xref: /openbmc/linux/security/keys/process_keys.c (revision c67e8ec0)
1 /* Manage a process's keyrings
2  *
3  * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version
9  * 2 of the License, or (at your option) any later version.
10  */
11 
12 #include <linux/init.h>
13 #include <linux/sched.h>
14 #include <linux/sched/user.h>
15 #include <linux/keyctl.h>
16 #include <linux/fs.h>
17 #include <linux/err.h>
18 #include <linux/mutex.h>
19 #include <linux/security.h>
20 #include <linux/user_namespace.h>
21 #include <linux/uaccess.h>
22 #include "internal.h"
23 
24 /* Session keyring create vs join semaphore */
25 static DEFINE_MUTEX(key_session_mutex);
26 
27 /* User keyring creation semaphore */
28 static DEFINE_MUTEX(key_user_keyring_mutex);
29 
30 /* The root user's tracking struct */
31 struct key_user root_key_user = {
32 	.usage		= REFCOUNT_INIT(3),
33 	.cons_lock	= __MUTEX_INITIALIZER(root_key_user.cons_lock),
34 	.lock		= __SPIN_LOCK_UNLOCKED(root_key_user.lock),
35 	.nkeys		= ATOMIC_INIT(2),
36 	.nikeys		= ATOMIC_INIT(2),
37 	.uid		= GLOBAL_ROOT_UID,
38 };
39 
40 /*
41  * Install the user and user session keyrings for the current process's UID.
42  */
43 int install_user_keyrings(void)
44 {
45 	struct user_struct *user;
46 	const struct cred *cred;
47 	struct key *uid_keyring, *session_keyring;
48 	key_perm_t user_keyring_perm;
49 	char buf[20];
50 	int ret;
51 	uid_t uid;
52 
53 	user_keyring_perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL;
54 	cred = current_cred();
55 	user = cred->user;
56 	uid = from_kuid(cred->user_ns, user->uid);
57 
58 	kenter("%p{%u}", user, uid);
59 
60 	if (user->uid_keyring && user->session_keyring) {
61 		kleave(" = 0 [exist]");
62 		return 0;
63 	}
64 
65 	mutex_lock(&key_user_keyring_mutex);
66 	ret = 0;
67 
68 	if (!user->uid_keyring) {
69 		/* get the UID-specific keyring
70 		 * - there may be one in existence already as it may have been
71 		 *   pinned by a session, but the user_struct pointing to it
72 		 *   may have been destroyed by setuid */
73 		sprintf(buf, "_uid.%u", uid);
74 
75 		uid_keyring = find_keyring_by_name(buf, true);
76 		if (IS_ERR(uid_keyring)) {
77 			uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
78 						    cred, user_keyring_perm,
79 						    KEY_ALLOC_UID_KEYRING |
80 							KEY_ALLOC_IN_QUOTA,
81 						    NULL, NULL);
82 			if (IS_ERR(uid_keyring)) {
83 				ret = PTR_ERR(uid_keyring);
84 				goto error;
85 			}
86 		}
87 
88 		/* get a default session keyring (which might also exist
89 		 * already) */
90 		sprintf(buf, "_uid_ses.%u", uid);
91 
92 		session_keyring = find_keyring_by_name(buf, true);
93 		if (IS_ERR(session_keyring)) {
94 			session_keyring =
95 				keyring_alloc(buf, user->uid, INVALID_GID,
96 					      cred, user_keyring_perm,
97 					      KEY_ALLOC_UID_KEYRING |
98 						  KEY_ALLOC_IN_QUOTA,
99 					      NULL, NULL);
100 			if (IS_ERR(session_keyring)) {
101 				ret = PTR_ERR(session_keyring);
102 				goto error_release;
103 			}
104 
105 			/* we install a link from the user session keyring to
106 			 * the user keyring */
107 			ret = key_link(session_keyring, uid_keyring);
108 			if (ret < 0)
109 				goto error_release_both;
110 		}
111 
112 		/* install the keyrings */
113 		user->uid_keyring = uid_keyring;
114 		user->session_keyring = session_keyring;
115 	}
116 
117 	mutex_unlock(&key_user_keyring_mutex);
118 	kleave(" = 0");
119 	return 0;
120 
121 error_release_both:
122 	key_put(session_keyring);
123 error_release:
124 	key_put(uid_keyring);
125 error:
126 	mutex_unlock(&key_user_keyring_mutex);
127 	kleave(" = %d", ret);
128 	return ret;
129 }
130 
131 /*
132  * Install a thread keyring to the given credentials struct if it didn't have
133  * one already.  This is allowed to overrun the quota.
134  *
135  * Return: 0 if a thread keyring is now present; -errno on failure.
136  */
137 int install_thread_keyring_to_cred(struct cred *new)
138 {
139 	struct key *keyring;
140 
141 	if (new->thread_keyring)
142 		return 0;
143 
144 	keyring = keyring_alloc("_tid", new->uid, new->gid, new,
145 				KEY_POS_ALL | KEY_USR_VIEW,
146 				KEY_ALLOC_QUOTA_OVERRUN,
147 				NULL, NULL);
148 	if (IS_ERR(keyring))
149 		return PTR_ERR(keyring);
150 
151 	new->thread_keyring = keyring;
152 	return 0;
153 }
154 
155 /*
156  * Install a thread keyring to the current task if it didn't have one already.
157  *
158  * Return: 0 if a thread keyring is now present; -errno on failure.
159  */
160 static int install_thread_keyring(void)
161 {
162 	struct cred *new;
163 	int ret;
164 
165 	new = prepare_creds();
166 	if (!new)
167 		return -ENOMEM;
168 
169 	ret = install_thread_keyring_to_cred(new);
170 	if (ret < 0) {
171 		abort_creds(new);
172 		return ret;
173 	}
174 
175 	return commit_creds(new);
176 }
177 
178 /*
179  * Install a process keyring to the given credentials struct if it didn't have
180  * one already.  This is allowed to overrun the quota.
181  *
182  * Return: 0 if a process keyring is now present; -errno on failure.
183  */
184 int install_process_keyring_to_cred(struct cred *new)
185 {
186 	struct key *keyring;
187 
188 	if (new->process_keyring)
189 		return 0;
190 
191 	keyring = keyring_alloc("_pid", new->uid, new->gid, new,
192 				KEY_POS_ALL | KEY_USR_VIEW,
193 				KEY_ALLOC_QUOTA_OVERRUN,
194 				NULL, NULL);
195 	if (IS_ERR(keyring))
196 		return PTR_ERR(keyring);
197 
198 	new->process_keyring = keyring;
199 	return 0;
200 }
201 
202 /*
203  * Install a process keyring to the current task if it didn't have one already.
204  *
205  * Return: 0 if a process keyring is now present; -errno on failure.
206  */
207 static int install_process_keyring(void)
208 {
209 	struct cred *new;
210 	int ret;
211 
212 	new = prepare_creds();
213 	if (!new)
214 		return -ENOMEM;
215 
216 	ret = install_process_keyring_to_cred(new);
217 	if (ret < 0) {
218 		abort_creds(new);
219 		return ret;
220 	}
221 
222 	return commit_creds(new);
223 }
224 
225 /*
226  * Install the given keyring as the session keyring of the given credentials
227  * struct, replacing the existing one if any.  If the given keyring is NULL,
228  * then install a new anonymous session keyring.
229  *
230  * Return: 0 on success; -errno on failure.
231  */
232 int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
233 {
234 	unsigned long flags;
235 	struct key *old;
236 
237 	might_sleep();
238 
239 	/* create an empty session keyring */
240 	if (!keyring) {
241 		flags = KEY_ALLOC_QUOTA_OVERRUN;
242 		if (cred->session_keyring)
243 			flags = KEY_ALLOC_IN_QUOTA;
244 
245 		keyring = keyring_alloc("_ses", cred->uid, cred->gid, cred,
246 					KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
247 					flags, NULL, NULL);
248 		if (IS_ERR(keyring))
249 			return PTR_ERR(keyring);
250 	} else {
251 		__key_get(keyring);
252 	}
253 
254 	/* install the keyring */
255 	old = cred->session_keyring;
256 	rcu_assign_pointer(cred->session_keyring, keyring);
257 
258 	if (old)
259 		key_put(old);
260 
261 	return 0;
262 }
263 
264 /*
265  * Install the given keyring as the session keyring of the current task,
266  * replacing the existing one if any.  If the given keyring is NULL, then
267  * install a new anonymous session keyring.
268  *
269  * Return: 0 on success; -errno on failure.
270  */
271 static int install_session_keyring(struct key *keyring)
272 {
273 	struct cred *new;
274 	int ret;
275 
276 	new = prepare_creds();
277 	if (!new)
278 		return -ENOMEM;
279 
280 	ret = install_session_keyring_to_cred(new, keyring);
281 	if (ret < 0) {
282 		abort_creds(new);
283 		return ret;
284 	}
285 
286 	return commit_creds(new);
287 }
288 
289 /*
290  * Handle the fsuid changing.
291  */
292 void key_fsuid_changed(struct task_struct *tsk)
293 {
294 	/* update the ownership of the thread keyring */
295 	BUG_ON(!tsk->cred);
296 	if (tsk->cred->thread_keyring) {
297 		down_write(&tsk->cred->thread_keyring->sem);
298 		tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
299 		up_write(&tsk->cred->thread_keyring->sem);
300 	}
301 }
302 
303 /*
304  * Handle the fsgid changing.
305  */
306 void key_fsgid_changed(struct task_struct *tsk)
307 {
308 	/* update the ownership of the thread keyring */
309 	BUG_ON(!tsk->cred);
310 	if (tsk->cred->thread_keyring) {
311 		down_write(&tsk->cred->thread_keyring->sem);
312 		tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
313 		up_write(&tsk->cred->thread_keyring->sem);
314 	}
315 }
316 
317 /*
318  * Search the process keyrings attached to the supplied cred for the first
319  * matching key.
320  *
321  * The search criteria are the type and the match function.  The description is
322  * given to the match function as a parameter, but doesn't otherwise influence
323  * the search.  Typically the match function will compare the description
324  * parameter to the key's description.
325  *
326  * This can only search keyrings that grant Search permission to the supplied
327  * credentials.  Keyrings linked to searched keyrings will also be searched if
328  * they grant Search permission too.  Keys can only be found if they grant
329  * Search permission to the credentials.
330  *
331  * Returns a pointer to the key with the key usage count incremented if
332  * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
333  * matched negative keys.
334  *
335  * In the case of a successful return, the possession attribute is set on the
336  * returned key reference.
337  */
338 key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
339 {
340 	key_ref_t key_ref, ret, err;
341 
342 	/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
343 	 * searchable, but we failed to find a key or we found a negative key;
344 	 * otherwise we want to return a sample error (probably -EACCES) if
345 	 * none of the keyrings were searchable
346 	 *
347 	 * in terms of priority: success > -ENOKEY > -EAGAIN > other error
348 	 */
349 	key_ref = NULL;
350 	ret = NULL;
351 	err = ERR_PTR(-EAGAIN);
352 
353 	/* search the thread keyring first */
354 	if (ctx->cred->thread_keyring) {
355 		key_ref = keyring_search_aux(
356 			make_key_ref(ctx->cred->thread_keyring, 1), ctx);
357 		if (!IS_ERR(key_ref))
358 			goto found;
359 
360 		switch (PTR_ERR(key_ref)) {
361 		case -EAGAIN: /* no key */
362 		case -ENOKEY: /* negative key */
363 			ret = key_ref;
364 			break;
365 		default:
366 			err = key_ref;
367 			break;
368 		}
369 	}
370 
371 	/* search the process keyring second */
372 	if (ctx->cred->process_keyring) {
373 		key_ref = keyring_search_aux(
374 			make_key_ref(ctx->cred->process_keyring, 1), ctx);
375 		if (!IS_ERR(key_ref))
376 			goto found;
377 
378 		switch (PTR_ERR(key_ref)) {
379 		case -EAGAIN: /* no key */
380 			if (ret)
381 				break;
382 			/* fall through */
383 		case -ENOKEY: /* negative key */
384 			ret = key_ref;
385 			break;
386 		default:
387 			err = key_ref;
388 			break;
389 		}
390 	}
391 
392 	/* search the session keyring */
393 	if (ctx->cred->session_keyring) {
394 		rcu_read_lock();
395 		key_ref = keyring_search_aux(
396 			make_key_ref(rcu_dereference(ctx->cred->session_keyring), 1),
397 			ctx);
398 		rcu_read_unlock();
399 
400 		if (!IS_ERR(key_ref))
401 			goto found;
402 
403 		switch (PTR_ERR(key_ref)) {
404 		case -EAGAIN: /* no key */
405 			if (ret)
406 				break;
407 			/* fall through */
408 		case -ENOKEY: /* negative key */
409 			ret = key_ref;
410 			break;
411 		default:
412 			err = key_ref;
413 			break;
414 		}
415 	}
416 	/* or search the user-session keyring */
417 	else if (ctx->cred->user->session_keyring) {
418 		key_ref = keyring_search_aux(
419 			make_key_ref(ctx->cred->user->session_keyring, 1),
420 			ctx);
421 		if (!IS_ERR(key_ref))
422 			goto found;
423 
424 		switch (PTR_ERR(key_ref)) {
425 		case -EAGAIN: /* no key */
426 			if (ret)
427 				break;
428 			/* fall through */
429 		case -ENOKEY: /* negative key */
430 			ret = key_ref;
431 			break;
432 		default:
433 			err = key_ref;
434 			break;
435 		}
436 	}
437 
438 	/* no key - decide on the error we're going to go for */
439 	key_ref = ret ? ret : err;
440 
441 found:
442 	return key_ref;
443 }
444 
445 /*
446  * Search the process keyrings attached to the supplied cred for the first
447  * matching key in the manner of search_my_process_keyrings(), but also search
448  * the keys attached to the assumed authorisation key using its credentials if
449  * one is available.
450  *
451  * Return same as search_my_process_keyrings().
452  */
453 key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
454 {
455 	struct request_key_auth *rka;
456 	key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
457 
458 	might_sleep();
459 
460 	key_ref = search_my_process_keyrings(ctx);
461 	if (!IS_ERR(key_ref))
462 		goto found;
463 	err = key_ref;
464 
465 	/* if this process has an instantiation authorisation key, then we also
466 	 * search the keyrings of the process mentioned there
467 	 * - we don't permit access to request_key auth keys via this method
468 	 */
469 	if (ctx->cred->request_key_auth &&
470 	    ctx->cred == current_cred() &&
471 	    ctx->index_key.type != &key_type_request_key_auth
472 	    ) {
473 		const struct cred *cred = ctx->cred;
474 
475 		/* defend against the auth key being revoked */
476 		down_read(&cred->request_key_auth->sem);
477 
478 		if (key_validate(ctx->cred->request_key_auth) == 0) {
479 			rka = ctx->cred->request_key_auth->payload.data[0];
480 
481 			ctx->cred = rka->cred;
482 			key_ref = search_process_keyrings(ctx);
483 			ctx->cred = cred;
484 
485 			up_read(&cred->request_key_auth->sem);
486 
487 			if (!IS_ERR(key_ref))
488 				goto found;
489 
490 			ret = key_ref;
491 		} else {
492 			up_read(&cred->request_key_auth->sem);
493 		}
494 	}
495 
496 	/* no key - decide on the error we're going to go for */
497 	if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
498 		key_ref = ERR_PTR(-ENOKEY);
499 	else if (err == ERR_PTR(-EACCES))
500 		key_ref = ret;
501 	else
502 		key_ref = err;
503 
504 found:
505 	return key_ref;
506 }
507 
508 /*
509  * See if the key we're looking at is the target key.
510  */
511 bool lookup_user_key_possessed(const struct key *key,
512 			       const struct key_match_data *match_data)
513 {
514 	return key == match_data->raw_data;
515 }
516 
517 /*
518  * Look up a key ID given us by userspace with a given permissions mask to get
519  * the key it refers to.
520  *
521  * Flags can be passed to request that special keyrings be created if referred
522  * to directly, to permit partially constructed keys to be found and to skip
523  * validity and permission checks on the found key.
524  *
525  * Returns a pointer to the key with an incremented usage count if successful;
526  * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
527  * to a key or the best found key was a negative key; -EKEYREVOKED or
528  * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
529  * found key doesn't grant the requested permit or the LSM denied access to it;
530  * or -ENOMEM if a special keyring couldn't be created.
531  *
532  * In the case of a successful return, the possession attribute is set on the
533  * returned key reference.
534  */
535 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
536 			  key_perm_t perm)
537 {
538 	struct keyring_search_context ctx = {
539 		.match_data.cmp		= lookup_user_key_possessed,
540 		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
541 		.flags			= KEYRING_SEARCH_NO_STATE_CHECK,
542 	};
543 	struct request_key_auth *rka;
544 	struct key *key;
545 	key_ref_t key_ref, skey_ref;
546 	int ret;
547 
548 try_again:
549 	ctx.cred = get_current_cred();
550 	key_ref = ERR_PTR(-ENOKEY);
551 
552 	switch (id) {
553 	case KEY_SPEC_THREAD_KEYRING:
554 		if (!ctx.cred->thread_keyring) {
555 			if (!(lflags & KEY_LOOKUP_CREATE))
556 				goto error;
557 
558 			ret = install_thread_keyring();
559 			if (ret < 0) {
560 				key_ref = ERR_PTR(ret);
561 				goto error;
562 			}
563 			goto reget_creds;
564 		}
565 
566 		key = ctx.cred->thread_keyring;
567 		__key_get(key);
568 		key_ref = make_key_ref(key, 1);
569 		break;
570 
571 	case KEY_SPEC_PROCESS_KEYRING:
572 		if (!ctx.cred->process_keyring) {
573 			if (!(lflags & KEY_LOOKUP_CREATE))
574 				goto error;
575 
576 			ret = install_process_keyring();
577 			if (ret < 0) {
578 				key_ref = ERR_PTR(ret);
579 				goto error;
580 			}
581 			goto reget_creds;
582 		}
583 
584 		key = ctx.cred->process_keyring;
585 		__key_get(key);
586 		key_ref = make_key_ref(key, 1);
587 		break;
588 
589 	case KEY_SPEC_SESSION_KEYRING:
590 		if (!ctx.cred->session_keyring) {
591 			/* always install a session keyring upon access if one
592 			 * doesn't exist yet */
593 			ret = install_user_keyrings();
594 			if (ret < 0)
595 				goto error;
596 			if (lflags & KEY_LOOKUP_CREATE)
597 				ret = join_session_keyring(NULL);
598 			else
599 				ret = install_session_keyring(
600 					ctx.cred->user->session_keyring);
601 
602 			if (ret < 0)
603 				goto error;
604 			goto reget_creds;
605 		} else if (ctx.cred->session_keyring ==
606 			   ctx.cred->user->session_keyring &&
607 			   lflags & KEY_LOOKUP_CREATE) {
608 			ret = join_session_keyring(NULL);
609 			if (ret < 0)
610 				goto error;
611 			goto reget_creds;
612 		}
613 
614 		rcu_read_lock();
615 		key = rcu_dereference(ctx.cred->session_keyring);
616 		__key_get(key);
617 		rcu_read_unlock();
618 		key_ref = make_key_ref(key, 1);
619 		break;
620 
621 	case KEY_SPEC_USER_KEYRING:
622 		if (!ctx.cred->user->uid_keyring) {
623 			ret = install_user_keyrings();
624 			if (ret < 0)
625 				goto error;
626 		}
627 
628 		key = ctx.cred->user->uid_keyring;
629 		__key_get(key);
630 		key_ref = make_key_ref(key, 1);
631 		break;
632 
633 	case KEY_SPEC_USER_SESSION_KEYRING:
634 		if (!ctx.cred->user->session_keyring) {
635 			ret = install_user_keyrings();
636 			if (ret < 0)
637 				goto error;
638 		}
639 
640 		key = ctx.cred->user->session_keyring;
641 		__key_get(key);
642 		key_ref = make_key_ref(key, 1);
643 		break;
644 
645 	case KEY_SPEC_GROUP_KEYRING:
646 		/* group keyrings are not yet supported */
647 		key_ref = ERR_PTR(-EINVAL);
648 		goto error;
649 
650 	case KEY_SPEC_REQKEY_AUTH_KEY:
651 		key = ctx.cred->request_key_auth;
652 		if (!key)
653 			goto error;
654 
655 		__key_get(key);
656 		key_ref = make_key_ref(key, 1);
657 		break;
658 
659 	case KEY_SPEC_REQUESTOR_KEYRING:
660 		if (!ctx.cred->request_key_auth)
661 			goto error;
662 
663 		down_read(&ctx.cred->request_key_auth->sem);
664 		if (test_bit(KEY_FLAG_REVOKED,
665 			     &ctx.cred->request_key_auth->flags)) {
666 			key_ref = ERR_PTR(-EKEYREVOKED);
667 			key = NULL;
668 		} else {
669 			rka = ctx.cred->request_key_auth->payload.data[0];
670 			key = rka->dest_keyring;
671 			__key_get(key);
672 		}
673 		up_read(&ctx.cred->request_key_auth->sem);
674 		if (!key)
675 			goto error;
676 		key_ref = make_key_ref(key, 1);
677 		break;
678 
679 	default:
680 		key_ref = ERR_PTR(-EINVAL);
681 		if (id < 1)
682 			goto error;
683 
684 		key = key_lookup(id);
685 		if (IS_ERR(key)) {
686 			key_ref = ERR_CAST(key);
687 			goto error;
688 		}
689 
690 		key_ref = make_key_ref(key, 0);
691 
692 		/* check to see if we possess the key */
693 		ctx.index_key.type		= key->type;
694 		ctx.index_key.description	= key->description;
695 		ctx.index_key.desc_len		= strlen(key->description);
696 		ctx.match_data.raw_data		= key;
697 		kdebug("check possessed");
698 		skey_ref = search_process_keyrings(&ctx);
699 		kdebug("possessed=%p", skey_ref);
700 
701 		if (!IS_ERR(skey_ref)) {
702 			key_put(key);
703 			key_ref = skey_ref;
704 		}
705 
706 		break;
707 	}
708 
709 	/* unlink does not use the nominated key in any way, so can skip all
710 	 * the permission checks as it is only concerned with the keyring */
711 	if (lflags & KEY_LOOKUP_FOR_UNLINK) {
712 		ret = 0;
713 		goto error;
714 	}
715 
716 	if (!(lflags & KEY_LOOKUP_PARTIAL)) {
717 		ret = wait_for_key_construction(key, true);
718 		switch (ret) {
719 		case -ERESTARTSYS:
720 			goto invalid_key;
721 		default:
722 			if (perm)
723 				goto invalid_key;
724 		case 0:
725 			break;
726 		}
727 	} else if (perm) {
728 		ret = key_validate(key);
729 		if (ret < 0)
730 			goto invalid_key;
731 	}
732 
733 	ret = -EIO;
734 	if (!(lflags & KEY_LOOKUP_PARTIAL) &&
735 	    key_read_state(key) == KEY_IS_UNINSTANTIATED)
736 		goto invalid_key;
737 
738 	/* check the permissions */
739 	ret = key_task_permission(key_ref, ctx.cred, perm);
740 	if (ret < 0)
741 		goto invalid_key;
742 
743 	key->last_used_at = ktime_get_real_seconds();
744 
745 error:
746 	put_cred(ctx.cred);
747 	return key_ref;
748 
749 invalid_key:
750 	key_ref_put(key_ref);
751 	key_ref = ERR_PTR(ret);
752 	goto error;
753 
754 	/* if we attempted to install a keyring, then it may have caused new
755 	 * creds to be installed */
756 reget_creds:
757 	put_cred(ctx.cred);
758 	goto try_again;
759 }
760 EXPORT_SYMBOL(lookup_user_key);
761 
762 /*
763  * Join the named keyring as the session keyring if possible else attempt to
764  * create a new one of that name and join that.
765  *
766  * If the name is NULL, an empty anonymous keyring will be installed as the
767  * session keyring.
768  *
769  * Named session keyrings are joined with a semaphore held to prevent the
770  * keyrings from going away whilst the attempt is made to going them and also
771  * to prevent a race in creating compatible session keyrings.
772  */
773 long join_session_keyring(const char *name)
774 {
775 	const struct cred *old;
776 	struct cred *new;
777 	struct key *keyring;
778 	long ret, serial;
779 
780 	new = prepare_creds();
781 	if (!new)
782 		return -ENOMEM;
783 	old = current_cred();
784 
785 	/* if no name is provided, install an anonymous keyring */
786 	if (!name) {
787 		ret = install_session_keyring_to_cred(new, NULL);
788 		if (ret < 0)
789 			goto error;
790 
791 		serial = new->session_keyring->serial;
792 		ret = commit_creds(new);
793 		if (ret == 0)
794 			ret = serial;
795 		goto okay;
796 	}
797 
798 	/* allow the user to join or create a named keyring */
799 	mutex_lock(&key_session_mutex);
800 
801 	/* look for an existing keyring of this name */
802 	keyring = find_keyring_by_name(name, false);
803 	if (PTR_ERR(keyring) == -ENOKEY) {
804 		/* not found - try and create a new one */
805 		keyring = keyring_alloc(
806 			name, old->uid, old->gid, old,
807 			KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ | KEY_USR_LINK,
808 			KEY_ALLOC_IN_QUOTA, NULL, NULL);
809 		if (IS_ERR(keyring)) {
810 			ret = PTR_ERR(keyring);
811 			goto error2;
812 		}
813 	} else if (IS_ERR(keyring)) {
814 		ret = PTR_ERR(keyring);
815 		goto error2;
816 	} else if (keyring == new->session_keyring) {
817 		ret = 0;
818 		goto error3;
819 	}
820 
821 	/* we've got a keyring - now to install it */
822 	ret = install_session_keyring_to_cred(new, keyring);
823 	if (ret < 0)
824 		goto error3;
825 
826 	commit_creds(new);
827 	mutex_unlock(&key_session_mutex);
828 
829 	ret = keyring->serial;
830 	key_put(keyring);
831 okay:
832 	return ret;
833 
834 error3:
835 	key_put(keyring);
836 error2:
837 	mutex_unlock(&key_session_mutex);
838 error:
839 	abort_creds(new);
840 	return ret;
841 }
842 
843 /*
844  * Replace a process's session keyring on behalf of one of its children when
845  * the target  process is about to resume userspace execution.
846  */
847 void key_change_session_keyring(struct callback_head *twork)
848 {
849 	const struct cred *old = current_cred();
850 	struct cred *new = container_of(twork, struct cred, rcu);
851 
852 	if (unlikely(current->flags & PF_EXITING)) {
853 		put_cred(new);
854 		return;
855 	}
856 
857 	new->  uid	= old->  uid;
858 	new-> euid	= old-> euid;
859 	new-> suid	= old-> suid;
860 	new->fsuid	= old->fsuid;
861 	new->  gid	= old->  gid;
862 	new-> egid	= old-> egid;
863 	new-> sgid	= old-> sgid;
864 	new->fsgid	= old->fsgid;
865 	new->user	= get_uid(old->user);
866 	new->user_ns	= get_user_ns(old->user_ns);
867 	new->group_info	= get_group_info(old->group_info);
868 
869 	new->securebits	= old->securebits;
870 	new->cap_inheritable	= old->cap_inheritable;
871 	new->cap_permitted	= old->cap_permitted;
872 	new->cap_effective	= old->cap_effective;
873 	new->cap_ambient	= old->cap_ambient;
874 	new->cap_bset		= old->cap_bset;
875 
876 	new->jit_keyring	= old->jit_keyring;
877 	new->thread_keyring	= key_get(old->thread_keyring);
878 	new->process_keyring	= key_get(old->process_keyring);
879 
880 	security_transfer_creds(new, old);
881 
882 	commit_creds(new);
883 }
884 
885 /*
886  * Make sure that root's user and user-session keyrings exist.
887  */
888 static int __init init_root_keyring(void)
889 {
890 	return install_user_keyrings();
891 }
892 
893 late_initcall(init_root_keyring);
894