CRED: Allow kernel services to override LSM settings for task actions
[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
278         mutex_init(&p->cred_exec_mutex);
279
280         if (
281 #ifdef CONFIG_KEYS
282                 !p->cred->thread_keyring &&
283 #endif
284                 clone_flags & CLONE_THREAD
285             ) {
286                 p->real_cred = get_cred(p->cred);
287                 get_cred(p->cred);
288                 atomic_inc(&p->cred->user->processes);
289                 return 0;
290         }
291
292         new = prepare_creds();
293         if (!new)
294                 return -ENOMEM;
295
296 #ifdef CONFIG_KEYS
297         /* new threads get their own thread keyrings if their parent already
298          * had one */
299         if (new->thread_keyring) {
300                 key_put(new->thread_keyring);
301                 new->thread_keyring = NULL;
302                 if (clone_flags & CLONE_THREAD)
303                         install_thread_keyring_to_cred(new);
304         }
305
306         /* we share the process and session keyrings between all the threads in
307          * a process - this is slightly icky as we violate COW credentials a
308          * bit */
309         if (!(clone_flags & CLONE_THREAD)) {
310                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
311                 if (!tgcred) {
312                         put_cred(new);
313                         return -ENOMEM;
314                 }
315                 atomic_set(&tgcred->usage, 1);
316                 spin_lock_init(&tgcred->lock);
317                 tgcred->process_keyring = NULL;
318                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
319
320                 release_tgcred(new);
321                 new->tgcred = tgcred;
322         }
323 #endif
324
325         atomic_inc(&new->user->processes);
326         p->cred = p->real_cred = get_cred(new);
327         return 0;
328 }
329
330 /**
331  * commit_creds - Install new credentials upon the current task
332  * @new: The credentials to be assigned
333  *
334  * Install a new set of credentials to the current task, using RCU to replace
335  * the old set.  Both the objective and the subjective credentials pointers are
336  * updated.  This function may not be called if the subjective credentials are
337  * in an overridden state.
338  *
339  * This function eats the caller's reference to the new credentials.
340  *
341  * Always returns 0 thus allowing this function to be tail-called at the end
342  * of, say, sys_setgid().
343  */
344 int commit_creds(struct cred *new)
345 {
346         struct task_struct *task = current;
347         const struct cred *old;
348
349         BUG_ON(task->cred != task->real_cred);
350         BUG_ON(atomic_read(&task->real_cred->usage) < 2);
351         BUG_ON(atomic_read(&new->usage) < 1);
352
353         old = task->real_cred;
354         security_commit_creds(new, old);
355
356         get_cred(new); /* we will require a ref for the subj creds too */
357
358         /* dumpability changes */
359         if (old->euid != new->euid ||
360             old->egid != new->egid ||
361             old->fsuid != new->fsuid ||
362             old->fsgid != new->fsgid ||
363             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
364                 set_dumpable(task->mm, suid_dumpable);
365                 task->pdeath_signal = 0;
366                 smp_wmb();
367         }
368
369         /* alter the thread keyring */
370         if (new->fsuid != old->fsuid)
371                 key_fsuid_changed(task);
372         if (new->fsgid != old->fsgid)
373                 key_fsgid_changed(task);
374
375         /* do it
376          * - What if a process setreuid()'s and this brings the
377          *   new uid over his NPROC rlimit?  We can check this now
378          *   cheaply with the new uid cache, so if it matters
379          *   we should be checking for it.  -DaveM
380          */
381         if (new->user != old->user)
382                 atomic_inc(&new->user->processes);
383         rcu_assign_pointer(task->real_cred, new);
384         rcu_assign_pointer(task->cred, new);
385         if (new->user != old->user)
386                 atomic_dec(&old->user->processes);
387
388         sched_switch_user(task);
389
390         /* send notifications */
391         if (new->uid   != old->uid  ||
392             new->euid  != old->euid ||
393             new->suid  != old->suid ||
394             new->fsuid != old->fsuid)
395                 proc_id_connector(task, PROC_EVENT_UID);
396
397         if (new->gid   != old->gid  ||
398             new->egid  != old->egid ||
399             new->sgid  != old->sgid ||
400             new->fsgid != old->fsgid)
401                 proc_id_connector(task, PROC_EVENT_GID);
402
403         /* release the old obj and subj refs both */
404         put_cred(old);
405         put_cred(old);
406         return 0;
407 }
408 EXPORT_SYMBOL(commit_creds);
409
410 /**
411  * abort_creds - Discard a set of credentials and unlock the current task
412  * @new: The credentials that were going to be applied
413  *
414  * Discard a set of credentials that were under construction and unlock the
415  * current task.
416  */
417 void abort_creds(struct cred *new)
418 {
419         BUG_ON(atomic_read(&new->usage) < 1);
420         put_cred(new);
421 }
422 EXPORT_SYMBOL(abort_creds);
423
424 /**
425  * override_creds - Override the current process's subjective credentials
426  * @new: The credentials to be assigned
427  *
428  * Install a set of temporary override subjective credentials on the current
429  * process, returning the old set for later reversion.
430  */
431 const struct cred *override_creds(const struct cred *new)
432 {
433         const struct cred *old = current->cred;
434
435         rcu_assign_pointer(current->cred, get_cred(new));
436         return old;
437 }
438 EXPORT_SYMBOL(override_creds);
439
440 /**
441  * revert_creds - Revert a temporary subjective credentials override
442  * @old: The credentials to be restored
443  *
444  * Revert a temporary set of override subjective credentials to an old set,
445  * discarding the override set.
446  */
447 void revert_creds(const struct cred *old)
448 {
449         const struct cred *override = current->cred;
450
451         rcu_assign_pointer(current->cred, old);
452         put_cred(override);
453 }
454 EXPORT_SYMBOL(revert_creds);
455
456 /*
457  * initialise the credentials stuff
458  */
459 void __init cred_init(void)
460 {
461         /* allocate a slab in which we can store credentials */
462         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
463                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
464 }
465
466 /**
467  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
468  * @daemon: A userspace daemon to be used as a reference
469  *
470  * Prepare a set of credentials for a kernel service.  This can then be used to
471  * override a task's own credentials so that work can be done on behalf of that
472  * task that requires a different subjective context.
473  *
474  * @daemon is used to provide a base for the security record, but can be NULL.
475  * If @daemon is supplied, then the security data will be derived from that;
476  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
477  *
478  * The caller may change these controls afterwards if desired.
479  *
480  * Returns the new credentials or NULL if out of memory.
481  *
482  * Does not take, and does not return holding current->cred_replace_mutex.
483  */
484 struct cred *prepare_kernel_cred(struct task_struct *daemon)
485 {
486         const struct cred *old;
487         struct cred *new;
488
489         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
490         if (!new)
491                 return NULL;
492
493         if (daemon)
494                 old = get_task_cred(daemon);
495         else
496                 old = get_cred(&init_cred);
497
498         get_uid(new->user);
499         get_group_info(new->group_info);
500
501 #ifdef CONFIG_KEYS
502         atomic_inc(&init_tgcred.usage);
503         new->tgcred = &init_tgcred;
504         new->request_key_auth = NULL;
505         new->thread_keyring = NULL;
506         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
507 #endif
508
509 #ifdef CONFIG_SECURITY
510         new->security = NULL;
511 #endif
512         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
513                 goto error;
514
515         atomic_set(&new->usage, 1);
516         put_cred(old);
517         return new;
518
519 error:
520         put_cred(new);
521         return NULL;
522 }
523 EXPORT_SYMBOL(prepare_kernel_cred);
524
525 /**
526  * set_security_override - Set the security ID in a set of credentials
527  * @new: The credentials to alter
528  * @secid: The LSM security ID to set
529  *
530  * Set the LSM security ID in a set of credentials so that the subjective
531  * security is overridden when an alternative set of credentials is used.
532  */
533 int set_security_override(struct cred *new, u32 secid)
534 {
535         return security_kernel_act_as(new, secid);
536 }
537 EXPORT_SYMBOL(set_security_override);
538
539 /**
540  * set_security_override_from_ctx - Set the security ID in a set of credentials
541  * @new: The credentials to alter
542  * @secctx: The LSM security context to generate the security ID from.
543  *
544  * Set the LSM security ID in a set of credentials so that the subjective
545  * security is overridden when an alternative set of credentials is used.  The
546  * security ID is specified in string form as a security context to be
547  * interpreted by the LSM.
548  */
549 int set_security_override_from_ctx(struct cred *new, const char *secctx)
550 {
551         u32 secid;
552         int ret;
553
554         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
555         if (ret < 0)
556                 return ret;
557
558         return set_security_override(new, secid);
559 }
560 EXPORT_SYMBOL(set_security_override_from_ctx);
561
562 /**
563  * set_create_files_as - Set the LSM file create context in a set of credentials
564  * @new: The credentials to alter
565  * @inode: The inode to take the context from
566  *
567  * Change the LSM file creation context in a set of credentials to be the same
568  * as the object context of the specified inode, so that the new inodes have
569  * the same MAC context as that inode.
570  */
571 int set_create_files_as(struct cred *new, struct inode *inode)
572 {
573         new->fsuid = inode->i_uid;
574         new->fsgid = inode->i_gid;
575         return security_kernel_create_files_as(new, inode);
576 }
577 EXPORT_SYMBOL(set_create_files_as);