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 #include <linux/export.h>
8 #include <linux/cred.h>
9 #include <linux/slab.h>
10 #include <linux/sched.h>
11 #include <linux/sched/coredump.h>
12 #include <linux/key.h>
13 #include <linux/keyctl.h>
14 #include <linux/init_task.h>
15 #include <linux/security.h>
16 #include <linux/binfmts.h>
17 #include <linux/cn_proc.h>
18 #include <linux/uidgid.h>
19
20 #if 0
21 #define kdebug(FMT, ...) \
22 printk("[%-5.5s%5u] " FMT "\n", \
23 current->comm, current->pid, ##__VA_ARGS__)
24 #else
25 #define kdebug(FMT, ...) \
26 do { \
27 if (0) \
28 no_printk("[%-5.5s%5u] " FMT "\n", \
29 current->comm, current->pid, ##__VA_ARGS__); \
30 } while (0)
31 #endif
32
33 static struct kmem_cache *cred_jar;
34
35 /* init to 2 - one for init_task, one to ensure it is never freed */
36 struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
37
38 /*
39 * The initial credentials for the initial task
40 */
41 struct cred init_cred = {
42 .usage = ATOMIC_INIT(4),
43 #ifdef CONFIG_DEBUG_CREDENTIALS
44 .subscribers = ATOMIC_INIT(2),
45 .magic = CRED_MAGIC,
46 #endif
47 .uid = GLOBAL_ROOT_UID,
48 .gid = GLOBAL_ROOT_GID,
49 .suid = GLOBAL_ROOT_UID,
50 .sgid = GLOBAL_ROOT_GID,
51 .euid = GLOBAL_ROOT_UID,
52 .egid = GLOBAL_ROOT_GID,
53 .fsuid = GLOBAL_ROOT_UID,
54 .fsgid = GLOBAL_ROOT_GID,
55 .securebits = SECUREBITS_DEFAULT,
56 .cap_inheritable = CAP_EMPTY_SET,
57 .cap_permitted = CAP_FULL_SET,
58 .cap_effective = CAP_FULL_SET,
59 .cap_bset = CAP_FULL_SET,
60 .user = INIT_USER,
61 .user_ns = &init_user_ns,
62 .group_info = &init_groups,
63 };
64
set_cred_subscribers(struct cred * cred,int n)65 static inline void set_cred_subscribers(struct cred *cred, int n)
66 {
67 #ifdef CONFIG_DEBUG_CREDENTIALS
68 atomic_set(&cred->subscribers, n);
69 #endif
70 }
71
read_cred_subscribers(const struct cred * cred)72 static inline int read_cred_subscribers(const struct cred *cred)
73 {
74 #ifdef CONFIG_DEBUG_CREDENTIALS
75 return atomic_read(&cred->subscribers);
76 #else
77 return 0;
78 #endif
79 }
80
alter_cred_subscribers(const struct cred * _cred,int n)81 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
82 {
83 #ifdef CONFIG_DEBUG_CREDENTIALS
84 struct cred *cred = (struct cred *) _cred;
85
86 atomic_add(n, &cred->subscribers);
87 #endif
88 }
89
90 /*
91 * The RCU callback to actually dispose of a set of credentials
92 */
put_cred_rcu(struct rcu_head * rcu)93 static void put_cred_rcu(struct rcu_head *rcu)
94 {
95 struct cred *cred = container_of(rcu, struct cred, rcu);
96
97 kdebug("put_cred_rcu(%p)", cred);
98
99 #ifdef CONFIG_DEBUG_CREDENTIALS
100 if (cred->magic != CRED_MAGIC_DEAD ||
101 atomic_read(&cred->usage) != 0 ||
102 read_cred_subscribers(cred) != 0)
103 panic("CRED: put_cred_rcu() sees %p with"
104 " mag %x, put %p, usage %d, subscr %d\n",
105 cred, cred->magic, cred->put_addr,
106 atomic_read(&cred->usage),
107 read_cred_subscribers(cred));
108 #else
109 if (atomic_read(&cred->usage) != 0)
110 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
111 cred, atomic_read(&cred->usage));
112 #endif
113
114 security_cred_free(cred);
115 key_put(cred->session_keyring);
116 key_put(cred->process_keyring);
117 key_put(cred->thread_keyring);
118 key_put(cred->request_key_auth);
119 if (cred->group_info)
120 put_group_info(cred->group_info);
121 free_uid(cred->user);
122 put_user_ns(cred->user_ns);
123 kmem_cache_free(cred_jar, cred);
124 }
125
126 /**
127 * __put_cred - Destroy a set of credentials
128 * @cred: The record to release
129 *
130 * Destroy a set of credentials on which no references remain.
131 */
__put_cred(struct cred * cred)132 void __put_cred(struct cred *cred)
133 {
134 kdebug("__put_cred(%p{%d,%d})", cred,
135 atomic_read(&cred->usage),
136 read_cred_subscribers(cred));
137
138 BUG_ON(atomic_read(&cred->usage) != 0);
139 #ifdef CONFIG_DEBUG_CREDENTIALS
140 BUG_ON(read_cred_subscribers(cred) != 0);
141 cred->magic = CRED_MAGIC_DEAD;
142 cred->put_addr = __builtin_return_address(0);
143 #endif
144 BUG_ON(cred == current->cred);
145 BUG_ON(cred == current->real_cred);
146
147 if (cred->non_rcu)
148 put_cred_rcu(&cred->rcu);
149 else
150 call_rcu(&cred->rcu, put_cred_rcu);
151 }
152 EXPORT_SYMBOL(__put_cred);
153
154 /*
155 * Clean up a task's credentials when it exits
156 */
exit_creds(struct task_struct * tsk)157 void exit_creds(struct task_struct *tsk)
158 {
159 struct cred *cred;
160
161 kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
162 atomic_read(&tsk->cred->usage),
163 read_cred_subscribers(tsk->cred));
164
165 cred = (struct cred *) tsk->real_cred;
166 tsk->real_cred = NULL;
167 validate_creds(cred);
168 alter_cred_subscribers(cred, -1);
169 put_cred(cred);
170
171 cred = (struct cred *) tsk->cred;
172 tsk->cred = NULL;
173 validate_creds(cred);
174 alter_cred_subscribers(cred, -1);
175 put_cred(cred);
176
177 #ifdef CONFIG_KEYS_REQUEST_CACHE
178 key_put(tsk->cached_requested_key);
179 tsk->cached_requested_key = NULL;
180 #endif
181 }
182
183 /**
184 * get_task_cred - Get another task's objective credentials
185 * @task: The task to query
186 *
187 * Get the objective credentials of a task, pinning them so that they can't go
188 * away. Accessing a task's credentials directly is not permitted.
189 *
190 * The caller must also make sure task doesn't get deleted, either by holding a
191 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
192 */
get_task_cred(struct task_struct * task)193 const struct cred *get_task_cred(struct task_struct *task)
194 {
195 const struct cred *cred;
196
197 rcu_read_lock();
198
199 do {
200 cred = __task_cred((task));
201 BUG_ON(!cred);
202 } while (!get_cred_rcu(cred));
203
204 rcu_read_unlock();
205 return cred;
206 }
207 EXPORT_SYMBOL(get_task_cred);
208
209 /*
210 * Allocate blank credentials, such that the credentials can be filled in at a
211 * later date without risk of ENOMEM.
212 */
cred_alloc_blank(void)213 struct cred *cred_alloc_blank(void)
214 {
215 struct cred *new;
216
217 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
218 if (!new)
219 return NULL;
220
221 atomic_set(&new->usage, 1);
222 #ifdef CONFIG_DEBUG_CREDENTIALS
223 new->magic = CRED_MAGIC;
224 #endif
225
226 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
227 goto error;
228
229 return new;
230
231 error:
232 abort_creds(new);
233 return NULL;
234 }
235
236 /**
237 * prepare_creds - Prepare a new set of credentials for modification
238 *
239 * Prepare a new set of task credentials for modification. A task's creds
240 * shouldn't generally be modified directly, therefore this function is used to
241 * prepare a new copy, which the caller then modifies and then commits by
242 * calling commit_creds().
243 *
244 * Preparation involves making a copy of the objective creds for modification.
245 *
246 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
247 *
248 * Call commit_creds() or abort_creds() to clean up.
249 */
prepare_creds(void)250 struct cred *prepare_creds(void)
251 {
252 struct task_struct *task = current;
253 const struct cred *old;
254 struct cred *new;
255
256 validate_process_creds();
257
258 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
259 if (!new)
260 return NULL;
261
262 kdebug("prepare_creds() alloc %p", new);
263
264 old = task->cred;
265 memcpy(new, old, sizeof(struct cred));
266
267 new->non_rcu = 0;
268 atomic_set(&new->usage, 1);
269 set_cred_subscribers(new, 0);
270 get_group_info(new->group_info);
271 get_uid(new->user);
272 get_user_ns(new->user_ns);
273
274 #ifdef CONFIG_KEYS
275 key_get(new->session_keyring);
276 key_get(new->process_keyring);
277 key_get(new->thread_keyring);
278 key_get(new->request_key_auth);
279 #endif
280
281 #ifdef CONFIG_SECURITY
282 new->security = NULL;
283 #endif
284
285 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
286 goto error;
287 validate_creds(new);
288 return new;
289
290 error:
291 abort_creds(new);
292 return NULL;
293 }
294 EXPORT_SYMBOL(prepare_creds);
295
296 /*
297 * Prepare credentials for current to perform an execve()
298 * - The caller must hold ->cred_guard_mutex
299 */
prepare_exec_creds(void)300 struct cred *prepare_exec_creds(void)
301 {
302 struct cred *new;
303
304 new = prepare_creds();
305 if (!new)
306 return new;
307
308 #ifdef CONFIG_KEYS
309 /* newly exec'd tasks don't get a thread keyring */
310 key_put(new->thread_keyring);
311 new->thread_keyring = NULL;
312
313 /* inherit the session keyring; new process keyring */
314 key_put(new->process_keyring);
315 new->process_keyring = NULL;
316 #endif
317
318 return new;
319 }
320
321 /*
322 * Copy credentials for the new process created by fork()
323 *
324 * We share if we can, but under some circumstances we have to generate a new
325 * set.
326 *
327 * The new process gets the current process's subjective credentials as its
328 * objective and subjective credentials
329 */
copy_creds(struct task_struct * p,unsigned long clone_flags)330 int copy_creds(struct task_struct *p, unsigned long clone_flags)
331 {
332 struct cred *new;
333 int ret;
334
335 #ifdef CONFIG_KEYS_REQUEST_CACHE
336 p->cached_requested_key = NULL;
337 #endif
338
339 if (
340 #ifdef CONFIG_KEYS
341 !p->cred->thread_keyring &&
342 #endif
343 clone_flags & CLONE_THREAD
344 ) {
345 p->real_cred = get_cred(p->cred);
346 get_cred(p->cred);
347 alter_cred_subscribers(p->cred, 2);
348 kdebug("share_creds(%p{%d,%d})",
349 p->cred, atomic_read(&p->cred->usage),
350 read_cred_subscribers(p->cred));
351 atomic_inc(&p->cred->user->processes);
352 return 0;
353 }
354
355 new = prepare_creds();
356 if (!new)
357 return -ENOMEM;
358
359 if (clone_flags & CLONE_NEWUSER) {
360 ret = create_user_ns(new);
361 if (ret < 0)
362 goto error_put;
363 }
364
365 #ifdef CONFIG_KEYS
366 /* new threads get their own thread keyrings if their parent already
367 * had one */
368 if (new->thread_keyring) {
369 key_put(new->thread_keyring);
370 new->thread_keyring = NULL;
371 if (clone_flags & CLONE_THREAD)
372 install_thread_keyring_to_cred(new);
373 }
374
375 /* The process keyring is only shared between the threads in a process;
376 * anything outside of those threads doesn't inherit.
377 */
378 if (!(clone_flags & CLONE_THREAD)) {
379 key_put(new->process_keyring);
380 new->process_keyring = NULL;
381 }
382 #endif
383
384 atomic_inc(&new->user->processes);
385 p->cred = p->real_cred = get_cred(new);
386 alter_cred_subscribers(new, 2);
387 validate_creds(new);
388 return 0;
389
390 error_put:
391 put_cred(new);
392 return ret;
393 }
394
cred_cap_issubset(const struct cred * set,const struct cred * subset)395 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
396 {
397 const struct user_namespace *set_ns = set->user_ns;
398 const struct user_namespace *subset_ns = subset->user_ns;
399
400 /* If the two credentials are in the same user namespace see if
401 * the capabilities of subset are a subset of set.
402 */
403 if (set_ns == subset_ns)
404 return cap_issubset(subset->cap_permitted, set->cap_permitted);
405
406 /* The credentials are in a different user namespaces
407 * therefore one is a subset of the other only if a set is an
408 * ancestor of subset and set->euid is owner of subset or one
409 * of subsets ancestors.
410 */
411 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
412 if ((set_ns == subset_ns->parent) &&
413 uid_eq(subset_ns->owner, set->euid))
414 return true;
415 }
416
417 return false;
418 }
419
420 /**
421 * commit_creds - Install new credentials upon the current task
422 * @new: The credentials to be assigned
423 *
424 * Install a new set of credentials to the current task, using RCU to replace
425 * the old set. Both the objective and the subjective credentials pointers are
426 * updated. This function may not be called if the subjective credentials are
427 * in an overridden state.
428 *
429 * This function eats the caller's reference to the new credentials.
430 *
431 * Always returns 0 thus allowing this function to be tail-called at the end
432 * of, say, sys_setgid().
433 */
commit_creds(struct cred * new)434 int commit_creds(struct cred *new)
435 {
436 struct task_struct *task = current;
437 const struct cred *old = task->real_cred;
438
439 kdebug("commit_creds(%p{%d,%d})", new,
440 atomic_read(&new->usage),
441 read_cred_subscribers(new));
442
443 BUG_ON(task->cred != old);
444 #ifdef CONFIG_DEBUG_CREDENTIALS
445 BUG_ON(read_cred_subscribers(old) < 2);
446 validate_creds(old);
447 validate_creds(new);
448 #endif
449 BUG_ON(atomic_read(&new->usage) < 1);
450
451 get_cred(new); /* we will require a ref for the subj creds too */
452
453 /* dumpability changes */
454 if (!uid_eq(old->euid, new->euid) ||
455 !gid_eq(old->egid, new->egid) ||
456 !uid_eq(old->fsuid, new->fsuid) ||
457 !gid_eq(old->fsgid, new->fsgid) ||
458 !cred_cap_issubset(old, new)) {
459 if (task->mm)
460 set_dumpable(task->mm, suid_dumpable);
461 task->pdeath_signal = 0;
462 /*
463 * If a task drops privileges and becomes nondumpable,
464 * the dumpability change must become visible before
465 * the credential change; otherwise, a __ptrace_may_access()
466 * racing with this change may be able to attach to a task it
467 * shouldn't be able to attach to (as if the task had dropped
468 * privileges without becoming nondumpable).
469 * Pairs with a read barrier in __ptrace_may_access().
470 */
471 smp_wmb();
472 }
473
474 /* alter the thread keyring */
475 if (!uid_eq(new->fsuid, old->fsuid))
476 key_fsuid_changed(new);
477 if (!gid_eq(new->fsgid, old->fsgid))
478 key_fsgid_changed(new);
479
480 /* do it
481 * RLIMIT_NPROC limits on user->processes have already been checked
482 * in set_user().
483 */
484 alter_cred_subscribers(new, 2);
485 if (new->user != old->user)
486 atomic_inc(&new->user->processes);
487 rcu_assign_pointer(task->real_cred, new);
488 rcu_assign_pointer(task->cred, new);
489 if (new->user != old->user)
490 atomic_dec(&old->user->processes);
491 alter_cred_subscribers(old, -2);
492
493 /* send notifications */
494 if (!uid_eq(new->uid, old->uid) ||
495 !uid_eq(new->euid, old->euid) ||
496 !uid_eq(new->suid, old->suid) ||
497 !uid_eq(new->fsuid, old->fsuid))
498 proc_id_connector(task, PROC_EVENT_UID);
499
500 if (!gid_eq(new->gid, old->gid) ||
501 !gid_eq(new->egid, old->egid) ||
502 !gid_eq(new->sgid, old->sgid) ||
503 !gid_eq(new->fsgid, old->fsgid))
504 proc_id_connector(task, PROC_EVENT_GID);
505
506 /* release the old obj and subj refs both */
507 put_cred(old);
508 put_cred(old);
509 return 0;
510 }
511 EXPORT_SYMBOL(commit_creds);
512
513 /**
514 * abort_creds - Discard a set of credentials and unlock the current task
515 * @new: The credentials that were going to be applied
516 *
517 * Discard a set of credentials that were under construction and unlock the
518 * current task.
519 */
abort_creds(struct cred * new)520 void abort_creds(struct cred *new)
521 {
522 kdebug("abort_creds(%p{%d,%d})", new,
523 atomic_read(&new->usage),
524 read_cred_subscribers(new));
525
526 #ifdef CONFIG_DEBUG_CREDENTIALS
527 BUG_ON(read_cred_subscribers(new) != 0);
528 #endif
529 BUG_ON(atomic_read(&new->usage) < 1);
530 put_cred(new);
531 }
532 EXPORT_SYMBOL(abort_creds);
533
534 /**
535 * override_creds - Override the current process's subjective credentials
536 * @new: The credentials to be assigned
537 *
538 * Install a set of temporary override subjective credentials on the current
539 * process, returning the old set for later reversion.
540 */
override_creds(const struct cred * new)541 const struct cred *override_creds(const struct cred *new)
542 {
543 const struct cred *old = current->cred;
544
545 kdebug("override_creds(%p{%d,%d})", new,
546 atomic_read(&new->usage),
547 read_cred_subscribers(new));
548
549 validate_creds(old);
550 validate_creds(new);
551
552 /*
553 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
554 *
555 * That means that we do not clear the 'non_rcu' flag, since
556 * we are only installing the cred into the thread-synchronous
557 * '->cred' pointer, not the '->real_cred' pointer that is
558 * visible to other threads under RCU.
559 *
560 * Also note that we did validate_creds() manually, not depending
561 * on the validation in 'get_cred()'.
562 */
563 get_new_cred((struct cred *)new);
564 alter_cred_subscribers(new, 1);
565 rcu_assign_pointer(current->cred, new);
566 alter_cred_subscribers(old, -1);
567
568 kdebug("override_creds() = %p{%d,%d}", old,
569 atomic_read(&old->usage),
570 read_cred_subscribers(old));
571 return old;
572 }
573 EXPORT_SYMBOL(override_creds);
574
575 /**
576 * revert_creds - Revert a temporary subjective credentials override
577 * @old: The credentials to be restored
578 *
579 * Revert a temporary set of override subjective credentials to an old set,
580 * discarding the override set.
581 */
revert_creds(const struct cred * old)582 void revert_creds(const struct cred *old)
583 {
584 const struct cred *override = current->cred;
585
586 kdebug("revert_creds(%p{%d,%d})", old,
587 atomic_read(&old->usage),
588 read_cred_subscribers(old));
589
590 validate_creds(old);
591 validate_creds(override);
592 alter_cred_subscribers(old, 1);
593 rcu_assign_pointer(current->cred, old);
594 alter_cred_subscribers(override, -1);
595 put_cred(override);
596 }
597 EXPORT_SYMBOL(revert_creds);
598
599 /**
600 * cred_fscmp - Compare two credentials with respect to filesystem access.
601 * @a: The first credential
602 * @b: The second credential
603 *
604 * cred_cmp() will return zero if both credentials have the same
605 * fsuid, fsgid, and supplementary groups. That is, if they will both
606 * provide the same access to files based on mode/uid/gid.
607 * If the credentials are different, then either -1 or 1 will
608 * be returned depending on whether @a comes before or after @b
609 * respectively in an arbitrary, but stable, ordering of credentials.
610 *
611 * Return: -1, 0, or 1 depending on comparison
612 */
cred_fscmp(const struct cred * a,const struct cred * b)613 int cred_fscmp(const struct cred *a, const struct cred *b)
614 {
615 struct group_info *ga, *gb;
616 int g;
617
618 if (a == b)
619 return 0;
620 if (uid_lt(a->fsuid, b->fsuid))
621 return -1;
622 if (uid_gt(a->fsuid, b->fsuid))
623 return 1;
624
625 if (gid_lt(a->fsgid, b->fsgid))
626 return -1;
627 if (gid_gt(a->fsgid, b->fsgid))
628 return 1;
629
630 ga = a->group_info;
631 gb = b->group_info;
632 if (ga == gb)
633 return 0;
634 if (ga == NULL)
635 return -1;
636 if (gb == NULL)
637 return 1;
638 if (ga->ngroups < gb->ngroups)
639 return -1;
640 if (ga->ngroups > gb->ngroups)
641 return 1;
642
643 for (g = 0; g < ga->ngroups; g++) {
644 if (gid_lt(ga->gid[g], gb->gid[g]))
645 return -1;
646 if (gid_gt(ga->gid[g], gb->gid[g]))
647 return 1;
648 }
649 return 0;
650 }
651 EXPORT_SYMBOL(cred_fscmp);
652
653 /*
654 * initialise the credentials stuff
655 */
cred_init(void)656 void __init cred_init(void)
657 {
658 /* allocate a slab in which we can store credentials */
659 cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
660 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
661 }
662
663 /**
664 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
665 * @daemon: A userspace daemon to be used as a reference
666 *
667 * Prepare a set of credentials for a kernel service. This can then be used to
668 * override a task's own credentials so that work can be done on behalf of that
669 * task that requires a different subjective context.
670 *
671 * @daemon is used to provide a base for the security record, but can be NULL.
672 * If @daemon is supplied, then the security data will be derived from that;
673 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
674 *
675 * The caller may change these controls afterwards if desired.
676 *
677 * Returns the new credentials or NULL if out of memory.
678 *
679 * Does not take, and does not return holding current->cred_replace_mutex.
680 */
prepare_kernel_cred(struct task_struct * daemon)681 struct cred *prepare_kernel_cred(struct task_struct *daemon)
682 {
683 const struct cred *old;
684 struct cred *new;
685
686 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
687 if (!new)
688 return NULL;
689
690 kdebug("prepare_kernel_cred() alloc %p", new);
691
692 if (daemon)
693 old = get_task_cred(daemon);
694 else
695 old = get_cred(&init_cred);
696
697 validate_creds(old);
698
699 *new = *old;
700 new->non_rcu = 0;
701 atomic_set(&new->usage, 1);
702 set_cred_subscribers(new, 0);
703 get_uid(new->user);
704 get_user_ns(new->user_ns);
705 get_group_info(new->group_info);
706
707 #ifdef CONFIG_KEYS
708 new->session_keyring = NULL;
709 new->process_keyring = NULL;
710 new->thread_keyring = NULL;
711 new->request_key_auth = NULL;
712 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
713 #endif
714
715 #ifdef CONFIG_SECURITY
716 new->security = NULL;
717 #endif
718 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
719 goto error;
720
721 put_cred(old);
722 validate_creds(new);
723 return new;
724
725 error:
726 put_cred(new);
727 put_cred(old);
728 return NULL;
729 }
730 EXPORT_SYMBOL(prepare_kernel_cred);
731
732 /**
733 * set_security_override - Set the security ID in a set of credentials
734 * @new: The credentials to alter
735 * @secid: The LSM security ID to set
736 *
737 * Set the LSM security ID in a set of credentials so that the subjective
738 * security is overridden when an alternative set of credentials is used.
739 */
set_security_override(struct cred * new,u32 secid)740 int set_security_override(struct cred *new, u32 secid)
741 {
742 return security_kernel_act_as(new, secid);
743 }
744 EXPORT_SYMBOL(set_security_override);
745
746 /**
747 * set_security_override_from_ctx - Set the security ID in a set of credentials
748 * @new: The credentials to alter
749 * @secctx: The LSM security context to generate the security ID from.
750 *
751 * Set the LSM security ID in a set of credentials so that the subjective
752 * security is overridden when an alternative set of credentials is used. The
753 * security ID is specified in string form as a security context to be
754 * interpreted by the LSM.
755 */
set_security_override_from_ctx(struct cred * new,const char * secctx)756 int set_security_override_from_ctx(struct cred *new, const char *secctx)
757 {
758 u32 secid;
759 int ret;
760
761 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
762 if (ret < 0)
763 return ret;
764
765 return set_security_override(new, secid);
766 }
767 EXPORT_SYMBOL(set_security_override_from_ctx);
768
769 /**
770 * set_create_files_as - Set the LSM file create context in a set of credentials
771 * @new: The credentials to alter
772 * @inode: The inode to take the context from
773 *
774 * Change the LSM file creation context in a set of credentials to be the same
775 * as the object context of the specified inode, so that the new inodes have
776 * the same MAC context as that inode.
777 */
set_create_files_as(struct cred * new,struct inode * inode)778 int set_create_files_as(struct cred *new, struct inode *inode)
779 {
780 if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
781 return -EINVAL;
782 new->fsuid = inode->i_uid;
783 new->fsgid = inode->i_gid;
784 return security_kernel_create_files_as(new, inode);
785 }
786 EXPORT_SYMBOL(set_create_files_as);
787
788 #ifdef CONFIG_DEBUG_CREDENTIALS
789
creds_are_invalid(const struct cred * cred)790 bool creds_are_invalid(const struct cred *cred)
791 {
792 if (cred->magic != CRED_MAGIC)
793 return true;
794 return false;
795 }
796 EXPORT_SYMBOL(creds_are_invalid);
797
798 /*
799 * dump invalid credentials
800 */
dump_invalid_creds(const struct cred * cred,const char * label,const struct task_struct * tsk)801 static void dump_invalid_creds(const struct cred *cred, const char *label,
802 const struct task_struct *tsk)
803 {
804 printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
805 label, cred,
806 cred == &init_cred ? "[init]" : "",
807 cred == tsk->real_cred ? "[real]" : "",
808 cred == tsk->cred ? "[eff]" : "");
809 printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
810 cred->magic, cred->put_addr);
811 printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
812 atomic_read(&cred->usage),
813 read_cred_subscribers(cred));
814 printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
815 from_kuid_munged(&init_user_ns, cred->uid),
816 from_kuid_munged(&init_user_ns, cred->euid),
817 from_kuid_munged(&init_user_ns, cred->suid),
818 from_kuid_munged(&init_user_ns, cred->fsuid));
819 printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
820 from_kgid_munged(&init_user_ns, cred->gid),
821 from_kgid_munged(&init_user_ns, cred->egid),
822 from_kgid_munged(&init_user_ns, cred->sgid),
823 from_kgid_munged(&init_user_ns, cred->fsgid));
824 #ifdef CONFIG_SECURITY
825 printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
826 if ((unsigned long) cred->security >= PAGE_SIZE &&
827 (((unsigned long) cred->security & 0xffffff00) !=
828 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
829 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
830 ((u32*)cred->security)[0],
831 ((u32*)cred->security)[1]);
832 #endif
833 }
834
835 /*
836 * report use of invalid credentials
837 */
__invalid_creds(const struct cred * cred,const char * file,unsigned line)838 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
839 {
840 printk(KERN_ERR "CRED: Invalid credentials\n");
841 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
842 dump_invalid_creds(cred, "Specified", current);
843 BUG();
844 }
845 EXPORT_SYMBOL(__invalid_creds);
846
847 /*
848 * check the credentials on a process
849 */
__validate_process_creds(struct task_struct * tsk,const char * file,unsigned line)850 void __validate_process_creds(struct task_struct *tsk,
851 const char *file, unsigned line)
852 {
853 if (tsk->cred == tsk->real_cred) {
854 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
855 creds_are_invalid(tsk->cred)))
856 goto invalid_creds;
857 } else {
858 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
859 read_cred_subscribers(tsk->cred) < 1 ||
860 creds_are_invalid(tsk->real_cred) ||
861 creds_are_invalid(tsk->cred)))
862 goto invalid_creds;
863 }
864 return;
865
866 invalid_creds:
867 printk(KERN_ERR "CRED: Invalid process credentials\n");
868 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
869
870 dump_invalid_creds(tsk->real_cred, "Real", tsk);
871 if (tsk->cred != tsk->real_cred)
872 dump_invalid_creds(tsk->cred, "Effective", tsk);
873 else
874 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
875 BUG();
876 }
877 EXPORT_SYMBOL(__validate_process_creds);
878
879 /*
880 * check creds for do_exit()
881 */
validate_creds_for_do_exit(struct task_struct * tsk)882 void validate_creds_for_do_exit(struct task_struct *tsk)
883 {
884 kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
885 tsk->real_cred, tsk->cred,
886 atomic_read(&tsk->cred->usage),
887 read_cred_subscribers(tsk->cred));
888
889 __validate_process_creds(tsk, __FILE__, __LINE__);
890 }
891
892 #endif /* CONFIG_DEBUG_CREDENTIALS */
893