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David Howells98870ab2008-11-14 10:39:26 +11001/* Task credentials management - see Documentation/credentials.txt
David Howellsf1752ee2008-11-14 10:39:17 +11002 *
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>
David Howellsd84f4f92008-11-14 10:39:23 +110018#include <linux/cn_proc.h>
19#include "cred-internals.h"
20
21static struct kmem_cache *cred_jar;
David Howellsf1752ee2008-11-14 10:39:17 +110022
23/*
David Howellsbb952bb2008-11-14 10:39:20 +110024 * The common credentials for the initial task's thread group
25 */
26#ifdef CONFIG_KEYS
27static struct thread_group_cred init_tgcred = {
28 .usage = ATOMIC_INIT(2),
29 .tgid = 0,
30 .lock = SPIN_LOCK_UNLOCKED,
31};
32#endif
33
34/*
David Howellsf1752ee2008-11-14 10:39:17 +110035 * The initial credentials for the initial task
36 */
37struct 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,
David Howellsbb952bb2008-11-14 10:39:20 +110046#ifdef CONFIG_KEYS
47 .tgcred = &init_tgcred,
48#endif
David Howellsf1752ee2008-11-14 10:39:17 +110049};
50
51/*
David Howellsbb952bb2008-11-14 10:39:20 +110052 * Dispose of the shared task group credentials
53 */
54#ifdef CONFIG_KEYS
55static 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 */
David Howellsa6f76f22008-11-14 10:39:24 +110071static void release_tgcred(struct cred *cred)
David Howellsbb952bb2008-11-14 10:39:20 +110072{
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/*
David Howellsf1752ee2008-11-14 10:39:17 +110082 * The RCU callback to actually dispose of a set of credentials
83 */
84static void put_cred_rcu(struct rcu_head *rcu)
85{
86 struct cred *cred = container_of(rcu, struct cred, rcu);
87
David Howellsd84f4f92008-11-14 10:39:23 +110088 if (atomic_read(&cred->usage) != 0)
89 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
90 cred, atomic_read(&cred->usage));
David Howellsf1752ee2008-11-14 10:39:17 +110091
David Howellsd84f4f92008-11-14 10:39:23 +110092 security_cred_free(cred);
David Howellsf1752ee2008-11-14 10:39:17 +110093 key_put(cred->thread_keyring);
94 key_put(cred->request_key_auth);
David Howellsbb952bb2008-11-14 10:39:20 +110095 release_tgcred(cred);
David Howellsf1752ee2008-11-14 10:39:17 +110096 put_group_info(cred->group_info);
97 free_uid(cred->user);
David Howellsd84f4f92008-11-14 10:39:23 +110098 kmem_cache_free(cred_jar, cred);
David Howellsf1752ee2008-11-14 10:39:17 +110099}
100
101/**
102 * __put_cred - Destroy a set of credentials
David Howellsd84f4f92008-11-14 10:39:23 +1100103 * @cred: The record to release
David Howellsf1752ee2008-11-14 10:39:17 +1100104 *
105 * Destroy a set of credentials on which no references remain.
106 */
107void __put_cred(struct cred *cred)
108{
David Howellsd84f4f92008-11-14 10:39:23 +1100109 BUG_ON(atomic_read(&cred->usage) != 0);
110
David Howellsf1752ee2008-11-14 10:39:17 +1100111 call_rcu(&cred->rcu, put_cred_rcu);
112}
113EXPORT_SYMBOL(__put_cred);
114
David Howellsd84f4f92008-11-14 10:39:23 +1100115/**
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.
David Howellsf1752ee2008-11-14 10:39:17 +1100126 */
David Howellsd84f4f92008-11-14 10:39:23 +1100127struct cred *prepare_creds(void)
David Howellsf1752ee2008-11-14 10:39:17 +1100128{
David Howellsd84f4f92008-11-14 10:39:23 +1100129 struct task_struct *task = current;
130 const struct cred *old;
131 struct cred *new;
David Howellsf1752ee2008-11-14 10:39:17 +1100132
David Howellsd84f4f92008-11-14 10:39:23 +1100133 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);
David Howellsf1752ee2008-11-14 10:39:17 +1100145
David Howellsbb952bb2008-11-14 10:39:20 +1100146#ifdef CONFIG_KEYS
David Howellsd84f4f92008-11-14 10:39:23 +1100147 key_get(new->thread_keyring);
148 key_get(new->request_key_auth);
149 atomic_inc(&new->tgcred->usage);
David Howellsbb952bb2008-11-14 10:39:20 +1100150#endif
151
David Howellsf1752ee2008-11-14 10:39:17 +1100152#ifdef CONFIG_SECURITY
David Howellsd84f4f92008-11-14 10:39:23 +1100153 new->security = NULL;
David Howellsf1752ee2008-11-14 10:39:17 +1100154#endif
155
David Howellsd84f4f92008-11-14 10:39:23 +1100156 if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
157 goto error;
158 return new;
159
160error:
161 abort_creds(new);
162 return NULL;
163}
164EXPORT_SYMBOL(prepare_creds);
165
166/*
David Howellsa6f76f22008-11-14 10:39:24 +1100167 * Prepare credentials for current to perform an execve()
168 * - The caller must hold current->cred_exec_mutex
169 */
170struct 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/*
David Howellsd84f4f92008-11-14 10:39:23 +1100211 * prepare new credentials for the usermode helper dispatcher
212 */
213struct 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
255error:
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 */
266int 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;
David Howellsf1752ee2008-11-14 10:39:17 +1100284 }
285
David Howellsd84f4f92008-11-14 10:39:23 +1100286 new = prepare_creds();
287 if (!new)
288 return -ENOMEM;
David Howellsf1752ee2008-11-14 10:39:17 +1100289
David Howellsd84f4f92008-11-14 10:39:23 +1100290#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 }
David Howellsf1752ee2008-11-14 10:39:17 +1100299
David Howellsd84f4f92008-11-14 10:39:23 +1100300 /* 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;
David Howellsf1752ee2008-11-14 10:39:17 +1100321 return 0;
322}
David Howellsd84f4f92008-11-14 10:39:23 +1100323
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 */
336int 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}
394EXPORT_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 */
403void abort_creds(struct cred *new)
404{
405 BUG_ON(atomic_read(&new->usage) < 1);
406 put_cred(new);
407}
408EXPORT_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 */
417const 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}
424EXPORT_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 */
433void 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}
440EXPORT_SYMBOL(revert_creds);
441
442/*
443 * initialise the credentials stuff
444 */
445void __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}