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 (dhowells@redhat.com)
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(v: &cred->usage) != 0)
48 panic(fmt: "CRED: put_cred_rcu() sees %p with usage %ld\n",
49 cred, atomic_long_read(v: &cred->usage));
50
51 security_cred_free(cred);
52 key_put(key: cred->session_keyring);
53 key_put(key: cred->process_keyring);
54 key_put(key: cred->thread_keyring);
55 key_put(key: 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(ucounts: cred->ucounts);
61 put_user_ns(ns: cred->user_ns);
62 kmem_cache_free(s: cred_jar, objp: 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(rcu: &cred->rcu);
82 else
83 call_rcu(head: &cred->rcu, func: 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: cred, nr: 2);
105 } else {
106 put_cred(cred: real_cred);
107 put_cred(cred);
108 }
109
110#ifdef CONFIG_KEYS_REQUEST_CACHE
111 key_put(key: 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(v: &new->usage, i: 1);
155 if (security_cred_alloc_blank(cred: 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(v: &new->usage, i: 1);
196 get_group_info(gi: new->group_info);
197 get_uid(u: new->user);
198 get_user_ns(ns: new->user_ns);
199
200#ifdef CONFIG_KEYS
201 key_get(key: new->session_keyring);
202 key_get(key: new->process_keyring);
203 key_get(key: new->thread_keyring);
204 key_get(key: new->request_key_auth);
205#endif
206
207#ifdef CONFIG_SECURITY
208 new->security = NULL;
209#endif
210
211 new->ucounts = get_ucounts(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(key: new->thread_keyring);
241 new->thread_keyring = NULL;
242
243 /* inherit the session keyring; new process keyring */
244 key_put(key: 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(cred: p->cred, nr: 2);
279 kdebug("share_creds(%p{%ld})",
280 p->cred, atomic_long_read(&p->cred->usage));
281 inc_rlimit_ucounts(task_ucounts(p), type: UCOUNT_RLIMIT_NPROC, v: 1);
282 get_cred_namespaces(tsk: 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(key: new->thread_keyring);
304 new->thread_keyring = NULL;
305 if (clone_flags & CLONE_THREAD)
306 install_thread_keyring_to_cred(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(key: new->process_keyring);
314 new->process_keyring = NULL;
315 }
316#endif
317
318 p->cred = p->real_cred = get_cred(cred: new);
319 inc_rlimit_ucounts(task_ucounts(p), type: UCOUNT_RLIMIT_NPROC, v: 1);
320 get_cred_namespaces(tsk: p);
321
322 return 0;
323
324error_put:
325 put_cred(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(a: subset->cap_permitted, set: 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(left: subset_ns->owner, right: 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(cred: new); /* we will require a ref for the subj creds too */
380
381 /* dumpability changes */
382 if (!uid_eq(left: old->euid, right: new->euid) ||
383 !gid_eq(left: old->egid, right: new->egid) ||
384 !uid_eq(left: old->fsuid, right: new->fsuid) ||
385 !gid_eq(left: old->fsgid, right: new->fsgid) ||
386 !cred_cap_issubset(set: old, subset: new)) {
387 if (task->mm)
388 set_dumpable(mm: task->mm, value: suid_dumpable);
389 task->pdeath_signal = 0;
390 /*
391 * If a task drops privileges and becomes nondumpable,
392 * the dumpability change must become visible before
393 * the credential change; otherwise, a __ptrace_may_access()
394 * racing with this change may be able to attach to a task it
395 * shouldn't be able to attach to (as if the task had dropped
396 * privileges without becoming nondumpable).
397 * Pairs with a read barrier in __ptrace_may_access().
398 */
399 smp_wmb();
400 }
401
402 /* alter the thread keyring */
403 if (!uid_eq(left: new->fsuid, right: old->fsuid))
404 key_fsuid_changed(new_cred: new);
405 if (!gid_eq(left: new->fsgid, right: old->fsgid))
406 key_fsgid_changed(new_cred: new);
407
408 /* do it
409 * RLIMIT_NPROC limits on user->processes have already been checked
410 * in set_user().
411 */
412 if (new->user != old->user || new->user_ns != old->user_ns)
413 inc_rlimit_ucounts(ucounts: new->ucounts, type: UCOUNT_RLIMIT_NPROC, v: 1);
414
415 rcu_assign_pointer(task->real_cred, new);
416 rcu_assign_pointer(task->cred, new);
417 if (new->user != old->user || new->user_ns != old->user_ns)
418 dec_rlimit_ucounts(ucounts: old->ucounts, type: UCOUNT_RLIMIT_NPROC, v: 1);
419 if (new->user_ns != old->user_ns)
420 switch_cred_namespaces(old, new);
421
422 /* send notifications */
423 if (!uid_eq(left: new->uid, right: old->uid) ||
424 !uid_eq(left: new->euid, right: old->euid) ||
425 !uid_eq(left: new->suid, right: old->suid) ||
426 !uid_eq(left: new->fsuid, right: old->fsuid))
427 proc_id_connector(task, which_id: PROC_EVENT_UID);
428
429 if (!gid_eq(left: new->gid, right: old->gid) ||
430 !gid_eq(left: new->egid, right: old->egid) ||
431 !gid_eq(left: new->sgid, right: old->sgid) ||
432 !gid_eq(left: new->fsgid, right: old->fsgid))
433 proc_id_connector(task, which_id: PROC_EVENT_GID);
434
435 /* release the old obj and subj refs both */
436 put_cred_many(cred: old, nr: 2);
437 return 0;
438}
439EXPORT_SYMBOL(commit_creds);
440
441/**
442 * abort_creds - Discard a set of credentials and unlock the current task
443 * @new: The credentials that were going to be applied
444 *
445 * Discard a set of credentials that were under construction and unlock the
446 * current task.
447 */
448void abort_creds(struct cred *new)
449{
450 kdebug("abort_creds(%p{%ld})", new,
451 atomic_long_read(&new->usage));
452
453 BUG_ON(atomic_long_read(&new->usage) < 1);
454 put_cred(cred: new);
455}
456EXPORT_SYMBOL(abort_creds);
457
458/**
459 * cred_fscmp - Compare two credentials with respect to filesystem access.
460 * @a: The first credential
461 * @b: The second credential
462 *
463 * cred_cmp() will return zero if both credentials have the same
464 * fsuid, fsgid, and supplementary groups. That is, if they will both
465 * provide the same access to files based on mode/uid/gid.
466 * If the credentials are different, then either -1 or 1 will
467 * be returned depending on whether @a comes before or after @b
468 * respectively in an arbitrary, but stable, ordering of credentials.
469 *
470 * Return: -1, 0, or 1 depending on comparison
471 */
472int cred_fscmp(const struct cred *a, const struct cred *b)
473{
474 struct group_info *ga, *gb;
475 int g;
476
477 if (a == b)
478 return 0;
479 if (uid_lt(left: a->fsuid, right: b->fsuid))
480 return -1;
481 if (uid_gt(left: a->fsuid, right: b->fsuid))
482 return 1;
483
484 if (gid_lt(left: a->fsgid, right: b->fsgid))
485 return -1;
486 if (gid_gt(left: a->fsgid, right: b->fsgid))
487 return 1;
488
489 ga = a->group_info;
490 gb = b->group_info;
491 if (ga == gb)
492 return 0;
493 if (ga == NULL)
494 return -1;
495 if (gb == NULL)
496 return 1;
497 if (ga->ngroups < gb->ngroups)
498 return -1;
499 if (ga->ngroups > gb->ngroups)
500 return 1;
501
502 for (g = 0; g < ga->ngroups; g++) {
503 if (gid_lt(left: ga->gid[g], right: gb->gid[g]))
504 return -1;
505 if (gid_gt(left: ga->gid[g], right: gb->gid[g]))
506 return 1;
507 }
508 return 0;
509}
510EXPORT_SYMBOL(cred_fscmp);
511
512int set_cred_ucounts(struct cred *new)
513{
514 struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
515
516 /*
517 * This optimization is needed because alloc_ucounts() uses locks
518 * for table lookups.
519 */
520 if (old_ucounts->ns == new->user_ns && uid_eq(left: old_ucounts->uid, right: new->uid))
521 return 0;
522
523 if (!(new_ucounts = alloc_ucounts(ns: new->user_ns, uid: new->uid)))
524 return -EAGAIN;
525
526 new->ucounts = new_ucounts;
527 put_ucounts(ucounts: old_ucounts);
528
529 return 0;
530}
531
532/*
533 * initialise the credentials stuff
534 */
535void __init cred_init(void)
536{
537 /* allocate a slab in which we can store credentials */
538 cred_jar = KMEM_CACHE(cred,
539 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
540}
541
542/**
543 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
544 * @daemon: A userspace daemon to be used as a reference
545 *
546 * Prepare a set of credentials for a kernel service. This can then be used to
547 * override a task's own credentials so that work can be done on behalf of that
548 * task that requires a different subjective context.
549 *
550 * @daemon is used to provide a base cred, with the security data derived from
551 * that; if this is "&init_task", they'll be set to 0, no groups, full
552 * capabilities, and no keys.
553 *
554 * The caller may change these controls afterwards if desired.
555 *
556 * Returns the new credentials or NULL if out of memory.
557 */
558struct cred *prepare_kernel_cred(struct task_struct *daemon)
559{
560 const struct cred *old;
561 struct cred *new;
562
563 if (WARN_ON_ONCE(!daemon))
564 return NULL;
565
566 new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
567 if (!new)
568 return NULL;
569
570 kdebug("prepare_kernel_cred() alloc %p", new);
571
572 old = get_task_cred(daemon);
573
574 *new = *old;
575 new->non_rcu = 0;
576 atomic_long_set(v: &new->usage, i: 1);
577 get_uid(u: new->user);
578 get_user_ns(ns: new->user_ns);
579 get_group_info(gi: new->group_info);
580
581#ifdef CONFIG_KEYS
582 new->session_keyring = NULL;
583 new->process_keyring = NULL;
584 new->thread_keyring = NULL;
585 new->request_key_auth = NULL;
586 new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
587#endif
588
589#ifdef CONFIG_SECURITY
590 new->security = NULL;
591#endif
592 new->ucounts = get_ucounts(ucounts: new->ucounts);
593 if (!new->ucounts)
594 goto error;
595
596 if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
597 goto error;
598
599 put_cred(cred: old);
600 return new;
601
602error:
603 put_cred(cred: new);
604 put_cred(cred: old);
605 return NULL;
606}
607EXPORT_SYMBOL(prepare_kernel_cred);
608
609/**
610 * set_security_override - Set the security ID in a set of credentials
611 * @new: The credentials to alter
612 * @secid: The LSM security ID to set
613 *
614 * Set the LSM security ID in a set of credentials so that the subjective
615 * security is overridden when an alternative set of credentials is used.
616 */
617int set_security_override(struct cred *new, u32 secid)
618{
619 return security_kernel_act_as(new, secid);
620}
621EXPORT_SYMBOL(set_security_override);
622
623/**
624 * set_security_override_from_ctx - Set the security ID in a set of credentials
625 * @new: The credentials to alter
626 * @secctx: The LSM security context to generate the security ID from.
627 *
628 * Set the LSM security ID in a set of credentials so that the subjective
629 * security is overridden when an alternative set of credentials is used. The
630 * security ID is specified in string form as a security context to be
631 * interpreted by the LSM.
632 */
633int set_security_override_from_ctx(struct cred *new, const char *secctx)
634{
635 u32 secid;
636 int ret;
637
638 ret = security_secctx_to_secid(secdata: secctx, strlen(secctx), secid: &secid);
639 if (ret < 0)
640 return ret;
641
642 return set_security_override(new, secid);
643}
644EXPORT_SYMBOL(set_security_override_from_ctx);
645
646/**
647 * set_create_files_as - Set the LSM file create context in a set of credentials
648 * @new: The credentials to alter
649 * @inode: The inode to take the context from
650 *
651 * Change the LSM file creation context in a set of credentials to be the same
652 * as the object context of the specified inode, so that the new inodes have
653 * the same MAC context as that inode.
654 */
655int set_create_files_as(struct cred *new, struct inode *inode)
656{
657 if (!uid_valid(uid: inode->i_uid) || !gid_valid(gid: inode->i_gid))
658 return -EINVAL;
659 new->fsuid = inode->i_uid;
660 new->fsgid = inode->i_gid;
661 return security_kernel_create_files_as(new, inode);
662}
663EXPORT_SYMBOL(set_create_files_as);
664

source code of linux/kernel/cred.c