1 /* Task credentials management - see Documentation/security/credentials.txt
3 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
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.
11 #include <linux/export.h>
12 #include <linux/cred.h>
13 #include <linux/slab.h>
14 #include <linux/sched.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>
23 #define kdebug(FMT, ...) \
24 printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
26 #define kdebug(FMT, ...) \
27 no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
30 static struct kmem_cache *cred_jar;
33 * The common credentials for the initial task's thread group
36 static struct thread_group_cred init_tgcred = {
37 .usage = ATOMIC_INIT(2),
39 .lock = __SPIN_LOCK_UNLOCKED(init_cred.tgcred.lock),
44 * The initial credentials for the initial task
46 struct cred init_cred = {
47 .usage = ATOMIC_INIT(4),
48 #ifdef CONFIG_DEBUG_CREDENTIALS
49 .subscribers = ATOMIC_INIT(2),
52 .uid = GLOBAL_ROOT_UID,
53 .gid = GLOBAL_ROOT_GID,
54 .suid = GLOBAL_ROOT_UID,
55 .sgid = GLOBAL_ROOT_GID,
56 .euid = GLOBAL_ROOT_UID,
57 .egid = GLOBAL_ROOT_GID,
58 .fsuid = GLOBAL_ROOT_UID,
59 .fsgid = GLOBAL_ROOT_GID,
60 .securebits = SECUREBITS_DEFAULT,
61 .cap_inheritable = CAP_EMPTY_SET,
62 .cap_permitted = CAP_FULL_SET,
63 .cap_effective = CAP_FULL_SET,
64 .cap_bset = CAP_FULL_SET,
66 .user_ns = &init_user_ns,
67 .group_info = &init_groups,
69 .tgcred = &init_tgcred,
73 static inline void set_cred_subscribers(struct cred *cred, int n)
75 #ifdef CONFIG_DEBUG_CREDENTIALS
76 atomic_set(&cred->subscribers, n);
80 static inline int read_cred_subscribers(const struct cred *cred)
82 #ifdef CONFIG_DEBUG_CREDENTIALS
83 return atomic_read(&cred->subscribers);
89 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
91 #ifdef CONFIG_DEBUG_CREDENTIALS
92 struct cred *cred = (struct cred *) _cred;
94 atomic_add(n, &cred->subscribers);
99 * Dispose of the shared task group credentials
102 static void release_tgcred_rcu(struct rcu_head *rcu)
104 struct thread_group_cred *tgcred =
105 container_of(rcu, struct thread_group_cred, rcu);
107 BUG_ON(atomic_read(&tgcred->usage) != 0);
109 key_put(tgcred->session_keyring);
110 key_put(tgcred->process_keyring);
116 * Release a set of thread group credentials.
118 static void release_tgcred(struct cred *cred)
121 struct thread_group_cred *tgcred = cred->tgcred;
123 if (atomic_dec_and_test(&tgcred->usage))
124 call_rcu(&tgcred->rcu, release_tgcred_rcu);
129 * The RCU callback to actually dispose of a set of credentials
131 static void put_cred_rcu(struct rcu_head *rcu)
133 struct cred *cred = container_of(rcu, struct cred, rcu);
135 kdebug("put_cred_rcu(%p)", cred);
137 #ifdef CONFIG_DEBUG_CREDENTIALS
138 if (cred->magic != CRED_MAGIC_DEAD ||
139 atomic_read(&cred->usage) != 0 ||
140 read_cred_subscribers(cred) != 0)
141 panic("CRED: put_cred_rcu() sees %p with"
142 " mag %x, put %p, usage %d, subscr %d\n",
143 cred, cred->magic, cred->put_addr,
144 atomic_read(&cred->usage),
145 read_cred_subscribers(cred));
147 if (atomic_read(&cred->usage) != 0)
148 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
149 cred, atomic_read(&cred->usage));
152 security_cred_free(cred);
153 key_put(cred->thread_keyring);
154 key_put(cred->request_key_auth);
155 release_tgcred(cred);
156 if (cred->group_info)
157 put_group_info(cred->group_info);
158 free_uid(cred->user);
159 put_user_ns(cred->user_ns);
160 kmem_cache_free(cred_jar, cred);
164 * __put_cred - Destroy a set of credentials
165 * @cred: The record to release
167 * Destroy a set of credentials on which no references remain.
169 void __put_cred(struct cred *cred)
171 kdebug("__put_cred(%p{%d,%d})", cred,
172 atomic_read(&cred->usage),
173 read_cred_subscribers(cred));
175 BUG_ON(atomic_read(&cred->usage) != 0);
176 #ifdef CONFIG_DEBUG_CREDENTIALS
177 BUG_ON(read_cred_subscribers(cred) != 0);
178 cred->magic = CRED_MAGIC_DEAD;
179 cred->put_addr = __builtin_return_address(0);
181 BUG_ON(cred == current->cred);
182 BUG_ON(cred == current->real_cred);
184 call_rcu(&cred->rcu, put_cred_rcu);
186 EXPORT_SYMBOL(__put_cred);
189 * Clean up a task's credentials when it exits
191 void exit_creds(struct task_struct *tsk)
195 kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
196 atomic_read(&tsk->cred->usage),
197 read_cred_subscribers(tsk->cred));
199 cred = (struct cred *) tsk->real_cred;
200 tsk->real_cred = NULL;
201 validate_creds(cred);
202 alter_cred_subscribers(cred, -1);
205 cred = (struct cred *) tsk->cred;
207 validate_creds(cred);
208 alter_cred_subscribers(cred, -1);
211 cred = (struct cred *) tsk->replacement_session_keyring;
213 tsk->replacement_session_keyring = NULL;
214 validate_creds(cred);
220 * get_task_cred - Get another task's objective credentials
221 * @task: The task to query
223 * Get the objective credentials of a task, pinning them so that they can't go
224 * away. Accessing a task's credentials directly is not permitted.
226 * The caller must also make sure task doesn't get deleted, either by holding a
227 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
229 const struct cred *get_task_cred(struct task_struct *task)
231 const struct cred *cred;
236 cred = __task_cred((task));
238 } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
245 * Allocate blank credentials, such that the credentials can be filled in at a
246 * later date without risk of ENOMEM.
248 struct cred *cred_alloc_blank(void)
252 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
257 new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
259 kmem_cache_free(cred_jar, new);
262 atomic_set(&new->tgcred->usage, 1);
265 atomic_set(&new->usage, 1);
266 #ifdef CONFIG_DEBUG_CREDENTIALS
267 new->magic = CRED_MAGIC;
270 if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
281 * prepare_creds - Prepare a new set of credentials for modification
283 * Prepare a new set of task credentials for modification. A task's creds
284 * shouldn't generally be modified directly, therefore this function is used to
285 * prepare a new copy, which the caller then modifies and then commits by
286 * calling commit_creds().
288 * Preparation involves making a copy of the objective creds for modification.
290 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
292 * Call commit_creds() or abort_creds() to clean up.
294 struct cred *prepare_creds(void)
296 struct task_struct *task = current;
297 const struct cred *old;
300 validate_process_creds();
302 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
306 kdebug("prepare_creds() alloc %p", new);
309 memcpy(new, old, sizeof(struct cred));
311 atomic_set(&new->usage, 1);
312 set_cred_subscribers(new, 0);
313 get_group_info(new->group_info);
315 get_user_ns(new->user_ns);
318 key_get(new->thread_keyring);
319 key_get(new->request_key_auth);
320 atomic_inc(&new->tgcred->usage);
323 #ifdef CONFIG_SECURITY
324 new->security = NULL;
327 if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
336 EXPORT_SYMBOL(prepare_creds);
339 * Prepare credentials for current to perform an execve()
340 * - The caller must hold ->cred_guard_mutex
342 struct cred *prepare_exec_creds(void)
344 struct thread_group_cred *tgcred = NULL;
348 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
353 new = prepare_creds();
360 /* newly exec'd tasks don't get a thread keyring */
361 key_put(new->thread_keyring);
362 new->thread_keyring = NULL;
364 /* create a new per-thread-group creds for all this set of threads to
366 memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
368 atomic_set(&tgcred->usage, 1);
369 spin_lock_init(&tgcred->lock);
371 /* inherit the session keyring; new process keyring */
372 key_get(tgcred->session_keyring);
373 tgcred->process_keyring = NULL;
376 new->tgcred = tgcred;
383 * Copy credentials for the new process created by fork()
385 * We share if we can, but under some circumstances we have to generate a new
388 * The new process gets the current process's subjective credentials as its
389 * objective and subjective credentials
391 int copy_creds(struct task_struct *p, unsigned long clone_flags)
394 struct thread_group_cred *tgcred;
401 !p->cred->thread_keyring &&
403 clone_flags & CLONE_THREAD
405 p->real_cred = get_cred(p->cred);
407 alter_cred_subscribers(p->cred, 2);
408 kdebug("share_creds(%p{%d,%d})",
409 p->cred, atomic_read(&p->cred->usage),
410 read_cred_subscribers(p->cred));
411 atomic_inc(&p->cred->user->processes);
415 new = prepare_creds();
419 if (clone_flags & CLONE_NEWUSER) {
420 ret = create_user_ns(new);
426 /* new threads get their own thread keyrings if their parent already
428 if (new->thread_keyring) {
429 key_put(new->thread_keyring);
430 new->thread_keyring = NULL;
431 if (clone_flags & CLONE_THREAD)
432 install_thread_keyring_to_cred(new);
435 /* we share the process and session keyrings between all the threads in
436 * a process - this is slightly icky as we violate COW credentials a
438 if (!(clone_flags & CLONE_THREAD)) {
439 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
444 atomic_set(&tgcred->usage, 1);
445 spin_lock_init(&tgcred->lock);
446 tgcred->process_keyring = NULL;
447 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
450 new->tgcred = tgcred;
454 atomic_inc(&new->user->processes);
455 p->cred = p->real_cred = get_cred(new);
456 alter_cred_subscribers(new, 2);
466 * commit_creds - Install new credentials upon the current task
467 * @new: The credentials to be assigned
469 * Install a new set of credentials to the current task, using RCU to replace
470 * the old set. Both the objective and the subjective credentials pointers are
471 * updated. This function may not be called if the subjective credentials are
472 * in an overridden state.
474 * This function eats the caller's reference to the new credentials.
476 * Always returns 0 thus allowing this function to be tail-called at the end
477 * of, say, sys_setgid().
479 int commit_creds(struct cred *new)
481 struct task_struct *task = current;
482 const struct cred *old = task->real_cred;
484 kdebug("commit_creds(%p{%d,%d})", new,
485 atomic_read(&new->usage),
486 read_cred_subscribers(new));
488 BUG_ON(task->cred != old);
489 #ifdef CONFIG_DEBUG_CREDENTIALS
490 BUG_ON(read_cred_subscribers(old) < 2);
494 BUG_ON(atomic_read(&new->usage) < 1);
496 get_cred(new); /* we will require a ref for the subj creds too */
498 /* dumpability changes */
499 if (!uid_eq(old->euid, new->euid) ||
500 !gid_eq(old->egid, new->egid) ||
501 !uid_eq(old->fsuid, new->fsuid) ||
502 !gid_eq(old->fsgid, new->fsgid) ||
503 !cap_issubset(new->cap_permitted, old->cap_permitted)) {
505 set_dumpable(task->mm, suid_dumpable);
506 task->pdeath_signal = 0;
510 /* alter the thread keyring */
511 if (!uid_eq(new->fsuid, old->fsuid))
512 key_fsuid_changed(task);
513 if (!gid_eq(new->fsgid, old->fsgid))
514 key_fsgid_changed(task);
517 * RLIMIT_NPROC limits on user->processes have already been checked
520 alter_cred_subscribers(new, 2);
521 if (new->user != old->user)
522 atomic_inc(&new->user->processes);
523 rcu_assign_pointer(task->real_cred, new);
524 rcu_assign_pointer(task->cred, new);
525 if (new->user != old->user)
526 atomic_dec(&old->user->processes);
527 alter_cred_subscribers(old, -2);
529 /* send notifications */
530 if (!uid_eq(new->uid, old->uid) ||
531 !uid_eq(new->euid, old->euid) ||
532 !uid_eq(new->suid, old->suid) ||
533 !uid_eq(new->fsuid, old->fsuid))
534 proc_id_connector(task, PROC_EVENT_UID);
536 if (!gid_eq(new->gid, old->gid) ||
537 !gid_eq(new->egid, old->egid) ||
538 !gid_eq(new->sgid, old->sgid) ||
539 !gid_eq(new->fsgid, old->fsgid))
540 proc_id_connector(task, PROC_EVENT_GID);
542 /* release the old obj and subj refs both */
547 EXPORT_SYMBOL(commit_creds);
550 * abort_creds - Discard a set of credentials and unlock the current task
551 * @new: The credentials that were going to be applied
553 * Discard a set of credentials that were under construction and unlock the
556 void abort_creds(struct cred *new)
558 kdebug("abort_creds(%p{%d,%d})", new,
559 atomic_read(&new->usage),
560 read_cred_subscribers(new));
562 #ifdef CONFIG_DEBUG_CREDENTIALS
563 BUG_ON(read_cred_subscribers(new) != 0);
565 BUG_ON(atomic_read(&new->usage) < 1);
568 EXPORT_SYMBOL(abort_creds);
571 * override_creds - Override the current process's subjective credentials
572 * @new: The credentials to be assigned
574 * Install a set of temporary override subjective credentials on the current
575 * process, returning the old set for later reversion.
577 const struct cred *override_creds(const struct cred *new)
579 const struct cred *old = current->cred;
581 kdebug("override_creds(%p{%d,%d})", new,
582 atomic_read(&new->usage),
583 read_cred_subscribers(new));
588 alter_cred_subscribers(new, 1);
589 rcu_assign_pointer(current->cred, new);
590 alter_cred_subscribers(old, -1);
592 kdebug("override_creds() = %p{%d,%d}", old,
593 atomic_read(&old->usage),
594 read_cred_subscribers(old));
597 EXPORT_SYMBOL(override_creds);
600 * revert_creds - Revert a temporary subjective credentials override
601 * @old: The credentials to be restored
603 * Revert a temporary set of override subjective credentials to an old set,
604 * discarding the override set.
606 void revert_creds(const struct cred *old)
608 const struct cred *override = current->cred;
610 kdebug("revert_creds(%p{%d,%d})", old,
611 atomic_read(&old->usage),
612 read_cred_subscribers(old));
615 validate_creds(override);
616 alter_cred_subscribers(old, 1);
617 rcu_assign_pointer(current->cred, old);
618 alter_cred_subscribers(override, -1);
621 EXPORT_SYMBOL(revert_creds);
624 * initialise the credentials stuff
626 void __init cred_init(void)
628 /* allocate a slab in which we can store credentials */
629 cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
630 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
634 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
635 * @daemon: A userspace daemon to be used as a reference
637 * Prepare a set of credentials for a kernel service. This can then be used to
638 * override a task's own credentials so that work can be done on behalf of that
639 * task that requires a different subjective context.
641 * @daemon is used to provide a base for the security record, but can be NULL.
642 * If @daemon is supplied, then the security data will be derived from that;
643 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
645 * The caller may change these controls afterwards if desired.
647 * Returns the new credentials or NULL if out of memory.
649 * Does not take, and does not return holding current->cred_replace_mutex.
651 struct cred *prepare_kernel_cred(struct task_struct *daemon)
654 struct thread_group_cred *tgcred;
656 const struct cred *old;
659 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
664 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
666 kmem_cache_free(cred_jar, new);
671 kdebug("prepare_kernel_cred() alloc %p", new);
674 old = get_task_cred(daemon);
676 old = get_cred(&init_cred);
681 atomic_set(&new->usage, 1);
682 set_cred_subscribers(new, 0);
684 get_user_ns(new->user_ns);
685 get_group_info(new->group_info);
688 atomic_set(&tgcred->usage, 1);
689 spin_lock_init(&tgcred->lock);
690 tgcred->process_keyring = NULL;
691 tgcred->session_keyring = NULL;
692 new->tgcred = tgcred;
693 new->request_key_auth = NULL;
694 new->thread_keyring = NULL;
695 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
698 #ifdef CONFIG_SECURITY
699 new->security = NULL;
701 if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
713 EXPORT_SYMBOL(prepare_kernel_cred);
716 * set_security_override - Set the security ID in a set of credentials
717 * @new: The credentials to alter
718 * @secid: The LSM security ID to set
720 * Set the LSM security ID in a set of credentials so that the subjective
721 * security is overridden when an alternative set of credentials is used.
723 int set_security_override(struct cred *new, u32 secid)
725 return security_kernel_act_as(new, secid);
727 EXPORT_SYMBOL(set_security_override);
730 * set_security_override_from_ctx - Set the security ID in a set of credentials
731 * @new: The credentials to alter
732 * @secctx: The LSM security context to generate the security ID from.
734 * Set the LSM security ID in a set of credentials so that the subjective
735 * security is overridden when an alternative set of credentials is used. The
736 * security ID is specified in string form as a security context to be
737 * interpreted by the LSM.
739 int set_security_override_from_ctx(struct cred *new, const char *secctx)
744 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
748 return set_security_override(new, secid);
750 EXPORT_SYMBOL(set_security_override_from_ctx);
753 * set_create_files_as - Set the LSM file create context in a set of credentials
754 * @new: The credentials to alter
755 * @inode: The inode to take the context from
757 * Change the LSM file creation context in a set of credentials to be the same
758 * as the object context of the specified inode, so that the new inodes have
759 * the same MAC context as that inode.
761 int set_create_files_as(struct cred *new, struct inode *inode)
763 new->fsuid = inode->i_uid;
764 new->fsgid = inode->i_gid;
765 return security_kernel_create_files_as(new, inode);
767 EXPORT_SYMBOL(set_create_files_as);
769 #ifdef CONFIG_DEBUG_CREDENTIALS
771 bool creds_are_invalid(const struct cred *cred)
773 if (cred->magic != CRED_MAGIC)
775 #ifdef CONFIG_SECURITY_SELINUX
777 * cred->security == NULL if security_cred_alloc_blank() or
778 * security_prepare_creds() returned an error.
780 if (selinux_is_enabled() && cred->security) {
781 if ((unsigned long) cred->security < PAGE_SIZE)
783 if ((*(u32 *)cred->security & 0xffffff00) ==
784 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
790 EXPORT_SYMBOL(creds_are_invalid);
793 * dump invalid credentials
795 static void dump_invalid_creds(const struct cred *cred, const char *label,
796 const struct task_struct *tsk)
798 printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
800 cred == &init_cred ? "[init]" : "",
801 cred == tsk->real_cred ? "[real]" : "",
802 cred == tsk->cred ? "[eff]" : "");
803 printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
804 cred->magic, cred->put_addr);
805 printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
806 atomic_read(&cred->usage),
807 read_cred_subscribers(cred));
808 printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
809 cred->uid, cred->euid, cred->suid, cred->fsuid);
810 printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
811 cred->gid, cred->egid, cred->sgid, cred->fsgid);
812 #ifdef CONFIG_SECURITY
813 printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
814 if ((unsigned long) cred->security >= PAGE_SIZE &&
815 (((unsigned long) cred->security & 0xffffff00) !=
816 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
817 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
818 ((u32*)cred->security)[0],
819 ((u32*)cred->security)[1]);
824 * report use of invalid credentials
826 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
828 printk(KERN_ERR "CRED: Invalid credentials\n");
829 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
830 dump_invalid_creds(cred, "Specified", current);
833 EXPORT_SYMBOL(__invalid_creds);
836 * check the credentials on a process
838 void __validate_process_creds(struct task_struct *tsk,
839 const char *file, unsigned line)
841 if (tsk->cred == tsk->real_cred) {
842 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
843 creds_are_invalid(tsk->cred)))
846 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
847 read_cred_subscribers(tsk->cred) < 1 ||
848 creds_are_invalid(tsk->real_cred) ||
849 creds_are_invalid(tsk->cred)))
855 printk(KERN_ERR "CRED: Invalid process credentials\n");
856 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
858 dump_invalid_creds(tsk->real_cred, "Real", tsk);
859 if (tsk->cred != tsk->real_cred)
860 dump_invalid_creds(tsk->cred, "Effective", tsk);
862 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
865 EXPORT_SYMBOL(__validate_process_creds);
868 * check creds for do_exit()
870 void validate_creds_for_do_exit(struct task_struct *tsk)
872 kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
873 tsk->real_cred, tsk->cred,
874 atomic_read(&tsk->cred->usage),
875 read_cred_subscribers(tsk->cred));
877 __validate_process_creds(tsk, __FILE__, __LINE__);
880 #endif /* CONFIG_DEBUG_CREDENTIALS */