1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* Task credentials management - see Documentation/security/credentials.rst 3 * 4 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells@redhat.com) 6 */ 7 8 #define pr_fmt(fmt) "CRED: " fmt 9 10 #include <linux/export.h> 11 #include <linux/cred.h> 12 #include <linux/slab.h> 13 #include <linux/sched.h> 14 #include <linux/sched/coredump.h> 15 #include <linux/key.h> 16 #include <linux/keyctl.h> 17 #include <linux/init_task.h> 18 #include <linux/security.h> 19 #include <linux/binfmts.h> 20 #include <linux/cn_proc.h> 21 #include <linux/uidgid.h> 22 23 #if 0 24 #define kdebug(FMT, ...) \ 25 printk("[%-5.5s%5u] " FMT "\n", \ 26 current->comm, current->pid, ##__VA_ARGS__) 27 #else 28 #define kdebug(FMT, ...) \ 29 do { \ 30 if (0) \ 31 no_printk("[%-5.5s%5u] " FMT "\n", \ 32 current->comm, current->pid, ##__VA_ARGS__); \ 33 } while (0) 34 #endif 35 36 static struct kmem_cache *cred_jar; 37 38 /* init to 2 - one for init_task, one to ensure it is never freed */ 39 static struct group_info init_groups = { .usage = REFCOUNT_INIT(2) }; 40 41 /* 42 * The initial credentials for the initial task 43 */ 44 struct cred init_cred = { 45 .usage = ATOMIC_INIT(4), 46 .uid = GLOBAL_ROOT_UID, 47 .gid = GLOBAL_ROOT_GID, 48 .suid = GLOBAL_ROOT_UID, 49 .sgid = GLOBAL_ROOT_GID, 50 .euid = GLOBAL_ROOT_UID, 51 .egid = GLOBAL_ROOT_GID, 52 .fsuid = GLOBAL_ROOT_UID, 53 .fsgid = GLOBAL_ROOT_GID, 54 .securebits = SECUREBITS_DEFAULT, 55 .cap_inheritable = CAP_EMPTY_SET, 56 .cap_permitted = CAP_FULL_SET, 57 .cap_effective = CAP_FULL_SET, 58 .cap_bset = CAP_FULL_SET, 59 .user = INIT_USER, 60 .user_ns = &init_user_ns, 61 .group_info = &init_groups, 62 .ucounts = &init_ucounts, 63 }; 64 65 /* 66 * The RCU callback to actually dispose of a set of credentials 67 */ 68 static void put_cred_rcu(struct rcu_head *rcu) 69 { 70 struct cred *cred = container_of(rcu, struct cred, rcu); 71 72 kdebug("put_cred_rcu(%p)", cred); 73 74 if (atomic_long_read(&cred->usage) != 0) 75 panic("CRED: put_cred_rcu() sees %p with usage %ld\n", 76 cred, atomic_long_read(&cred->usage)); 77 78 security_cred_free(cred); 79 key_put(cred->session_keyring); 80 key_put(cred->process_keyring); 81 key_put(cred->thread_keyring); 82 key_put(cred->request_key_auth); 83 if (cred->group_info) 84 put_group_info(cred->group_info); 85 free_uid(cred->user); 86 if (cred->ucounts) 87 put_ucounts(cred->ucounts); 88 put_user_ns(cred->user_ns); 89 kmem_cache_free(cred_jar, cred); 90 } 91 92 /** 93 * __put_cred - Destroy a set of credentials 94 * @cred: The record to release 95 * 96 * Destroy a set of credentials on which no references remain. 97 */ 98 void __put_cred(struct cred *cred) 99 { 100 kdebug("__put_cred(%p{%ld})", cred, 101 atomic_long_read(&cred->usage)); 102 103 BUG_ON(atomic_long_read(&cred->usage) != 0); 104 BUG_ON(cred == current->cred); 105 BUG_ON(cred == current->real_cred); 106 107 if (cred->non_rcu) 108 put_cred_rcu(&cred->rcu); 109 else 110 call_rcu(&cred->rcu, put_cred_rcu); 111 } 112 EXPORT_SYMBOL(__put_cred); 113 114 /* 115 * Clean up a task's credentials when it exits 116 */ 117 void exit_creds(struct task_struct *tsk) 118 { 119 struct cred *real_cred, *cred; 120 121 kdebug("exit_creds(%u,%p,%p,{%ld})", tsk->pid, tsk->real_cred, tsk->cred, 122 atomic_long_read(&tsk->cred->usage)); 123 124 real_cred = (struct cred *) tsk->real_cred; 125 tsk->real_cred = NULL; 126 127 cred = (struct cred *) tsk->cred; 128 tsk->cred = NULL; 129 130 if (real_cred == cred) { 131 put_cred_many(cred, 2); 132 } else { 133 put_cred(real_cred); 134 put_cred(cred); 135 } 136 137 #ifdef CONFIG_KEYS_REQUEST_CACHE 138 key_put(tsk->cached_requested_key); 139 tsk->cached_requested_key = NULL; 140 #endif 141 } 142 143 /** 144 * get_task_cred - Get another task's objective credentials 145 * @task: The task to query 146 * 147 * Get the objective credentials of a task, pinning them so that they can't go 148 * away. Accessing a task's credentials directly is not permitted. 149 * 150 * The caller must also make sure task doesn't get deleted, either by holding a 151 * ref on task or by holding tasklist_lock to prevent it from being unlinked. 152 */ 153 const struct cred *get_task_cred(struct task_struct *task) 154 { 155 const struct cred *cred; 156 157 rcu_read_lock(); 158 159 do { 160 cred = __task_cred((task)); 161 BUG_ON(!cred); 162 } while (!get_cred_rcu(cred)); 163 164 rcu_read_unlock(); 165 return cred; 166 } 167 EXPORT_SYMBOL(get_task_cred); 168 169 /* 170 * Allocate blank credentials, such that the credentials can be filled in at a 171 * later date without risk of ENOMEM. 172 */ 173 struct cred *cred_alloc_blank(void) 174 { 175 struct cred *new; 176 177 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL); 178 if (!new) 179 return NULL; 180 181 atomic_long_set(&new->usage, 1); 182 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0) 183 goto error; 184 185 return new; 186 187 error: 188 abort_creds(new); 189 return NULL; 190 } 191 192 /** 193 * prepare_creds - Prepare a new set of credentials for modification 194 * 195 * Prepare a new set of task credentials for modification. A task's creds 196 * shouldn't generally be modified directly, therefore this function is used to 197 * prepare a new copy, which the caller then modifies and then commits by 198 * calling commit_creds(). 199 * 200 * Preparation involves making a copy of the objective creds for modification. 201 * 202 * Returns a pointer to the new creds-to-be if successful, NULL otherwise. 203 * 204 * Call commit_creds() or abort_creds() to clean up. 205 */ 206 struct cred *prepare_creds(void) 207 { 208 struct task_struct *task = current; 209 const struct cred *old; 210 struct cred *new; 211 212 new = kmem_cache_alloc(cred_jar, GFP_KERNEL); 213 if (!new) 214 return NULL; 215 216 kdebug("prepare_creds() alloc %p", new); 217 218 old = task->cred; 219 memcpy(new, old, sizeof(struct cred)); 220 221 new->non_rcu = 0; 222 atomic_long_set(&new->usage, 1); 223 get_group_info(new->group_info); 224 get_uid(new->user); 225 get_user_ns(new->user_ns); 226 227 #ifdef CONFIG_KEYS 228 key_get(new->session_keyring); 229 key_get(new->process_keyring); 230 key_get(new->thread_keyring); 231 key_get(new->request_key_auth); 232 #endif 233 234 #ifdef CONFIG_SECURITY 235 new->security = NULL; 236 #endif 237 238 new->ucounts = get_ucounts(new->ucounts); 239 if (!new->ucounts) 240 goto error; 241 242 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) 243 goto error; 244 245 return new; 246 247 error: 248 abort_creds(new); 249 return NULL; 250 } 251 EXPORT_SYMBOL(prepare_creds); 252 253 /* 254 * Prepare credentials for current to perform an execve() 255 * - The caller must hold ->cred_guard_mutex 256 */ 257 struct cred *prepare_exec_creds(void) 258 { 259 struct cred *new; 260 261 new = prepare_creds(); 262 if (!new) 263 return new; 264 265 #ifdef CONFIG_KEYS 266 /* newly exec'd tasks don't get a thread keyring */ 267 key_put(new->thread_keyring); 268 new->thread_keyring = NULL; 269 270 /* inherit the session keyring; new process keyring */ 271 key_put(new->process_keyring); 272 new->process_keyring = NULL; 273 #endif 274 275 new->suid = new->fsuid = new->euid; 276 new->sgid = new->fsgid = new->egid; 277 278 return new; 279 } 280 281 /* 282 * Copy credentials for the new process created by fork() 283 * 284 * We share if we can, but under some circumstances we have to generate a new 285 * set. 286 * 287 * The new process gets the current process's subjective credentials as its 288 * objective and subjective credentials 289 */ 290 int copy_creds(struct task_struct *p, unsigned long clone_flags) 291 { 292 struct cred *new; 293 int ret; 294 295 #ifdef CONFIG_KEYS_REQUEST_CACHE 296 p->cached_requested_key = NULL; 297 #endif 298 299 if ( 300 #ifdef CONFIG_KEYS 301 !p->cred->thread_keyring && 302 #endif 303 clone_flags & CLONE_THREAD 304 ) { 305 p->real_cred = get_cred_many(p->cred, 2); 306 kdebug("share_creds(%p{%ld})", 307 p->cred, atomic_long_read(&p->cred->usage)); 308 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); 309 return 0; 310 } 311 312 new = prepare_creds(); 313 if (!new) 314 return -ENOMEM; 315 316 if (clone_flags & CLONE_NEWUSER) { 317 ret = create_user_ns(new); 318 if (ret < 0) 319 goto error_put; 320 ret = set_cred_ucounts(new); 321 if (ret < 0) 322 goto error_put; 323 } 324 325 #ifdef CONFIG_KEYS 326 /* new threads get their own thread keyrings if their parent already 327 * had one */ 328 if (new->thread_keyring) { 329 key_put(new->thread_keyring); 330 new->thread_keyring = NULL; 331 if (clone_flags & CLONE_THREAD) 332 install_thread_keyring_to_cred(new); 333 } 334 335 /* The process keyring is only shared between the threads in a process; 336 * anything outside of those threads doesn't inherit. 337 */ 338 if (!(clone_flags & CLONE_THREAD)) { 339 key_put(new->process_keyring); 340 new->process_keyring = NULL; 341 } 342 #endif 343 344 p->cred = p->real_cred = get_cred(new); 345 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); 346 return 0; 347 348 error_put: 349 put_cred(new); 350 return ret; 351 } 352 353 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset) 354 { 355 const struct user_namespace *set_ns = set->user_ns; 356 const struct user_namespace *subset_ns = subset->user_ns; 357 358 /* If the two credentials are in the same user namespace see if 359 * the capabilities of subset are a subset of set. 360 */ 361 if (set_ns == subset_ns) 362 return cap_issubset(subset->cap_permitted, set->cap_permitted); 363 364 /* The credentials are in a different user namespaces 365 * therefore one is a subset of the other only if a set is an 366 * ancestor of subset and set->euid is owner of subset or one 367 * of subsets ancestors. 368 */ 369 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) { 370 if ((set_ns == subset_ns->parent) && 371 uid_eq(subset_ns->owner, set->euid)) 372 return true; 373 } 374 375 return false; 376 } 377 378 /** 379 * commit_creds - Install new credentials upon the current task 380 * @new: The credentials to be assigned 381 * 382 * Install a new set of credentials to the current task, using RCU to replace 383 * the old set. Both the objective and the subjective credentials pointers are 384 * updated. This function may not be called if the subjective credentials are 385 * in an overridden state. 386 * 387 * This function eats the caller's reference to the new credentials. 388 * 389 * Always returns 0 thus allowing this function to be tail-called at the end 390 * of, say, sys_setgid(). 391 */ 392 int commit_creds(struct cred *new) 393 { 394 struct task_struct *task = current; 395 const struct cred *old = task->real_cred; 396 397 kdebug("commit_creds(%p{%ld})", new, 398 atomic_long_read(&new->usage)); 399 400 BUG_ON(task->cred != old); 401 BUG_ON(atomic_long_read(&new->usage) < 1); 402 403 get_cred(new); /* we will require a ref for the subj creds too */ 404 405 /* dumpability changes */ 406 if (!uid_eq(old->euid, new->euid) || 407 !gid_eq(old->egid, new->egid) || 408 !uid_eq(old->fsuid, new->fsuid) || 409 !gid_eq(old->fsgid, new->fsgid) || 410 !cred_cap_issubset(old, new)) { 411 if (task->mm) 412 set_dumpable(task->mm, suid_dumpable); 413 task->pdeath_signal = 0; 414 /* 415 * If a task drops privileges and becomes nondumpable, 416 * the dumpability change must become visible before 417 * the credential change; otherwise, a __ptrace_may_access() 418 * racing with this change may be able to attach to a task it 419 * shouldn't be able to attach to (as if the task had dropped 420 * privileges without becoming nondumpable). 421 * Pairs with a read barrier in __ptrace_may_access(). 422 */ 423 smp_wmb(); 424 } 425 426 /* alter the thread keyring */ 427 if (!uid_eq(new->fsuid, old->fsuid)) 428 key_fsuid_changed(new); 429 if (!gid_eq(new->fsgid, old->fsgid)) 430 key_fsgid_changed(new); 431 432 /* do it 433 * RLIMIT_NPROC limits on user->processes have already been checked 434 * in set_user(). 435 */ 436 if (new->user != old->user || new->user_ns != old->user_ns) 437 inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1); 438 rcu_assign_pointer(task->real_cred, new); 439 rcu_assign_pointer(task->cred, new); 440 if (new->user != old->user || new->user_ns != old->user_ns) 441 dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1); 442 443 /* send notifications */ 444 if (!uid_eq(new->uid, old->uid) || 445 !uid_eq(new->euid, old->euid) || 446 !uid_eq(new->suid, old->suid) || 447 !uid_eq(new->fsuid, old->fsuid)) 448 proc_id_connector(task, PROC_EVENT_UID); 449 450 if (!gid_eq(new->gid, old->gid) || 451 !gid_eq(new->egid, old->egid) || 452 !gid_eq(new->sgid, old->sgid) || 453 !gid_eq(new->fsgid, old->fsgid)) 454 proc_id_connector(task, PROC_EVENT_GID); 455 456 /* release the old obj and subj refs both */ 457 put_cred_many(old, 2); 458 return 0; 459 } 460 EXPORT_SYMBOL(commit_creds); 461 462 /** 463 * abort_creds - Discard a set of credentials and unlock the current task 464 * @new: The credentials that were going to be applied 465 * 466 * Discard a set of credentials that were under construction and unlock the 467 * current task. 468 */ 469 void abort_creds(struct cred *new) 470 { 471 kdebug("abort_creds(%p{%ld})", new, 472 atomic_long_read(&new->usage)); 473 474 BUG_ON(atomic_long_read(&new->usage) < 1); 475 put_cred(new); 476 } 477 EXPORT_SYMBOL(abort_creds); 478 479 /** 480 * override_creds - Override the current process's subjective credentials 481 * @new: The credentials to be assigned 482 * 483 * Install a set of temporary override subjective credentials on the current 484 * process, returning the old set for later reversion. 485 */ 486 const struct cred *override_creds(const struct cred *new) 487 { 488 const struct cred *old = current->cred; 489 490 kdebug("override_creds(%p{%ld})", new, 491 atomic_long_read(&new->usage)); 492 493 /* 494 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'. 495 * 496 * That means that we do not clear the 'non_rcu' flag, since 497 * we are only installing the cred into the thread-synchronous 498 * '->cred' pointer, not the '->real_cred' pointer that is 499 * visible to other threads under RCU. 500 */ 501 get_new_cred((struct cred *)new); 502 rcu_assign_pointer(current->cred, new); 503 504 kdebug("override_creds() = %p{%ld}", old, 505 atomic_long_read(&old->usage)); 506 return old; 507 } 508 EXPORT_SYMBOL(override_creds); 509 510 /** 511 * revert_creds - Revert a temporary subjective credentials override 512 * @old: The credentials to be restored 513 * 514 * Revert a temporary set of override subjective credentials to an old set, 515 * discarding the override set. 516 */ 517 void revert_creds(const struct cred *old) 518 { 519 const struct cred *override = current->cred; 520 521 kdebug("revert_creds(%p{%ld})", old, 522 atomic_long_read(&old->usage)); 523 524 rcu_assign_pointer(current->cred, old); 525 put_cred(override); 526 } 527 EXPORT_SYMBOL(revert_creds); 528 529 /** 530 * cred_fscmp - Compare two credentials with respect to filesystem access. 531 * @a: The first credential 532 * @b: The second credential 533 * 534 * cred_cmp() will return zero if both credentials have the same 535 * fsuid, fsgid, and supplementary groups. That is, if they will both 536 * provide the same access to files based on mode/uid/gid. 537 * If the credentials are different, then either -1 or 1 will 538 * be returned depending on whether @a comes before or after @b 539 * respectively in an arbitrary, but stable, ordering of credentials. 540 * 541 * Return: -1, 0, or 1 depending on comparison 542 */ 543 int cred_fscmp(const struct cred *a, const struct cred *b) 544 { 545 struct group_info *ga, *gb; 546 int g; 547 548 if (a == b) 549 return 0; 550 if (uid_lt(a->fsuid, b->fsuid)) 551 return -1; 552 if (uid_gt(a->fsuid, b->fsuid)) 553 return 1; 554 555 if (gid_lt(a->fsgid, b->fsgid)) 556 return -1; 557 if (gid_gt(a->fsgid, b->fsgid)) 558 return 1; 559 560 ga = a->group_info; 561 gb = b->group_info; 562 if (ga == gb) 563 return 0; 564 if (ga == NULL) 565 return -1; 566 if (gb == NULL) 567 return 1; 568 if (ga->ngroups < gb->ngroups) 569 return -1; 570 if (ga->ngroups > gb->ngroups) 571 return 1; 572 573 for (g = 0; g < ga->ngroups; g++) { 574 if (gid_lt(ga->gid[g], gb->gid[g])) 575 return -1; 576 if (gid_gt(ga->gid[g], gb->gid[g])) 577 return 1; 578 } 579 return 0; 580 } 581 EXPORT_SYMBOL(cred_fscmp); 582 583 int set_cred_ucounts(struct cred *new) 584 { 585 struct ucounts *new_ucounts, *old_ucounts = new->ucounts; 586 587 /* 588 * This optimization is needed because alloc_ucounts() uses locks 589 * for table lookups. 590 */ 591 if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid)) 592 return 0; 593 594 if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid))) 595 return -EAGAIN; 596 597 new->ucounts = new_ucounts; 598 put_ucounts(old_ucounts); 599 600 return 0; 601 } 602 603 /* 604 * initialise the credentials stuff 605 */ 606 void __init cred_init(void) 607 { 608 /* allocate a slab in which we can store credentials */ 609 cred_jar = KMEM_CACHE(cred, 610 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); 611 } 612 613 /** 614 * prepare_kernel_cred - Prepare a set of credentials for a kernel service 615 * @daemon: A userspace daemon to be used as a reference 616 * 617 * Prepare a set of credentials for a kernel service. This can then be used to 618 * override a task's own credentials so that work can be done on behalf of that 619 * task that requires a different subjective context. 620 * 621 * @daemon is used to provide a base cred, with the security data derived from 622 * that; if this is "&init_task", they'll be set to 0, no groups, full 623 * capabilities, and no keys. 624 * 625 * The caller may change these controls afterwards if desired. 626 * 627 * Returns the new credentials or NULL if out of memory. 628 */ 629 struct cred *prepare_kernel_cred(struct task_struct *daemon) 630 { 631 const struct cred *old; 632 struct cred *new; 633 634 if (WARN_ON_ONCE(!daemon)) 635 return NULL; 636 637 new = kmem_cache_alloc(cred_jar, GFP_KERNEL); 638 if (!new) 639 return NULL; 640 641 kdebug("prepare_kernel_cred() alloc %p", new); 642 643 old = get_task_cred(daemon); 644 645 *new = *old; 646 new->non_rcu = 0; 647 atomic_long_set(&new->usage, 1); 648 get_uid(new->user); 649 get_user_ns(new->user_ns); 650 get_group_info(new->group_info); 651 652 #ifdef CONFIG_KEYS 653 new->session_keyring = NULL; 654 new->process_keyring = NULL; 655 new->thread_keyring = NULL; 656 new->request_key_auth = NULL; 657 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; 658 #endif 659 660 #ifdef CONFIG_SECURITY 661 new->security = NULL; 662 #endif 663 new->ucounts = get_ucounts(new->ucounts); 664 if (!new->ucounts) 665 goto error; 666 667 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) 668 goto error; 669 670 put_cred(old); 671 return new; 672 673 error: 674 put_cred(new); 675 put_cred(old); 676 return NULL; 677 } 678 EXPORT_SYMBOL(prepare_kernel_cred); 679 680 /** 681 * set_security_override - Set the security ID in a set of credentials 682 * @new: The credentials to alter 683 * @secid: The LSM security ID to set 684 * 685 * Set the LSM security ID in a set of credentials so that the subjective 686 * security is overridden when an alternative set of credentials is used. 687 */ 688 int set_security_override(struct cred *new, u32 secid) 689 { 690 return security_kernel_act_as(new, secid); 691 } 692 EXPORT_SYMBOL(set_security_override); 693 694 /** 695 * set_security_override_from_ctx - Set the security ID in a set of credentials 696 * @new: The credentials to alter 697 * @secctx: The LSM security context to generate the security ID from. 698 * 699 * Set the LSM security ID in a set of credentials so that the subjective 700 * security is overridden when an alternative set of credentials is used. The 701 * security ID is specified in string form as a security context to be 702 * interpreted by the LSM. 703 */ 704 int set_security_override_from_ctx(struct cred *new, const char *secctx) 705 { 706 u32 secid; 707 int ret; 708 709 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid); 710 if (ret < 0) 711 return ret; 712 713 return set_security_override(new, secid); 714 } 715 EXPORT_SYMBOL(set_security_override_from_ctx); 716 717 /** 718 * set_create_files_as - Set the LSM file create context in a set of credentials 719 * @new: The credentials to alter 720 * @inode: The inode to take the context from 721 * 722 * Change the LSM file creation context in a set of credentials to be the same 723 * as the object context of the specified inode, so that the new inodes have 724 * the same MAC context as that inode. 725 */ 726 int set_create_files_as(struct cred *new, struct inode *inode) 727 { 728 if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid)) 729 return -EINVAL; 730 new->fsuid = inode->i_uid; 731 new->fsgid = inode->i_gid; 732 return security_kernel_create_files_as(new, inode); 733 } 734 EXPORT_SYMBOL(set_create_files_as); 735