1 /* Task credentials management - see Documentation/security/credentials.rst
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/sched/coredump.h>
16 #include <linux/key.h>
17 #include <linux/keyctl.h>
18 #include <linux/init_task.h>
19 #include <linux/security.h>
20 #include <linux/binfmts.h>
21 #include <linux/cn_proc.h>
24 #define kdebug(FMT, ...) \
25 printk("[%-5.5s%5u] " FMT "\n", \
26 current->comm, current->pid, ##__VA_ARGS__)
28 #define kdebug(FMT, ...) \
31 no_printk("[%-5.5s%5u] " FMT "\n", \
32 current->comm, current->pid, ##__VA_ARGS__); \
36 static struct kmem_cache *cred_jar;
38 /* init to 2 - one for init_task, one to ensure it is never freed */
39 struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
42 * The initial credentials for the initial task
44 struct cred init_cred = {
45 .usage = ATOMIC_INIT(4),
46 #ifdef CONFIG_DEBUG_CREDENTIALS
47 .subscribers = ATOMIC_INIT(2),
50 .uid = GLOBAL_ROOT_UID,
51 .gid = GLOBAL_ROOT_GID,
52 .suid = GLOBAL_ROOT_UID,
53 .sgid = GLOBAL_ROOT_GID,
54 .euid = GLOBAL_ROOT_UID,
55 .egid = GLOBAL_ROOT_GID,
56 .fsuid = GLOBAL_ROOT_UID,
57 .fsgid = GLOBAL_ROOT_GID,
58 .securebits = SECUREBITS_DEFAULT,
59 .cap_inheritable = CAP_EMPTY_SET,
60 .cap_permitted = CAP_FULL_SET,
61 .cap_effective = CAP_FULL_SET,
62 .cap_bset = CAP_FULL_SET,
64 .user_ns = &init_user_ns,
65 .group_info = &init_groups,
68 static inline void set_cred_subscribers(struct cred *cred, int n)
70 #ifdef CONFIG_DEBUG_CREDENTIALS
71 atomic_set(&cred->subscribers, n);
75 static inline int read_cred_subscribers(const struct cred *cred)
77 #ifdef CONFIG_DEBUG_CREDENTIALS
78 return atomic_read(&cred->subscribers);
84 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
86 #ifdef CONFIG_DEBUG_CREDENTIALS
87 struct cred *cred = (struct cred *) _cred;
89 atomic_add(n, &cred->subscribers);
94 * The RCU callback to actually dispose of a set of credentials
96 static void put_cred_rcu(struct rcu_head *rcu)
98 struct cred *cred = container_of(rcu, struct cred, rcu);
100 kdebug("put_cred_rcu(%p)", cred);
102 #ifdef CONFIG_DEBUG_CREDENTIALS
103 if (cred->magic != CRED_MAGIC_DEAD ||
104 atomic_read(&cred->usage) != 0 ||
105 read_cred_subscribers(cred) != 0)
106 panic("CRED: put_cred_rcu() sees %p with"
107 " mag %x, put %p, usage %d, subscr %d\n",
108 cred, cred->magic, cred->put_addr,
109 atomic_read(&cred->usage),
110 read_cred_subscribers(cred));
112 if (atomic_read(&cred->usage) != 0)
113 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
114 cred, atomic_read(&cred->usage));
117 security_cred_free(cred);
118 key_put(cred->session_keyring);
119 key_put(cred->process_keyring);
120 key_put(cred->thread_keyring);
121 key_put(cred->request_key_auth);
122 if (cred->group_info)
123 put_group_info(cred->group_info);
124 free_uid(cred->user);
125 put_user_ns(cred->user_ns);
126 kmem_cache_free(cred_jar, cred);
130 * __put_cred - Destroy a set of credentials
131 * @cred: The record to release
133 * Destroy a set of credentials on which no references remain.
135 void __put_cred(struct cred *cred)
137 kdebug("__put_cred(%p{%d,%d})", cred,
138 atomic_read(&cred->usage),
139 read_cred_subscribers(cred));
141 BUG_ON(atomic_read(&cred->usage) != 0);
142 #ifdef CONFIG_DEBUG_CREDENTIALS
143 BUG_ON(read_cred_subscribers(cred) != 0);
144 cred->magic = CRED_MAGIC_DEAD;
145 cred->put_addr = __builtin_return_address(0);
147 BUG_ON(cred == current->cred);
148 BUG_ON(cred == current->real_cred);
151 put_cred_rcu(&cred->rcu);
153 call_rcu(&cred->rcu, put_cred_rcu);
155 EXPORT_SYMBOL(__put_cred);
158 * Clean up a task's credentials when it exits
160 void exit_creds(struct task_struct *tsk)
164 kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
165 atomic_read(&tsk->cred->usage),
166 read_cred_subscribers(tsk->cred));
168 cred = (struct cred *) tsk->real_cred;
169 tsk->real_cred = NULL;
170 validate_creds(cred);
171 alter_cred_subscribers(cred, -1);
174 cred = (struct cred *) tsk->cred;
176 validate_creds(cred);
177 alter_cred_subscribers(cred, -1);
182 * get_task_cred - Get another task's objective credentials
183 * @task: The task to query
185 * Get the objective credentials of a task, pinning them so that they can't go
186 * away. Accessing a task's credentials directly is not permitted.
188 * The caller must also make sure task doesn't get deleted, either by holding a
189 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
191 const struct cred *get_task_cred(struct task_struct *task)
193 const struct cred *cred;
198 cred = __task_cred((task));
200 } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
207 * Allocate blank credentials, such that the credentials can be filled in at a
208 * later date without risk of ENOMEM.
210 struct cred *cred_alloc_blank(void)
214 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
218 atomic_set(&new->usage, 1);
219 #ifdef CONFIG_DEBUG_CREDENTIALS
220 new->magic = CRED_MAGIC;
223 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
234 * prepare_creds - Prepare a new set of credentials for modification
236 * Prepare a new set of task credentials for modification. A task's creds
237 * shouldn't generally be modified directly, therefore this function is used to
238 * prepare a new copy, which the caller then modifies and then commits by
239 * calling commit_creds().
241 * Preparation involves making a copy of the objective creds for modification.
243 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
245 * Call commit_creds() or abort_creds() to clean up.
247 struct cred *prepare_creds(void)
249 struct task_struct *task = current;
250 const struct cred *old;
253 validate_process_creds();
255 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
259 kdebug("prepare_creds() alloc %p", new);
262 memcpy(new, old, sizeof(struct cred));
265 atomic_set(&new->usage, 1);
266 set_cred_subscribers(new, 0);
267 get_group_info(new->group_info);
269 get_user_ns(new->user_ns);
272 key_get(new->session_keyring);
273 key_get(new->process_keyring);
274 key_get(new->thread_keyring);
275 key_get(new->request_key_auth);
278 #ifdef CONFIG_SECURITY
279 new->security = NULL;
282 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
291 EXPORT_SYMBOL(prepare_creds);
294 * Prepare credentials for current to perform an execve()
295 * - The caller must hold ->cred_guard_mutex
297 struct cred *prepare_exec_creds(void)
301 new = prepare_creds();
306 /* newly exec'd tasks don't get a thread keyring */
307 key_put(new->thread_keyring);
308 new->thread_keyring = NULL;
310 /* inherit the session keyring; new process keyring */
311 key_put(new->process_keyring);
312 new->process_keyring = NULL;
319 * Copy credentials for the new process created by fork()
321 * We share if we can, but under some circumstances we have to generate a new
324 * The new process gets the current process's subjective credentials as its
325 * objective and subjective credentials
327 int copy_creds(struct task_struct *p, unsigned long clone_flags)
334 !p->cred->thread_keyring &&
336 clone_flags & CLONE_THREAD
338 p->real_cred = get_cred(p->cred);
340 alter_cred_subscribers(p->cred, 2);
341 kdebug("share_creds(%p{%d,%d})",
342 p->cred, atomic_read(&p->cred->usage),
343 read_cred_subscribers(p->cred));
344 atomic_inc(&p->cred->user->processes);
348 new = prepare_creds();
352 if (clone_flags & CLONE_NEWUSER) {
353 ret = create_user_ns(new);
359 /* new threads get their own thread keyrings if their parent already
361 if (new->thread_keyring) {
362 key_put(new->thread_keyring);
363 new->thread_keyring = NULL;
364 if (clone_flags & CLONE_THREAD)
365 install_thread_keyring_to_cred(new);
368 /* The process keyring is only shared between the threads in a process;
369 * anything outside of those threads doesn't inherit.
371 if (!(clone_flags & CLONE_THREAD)) {
372 key_put(new->process_keyring);
373 new->process_keyring = NULL;
377 atomic_inc(&new->user->processes);
378 p->cred = p->real_cred = get_cred(new);
379 alter_cred_subscribers(new, 2);
388 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
390 const struct user_namespace *set_ns = set->user_ns;
391 const struct user_namespace *subset_ns = subset->user_ns;
393 /* If the two credentials are in the same user namespace see if
394 * the capabilities of subset are a subset of set.
396 if (set_ns == subset_ns)
397 return cap_issubset(subset->cap_permitted, set->cap_permitted);
399 /* The credentials are in a different user namespaces
400 * therefore one is a subset of the other only if a set is an
401 * ancestor of subset and set->euid is owner of subset or one
402 * of subsets ancestors.
404 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
405 if ((set_ns == subset_ns->parent) &&
406 uid_eq(subset_ns->owner, set->euid))
414 * commit_creds - Install new credentials upon the current task
415 * @new: The credentials to be assigned
417 * Install a new set of credentials to the current task, using RCU to replace
418 * the old set. Both the objective and the subjective credentials pointers are
419 * updated. This function may not be called if the subjective credentials are
420 * in an overridden state.
422 * This function eats the caller's reference to the new credentials.
424 * Always returns 0 thus allowing this function to be tail-called at the end
425 * of, say, sys_setgid().
427 int commit_creds(struct cred *new)
429 struct task_struct *task = current;
430 const struct cred *old = task->real_cred;
432 kdebug("commit_creds(%p{%d,%d})", new,
433 atomic_read(&new->usage),
434 read_cred_subscribers(new));
436 BUG_ON(task->cred != old);
437 #ifdef CONFIG_DEBUG_CREDENTIALS
438 BUG_ON(read_cred_subscribers(old) < 2);
442 BUG_ON(atomic_read(&new->usage) < 1);
444 get_cred(new); /* we will require a ref for the subj creds too */
446 /* dumpability changes */
447 if (!uid_eq(old->euid, new->euid) ||
448 !gid_eq(old->egid, new->egid) ||
449 !uid_eq(old->fsuid, new->fsuid) ||
450 !gid_eq(old->fsgid, new->fsgid) ||
451 !cred_cap_issubset(old, new)) {
453 set_dumpable(task->mm, suid_dumpable);
454 task->pdeath_signal = 0;
456 * If a task drops privileges and becomes nondumpable,
457 * the dumpability change must become visible before
458 * the credential change; otherwise, a __ptrace_may_access()
459 * racing with this change may be able to attach to a task it
460 * shouldn't be able to attach to (as if the task had dropped
461 * privileges without becoming nondumpable).
462 * Pairs with a read barrier in __ptrace_may_access().
467 /* alter the thread keyring */
468 if (!uid_eq(new->fsuid, old->fsuid))
469 key_fsuid_changed(task);
470 if (!gid_eq(new->fsgid, old->fsgid))
471 key_fsgid_changed(task);
474 * RLIMIT_NPROC limits on user->processes have already been checked
477 alter_cred_subscribers(new, 2);
478 if (new->user != old->user)
479 atomic_inc(&new->user->processes);
480 rcu_assign_pointer(task->real_cred, new);
481 rcu_assign_pointer(task->cred, new);
482 if (new->user != old->user)
483 atomic_dec(&old->user->processes);
484 alter_cred_subscribers(old, -2);
486 /* send notifications */
487 if (!uid_eq(new->uid, old->uid) ||
488 !uid_eq(new->euid, old->euid) ||
489 !uid_eq(new->suid, old->suid) ||
490 !uid_eq(new->fsuid, old->fsuid))
491 proc_id_connector(task, PROC_EVENT_UID);
493 if (!gid_eq(new->gid, old->gid) ||
494 !gid_eq(new->egid, old->egid) ||
495 !gid_eq(new->sgid, old->sgid) ||
496 !gid_eq(new->fsgid, old->fsgid))
497 proc_id_connector(task, PROC_EVENT_GID);
499 /* release the old obj and subj refs both */
504 EXPORT_SYMBOL(commit_creds);
507 * abort_creds - Discard a set of credentials and unlock the current task
508 * @new: The credentials that were going to be applied
510 * Discard a set of credentials that were under construction and unlock the
513 void abort_creds(struct cred *new)
515 kdebug("abort_creds(%p{%d,%d})", new,
516 atomic_read(&new->usage),
517 read_cred_subscribers(new));
519 #ifdef CONFIG_DEBUG_CREDENTIALS
520 BUG_ON(read_cred_subscribers(new) != 0);
522 BUG_ON(atomic_read(&new->usage) < 1);
525 EXPORT_SYMBOL(abort_creds);
528 * override_creds - Override the current process's subjective credentials
529 * @new: The credentials to be assigned
531 * Install a set of temporary override subjective credentials on the current
532 * process, returning the old set for later reversion.
534 const struct cred *override_creds(const struct cred *new)
536 const struct cred *old = current->cred;
538 kdebug("override_creds(%p{%d,%d})", new,
539 atomic_read(&new->usage),
540 read_cred_subscribers(new));
546 * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
548 * That means that we do not clear the 'non_rcu' flag, since
549 * we are only installing the cred into the thread-synchronous
550 * '->cred' pointer, not the '->real_cred' pointer that is
551 * visible to other threads under RCU.
553 * Also note that we did validate_creds() manually, not depending
554 * on the validation in 'get_cred()'.
556 get_new_cred((struct cred *)new);
557 alter_cred_subscribers(new, 1);
558 rcu_assign_pointer(current->cred, new);
559 alter_cred_subscribers(old, -1);
561 kdebug("override_creds() = %p{%d,%d}", old,
562 atomic_read(&old->usage),
563 read_cred_subscribers(old));
566 EXPORT_SYMBOL(override_creds);
569 * revert_creds - Revert a temporary subjective credentials override
570 * @old: The credentials to be restored
572 * Revert a temporary set of override subjective credentials to an old set,
573 * discarding the override set.
575 void revert_creds(const struct cred *old)
577 const struct cred *override = current->cred;
579 kdebug("revert_creds(%p{%d,%d})", old,
580 atomic_read(&old->usage),
581 read_cred_subscribers(old));
584 validate_creds(override);
585 alter_cred_subscribers(old, 1);
586 rcu_assign_pointer(current->cred, old);
587 alter_cred_subscribers(override, -1);
590 EXPORT_SYMBOL(revert_creds);
593 * initialise the credentials stuff
595 void __init cred_init(void)
597 /* allocate a slab in which we can store credentials */
598 cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
599 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
603 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
604 * @daemon: A userspace daemon to be used as a reference
606 * Prepare a set of credentials for a kernel service. This can then be used to
607 * override a task's own credentials so that work can be done on behalf of that
608 * task that requires a different subjective context.
610 * @daemon is used to provide a base for the security record, but can be NULL.
611 * If @daemon is supplied, then the security data will be derived from that;
612 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
614 * The caller may change these controls afterwards if desired.
616 * Returns the new credentials or NULL if out of memory.
618 * Does not take, and does not return holding current->cred_replace_mutex.
620 struct cred *prepare_kernel_cred(struct task_struct *daemon)
622 const struct cred *old;
625 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
629 kdebug("prepare_kernel_cred() alloc %p", new);
632 old = get_task_cred(daemon);
634 old = get_cred(&init_cred);
640 atomic_set(&new->usage, 1);
641 set_cred_subscribers(new, 0);
643 get_user_ns(new->user_ns);
644 get_group_info(new->group_info);
647 new->session_keyring = NULL;
648 new->process_keyring = NULL;
649 new->thread_keyring = NULL;
650 new->request_key_auth = NULL;
651 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
654 #ifdef CONFIG_SECURITY
655 new->security = NULL;
657 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
669 EXPORT_SYMBOL(prepare_kernel_cred);
672 * set_security_override - Set the security ID in a set of credentials
673 * @new: The credentials to alter
674 * @secid: The LSM security ID to set
676 * Set the LSM security ID in a set of credentials so that the subjective
677 * security is overridden when an alternative set of credentials is used.
679 int set_security_override(struct cred *new, u32 secid)
681 return security_kernel_act_as(new, secid);
683 EXPORT_SYMBOL(set_security_override);
686 * set_security_override_from_ctx - Set the security ID in a set of credentials
687 * @new: The credentials to alter
688 * @secctx: The LSM security context to generate the security ID from.
690 * Set the LSM security ID in a set of credentials so that the subjective
691 * security is overridden when an alternative set of credentials is used. The
692 * security ID is specified in string form as a security context to be
693 * interpreted by the LSM.
695 int set_security_override_from_ctx(struct cred *new, const char *secctx)
700 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
704 return set_security_override(new, secid);
706 EXPORT_SYMBOL(set_security_override_from_ctx);
709 * set_create_files_as - Set the LSM file create context in a set of credentials
710 * @new: The credentials to alter
711 * @inode: The inode to take the context from
713 * Change the LSM file creation context in a set of credentials to be the same
714 * as the object context of the specified inode, so that the new inodes have
715 * the same MAC context as that inode.
717 int set_create_files_as(struct cred *new, struct inode *inode)
719 if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
721 new->fsuid = inode->i_uid;
722 new->fsgid = inode->i_gid;
723 return security_kernel_create_files_as(new, inode);
725 EXPORT_SYMBOL(set_create_files_as);
727 #ifdef CONFIG_DEBUG_CREDENTIALS
729 bool creds_are_invalid(const struct cred *cred)
731 if (cred->magic != CRED_MAGIC)
733 #ifdef CONFIG_SECURITY_SELINUX
735 * cred->security == NULL if security_cred_alloc_blank() or
736 * security_prepare_creds() returned an error.
738 if (selinux_is_enabled() && cred->security) {
739 if ((unsigned long) cred->security < PAGE_SIZE)
741 if ((*(u32 *)cred->security & 0xffffff00) ==
742 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
748 EXPORT_SYMBOL(creds_are_invalid);
751 * dump invalid credentials
753 static void dump_invalid_creds(const struct cred *cred, const char *label,
754 const struct task_struct *tsk)
756 printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
758 cred == &init_cred ? "[init]" : "",
759 cred == tsk->real_cred ? "[real]" : "",
760 cred == tsk->cred ? "[eff]" : "");
761 printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
762 cred->magic, cred->put_addr);
763 printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
764 atomic_read(&cred->usage),
765 read_cred_subscribers(cred));
766 printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
767 from_kuid_munged(&init_user_ns, cred->uid),
768 from_kuid_munged(&init_user_ns, cred->euid),
769 from_kuid_munged(&init_user_ns, cred->suid),
770 from_kuid_munged(&init_user_ns, cred->fsuid));
771 printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
772 from_kgid_munged(&init_user_ns, cred->gid),
773 from_kgid_munged(&init_user_ns, cred->egid),
774 from_kgid_munged(&init_user_ns, cred->sgid),
775 from_kgid_munged(&init_user_ns, cred->fsgid));
776 #ifdef CONFIG_SECURITY
777 printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
778 if ((unsigned long) cred->security >= PAGE_SIZE &&
779 (((unsigned long) cred->security & 0xffffff00) !=
780 (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
781 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
782 ((u32*)cred->security)[0],
783 ((u32*)cred->security)[1]);
788 * report use of invalid credentials
790 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
792 printk(KERN_ERR "CRED: Invalid credentials\n");
793 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
794 dump_invalid_creds(cred, "Specified", current);
797 EXPORT_SYMBOL(__invalid_creds);
800 * check the credentials on a process
802 void __validate_process_creds(struct task_struct *tsk,
803 const char *file, unsigned line)
805 if (tsk->cred == tsk->real_cred) {
806 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
807 creds_are_invalid(tsk->cred)))
810 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
811 read_cred_subscribers(tsk->cred) < 1 ||
812 creds_are_invalid(tsk->real_cred) ||
813 creds_are_invalid(tsk->cred)))
819 printk(KERN_ERR "CRED: Invalid process credentials\n");
820 printk(KERN_ERR "CRED: At %s:%u\n", file, line);
822 dump_invalid_creds(tsk->real_cred, "Real", tsk);
823 if (tsk->cred != tsk->real_cred)
824 dump_invalid_creds(tsk->cred, "Effective", tsk);
826 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
829 EXPORT_SYMBOL(__validate_process_creds);
832 * check creds for do_exit()
834 void validate_creds_for_do_exit(struct task_struct *tsk)
836 kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
837 tsk->real_cred, tsk->cred,
838 atomic_read(&tsk->cred->usage),
839 read_cred_subscribers(tsk->cred));
841 __validate_process_creds(tsk, __FILE__, __LINE__);
844 #endif /* CONFIG_DEBUG_CREDENTIALS */