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 #include <trace/hooks/creds.h>
21
22 #if 0
23 #define kdebug(FMT, ...) \
24 printk("[%-5.5s%5u] " FMT "\n", \
25 current->comm, current->pid, ##__VA_ARGS__)
26 #else
27 #define kdebug(FMT, ...) \
28 do { \
29 if (0) \
30 no_printk("[%-5.5s%5u] " FMT "\n", \
31 current->comm, current->pid, ##__VA_ARGS__); \
32 } while (0)
33 #endif
34
35 static struct kmem_cache *cred_jar;
36
37 /* init to 2 - one for init_task, one to ensure it is never freed */
38 static struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
39
40 /*
41 * The initial credentials for the initial task
42 */
43 struct cred init_cred = {
44 .usage = ATOMIC_INIT(4),
45 #ifdef CONFIG_DEBUG_CREDENTIALS
46 .subscribers = ATOMIC_INIT(2),
47 .magic = CRED_MAGIC,
48 #endif
49 .uid = GLOBAL_ROOT_UID,
50 .gid = GLOBAL_ROOT_GID,
51 .suid = GLOBAL_ROOT_UID,
52 .sgid = GLOBAL_ROOT_GID,
53 .euid = GLOBAL_ROOT_UID,
54 .egid = GLOBAL_ROOT_GID,
55 .fsuid = GLOBAL_ROOT_UID,
56 .fsgid = GLOBAL_ROOT_GID,
57 .securebits = SECUREBITS_DEFAULT,
58 .cap_inheritable = CAP_EMPTY_SET,
59 .cap_permitted = CAP_FULL_SET,
60 .cap_effective = CAP_FULL_SET,
61 .cap_bset = CAP_FULL_SET,
62 .user = INIT_USER,
63 .user_ns = &init_user_ns,
64 .group_info = &init_groups,
65 .ucounts = &init_ucounts,
66 };
67
set_cred_subscribers(struct cred * cred,int n)68 static inline void set_cred_subscribers(struct cred *cred, int n)
69 {
70 #ifdef CONFIG_DEBUG_CREDENTIALS
71 atomic_set(&cred->subscribers, n);
72 #endif
73 }
74
read_cred_subscribers(const struct cred * cred)75 static inline int read_cred_subscribers(const struct cred *cred)
76 {
77 #ifdef CONFIG_DEBUG_CREDENTIALS
78 return atomic_read(&cred->subscribers);
79 #else
80 return 0;
81 #endif
82 }
83
alter_cred_subscribers(const struct cred * _cred,int n)84 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
85 {
86 #ifdef CONFIG_DEBUG_CREDENTIALS
87 struct cred *cred = (struct cred *) _cred;
88
89 atomic_add(n, &cred->subscribers);
90 #endif
91 }
92
93 /*
94 * The RCU callback to actually dispose of a set of credentials
95 */
put_cred_rcu(struct rcu_head * rcu)96 static void put_cred_rcu(struct rcu_head *rcu)
97 {
98 struct cred *cred = container_of(rcu, struct cred, rcu);
99
100 kdebug("put_cred_rcu(%p)", cred);
101
102 #ifdef CONFIG_DEBUG_CREDENTIALS
103 if (cred->magic != CRED_MAGIC_DEAD ||
104 atomic_read(&cred->usage) != 0 ||
105 read_cred_subscribers(cred) != 0)
106 panic("CRED: put_cred_rcu() sees %p with"
107 " mag %x, put %p, usage %d, subscr %d\n",
108 cred, cred->magic, cred->put_addr,
109 atomic_read(&cred->usage),
110 read_cred_subscribers(cred));
111 #else
112 if (atomic_read(&cred->usage) != 0)
113 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
114 cred, atomic_read(&cred->usage));
115 #endif
116
117 security_cred_free(cred);
118 key_put(cred->session_keyring);
119 key_put(cred->process_keyring);
120 key_put(cred->thread_keyring);
121 key_put(cred->request_key_auth);
122 if (cred->group_info)
123 put_group_info(cred->group_info);
124 free_uid(cred->user);
125 if (cred->ucounts)
126 put_ucounts(cred->ucounts);
127 put_user_ns(cred->user_ns);
128 kmem_cache_free(cred_jar, cred);
129 }
130
131 /**
132 * __put_cred - Destroy a set of credentials
133 * @cred: The record to release
134 *
135 * Destroy a set of credentials on which no references remain.
136 */
__put_cred(struct cred * cred)137 void __put_cred(struct cred *cred)
138 {
139 kdebug("__put_cred(%p{%d,%d})", cred,
140 atomic_read(&cred->usage),
141 read_cred_subscribers(cred));
142
143 BUG_ON(atomic_read(&cred->usage) != 0);
144 #ifdef CONFIG_DEBUG_CREDENTIALS
145 BUG_ON(read_cred_subscribers(cred) != 0);
146 cred->magic = CRED_MAGIC_DEAD;
147 cred->put_addr = __builtin_return_address(0);
148 #endif
149 BUG_ON(cred == current->cred);
150 BUG_ON(cred == current->real_cred);
151
152 if (cred->non_rcu)
153 put_cred_rcu(&cred->rcu);
154 else
155 call_rcu(&cred->rcu, put_cred_rcu);
156 }
157 EXPORT_SYMBOL(__put_cred);
158
159 /*
160 * Clean up a task's credentials when it exits
161 */
exit_creds(struct task_struct * tsk)162 void exit_creds(struct task_struct *tsk)
163 {
164 struct cred *cred;
165
166 kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
167 atomic_read(&tsk->cred->usage),
168 read_cred_subscribers(tsk->cred));
169
170 cred = (struct cred *) tsk->real_cred;
171 tsk->real_cred = NULL;
172 validate_creds(cred);
173 alter_cred_subscribers(cred, -1);
174 put_cred(cred);
175
176 cred = (struct cred *) tsk->cred;
177 tsk->cred = NULL;
178 validate_creds(cred);
179 alter_cred_subscribers(cred, -1);
180 put_cred(cred);
181
182 #ifdef CONFIG_KEYS_REQUEST_CACHE
183 key_put(tsk->cached_requested_key);
184 tsk->cached_requested_key = NULL;
185 #endif
186 trace_android_rvh_exit_creds(tsk, cred);
187 }
188
189 /**
190 * get_task_cred - Get another task's objective credentials
191 * @task: The task to query
192 *
193 * Get the objective credentials of a task, pinning them so that they can't go
194 * away. Accessing a task's credentials directly is not permitted.
195 *
196 * The caller must also make sure task doesn't get deleted, either by holding a
197 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
198 */
get_task_cred(struct task_struct * task)199 const struct cred *get_task_cred(struct task_struct *task)
200 {
201 const struct cred *cred;
202
203 rcu_read_lock();
204
205 do {
206 cred = __task_cred((task));
207 BUG_ON(!cred);
208 } while (!get_cred_rcu(cred));
209
210 rcu_read_unlock();
211 return cred;
212 }
213 EXPORT_SYMBOL(get_task_cred);
214
215 /*
216 * Allocate blank credentials, such that the credentials can be filled in at a
217 * later date without risk of ENOMEM.
218 */
cred_alloc_blank(void)219 struct cred *cred_alloc_blank(void)
220 {
221 struct cred *new;
222
223 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
224 if (!new)
225 return NULL;
226
227 atomic_set(&new->usage, 1);
228 #ifdef CONFIG_DEBUG_CREDENTIALS
229 new->magic = CRED_MAGIC;
230 #endif
231 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
232 goto error;
233
234 return new;
235
236 error:
237 abort_creds(new);
238 return NULL;
239 }
240
241 /**
242 * prepare_creds - Prepare a new set of credentials for modification
243 *
244 * Prepare a new set of task credentials for modification. A task's creds
245 * shouldn't generally be modified directly, therefore this function is used to
246 * prepare a new copy, which the caller then modifies and then commits by
247 * calling commit_creds().
248 *
249 * Preparation involves making a copy of the objective creds for modification.
250 *
251 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
252 *
253 * Call commit_creds() or abort_creds() to clean up.
254 */
prepare_creds(void)255 struct cred *prepare_creds(void)
256 {
257 struct task_struct *task = current;
258 const struct cred *old;
259 struct cred *new;
260
261 validate_process_creds();
262
263 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
264 if (!new)
265 return NULL;
266
267 kdebug("prepare_creds() alloc %p", new);
268
269 old = task->cred;
270 memcpy(new, old, sizeof(struct cred));
271
272 new->non_rcu = 0;
273 atomic_set(&new->usage, 1);
274 set_cred_subscribers(new, 0);
275 get_group_info(new->group_info);
276 get_uid(new->user);
277 get_user_ns(new->user_ns);
278
279 #ifdef CONFIG_KEYS
280 key_get(new->session_keyring);
281 key_get(new->process_keyring);
282 key_get(new->thread_keyring);
283 key_get(new->request_key_auth);
284 #endif
285
286 #ifdef CONFIG_SECURITY
287 new->security = NULL;
288 #endif
289
290 new->ucounts = get_ucounts(new->ucounts);
291 if (!new->ucounts)
292 goto error;
293
294 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
295 goto error;
296
297 validate_creds(new);
298 return new;
299
300 error:
301 abort_creds(new);
302 return NULL;
303 }
304 EXPORT_SYMBOL(prepare_creds);
305
306 /*
307 * Prepare credentials for current to perform an execve()
308 * - The caller must hold ->cred_guard_mutex
309 */
prepare_exec_creds(void)310 struct cred *prepare_exec_creds(void)
311 {
312 struct cred *new;
313
314 new = prepare_creds();
315 if (!new)
316 return new;
317
318 #ifdef CONFIG_KEYS
319 /* newly exec'd tasks don't get a thread keyring */
320 key_put(new->thread_keyring);
321 new->thread_keyring = NULL;
322
323 /* inherit the session keyring; new process keyring */
324 key_put(new->process_keyring);
325 new->process_keyring = NULL;
326 #endif
327
328 new->suid = new->fsuid = new->euid;
329 new->sgid = new->fsgid = new->egid;
330
331 return new;
332 }
333
334 /*
335 * Copy credentials for the new process created by fork()
336 *
337 * We share if we can, but under some circumstances we have to generate a new
338 * set.
339 *
340 * The new process gets the current process's subjective credentials as its
341 * objective and subjective credentials
342 */
copy_creds(struct task_struct * p,unsigned long clone_flags)343 int copy_creds(struct task_struct *p, unsigned long clone_flags)
344 {
345 struct cred *new;
346 int ret;
347
348 #ifdef CONFIG_KEYS_REQUEST_CACHE
349 p->cached_requested_key = NULL;
350 #endif
351
352 if (
353 #ifdef CONFIG_KEYS
354 !p->cred->thread_keyring &&
355 #endif
356 clone_flags & CLONE_THREAD
357 ) {
358 p->real_cred = get_cred(p->cred);
359 get_cred(p->cred);
360 alter_cred_subscribers(p->cred, 2);
361 kdebug("share_creds(%p{%d,%d})",
362 p->cred, atomic_read(&p->cred->usage),
363 read_cred_subscribers(p->cred));
364 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
365 return 0;
366 }
367
368 new = prepare_creds();
369 if (!new)
370 return -ENOMEM;
371
372 if (clone_flags & CLONE_NEWUSER) {
373 ret = create_user_ns(new);
374 if (ret < 0)
375 goto error_put;
376 ret = set_cred_ucounts(new);
377 if (ret < 0)
378 goto error_put;
379 }
380
381 #ifdef CONFIG_KEYS
382 /* new threads get their own thread keyrings if their parent already
383 * had one */
384 if (new->thread_keyring) {
385 key_put(new->thread_keyring);
386 new->thread_keyring = NULL;
387 if (clone_flags & CLONE_THREAD)
388 install_thread_keyring_to_cred(new);
389 }
390
391 /* The process keyring is only shared between the threads in a process;
392 * anything outside of those threads doesn't inherit.
393 */
394 if (!(clone_flags & CLONE_THREAD)) {
395 key_put(new->process_keyring);
396 new->process_keyring = NULL;
397 }
398 #endif
399
400 p->cred = p->real_cred = get_cred(new);
401 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
402 alter_cred_subscribers(new, 2);
403 validate_creds(new);
404 return 0;
405
406 error_put:
407 put_cred(new);
408 return ret;
409 }
410
cred_cap_issubset(const struct cred * set,const struct cred * subset)411 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
412 {
413 const struct user_namespace *set_ns = set->user_ns;
414 const struct user_namespace *subset_ns = subset->user_ns;
415
416 /* If the two credentials are in the same user namespace see if
417 * the capabilities of subset are a subset of set.
418 */
419 if (set_ns == subset_ns)
420 return cap_issubset(subset->cap_permitted, set->cap_permitted);
421
422 /* The credentials are in a different user namespaces
423 * therefore one is a subset of the other only if a set is an
424 * ancestor of subset and set->euid is owner of subset or one
425 * of subsets ancestors.
426 */
427 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
428 if ((set_ns == subset_ns->parent) &&
429 uid_eq(subset_ns->owner, set->euid))
430 return true;
431 }
432
433 return false;
434 }
435
436 /**
437 * commit_creds - Install new credentials upon the current task
438 * @new: The credentials to be assigned
439 *
440 * Install a new set of credentials to the current task, using RCU to replace
441 * the old set. Both the objective and the subjective credentials pointers are
442 * updated. This function may not be called if the subjective credentials are
443 * in an overridden state.
444 *
445 * This function eats the caller's reference to the new credentials.
446 *
447 * Always returns 0 thus allowing this function to be tail-called at the end
448 * of, say, sys_setgid().
449 */
commit_creds(struct cred * new)450 int commit_creds(struct cred *new)
451 {
452 struct task_struct *task = current;
453 const struct cred *old = task->real_cred;
454
455 kdebug("commit_creds(%p{%d,%d})", new,
456 atomic_read(&new->usage),
457 read_cred_subscribers(new));
458
459 BUG_ON(task->cred != old);
460 #ifdef CONFIG_DEBUG_CREDENTIALS
461 BUG_ON(read_cred_subscribers(old) < 2);
462 validate_creds(old);
463 validate_creds(new);
464 #endif
465 BUG_ON(atomic_read(&new->usage) < 1);
466
467 get_cred(new); /* we will require a ref for the subj creds too */
468
469 /* dumpability changes */
470 if (!uid_eq(old->euid, new->euid) ||
471 !gid_eq(old->egid, new->egid) ||
472 !uid_eq(old->fsuid, new->fsuid) ||
473 !gid_eq(old->fsgid, new->fsgid) ||
474 !cred_cap_issubset(old, new)) {
475 if (task->mm)
476 set_dumpable(task->mm, suid_dumpable);
477 task->pdeath_signal = 0;
478 /*
479 * If a task drops privileges and becomes nondumpable,
480 * the dumpability change must become visible before
481 * the credential change; otherwise, a __ptrace_may_access()
482 * racing with this change may be able to attach to a task it
483 * shouldn't be able to attach to (as if the task had dropped
484 * privileges without becoming nondumpable).
485 * Pairs with a read barrier in __ptrace_may_access().
486 */
487 smp_wmb();
488 }
489
490 /* alter the thread keyring */
491 if (!uid_eq(new->fsuid, old->fsuid))
492 key_fsuid_changed(new);
493 if (!gid_eq(new->fsgid, old->fsgid))
494 key_fsgid_changed(new);
495
496 /* do it
497 * RLIMIT_NPROC limits on user->processes have already been checked
498 * in set_user().
499 */
500 alter_cred_subscribers(new, 2);
501 if (new->user != old->user || new->user_ns != old->user_ns)
502 inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
503 rcu_assign_pointer(task->real_cred, new);
504 rcu_assign_pointer(task->cred, new);
505 trace_android_rvh_commit_creds(task, new);
506 if (new->user != old->user || new->user_ns != old->user_ns)
507 dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
508 alter_cred_subscribers(old, -2);
509
510 /* send notifications */
511 if (!uid_eq(new->uid, old->uid) ||
512 !uid_eq(new->euid, old->euid) ||
513 !uid_eq(new->suid, old->suid) ||
514 !uid_eq(new->fsuid, old->fsuid))
515 proc_id_connector(task, PROC_EVENT_UID);
516
517 if (!gid_eq(new->gid, old->gid) ||
518 !gid_eq(new->egid, old->egid) ||
519 !gid_eq(new->sgid, old->sgid) ||
520 !gid_eq(new->fsgid, old->fsgid))
521 proc_id_connector(task, PROC_EVENT_GID);
522
523 /* release the old obj and subj refs both */
524 put_cred(old);
525 put_cred(old);
526 return 0;
527 }
528 EXPORT_SYMBOL(commit_creds);
529
530 /**
531 * abort_creds - Discard a set of credentials and unlock the current task
532 * @new: The credentials that were going to be applied
533 *
534 * Discard a set of credentials that were under construction and unlock the
535 * current task.
536 */
abort_creds(struct cred * new)537 void abort_creds(struct cred *new)
538 {
539 kdebug("abort_creds(%p{%d,%d})", new,
540 atomic_read(&new->usage),
541 read_cred_subscribers(new));
542
543 #ifdef CONFIG_DEBUG_CREDENTIALS
544 BUG_ON(read_cred_subscribers(new) != 0);
545 #endif
546 BUG_ON(atomic_read(&new->usage) < 1);
547 put_cred(new);
548 }
549 EXPORT_SYMBOL(abort_creds);
550
551 /**
552 * override_creds - Override the current process's subjective credentials
553 * @new: The credentials to be assigned
554 *
555 * Install a set of temporary override subjective credentials on the current
556 * process, returning the old set for later reversion.
557 */
override_creds(const struct cred * new)558 const struct cred *override_creds(const struct cred *new)
559 {
560 const struct cred *old = current->cred;
561
562 kdebug("override_creds(%p{%d,%d})", new,
563 atomic_read(&new->usage),
564 read_cred_subscribers(new));
565
566 validate_creds(old);
567 validate_creds(new);
568
569 /*
570 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
571 *
572 * That means that we do not clear the 'non_rcu' flag, since
573 * we are only installing the cred into the thread-synchronous
574 * '->cred' pointer, not the '->real_cred' pointer that is
575 * visible to other threads under RCU.
576 *
577 * Also note that we did validate_creds() manually, not depending
578 * on the validation in 'get_cred()'.
579 */
580 get_new_cred((struct cred *)new);
581 alter_cred_subscribers(new, 1);
582 rcu_assign_pointer(current->cred, new);
583 trace_android_rvh_override_creds(current, new);
584 alter_cred_subscribers(old, -1);
585
586 kdebug("override_creds() = %p{%d,%d}", old,
587 atomic_read(&old->usage),
588 read_cred_subscribers(old));
589 return old;
590 }
591 EXPORT_SYMBOL(override_creds);
592
593 /**
594 * revert_creds - Revert a temporary subjective credentials override
595 * @old: The credentials to be restored
596 *
597 * Revert a temporary set of override subjective credentials to an old set,
598 * discarding the override set.
599 */
revert_creds(const struct cred * old)600 void revert_creds(const struct cred *old)
601 {
602 const struct cred *override = current->cred;
603
604 kdebug("revert_creds(%p{%d,%d})", old,
605 atomic_read(&old->usage),
606 read_cred_subscribers(old));
607
608 validate_creds(old);
609 validate_creds(override);
610 alter_cred_subscribers(old, 1);
611 rcu_assign_pointer(current->cred, old);
612 trace_android_rvh_revert_creds(current, old);
613 alter_cred_subscribers(override, -1);
614 put_cred(override);
615 }
616 EXPORT_SYMBOL(revert_creds);
617
618 /**
619 * cred_fscmp - Compare two credentials with respect to filesystem access.
620 * @a: The first credential
621 * @b: The second credential
622 *
623 * cred_cmp() will return zero if both credentials have the same
624 * fsuid, fsgid, and supplementary groups. That is, if they will both
625 * provide the same access to files based on mode/uid/gid.
626 * If the credentials are different, then either -1 or 1 will
627 * be returned depending on whether @a comes before or after @b
628 * respectively in an arbitrary, but stable, ordering of credentials.
629 *
630 * Return: -1, 0, or 1 depending on comparison
631 */
cred_fscmp(const struct cred * a,const struct cred * b)632 int cred_fscmp(const struct cred *a, const struct cred *b)
633 {
634 struct group_info *ga, *gb;
635 int g;
636
637 if (a == b)
638 return 0;
639 if (uid_lt(a->fsuid, b->fsuid))
640 return -1;
641 if (uid_gt(a->fsuid, b->fsuid))
642 return 1;
643
644 if (gid_lt(a->fsgid, b->fsgid))
645 return -1;
646 if (gid_gt(a->fsgid, b->fsgid))
647 return 1;
648
649 ga = a->group_info;
650 gb = b->group_info;
651 if (ga == gb)
652 return 0;
653 if (ga == NULL)
654 return -1;
655 if (gb == NULL)
656 return 1;
657 if (ga->ngroups < gb->ngroups)
658 return -1;
659 if (ga->ngroups > gb->ngroups)
660 return 1;
661
662 for (g = 0; g < ga->ngroups; g++) {
663 if (gid_lt(ga->gid[g], gb->gid[g]))
664 return -1;
665 if (gid_gt(ga->gid[g], gb->gid[g]))
666 return 1;
667 }
668 return 0;
669 }
670 EXPORT_SYMBOL(cred_fscmp);
671
set_cred_ucounts(struct cred * new)672 int set_cred_ucounts(struct cred *new)
673 {
674 struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
675
676 /*
677 * This optimization is needed because alloc_ucounts() uses locks
678 * for table lookups.
679 */
680 if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid))
681 return 0;
682
683 if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid)))
684 return -EAGAIN;
685
686 new->ucounts = new_ucounts;
687 put_ucounts(old_ucounts);
688
689 return 0;
690 }
691
692 /*
693 * initialise the credentials stuff
694 */
cred_init(void)695 void __init cred_init(void)
696 {
697 /* allocate a slab in which we can store credentials */
698 cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
699 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
700 }
701
702 /**
703 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
704 * @daemon: A userspace daemon to be used as a reference
705 *
706 * Prepare a set of credentials for a kernel service. This can then be used to
707 * override a task's own credentials so that work can be done on behalf of that
708 * task that requires a different subjective context.
709 *
710 * @daemon is used to provide a base for the security record, but can be NULL.
711 * If @daemon is supplied, then the security data will be derived from that;
712 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
713 *
714 * The caller may change these controls afterwards if desired.
715 *
716 * Returns the new credentials or NULL if out of memory.
717 */
prepare_kernel_cred(struct task_struct * daemon)718 struct cred *prepare_kernel_cred(struct task_struct *daemon)
719 {
720 const struct cred *old;
721 struct cred *new;
722
723 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
724 if (!new)
725 return NULL;
726
727 kdebug("prepare_kernel_cred() alloc %p", new);
728
729 if (daemon)
730 old = get_task_cred(daemon);
731 else
732 old = get_cred(&init_cred);
733
734 validate_creds(old);
735
736 *new = *old;
737 new->non_rcu = 0;
738 atomic_set(&new->usage, 1);
739 set_cred_subscribers(new, 0);
740 get_uid(new->user);
741 get_user_ns(new->user_ns);
742 get_group_info(new->group_info);
743
744 #ifdef CONFIG_KEYS
745 new->session_keyring = NULL;
746 new->process_keyring = NULL;
747 new->thread_keyring = NULL;
748 new->request_key_auth = NULL;
749 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
750 #endif
751
752 #ifdef CONFIG_SECURITY
753 new->security = NULL;
754 #endif
755 new->ucounts = get_ucounts(new->ucounts);
756 if (!new->ucounts)
757 goto error;
758
759 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
760 goto error;
761
762 put_cred(old);
763 validate_creds(new);
764 return new;
765
766 error:
767 put_cred(new);
768 put_cred(old);
769 return NULL;
770 }
771 EXPORT_SYMBOL(prepare_kernel_cred);
772
773 /**
774 * set_security_override - Set the security ID in a set of credentials
775 * @new: The credentials to alter
776 * @secid: The LSM security ID to set
777 *
778 * Set the LSM security ID in a set of credentials so that the subjective
779 * security is overridden when an alternative set of credentials is used.
780 */
set_security_override(struct cred * new,u32 secid)781 int set_security_override(struct cred *new, u32 secid)
782 {
783 return security_kernel_act_as(new, secid);
784 }
785 EXPORT_SYMBOL(set_security_override);
786
787 /**
788 * set_security_override_from_ctx - Set the security ID in a set of credentials
789 * @new: The credentials to alter
790 * @secctx: The LSM security context to generate the security ID from.
791 *
792 * Set the LSM security ID in a set of credentials so that the subjective
793 * security is overridden when an alternative set of credentials is used. The
794 * security ID is specified in string form as a security context to be
795 * interpreted by the LSM.
796 */
set_security_override_from_ctx(struct cred * new,const char * secctx)797 int set_security_override_from_ctx(struct cred *new, const char *secctx)
798 {
799 u32 secid;
800 int ret;
801
802 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
803 if (ret < 0)
804 return ret;
805
806 return set_security_override(new, secid);
807 }
808 EXPORT_SYMBOL(set_security_override_from_ctx);
809
810 /**
811 * set_create_files_as - Set the LSM file create context in a set of credentials
812 * @new: The credentials to alter
813 * @inode: The inode to take the context from
814 *
815 * Change the LSM file creation context in a set of credentials to be the same
816 * as the object context of the specified inode, so that the new inodes have
817 * the same MAC context as that inode.
818 */
set_create_files_as(struct cred * new,struct inode * inode)819 int set_create_files_as(struct cred *new, struct inode *inode)
820 {
821 if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
822 return -EINVAL;
823 new->fsuid = inode->i_uid;
824 new->fsgid = inode->i_gid;
825 return security_kernel_create_files_as(new, inode);
826 }
827 EXPORT_SYMBOL(set_create_files_as);
828
829 #ifdef CONFIG_DEBUG_CREDENTIALS
830
creds_are_invalid(const struct cred * cred)831 bool creds_are_invalid(const struct cred *cred)
832 {
833 if (cred->magic != CRED_MAGIC)
834 return true;
835 return false;
836 }
837 EXPORT_SYMBOL(creds_are_invalid);
838
839 /*
840 * dump invalid credentials
841 */
dump_invalid_creds(const struct cred * cred,const char * label,const struct task_struct * tsk)842 static void dump_invalid_creds(const struct cred *cred, const char *label,
843 const struct task_struct *tsk)
844 {
845 printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
846 label, cred,
847 cred == &init_cred ? "[init]" : "",
848 cred == tsk->real_cred ? "[real]" : "",
849 cred == tsk->cred ? "[eff]" : "");
850 printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
851 cred->magic, cred->put_addr);
852 printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
853 atomic_read(&cred->usage),
854 read_cred_subscribers(cred));
855 printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
856 from_kuid_munged(&init_user_ns, cred->uid),
857 from_kuid_munged(&init_user_ns, cred->euid),
858 from_kuid_munged(&init_user_ns, cred->suid),
859 from_kuid_munged(&init_user_ns, cred->fsuid));
860 printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
861 from_kgid_munged(&init_user_ns, cred->gid),
862 from_kgid_munged(&init_user_ns, cred->egid),
863 from_kgid_munged(&init_user_ns, cred->sgid),
864 from_kgid_munged(&init_user_ns, cred->fsgid));
865 #ifdef CONFIG_SECURITY
866 printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
867 if ((unsigned long) cred->security >= PAGE_SIZE &&
868 (((unsigned long) cred->security & 0xffffff00) !=
869 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
870 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
871 ((u32*)cred->security)[0],
872 ((u32*)cred->security)[1]);
873 #endif
874 }
875
876 /*
877 * report use of invalid credentials
878 */
__invalid_creds(const struct cred * cred,const char * file,unsigned line)879 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
880 {
881 printk(KERN_ERR "CRED: Invalid credentials\n");
882 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
883 dump_invalid_creds(cred, "Specified", current);
884 BUG();
885 }
886 EXPORT_SYMBOL(__invalid_creds);
887
888 /*
889 * check the credentials on a process
890 */
__validate_process_creds(struct task_struct * tsk,const char * file,unsigned line)891 void __validate_process_creds(struct task_struct *tsk,
892 const char *file, unsigned line)
893 {
894 if (tsk->cred == tsk->real_cred) {
895 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
896 creds_are_invalid(tsk->cred)))
897 goto invalid_creds;
898 } else {
899 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
900 read_cred_subscribers(tsk->cred) < 1 ||
901 creds_are_invalid(tsk->real_cred) ||
902 creds_are_invalid(tsk->cred)))
903 goto invalid_creds;
904 }
905 return;
906
907 invalid_creds:
908 printk(KERN_ERR "CRED: Invalid process credentials\n");
909 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
910
911 dump_invalid_creds(tsk->real_cred, "Real", tsk);
912 if (tsk->cred != tsk->real_cred)
913 dump_invalid_creds(tsk->cred, "Effective", tsk);
914 else
915 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
916 BUG();
917 }
918 EXPORT_SYMBOL(__validate_process_creds);
919
920 /*
921 * check creds for do_exit()
922 */
validate_creds_for_do_exit(struct task_struct * tsk)923 void validate_creds_for_do_exit(struct task_struct *tsk)
924 {
925 kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
926 tsk->real_cred, tsk->cred,
927 atomic_read(&tsk->cred->usage),
928 read_cred_subscribers(tsk->cred));
929
930 __validate_process_creds(tsk, __FILE__, __LINE__);
931 }
932
933 #endif /* CONFIG_DEBUG_CREDENTIALS */
934