CRED: Inaugurate COW credentials
[linux-2.6.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 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 new credentials for the usermode helper dispatcher
168  */
169 struct cred *prepare_usermodehelper_creds(void)
170 {
171 #ifdef CONFIG_KEYS
172         struct thread_group_cred *tgcred = NULL;
173 #endif
174         struct cred *new;
175
176 #ifdef CONFIG_KEYS
177         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
178         if (!tgcred)
179                 return NULL;
180 #endif
181
182         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
183         if (!new)
184                 return NULL;
185
186         memcpy(new, &init_cred, sizeof(struct cred));
187
188         atomic_set(&new->usage, 1);
189         get_group_info(new->group_info);
190         get_uid(new->user);
191
192 #ifdef CONFIG_KEYS
193         new->thread_keyring = NULL;
194         new->request_key_auth = NULL;
195         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
196
197         atomic_set(&tgcred->usage, 1);
198         spin_lock_init(&tgcred->lock);
199         new->tgcred = tgcred;
200 #endif
201
202 #ifdef CONFIG_SECURITY
203         new->security = NULL;
204 #endif
205         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
206                 goto error;
207
208         BUG_ON(atomic_read(&new->usage) != 1);
209         return new;
210
211 error:
212         put_cred(new);
213         return NULL;
214 }
215
216 /*
217  * Copy credentials for the new process created by fork()
218  *
219  * We share if we can, but under some circumstances we have to generate a new
220  * set.
221  */
222 int copy_creds(struct task_struct *p, unsigned long clone_flags)
223 {
224 #ifdef CONFIG_KEYS
225         struct thread_group_cred *tgcred;
226 #endif
227         struct cred *new;
228
229         mutex_init(&p->cred_exec_mutex);
230
231         if (
232 #ifdef CONFIG_KEYS
233                 !p->cred->thread_keyring &&
234 #endif
235                 clone_flags & CLONE_THREAD
236             ) {
237                 get_cred(p->cred);
238                 atomic_inc(&p->cred->user->processes);
239                 return 0;
240         }
241
242         new = prepare_creds();
243         if (!new)
244                 return -ENOMEM;
245
246 #ifdef CONFIG_KEYS
247         /* new threads get their own thread keyrings if their parent already
248          * had one */
249         if (new->thread_keyring) {
250                 key_put(new->thread_keyring);
251                 new->thread_keyring = NULL;
252                 if (clone_flags & CLONE_THREAD)
253                         install_thread_keyring_to_cred(new);
254         }
255
256         /* we share the process and session keyrings between all the threads in
257          * a process - this is slightly icky as we violate COW credentials a
258          * bit */
259         if (!(clone_flags & CLONE_THREAD)) {
260                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
261                 if (!tgcred) {
262                         put_cred(new);
263                         return -ENOMEM;
264                 }
265                 atomic_set(&tgcred->usage, 1);
266                 spin_lock_init(&tgcred->lock);
267                 tgcred->process_keyring = NULL;
268                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
269
270                 release_tgcred(new);
271                 new->tgcred = tgcred;
272         }
273 #endif
274
275         atomic_inc(&new->user->processes);
276         p->cred = new;
277         return 0;
278 }
279
280 /**
281  * commit_creds - Install new credentials upon the current task
282  * @new: The credentials to be assigned
283  *
284  * Install a new set of credentials to the current task, using RCU to replace
285  * the old set.
286  *
287  * This function eats the caller's reference to the new credentials.
288  *
289  * Always returns 0 thus allowing this function to be tail-called at the end
290  * of, say, sys_setgid().
291  */
292 int commit_creds(struct cred *new)
293 {
294         struct task_struct *task = current;
295         const struct cred *old;
296
297         BUG_ON(atomic_read(&new->usage) < 1);
298         BUG_ON(atomic_read(&task->cred->usage) < 1);
299
300         old = task->cred;
301         security_commit_creds(new, old);
302
303         /* dumpability changes */
304         if (old->euid != new->euid ||
305             old->egid != new->egid ||
306             old->fsuid != new->fsuid ||
307             old->fsgid != new->fsgid ||
308             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
309                 set_dumpable(task->mm, suid_dumpable);
310                 task->pdeath_signal = 0;
311                 smp_wmb();
312         }
313
314         /* alter the thread keyring */
315         if (new->fsuid != old->fsuid)
316                 key_fsuid_changed(task);
317         if (new->fsgid != old->fsgid)
318                 key_fsgid_changed(task);
319
320         /* do it
321          * - What if a process setreuid()'s and this brings the
322          *   new uid over his NPROC rlimit?  We can check this now
323          *   cheaply with the new uid cache, so if it matters
324          *   we should be checking for it.  -DaveM
325          */
326         if (new->user != old->user)
327                 atomic_inc(&new->user->processes);
328         rcu_assign_pointer(task->cred, new);
329         if (new->user != old->user)
330                 atomic_dec(&old->user->processes);
331
332         sched_switch_user(task);
333
334         /* send notifications */
335         if (new->uid   != old->uid  ||
336             new->euid  != old->euid ||
337             new->suid  != old->suid ||
338             new->fsuid != old->fsuid)
339                 proc_id_connector(task, PROC_EVENT_UID);
340
341         if (new->gid   != old->gid  ||
342             new->egid  != old->egid ||
343             new->sgid  != old->sgid ||
344             new->fsgid != old->fsgid)
345                 proc_id_connector(task, PROC_EVENT_GID);
346
347         put_cred(old);
348         return 0;
349 }
350 EXPORT_SYMBOL(commit_creds);
351
352 /**
353  * abort_creds - Discard a set of credentials and unlock the current task
354  * @new: The credentials that were going to be applied
355  *
356  * Discard a set of credentials that were under construction and unlock the
357  * current task.
358  */
359 void abort_creds(struct cred *new)
360 {
361         BUG_ON(atomic_read(&new->usage) < 1);
362         put_cred(new);
363 }
364 EXPORT_SYMBOL(abort_creds);
365
366 /**
367  * override_creds - Temporarily override the current process's credentials
368  * @new: The credentials to be assigned
369  *
370  * Install a set of temporary override credentials on the current process,
371  * returning the old set for later reversion.
372  */
373 const struct cred *override_creds(const struct cred *new)
374 {
375         const struct cred *old = current->cred;
376
377         rcu_assign_pointer(current->cred, get_cred(new));
378         return old;
379 }
380 EXPORT_SYMBOL(override_creds);
381
382 /**
383  * revert_creds - Revert a temporary credentials override
384  * @old: The credentials to be restored
385  *
386  * Revert a temporary set of override credentials to an old set, discarding the
387  * override set.
388  */
389 void revert_creds(const struct cred *old)
390 {
391         const struct cred *override = current->cred;
392
393         rcu_assign_pointer(current->cred, old);
394         put_cred(override);
395 }
396 EXPORT_SYMBOL(revert_creds);
397
398 /*
399  * initialise the credentials stuff
400  */
401 void __init cred_init(void)
402 {
403         /* allocate a slab in which we can store credentials */
404         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
405                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
406 }