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 static 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 .ucounts = &init_ucounts,
64 };
65
set_cred_subscribers(struct cred * cred,int n)66 static inline void set_cred_subscribers(struct cred *cred, int n)
67 {
68 #ifdef CONFIG_DEBUG_CREDENTIALS
69 atomic_set(&cred->subscribers, n);
70 #endif
71 }
72
read_cred_subscribers(const struct cred * cred)73 static inline int read_cred_subscribers(const struct cred *cred)
74 {
75 #ifdef CONFIG_DEBUG_CREDENTIALS
76 return atomic_read(&cred->subscribers);
77 #else
78 return 0;
79 #endif
80 }
81
alter_cred_subscribers(const struct cred * _cred,int n)82 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
83 {
84 #ifdef CONFIG_DEBUG_CREDENTIALS
85 struct cred *cred = (struct cred *) _cred;
86
87 atomic_add(n, &cred->subscribers);
88 #endif
89 }
90
91 /*
92 * The RCU callback to actually dispose of a set of credentials
93 */
put_cred_rcu(struct rcu_head * rcu)94 static void put_cred_rcu(struct rcu_head *rcu)
95 {
96 struct cred *cred = container_of(rcu, struct cred, rcu);
97
98 kdebug("put_cred_rcu(%p)", cred);
99
100 #ifdef CONFIG_DEBUG_CREDENTIALS
101 if (cred->magic != CRED_MAGIC_DEAD ||
102 atomic_read(&cred->usage) != 0 ||
103 read_cred_subscribers(cred) != 0)
104 panic("CRED: put_cred_rcu() sees %p with"
105 " mag %x, put %p, usage %d, subscr %d\n",
106 cred, cred->magic, cred->put_addr,
107 atomic_read(&cred->usage),
108 read_cred_subscribers(cred));
109 #else
110 if (atomic_read(&cred->usage) != 0)
111 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
112 cred, atomic_read(&cred->usage));
113 #endif
114
115 security_cred_free(cred);
116 key_put(cred->session_keyring);
117 key_put(cred->process_keyring);
118 key_put(cred->thread_keyring);
119 key_put(cred->request_key_auth);
120 if (cred->group_info)
121 put_group_info(cred->group_info);
122 free_uid(cred->user);
123 if (cred->ucounts)
124 put_ucounts(cred->ucounts);
125 put_user_ns(cred->user_ns);
126 kmem_cache_free(cred_jar, cred);
127 }
128
129 /**
130 * __put_cred - Destroy a set of credentials
131 * @cred: The record to release
132 *
133 * Destroy a set of credentials on which no references remain.
134 */
__put_cred(struct cred * cred)135 void __put_cred(struct cred *cred)
136 {
137 kdebug("__put_cred(%p{%d,%d})", cred,
138 atomic_read(&cred->usage),
139 read_cred_subscribers(cred));
140
141 BUG_ON(atomic_read(&cred->usage) != 0);
142 #ifdef CONFIG_DEBUG_CREDENTIALS
143 BUG_ON(read_cred_subscribers(cred) != 0);
144 cred->magic = CRED_MAGIC_DEAD;
145 cred->put_addr = __builtin_return_address(0);
146 #endif
147 BUG_ON(cred == current->cred);
148 BUG_ON(cred == current->real_cred);
149
150 if (cred->non_rcu)
151 put_cred_rcu(&cred->rcu);
152 else
153 call_rcu(&cred->rcu, put_cred_rcu);
154 }
155 EXPORT_SYMBOL(__put_cred);
156
157 /*
158 * Clean up a task's credentials when it exits
159 */
exit_creds(struct task_struct * tsk)160 void exit_creds(struct task_struct *tsk)
161 {
162 struct cred *cred;
163
164 kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
165 atomic_read(&tsk->cred->usage),
166 read_cred_subscribers(tsk->cred));
167
168 cred = (struct cred *) tsk->real_cred;
169 tsk->real_cred = NULL;
170 validate_creds(cred);
171 alter_cred_subscribers(cred, -1);
172 put_cred(cred);
173
174 cred = (struct cred *) tsk->cred;
175 tsk->cred = NULL;
176 validate_creds(cred);
177 alter_cred_subscribers(cred, -1);
178 put_cred(cred);
179
180 #ifdef CONFIG_KEYS_REQUEST_CACHE
181 key_put(tsk->cached_requested_key);
182 tsk->cached_requested_key = NULL;
183 #endif
184 }
185
186 /**
187 * get_task_cred - Get another task's objective credentials
188 * @task: The task to query
189 *
190 * Get the objective credentials of a task, pinning them so that they can't go
191 * away. Accessing a task's credentials directly is not permitted.
192 *
193 * The caller must also make sure task doesn't get deleted, either by holding a
194 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
195 */
get_task_cred(struct task_struct * task)196 const struct cred *get_task_cred(struct task_struct *task)
197 {
198 const struct cred *cred;
199
200 rcu_read_lock();
201
202 do {
203 cred = __task_cred((task));
204 BUG_ON(!cred);
205 } while (!get_cred_rcu(cred));
206
207 rcu_read_unlock();
208 return cred;
209 }
210 EXPORT_SYMBOL(get_task_cred);
211
212 /*
213 * Allocate blank credentials, such that the credentials can be filled in at a
214 * later date without risk of ENOMEM.
215 */
cred_alloc_blank(void)216 struct cred *cred_alloc_blank(void)
217 {
218 struct cred *new;
219
220 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
221 if (!new)
222 return NULL;
223
224 atomic_set(&new->usage, 1);
225 #ifdef CONFIG_DEBUG_CREDENTIALS
226 new->magic = CRED_MAGIC;
227 #endif
228 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
229 goto error;
230
231 return new;
232
233 error:
234 abort_creds(new);
235 return NULL;
236 }
237
238 /**
239 * prepare_creds - Prepare a new set of credentials for modification
240 *
241 * Prepare a new set of task credentials for modification. A task's creds
242 * shouldn't generally be modified directly, therefore this function is used to
243 * prepare a new copy, which the caller then modifies and then commits by
244 * calling commit_creds().
245 *
246 * Preparation involves making a copy of the objective creds for modification.
247 *
248 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
249 *
250 * Call commit_creds() or abort_creds() to clean up.
251 */
prepare_creds(void)252 struct cred *prepare_creds(void)
253 {
254 struct task_struct *task = current;
255 const struct cred *old;
256 struct cred *new;
257
258 validate_process_creds();
259
260 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
261 if (!new)
262 return NULL;
263
264 kdebug("prepare_creds() alloc %p", new);
265
266 old = task->cred;
267 memcpy(new, old, sizeof(struct cred));
268
269 new->non_rcu = 0;
270 atomic_set(&new->usage, 1);
271 set_cred_subscribers(new, 0);
272 get_group_info(new->group_info);
273 get_uid(new->user);
274 get_user_ns(new->user_ns);
275
276 #ifdef CONFIG_KEYS
277 key_get(new->session_keyring);
278 key_get(new->process_keyring);
279 key_get(new->thread_keyring);
280 key_get(new->request_key_auth);
281 #endif
282
283 #ifdef CONFIG_SECURITY
284 new->security = NULL;
285 #endif
286
287 new->ucounts = get_ucounts(new->ucounts);
288 if (!new->ucounts)
289 goto error;
290
291 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
292 goto error;
293
294 validate_creds(new);
295 return new;
296
297 error:
298 abort_creds(new);
299 return NULL;
300 }
301 EXPORT_SYMBOL(prepare_creds);
302
303 /*
304 * Prepare credentials for current to perform an execve()
305 * - The caller must hold ->cred_guard_mutex
306 */
prepare_exec_creds(void)307 struct cred *prepare_exec_creds(void)
308 {
309 struct cred *new;
310
311 new = prepare_creds();
312 if (!new)
313 return new;
314
315 #ifdef CONFIG_KEYS
316 /* newly exec'd tasks don't get a thread keyring */
317 key_put(new->thread_keyring);
318 new->thread_keyring = NULL;
319
320 /* inherit the session keyring; new process keyring */
321 key_put(new->process_keyring);
322 new->process_keyring = NULL;
323 #endif
324
325 new->suid = new->fsuid = new->euid;
326 new->sgid = new->fsgid = new->egid;
327
328 return new;
329 }
330
331 /*
332 * Copy credentials for the new process created by fork()
333 *
334 * We share if we can, but under some circumstances we have to generate a new
335 * set.
336 *
337 * The new process gets the current process's subjective credentials as its
338 * objective and subjective credentials
339 */
copy_creds(struct task_struct * p,unsigned long clone_flags)340 int copy_creds(struct task_struct *p, unsigned long clone_flags)
341 {
342 struct cred *new;
343 int ret;
344
345 #ifdef CONFIG_KEYS_REQUEST_CACHE
346 p->cached_requested_key = NULL;
347 #endif
348
349 if (
350 #ifdef CONFIG_KEYS
351 !p->cred->thread_keyring &&
352 #endif
353 clone_flags & CLONE_THREAD
354 ) {
355 p->real_cred = get_cred(p->cred);
356 get_cred(p->cred);
357 alter_cred_subscribers(p->cred, 2);
358 kdebug("share_creds(%p{%d,%d})",
359 p->cred, atomic_read(&p->cred->usage),
360 read_cred_subscribers(p->cred));
361 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
362 return 0;
363 }
364
365 new = prepare_creds();
366 if (!new)
367 return -ENOMEM;
368
369 if (clone_flags & CLONE_NEWUSER) {
370 ret = create_user_ns(new);
371 if (ret < 0)
372 goto error_put;
373 ret = set_cred_ucounts(new);
374 if (ret < 0)
375 goto error_put;
376 }
377
378 #ifdef CONFIG_KEYS
379 /* new threads get their own thread keyrings if their parent already
380 * had one */
381 if (new->thread_keyring) {
382 key_put(new->thread_keyring);
383 new->thread_keyring = NULL;
384 if (clone_flags & CLONE_THREAD)
385 install_thread_keyring_to_cred(new);
386 }
387
388 /* The process keyring is only shared between the threads in a process;
389 * anything outside of those threads doesn't inherit.
390 */
391 if (!(clone_flags & CLONE_THREAD)) {
392 key_put(new->process_keyring);
393 new->process_keyring = NULL;
394 }
395 #endif
396
397 p->cred = p->real_cred = get_cred(new);
398 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
399 alter_cred_subscribers(new, 2);
400 validate_creds(new);
401 return 0;
402
403 error_put:
404 put_cred(new);
405 return ret;
406 }
407
cred_cap_issubset(const struct cred * set,const struct cred * subset)408 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
409 {
410 const struct user_namespace *set_ns = set->user_ns;
411 const struct user_namespace *subset_ns = subset->user_ns;
412
413 /* If the two credentials are in the same user namespace see if
414 * the capabilities of subset are a subset of set.
415 */
416 if (set_ns == subset_ns)
417 return cap_issubset(subset->cap_permitted, set->cap_permitted);
418
419 /* The credentials are in a different user namespaces
420 * therefore one is a subset of the other only if a set is an
421 * ancestor of subset and set->euid is owner of subset or one
422 * of subsets ancestors.
423 */
424 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
425 if ((set_ns == subset_ns->parent) &&
426 uid_eq(subset_ns->owner, set->euid))
427 return true;
428 }
429
430 return false;
431 }
432
433 /**
434 * commit_creds - Install new credentials upon the current task
435 * @new: The credentials to be assigned
436 *
437 * Install a new set of credentials to the current task, using RCU to replace
438 * the old set. Both the objective and the subjective credentials pointers are
439 * updated. This function may not be called if the subjective credentials are
440 * in an overridden state.
441 *
442 * This function eats the caller's reference to the new credentials.
443 *
444 * Always returns 0 thus allowing this function to be tail-called at the end
445 * of, say, sys_setgid().
446 */
commit_creds(struct cred * new)447 int commit_creds(struct cred *new)
448 {
449 struct task_struct *task = current;
450 const struct cred *old = task->real_cred;
451
452 kdebug("commit_creds(%p{%d,%d})", new,
453 atomic_read(&new->usage),
454 read_cred_subscribers(new));
455
456 BUG_ON(task->cred != old);
457 #ifdef CONFIG_DEBUG_CREDENTIALS
458 BUG_ON(read_cred_subscribers(old) < 2);
459 validate_creds(old);
460 validate_creds(new);
461 #endif
462 BUG_ON(atomic_read(&new->usage) < 1);
463
464 get_cred(new); /* we will require a ref for the subj creds too */
465
466 /* dumpability changes */
467 if (!uid_eq(old->euid, new->euid) ||
468 !gid_eq(old->egid, new->egid) ||
469 !uid_eq(old->fsuid, new->fsuid) ||
470 !gid_eq(old->fsgid, new->fsgid) ||
471 !cred_cap_issubset(old, new)) {
472 if (task->mm)
473 set_dumpable(task->mm, suid_dumpable);
474 task->pdeath_signal = 0;
475 /*
476 * If a task drops privileges and becomes nondumpable,
477 * the dumpability change must become visible before
478 * the credential change; otherwise, a __ptrace_may_access()
479 * racing with this change may be able to attach to a task it
480 * shouldn't be able to attach to (as if the task had dropped
481 * privileges without becoming nondumpable).
482 * Pairs with a read barrier in __ptrace_may_access().
483 */
484 smp_wmb();
485 }
486
487 /* alter the thread keyring */
488 if (!uid_eq(new->fsuid, old->fsuid))
489 key_fsuid_changed(new);
490 if (!gid_eq(new->fsgid, old->fsgid))
491 key_fsgid_changed(new);
492
493 /* do it
494 * RLIMIT_NPROC limits on user->processes have already been checked
495 * in set_user().
496 */
497 alter_cred_subscribers(new, 2);
498 if (new->user != old->user || new->user_ns != old->user_ns)
499 inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
500 rcu_assign_pointer(task->real_cred, new);
501 rcu_assign_pointer(task->cred, new);
502 if (new->user != old->user || new->user_ns != old->user_ns)
503 dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
504 alter_cred_subscribers(old, -2);
505
506 /* send notifications */
507 if (!uid_eq(new->uid, old->uid) ||
508 !uid_eq(new->euid, old->euid) ||
509 !uid_eq(new->suid, old->suid) ||
510 !uid_eq(new->fsuid, old->fsuid))
511 proc_id_connector(task, PROC_EVENT_UID);
512
513 if (!gid_eq(new->gid, old->gid) ||
514 !gid_eq(new->egid, old->egid) ||
515 !gid_eq(new->sgid, old->sgid) ||
516 !gid_eq(new->fsgid, old->fsgid))
517 proc_id_connector(task, PROC_EVENT_GID);
518
519 /* release the old obj and subj refs both */
520 put_cred(old);
521 put_cred(old);
522 return 0;
523 }
524 EXPORT_SYMBOL(commit_creds);
525
526 /**
527 * abort_creds - Discard a set of credentials and unlock the current task
528 * @new: The credentials that were going to be applied
529 *
530 * Discard a set of credentials that were under construction and unlock the
531 * current task.
532 */
abort_creds(struct cred * new)533 void abort_creds(struct cred *new)
534 {
535 kdebug("abort_creds(%p{%d,%d})", new,
536 atomic_read(&new->usage),
537 read_cred_subscribers(new));
538
539 #ifdef CONFIG_DEBUG_CREDENTIALS
540 BUG_ON(read_cred_subscribers(new) != 0);
541 #endif
542 BUG_ON(atomic_read(&new->usage) < 1);
543 put_cred(new);
544 }
545 EXPORT_SYMBOL(abort_creds);
546
547 /**
548 * override_creds - Override the current process's subjective credentials
549 * @new: The credentials to be assigned
550 *
551 * Install a set of temporary override subjective credentials on the current
552 * process, returning the old set for later reversion.
553 */
override_creds(const struct cred * new)554 const struct cred *override_creds(const struct cred *new)
555 {
556 const struct cred *old = current->cred;
557
558 kdebug("override_creds(%p{%d,%d})", new,
559 atomic_read(&new->usage),
560 read_cred_subscribers(new));
561
562 validate_creds(old);
563 validate_creds(new);
564
565 /*
566 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
567 *
568 * That means that we do not clear the 'non_rcu' flag, since
569 * we are only installing the cred into the thread-synchronous
570 * '->cred' pointer, not the '->real_cred' pointer that is
571 * visible to other threads under RCU.
572 *
573 * Also note that we did validate_creds() manually, not depending
574 * on the validation in 'get_cred()'.
575 */
576 get_new_cred((struct cred *)new);
577 alter_cred_subscribers(new, 1);
578 rcu_assign_pointer(current->cred, new);
579 alter_cred_subscribers(old, -1);
580
581 kdebug("override_creds() = %p{%d,%d}", old,
582 atomic_read(&old->usage),
583 read_cred_subscribers(old));
584 return old;
585 }
586 EXPORT_SYMBOL(override_creds);
587
588 /**
589 * revert_creds - Revert a temporary subjective credentials override
590 * @old: The credentials to be restored
591 *
592 * Revert a temporary set of override subjective credentials to an old set,
593 * discarding the override set.
594 */
revert_creds(const struct cred * old)595 void revert_creds(const struct cred *old)
596 {
597 const struct cred *override = current->cred;
598
599 kdebug("revert_creds(%p{%d,%d})", old,
600 atomic_read(&old->usage),
601 read_cred_subscribers(old));
602
603 validate_creds(old);
604 validate_creds(override);
605 alter_cred_subscribers(old, 1);
606 rcu_assign_pointer(current->cred, old);
607 alter_cred_subscribers(override, -1);
608 put_cred(override);
609 }
610 EXPORT_SYMBOL(revert_creds);
611
612 /**
613 * cred_fscmp - Compare two credentials with respect to filesystem access.
614 * @a: The first credential
615 * @b: The second credential
616 *
617 * cred_cmp() will return zero if both credentials have the same
618 * fsuid, fsgid, and supplementary groups. That is, if they will both
619 * provide the same access to files based on mode/uid/gid.
620 * If the credentials are different, then either -1 or 1 will
621 * be returned depending on whether @a comes before or after @b
622 * respectively in an arbitrary, but stable, ordering of credentials.
623 *
624 * Return: -1, 0, or 1 depending on comparison
625 */
cred_fscmp(const struct cred * a,const struct cred * b)626 int cred_fscmp(const struct cred *a, const struct cred *b)
627 {
628 struct group_info *ga, *gb;
629 int g;
630
631 if (a == b)
632 return 0;
633 if (uid_lt(a->fsuid, b->fsuid))
634 return -1;
635 if (uid_gt(a->fsuid, b->fsuid))
636 return 1;
637
638 if (gid_lt(a->fsgid, b->fsgid))
639 return -1;
640 if (gid_gt(a->fsgid, b->fsgid))
641 return 1;
642
643 ga = a->group_info;
644 gb = b->group_info;
645 if (ga == gb)
646 return 0;
647 if (ga == NULL)
648 return -1;
649 if (gb == NULL)
650 return 1;
651 if (ga->ngroups < gb->ngroups)
652 return -1;
653 if (ga->ngroups > gb->ngroups)
654 return 1;
655
656 for (g = 0; g < ga->ngroups; g++) {
657 if (gid_lt(ga->gid[g], gb->gid[g]))
658 return -1;
659 if (gid_gt(ga->gid[g], gb->gid[g]))
660 return 1;
661 }
662 return 0;
663 }
664 EXPORT_SYMBOL(cred_fscmp);
665
set_cred_ucounts(struct cred * new)666 int set_cred_ucounts(struct cred *new)
667 {
668 struct task_struct *task = current;
669 const struct cred *old = task->real_cred;
670 struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
671
672 if (new->user == old->user && new->user_ns == old->user_ns)
673 return 0;
674
675 /*
676 * This optimization is needed because alloc_ucounts() uses locks
677 * for table lookups.
678 */
679 if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
680 return 0;
681
682 if (!(new_ucounts = alloc_ucounts(new->user_ns, new->euid)))
683 return -EAGAIN;
684
685 new->ucounts = new_ucounts;
686 if (old_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
