xref: /linux/kernel/cred.c (revision edc66702)
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 
8 #define pr_fmt(fmt) "CRED: " fmt
9 
10 #include <linux/export.h>
11 #include <linux/cred.h>
12 #include <linux/slab.h>
13 #include <linux/sched.h>
14 #include <linux/sched/coredump.h>
15 #include <linux/key.h>
16 #include <linux/keyctl.h>
17 #include <linux/init_task.h>
18 #include <linux/security.h>
19 #include <linux/binfmts.h>
20 #include <linux/cn_proc.h>
21 #include <linux/uidgid.h>
22 
23 #if 0
24 #define kdebug(FMT, ...)						\
25 	printk("[%-5.5s%5u] " FMT "\n",					\
26 	       current->comm, current->pid, ##__VA_ARGS__)
27 #else
28 #define kdebug(FMT, ...)						\
29 do {									\
30 	if (0)								\
31 		no_printk("[%-5.5s%5u] " FMT "\n",			\
32 			  current->comm, current->pid, ##__VA_ARGS__);	\
33 } while (0)
34 #endif
35 
36 static struct kmem_cache *cred_jar;
37 
38 /* init to 2 - one for init_task, one to ensure it is never freed */
39 static struct group_info init_groups = { .usage = REFCOUNT_INIT(2) };
40 
41 /*
42  * The initial credentials for the initial task
43  */
44 struct cred init_cred = {
45 	.usage			= ATOMIC_INIT(4),
46 	.uid			= GLOBAL_ROOT_UID,
47 	.gid			= GLOBAL_ROOT_GID,
48 	.suid			= GLOBAL_ROOT_UID,
49 	.sgid			= GLOBAL_ROOT_GID,
50 	.euid			= GLOBAL_ROOT_UID,
51 	.egid			= GLOBAL_ROOT_GID,
52 	.fsuid			= GLOBAL_ROOT_UID,
53 	.fsgid			= GLOBAL_ROOT_GID,
54 	.securebits		= SECUREBITS_DEFAULT,
55 	.cap_inheritable	= CAP_EMPTY_SET,
56 	.cap_permitted		= CAP_FULL_SET,
57 	.cap_effective		= CAP_FULL_SET,
58 	.cap_bset		= CAP_FULL_SET,
59 	.user			= INIT_USER,
60 	.user_ns		= &init_user_ns,
61 	.group_info		= &init_groups,
62 	.ucounts		= &init_ucounts,
63 };
64 
65 /*
66  * The RCU callback to actually dispose of a set of credentials
67  */
put_cred_rcu(struct rcu_head * rcu)68 static void put_cred_rcu(struct rcu_head *rcu)
69 {
70 	struct cred *cred = container_of(rcu, struct cred, rcu);
71 
72 	kdebug("put_cred_rcu(%p)", cred);
73 
74 	if (atomic_long_read(&cred->usage) != 0)
75 		panic("CRED: put_cred_rcu() sees %p with usage %ld\n",
76 		      cred, atomic_long_read(&cred->usage));
77 
78 	security_cred_free(cred);
79 	key_put(cred->session_keyring);
80 	key_put(cred->process_keyring);
81 	key_put(cred->thread_keyring);
82 	key_put(cred->request_key_auth);
83 	if (cred->group_info)
84 		put_group_info(cred->group_info);
85 	free_uid(cred->user);
86 	if (cred->ucounts)
87 		put_ucounts(cred->ucounts);
88 	put_user_ns(cred->user_ns);
89 	kmem_cache_free(cred_jar, cred);
90 }
91 
92 /**
93  * __put_cred - Destroy a set of credentials
94  * @cred: The record to release
95  *
96  * Destroy a set of credentials on which no references remain.
97  */
__put_cred(struct cred * cred)98 void __put_cred(struct cred *cred)
99 {
100 	kdebug("__put_cred(%p{%ld})", cred,
101 	       atomic_long_read(&cred->usage));
102 
103 	BUG_ON(atomic_long_read(&cred->usage) != 0);
104 	BUG_ON(cred == current->cred);
105 	BUG_ON(cred == current->real_cred);
106 
107 	if (cred->non_rcu)
108 		put_cred_rcu(&cred->rcu);
109 	else
110 		call_rcu(&cred->rcu, put_cred_rcu);
111 }
112 EXPORT_SYMBOL(__put_cred);
113 
114 /*
115  * Clean up a task's credentials when it exits
116  */
exit_creds(struct task_struct * tsk)117 void exit_creds(struct task_struct *tsk)
118 {
119 	struct cred *real_cred, *cred;
120 
121 	kdebug("exit_creds(%u,%p,%p,{%ld})", tsk->pid, tsk->real_cred, tsk->cred,
122 	       atomic_long_read(&tsk->cred->usage));
123 
124 	real_cred = (struct cred *) tsk->real_cred;
125 	tsk->real_cred = NULL;
126 
127 	cred = (struct cred *) tsk->cred;
128 	tsk->cred = NULL;
129 
130 	if (real_cred == cred) {
131 		put_cred_many(cred, 2);
132 	} else {
133 		put_cred(real_cred);
134 		put_cred(cred);
135 	}
136 
137 #ifdef CONFIG_KEYS_REQUEST_CACHE
138 	key_put(tsk->cached_requested_key);
139 	tsk->cached_requested_key = NULL;
140 #endif
141 }
142 
143 /**
144  * get_task_cred - Get another task's objective credentials
145  * @task: The task to query
146  *
147  * Get the objective credentials of a task, pinning them so that they can't go
148  * away.  Accessing a task's credentials directly is not permitted.
149  *
150  * The caller must also make sure task doesn't get deleted, either by holding a
151  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
152  */
get_task_cred(struct task_struct * task)153 const struct cred *get_task_cred(struct task_struct *task)
154 {
155 	const struct cred *cred;
156 
157 	rcu_read_lock();
158 
159 	do {
160 		cred = __task_cred((task));
161 		BUG_ON(!cred);
162 	} while (!get_cred_rcu(cred));
163 
164 	rcu_read_unlock();
165 	return cred;
166 }
167 EXPORT_SYMBOL(get_task_cred);
168 
169 /*
170  * Allocate blank credentials, such that the credentials can be filled in at a
171  * later date without risk of ENOMEM.
172  */
cred_alloc_blank(void)173 struct cred *cred_alloc_blank(void)
174 {
175 	struct cred *new;
176 
177 	new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
178 	if (!new)
179 		return NULL;
180 
181 	atomic_long_set(&new->usage, 1);
182 	if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
183 		goto error;
184 
185 	return new;
186 
187 error:
188 	abort_creds(new);
189 	return NULL;
190 }
191 
192 /**
193  * prepare_creds - Prepare a new set of credentials for modification
194  *
195  * Prepare a new set of task credentials for modification.  A task's creds
196  * shouldn't generally be modified directly, therefore this function is used to
197  * prepare a new copy, which the caller then modifies and then commits by
198  * calling commit_creds().
199  *
200  * Preparation involves making a copy of the objective creds for modification.
201  *
202  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
203  *
204  * Call commit_creds() or abort_creds() to clean up.
205  */
prepare_creds(void)206 struct cred *prepare_creds(void)
207 {
208 	struct task_struct *task = current;
209 	const struct cred *old;
210 	struct cred *new;
211 
212 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
213 	if (!new)
214 		return NULL;
215 
216 	kdebug("prepare_creds() alloc %p", new);
217 
218 	old = task->cred;
219 	memcpy(new, old, sizeof(struct cred));
220 
221 	new->non_rcu = 0;
222 	atomic_long_set(&new->usage, 1);
223 	get_group_info(new->group_info);
224 	get_uid(new->user);
225 	get_user_ns(new->user_ns);
226 
227 #ifdef CONFIG_KEYS
228 	key_get(new->session_keyring);
229 	key_get(new->process_keyring);
230 	key_get(new->thread_keyring);
231 	key_get(new->request_key_auth);
232 #endif
233 
234 #ifdef CONFIG_SECURITY
235 	new->security = NULL;
236 #endif
237 
238 	new->ucounts = get_ucounts(new->ucounts);
239 	if (!new->ucounts)
240 		goto error;
241 
242 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
243 		goto error;
244 
245 	return new;
246 
247 error:
248 	abort_creds(new);
249 	return NULL;
250 }
251 EXPORT_SYMBOL(prepare_creds);
252 
253 /*
254  * Prepare credentials for current to perform an execve()
255  * - The caller must hold ->cred_guard_mutex
256  */
prepare_exec_creds(void)257 struct cred *prepare_exec_creds(void)
258 {
259 	struct cred *new;
260 
261 	new = prepare_creds();
262 	if (!new)
263 		return new;
264 
265 #ifdef CONFIG_KEYS
266 	/* newly exec'd tasks don't get a thread keyring */
267 	key_put(new->thread_keyring);
268 	new->thread_keyring = NULL;
269 
270 	/* inherit the session keyring; new process keyring */
271 	key_put(new->process_keyring);
272 	new->process_keyring = NULL;
273 #endif
274 
275 	new->suid = new->fsuid = new->euid;
276 	new->sgid = new->fsgid = new->egid;
277 
278 	return new;
279 }
280 
281 /*
282  * Copy credentials for the new process created by fork()
283  *
284  * We share if we can, but under some circumstances we have to generate a new
285  * set.
286  *
287  * The new process gets the current process's subjective credentials as its
288  * objective and subjective credentials
289  */
copy_creds(struct task_struct * p,unsigned long clone_flags)290 int copy_creds(struct task_struct *p, unsigned long clone_flags)
291 {
292 	struct cred *new;
293 	int ret;
294 
295 #ifdef CONFIG_KEYS_REQUEST_CACHE
296 	p->cached_requested_key = NULL;
297 #endif
298 
299 	if (
300 #ifdef CONFIG_KEYS
301 		!p->cred->thread_keyring &&
302 #endif
303 		clone_flags & CLONE_THREAD
304 	    ) {
305 		p->real_cred = get_cred_many(p->cred, 2);
306 		kdebug("share_creds(%p{%ld})",
307 		       p->cred, atomic_long_read(&p->cred->usage));
308 		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
309 		return 0;
310 	}
311 
312 	new = prepare_creds();
313 	if (!new)
314 		return -ENOMEM;
315 
316 	if (clone_flags & CLONE_NEWUSER) {
317 		ret = create_user_ns(new);
318 		if (ret < 0)
319 			goto error_put;
320 		ret = set_cred_ucounts(new);
321 		if (ret < 0)
322 			goto error_put;
323 	}
324 
325 #ifdef CONFIG_KEYS
326 	/* new threads get their own thread keyrings if their parent already
327 	 * had one */
328 	if (new->thread_keyring) {
329 		key_put(new->thread_keyring);
330 		new->thread_keyring = NULL;
331 		if (clone_flags & CLONE_THREAD)
332 			install_thread_keyring_to_cred(new);
333 	}
334 
335 	/* The process keyring is only shared between the threads in a process;
336 	 * anything outside of those threads doesn't inherit.
337 	 */
338 	if (!(clone_flags & CLONE_THREAD)) {
339 		key_put(new->process_keyring);
340 		new->process_keyring = NULL;
341 	}
342 #endif
343 
344 	p->cred = p->real_cred = get_cred(new);
345 	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
346 	return 0;
347 
348 error_put:
349 	put_cred(new);
350 	return ret;
351 }
352 
cred_cap_issubset(const struct cred * set,const struct cred * subset)353 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
354 {
355 	const struct user_namespace *set_ns = set->user_ns;
356 	const struct user_namespace *subset_ns = subset->user_ns;
357 
358 	/* If the two credentials are in the same user namespace see if
359 	 * the capabilities of subset are a subset of set.
360 	 */
361 	if (set_ns == subset_ns)
362 		return cap_issubset(subset->cap_permitted, set->cap_permitted);
363 
364 	/* The credentials are in a different user namespaces
365 	 * therefore one is a subset of the other only if a set is an
366 	 * ancestor of subset and set->euid is owner of subset or one
367 	 * of subsets ancestors.
368 	 */
369 	for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
370 		if ((set_ns == subset_ns->parent)  &&
371 		    uid_eq(subset_ns->owner, set->euid))
372 			return true;
373 	}
374 
375 	return false;
376 }
377 
378 /**
379  * commit_creds - Install new credentials upon the current task
380  * @new: The credentials to be assigned
381  *
382  * Install a new set of credentials to the current task, using RCU to replace
383  * the old set.  Both the objective and the subjective credentials pointers are
384  * updated.  This function may not be called if the subjective credentials are
385  * in an overridden state.
386  *
387  * This function eats the caller's reference to the new credentials.
388  *
389  * Always returns 0 thus allowing this function to be tail-called at the end
390  * of, say, sys_setgid().
391  */
commit_creds(struct cred * new)392 int commit_creds(struct cred *new)
393 {
394 	struct task_struct *task = current;
395 	const struct cred *old = task->real_cred;
396 
397 	kdebug("commit_creds(%p{%ld})", new,
398 	       atomic_long_read(&new->usage));
399 
400 	BUG_ON(task->cred != old);
401 	BUG_ON(atomic_long_read(&new->usage) < 1);
402 
403 	get_cred(new); /* we will require a ref for the subj creds too */
404 
405 	/* dumpability changes */
406 	if (!uid_eq(old->euid, new->euid) ||
407 	    !gid_eq(old->egid, new->egid) ||
408 	    !uid_eq(old->fsuid, new->fsuid) ||
409 	    !gid_eq(old->fsgid, new->fsgid) ||
410 	    !cred_cap_issubset(old, new)) {
411 		if (task->mm)
412 			set_dumpable(task->mm, suid_dumpable);
413 		task->pdeath_signal = 0;
414 		/*
415 		 * If a task drops privileges and becomes nondumpable,
416 		 * the dumpability change must become visible before
417 		 * the credential change; otherwise, a __ptrace_may_access()
418 		 * racing with this change may be able to attach to a task it
419 		 * shouldn't be able to attach to (as if the task had dropped
420 		 * privileges without becoming nondumpable).
421 		 * Pairs with a read barrier in __ptrace_may_access().
422 		 */
423 		smp_wmb();
424 	}
425 
426 	/* alter the thread keyring */
427 	if (!uid_eq(new->fsuid, old->fsuid))
428 		key_fsuid_changed(new);
429 	if (!gid_eq(new->fsgid, old->fsgid))
430 		key_fsgid_changed(new);
431 
432 	/* do it
433 	 * RLIMIT_NPROC limits on user->processes have already been checked
434 	 * in set_user().
435 	 */
436 	if (new->user != old->user || new->user_ns != old->user_ns)
437 		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
438 	rcu_assign_pointer(task->real_cred, new);
439 	rcu_assign_pointer(task->cred, new);
440 	if (new->user != old->user || new->user_ns != old->user_ns)
441 		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
442 
443 	/* send notifications */
444 	if (!uid_eq(new->uid,   old->uid)  ||
445 	    !uid_eq(new->euid,  old->euid) ||
446 	    !uid_eq(new->suid,  old->suid) ||
447 	    !uid_eq(new->fsuid, old->fsuid))
448 		proc_id_connector(task, PROC_EVENT_UID);
449 
450 	if (!gid_eq(new->gid,   old->gid)  ||
451 	    !gid_eq(new->egid,  old->egid) ||
452 	    !gid_eq(new->sgid,  old->sgid) ||
453 	    !gid_eq(new->fsgid, old->fsgid))
454 		proc_id_connector(task, PROC_EVENT_GID);
455 
456 	/* release the old obj and subj refs both */
457 	put_cred_many(old, 2);
458 	return 0;
459 }
460 EXPORT_SYMBOL(commit_creds);
461 
462 /**
463  * abort_creds - Discard a set of credentials and unlock the current task
464  * @new: The credentials that were going to be applied
465  *
466  * Discard a set of credentials that were under construction and unlock the
467  * current task.
468  */
abort_creds(struct cred * new)469 void abort_creds(struct cred *new)
470 {
471 	kdebug("abort_creds(%p{%ld})", new,
472 	       atomic_long_read(&new->usage));
473 
474 	BUG_ON(atomic_long_read(&new->usage) < 1);
475 	put_cred(new);
476 }
477 EXPORT_SYMBOL(abort_creds);
478 
479 /**
480  * override_creds - Override the current process's subjective credentials
481  * @new: The credentials to be assigned
482  *
483  * Install a set of temporary override subjective credentials on the current
484  * process, returning the old set for later reversion.
485  */
override_creds(const struct cred * new)486 const struct cred *override_creds(const struct cred *new)
487 {
488 	const struct cred *old = current->cred;
489 
490 	kdebug("override_creds(%p{%ld})", new,
491 	       atomic_long_read(&new->usage));
492 
493 	/*
494 	 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
495 	 *
496 	 * That means that we do not clear the 'non_rcu' flag, since
497 	 * we are only installing the cred into the thread-synchronous
498 	 * '->cred' pointer, not the '->real_cred' pointer that is
499 	 * visible to other threads under RCU.
500 	 */
501 	get_new_cred((struct cred *)new);
502 	rcu_assign_pointer(current->cred, new);
503 
504 	kdebug("override_creds() = %p{%ld}", old,
505 	       atomic_long_read(&old->usage));
506 	return old;
507 }
508 EXPORT_SYMBOL(override_creds);
509 
510 /**
511  * revert_creds - Revert a temporary subjective credentials override
512  * @old: The credentials to be restored
513  *
514  * Revert a temporary set of override subjective credentials to an old set,
515  * discarding the override set.
516  */
revert_creds(const struct cred * old)517 void revert_creds(const struct cred *old)
518 {
519 	const struct cred *override = current->cred;
520 
521 	kdebug("revert_creds(%p{%ld})", old,
522 	       atomic_long_read(&old->usage));
523 
524 	rcu_assign_pointer(current->cred, old);
525 	put_cred(override);
526 }
527 EXPORT_SYMBOL(revert_creds);
528 
529 /**
530  * cred_fscmp - Compare two credentials with respect to filesystem access.
531  * @a: The first credential
532  * @b: The second credential
533  *
534  * cred_cmp() will return zero if both credentials have the same
535  * fsuid, fsgid, and supplementary groups.  That is, if they will both
536  * provide the same access to files based on mode/uid/gid.
537  * If the credentials are different, then either -1 or 1 will
538  * be returned depending on whether @a comes before or after @b
539  * respectively in an arbitrary, but stable, ordering of credentials.
540  *
541  * Return: -1, 0, or 1 depending on comparison
542  */
cred_fscmp(const struct cred * a,const struct cred * b)543 int cred_fscmp(const struct cred *a, const struct cred *b)
544 {
545 	struct group_info *ga, *gb;
546 	int g;
547 
548 	if (a == b)
549 		return 0;
550 	if (uid_lt(a->fsuid, b->fsuid))
551 		return -1;
552 	if (uid_gt(a->fsuid, b->fsuid))
553 		return 1;
554 
555 	if (gid_lt(a->fsgid, b->fsgid))
556 		return -1;
557 	if (gid_gt(a->fsgid, b->fsgid))
558 		return 1;
559 
560 	ga = a->group_info;
561 	gb = b->group_info;
562 	if (ga == gb)
563 		return 0;
564 	if (ga == NULL)
565 		return -1;
566 	if (gb == NULL)
567 		return 1;
568 	if (ga->ngroups < gb->ngroups)
569 		return -1;
570 	if (ga->ngroups > gb->ngroups)
571 		return 1;
572 
573 	for (g = 0; g < ga->ngroups; g++) {
574 		if (gid_lt(ga->gid[g], gb->gid[g]))
575 			return -1;
576 		if (gid_gt(ga->gid[g], gb->gid[g]))
577 			return 1;
578 	}
579 	return 0;
580 }
581 EXPORT_SYMBOL(cred_fscmp);
582 
set_cred_ucounts(struct cred * new)583 int set_cred_ucounts(struct cred *new)
584 {
585 	struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
586 
587 	/*
588 	 * This optimization is needed because alloc_ucounts() uses locks
589 	 * for table lookups.
590 	 */
591 	if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid))
592 		return 0;
593 
594 	if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid)))
595 		return -EAGAIN;
596 
597 	new->ucounts = new_ucounts;
598 	put_ucounts(old_ucounts);
599 
600 	return 0;
601 }
602 
603 /*
604  * initialise the credentials stuff
605  */
cred_init(void)606 void __init cred_init(void)
607 {
608 	/* allocate a slab in which we can store credentials */
609 	cred_jar = KMEM_CACHE(cred,
610 			      SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
611 }
612 
613 /**
614  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
615  * @daemon: A userspace daemon to be used as a reference
616  *
617  * Prepare a set of credentials for a kernel service.  This can then be used to
618  * override a task's own credentials so that work can be done on behalf of that
619  * task that requires a different subjective context.
620  *
621  * @daemon is used to provide a base cred, with the security data derived from
622  * that; if this is "&init_task", they'll be set to 0, no groups, full
623  * capabilities, and no keys.
624  *
625  * The caller may change these controls afterwards if desired.
626  *
627  * Returns the new credentials or NULL if out of memory.
628  */
prepare_kernel_cred(struct task_struct * daemon)629 struct cred *prepare_kernel_cred(struct task_struct *daemon)
630 {
631 	const struct cred *old;
632 	struct cred *new;
633 
634 	if (WARN_ON_ONCE(!daemon))
635 		return NULL;
636 
637 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
638 	if (!new)
639 		return NULL;
640 
641 	kdebug("prepare_kernel_cred() alloc %p", new);
642 
643 	old = get_task_cred(daemon);
644 
645 	*new = *old;
646 	new->non_rcu = 0;
647 	atomic_long_set(&new->usage, 1);
648 	get_uid(new->user);
649 	get_user_ns(new->user_ns);
650 	get_group_info(new->group_info);
651 
652 #ifdef CONFIG_KEYS
653 	new->session_keyring = NULL;
654 	new->process_keyring = NULL;
655 	new->thread_keyring = NULL;
656 	new->request_key_auth = NULL;
657 	new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
658 #endif
659 
660 #ifdef CONFIG_SECURITY
661 	new->security = NULL;
662 #endif
663 	new->ucounts = get_ucounts(new->ucounts);
664 	if (!new->ucounts)
665 		goto error;
666 
667 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
668 		goto error;
669 
670 	put_cred(old);
671 	return new;
672 
673 error:
674 	put_cred(new);
675 	put_cred(old);
676 	return NULL;
677 }
678 EXPORT_SYMBOL(prepare_kernel_cred);
679 
680 /**
681  * set_security_override - Set the security ID in a set of credentials
682  * @new: The credentials to alter
683  * @secid: The LSM security ID to set
684  *
685  * Set the LSM security ID in a set of credentials so that the subjective
686  * security is overridden when an alternative set of credentials is used.
687  */
set_security_override(struct cred * new,u32 secid)688 int set_security_override(struct cred *new, u32 secid)
689 {
690 	return security_kernel_act_as(new, secid);
691 }
692 EXPORT_SYMBOL(set_security_override);
693 
694 /**
695  * set_security_override_from_ctx - Set the security ID in a set of credentials
696  * @new: The credentials to alter
697  * @secctx: The LSM security context to generate the security ID from.
698  *
699  * Set the LSM security ID in a set of credentials so that the subjective
700  * security is overridden when an alternative set of credentials is used.  The
701  * security ID is specified in string form as a security context to be
702  * interpreted by the LSM.
703  */
set_security_override_from_ctx(struct cred * new,const char * secctx)704 int set_security_override_from_ctx(struct cred *new, const char *secctx)
705 {
706 	u32 secid;
707 	int ret;
708 
709 	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
710 	if (ret < 0)
711 		return ret;
712 
713 	return set_security_override(new, secid);
714 }
715 EXPORT_SYMBOL(set_security_override_from_ctx);
716 
717 /**
718  * set_create_files_as - Set the LSM file create context in a set of credentials
719  * @new: The credentials to alter
720  * @inode: The inode to take the context from
721  *
722  * Change the LSM file creation context in a set of credentials to be the same
723  * as the object context of the specified inode, so that the new inodes have
724  * the same MAC context as that inode.
725  */
set_create_files_as(struct cred * new,struct inode * inode)726 int set_create_files_as(struct cred *new, struct inode *inode)
727 {
728 	if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
729 		return -EINVAL;
730 	new->fsuid = inode->i_uid;
731 	new->fsgid = inode->i_gid;
732 	return security_kernel_create_files_as(new, inode);
733 }
734 EXPORT_SYMBOL(set_create_files_as);
735