xref: /openbmc/linux/kernel/cred.c (revision 2010776f)
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 
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 
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 
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  */
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  */
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  */
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  */
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  */
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 	new->ucounts = get_ucounts(&init_ucounts);
229 
230 	if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
231 		goto error;
232 
233 	return new;
234 
235 error:
236 	abort_creds(new);
237 	return NULL;
238 }
239 
240 /**
241  * prepare_creds - Prepare a new set of credentials for modification
242  *
243  * Prepare a new set of task credentials for modification.  A task's creds
244  * shouldn't generally be modified directly, therefore this function is used to
245  * prepare a new copy, which the caller then modifies and then commits by
246  * calling commit_creds().
247  *
248  * Preparation involves making a copy of the objective creds for modification.
249  *
250  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
251  *
252  * Call commit_creds() or abort_creds() to clean up.
253  */
254 struct cred *prepare_creds(void)
255 {
256 	struct task_struct *task = current;
257 	const struct cred *old;
258 	struct cred *new;
259 
260 	validate_process_creds();
261 
262 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
263 	if (!new)
264 		return NULL;
265 
266 	kdebug("prepare_creds() alloc %p", new);
267 
268 	old = task->cred;
269 	memcpy(new, old, sizeof(struct cred));
270 
271 	new->non_rcu = 0;
272 	atomic_set(&new->usage, 1);
273 	set_cred_subscribers(new, 0);
274 	get_group_info(new->group_info);
275 	get_uid(new->user);
276 	get_user_ns(new->user_ns);
277 
278 #ifdef CONFIG_KEYS
279 	key_get(new->session_keyring);
280 	key_get(new->process_keyring);
281 	key_get(new->thread_keyring);
282 	key_get(new->request_key_auth);
283 #endif
284 
285 #ifdef CONFIG_SECURITY
286 	new->security = NULL;
287 #endif
288 
289 	new->ucounts = get_ucounts(new->ucounts);
290 	if (!new->ucounts)
291 		goto error;
292 
293 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
294 		goto error;
295 
296 	validate_creds(new);
297 	return new;
298 
299 error:
300 	abort_creds(new);
301 	return NULL;
302 }
303 EXPORT_SYMBOL(prepare_creds);
304 
305 /*
306  * Prepare credentials for current to perform an execve()
307  * - The caller must hold ->cred_guard_mutex
308  */
309 struct cred *prepare_exec_creds(void)
310 {
311 	struct cred *new;
312 
313 	new = prepare_creds();
314 	if (!new)
315 		return new;
316 
317 #ifdef CONFIG_KEYS
318 	/* newly exec'd tasks don't get a thread keyring */
319 	key_put(new->thread_keyring);
320 	new->thread_keyring = NULL;
321 
322 	/* inherit the session keyring; new process keyring */
323 	key_put(new->process_keyring);
324 	new->process_keyring = NULL;
325 #endif
326 
327 	new->suid = new->fsuid = new->euid;
328 	new->sgid = new->fsgid = new->egid;
329 
330 	return new;
331 }
332 
333 /*
334  * Copy credentials for the new process created by fork()
335  *
336  * We share if we can, but under some circumstances we have to generate a new
337  * set.
338  *
339  * The new process gets the current process's subjective credentials as its
340  * objective and subjective credentials
341  */
342 int copy_creds(struct task_struct *p, unsigned long clone_flags)
343 {
344 	struct cred *new;
345 	int ret;
346 
347 #ifdef CONFIG_KEYS_REQUEST_CACHE
348 	p->cached_requested_key = NULL;
349 #endif
350 
351 	if (
352 #ifdef CONFIG_KEYS
353 		!p->cred->thread_keyring &&
354 #endif
355 		clone_flags & CLONE_THREAD
356 	    ) {
357 		p->real_cred = get_cred(p->cred);
358 		get_cred(p->cred);
359 		alter_cred_subscribers(p->cred, 2);
360 		kdebug("share_creds(%p{%d,%d})",
361 		       p->cred, atomic_read(&p->cred->usage),
362 		       read_cred_subscribers(p->cred));
363 		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
364 		return 0;
365 	}
366 
367 	new = prepare_creds();
368 	if (!new)
369 		return -ENOMEM;
370 
371 	if (clone_flags & CLONE_NEWUSER) {
372 		ret = create_user_ns(new);
373 		if (ret < 0)
374 			goto error_put;
375 		ret = set_cred_ucounts(new);
376 		if (ret < 0)
377 			goto error_put;
378 	}
379 
380 #ifdef CONFIG_KEYS
381 	/* new threads get their own thread keyrings if their parent already
382 	 * had one */
383 	if (new->thread_keyring) {
384 		key_put(new->thread_keyring);
385 		new->thread_keyring = NULL;
386 		if (clone_flags & CLONE_THREAD)
387 			install_thread_keyring_to_cred(new);
388 	}
389 
390 	/* The process keyring is only shared between the threads in a process;
391 	 * anything outside of those threads doesn't inherit.
392 	 */
393 	if (!(clone_flags & CLONE_THREAD)) {
394 		key_put(new->process_keyring);
395 		new->process_keyring = NULL;
396 	}
397 #endif
398 
399 	p->cred = p->real_cred = get_cred(new);
400 	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
401 	alter_cred_subscribers(new, 2);
402 	validate_creds(new);
403 	return 0;
404 
405 error_put:
406 	put_cred(new);
407 	return ret;
408 }
409 
410 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
411 {
412 	const struct user_namespace *set_ns = set->user_ns;
413 	const struct user_namespace *subset_ns = subset->user_ns;
414 
415 	/* If the two credentials are in the same user namespace see if
416 	 * the capabilities of subset are a subset of set.
417 	 */
418 	if (set_ns == subset_ns)
419 		return cap_issubset(subset->cap_permitted, set->cap_permitted);
420 
421 	/* The credentials are in a different user namespaces
422 	 * therefore one is a subset of the other only if a set is an
423 	 * ancestor of subset and set->euid is owner of subset or one
424 	 * of subsets ancestors.
425 	 */
426 	for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
427 		if ((set_ns == subset_ns->parent)  &&
428 		    uid_eq(subset_ns->owner, set->euid))
429 			return true;
430 	}
431 
432 	return false;
433 }
434 
435 /**
436  * commit_creds - Install new credentials upon the current task
437  * @new: The credentials to be assigned
438  *
439  * Install a new set of credentials to the current task, using RCU to replace
440  * the old set.  Both the objective and the subjective credentials pointers are
441  * updated.  This function may not be called if the subjective credentials are
442  * in an overridden state.
443  *
444  * This function eats the caller's reference to the new credentials.
445  *
446  * Always returns 0 thus allowing this function to be tail-called at the end
447  * of, say, sys_setgid().
448  */
449 int commit_creds(struct cred *new)
450 {
451 	struct task_struct *task = current;
452 	const struct cred *old = task->real_cred;
453 
454 	kdebug("commit_creds(%p{%d,%d})", new,
455 	       atomic_read(&new->usage),
456 	       read_cred_subscribers(new));
457 
458 	BUG_ON(task->cred != old);
459 #ifdef CONFIG_DEBUG_CREDENTIALS
460 	BUG_ON(read_cred_subscribers(old) < 2);
461 	validate_creds(old);
462 	validate_creds(new);
463 #endif
464 	BUG_ON(atomic_read(&new->usage) < 1);
465 
466 	get_cred(new); /* we will require a ref for the subj creds too */
467 
468 	/* dumpability changes */
469 	if (!uid_eq(old->euid, new->euid) ||
470 	    !gid_eq(old->egid, new->egid) ||
471 	    !uid_eq(old->fsuid, new->fsuid) ||
472 	    !gid_eq(old->fsgid, new->fsgid) ||
473 	    !cred_cap_issubset(old, new)) {
474 		if (task->mm)
475 			set_dumpable(task->mm, suid_dumpable);
476 		task->pdeath_signal = 0;
477 		/*
478 		 * If a task drops privileges and becomes nondumpable,
479 		 * the dumpability change must become visible before
480 		 * the credential change; otherwise, a __ptrace_may_access()
481 		 * racing with this change may be able to attach to a task it
482 		 * shouldn't be able to attach to (as if the task had dropped
483 		 * privileges without becoming nondumpable).
484 		 * Pairs with a read barrier in __ptrace_may_access().
485 		 */
486 		smp_wmb();
487 	}
488 
489 	/* alter the thread keyring */
490 	if (!uid_eq(new->fsuid, old->fsuid))
491 		key_fsuid_changed(new);
492 	if (!gid_eq(new->fsgid, old->fsgid))
493 		key_fsgid_changed(new);
494 
495 	/* do it
496 	 * RLIMIT_NPROC limits on user->processes have already been checked
497 	 * in set_user().
498 	 */
499 	alter_cred_subscribers(new, 2);
500 	if (new->user != old->user || new->user_ns != old->user_ns)
501 		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
502 	rcu_assign_pointer(task->real_cred, new);
503 	rcu_assign_pointer(task->cred, new);
504 	if (new->user != old->user)
505 		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
506 	alter_cred_subscribers(old, -2);
507 
508 	/* send notifications */
509 	if (!uid_eq(new->uid,   old->uid)  ||
510 	    !uid_eq(new->euid,  old->euid) ||
511 	    !uid_eq(new->suid,  old->suid) ||
512 	    !uid_eq(new->fsuid, old->fsuid))
513 		proc_id_connector(task, PROC_EVENT_UID);
514 
515 	if (!gid_eq(new->gid,   old->gid)  ||
516 	    !gid_eq(new->egid,  old->egid) ||
517 	    !gid_eq(new->sgid,  old->sgid) ||
518 	    !gid_eq(new->fsgid, old->fsgid))
519 		proc_id_connector(task, PROC_EVENT_GID);
520 
521 	/* release the old obj and subj refs both */
522 	put_cred(old);
523 	put_cred(old);
524 	return 0;
525 }
526 EXPORT_SYMBOL(commit_creds);
527 
528 /**
529  * abort_creds - Discard a set of credentials and unlock the current task
530  * @new: The credentials that were going to be applied
531  *
532  * Discard a set of credentials that were under construction and unlock the
533  * current task.
534  */
535 void abort_creds(struct cred *new)
536 {
537 	kdebug("abort_creds(%p{%d,%d})", new,
538 	       atomic_read(&new->usage),
539 	       read_cred_subscribers(new));
540 
541 #ifdef CONFIG_DEBUG_CREDENTIALS
542 	BUG_ON(read_cred_subscribers(new) != 0);
543 #endif
544 	BUG_ON(atomic_read(&new->usage) < 1);
545 	put_cred(new);
546 }
547 EXPORT_SYMBOL(abort_creds);
548 
549 /**
550  * override_creds - Override the current process's subjective credentials
551  * @new: The credentials to be assigned
552  *
553  * Install a set of temporary override subjective credentials on the current
554  * process, returning the old set for later reversion.
555  */
556 const struct cred *override_creds(const struct cred *new)
557 {
558 	const struct cred *old = current->cred;
559 
560 	kdebug("override_creds(%p{%d,%d})", new,
561 	       atomic_read(&new->usage),
562 	       read_cred_subscribers(new));
563 
564 	validate_creds(old);
565 	validate_creds(new);
566 
567 	/*
568 	 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
569 	 *
570 	 * That means that we do not clear the 'non_rcu' flag, since
571 	 * we are only installing the cred into the thread-synchronous
572 	 * '->cred' pointer, not the '->real_cred' pointer that is
573 	 * visible to other threads under RCU.
574 	 *
575 	 * Also note that we did validate_creds() manually, not depending
576 	 * on the validation in 'get_cred()'.
577 	 */
578 	get_new_cred((struct cred *)new);
579 	alter_cred_subscribers(new, 1);
580 	rcu_assign_pointer(current->cred, new);
581 	alter_cred_subscribers(old, -1);
582 
583 	kdebug("override_creds() = %p{%d,%d}", old,
584 	       atomic_read(&old->usage),
585 	       read_cred_subscribers(old));
586 	return old;
587 }
588 EXPORT_SYMBOL(override_creds);
589 
590 /**
591  * revert_creds - Revert a temporary subjective credentials override
592  * @old: The credentials to be restored
593  *
594  * Revert a temporary set of override subjective credentials to an old set,
595  * discarding the override set.
596  */
597 void revert_creds(const struct cred *old)
598 {
599 	const struct cred *override = current->cred;
600 
601 	kdebug("revert_creds(%p{%d,%d})", old,
602 	       atomic_read(&old->usage),
603 	       read_cred_subscribers(old));
604 
605 	validate_creds(old);
606 	validate_creds(override);
607 	alter_cred_subscribers(old, 1);
608 	rcu_assign_pointer(current->cred, old);
609 	alter_cred_subscribers(override, -1);
610 	put_cred(override);
611 }
612 EXPORT_SYMBOL(revert_creds);
613 
614 /**
615  * cred_fscmp - Compare two credentials with respect to filesystem access.
616  * @a: The first credential
617  * @b: The second credential
618  *
619  * cred_cmp() will return zero if both credentials have the same
620  * fsuid, fsgid, and supplementary groups.  That is, if they will both
621  * provide the same access to files based on mode/uid/gid.
622  * If the credentials are different, then either -1 or 1 will
623  * be returned depending on whether @a comes before or after @b
624  * respectively in an arbitrary, but stable, ordering of credentials.
625  *
626  * Return: -1, 0, or 1 depending on comparison
627  */
628 int cred_fscmp(const struct cred *a, const struct cred *b)
629 {
630 	struct group_info *ga, *gb;
631 	int g;
632 
633 	if (a == b)
634 		return 0;
635 	if (uid_lt(a->fsuid, b->fsuid))
636 		return -1;
637 	if (uid_gt(a->fsuid, b->fsuid))
638 		return 1;
639 
640 	if (gid_lt(a->fsgid, b->fsgid))
641 		return -1;
642 	if (gid_gt(a->fsgid, b->fsgid))
643 		return 1;
644 
645 	ga = a->group_info;
646 	gb = b->group_info;
647 	if (ga == gb)
648 		return 0;
649 	if (ga == NULL)
650 		return -1;
651 	if (gb == NULL)
652 		return 1;
653 	if (ga->ngroups < gb->ngroups)
654 		return -1;
655 	if (ga->ngroups > gb->ngroups)
656 		return 1;
657 
658 	for (g = 0; g < ga->ngroups; g++) {
659 		if (gid_lt(ga->gid[g], gb->gid[g]))
660 			return -1;
661 		if (gid_gt(ga->gid[g], gb->gid[g]))
662 			return 1;
663 	}
664 	return 0;
665 }
666 EXPORT_SYMBOL(cred_fscmp);
667 
668 int set_cred_ucounts(struct cred *new)
669 {
670 	struct task_struct *task = current;
671 	const struct cred *old = task->real_cred;
672 	struct ucounts *old_ucounts = new->ucounts;
673 
674 	if (new->user == old->user && new->user_ns == old->user_ns)
675 		return 0;
676 
677 	/*
678 	 * This optimization is needed because alloc_ucounts() uses locks
679 	 * for table lookups.
680 	 */
681 	if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
682 		return 0;
683 
684 	if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
685 		return -EAGAIN;
686 
687 	if (old_ucounts)
688 		put_ucounts(old_ucounts);
689 
690 	return 0;
691 }
692 
693 /*
694  * initialise the credentials stuff
695  */
696 void __init cred_init(void)
697 {
698 	/* allocate a slab in which we can store credentials */
699 	cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
700 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
701 }
702 
703 /**
704  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
705  * @daemon: A userspace daemon to be used as a reference
706  *
707  * Prepare a set of credentials for a kernel service.  This can then be used to
708  * override a task's own credentials so that work can be done on behalf of that
709  * task that requires a different subjective context.
710  *
711  * @daemon is used to provide a base for the security record, but can be NULL.
712  * If @daemon is supplied, then the security data will be derived from that;
713  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
714  *
715  * The caller may change these controls afterwards if desired.
716  *
717  * Returns the new credentials or NULL if out of memory.
718  */
719 struct cred *prepare_kernel_cred(struct task_struct *daemon)
720 {
721 	const struct cred *old;
722 	struct cred *new;
723 
724 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
725 	if (!new)
726 		return NULL;
727 
728 	kdebug("prepare_kernel_cred() alloc %p", new);
729 
730 	if (daemon)
731 		old = get_task_cred(daemon);
732 	else
733 		old = get_cred(&init_cred);
734 
735 	validate_creds(old);
736 
737 	*new = *old;
738 	new->non_rcu = 0;
739 	atomic_set(&new->usage, 1);
740 	set_cred_subscribers(new, 0);
741 	get_uid(new->user);
742 	get_user_ns(new->user_ns);
743 	get_group_info(new->group_info);
744 
745 #ifdef CONFIG_KEYS
746 	new->session_keyring = NULL;
747 	new->process_keyring = NULL;
748 	new->thread_keyring = NULL;
749 	new->request_key_auth = NULL;
750 	new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
751 #endif
752 
753 #ifdef CONFIG_SECURITY
754 	new->security = NULL;
755 #endif
756 	new->ucounts = get_ucounts(new->ucounts);
757 	if (!new->ucounts)
758 		goto error;
759 
760 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
761 		goto error;
762 
763 	put_cred(old);
764 	validate_creds(new);
765 	return new;
766 
767 error:
768 	put_cred(new);
769 	put_cred(old);
770 	return NULL;
771 }
772 EXPORT_SYMBOL(prepare_kernel_cred);
773 
774 /**
775  * set_security_override - Set the security ID in a set of credentials
776  * @new: The credentials to alter
777  * @secid: The LSM security ID to set
778  *
779  * Set the LSM security ID in a set of credentials so that the subjective
780  * security is overridden when an alternative set of credentials is used.
781  */
782 int set_security_override(struct cred *new, u32 secid)
783 {
784 	return security_kernel_act_as(new, secid);
785 }
786 EXPORT_SYMBOL(set_security_override);
787 
788 /**
789  * set_security_override_from_ctx - Set the security ID in a set of credentials
790  * @new: The credentials to alter
791  * @secctx: The LSM security context to generate the security ID from.
792  *
793  * Set the LSM security ID in a set of credentials so that the subjective
794  * security is overridden when an alternative set of credentials is used.  The
795  * security ID is specified in string form as a security context to be
796  * interpreted by the LSM.
797  */
798 int set_security_override_from_ctx(struct cred *new, const char *secctx)
799 {
800 	u32 secid;
801 	int ret;
802 
803 	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
804 	if (ret < 0)
805 		return ret;
806 
807 	return set_security_override(new, secid);
808 }
809 EXPORT_SYMBOL(set_security_override_from_ctx);
810 
811 /**
812  * set_create_files_as - Set the LSM file create context in a set of credentials
813  * @new: The credentials to alter
814  * @inode: The inode to take the context from
815  *
816  * Change the LSM file creation context in a set of credentials to be the same
817  * as the object context of the specified inode, so that the new inodes have
818  * the same MAC context as that inode.
819  */
820 int set_create_files_as(struct cred *new, struct inode *inode)
821 {
822 	if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
823 		return -EINVAL;
824 	new->fsuid = inode->i_uid;
825 	new->fsgid = inode->i_gid;
826 	return security_kernel_create_files_as(new, inode);
827 }
828 EXPORT_SYMBOL(set_create_files_as);
829 
830 #ifdef CONFIG_DEBUG_CREDENTIALS
831 
832 bool creds_are_invalid(const struct cred *cred)
833 {
834 	if (cred->magic != CRED_MAGIC)
835 		return true;
836 	return false;
837 }
838 EXPORT_SYMBOL(creds_are_invalid);
839 
840 /*
841  * dump invalid credentials
842  */
843 static void dump_invalid_creds(const struct cred *cred, const char *label,
844 			       const struct task_struct *tsk)
845 {
846 	printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
847 	       label, cred,
848 	       cred == &init_cred ? "[init]" : "",
849 	       cred == tsk->real_cred ? "[real]" : "",
850 	       cred == tsk->cred ? "[eff]" : "");
851 	printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
852 	       cred->magic, cred->put_addr);
853 	printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
854 	       atomic_read(&cred->usage),
855 	       read_cred_subscribers(cred));
856 	printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
857 		from_kuid_munged(&init_user_ns, cred->uid),
858 		from_kuid_munged(&init_user_ns, cred->euid),
859 		from_kuid_munged(&init_user_ns, cred->suid),
860 		from_kuid_munged(&init_user_ns, cred->fsuid));
861 	printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
862 		from_kgid_munged(&init_user_ns, cred->gid),
863 		from_kgid_munged(&init_user_ns, cred->egid),
864 		from_kgid_munged(&init_user_ns, cred->sgid),
865 		from_kgid_munged(&init_user_ns, cred->fsgid));
866 #ifdef CONFIG_SECURITY
867 	printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
868 	if ((unsigned long) cred->security >= PAGE_SIZE &&
869 	    (((unsigned long) cred->security & 0xffffff00) !=
870 	     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
871 		printk(KERN_ERR "CRED: ->security {%x, %x}\n",
872 		       ((u32*)cred->security)[0],
873 		       ((u32*)cred->security)[1]);
874 #endif
875 }
876 
877 /*
878  * report use of invalid credentials
879  */
880 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
881 {
882 	printk(KERN_ERR "CRED: Invalid credentials\n");
883 	printk(KERN_ERR "CRED: At %s:%u\n", file, line);
884 	dump_invalid_creds(cred, "Specified", current);
885 	BUG();
886 }
887 EXPORT_SYMBOL(__invalid_creds);
888 
889 /*
890  * check the credentials on a process
891  */
892 void __validate_process_creds(struct task_struct *tsk,
893 			      const char *file, unsigned line)
894 {
895 	if (tsk->cred == tsk->real_cred) {
896 		if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
897 			     creds_are_invalid(tsk->cred)))
898 			goto invalid_creds;
899 	} else {
900 		if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
901 			     read_cred_subscribers(tsk->cred) < 1 ||
902 			     creds_are_invalid(tsk->real_cred) ||
903 			     creds_are_invalid(tsk->cred)))
904 			goto invalid_creds;
905 	}
906 	return;
907 
908 invalid_creds:
909 	printk(KERN_ERR "CRED: Invalid process credentials\n");
910 	printk(KERN_ERR "CRED: At %s:%u\n", file, line);
911 
912 	dump_invalid_creds(tsk->real_cred, "Real", tsk);
913 	if (tsk->cred != tsk->real_cred)
914 		dump_invalid_creds(tsk->cred, "Effective", tsk);
915 	else
916 		printk(KERN_ERR "CRED: Effective creds == Real creds\n");
917 	BUG();
918 }
919 EXPORT_SYMBOL(__validate_process_creds);
920 
921 /*
922  * check creds for do_exit()
923  */
924 void validate_creds_for_do_exit(struct task_struct *tsk)
925 {
926 	kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
927 	       tsk->real_cred, tsk->cred,
928 	       atomic_read(&tsk->cred->usage),
929 	       read_cred_subscribers(tsk->cred));
930 
931 	__validate_process_creds(tsk, __FILE__, __LINE__);
932 }
933 
934 #endif /* CONFIG_DEBUG_CREDENTIALS */
935