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-rw-r--r--kernel/cred.c588
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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
21static struct kmem_cache *cred_jar;
22
23/*
24 * 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/*
35 * The initial credentials for the initial task
36 */
37struct 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
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 */
71static 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 */
84static 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 */
107void __put_cred(struct cred *cred)
108{
109 BUG_ON(atomic_read(&cred->usage) != 0);
110
111 call_rcu(&cred->rcu, put_cred_rcu);
112}
113EXPORT_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 */
129struct 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
162error:
163 abort_creds(new);
164 return NULL;
165}
166EXPORT_SYMBOL(prepare_creds);
167
168/*
169 * Prepare credentials for current to perform an execve()
170 * - The caller must hold current->cred_exec_mutex
171 */
172struct 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 */
215struct 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
257error:
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 */
271int 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
336error_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 */
355int 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 set_dumpable(task->mm, suid_dumpable);
376 task->pdeath_signal = 0;
377 smp_wmb();
378 }
379
380 /* alter the thread keyring */
381 if (new->fsuid != old->fsuid)
382 key_fsuid_changed(task);
383 if (new->fsgid != old->fsgid)
384 key_fsgid_changed(task);
385
386 /* do it
387 * - What if a process setreuid()'s and this brings the
388 * new uid over his NPROC rlimit? We can check this now
389 * cheaply with the new uid cache, so if it matters
390 * we should be checking for it. -DaveM
391 */
392 if (new->user != old->user)
393 atomic_inc(&new->user->processes);
394 rcu_assign_pointer(task->real_cred, new);
395 rcu_assign_pointer(task->cred, new);
396 if (new->user != old->user)
397 atomic_dec(&old->user->processes);
398
399 sched_switch_user(task);
400
401 /* send notifications */
402 if (new->uid != old->uid ||
403 new->euid != old->euid ||
404 new->suid != old->suid ||
405 new->fsuid != old->fsuid)
406 proc_id_connector(task, PROC_EVENT_UID);
407
408 if (new->gid != old->gid ||
409 new->egid != old->egid ||
410 new->sgid != old->sgid ||
411 new->fsgid != old->fsgid)
412 proc_id_connector(task, PROC_EVENT_GID);
413
414 /* release the old obj and subj refs both */
415 put_cred(old);
416 put_cred(old);
417 return 0;
418}
419EXPORT_SYMBOL(commit_creds);
420
421/**
422 * abort_creds - Discard a set of credentials and unlock the current task
423 * @new: The credentials that were going to be applied
424 *
425 * Discard a set of credentials that were under construction and unlock the
426 * current task.
427 */
428void abort_creds(struct cred *new)
429{
430 BUG_ON(atomic_read(&new->usage) < 1);
431 put_cred(new);
432}
433EXPORT_SYMBOL(abort_creds);
434
435/**
436 * override_creds - Override the current process's subjective credentials
437 * @new: The credentials to be assigned
438 *
439 * Install a set of temporary override subjective credentials on the current
440 * process, returning the old set for later reversion.
441 */
442const struct cred *override_creds(const struct cred *new)
443{
444 const struct cred *old = current->cred;
445
446 rcu_assign_pointer(current->cred, get_cred(new));
447 return old;
448}
449EXPORT_SYMBOL(override_creds);
450
451/**
452 * revert_creds - Revert a temporary subjective credentials override
453 * @old: The credentials to be restored
454 *
455 * Revert a temporary set of override subjective credentials to an old set,
456 * discarding the override set.
457 */
458void revert_creds(const struct cred *old)
459{
460 const struct cred *override = current->cred;
461
462 rcu_assign_pointer(current->cred, old);
463 put_cred(override);
464}
465EXPORT_SYMBOL(revert_creds);
466
467/*
468 * initialise the credentials stuff
469 */
470void __init cred_init(void)
471{
472 /* allocate a slab in which we can store credentials */
473 cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
474 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
475}
476
477/**
478 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
479 * @daemon: A userspace daemon to be used as a reference
480 *
481 * Prepare a set of credentials for a kernel service. This can then be used to
482 * override a task's own credentials so that work can be done on behalf of that
483 * task that requires a different subjective context.
484 *
485 * @daemon is used to provide a base for the security record, but can be NULL.
486 * If @daemon is supplied, then the security data will be derived from that;
487 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
488 *
489 * The caller may change these controls afterwards if desired.
490 *
491 * Returns the new credentials or NULL if out of memory.
492 *
493 * Does not take, and does not return holding current->cred_replace_mutex.
494 */
495struct cred *prepare_kernel_cred(struct task_struct *daemon)
496{
497 const struct cred *old;
498 struct cred *new;
499
500 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
501 if (!new)
502 return NULL;
503
504 if (daemon)
505 old = get_task_cred(daemon);
506 else
507 old = get_cred(&init_cred);
508
509 get_uid(new->user);
510 get_group_info(new->group_info);
511
512#ifdef CONFIG_KEYS
513 atomic_inc(&init_tgcred.usage);
514 new->tgcred = &init_tgcred;
515 new->request_key_auth = NULL;
516 new->thread_keyring = NULL;
517 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
518#endif
519
520#ifdef CONFIG_SECURITY
521 new->security = NULL;
522#endif
523 if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
524 goto error;
525
526 atomic_set(&new->usage, 1);
527 put_cred(old);
528 return new;
529
530error:
531 put_cred(new);
532 return NULL;
533}
534EXPORT_SYMBOL(prepare_kernel_cred);
535
536/**
537 * set_security_override - Set the security ID in a set of credentials
538 * @new: The credentials to alter
539 * @secid: The LSM security ID to set
540 *
541 * Set the LSM security ID in a set of credentials so that the subjective
542 * security is overridden when an alternative set of credentials is used.
543 */
544int set_security_override(struct cred *new, u32 secid)
545{
546 return security_kernel_act_as(new, secid);
547}
548EXPORT_SYMBOL(set_security_override);
549
550/**
551 * set_security_override_from_ctx - Set the security ID in a set of credentials
552 * @new: The credentials to alter
553 * @secctx: The LSM security context to generate the security ID from.
554 *
555 * Set the LSM security ID in a set of credentials so that the subjective
556 * security is overridden when an alternative set of credentials is used. The
557 * security ID is specified in string form as a security context to be
558 * interpreted by the LSM.
559 */
560int set_security_override_from_ctx(struct cred *new, const char *secctx)
561{
562 u32 secid;
563 int ret;
564
565 ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
566 if (ret < 0)
567 return ret;
568
569 return set_security_override(new, secid);
570}
571EXPORT_SYMBOL(set_security_override_from_ctx);
572
573/**
574 * set_create_files_as - Set the LSM file create context in a set of credentials
575 * @new: The credentials to alter
576 * @inode: The inode to take the context from
577 *
578 * Change the LSM file creation context in a set of credentials to be the same
579 * as the object context of the specified inode, so that the new inodes have
580 * the same MAC context as that inode.
581 */
582int set_create_files_as(struct cred *new, struct inode *inode)
583{
584 new->fsuid = inode->i_uid;
585 new->fsgid = inode->i_gid;
586 return security_kernel_create_files_as(new, inode);
587}
588EXPORT_SYMBOL(set_create_files_as);