CRED: Fix commit_creds() on a process that has no mm
[linux-2.6.git] / kernel / cred.c
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 #include "cred-internals.h"
20
21 static struct kmem_cache *cred_jar;
22
23 /*
24  * The common credentials for the initial task's thread group
25  */
26 #ifdef CONFIG_KEYS
27 static struct thread_group_cred init_tgcred = {
28         .usage  = ATOMIC_INIT(2),
29         .tgid   = 0,
30         .lock   = SPIN_LOCK_UNLOCKED,
31 };
32 #endif
33
34 /*
35  * The initial credentials for the initial task
36  */
37 struct cred init_cred = {
38         .usage                  = ATOMIC_INIT(4),
39         .securebits             = SECUREBITS_DEFAULT,
40         .cap_inheritable        = CAP_INIT_INH_SET,
41         .cap_permitted          = CAP_FULL_SET,
42         .cap_effective          = CAP_INIT_EFF_SET,
43         .cap_bset               = CAP_INIT_BSET,
44         .user                   = INIT_USER,
45         .group_info             = &init_groups,
46 #ifdef CONFIG_KEYS
47         .tgcred                 = &init_tgcred,
48 #endif
49 };
50
51 /*
52  * Dispose of the shared task group credentials
53  */
54 #ifdef CONFIG_KEYS
55 static void release_tgcred_rcu(struct rcu_head *rcu)
56 {
57         struct thread_group_cred *tgcred =
58                 container_of(rcu, struct thread_group_cred, rcu);
59
60         BUG_ON(atomic_read(&tgcred->usage) != 0);
61
62         key_put(tgcred->session_keyring);
63         key_put(tgcred->process_keyring);
64         kfree(tgcred);
65 }
66 #endif
67
68 /*
69  * Release a set of thread group credentials.
70  */
71 static void release_tgcred(struct cred *cred)
72 {
73 #ifdef CONFIG_KEYS
74         struct thread_group_cred *tgcred = cred->tgcred;
75
76         if (atomic_dec_and_test(&tgcred->usage))
77                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
78 #endif
79 }
80
81 /*
82  * The RCU callback to actually dispose of a set of credentials
83  */
84 static void put_cred_rcu(struct rcu_head *rcu)
85 {
86         struct cred *cred = container_of(rcu, struct cred, rcu);
87
88         if (atomic_read(&cred->usage) != 0)
89                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
90                       cred, atomic_read(&cred->usage));
91
92         security_cred_free(cred);
93         key_put(cred->thread_keyring);
94         key_put(cred->request_key_auth);
95         release_tgcred(cred);
96         put_group_info(cred->group_info);
97         free_uid(cred->user);
98         kmem_cache_free(cred_jar, cred);
99 }
100
101 /**
102  * __put_cred - Destroy a set of credentials
103  * @cred: The record to release
104  *
105  * Destroy a set of credentials on which no references remain.
106  */
107 void __put_cred(struct cred *cred)
108 {
109         BUG_ON(atomic_read(&cred->usage) != 0);
110
111         call_rcu(&cred->rcu, put_cred_rcu);
112 }
113 EXPORT_SYMBOL(__put_cred);
114
115 /**
116  * prepare_creds - Prepare a new set of credentials for modification
117  *
118  * Prepare a new set of task credentials for modification.  A task's creds
119  * shouldn't generally be modified directly, therefore this function is used to
120  * prepare a new copy, which the caller then modifies and then commits by
121  * calling commit_creds().
122  *
123  * Preparation involves making a copy of the objective creds for modification.
124  *
125  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
126  *
127  * Call commit_creds() or abort_creds() to clean up.
128  */
129 struct cred *prepare_creds(void)
130 {
131         struct task_struct *task = current;
132         const struct cred *old;
133         struct cred *new;
134
135         BUG_ON(atomic_read(&task->real_cred->usage) < 1);
136
137         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
138         if (!new)
139                 return NULL;
140
141         old = task->cred;
142         memcpy(new, old, sizeof(struct cred));
143
144         atomic_set(&new->usage, 1);
145         get_group_info(new->group_info);
146         get_uid(new->user);
147
148 #ifdef CONFIG_KEYS
149         key_get(new->thread_keyring);
150         key_get(new->request_key_auth);
151         atomic_inc(&new->tgcred->usage);
152 #endif
153
154 #ifdef CONFIG_SECURITY
155         new->security = NULL;
156 #endif
157
158         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
159                 goto error;
160         return new;
161
162 error:
163         abort_creds(new);
164         return NULL;
165 }
166 EXPORT_SYMBOL(prepare_creds);
167
168 /*
169  * Prepare credentials for current to perform an execve()
170  * - The caller must hold current->cred_exec_mutex
171  */
172 struct cred *prepare_exec_creds(void)
173 {
174         struct thread_group_cred *tgcred = NULL;
175         struct cred *new;
176
177 #ifdef CONFIG_KEYS
178         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
179         if (!tgcred)
180                 return NULL;
181 #endif
182
183         new = prepare_creds();
184         if (!new) {
185                 kfree(tgcred);
186                 return new;
187         }
188
189 #ifdef CONFIG_KEYS
190         /* newly exec'd tasks don't get a thread keyring */
191         key_put(new->thread_keyring);
192         new->thread_keyring = NULL;
193
194         /* create a new per-thread-group creds for all this set of threads to
195          * share */
196         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
197
198         atomic_set(&tgcred->usage, 1);
199         spin_lock_init(&tgcred->lock);
200
201         /* inherit the session keyring; new process keyring */
202         key_get(tgcred->session_keyring);
203         tgcred->process_keyring = NULL;
204
205         release_tgcred(new);
206         new->tgcred = tgcred;
207 #endif
208
209         return new;
210 }
211
212 /*
213  * prepare new credentials for the usermode helper dispatcher
214  */
215 struct cred *prepare_usermodehelper_creds(void)
216 {
217 #ifdef CONFIG_KEYS
218         struct thread_group_cred *tgcred = NULL;
219 #endif
220         struct cred *new;
221
222 #ifdef CONFIG_KEYS
223         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
224         if (!tgcred)
225                 return NULL;
226 #endif
227
228         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
229         if (!new)
230                 return NULL;
231
232         memcpy(new, &init_cred, sizeof(struct cred));
233
234         atomic_set(&new->usage, 1);
235         get_group_info(new->group_info);
236         get_uid(new->user);
237
238 #ifdef CONFIG_KEYS
239         new->thread_keyring = NULL;
240         new->request_key_auth = NULL;
241         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
242
243         atomic_set(&tgcred->usage, 1);
244         spin_lock_init(&tgcred->lock);
245         new->tgcred = tgcred;
246 #endif
247
248 #ifdef CONFIG_SECURITY
249         new->security = NULL;
250 #endif
251         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
252                 goto error;
253
254         BUG_ON(atomic_read(&new->usage) != 1);
255         return new;
256
257 error:
258         put_cred(new);
259         return NULL;
260 }
261
262 /*
263  * Copy credentials for the new process created by fork()
264  *
265  * We share if we can, but under some circumstances we have to generate a new
266  * set.
267  *
268  * The new process gets the current process's subjective credentials as its
269  * objective and subjective credentials
270  */
271 int copy_creds(struct task_struct *p, unsigned long clone_flags)
272 {
273 #ifdef CONFIG_KEYS
274         struct thread_group_cred *tgcred;
275 #endif
276         struct cred *new;
277         int ret;
278
279         mutex_init(&p->cred_exec_mutex);
280
281         if (
282 #ifdef CONFIG_KEYS
283                 !p->cred->thread_keyring &&
284 #endif
285                 clone_flags & CLONE_THREAD
286             ) {
287                 p->real_cred = get_cred(p->cred);
288                 get_cred(p->cred);
289                 atomic_inc(&p->cred->user->processes);
290                 return 0;
291         }
292
293         new = prepare_creds();
294         if (!new)
295                 return -ENOMEM;
296
297         if (clone_flags & CLONE_NEWUSER) {
298                 ret = create_user_ns(new);
299                 if (ret < 0)
300                         goto error_put;
301         }
302
303 #ifdef CONFIG_KEYS
304         /* new threads get their own thread keyrings if their parent already
305          * had one */
306         if (new->thread_keyring) {
307                 key_put(new->thread_keyring);
308                 new->thread_keyring = NULL;
309                 if (clone_flags & CLONE_THREAD)
310                         install_thread_keyring_to_cred(new);
311         }
312
313         /* we share the process and session keyrings between all the threads in
314          * a process - this is slightly icky as we violate COW credentials a
315          * bit */
316         if (!(clone_flags & CLONE_THREAD)) {
317                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
318                 if (!tgcred) {
319                         ret = -ENOMEM;
320                         goto error_put;
321                 }
322                 atomic_set(&tgcred->usage, 1);
323                 spin_lock_init(&tgcred->lock);
324                 tgcred->process_keyring = NULL;
325                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
326
327                 release_tgcred(new);
328                 new->tgcred = tgcred;
329         }
330 #endif
331
332         atomic_inc(&new->user->processes);
333         p->cred = p->real_cred = get_cred(new);
334         return 0;
335
336 error_put:
337         put_cred(new);
338         return ret;
339 }
340
341 /**
342  * commit_creds - Install new credentials upon the current task
343  * @new: The credentials to be assigned
344  *
345  * Install a new set of credentials to the current task, using RCU to replace
346  * the old set.  Both the objective and the subjective credentials pointers are
347  * updated.  This function may not be called if the subjective credentials are
348  * in an overridden state.
349  *
350  * This function eats the caller's reference to the new credentials.
351  *
352  * Always returns 0 thus allowing this function to be tail-called at the end
353  * of, say, sys_setgid().
354  */
355 int commit_creds(struct cred *new)
356 {
357         struct task_struct *task = current;
358         const struct cred *old;
359
360         BUG_ON(task->cred != task->real_cred);
361         BUG_ON(atomic_read(&task->real_cred->usage) < 2);
362         BUG_ON(atomic_read(&new->usage) < 1);
363
364         old = task->real_cred;
365         security_commit_creds(new, old);
366
367         get_cred(new); /* we will require a ref for the subj creds too */
368
369         /* dumpability changes */
370         if (old->euid != new->euid ||
371             old->egid != new->egid ||
372             old->fsuid != new->fsuid ||
373             old->fsgid != new->fsgid ||
374             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
375                 if (task->mm)
376                         set_dumpable(task->mm, suid_dumpable);
377                 task->pdeath_signal = 0;
378                 smp_wmb();
379         }
380
381         /* alter the thread keyring */
382         if (new->fsuid != old->fsuid)
383                 key_fsuid_changed(task);
384         if (new->fsgid != old->fsgid)
385                 key_fsgid_changed(task);
386
387         /* do it
388          * - What if a process setreuid()'s and this brings the
389          *   new uid over his NPROC rlimit?  We can check this now
390          *   cheaply with the new uid cache, so if it matters
391          *   we should be checking for it.  -DaveM
392          */
393         if (new->user != old->user)
394                 atomic_inc(&new->user->processes);
395         rcu_assign_pointer(task->real_cred, new);
396         rcu_assign_pointer(task->cred, new);
397         if (new->user != old->user)
398                 atomic_dec(&old->user->processes);
399
400         sched_switch_user(task);
401
402         /* send notifications */
403         if (new->uid   != old->uid  ||
404             new->euid  != old->euid ||
405             new->suid  != old->suid ||
406             new->fsuid != old->fsuid)
407                 proc_id_connector(task, PROC_EVENT_UID);
408
409         if (new->gid   != old->gid  ||
410             new->egid  != old->egid ||
411             new->sgid  != old->sgid ||
412             new->fsgid != old->fsgid)
413                 proc_id_connector(task, PROC_EVENT_GID);
414
415         /* release the old obj and subj refs both */
416         put_cred(old);
417         put_cred(old);
418         return 0;
419 }
420 EXPORT_SYMBOL(commit_creds);
421
422 /**
423  * abort_creds - Discard a set of credentials and unlock the current task
424  * @new: The credentials that were going to be applied
425  *
426  * Discard a set of credentials that were under construction and unlock the
427  * current task.
428  */
429 void abort_creds(struct cred *new)
430 {
431         BUG_ON(atomic_read(&new->usage) < 1);
432         put_cred(new);
433 }
434 EXPORT_SYMBOL(abort_creds);
435
436 /**
437  * override_creds - Override the current process's subjective credentials
438  * @new: The credentials to be assigned
439  *
440  * Install a set of temporary override subjective credentials on the current
441  * process, returning the old set for later reversion.
442  */
443 const struct cred *override_creds(const struct cred *new)
444 {
445         const struct cred *old = current->cred;
446
447         rcu_assign_pointer(current->cred, get_cred(new));
448         return old;
449 }
450 EXPORT_SYMBOL(override_creds);
451
452 /**
453  * revert_creds - Revert a temporary subjective credentials override
454  * @old: The credentials to be restored
455  *
456  * Revert a temporary set of override subjective credentials to an old set,
457  * discarding the override set.
458  */
459 void revert_creds(const struct cred *old)
460 {
461         const struct cred *override = current->cred;
462
463         rcu_assign_pointer(current->cred, old);
464         put_cred(override);
465 }
466 EXPORT_SYMBOL(revert_creds);
467
468 /*
469  * initialise the credentials stuff
470  */
471 void __init cred_init(void)
472 {
473         /* allocate a slab in which we can store credentials */
474         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
475                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
476 }
477
478 /**
479  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
480  * @daemon: A userspace daemon to be used as a reference
481  *
482  * Prepare a set of credentials for a kernel service.  This can then be used to
483  * override a task's own credentials so that work can be done on behalf of that
484  * task that requires a different subjective context.
485  *
486  * @daemon is used to provide a base for the security record, but can be NULL.
487  * If @daemon is supplied, then the security data will be derived from that;
488  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
489  *
490  * The caller may change these controls afterwards if desired.
491  *
492  * Returns the new credentials or NULL if out of memory.
493  *
494  * Does not take, and does not return holding current->cred_replace_mutex.
495  */
496 struct cred *prepare_kernel_cred(struct task_struct *daemon)
497 {
498         const struct cred *old;
499         struct cred *new;
500
501         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
502         if (!new)
503                 return NULL;
504
505         if (daemon)
506                 old = get_task_cred(daemon);
507         else
508                 old = get_cred(&init_cred);
509
510         get_uid(new->user);
511         get_group_info(new->group_info);
512
513 #ifdef CONFIG_KEYS
514         atomic_inc(&init_tgcred.usage);
515         new->tgcred = &init_tgcred;
516         new->request_key_auth = NULL;
517         new->thread_keyring = NULL;
518         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
519 #endif
520
521 #ifdef CONFIG_SECURITY
522         new->security = NULL;
523 #endif
524         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
525                 goto error;
526
527         atomic_set(&new->usage, 1);
528         put_cred(old);
529         return new;
530
531 error:
532         put_cred(new);
533         return NULL;
534 }
535 EXPORT_SYMBOL(prepare_kernel_cred);
536
537 /**
538  * set_security_override - Set the security ID in a set of credentials
539  * @new: The credentials to alter
540  * @secid: The LSM security ID to set
541  *
542  * Set the LSM security ID in a set of credentials so that the subjective
543  * security is overridden when an alternative set of credentials is used.
544  */
545 int set_security_override(struct cred *new, u32 secid)
546 {
547         return security_kernel_act_as(new, secid);
548 }
549 EXPORT_SYMBOL(set_security_override);
550
551 /**
552  * set_security_override_from_ctx - Set the security ID in a set of credentials
553  * @new: The credentials to alter
554  * @secctx: The LSM security context to generate the security ID from.
555  *
556  * Set the LSM security ID in a set of credentials so that the subjective
557  * security is overridden when an alternative set of credentials is used.  The
558  * security ID is specified in string form as a security context to be
559  * interpreted by the LSM.
560  */
561 int set_security_override_from_ctx(struct cred *new, const char *secctx)
562 {
563         u32 secid;
564         int ret;
565
566         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
567         if (ret < 0)
568                 return ret;
569
570         return set_security_override(new, secid);
571 }
572 EXPORT_SYMBOL(set_security_override_from_ctx);
573
574 /**
575  * set_create_files_as - Set the LSM file create context in a set of credentials
576  * @new: The credentials to alter
577  * @inode: The inode to take the context from
578  *
579  * Change the LSM file creation context in a set of credentials to be the same
580  * as the object context of the specified inode, so that the new inodes have
581  * the same MAC context as that inode.
582  */
583 int set_create_files_as(struct cred *new, struct inode *inode)
584 {
585         new->fsuid = inode->i_uid;
586         new->fsgid = inode->i_gid;
587         return security_kernel_create_files_as(new, inode);
588 }
589 EXPORT_SYMBOL(set_create_files_as);