returns the amount of data it could 532 produce, even if that's too big for the buffer, but it won't copy more 533 than requested to userspace. If the buffer pointer is NULL then no copy 534 will take place. 535 536 A process must have view permission on the key for this function to be 537 successful. 538 539 If successful, a string is placed in the buffer in the following format:: 540 541 <type>;<uid>;<gid>;<perm>;<description> 542 543 Where type and description are strings, uid and gid are decimal, and perm 544 is hexadecimal. A NUL character is included at the end of the string if 545 the buffer is sufficiently big. 546 547 This can be parsed with:: 548 549 sscanf(buffer, "%[^;];%d;%d;%o;%s", type, &uid, &gid, &mode, desc); 550 551 552 * Clear out a keyring:: 553 554 long keyctl(KEYCTL_CLEAR, key_serial_t keyring); 555 556 This function clears the list of keys attached to a keyring. The calling 557 process must have write permission on the keyring, and it must be a 558 keyring (or else error ENOTDIR will result). 559 560 This function can also be used to clear special kernel keyrings if they 561 are appropriately marked if the user has CAP_SYS_ADMIN capability. The 562 DNS resolver cache keyring is an example of this. 563 564 565 * Link a key into a keyring:: 566 567 long keyctl(KEYCTL_LINK, key_serial_t keyring, key_serial_t key); 568 569 This function creates a link from the keyring to the key. The process must 570 have write permission on the keyring and must have link permission on the 571 key. 572 573 Should the keyring not be a keyring, error ENOTDIR will result; and if the 574 keyring is full, error ENFILE will result. 575 576 The link procedure checks the nesting of the keyrings, returning ELOOP if 577 it appears too deep or EDEADLK if the link would introduce a cycle. 578 579 Any links within the keyring to keys that match the new key in terms of 580 type and description will be discarded from the keyring as the new one is 581 added. 582 583 584 * Move a key from one keyring to another:: 585 586 long keyctl(KEYCTL_MOVE, 587 key_serial_t id, 588 key_serial_t from_ring_id, 589 key_serial_t to_ring_id, 590 unsigned int flags); 591 592 Move the key specified by "id" from the keyring specified by 593 "from_ring_id" to the keyring specified by "to_ring_id". If the two 594 keyrings are the same, nothing is done. 595 596 "flags" can have KEYCTL_MOVE_EXCL set in it to cause the operation to fail 597 with EEXIST if a matching key exists in the destination keyring, otherwise 598 such a key will be replaced. 599 600 A process must have link permission on the key for this function to be 601 successful and write permission on both keyrings. Any errors that can 602 occur from KEYCTL_LINK also apply on the destination keyring here. 603 604 605 * Unlink a key or keyring from another keyring:: 606 607 long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key); 608 609 This function looks through the keyring for the first link to the 610 specified key, and removes it if found. Subsequent links to that key are 611 ignored. The process must have write permission on the keyring. 612 613 If the keyring is not a keyring, error ENOTDIR will result; and if the key 614 is not present, error ENOENT will be the result. 615 616 617 * Search a keyring tree for a key:: 618 619 key_serial_t keyctl(KEYCTL_SEARCH, key_serial_t keyring, 620 const char *type, const char *description, 621 key_serial_t dest_keyring); 622 623 This searches the keyring tree headed by the specified keyring until a key 624 is found that matches the type and description criteria. Each keyring is 625 checked for keys before recursion into its children occurs. 626 627 The process must have search permission on the top level keyring, or else 628 error EACCES will result. Only keyrings that the process has search 629 permission on will be recursed into, and only keys and keyrings for which 630 a process has search permission can be matched. If the specified keyring 631 is not a keyring, ENOTDIR will result. 632 633 If the search succeeds, the function will attempt to link the found key 634 into the destination keyring if one is supplied (non-zero ID). All the 635 constraints applicable to KEYCTL_LINK apply in this case too. 636 637 Error ENOKEY, EKEYREVOKED or EKEYEXPIRED will be returned if the search 638 fails. On success, the resulting key ID will be returned. 639 640 641 * Read the payload data from a key:: 642 643 long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer, 644 size_t buflen); 645 646 This function attempts to read the payload data from the specified key 647 into the buffer. The process must have read permission on the key to 648 succeed. 649 650 The returned data will be processed for presentation by the key type. For 651 instance, a keyring will return an array of key_serial_t entries 652 representing the IDs of all the keys to which it is subscribed. The user 653 defined key type will return its data as is. If a key type does not 654 implement this function, error EOPNOTSUPP will result. 655 656 If the specified buffer is too small, then the size of the buffer required 657 will be returned. Note that in this case, the contents of the buffer may 658 have been overwritten in some undefined way. 659 660 Otherwise, on success, the function will return the amount of data copied 661 into the buffer. 662 663 * Instantiate a partially constructed key:: 664 665 long keyctl(KEYCTL_INSTANTIATE, key_serial_t key, 666 const void *payload, size_t plen, 667 key_serial_t keyring); 668 long keyctl(KEYCTL_INSTANTIATE_IOV, key_serial_t key, 669 const struct iovec *payload_iov, unsigned ioc, 670 key_serial_t keyring); 671 672 If the kernel calls back to userspace to complete the instantiation of a 673 key, userspace should use this call to supply data for the key before the 674 invoked process returns, or else the key will be marked negative 675 automatically. 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 681 that keyring, however all the constraints applying in KEYCTL_LINK apply in 682 this case too. 683 684 The payload and plen arguments describe the payload data as for add_key(). 685 686 The payload_iov and ioc arguments describe the payload data in an iovec 687 array instead of a single buffer. 688 689 690 * Negatively instantiate a partially constructed key:: 691 692 long keyctl(KEYCTL_NEGATE, key_serial_t key, 693 unsigned timeout, key_serial_t keyring); 694 long keyctl(KEYCTL_REJECT, key_serial_t key, 695 unsigned timeout, unsigned error, key_serial_t keyring); 696 697 If the kernel calls back to userspace to complete the instantiation of a 698 key, userspace should use this call mark the key as negative before the 699 invoked process returns if it is unable to fulfill the request. 700 701 The process must have write access on the key to be able to instantiate 702 it, and the key must be uninstantiated. 703 704 If a keyring is specified (non-zero), the key will also be linked into 705 that keyring, however all the constraints applying in KEYCTL_LINK apply in 706 this case too. 707 708 If the key is rejected, future searches for it will return the specified 709 error code until the rejected key expires. Negating the key is the same 710 as rejecting the key with ENOKEY as the error code. 711 712 713 * Set the default request-key destination keyring:: 714 715 long keyctl(KEYCTL_SET_REQKEY_KEYRING, int reqkey_defl); 716 717 This sets the default keyring to which implicitly requested keys will be 718 attached for this thread. reqkey_defl should be one of these constants:: 719 720 CONSTANT VALUE NEW DEFAULT KEYRING 721 ====================================== ====== ======================= 722 KEY_REQKEY_DEFL_NO_CHANGE -1 No change 723 KEY_REQKEY_DEFL_DEFAULT 0 Default[1] 724 KEY_REQKEY_DEFL_THREAD_KEYRING 1 Thread keyring 725 KEY_REQKEY_DEFL_PROCESS_KEYRING 2 Process keyring 726 KEY_REQKEY_DEFL_SESSION_KEYRING 3 Session keyring 727 KEY_REQKEY_DEFL_USER_KEYRING 4 User keyring 728 KEY_REQKEY_DEFL_USER_SESSION_KEYRING 5 User session keyring 729 KEY_REQKEY_DEFL_GROUP_KEYRING 6 Group keyring 730 731 The old default will be returned if successful and error EINVAL will be 732 returned if reqkey_defl is not one of the above values. 733 734 The default keyring can be overridden by the keyring indicated to the 735 request_key() system call. 736 737 Note that this setting is inherited across fork/exec. 738 739 [1] The default is: the thread keyring if there is one, otherwise 740 the process keyring if there is one, otherwise the session keyring if 741 there is one, otherwise the user default session keyring. 742 743 744 * Set the timeout on a key:: 745 746 long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout); 747 748 This sets or clears the timeout on a key. The timeout can be 0 to clear 749 the timeout or a number of seconds to set the expiry time that far into 750 the future. 751 752 The process must have attribute modification access on a key to set its 753 timeout. Timeouts may not be set with this function on negative, revoked 754 or expired keys. 755 756 757 * Assume the authority granted to instantiate a key:: 758 759 long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key); 760 761 This assumes or divests the authority required to instantiate the 762 specified key. Authority can only be assumed if the thread has the 763 authorisation key associated with the specified key in its keyrings 764 somewhere. 765 766 Once authority is assumed, searches for keys will also search the 767 requester's keyrings using the requester's security label, UID, GID and 768 groups. 769 770 If the requested authority is unavailable, error EPERM will be returned, 771 likewise if the authority has been revoked because the target key is 772 already instantiated. 773 774 If the specified key is 0, then any assumed authority will be divested. 775 776 The assumed authoritative key is inherited across fork and exec. 777 778 779 * Get the LSM security context attached to a key:: 780 781 long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer, 782 size_t buflen) 783 784 This function returns a string that represents the LSM security context 785 attached to a key in the buffer provided. 786 787 Unless there's an error, it always returns the amount of data it could 788 produce, even if that's too big for the buffer, but it won't copy more 789 than requested to userspace. If the buffer pointer is NULL then no copy 790 will take place. 791 792 A NUL character is included at the end of the string if the buffer is 793 sufficiently big. This is included in the returned count. If no LSM is 794 in force then an empty string will be returned. 795 796 A process must have view permission on the key for this function to be 797 successful. 798 799 800 * Install the calling process's session keyring on its parent:: 801 802 long keyctl(KEYCTL_SESSION_TO_PARENT); 803 804 This functions attempts to install the calling process's session keyring 805 on to the calling process's parent, replacing the parent's current session 806 keyring. 807 808 The calling process must have the same ownership as its parent, the 809 keyring must have the same ownership as the calling process, the calling 810 process must have LINK permission on the keyring and the active LSM module 811 mustn't deny permission, otherwise error EPERM will be returned. 812 813 Error ENOMEM will be returned if there was insufficient memory to complete 814 the operation, otherwise 0 will be returned to indicate success. 815 816 The keyring will be replaced next time the parent process leaves the 817 kernel and resumes executing userspace. 818 819 820 * Invalidate a key:: 821 822 long keyctl(KEYCTL_INVALIDATE, key_serial_t key); 823 824 This function marks a key as being invalidated and then wakes up the 825 garbage collector. The garbage collector immediately removes invalidated 826 keys from all keyrings and deletes the key when its reference count 827 reaches zero. 828 829 Keys that are marked invalidated become invisible to normal key operations 830 immediately, though they are still visible in /proc/keys until deleted 831 (they're marked with an 'i' flag). 832 833 A process must have search permission on the key for this function to be 834 successful. 835 836 * Compute a Diffie-Hellman shared secret or public key:: 837 838 long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params, 839 char *buffer, size_t buflen, struct keyctl_kdf_params *kdf); 840 841 The params struct contains serial numbers for three keys:: 842 843 - The prime, p, known to both parties 844 - The local private key 845 - The base integer, which is either a shared generator or the 846 remote public key 847 848 The value computed is:: 849 850 result = base ^ private (mod prime) 851 852 If the base is the shared generator, the result is the local 853 public key. If the base is the remote public key, the result is 854 the shared secret. 855 856 If the parameter kdf is NULL, the following applies: 857 858 - The buffer length must be at least the length of the prime, or zero. 859 860 - If the buffer length is nonzero, the length of the result is 861 returned when it is successfully calculated and copied in to the 862 buffer. When the buffer length is zero, the minimum required 863 buffer length is returned. 864 865 The kdf parameter allows the caller to apply a key derivation function 866 (KDF) on the Diffie-Hellman computation where only the result 867 of the KDF is returned to the caller. The KDF is characterized with 868 struct keyctl_kdf_params as follows: 869 870 - ``char *hashname`` specifies the NUL terminated string identifying 871 the hash used from the kernel crypto API and applied for the KDF 872 operation. The KDF implementation complies with SP800-56A as well 873 as with SP800-108 (the counter KDF). 874 875 - ``char *otherinfo`` specifies the OtherInfo data as documented in 876 SP800-56A section 5.8.1.2. The length of the buffer is given with 877 otherinfolen. The format of OtherInfo is defined by the caller. 878 The otherinfo pointer may be NULL if no OtherInfo shall be used. 879 880 This function will return error EOPNOTSUPP if the key type is not 881 supported, error ENOKEY if the key could not be found, or error 882 EACCES if the key is not readable by the caller. In addition, the 883 function will return EMSGSIZE when the parameter kdf is non-NULL 884 and either the buffer length or the OtherInfo length exceeds the 885 allowed length. 886 887 888 * Restrict keyring linkage:: 889 890 long keyctl(KEYCTL_RESTRICT_KEYRING, key_serial_t keyring, 891 const char *type, const char *restriction); 892 893 An existing keyring can restrict linkage of additional keys by evaluating 894 the contents of the key according to a restriction scheme. 895 896 "keyring" is the key ID for an existing keyring to apply a restriction 897 to. It may be empty or may already have keys linked. Existing linked keys 898 will remain in the keyring even if the new restriction would reject them. 899 900 "type" is a registered key type. 901 902 "restriction" is a string describing how key linkage is to be restricted. 903 The format varies depending on the key type, and the string is passed to 904 the lookup_restriction() function for the requested type. It may specify 905 a method and relevant data for the restriction such as signature 906 verification or constraints on key payload. If the requested key type is 907 later unregistered, no keys may be added to the keyring after the key type 908 is removed. 909 910 To apply a keyring restriction the process must have Set Attribute 911 permission and the keyring must not be previously restricted. 912 913 One application of restricted keyrings is to verify X.509 certificate 914 chains or individual certificate signatures using the asymmetric key type. 915 See Documentation/crypto/asymmetric-keys.rst for specific restrictions 916 applicable to the asymmetric key type. 917 918 919 * Query an asymmetric key:: 920 921 long keyctl(KEYCTL_PKEY_QUERY, 922 key_serial_t key_id, unsigned long reserved, 923 const char *params, 924 struct keyctl_pkey_query *info); 925 926 Get information about an asymmetric key. Specific algorithms and 927 encodings may be queried by using the ``params`` argument. This is a 928 string containing a space- or tab-separated string of key-value pairs. 929 Currently supported keys include ``enc`` and ``hash``. The information 930 is returned in the keyctl_pkey_query struct:: 931 932 __u32 supported_ops; 933 __u32 key_size; 934 __u16 max_data_size; 935 __u16 max_sig_size; 936 __u16 max_enc_size; 937 __u16 max_dec_size; 938 __u32 __spare[10]; 939 940 ``supported_ops`` contains a bit mask of flags indicating which ops are 941 supported. This is constructed from a bitwise-OR of:: 942 943 KEYCTL_SUPPORTS_{ENCRYPT,DECRYPT,SIGN,VERIFY} 944 945 ``key_size`` indicated the size of the key in bits. 946 947 ``max_*_size`` indicate the maximum sizes in bytes of a blob of data to be 948 signed, a signature blob, a blob to be encrypted and a blob to be 949 decrypted. 950 951 ``__spare[]`` must be set to 0. This is intended for future use to hand 952 over one or more passphrases needed unlock a key. 953 954 If successful, 0 is returned. If the key is not an asymmetric key, 955 EOPNOTSUPP is returned. 956 957 958 * Encrypt, decrypt, sign or verify a blob using an asymmetric key:: 959 960 long keyctl(KEYCTL_PKEY_ENCRYPT, 961 const struct keyctl_pkey_params *params, 962 const char *info, 963 const void *in, 964 void *out); 965 966 long keyctl(KEYCTL_PKEY_DECRYPT, 967 const struct keyctl_pkey_params *params, 968 const char *info, 969 const void *in, 970 void *out); 971 972 long keyctl(KEYCTL_PKEY_SIGN, 973 const struct keyctl_pkey_params *params, 974 const char *info, 975 const void *in, 976 void *out); 977 978 long keyctl(KEYCTL_PKEY_VERIFY, 979 const struct keyctl_pkey_params *params, 980 const char *info, 981 const void *in, 982 const void *in2); 983 984 Use an asymmetric key to perform a public-key cryptographic operation a 985 blob of data. For encryption and verification, the asymmetric key may 986 only need the public parts to be available, but for decryption and signing 987 the private parts are required also. 988 989 The parameter block pointed to by params contains a number of integer 990 values:: 991 992 __s32 key_id; 993 __u32 in_len; 994 __u32 out_len; 995 __u32 in2_len; 996 997 ``key_id`` is the ID of the asymmetric key to be used. ``in_len`` and 998 ``in2_len`` indicate the amount of data in the in and in2 buffers and 999 ``out_len`` indicates the size of the out buffer as appropriate for the 1000 above operations. 1001 1002 For a given operation, the in and out buffers are used as follows:: 1003 1004 Operation ID in,in_len out,out_len in2,in2_len 1005 ======================= =============== =============== =============== 1006 KEYCTL_PKEY_ENCRYPT Raw data Encrypted data - 1007 KEYCTL_PKEY_DECRYPT Encrypted data Raw data - 1008 KEYCTL_PKEY_SIGN Raw data Signature - 1009 KEYCTL_PKEY_VERIFY Raw data - Signature 1010 1011 ``info`` is a string of key=value pairs that supply supplementary 1012 information. These include: 1013 1014 ``enc=<encoding>`` The encoding of the encrypted/signature blob. This 1015 can be "pkcs1" for RSASSA-PKCS1-v1.5 or 1016 RSAES-PKCS1-v1.5; "pss" for "RSASSA-PSS"; "oaep" for 1017 "RSAES-OAEP". If omitted or is "raw", the raw output 1018 of the encryption function is specified. 1019 1020 ``hash=<algo>`` If the data buffer contains the output of a hash 1021 function and the encoding includes some indication of 1022 which hash function was used, the hash function can be 1023 specified with this, eg. "hash=sha256". 1024 1025 The ``__spare[]`` space in the parameter block must be set to 0. This is 1026 intended, amongst other things, to allow the passing of passphrases 1027 required to unlock a key. 1028 1029 If successful, encrypt, decrypt and sign all return the amount of data 1030 written into the output buffer. Verification returns 0 on success. 1031 1032 1033 * Watch a key or keyring for changes:: 1034 1035 long keyctl(KEYCTL_WATCH_KEY, key_serial_t key, int queue_fd, 1036 const struct watch_notification_filter *filter); 1037 1038 This will set or remove a watch for changes on the specified key or 1039 keyring. 1040 1041 "key" is the ID of the key to be watched. 1042 1043 "queue_fd" is a file descriptor referring to an open pipe which 1044 manages the buffer into which notifications will be delivered. 1045 1046 "filter" is either NULL to remove a watch or a filter specification to 1047 indicate what events are required from the key. 1048 1049 See Documentation/core-api/watch_queue.rst for more information. 1050 1051 Note that only one watch may be emplaced for any particular { key, 1052 queue_fd } combination. 1053 1054 Notification records look like:: 1055 1056 struct key_notification { 1057 struct watch_notification watch; 1058 __u32 key_id; 1059 __u32 aux; 1060 }; 1061 1062 In this, watch::type will be "WATCH_TYPE_KEY_NOTIFY" and subtype will be 1063 one of:: 1064 1065 NOTIFY_KEY_INSTANTIATED 1066 NOTIFY_KEY_UPDATED 1067 NOTIFY_KEY_LINKED 1068 NOTIFY_KEY_UNLINKED 1069 NOTIFY_KEY_CLEARED 1070 NOTIFY_KEY_REVOKED 1071 NOTIFY_KEY_INVALIDATED 1072 NOTIFY_KEY_SETATTR 1073 1074 Where these indicate a key being instantiated/rejected, updated, a link 1075 being made in a keyring, a link being removed from a keyring, a keyring 1076 being cleared, a key being revoked, a key being invalidated or a key 1077 having one of its attributes changed (user, group, perm, timeout, 1078 restriction). 1079 1080 If a watched key is deleted, a basic watch_notification will be issued 1081 with "type" set to WATCH_TYPE_META and "subtype" set to 1082 watch_meta_removal_notification. The watchpoint ID will be set in the 1083 "info" field. 1084 1085 This needs to be configured by enabling: 1086 1087 "Provide key/keyring change notifications" (KEY_NOTIFICATIONS) 1088 1089 1090Kernel Services 1091=============== 1092 1093The kernel services for key management are fairly simple to deal with. They can 1094be broken down into two areas: keys and key types. 1095 1096Dealing with keys is fairly straightforward. Firstly, the kernel service 1097registers its type, then it searches for a key of that type. It should retain 1098the key as long as it has need of it, and then it should release it. For a 1099filesystem or device file, a search would probably be performed during the open 1100call, and the key released upon close. How to deal with conflicting keys due to 1101two different users opening the same file is left to the filesystem author to 1102solve. 1103 1104To access the key manager, the following header must be #included:: 1105 1106 <linux/key.h> 1107 1108Specific key types should have a header file under include/keys/ that should be 1109used to access that type. For keys of type "user", for example, that would be:: 1110 1111 <keys/user-type.h> 1112 1113Note that there are two different types of pointers to keys that may be 1114encountered: 1115 1116 * struct key * 1117 1118 This simply points to the key structure itself. Key structures will be at 1119 least four-byte aligned. 1120 1121 * key_ref_t 1122 1123 This is equivalent to a ``struct key *``, but the least significant bit is set 1124 if the caller "possesses" the key. By "possession" it is meant that the 1125 calling processes has a searchable link to the key from one of its 1126 keyrings. There are three functions for dealing with these:: 1127 1128 key_ref_t make_key_ref(const struct key *key, bool possession); 1129 1130 struct key *key_ref_to_ptr(const key_ref_t key_ref); 1131 1132 bool is_key_possessed(const key_ref_t key_ref); 1133 1134 The first function constructs a key reference from a key pointer and 1135 possession information (which must be true or false). 1136 1137 The second function retrieves the key pointer from a reference and the 1138 third retrieves the possession flag. 1139 1140When accessing a key's payload contents, certain precautions must be taken to 1141prevent access vs modification races. See the section "Notes on accessing 1142payload contents" for more information. 1143 1144 * To search for a key, call:: 1145 1146 struct key *request_key(const struct key_type *type, 1147 const char *description, 1148 const char *callout_info); 1149 1150 This is used to request a key or keyring with a description that matches 1151 the description specified according to the key type's match_preparse() 1152 method. This permits approximate matching to occur. If callout_string is 1153 not NULL, then /sbin/request-key will be invoked in an attempt to obtain 1154 the key from userspace. In that case, callout_string will be passed as an 1155 argument to the program. 1156 1157 Should the function fail error ENOKEY, EKEYEXPIRED or EKEYREVOKED will be 1158 returned. 1159 1160 If successful, the key will have been attached to the default keyring for 1161 implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING. 1162 1163 See also Documentation/security/keys/request-key.rst. 1164 1165 1166 * To search for a key in a specific domain, call:: 1167 1168 struct key *request_key_tag(const struct key_type *type, 1169 const char *description, 1170 struct key_tag *domain_tag, 1171 const char *callout_info); 1172 1173 This is identical to request_key(), except that a domain tag may be 1174 specifies that causes search algorithm to only match keys matching that 1175 tag. The domain_tag may be NULL, specifying a global domain that is 1176 separate from any nominated domain. 1177 1178 1179 * To search for a key, passing auxiliary data to the upcaller, call:: 1180 1181 struct key *request_key_with_auxdata(const struct key_type *type, 1182 const char *description, 1183 struct key_tag *domain_tag, 1184 const void *callout_info, 1185 size_t callout_len, 1186 void *aux); 1187 1188 This is identical to request_key_tag(), except that the auxiliary data is 1189 passed to the key_type->request_key() op if it exists, and the 1190 callout_info is a blob of length callout_len, if given (the length may be 1191 0). 1192 1193 1194 * To search for a key under RCU conditions, call:: 1195 1196 struct key *request_key_rcu(const struct key_type *type, 1197 const char *description, 1198 struct key_tag *domain_tag); 1199 1200 which is similar to request_key_tag() except that it does not check for 1201 keys that are under construction and it will not call out to userspace to 1202 construct a key if it can't find a match. 1203 1204 1205 * When it is no longer required, the key should be released using:: 1206 1207 void key_put(struct key *key); 1208 1209 Or:: 1210 1211 void key_ref_put(key_ref_t key_ref); 1212 1213 These can be called from interrupt context. If CONFIG_KEYS is not set then 1214 the argument will not be parsed. 1215 1216 1217 * Extra references can be made to a key by calling one of the following 1218 functions:: 1219 1220 struct key *__key_get(struct key *key); 1221 struct key *key_get(struct key *key); 1222 1223 Keys so references will need to be disposed of by calling key_put() when 1224 they've been finished with. The key pointer passed in will be returned. 1225 1226 In the case of key_get(), if the pointer is NULL or CONFIG_KEYS is not set 1227 then the key will not be dereferenced and no increment will take place. 1228 1229 1230 * A key's serial number can be obtained by calling:: 1231 1232 key_serial_t key_serial(struct key *key); 1233 1234 If key is NULL or if CONFIG_KEYS is not set then 0 will be returned (in the 1235 latter case without parsing the argument). 1236 1237 1238 * If a keyring was found in the search, this can be further searched by:: 1239 1240 key_ref_t keyring_search(key_ref_t keyring_ref, 1241 const struct key_type *type, 1242 const char *description, 1243 bool recurse) 1244 1245 This searches the specified keyring only (recurse == false) or keyring tree 1246 (recurse == true) specified for a matching key. Error ENOKEY is returned 1247 upon failure (use IS_ERR/PTR_ERR to determine). If successful, the returned 1248 key will need to be released. 1249 1250 The possession attribute from the keyring reference is used to control 1251 access through the permissions mask and is propagated to the returned key 1252 reference pointer if successful. 1253 1254 1255 * A keyring can be created by:: 1256 1257 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid, 1258 const struct cred *cred, 1259 key_perm_t perm, 1260 struct key_restriction *restrict_link, 1261 unsigned long flags, 1262 struct key *dest); 1263 1264 This creates a keyring with the given attributes and returns it. If dest 1265 is not NULL, the new keyring will be linked into the keyring to which it 1266 points. No permission checks are made upon the destination keyring. 1267 1268 Error EDQUOT can be returned if the keyring would overload the quota (pass 1269 KEY_ALLOC_NOT_IN_QUOTA in flags if the keyring shouldn't be accounted 1270 towards the user's quota). Error ENOMEM can also be returned. 1271 1272 If restrict_link is not NULL, it should point to a structure that contains 1273 the function that will be called each time an attempt is made to link a 1274 key into the new keyring. The structure may also contain a key pointer 1275 and an associated key type. The function is called to check whether a key 1276 may be added into the keyring or not. The key type is used by the garbage 1277 collector to clean up function or data pointers in this structure if the 1278 given key type is unregistered. Callers of key_create_or_update() within 1279 the kernel can pass KEY_ALLOC_BYPASS_RESTRICTION to suppress the check. 1280 An example of using this is to manage rings of cryptographic keys that are 1281 set up when the kernel boots where userspace is also permitted to add keys 1282 - provided they can be verified by a key the kernel already has. 1283 1284 When called, the restriction function will be passed the keyring being 1285 added to, the key type, the payload of the key being added, and data to be 1286 used in the restriction check. Note that when a new key is being created, 1287 this is called between payload preparsing and actual key creation. The 1288 function should return 0 to allow the link or an error to reject it. 1289 1290 A convenience function, restrict_link_reject, exists to always return 1291 -EPERM to in this case. 1292 1293 1294 * To check the validity of a key, this function can be called:: 1295 1296 int validate_key(struct key *key); 1297 1298 This checks that the key in question hasn't expired or and hasn't been 1299 revoked. Should the key be invalid, error EKEYEXPIRED or EKEYREVOKED will 1300 be returned. If the key is NULL or if CONFIG_KEYS is not set then 0 will be 1301 returned (in the latter case without parsing the argument). 1302 1303 1304 * To register a key type, the following function should be called:: 1305 1306 int register_key_type(struct key_type *type); 1307 1308 This will return error EEXIST if a type of the same name is already 1309 present. 1310 1311 1312 * To unregister a key type, call:: 1313 1314 void unregister_key_type(struct key_type *type); 1315 1316 1317Under some circumstances, it may be desirable to deal with a bundle of keys. 1318The facility provides access to the keyring type for managing such a bundle:: 1319 1320 struct key_type key_type_keyring; 1321 1322This can be used with a function such as request_key() to find a specific 1323keyring in a process's keyrings. A keyring thus found can then be searched 1324with keyring_search(). Note that it is not possible to use request_key() to 1325search a specific keyring, so using keyrings in this way is of limited utility. 1326 1327 1328Notes On Accessing Payload Contents 1329=================================== 1330 1331The simplest payload is just data stored in key->payload directly. In this 1332case, there's no need to indulge in RCU or locking when accessing the payload. 1333 1334More complex payload contents must be allocated and pointers to them set in the 1335key->payload.data[] array. One of the following ways must be selected to 1336access the data: 1337 1338 1) Unmodifiable key type. 1339 1340 If the key type does not have a modify method, then the key's payload can 1341 be accessed without any form of locking, provided that it's known to be 1342 instantiated (uninstantiated keys cannot be "found"). 1343 1344 2) The key's semaphore. 1345 1346 The semaphore could be used to govern access to the payload and to control 1347 the payload pointer. It must be write-locked for modifications and would 1348 have to be read-locked for general access. The disadvantage of doing this 1349 is that the accessor may be required to sleep. 1350 1351 3) RCU. 1352 1353 RCU must be used when the semaphore isn't already held; if the semaphore 1354 is held then the contents can't change under you unexpectedly as the 1355 semaphore must still be used to serialise modifications to the key. The 1356 key management code takes care of this for the key type. 1357 1358 However, this means using:: 1359 1360 rcu_read_lock() ... rcu_dereference() ... rcu_read_unlock() 1361 1362 to read the pointer, and:: 1363 1364 rcu_dereference() ... rcu_assign_pointer() ... call_rcu() 1365 1366 to set the pointer and dispose of the old contents after a grace period. 1367 Note that only the key type should ever modify a key's payload. 1368 1369 Furthermore, an RCU controlled payload must hold a struct rcu_head for the 1370 use of call_rcu() and, if the payload is of variable size, the length of 1371 the payload. key->datalen cannot be relied upon to be consistent with the 1372 payload just dereferenced if the key's semaphore is not held. 1373 1374 Note that key->payload.data[0] has a shadow that is marked for __rcu 1375 usage. This is called key->payload.rcu_data0. The following accessors 1376 wrap the RCU calls to this element: 1377 1378 a) Set or change the first payload pointer:: 1379 1380 rcu_assign_keypointer(struct key *key, void *data); 1381 1382 b) Read the first payload pointer with the key semaphore held:: 1383 1384 [const] void *dereference_key_locked([const] struct key *key); 1385 1386 Note that the return value will inherit its constness from the key 1387 parameter. Static analysis will give an error if it things the lock 1388 isn't held. 1389 1390 c) Read the first payload pointer with the RCU read lock held:: 1391 1392 const void *dereference_key_rcu(const struct key *key); 1393 1394 1395Defining a Key Type 1396=================== 1397 1398A kernel service may want to define its own key type. For instance, an AFS 1399filesystem might want to define a Kerberos 5 ticket key type. To do this, it 1400author fills in a key_type struct and registers it with the system. 1401 1402Source files that implement key types should include the following header file:: 1403 1404 <linux/key-type.h> 1405 1406The structure has a number of fields, some of which are mandatory: 1407 1408 * ``const char *name`` 1409 1410 The name of the key type. This is used to translate a key type name 1411 supplied by userspace into a pointer to the structure. 1412 1413 1414 * ``size_t def_datalen`` 1415 1416 This is optional - it supplies the default payload data length as 1417 contributed to the quota. If the key type's payload is always or almost 1418 always the same size, then this is a more efficient way to do things. 1419 1420 The data length (and quota) on a particular key can always be changed 1421 during instantiation or update by calling:: 1422 1423 int key_payload_reserve(struct key *key, size_t datalen); 1424 1425 With the revised data length. Error EDQUOT will be returned if this is not 1426 viable. 1427 1428 1429 * ``int (*vet_description)(const char *description);`` 1430 1431 This optional method is called to vet a key description. If the key type 1432 doesn't approve of the key description, it may return an error, otherwise 1433 it should return 0. 1434 1435 1436 * ``int (*preparse)(struct key_preparsed_payload *prep);`` 1437 1438 This optional method permits the key type to attempt to parse payload 1439 before a key is created (add key) or the key semaphore is taken (update or 1440 instantiate key). The structure pointed to by prep looks like:: 1441 1442 struct key_preparsed_payload { 1443 char *description; 1444 union key_payload payload; 1445 const void *data; 1446 size_t datalen; 1447 size_t quotalen; 1448 time_t expiry; 1449 }; 1450 1451 Before calling the method, the caller will fill in data and datalen with 1452 the payload blob parameters; quotalen will be filled in with the default 1453 quota size from the key type; expiry will be set to TIME_T_MAX and the 1454 rest will be cleared. 1455 1456 If a description can be proposed from the payload contents, that should be 1457 attached as a string to the description field. This will be used for the 1458 key description if the caller of add_key() passes NULL or "". 1459 1460 The method can attach anything it likes to payload. This is merely passed 1461 along to the instantiate() or update() operations. If set, the expiry 1462 time will be applied to the key if it is instantiated from this data. 1463 1464 The method should return 0 if successful or a negative error code 1465 otherwise. 1466 1467 1468 * ``void (*free_preparse)(struct key_preparsed_payload *prep);`` 1469 1470 This method is only required if the preparse() method is provided, 1471 otherwise it is unused. It cleans up anything attached to the description 1472 and payload fields of the key_preparsed_payload struct as filled in by the 1473 preparse() method. It will always be called after preparse() returns 1474 successfully, even if instantiate() or update() succeed. 1475 1476 1477 * ``int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);`` 1478 1479 This method is called to attach a payload to a key during construction. 1480 The payload attached need not bear any relation to the data passed to this 1481 function. 1482 1483 The prep->data and prep->datalen fields will define the original payload 1484 blob. If preparse() was supplied then other fields may be filled in also. 1485 1486 If the amount of data attached to the key differs from the size in 1487 keytype->def_datalen, then key_payload_reserve() should be called. 1488 1489 This method does not have to lock the key in order to attach a payload. 1490 The fact that KEY_FLAG_INSTANTIATED is not set in key->flags prevents 1491 anything else from gaining access to the key. 1492 1493 It is safe to sleep in this method. 1494 1495 generic_key_instantiate() is provided to simply copy the data from 1496 prep->payload.data[] to key->payload.data[], with RCU-safe assignment on 1497 the first element. It will then clear prep->payload.data[] so that the 1498 free_preparse method doesn't release the data. 1499 1500 1501 * ``int (*update)(struct key *key, const void *data, size_t datalen);`` 1502 1503 If this type of key can be updated, then this method should be provided. 1504 It is called to update a key's payload from the blob of data provided. 1505 1506 The prep->data and prep->datalen fields will define the original payload 1507 blob. If preparse() was supplied then other fields may be filled in also. 1508 1509 key_payload_reserve() should be called if the data length might change 1510 before any changes are actually made. Note that if this succeeds, the type 1511 is committed to changing the key because it's already been altered, so all 1512 memory allocation must be done first. 1513 1514 The key will have its semaphore write-locked before this method is called, 1515 but this only deters other writers; any changes to the key's payload must 1516 be made under RCU conditions, and call_rcu() must be used to dispose of 1517 the old payload. 1518 1519 key_payload_reserve() should be called before the changes are made, but 1520 after all allocations and other potentially failing function calls are 1521 made. 1522 1523 It is safe to sleep in this method. 1524 1525 1526 * ``int (*match_preparse)(struct key_match_data *match_data);`` 1527 1528 This method is optional. It is called when a key search is about to be 1529 performed. It is given the following structure:: 1530 1531 struct key_match_data { 1532 bool (*cmp)(const struct key *key, 1533 const struct key_match_data *match_data); 1534 const void *raw_data; 1535 void *preparsed; 1536 unsigned lookup_type; 1537 }; 1538 1539 On entry, raw_data will be pointing to the criteria to be used in matching 1540 a key by the caller and should not be modified. ``(*cmp)()`` will be pointing 1541 to the default matcher function (which does an exact description match 1542 against raw_data) and lookup_type will be set to indicate a direct lookup. 1543 1544 The following lookup_type values are available: 1545 1546 * KEYRING_SEARCH_LOOKUP_DIRECT - A direct lookup hashes the type and 1547 description to narrow down the search to a small number of keys. 1548 1549 * KEYRING_SEARCH_LOOKUP_ITERATE - An iterative lookup walks all the 1550 keys in the keyring until one is matched. This must be used for any 1551 search that's not doing a simple direct match on the key description. 1552 1553 The method may set cmp to point to a function of its choice that does some 1554 other form of match, may set lookup_type to KEYRING_SEARCH_LOOKUP_ITERATE 1555 and may attach something to the preparsed pointer for use by ``(*cmp)()``. 1556 ``(*cmp)()`` should return true if a key matches and false otherwise. 1557 1558 If preparsed is set, it may be necessary to use the match_free() method to 1559 clean it up. 1560 1561 The method should return 0 if successful or a negative error code 1562 otherwise. 1563 1564 It is permitted to sleep in this method, but ``(*cmp)()`` may not sleep as 1565 locks will be held over it. 1566 1567 If match_preparse() is not provided, keys of this type will be matched 1568 exactly by their description. 1569 1570 1571 * ``void (*match_free)(struct key_match_data *match_data);`` 1572 1573 This method is optional. If given, it called to clean up 1574 match_data->preparsed after a successful call to match_preparse(). 1575 1576 1577 * ``void (*revoke)(struct key *key);`` 1578 1579 This method is optional. It is called to discard part of the payload 1580 data upon a key being revoked. The caller will have the key semaphore 1581 write-locked. 1582 1583 It is safe to sleep in this method, though care should be taken to avoid 1584 a deadlock against the key semaphore. 1585 1586 1587 * ``void (*destroy)(struct key *key);`` 1588 1589 This method is optional. It is called to discard the payload data on a key 1590 when it is being destroyed. 1591 1592 This method does not need to lock the key to access the payload; it can 1593 consider the key as being inaccessible at this time. Note that the key's 1594 type may have been changed before this function is called. 1595 1596 It is not safe to sleep in this method; the caller may hold spinlocks. 1597 1598 1599 * ``void (*describe)(const struct key *key, struct seq_file *p);`` 1600 1601 This method is optional. It is called during /proc/keys reading to 1602 summarise a key's description and payload in text form. 1603 1604 This method will be called with the RCU read lock held. rcu_dereference() 1605 should be used to read the payload pointer if the payload is to be 1606 accessed. key->datalen cannot be trusted to stay consistent with the 1607 contents of the payload. 1608 1609 The description will not change, though the key's state may. 1610 1611 It is not safe to sleep in this method; the RCU read lock is held by the 1612 caller. 1613 1614 1615 * ``long (*read)(const struct key *key, char __user *buffer, size_t buflen);`` 1616 1617 This method is optional. It is called by KEYCTL_READ to translate the 1618 key's payload into something a blob of data for userspace to deal with. 1619 Ideally, the blob should be in the same format as that passed in to the 1620 instantiate and update methods. 1621 1622 If successful, the blob size that could be produced should be returned 1623 rather than the size copied. 1624 1625 This method will be called with the key's semaphore read-locked. This will 1626 prevent the key's payload changing. It is not necessary to use RCU locking 1627 when accessing the key's payload. It is safe to sleep in this method, such 1628 as might happen when the userspace buffer is accessed. 1629 1630 1631 * ``int (*request_key)(struct key_construction *cons, const char *op, void *aux);`` 1632 1633 This method is optional. If provided, request_key() and friends will 1634 invoke this function rather than upcalling to /sbin/request-key to operate 1635 upon a key of this type. 1636 1637 The aux parameter is as passed to request_key_async_with_auxdata() and 1638 similar or is NULL otherwise. Also passed are the construction record for 1639 the key to be operated upon and the operation type (currently only 1640 "create"). 1641 1642 This method is permitted to return before the upcall is complete, but the 1643 following function must be called under all circumstances to complete the 1644 instantiation process, whether or not it succeeds, whether or not there's 1645 an error:: 1646 1647 void complete_request_key(struct key_construction *cons, int error); 1648 1649 The error parameter should be 0 on success, -ve on error. The 1650 construction record is destroyed by this action and the authorisation key 1651 will be revoked. If an error is indicated, the key under construction 1652 will be negatively instantiated if it wasn't already instantiated. 1653 1654 If this method returns an error, that error will be returned to the 1655 caller of request_key*(). complete_request_key() must be called prior to 1656 returning. 1657 1658 The key under construction and the authorisation key can be found in the 1659 key_construction struct pointed to by cons: 1660 1661 * ``struct key *key;`` 1662 1663 The key under construction. 1664 1665 * ``struct key *authkey;`` 1666 1667 The authorisation key. 1668 1669 1670 * ``struct key_restriction *(*lookup_restriction)(const char *params);`` 1671 1672 This optional method is used to enable userspace configuration of keyring 1673 restrictions. The restriction parameter string (not including the key type 1674 name) is passed in, and this method returns a pointer to a key_restriction 1675 structure containing the relevant functions and data to evaluate each 1676 attempted key link operation. If there is no match, -EINVAL is returned. 1677 1678 1679 * ``asym_eds_op`` and ``asym_verify_signature``:: 1680 1681 int (*asym_eds_op)(struct kernel_pkey_params *params, 1682 const void *in, void *out); 1683 int (*asym_verify_signature)(struct kernel_pkey_params *params, 1684 const void *in, const void *in2); 1685 1686 These methods are optional. If provided the first allows a key to be 1687 used to encrypt, decrypt or sign a blob of data, and the second allows a 1688 key to verify a signature. 1689 1690 In all cases, the following information is provided in the params block:: 1691 1692 struct kernel_pkey_params { 1693 struct key *key; 1694 const char *encoding; 1695 const char *hash_algo; 1696 char *info; 1697 __u32 in_len; 1698 union { 1699 __u32 out_len; 1700 __u32 in2_len; 1701 }; 1702 enum kernel_pkey_operation op : 8; 1703 }; 1704 1705 This includes the key to be used; a string indicating the encoding to use 1706 (for instance, "pkcs1" may be used with an RSA key to indicate 1707 RSASSA-PKCS1-v1.5 or RSAES-PKCS1-v1.5 encoding or "raw" if no encoding); 1708 the name of the hash algorithm used to generate the data for a signature 1709 (if appropriate); the sizes of the input and output (or second input) 1710 buffers; and the ID of the operation to be performed. 1711 1712 For a given operation ID, the input and output buffers are used as 1713 follows:: 1714 1715 Operation ID in,in_len out,out_len in2,in2_len 1716 ======================= =============== =============== =============== 1717 kernel_pkey_encrypt Raw data Encrypted data - 1718 kernel_pkey_decrypt Encrypted data Raw data - 1719 kernel_pkey_sign Raw data Signature - 1720 kernel_pkey_verify Raw data - Signature 1721 1722 asym_eds_op() deals with encryption, decryption and signature creation as 1723 specified by params->op. Note that params->op is also set for 1724 asym_verify_signature(). 1725 1726 Encrypting and signature creation both take raw data in the input buffer 1727 and return the encrypted result in the output buffer. Padding may have 1728 been added if an encoding was set. In the case of signature creation, 1729 depending on the encoding, the padding created may need to indicate the 1730 digest algorithm - the name of which should be supplied in hash_algo. 1731 1732 Decryption takes encrypted data in the input buffer and returns the raw 1733 data in the output buffer. Padding will get checked and stripped off if 1734 an encoding was set. 1735 1736 Verification takes raw data in the input buffer and the signature in the 1737 second input buffer and checks that the one matches the other. Padding 1738 will be validated. Depending on the encoding, the digest algorithm used 1739 to generate the raw data may need to be indicated in hash_algo. 1740 1741 If successful, asym_eds_op() should return the number of bytes written 1742 into the output buffer. asym_verify_signature() should return 0. 1743 1744 A variety of errors may be returned, including EOPNOTSUPP if the operation 1745 is not supported; EKEYREJECTED if verification fails; ENOPKG if the 1746 required crypto isn't available. 1747 1748 1749 * ``asym_query``:: 1750 1751 int (*asym_query)(const struct kernel_pkey_params *params, 1752 struct kernel_pkey_query *info); 1753 1754 This method is optional. If provided it allows information about the 1755 public or asymmetric key held in the key to be determined. 1756 1757 The parameter block is as for asym_eds_op() and co. but in_len and out_len 1758 are unused. The encoding and hash_algo fields should be used to reduce 1759 the returned buffer/data sizes as appropriate. 1760 1761 If successful, the following information is filled in:: 1762 1763 struct kernel_pkey_query { 1764 __u32 supported_ops; 1765 __u32 key_size; 1766 __u16 max_data_size; 1767 __u16 max_sig_size; 1768 __u16 max_enc_size; 1769 __u16 max_dec_size; 1770 }; 1771 1772 The supported_ops field will contain a bitmask indicating what operations 1773 are supported by the key, including encryption of a blob, decryption of a 1774 blob, signing a blob and verifying the signature on a blob. The following 1775 constants are defined for this:: 1776 1777 KEYCTL_SUPPORTS_{ENCRYPT,DECRYPT,SIGN,VERIFY} 1778 1779 The key_size field is the size of the key in bits. max_data_size and 1780 max_sig_size are the maximum raw data and signature sizes for creation and 1781 verification of a signature; max_enc_size and max_dec_size are the maximum 1782 raw data and signature sizes for encryption and decryption. The 1783 max_*_size fields are measured in bytes. 1784 1785 If successful, 0 will be returned. If the key doesn't support this, 1786 EOPNOTSUPP will be returned. 1787 1788 1789Request-Key Callback Service 1790============================ 1791 1792To create a new key, the kernel will attempt to execute the following command 1793line:: 1794 1795 /sbin/request-key create <key> <uid> <gid> \ 1796 <threadring> <processring> <sessionring> <callout_info> 1797 1798<key> is the key being constructed, and the three keyrings are the process 1799keyrings from the process that caused the search to be issued. These are 1800included for two reasons: 1801 1802 1 There may be an authentication token in one of the keyrings that is 1803 required to obtain the key, eg: a Kerberos Ticket-Granting Ticket. 1804 1805 2 The new key should probably be cached in one of these rings. 1806 1807This program should set it UID and GID to those specified before attempting to 1808access any more keys. It may then look around for a user specific process to 1809hand the request off to (perhaps a path held in placed in another key by, for 1810example, the KDE desktop manager). 1811 1812The program (or whatever it calls) should finish construction of the key by 1813calling KEYCTL_INSTANTIATE or KEYCTL_INSTANTIATE_IOV, which also permits it to 1814cache the key in one of the keyrings (probably the session ring) before 1815returning. Alternatively, the key can be marked as negative with KEYCTL_NEGATE 1816or KEYCTL_REJECT; this also permits the key to be cached in one of the 1817keyrings. 1818 1819If it returns with the key remaining in the unconstructed state, the key will 1820be marked as being negative, it will be added to the session keyring, and an 1821error will be returned to the key requestor. 1822 1823Supplementary information may be provided from whoever or whatever invoked this 1824service. This will be passed as the <callout_info> parameter. If no such 1825information was made available, then "-" will be passed as this parameter 1826instead. 1827 1828 1829Similarly, the kernel may attempt to update an expired or a soon to expire key 1830by executing:: 1831 1832 /sbin/request-key update <key> <uid> <gid> \ 1833 <threadring> <processring> <sessionring> 1834 1835In this case, the program isn't required to actually attach the key to a ring; 1836the rings are provided for reference. 1837 1838 1839Garbage Collection 1840================== 1841 1842Dead keys (for which the type has been removed) will be automatically unlinked 1843from those keyrings that point to them and deleted as soon as possible by a 1844background garbage collector. 1845 1846Similarly, revoked and expired keys will be garbage collected, but only after a 1847certain amount of time has passed. This time is set as a number of seconds in:: 1848 1849 /proc/sys/kernel/keys/gc_delay
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