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TOMOYO Linux Cross Reference
Linux/kernel/cred.c

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  1 /* Task credentials management - see Documentation/credentials.txt
  2  *
  3  * Copyright (C) 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 Licence
  8  * as published by the Free Software Foundation; either version
  9  * 2 of the Licence, or (at your option) any later version.
 10  */
 11 #include <linux/module.h>
 12 #include <linux/cred.h>
 13 #include <linux/sched.h>
 14 #include <linux/key.h>
 15 #include <linux/keyctl.h>
 16 #include <linux/init_task.h>
 17 #include <linux/security.h>
 18 #include <linux/cn_proc.h>
 19 
 20 #if 0
 21 #define kdebug(FMT, ...) \
 22         printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
 23 #else
 24 static inline __attribute__((format(printf, 1, 2)))
 25 void no_printk(const char *fmt, ...)
 26 {
 27 }
 28 #define kdebug(FMT, ...) \
 29         no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
 30 #endif
 31 
 32 static struct kmem_cache *cred_jar;
 33 
 34 /*
 35  * The common credentials for the initial task's thread group
 36  */
 37 #ifdef CONFIG_KEYS
 38 static struct thread_group_cred init_tgcred = {
 39         .usage  = ATOMIC_INIT(2),
 40         .tgid   = 0,
 41         .lock   = SPIN_LOCK_UNLOCKED,
 42 };
 43 #endif
 44 
 45 /*
 46  * The initial credentials for the initial task
 47  */
 48 struct cred init_cred = {
 49         .usage                  = ATOMIC_INIT(4),
 50 #ifdef CONFIG_DEBUG_CREDENTIALS
 51         .subscribers            = ATOMIC_INIT(2),
 52         .magic                  = CRED_MAGIC,
 53 #endif
 54         .securebits             = SECUREBITS_DEFAULT,
 55         .cap_inheritable        = CAP_INIT_INH_SET,
 56         .cap_permitted          = CAP_FULL_SET,
 57         .cap_effective          = CAP_INIT_EFF_SET,
 58         .cap_bset               = CAP_INIT_BSET,
 59         .user                   = INIT_USER,
 60         .group_info             = &init_groups,
 61 #ifdef CONFIG_KEYS
 62         .tgcred                 = &init_tgcred,
 63 #endif
 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  * Dispose of the shared task group credentials
 93  */
 94 #ifdef CONFIG_KEYS
 95 static void release_tgcred_rcu(struct rcu_head *rcu)
 96 {
 97         struct thread_group_cred *tgcred =
 98                 container_of(rcu, struct thread_group_cred, rcu);
 99 
100         BUG_ON(atomic_read(&tgcred->usage) != 0);
101 
102         key_put(tgcred->session_keyring);
103         key_put(tgcred->process_keyring);
104         kfree(tgcred);
105 }
106 #endif
107 
108 /*
109  * Release a set of thread group credentials.
110  */
111 static void release_tgcred(struct cred *cred)
112 {
113 #ifdef CONFIG_KEYS
114         struct thread_group_cred *tgcred = cred->tgcred;
115 
116         if (atomic_dec_and_test(&tgcred->usage))
117                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
118 #endif
119 }
120 
121 /*
122  * The RCU callback to actually dispose of a set of credentials
123  */
124 static void put_cred_rcu(struct rcu_head *rcu)
125 {
126         struct cred *cred = container_of(rcu, struct cred, rcu);
127 
128         kdebug("put_cred_rcu(%p)", cred);
129 
130 #ifdef CONFIG_DEBUG_CREDENTIALS
131         if (cred->magic != CRED_MAGIC_DEAD ||
132             atomic_read(&cred->usage) != 0 ||
133             read_cred_subscribers(cred) != 0)
134                 panic("CRED: put_cred_rcu() sees %p with"
135                       " mag %x, put %p, usage %d, subscr %d\n",
136                       cred, cred->magic, cred->put_addr,
137                       atomic_read(&cred->usage),
138                       read_cred_subscribers(cred));
139 #else
140         if (atomic_read(&cred->usage) != 0)
141                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
142                       cred, atomic_read(&cred->usage));
143 #endif
144 
145         security_cred_free(cred);
146         key_put(cred->thread_keyring);
147         key_put(cred->request_key_auth);
148         release_tgcred(cred);
149         if (cred->group_info)
150                 put_group_info(cred->group_info);
151         free_uid(cred->user);
152         kmem_cache_free(cred_jar, cred);
153 }
154 
155 /**
156  * __put_cred - Destroy a set of credentials
157  * @cred: The record to release
158  *
159  * Destroy a set of credentials on which no references remain.
160  */
161 void __put_cred(struct cred *cred)
162 {
163         kdebug("__put_cred(%p{%d,%d})", cred,
164                atomic_read(&cred->usage),
165                read_cred_subscribers(cred));
166 
167         BUG_ON(atomic_read(&cred->usage) != 0);
168 #ifdef CONFIG_DEBUG_CREDENTIALS
169         BUG_ON(read_cred_subscribers(cred) != 0);
170         cred->magic = CRED_MAGIC_DEAD;
171         cred->put_addr = __builtin_return_address(0);
172 #endif
173         BUG_ON(cred == current->cred);
174         BUG_ON(cred == current->real_cred);
175 
176         call_rcu(&cred->rcu, put_cred_rcu);
177 }
178 EXPORT_SYMBOL(__put_cred);
179 
180 /*
181  * Clean up a task's credentials when it exits
182  */
183 void exit_creds(struct task_struct *tsk)
184 {
185         struct cred *cred;
186 
187         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
188                atomic_read(&tsk->cred->usage),
189                read_cred_subscribers(tsk->cred));
190 
191         cred = (struct cred *) tsk->real_cred;
192         tsk->real_cred = NULL;
193         validate_creds(cred);
194         alter_cred_subscribers(cred, -1);
195         put_cred(cred);
196 
197         cred = (struct cred *) tsk->cred;
198         tsk->cred = NULL;
199         validate_creds(cred);
200         alter_cred_subscribers(cred, -1);
201         put_cred(cred);
202 
203         cred = (struct cred *) tsk->replacement_session_keyring;
204         if (cred) {
205                 tsk->replacement_session_keyring = NULL;
206                 validate_creds(cred);
207                 put_cred(cred);
208         }
209 }
210 
211 /**
212  * get_task_cred - Get another task's objective credentials
213  * @task: The task to query
214  *
215  * Get the objective credentials of a task, pinning them so that they can't go
216  * away.  Accessing a task's credentials directly is not permitted.
217  *
218  * The caller must also make sure task doesn't get deleted, either by holding a
219  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
220  */
221 const struct cred *get_task_cred(struct task_struct *task)
222 {
223         const struct cred *cred;
224 
225         rcu_read_lock();
226 
227         do {
228                 cred = __task_cred((task));
229                 BUG_ON(!cred);
230         } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
231 
232         rcu_read_unlock();
233         return cred;
234 }
235 
236 /*
237  * Allocate blank credentials, such that the credentials can be filled in at a
238  * later date without risk of ENOMEM.
239  */
240 struct cred *cred_alloc_blank(void)
241 {
242         struct cred *new;
243 
244         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
245         if (!new)
246                 return NULL;
247 
248 #ifdef CONFIG_KEYS
249         new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
250         if (!new->tgcred) {
251                 kmem_cache_free(cred_jar, new);
252                 return NULL;
253         }
254         atomic_set(&new->tgcred->usage, 1);
255 #endif
256 
257         atomic_set(&new->usage, 1);
258 #ifdef CONFIG_DEBUG_CREDENTIALS
259         new->magic = CRED_MAGIC;
260 #endif
261 
262         if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
263                 goto error;
264 
265         return new;
266 
267 error:
268         abort_creds(new);
269         return NULL;
270 }
271 
272 /**
273  * prepare_creds - Prepare a new set of credentials for modification
274  *
275  * Prepare a new set of task credentials for modification.  A task's creds
276  * shouldn't generally be modified directly, therefore this function is used to
277  * prepare a new copy, which the caller then modifies and then commits by
278  * calling commit_creds().
279  *
280  * Preparation involves making a copy of the objective creds for modification.
281  *
282  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
283  *
284  * Call commit_creds() or abort_creds() to clean up.
285  */
286 struct cred *prepare_creds(void)
287 {
288         struct task_struct *task = current;
289         const struct cred *old;
290         struct cred *new;
291 
292         validate_process_creds();
293 
294         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
295         if (!new)
296                 return NULL;
297 
298         kdebug("prepare_creds() alloc %p", new);
299 
300         old = task->cred;
301         memcpy(new, old, sizeof(struct cred));
302 
303         atomic_set(&new->usage, 1);
304         set_cred_subscribers(new, 0);
305         get_group_info(new->group_info);
306         get_uid(new->user);
307 
308 #ifdef CONFIG_KEYS
309         key_get(new->thread_keyring);
310         key_get(new->request_key_auth);
311         atomic_inc(&new->tgcred->usage);
312 #endif
313 
314 #ifdef CONFIG_SECURITY
315         new->security = NULL;
316 #endif
317 
318         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
319                 goto error;
320         validate_creds(new);
321         return new;
322 
323 error:
324         abort_creds(new);
325         return NULL;
326 }
327 EXPORT_SYMBOL(prepare_creds);
328 
329 /*
330  * Prepare credentials for current to perform an execve()
331  * - The caller must hold current->cred_guard_mutex
332  */
333 struct cred *prepare_exec_creds(void)
334 {
335         struct thread_group_cred *tgcred = NULL;
336         struct cred *new;
337 
338 #ifdef CONFIG_KEYS
339         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
340         if (!tgcred)
341                 return NULL;
342 #endif
343 
344         new = prepare_creds();
345         if (!new) {
346                 kfree(tgcred);
347                 return new;
348         }
349 
350 #ifdef CONFIG_KEYS
351         /* newly exec'd tasks don't get a thread keyring */
352         key_put(new->thread_keyring);
353         new->thread_keyring = NULL;
354 
355         /* create a new per-thread-group creds for all this set of threads to
356          * share */
357         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
358 
359         atomic_set(&tgcred->usage, 1);
360         spin_lock_init(&tgcred->lock);
361 
362         /* inherit the session keyring; new process keyring */
363         key_get(tgcred->session_keyring);
364         tgcred->process_keyring = NULL;
365 
366         release_tgcred(new);
367         new->tgcred = tgcred;
368 #endif
369 
370         return new;
371 }
372 
373 /*
374  * prepare new credentials for the usermode helper dispatcher
375  */
376 struct cred *prepare_usermodehelper_creds(void)
377 {
378 #ifdef CONFIG_KEYS
379         struct thread_group_cred *tgcred = NULL;
380 #endif
381         struct cred *new;
382 
383 #ifdef CONFIG_KEYS
384         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
385         if (!tgcred)
386                 return NULL;
387 #endif
388 
389         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
390         if (!new)
391                 return NULL;
392 
393         kdebug("prepare_usermodehelper_creds() alloc %p", new);
394 
395         memcpy(new, &init_cred, sizeof(struct cred));
396 
397         atomic_set(&new->usage, 1);
398         set_cred_subscribers(new, 0);
399         get_group_info(new->group_info);
400         get_uid(new->user);
401 
402 #ifdef CONFIG_KEYS
403         new->thread_keyring = NULL;
404         new->request_key_auth = NULL;
405         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
406 
407         atomic_set(&tgcred->usage, 1);
408         spin_lock_init(&tgcred->lock);
409         new->tgcred = tgcred;
410 #endif
411 
412 #ifdef CONFIG_SECURITY
413         new->security = NULL;
414 #endif
415         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
416                 goto error;
417         validate_creds(new);
418 
419         BUG_ON(atomic_read(&new->usage) != 1);
420         return new;
421 
422 error:
423         put_cred(new);
424         return NULL;
425 }
426 
427 /*
428  * Copy credentials for the new process created by fork()
429  *
430  * We share if we can, but under some circumstances we have to generate a new
431  * set.
432  *
433  * The new process gets the current process's subjective credentials as its
434  * objective and subjective credentials
435  */
436 int copy_creds(struct task_struct *p, unsigned long clone_flags)
437 {
438 #ifdef CONFIG_KEYS
439         struct thread_group_cred *tgcred;
440 #endif
441         struct cred *new;
442         int ret;
443 
444         mutex_init(&p->cred_guard_mutex);
445 
446         p->replacement_session_keyring = NULL;
447 
448         if (
449 #ifdef CONFIG_KEYS
450                 !p->cred->thread_keyring &&
451 #endif
452                 clone_flags & CLONE_THREAD
453             ) {
454                 p->real_cred = get_cred(p->cred);
455                 get_cred(p->cred);
456                 alter_cred_subscribers(p->cred, 2);
457                 kdebug("share_creds(%p{%d,%d})",
458                        p->cred, atomic_read(&p->cred->usage),
459                        read_cred_subscribers(p->cred));
460                 atomic_inc(&p->cred->user->processes);
461                 return 0;
462         }
463 
464         new = prepare_creds();
465         if (!new)
466                 return -ENOMEM;
467 
468         if (clone_flags & CLONE_NEWUSER) {
469                 ret = create_user_ns(new);
470                 if (ret < 0)
471                         goto error_put;
472         }
473 
474 #ifdef CONFIG_KEYS
475         /* new threads get their own thread keyrings if their parent already
476          * had one */
477         if (new->thread_keyring) {
478                 key_put(new->thread_keyring);
479                 new->thread_keyring = NULL;
480                 if (clone_flags & CLONE_THREAD)
481                         install_thread_keyring_to_cred(new);
482         }
483 
484         /* we share the process and session keyrings between all the threads in
485          * a process - this is slightly icky as we violate COW credentials a
486          * bit */
487         if (!(clone_flags & CLONE_THREAD)) {
488                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
489                 if (!tgcred) {
490                         ret = -ENOMEM;
491                         goto error_put;
492                 }
493                 atomic_set(&tgcred->usage, 1);
494                 spin_lock_init(&tgcred->lock);
495                 tgcred->process_keyring = NULL;
496                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
497 
498                 release_tgcred(new);
499                 new->tgcred = tgcred;
500         }
501 #endif
502 
503         atomic_inc(&new->user->processes);
504         p->cred = p->real_cred = get_cred(new);
505         alter_cred_subscribers(new, 2);
506         validate_creds(new);
507         return 0;
508 
509 error_put:
510         put_cred(new);
511         return ret;
512 }
513 
514 /**
515  * commit_creds - Install new credentials upon the current task
516  * @new: The credentials to be assigned
517  *
518  * Install a new set of credentials to the current task, using RCU to replace
519  * the old set.  Both the objective and the subjective credentials pointers are
520  * updated.  This function may not be called if the subjective credentials are
521  * in an overridden state.
522  *
523  * This function eats the caller's reference to the new credentials.
524  *
525  * Always returns 0 thus allowing this function to be tail-called at the end
526  * of, say, sys_setgid().
527  */
528 int commit_creds(struct cred *new)
529 {
530         struct task_struct *task = current;
531         const struct cred *old = task->real_cred;
532 
533         kdebug("commit_creds(%p{%d,%d})", new,
534                atomic_read(&new->usage),
535                read_cred_subscribers(new));
536 
537         BUG_ON(task->cred != old);
538 #ifdef CONFIG_DEBUG_CREDENTIALS
539         BUG_ON(read_cred_subscribers(old) < 2);
540         validate_creds(old);
541         validate_creds(new);
542 #endif
543         BUG_ON(atomic_read(&new->usage) < 1);
544 
545         security_commit_creds(new, old);
546 
547         get_cred(new); /* we will require a ref for the subj creds too */
548 
549         /* dumpability changes */
550         if (old->euid != new->euid ||
551             old->egid != new->egid ||
552             old->fsuid != new->fsuid ||
553             old->fsgid != new->fsgid ||
554             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
555                 if (task->mm)
556                         set_dumpable(task->mm, suid_dumpable);
557                 task->pdeath_signal = 0;
558                 smp_wmb();
559         }
560 
561         /* alter the thread keyring */
562         if (new->fsuid != old->fsuid)
563                 key_fsuid_changed(task);
564         if (new->fsgid != old->fsgid)
565                 key_fsgid_changed(task);
566 
567         /* do it
568          * - What if a process setreuid()'s and this brings the
569          *   new uid over his NPROC rlimit?  We can check this now
570          *   cheaply with the new uid cache, so if it matters
571          *   we should be checking for it.  -DaveM
572          */
573         alter_cred_subscribers(new, 2);
574         if (new->user != old->user)
575                 atomic_inc(&new->user->processes);
576         rcu_assign_pointer(task->real_cred, new);
577         rcu_assign_pointer(task->cred, new);
578         if (new->user != old->user)
579                 atomic_dec(&old->user->processes);
580         alter_cred_subscribers(old, -2);
581 
582         /* send notifications */
583         if (new->uid   != old->uid  ||
584             new->euid  != old->euid ||
585             new->suid  != old->suid ||
586             new->fsuid != old->fsuid)
587                 proc_id_connector(task, PROC_EVENT_UID);
588 
589         if (new->gid   != old->gid  ||
590             new->egid  != old->egid ||
591             new->sgid  != old->sgid ||
592             new->fsgid != old->fsgid)
593                 proc_id_connector(task, PROC_EVENT_GID);
594 
595         /* release the old obj and subj refs both */
596         put_cred(old);
597         put_cred(old);
598         return 0;
599 }
600 EXPORT_SYMBOL(commit_creds);
601 
602 /**
603  * abort_creds - Discard a set of credentials and unlock the current task
604  * @new: The credentials that were going to be applied
605  *
606  * Discard a set of credentials that were under construction and unlock the
607  * current task.
608  */
609 void abort_creds(struct cred *new)
610 {
611         kdebug("abort_creds(%p{%d,%d})", new,
612                atomic_read(&new->usage),
613                read_cred_subscribers(new));
614 
615 #ifdef CONFIG_DEBUG_CREDENTIALS
616         BUG_ON(read_cred_subscribers(new) != 0);
617 #endif
618         BUG_ON(atomic_read(&new->usage) < 1);
619         put_cred(new);
620 }
621 EXPORT_SYMBOL(abort_creds);
622 
623 /**
624  * override_creds - Override the current process's subjective credentials
625  * @new: The credentials to be assigned
626  *
627  * Install a set of temporary override subjective credentials on the current
628  * process, returning the old set for later reversion.
629  */
630 const struct cred *override_creds(const struct cred *new)
631 {
632         const struct cred *old = current->cred;
633 
634         kdebug("override_creds(%p{%d,%d})", new,
635                atomic_read(&new->usage),
636                read_cred_subscribers(new));
637 
638         validate_creds(old);
639         validate_creds(new);
640         get_cred(new);
641         alter_cred_subscribers(new, 1);
642         rcu_assign_pointer(current->cred, new);
643         alter_cred_subscribers(old, -1);
644 
645         kdebug("override_creds() = %p{%d,%d}", old,
646                atomic_read(&old->usage),
647                read_cred_subscribers(old));
648         return old;
649 }
650 EXPORT_SYMBOL(override_creds);
651 
652 /**
653  * revert_creds - Revert a temporary subjective credentials override
654  * @old: The credentials to be restored
655  *
656  * Revert a temporary set of override subjective credentials to an old set,
657  * discarding the override set.
658  */
659 void revert_creds(const struct cred *old)
660 {
661         const struct cred *override = current->cred;
662 
663         kdebug("revert_creds(%p{%d,%d})", old,
664                atomic_read(&old->usage),
665                read_cred_subscribers(old));
666 
667         validate_creds(old);
668         validate_creds(override);
669         alter_cred_subscribers(old, 1);
670         rcu_assign_pointer(current->cred, old);
671         alter_cred_subscribers(override, -1);
672         put_cred(override);
673 }
674 EXPORT_SYMBOL(revert_creds);
675 
676 /*
677  * initialise the credentials stuff
678  */
679 void __init cred_init(void)
680 {
681         /* allocate a slab in which we can store credentials */
682         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
683                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
684 }
685 
686 /**
687  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
688  * @daemon: A userspace daemon to be used as a reference
689  *
690  * Prepare a set of credentials for a kernel service.  This can then be used to
691  * override a task's own credentials so that work can be done on behalf of that
692  * task that requires a different subjective context.
693  *
694  * @daemon is used to provide a base for the security record, but can be NULL.
695  * If @daemon is supplied, then the security data will be derived from that;
696  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
697  *
698  * The caller may change these controls afterwards if desired.
699  *
700  * Returns the new credentials or NULL if out of memory.
701  *
702  * Does not take, and does not return holding current->cred_replace_mutex.
703  */
704 struct cred *prepare_kernel_cred(struct task_struct *daemon)
705 {
706         const struct cred *old;
707         struct cred *new;
708 
709         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
710         if (!new)
711                 return NULL;
712 
713         kdebug("prepare_kernel_cred() alloc %p", new);
714 
715         if (daemon)
716                 old = get_task_cred(daemon);
717         else
718                 old = get_cred(&init_cred);
719 
720         validate_creds(old);
721 
722         *new = *old;
723         atomic_set(&new->usage, 1);
724         set_cred_subscribers(new, 0);
725         get_uid(new->user);
726         get_group_info(new->group_info);
727 
728 #ifdef CONFIG_KEYS
729         atomic_inc(&init_tgcred.usage);
730         new->tgcred = &init_tgcred;
731         new->request_key_auth = NULL;
732         new->thread_keyring = NULL;
733         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
734 #endif
735 
736 #ifdef CONFIG_SECURITY
737         new->security = NULL;
738 #endif
739         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
740                 goto error;
741 
742         put_cred(old);
743         validate_creds(new);
744         return new;
745 
746 error:
747         put_cred(new);
748         put_cred(old);
749         return NULL;
750 }
751 EXPORT_SYMBOL(prepare_kernel_cred);
752 
753 /**
754  * set_security_override - Set the security ID in a set of credentials
755  * @new: The credentials to alter
756  * @secid: The LSM security ID to set
757  *
758  * Set the LSM security ID in a set of credentials so that the subjective
759  * security is overridden when an alternative set of credentials is used.
760  */
761 int set_security_override(struct cred *new, u32 secid)
762 {
763         return security_kernel_act_as(new, secid);
764 }
765 EXPORT_SYMBOL(set_security_override);
766 
767 /**
768  * set_security_override_from_ctx - Set the security ID in a set of credentials
769  * @new: The credentials to alter
770  * @secctx: The LSM security context to generate the security ID from.
771  *
772  * Set the LSM security ID in a set of credentials so that the subjective
773  * security is overridden when an alternative set of credentials is used.  The
774  * security ID is specified in string form as a security context to be
775  * interpreted by the LSM.
776  */
777 int set_security_override_from_ctx(struct cred *new, const char *secctx)
778 {
779         u32 secid;
780         int ret;
781 
782         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
783         if (ret < 0)
784                 return ret;
785 
786         return set_security_override(new, secid);
787 }
788 EXPORT_SYMBOL(set_security_override_from_ctx);
789 
790 /**
791  * set_create_files_as - Set the LSM file create context in a set of credentials
792  * @new: The credentials to alter
793  * @inode: The inode to take the context from
794  *
795  * Change the LSM file creation context in a set of credentials to be the same
796  * as the object context of the specified inode, so that the new inodes have
797  * the same MAC context as that inode.
798  */
799 int set_create_files_as(struct cred *new, struct inode *inode)
800 {
801         new->fsuid = inode->i_uid;
802         new->fsgid = inode->i_gid;
803         return security_kernel_create_files_as(new, inode);
804 }
805 EXPORT_SYMBOL(set_create_files_as);
806 
807 #ifdef CONFIG_DEBUG_CREDENTIALS
808 
809 bool creds_are_invalid(const struct cred *cred)
810 {
811         if (cred->magic != CRED_MAGIC)
812                 return true;
813 #ifdef CONFIG_SECURITY_SELINUX
814         /*
815          * cred->security == NULL if security_cred_alloc_blank() or
816          * security_prepare_creds() returned an error.
817          */
818         if (selinux_is_enabled() && cred->security) {
819                 if ((unsigned long) cred->security < PAGE_SIZE)
820                         return true;
821                 if ((*(u32 *)cred->security & 0xffffff00) ==
822                     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
823                         return true;
824         }
825 #endif
826         return false;
827 }
828 EXPORT_SYMBOL(creds_are_invalid);
829 
830 /*
831  * dump invalid credentials
832  */
833 static void dump_invalid_creds(const struct cred *cred, const char *label,
834                                const struct task_struct *tsk)
835 {
836         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
837                label, cred,
838                cred == &init_cred ? "[init]" : "",
839                cred == tsk->real_cred ? "[real]" : "",
840                cred == tsk->cred ? "[eff]" : "");
841         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
842                cred->magic, cred->put_addr);
843         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
844                atomic_read(&cred->usage),
845                read_cred_subscribers(cred));
846         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
847                cred->uid, cred->euid, cred->suid, cred->fsuid);
848         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
849                cred->gid, cred->egid, cred->sgid, cred->fsgid);
850 #ifdef CONFIG_SECURITY
851         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
852         if ((unsigned long) cred->security >= PAGE_SIZE &&
853             (((unsigned long) cred->security & 0xffffff00) !=
854              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
855                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
856                        ((u32*)cred->security)[0],
857                        ((u32*)cred->security)[1]);
858 #endif
859 }
860 
861 /*
862  * report use of invalid credentials
863  */
864 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
865 {
866         printk(KERN_ERR "CRED: Invalid credentials\n");
867         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
868         dump_invalid_creds(cred, "Specified", current);
869         BUG();
870 }
871 EXPORT_SYMBOL(__invalid_creds);
872 
873 /*
874  * check the credentials on a process
875  */
876 void __validate_process_creds(struct task_struct *tsk,
877                               const char *file, unsigned line)
878 {
879         if (tsk->cred == tsk->real_cred) {
880                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
881                              creds_are_invalid(tsk->cred)))
882                         goto invalid_creds;
883         } else {
884                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
885                              read_cred_subscribers(tsk->cred) < 1 ||
886                              creds_are_invalid(tsk->real_cred) ||
887                              creds_are_invalid(tsk->cred)))
888                         goto invalid_creds;
889         }
890         return;
891 
892 invalid_creds:
893         printk(KERN_ERR "CRED: Invalid process credentials\n");
894         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
895 
896         dump_invalid_creds(tsk->real_cred, "Real", tsk);
897         if (tsk->cred != tsk->real_cred)
898                 dump_invalid_creds(tsk->cred, "Effective", tsk);
899         else
900                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
901         BUG();
902 }
903 EXPORT_SYMBOL(__validate_process_creds);
904 
905 /*
906  * check creds for do_exit()
907  */
908 void validate_creds_for_do_exit(struct task_struct *tsk)
909 {
910         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
911                tsk->real_cred, tsk->cred,
912                atomic_read(&tsk->cred->usage),
913                read_cred_subscribers(tsk->cred));
914 
915         __validate_process_creds(tsk, __FILE__, __LINE__);
916 }
917 
918 #endif /* CONFIG_DEBUG_CREDENTIALS */
919 

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