CRED: Make execve() take advantage of copy-on-write credentials
[linux-3.10.git] / kernel / cred.c
1 /* Task credentials management
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(3),
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  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
124  *
125  * Call commit_creds() or abort_creds() to clean up.
126  */
127 struct cred *prepare_creds(void)
128 {
129         struct task_struct *task = current;
130         const struct cred *old;
131         struct cred *new;
132
133         BUG_ON(atomic_read(&task->cred->usage) < 1);
134
135         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
136         if (!new)
137                 return NULL;
138
139         old = task->cred;
140         memcpy(new, old, sizeof(struct cred));
141
142         atomic_set(&new->usage, 1);
143         get_group_info(new->group_info);
144         get_uid(new->user);
145
146 #ifdef CONFIG_KEYS
147         key_get(new->thread_keyring);
148         key_get(new->request_key_auth);
149         atomic_inc(&new->tgcred->usage);
150 #endif
151
152 #ifdef CONFIG_SECURITY
153         new->security = NULL;
154 #endif
155
156         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
157                 goto error;
158         return new;
159
160 error:
161         abort_creds(new);
162         return NULL;
163 }
164 EXPORT_SYMBOL(prepare_creds);
165
166 /*
167  * Prepare credentials for current to perform an execve()
168  * - The caller must hold current->cred_exec_mutex
169  */
170 struct cred *prepare_exec_creds(void)
171 {
172         struct thread_group_cred *tgcred = NULL;
173         struct cred *new;
174
175 #ifdef CONFIG_KEYS
176         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
177         if (!tgcred)
178                 return NULL;
179 #endif
180
181         new = prepare_creds();
182         if (!new) {
183                 kfree(tgcred);
184                 return new;
185         }
186
187 #ifdef CONFIG_KEYS
188         /* newly exec'd tasks don't get a thread keyring */
189         key_put(new->thread_keyring);
190         new->thread_keyring = NULL;
191
192         /* create a new per-thread-group creds for all this set of threads to
193          * share */
194         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
195
196         atomic_set(&tgcred->usage, 1);
197         spin_lock_init(&tgcred->lock);
198
199         /* inherit the session keyring; new process keyring */
200         key_get(tgcred->session_keyring);
201         tgcred->process_keyring = NULL;
202
203         release_tgcred(new);
204         new->tgcred = tgcred;
205 #endif
206
207         return new;
208 }
209
210 /*
211  * prepare new credentials for the usermode helper dispatcher
212  */
213 struct cred *prepare_usermodehelper_creds(void)
214 {
215 #ifdef CONFIG_KEYS
216         struct thread_group_cred *tgcred = NULL;
217 #endif
218         struct cred *new;
219
220 #ifdef CONFIG_KEYS
221         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
222         if (!tgcred)
223                 return NULL;
224 #endif
225
226         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
227         if (!new)
228                 return NULL;
229
230         memcpy(new, &init_cred, sizeof(struct cred));
231
232         atomic_set(&new->usage, 1);
233         get_group_info(new->group_info);
234         get_uid(new->user);
235
236 #ifdef CONFIG_KEYS
237         new->thread_keyring = NULL;
238         new->request_key_auth = NULL;
239         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
240
241         atomic_set(&tgcred->usage, 1);
242         spin_lock_init(&tgcred->lock);
243         new->tgcred = tgcred;
244 #endif
245
246 #ifdef CONFIG_SECURITY
247         new->security = NULL;
248 #endif
249         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
250                 goto error;
251
252         BUG_ON(atomic_read(&new->usage) != 1);
253         return new;
254
255 error:
256         put_cred(new);
257         return NULL;
258 }
259
260 /*
261  * Copy credentials for the new process created by fork()
262  *
263  * We share if we can, but under some circumstances we have to generate a new
264  * set.
265  */
266 int copy_creds(struct task_struct *p, unsigned long clone_flags)
267 {
268 #ifdef CONFIG_KEYS
269         struct thread_group_cred *tgcred;
270 #endif
271         struct cred *new;
272
273         mutex_init(&p->cred_exec_mutex);
274
275         if (
276 #ifdef CONFIG_KEYS
277                 !p->cred->thread_keyring &&
278 #endif
279                 clone_flags & CLONE_THREAD
280             ) {
281                 get_cred(p->cred);
282                 atomic_inc(&p->cred->user->processes);
283                 return 0;
284         }
285
286         new = prepare_creds();
287         if (!new)
288                 return -ENOMEM;
289
290 #ifdef CONFIG_KEYS
291         /* new threads get their own thread keyrings if their parent already
292          * had one */
293         if (new->thread_keyring) {
294                 key_put(new->thread_keyring);
295                 new->thread_keyring = NULL;
296                 if (clone_flags & CLONE_THREAD)
297                         install_thread_keyring_to_cred(new);
298         }
299
300         /* we share the process and session keyrings between all the threads in
301          * a process - this is slightly icky as we violate COW credentials a
302          * bit */
303         if (!(clone_flags & CLONE_THREAD)) {
304                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
305                 if (!tgcred) {
306                         put_cred(new);
307                         return -ENOMEM;
308                 }
309                 atomic_set(&tgcred->usage, 1);
310                 spin_lock_init(&tgcred->lock);
311                 tgcred->process_keyring = NULL;
312                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
313
314                 release_tgcred(new);
315                 new->tgcred = tgcred;
316         }
317 #endif
318
319         atomic_inc(&new->user->processes);
320         p->cred = new;
321         return 0;
322 }
323
324 /**
325  * commit_creds - Install new credentials upon the current task
326  * @new: The credentials to be assigned
327  *
328  * Install a new set of credentials to the current task, using RCU to replace
329  * the old set.
330  *
331  * This function eats the caller's reference to the new credentials.
332  *
333  * Always returns 0 thus allowing this function to be tail-called at the end
334  * of, say, sys_setgid().
335  */
336 int commit_creds(struct cred *new)
337 {
338         struct task_struct *task = current;
339         const struct cred *old;
340
341         BUG_ON(atomic_read(&new->usage) < 1);
342         BUG_ON(atomic_read(&task->cred->usage) < 1);
343
344         old = task->cred;
345         security_commit_creds(new, old);
346
347         /* dumpability changes */
348         if (old->euid != new->euid ||
349             old->egid != new->egid ||
350             old->fsuid != new->fsuid ||
351             old->fsgid != new->fsgid ||
352             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
353                 set_dumpable(task->mm, suid_dumpable);
354                 task->pdeath_signal = 0;
355                 smp_wmb();
356         }
357
358         /* alter the thread keyring */
359         if (new->fsuid != old->fsuid)
360                 key_fsuid_changed(task);
361         if (new->fsgid != old->fsgid)
362                 key_fsgid_changed(task);
363
364         /* do it
365          * - What if a process setreuid()'s and this brings the
366          *   new uid over his NPROC rlimit?  We can check this now
367          *   cheaply with the new uid cache, so if it matters
368          *   we should be checking for it.  -DaveM
369          */
370         if (new->user != old->user)
371                 atomic_inc(&new->user->processes);
372         rcu_assign_pointer(task->cred, new);
373         if (new->user != old->user)
374                 atomic_dec(&old->user->processes);
375
376         sched_switch_user(task);
377
378         /* send notifications */
379         if (new->uid   != old->uid  ||
380             new->euid  != old->euid ||
381             new->suid  != old->suid ||
382             new->fsuid != old->fsuid)
383                 proc_id_connector(task, PROC_EVENT_UID);
384
385         if (new->gid   != old->gid  ||
386             new->egid  != old->egid ||
387             new->sgid  != old->sgid ||
388             new->fsgid != old->fsgid)
389                 proc_id_connector(task, PROC_EVENT_GID);
390
391         put_cred(old);
392         return 0;
393 }
394 EXPORT_SYMBOL(commit_creds);
395
396 /**
397  * abort_creds - Discard a set of credentials and unlock the current task
398  * @new: The credentials that were going to be applied
399  *
400  * Discard a set of credentials that were under construction and unlock the
401  * current task.
402  */
403 void abort_creds(struct cred *new)
404 {
405         BUG_ON(atomic_read(&new->usage) < 1);
406         put_cred(new);
407 }
408 EXPORT_SYMBOL(abort_creds);
409
410 /**
411  * override_creds - Temporarily override the current process's credentials
412  * @new: The credentials to be assigned
413  *
414  * Install a set of temporary override credentials on the current process,
415  * returning the old set for later reversion.
416  */
417 const struct cred *override_creds(const struct cred *new)
418 {
419         const struct cred *old = current->cred;
420
421         rcu_assign_pointer(current->cred, get_cred(new));
422         return old;
423 }
424 EXPORT_SYMBOL(override_creds);
425
426 /**
427  * revert_creds - Revert a temporary credentials override
428  * @old: The credentials to be restored
429  *
430  * Revert a temporary set of override credentials to an old set, discarding the
431  * override set.
432  */
433 void revert_creds(const struct cred *old)
434 {
435         const struct cred *override = current->cred;
436
437         rcu_assign_pointer(current->cred, old);
438         put_cred(override);
439 }
440 EXPORT_SYMBOL(revert_creds);
441
442 /*
443  * initialise the credentials stuff
444  */
445 void __init cred_init(void)
446 {
447         /* allocate a slab in which we can store credentials */
448         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
449                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
450 }