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1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Task credentials management - see Documentation/security/credentials.rst
3 *
4 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells ([email protected])
6 */
7
8#define pr_fmt(fmt) "CRED: " fmt
9
10#include <linux/export.h>
11#include <linux/cred.h>
12#include <linux/slab.h>
13#include <linux/sched.h>
14#include <linux/sched/coredump.h>
15#include <linux/key.h>
16#include <linux/keyctl.h>
17#include <linux/init_task.h>
18#include <linux/security.h>
19#include <linux/binfmts.h>
20#include <linux/cn_proc.h>
21#include <linux/uidgid.h>
22
23#if 0
24#define kdebug(FMT, ...) \
25 printk("[%-5.5s%5u] " FMT "\n", \
26 current->comm, current->pid, ##__VA_ARGS__)
27#else
28#define kdebug(FMT, ...) \
29do { \
30 if (0) \
31 no_printk("[%-5.5s%5u] " FMT "\n", \
32 current->comm, current->pid, ##__VA_ARGS__); \
33} while (0)
34#endif
35
36static struct kmem_cache *cred_jar;
37
38/*
39 * The RCU callback to actually dispose of a set of credentials
40 */
41static void put_cred_rcu(struct rcu_head *rcu)
42{
43 struct cred *cred = container_of(rcu, struct cred, rcu);
44
45 kdebug("put_cred_rcu(%p)", cred);
46
47 if (atomic_long_read(&cred->usage) != 0)
48 panic("CRED: put_cred_rcu() sees %p with usage %ld\n",
49 cred, atomic_long_read(&cred->usage));
50
51 security_cred_free(cred);
52 key_put(cred->session_keyring);
53 key_put(cred->process_keyring);
54 key_put(cred->thread_keyring);
55 key_put(cred->request_key_auth);
56 if (cred->group_info)
57 put_group_info(cred->group_info);
58 free_uid(cred->user);
59 if (cred->ucounts)
60 put_ucounts(cred->ucounts);
61 put_user_ns(cred->user_ns);
62 kmem_cache_free(cred_jar, cred);
63}
64
65/**
66 * __put_cred - Destroy a set of credentials
67 * @cred: The record to release
68 *
69 * Destroy a set of credentials on which no references remain.
70 */
71void __put_cred(struct cred *cred)
72{
73 kdebug("__put_cred(%p{%ld})", cred,
74 atomic_long_read(&cred->usage));
75
76 BUG_ON(atomic_long_read(&cred->usage) != 0);
77 BUG_ON(cred == current->cred);
78 BUG_ON(cred == current->real_cred);
79
80 if (cred->non_rcu)
81 put_cred_rcu(&cred->rcu);
82 else
83 call_rcu(&cred->rcu, put_cred_rcu);
84}
85EXPORT_SYMBOL(__put_cred);
86
87/*
88 * Clean up a task's credentials when it exits
89 */
90void exit_creds(struct task_struct *tsk)
91{
92 struct cred *real_cred, *cred;
93
94 kdebug("exit_creds(%u,%p,%p,{%ld})", tsk->pid, tsk->real_cred, tsk->cred,
95 atomic_long_read(&tsk->cred->usage));
96
97 real_cred = (struct cred *) tsk->real_cred;
98 tsk->real_cred = NULL;
99
100 cred = (struct cred *) tsk->cred;
101 tsk->cred = NULL;
102
103 if (real_cred == cred) {
104 put_cred_many(cred, 2);
105 } else {
106 put_cred(real_cred);
107 put_cred(cred);
108 }
109
110#ifdef CONFIG_KEYS_REQUEST_CACHE
111 key_put(tsk->cached_requested_key);
112 tsk->cached_requested_key = NULL;
113#endif
114}
115
116/**
117 * get_task_cred - Get another task's objective credentials
118 * @task: The task to query
119 *
120 * Get the objective credentials of a task, pinning them so that they can't go
121 * away. Accessing a task's credentials directly is not permitted.
122 *
123 * The caller must also make sure task doesn't get deleted, either by holding a
124 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
125 */
126const struct cred *get_task_cred(struct task_struct *task)
127{
128 const struct cred *cred;
129
130 rcu_read_lock();
131
132 do {
133 cred = __task_cred((task));
134 BUG_ON(!cred);
135 } while (!get_cred_rcu(cred));
136
137 rcu_read_unlock();
138 return cred;
139}
140EXPORT_SYMBOL(get_task_cred);
141
142/*
143 * Allocate blank credentials, such that the credentials can be filled in at a
144 * later date without risk of ENOMEM.
145 */
146struct cred *cred_alloc_blank(void)
147{
148 struct cred *new;
149
150 new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
151 if (!new)
152 return NULL;
153
154 atomic_long_set(&new->usage, 1);
155 if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
156 goto error;
157
158 return new;
159
160error:
161 abort_creds(new);
162 return NULL;
163}
164
165/**
166 * prepare_creds - Prepare a new set of credentials for modification
167 *
168 * Prepare a new set of task credentials for modification. A task's creds
169 * shouldn't generally be modified directly, therefore this function is used to
170 * prepare a new copy, which the caller then modifies and then commits by
171 * calling commit_creds().
172 *
173 * Preparation involves making a copy of the objective creds for modification.
174 *
175 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
176 *
177 * Call commit_creds() or abort_creds() to clean up.
178 */
179struct cred *prepare_creds(void)
180{
181 struct task_struct *task = current;
182 const struct cred *old;
183 struct cred *new;
184
185 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
186 if (!new)
187 return NULL;
188
189 kdebug("prepare_creds() alloc %p", new);
190
191 old = task->cred;
192 memcpy(new, old, sizeof(struct cred));
193
194 new->non_rcu = 0;
195 atomic_long_set(&new->usage, 1);
196 get_group_info(new->group_info);
197 get_uid(new->user);
198 get_user_ns(new->user_ns);
199
200#ifdef CONFIG_KEYS
201 key_get(new->session_keyring);
202 key_get(new->process_keyring);
203 key_get(new->thread_keyring);
204 key_get(new->request_key_auth);
205#endif
206
207#ifdef CONFIG_SECURITY
208 new->security = NULL;
209#endif
210
211 new->ucounts = get_ucounts(new->ucounts);
212 if (!new->ucounts)
213 goto error;
214
215 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
216 goto error;
217
218 return new;
219
220error:
221 abort_creds(new);
222 return NULL;
223}
224EXPORT_SYMBOL(prepare_creds);
225
226/*
227 * Prepare credentials for current to perform an execve()
228 * - The caller must hold ->cred_guard_mutex
229 */
230struct cred *prepare_exec_creds(void)
231{
232 struct cred *new;
233
234 new = prepare_creds();
235 if (!new)
236 return new;
237
238#ifdef CONFIG_KEYS
239 /* newly exec'd tasks don't get a thread keyring */
240 key_put(new->thread_keyring);
241 new->thread_keyring = NULL;
242
243 /* inherit the session keyring; new process keyring */
244 key_put(new->process_keyring);
245 new->process_keyring = NULL;
246#endif
247
248 new->suid = new->fsuid = new->euid;
249 new->sgid = new->fsgid = new->egid;
250
251 return new;
252}
253
254/*
255 * Copy credentials for the new process created by fork()
256 *
257 * We share if we can, but under some circumstances we have to generate a new
258 * set.
259 *
260 * The new process gets the current process's subjective credentials as its
261 * objective and subjective credentials
262 */
263int copy_creds(struct task_struct *p, u64 clone_flags)
264{
265 struct cred *new;
266 int ret;
267
268#ifdef CONFIG_KEYS_REQUEST_CACHE
269 p->cached_requested_key = NULL;
270#endif
271
272 if (
273#ifdef CONFIG_KEYS
274 !p->cred->thread_keyring &&
275#endif
276 clone_flags & CLONE_THREAD
277 ) {
278 p->real_cred = get_cred_many(p->cred, 2);
279 kdebug("share_creds(%p{%ld})",
280 p->cred, atomic_long_read(&p->cred->usage));
281 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
282 get_cred_namespaces(p);
283 return 0;
284 }
285
286 new = prepare_creds();
287 if (!new)
288 return -ENOMEM;
289
290 if (clone_flags & CLONE_NEWUSER) {
291 ret = create_user_ns(new);
292 if (ret < 0)
293 goto error_put;
294 ret = set_cred_ucounts(new);
295 if (ret < 0)
296 goto error_put;
297 }
298
299#ifdef CONFIG_KEYS
300 /* new threads get their own thread keyrings if their parent already
301 * had one */
302 if (new->thread_keyring) {
303 key_put(new->thread_keyring);
304 new->thread_keyring = NULL;
305 if (clone_flags & CLONE_THREAD)
306 install_thread_keyring_to_cred(new);
307 }
308
309 /* The process keyring is only shared between the threads in a process;
310 * anything outside of those threads doesn't inherit.
311 */
312 if (!(clone_flags & CLONE_THREAD)) {
313 key_put(new->process_keyring);
314 new->process_keyring = NULL;
315 }
316#endif
317
318 p->cred = p->real_cred = get_cred(new);
319 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
320 get_cred_namespaces(p);
321
322 return 0;
323
324error_put:
325 put_cred(new);
326 return ret;
327}
328
329static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
330{
331 const struct user_namespace *set_ns = set->user_ns;
332 const struct user_namespace *subset_ns = subset->user_ns;
333
334 /* If the two credentials are in the same user namespace see if
335 * the capabilities of subset are a subset of set.
336 */
337 if (set_ns == subset_ns)
338 return cap_issubset(subset->cap_permitted, set->cap_permitted);
339
340 /* The credentials are in a different user namespaces
341 * therefore one is a subset of the other only if a set is an
342 * ancestor of subset and set->euid is owner of subset or one
343 * of subsets ancestors.
344 */
345 for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
346 if ((set_ns == subset_ns->parent) &&
347 uid_eq(subset_ns->owner, set->euid))
348 return true;
349 }
350
351 return false;
352}
353
354/**
355 * commit_creds - Install new credentials upon the current task
356 * @new: The credentials to be assigned
357 *
358 * Install a new set of credentials to the current task, using RCU to replace
359 * the old set. Both the objective and the subjective credentials pointers are
360 * updated. This function may not be called if the subjective credentials are
361 * in an overridden state.
362 *
363 * This function eats the caller's reference to the new credentials.
364 *
365 * Always returns 0 thus allowing this function to be tail-called at the end
366 * of, say, sys_setgid().
367 */
368int commit_creds(struct cred *new)
369{
370 struct task_struct *task = current;
371 const struct cred *old = task->real_cred;
372
373 kdebug("commit_creds(%p{%ld})", new,
374 atomic_long_read(&new->usage));
375
376 BUG_ON(task->cred != old);
377 BUG_ON(atomic_long_read(&new->usage) < 1);
378
379 get_cred(new); /* we will require a ref for the subj creds too */
380
381 /* dumpability changes */
382 if (!uid_eq(old->euid, new->euid) ||
383 !gid_eq(old->egid, new->egid) ||
384 !uid_eq(old->fsuid, new->fsuid) ||
385 !gid_eq(old->fsgid, new->fsgid) ||
386 !cred_cap_issubset(old, new)) {
387 /* mm-less tasks share init_task's exec_state */
388 if (task->mm)
389 task_exec_state_set_dumpable(suid_dumpable);
390 task->pdeath_signal = 0;
391 /*
392 * If a task drops privileges and becomes nondumpable,
393 * the dumpability change must become visible before
394 * the credential change; otherwise, a __ptrace_may_access()
395 * racing with this change may be able to attach to a task it
396 * shouldn't be able to attach to (as if the task had dropped
397 * privileges without becoming nondumpable).
398 * Pairs with a read barrier in __ptrace_may_access().
399 */
400 smp_wmb();
401 }
402
403 /* alter the thread keyring */
404 if (!uid_eq(new->fsuid, old->fsuid))
405 key_fsuid_changed(new);
406 if (!gid_eq(new->fsgid, old->fsgid))
407 key_fsgid_changed(new);
408
409 /* do it
410 * RLIMIT_NPROC limits on user->processes have already been checked
411 * in set_user().
412 */
413 if (new->user != old->user || new->user_ns != old->user_ns)
414 inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
415
416 rcu_assign_pointer(task->real_cred, new);
417 rcu_assign_pointer(task->cred, new);
418 if (new->user != old->user || new->user_ns != old->user_ns)
419 dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
420 if (new->user_ns != old->user_ns)
421 switch_cred_namespaces(old, new);
422
423 /* send notifications */
424 if (!uid_eq(new->uid, old->uid) ||
425 !uid_eq(new->euid, old->euid) ||
426 !uid_eq(new->suid, old->suid) ||
427 !uid_eq(new->fsuid, old->fsuid))
428 proc_id_connector(task, PROC_EVENT_UID);
429
430 if (!gid_eq(new->gid, old->gid) ||
431 !gid_eq(new->egid, old->egid) ||
432 !gid_eq(new->sgid, old->sgid) ||
433 !gid_eq(new->fsgid, old->fsgid))
434 proc_id_connector(task, PROC_EVENT_GID);
435
436 /* release the old obj and subj refs both */
437 put_cred_many(old, 2);
438 return 0;
439}
440EXPORT_SYMBOL(commit_creds);
441
442/**
443 * abort_creds - Discard a set of credentials and unlock the current task
444 * @new: The credentials that were going to be applied
445 *
446 * Discard a set of credentials that were under construction and unlock the
447 * current task.
448 */
449void abort_creds(struct cred *new)
450{
451 kdebug("abort_creds(%p{%ld})", new,
452 atomic_long_read(&new->usage));
453
454 BUG_ON(atomic_long_read(&new->usage) < 1);
455 put_cred(new);
456}
457EXPORT_SYMBOL(abort_creds);
458
459/**
460 * cred_fscmp - Compare two credentials with respect to filesystem access.
461 * @a: The first credential
462 * @b: The second credential
463 *
464 * cred_cmp() will return zero if both credentials have the same
465 * fsuid, fsgid, and supplementary groups. That is, if they will both
466 * provide the same access to files based on mode/uid/gid.
467 * If the credentials are different, then either -1 or 1 will
468 * be returned depending on whether @a comes before or after @b
469 * respectively in an arbitrary, but stable, ordering of credentials.
470 *
471 * Return: -1, 0, or 1 depending on comparison
472 */
473int cred_fscmp(const struct cred *a, const struct cred *b)
474{
475 struct group_info *ga, *gb;
476 int g;
477
478 if (a == b)
479 return 0;
480 if (uid_lt(a->fsuid, b->fsuid))
481 return -1;
482 if (uid_gt(a->fsuid, b->fsuid))
483 return 1;
484
485 if (gid_lt(a->fsgid, b->fsgid))
486 return -1;
487 if (gid_gt(a->fsgid, b->fsgid))
488 return 1;
489
490 ga = a->group_info;
491 gb = b->group_info;
492 if (ga == gb)
493 return 0;
494 if (ga == NULL)
495 return -1;
496 if (gb == NULL)
497 return 1;
498 if (ga->ngroups < gb->ngroups)
499 return -1;
500 if (ga->ngroups > gb->ngroups)
501 return 1;
502
503 for (g = 0; g < ga->ngroups; g++) {
504 if (gid_lt(ga->gid[g], gb->gid[g]))
505 return -1;
506 if (gid_gt(ga->gid[g], gb->gid[g]))
507 return 1;
508 }
509 return 0;
510}
511EXPORT_SYMBOL(cred_fscmp);
512
513int set_cred_ucounts(struct cred *new)
514{
515 struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
516
517 /*
518 * This optimization is needed because alloc_ucounts() uses locks
519 * for table lookups.
520 */
521 if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid))
522 return 0;
523
524 if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid)))
525 return -EAGAIN;
526
527 new->ucounts = new_ucounts;
528 put_ucounts(old_ucounts);
529
530 return 0;
531}
532
533/*
534 * initialise the credentials stuff
535 */
536void __init cred_init(void)
537{
538 /* allocate a slab in which we can store credentials */
539 cred_jar = KMEM_CACHE(cred,
540 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
541}
542
543/**
544 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
545 * @daemon: A userspace daemon to be used as a reference
546 *
547 * Prepare a set of credentials for a kernel service. This can then be used to
548 * override a task's own credentials so that work can be done on behalf of that
549 * task that requires a different subjective context.
550 *
551 * @daemon is used to provide a base cred, with the security data derived from
552 * that; if this is "&init_task", they'll be set to 0, no groups, full
553 * capabilities, and no keys.
554 *
555 * The caller may change these controls afterwards if desired.
556 *
557 * Returns the new credentials or NULL if out of memory.
558 */
559struct cred *prepare_kernel_cred(struct task_struct *daemon)
560{
561 const struct cred *old;
562 struct cred *new;
563
564 if (WARN_ON_ONCE(!daemon))
565 return NULL;
566
567 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
568 if (!new)
569 return NULL;
570
571 kdebug("prepare_kernel_cred() alloc %p", new);
572
573 old = get_task_cred(daemon);
574
575 *new = *old;
576 new->non_rcu = 0;
577 atomic_long_set(&new->usage, 1);
578 get_uid(new->user);
579 get_user_ns(new->user_ns);
580 get_group_info(new->group_info);
581
582#ifdef CONFIG_KEYS
583 new->session_keyring = NULL;
584 new->process_keyring = NULL;
585 new->thread_keyring = NULL;
586 new->request_key_auth = NULL;
587 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
588#endif
589
590#ifdef CONFIG_SECURITY
591 new->security = NULL;
592#endif
593 new->ucounts = get_ucounts(new->ucounts);
594 if (!new->ucounts)
595 goto error;
596
597 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
598 goto error;
599
600 put_cred(old);
601 return new;
602
603error:
604 put_cred(new);
605 put_cred(old);
606 return NULL;
607}
608EXPORT_SYMBOL(prepare_kernel_cred);
609
610/**
611 * set_security_override - Set the security ID in a set of credentials
612 * @new: The credentials to alter
613 * @secid: The LSM security ID to set
614 *
615 * Set the LSM security ID in a set of credentials so that the subjective
616 * security is overridden when an alternative set of credentials is used.
617 */
618int set_security_override(struct cred *new, u32 secid)
619{
620 return security_kernel_act_as(new, secid);
621}
622EXPORT_SYMBOL(set_security_override);
623
624/**
625 * set_create_files_as - Set the LSM file create context in a set of credentials
626 * @new: The credentials to alter
627 * @inode: The inode to take the context from
628 *
629 * Change the LSM file creation context in a set of credentials to be the same
630 * as the object context of the specified inode, so that the new inodes have
631 * the same MAC context as that inode.
632 */
633int set_create_files_as(struct cred *new, struct inode *inode)
634{
635 if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
636 return -EINVAL;
637 new->fsuid = inode->i_uid;
638 new->fsgid = inode->i_gid;
639 return security_kernel_create_files_as(new, inode);
640}
641EXPORT_SYMBOL(set_create_files_as);