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 ucounts *new_ucounts, *old_ucounts = new->ucounts;
669 
670 	/*
671 	 * This optimization is needed because alloc_ucounts() uses locks
672 	 * for table lookups.
673 	 */
674 	if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid))
675 		return 0;
676 
677 	if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid)))
678 		return -EAGAIN;
679 
680 	new->ucounts = new_ucounts;
681 	put_ucounts(old_ucounts);
682 
683 	return 0;
684 }
685 
686 /*
687  * initialise the credentials stuff
688  */
cred_init(void)689 void __init cred_init(void)
690 {
691 	/* allocate a slab in which we can store credentials */
692 	cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
693 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
694 }
695 
696 /**
697  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
698  * @daemon: A userspace daemon to be used as a reference
699  *
700  * Prepare a set of credentials for a kernel service.  This can then be used to
701  * override a task's own credentials so that work can be done on behalf of that
702  * task that requires a different subjective context.
703  *
704  * @daemon is used to provide a base cred, with the security data derived from
705  * that; if this is "&init_task", they'll be set to 0, no groups, full
706  * capabilities, and no keys.
707  *
708  * The caller may change these controls afterwards if desired.
709  *
710  * Returns the new credentials or NULL if out of memory.
711  */
prepare_kernel_cred(struct task_struct * daemon)712 struct cred *prepare_kernel_cred(struct task_struct *daemon)
713 {
714 	const struct cred *old;
715 	struct cred *new;
716 
717 	if (WARN_ON_ONCE(!daemon))
718 		return NULL;
719 
720 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
721 	if (!new)
722 		return NULL;
723 
724 	kdebug("prepare_kernel_cred() alloc %p", new);
725 
726 	old = get_task_cred(daemon);
727 	validate_creds(old);
728 
729 	*new = *old;
730 	new->non_rcu = 0;
731 	atomic_set(&new->usage, 1);
732 	set_cred_subscribers(new, 0);
733 	get_uid(new->user);
734 	get_user_ns(new->user_ns);
735 	get_group_info(new->group_info);
736 
737 #ifdef CONFIG_KEYS
738 	new->session_keyring = NULL;
739 	new->process_keyring = NULL;
740 	new->thread_keyring = NULL;
741 	new->request_key_auth = NULL;
742 	new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
743 #endif
744 
745 #ifdef CONFIG_SECURITY
746 	new->security = NULL;
747 #endif
748 	new->ucounts = get_ucounts(new->ucounts);
749 	if (!new->ucounts)
750 		goto error;
751 
752 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
753 		goto error;
754 
755 	put_cred(old);
756 	validate_creds(new);
757 	return new;
758 
759 error:
760 	put_cred(new);
761 	put_cred(old);
762 	return NULL;
763 }
764 EXPORT_SYMBOL(prepare_kernel_cred);
765 
766 /**
767  * set_security_override - Set the security ID in a set of credentials
768  * @new: The credentials to alter
769  * @secid: The LSM security ID to set
770  *
771  * Set the LSM security ID in a set of credentials so that the subjective
772  * security is overridden when an alternative set of credentials is used.
773  */
set_security_override(struct cred * new,u32 secid)774 int set_security_override(struct cred *new, u32 secid)
775 {
776 	return security_kernel_act_as(new, secid);
777 }
778 EXPORT_SYMBOL(set_security_override);
779 
780 /**
781  * set_security_override_from_ctx - Set the security ID in a set of credentials
782  * @new: The credentials to alter
783  * @secctx: The LSM security context to generate the security ID from.
784  *
785  * Set the LSM security ID in a set of credentials so that the subjective
786  * security is overridden when an alternative set of credentials is used.  The
787  * security ID is specified in string form as a security context to be
788  * interpreted by the LSM.
789  */
set_security_override_from_ctx(struct cred * new,const char * secctx)790 int set_security_override_from_ctx(struct cred *new, const char *secctx)
791 {
792 	u32 secid;
793 	int ret;
794 
795 	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
796 	if (ret < 0)
797 		return ret;
798 
799 	return set_security_override(new, secid);
800 }
801 EXPORT_SYMBOL(set_security_override_from_ctx);
802 
803 /**
804  * set_create_files_as - Set the LSM file create context in a set of credentials
805  * @new: The credentials to alter
806  * @inode: The inode to take the context from
807  *
808  * Change the LSM file creation context in a set of credentials to be the same
809  * as the object context of the specified inode, so that the new inodes have
810  * the same MAC context as that inode.
811  */
set_create_files_as(struct cred * new,struct inode * inode)812 int set_create_files_as(struct cred *new, struct inode *inode)
813 {
814 	if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
815 		return -EINVAL;
816 	new->fsuid = inode->i_uid;
817 	new->fsgid = inode->i_gid;
818 	return security_kernel_create_files_as(new, inode);
819 }
820 EXPORT_SYMBOL(set_create_files_as);
821 
822 #ifdef CONFIG_DEBUG_CREDENTIALS
823 
creds_are_invalid(const struct cred * cred)824 bool creds_are_invalid(const struct cred *cred)
825 {
826 	if (cred->magic != CRED_MAGIC)
827 		return true;
828 	return false;
829 }
830 EXPORT_SYMBOL(creds_are_invalid);
831 
832 /*
833  * dump invalid credentials
834  */
dump_invalid_creds(const struct cred * cred,const char * label,const struct task_struct * tsk)835 static void dump_invalid_creds(const struct cred *cred, const char *label,
836 			       const struct task_struct *tsk)
837 {
838 	printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
839 	       label, cred,
840 	       cred == &init_cred ? "[init]" : "",
841 	       cred == tsk->real_cred ? "[real]" : "",
842 	       cred == tsk->cred ? "[eff]" : "");
843 	printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
844 	       cred->magic, cred->put_addr);
845 	printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
846 	       atomic_read(&cred->usage),
847 	       read_cred_subscribers(cred));
848 	printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
849 		from_kuid_munged(&init_user_ns, cred->uid),
850 		from_kuid_munged(&init_user_ns, cred->euid),
851 		from_kuid_munged(&init_user_ns, cred->suid),
852 		from_kuid_munged(&init_user_ns, cred->fsuid));
853 	printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
854 		from_kgid_munged(&init_user_ns, cred->gid),
855 		from_kgid_munged(&init_user_ns, cred->egid),
856 		from_kgid_munged(&init_user_ns, cred->sgid),
857 		from_kgid_munged(&init_user_ns, cred->fsgid));
858 #ifdef CONFIG_SECURITY
859 	printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
860 	if ((unsigned long) cred->security >= PAGE_SIZE &&
861 	    (((unsigned long) cred->security & 0xffffff00) !=
862 	     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
863 		printk(KERN_ERR "CRED: ->security {%x, %x}\n",
864 		       ((u32*)cred->security)[0],
865 		       ((u32*)cred->security)[1]);
866 #endif
867 }
868 
869 /*
870  * report use of invalid credentials
871  */
__invalid_creds(const struct cred * cred,const char * file,unsigned line)872 void __noreturn __invalid_creds(const struct cred *cred, const char *file, unsigned line)
873 {
874 	printk(KERN_ERR "CRED: Invalid credentials\n");
875 	printk(KERN_ERR "CRED: At %s:%u\n", file, line);
876 	dump_invalid_creds(cred, "Specified", current);
877 	BUG();
878 }
879 EXPORT_SYMBOL(__invalid_creds);
880 
881 /*
882  * check the credentials on a process
883  */
__validate_process_creds(struct task_struct * tsk,const char * file,unsigned line)884 void __validate_process_creds(struct task_struct *tsk,
885 			      const char *file, unsigned line)
886 {
887 	if (tsk->cred == tsk->real_cred) {
888 		if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
889 			     creds_are_invalid(tsk->cred)))
890 			goto invalid_creds;
891 	} else {
892 		if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
893 			     read_cred_subscribers(tsk->cred) < 1 ||
894 			     creds_are_invalid(tsk->real_cred) ||
895 			     creds_are_invalid(tsk->cred)))
896 			goto invalid_creds;
897 	}
898 	return;
899 
900 invalid_creds:
901 	printk(KERN_ERR "CRED: Invalid process credentials\n");
902 	printk(KERN_ERR "CRED: At %s:%u\n", file, line);
903 
904 	dump_invalid_creds(tsk->real_cred, "Real", tsk);
905 	if (tsk->cred != tsk->real_cred)
906 		dump_invalid_creds(tsk->cred, "Effective", tsk);
907 	else
908 		printk(KERN_ERR "CRED: Effective creds == Real creds\n");
909 	BUG();
910 }
911 EXPORT_SYMBOL(__validate_process_creds);
912 
913 /*
914  * check creds for do_exit()
915  */
validate_creds_for_do_exit(struct task_struct * tsk)916 void validate_creds_for_do_exit(struct task_struct *tsk)
917 {
918 	kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
919 	       tsk->real_cred, tsk->cred,
920 	       atomic_read(&tsk->cred->usage),
921 	       read_cred_subscribers(tsk->cred));
922 
923 	__validate_process_creds(tsk, __FILE__, __LINE__);
924 }
925 
926 #endif /* CONFIG_DEBUG_CREDENTIALS */
927