1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Landlock LSM - Filesystem management and hooks
4 *
5 * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
6 * Copyright © 2018-2020 ANSSI
7 * Copyright © 2021-2022 Microsoft Corporation
8 * Copyright © 2022 Günther Noack <gnoack3000@gmail.com>
9 * Copyright © 2023-2024 Google LLC
10 */
11
12 #include <asm/ioctls.h>
13 #include <kunit/test.h>
14 #include <linux/atomic.h>
15 #include <linux/bitops.h>
16 #include <linux/bits.h>
17 #include <linux/compiler_types.h>
18 #include <linux/dcache.h>
19 #include <linux/err.h>
20 #include <linux/falloc.h>
21 #include <linux/fs.h>
22 #include <linux/init.h>
23 #include <linux/kernel.h>
24 #include <linux/limits.h>
25 #include <linux/list.h>
26 #include <linux/lsm_hooks.h>
27 #include <linux/mount.h>
28 #include <linux/namei.h>
29 #include <linux/path.h>
30 #include <linux/rcupdate.h>
31 #include <linux/spinlock.h>
32 #include <linux/stat.h>
33 #include <linux/types.h>
34 #include <linux/wait_bit.h>
35 #include <linux/workqueue.h>
36 #include <uapi/linux/fiemap.h>
37 #include <uapi/linux/landlock.h>
38
39 #include "common.h"
40 #include "cred.h"
41 #include "fs.h"
42 #include "limits.h"
43 #include "object.h"
44 #include "ruleset.h"
45 #include "setup.h"
46
47 /* Underlying object management */
48
release_inode(struct landlock_object * const object)49 static void release_inode(struct landlock_object *const object)
50 __releases(object->lock)
51 {
52 struct inode *const inode = object->underobj;
53 struct super_block *sb;
54
55 if (!inode) {
56 spin_unlock(&object->lock);
57 return;
58 }
59
60 /*
61 * Protects against concurrent use by hook_sb_delete() of the reference
62 * to the underlying inode.
63 */
64 object->underobj = NULL;
65 /*
66 * Makes sure that if the filesystem is concurrently unmounted,
67 * hook_sb_delete() will wait for us to finish iput().
68 */
69 sb = inode->i_sb;
70 atomic_long_inc(&landlock_superblock(sb)->inode_refs);
71 spin_unlock(&object->lock);
72 /*
73 * Because object->underobj was not NULL, hook_sb_delete() and
74 * get_inode_object() guarantee that it is safe to reset
75 * landlock_inode(inode)->object while it is not NULL. It is therefore
76 * not necessary to lock inode->i_lock.
77 */
78 rcu_assign_pointer(landlock_inode(inode)->object, NULL);
79 /*
80 * Now, new rules can safely be tied to @inode with get_inode_object().
81 */
82
83 iput(inode);
84 if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs))
85 wake_up_var(&landlock_superblock(sb)->inode_refs);
86 }
87
88 static const struct landlock_object_underops landlock_fs_underops = {
89 .release = release_inode
90 };
91
92 /* IOCTL helpers */
93
94 /**
95 * is_masked_device_ioctl - Determine whether an IOCTL command is always
96 * permitted with Landlock for device files. These commands can not be
97 * restricted on device files by enforcing a Landlock policy.
98 *
99 * @cmd: The IOCTL command that is supposed to be run.
100 *
101 * By default, any IOCTL on a device file requires the
102 * LANDLOCK_ACCESS_FS_IOCTL_DEV right. However, we blanket-permit some
103 * commands, if:
104 *
105 * 1. The command is implemented in fs/ioctl.c's do_vfs_ioctl(),
106 * not in f_ops->unlocked_ioctl() or f_ops->compat_ioctl().
107 *
108 * 2. The command is harmless when invoked on devices.
109 *
110 * We also permit commands that do not make sense for devices, but where the
111 * do_vfs_ioctl() implementation returns a more conventional error code.
112 *
113 * Any new IOCTL commands that are implemented in fs/ioctl.c's do_vfs_ioctl()
114 * should be considered for inclusion here.
115 *
116 * Returns: true if the IOCTL @cmd can not be restricted with Landlock for
117 * device files.
118 */
is_masked_device_ioctl(const unsigned int cmd)119 static __attribute_const__ bool is_masked_device_ioctl(const unsigned int cmd)
120 {
121 switch (cmd) {
122 /*
123 * FIOCLEX, FIONCLEX, FIONBIO and FIOASYNC manipulate the FD's
124 * close-on-exec and the file's buffered-IO and async flags. These
125 * operations are also available through fcntl(2), and are
126 * unconditionally permitted in Landlock.
127 */
128 case FIOCLEX:
129 case FIONCLEX:
130 case FIONBIO:
131 case FIOASYNC:
132 /*
133 * FIOQSIZE queries the size of a regular file, directory, or link.
134 *
135 * We still permit it, because it always returns -ENOTTY for
136 * other file types.
137 */
138 case FIOQSIZE:
139 /*
140 * FIFREEZE and FITHAW freeze and thaw the file system which the
141 * given file belongs to. Requires CAP_SYS_ADMIN.
142 *
143 * These commands operate on the file system's superblock rather
144 * than on the file itself. The same operations can also be
145 * done through any other file or directory on the same file
146 * system, so it is safe to permit these.
147 */
148 case FIFREEZE:
149 case FITHAW:
150 /*
151 * FS_IOC_FIEMAP queries information about the allocation of
152 * blocks within a file.
153 *
154 * This IOCTL command only makes sense for regular files and is
155 * not implemented by devices. It is harmless to permit.
156 */
157 case FS_IOC_FIEMAP:
158 /*
159 * FIGETBSZ queries the file system's block size for a file or
160 * directory.
161 *
162 * This command operates on the file system's superblock rather
163 * than on the file itself. The same operation can also be done
164 * through any other file or directory on the same file system,
165 * so it is safe to permit it.
166 */
167 case FIGETBSZ:
168 /*
169 * FICLONE, FICLONERANGE and FIDEDUPERANGE make files share
170 * their underlying storage ("reflink") between source and
171 * destination FDs, on file systems which support that.
172 *
173 * These IOCTL commands only apply to regular files
174 * and are harmless to permit for device files.
175 */
176 case FICLONE:
177 case FICLONERANGE:
178 case FIDEDUPERANGE:
179 /*
180 * FS_IOC_GETFSUUID and FS_IOC_GETFSSYSFSPATH both operate on
181 * the file system superblock, not on the specific file, so
182 * these operations are available through any other file on the
183 * same file system as well.
184 */
185 case FS_IOC_GETFSUUID:
186 case FS_IOC_GETFSSYSFSPATH:
187 return true;
188
189 /*
190 * FIONREAD, FS_IOC_GETFLAGS, FS_IOC_SETFLAGS, FS_IOC_FSGETXATTR and
191 * FS_IOC_FSSETXATTR are forwarded to device implementations.
192 */
193
194 /*
195 * file_ioctl() commands (FIBMAP, FS_IOC_RESVSP, FS_IOC_RESVSP64,
196 * FS_IOC_UNRESVSP, FS_IOC_UNRESVSP64 and FS_IOC_ZERO_RANGE) are
197 * forwarded to device implementations, so not permitted.
198 */
199
200 /* Other commands are guarded by the access right. */
201 default:
202 return false;
203 }
204 }
205
206 /*
207 * is_masked_device_ioctl_compat - same as the helper above, but checking the
208 * "compat" IOCTL commands.
209 *
210 * The IOCTL commands with special handling in compat-mode should behave the
211 * same as their non-compat counterparts.
212 */
213 static __attribute_const__ bool
is_masked_device_ioctl_compat(const unsigned int cmd)214 is_masked_device_ioctl_compat(const unsigned int cmd)
215 {
216 switch (cmd) {
217 /* FICLONE is permitted, same as in the non-compat variant. */
218 case FICLONE:
219 return true;
220
221 #if defined(CONFIG_X86_64)
222 /*
223 * FS_IOC_RESVSP_32, FS_IOC_RESVSP64_32, FS_IOC_UNRESVSP_32,
224 * FS_IOC_UNRESVSP64_32, FS_IOC_ZERO_RANGE_32: not blanket-permitted,
225 * for consistency with their non-compat variants.
226 */
227 case FS_IOC_RESVSP_32:
228 case FS_IOC_RESVSP64_32:
229 case FS_IOC_UNRESVSP_32:
230 case FS_IOC_UNRESVSP64_32:
231 case FS_IOC_ZERO_RANGE_32:
232 #endif
233
234 /*
235 * FS_IOC32_GETFLAGS, FS_IOC32_SETFLAGS are forwarded to their device
236 * implementations.
237 */
238 case FS_IOC32_GETFLAGS:
239 case FS_IOC32_SETFLAGS:
240 return false;
241 default:
242 return is_masked_device_ioctl(cmd);
243 }
244 }
245
246 /* Ruleset management */
247
get_inode_object(struct inode * const inode)248 static struct landlock_object *get_inode_object(struct inode *const inode)
249 {
250 struct landlock_object *object, *new_object;
251 struct landlock_inode_security *inode_sec = landlock_inode(inode);
252
253 rcu_read_lock();
254 retry:
255 object = rcu_dereference(inode_sec->object);
256 if (object) {
257 if (likely(refcount_inc_not_zero(&object->usage))) {
258 rcu_read_unlock();
259 return object;
260 }
261 /*
262 * We are racing with release_inode(), the object is going
263 * away. Wait for release_inode(), then retry.
264 */
265 spin_lock(&object->lock);
266 spin_unlock(&object->lock);
267 goto retry;
268 }
269 rcu_read_unlock();
270
271 /*
272 * If there is no object tied to @inode, then create a new one (without
273 * holding any locks).
274 */
275 new_object = landlock_create_object(&landlock_fs_underops, inode);
276 if (IS_ERR(new_object))
277 return new_object;
278
279 /*
280 * Protects against concurrent calls to get_inode_object() or
281 * hook_sb_delete().
282 */
283 spin_lock(&inode->i_lock);
284 if (unlikely(rcu_access_pointer(inode_sec->object))) {
285 /* Someone else just created the object, bail out and retry. */
286 spin_unlock(&inode->i_lock);
287 kfree(new_object);
288
289 rcu_read_lock();
290 goto retry;
291 }
292
293 /*
294 * @inode will be released by hook_sb_delete() on its superblock
295 * shutdown, or by release_inode() when no more ruleset references the
296 * related object.
297 */
298 ihold(inode);
299 rcu_assign_pointer(inode_sec->object, new_object);
300 spin_unlock(&inode->i_lock);
301 return new_object;
302 }
303
304 /* All access rights that can be tied to files. */
305 /* clang-format off */
306 #define ACCESS_FILE ( \
307 LANDLOCK_ACCESS_FS_EXECUTE | \
308 LANDLOCK_ACCESS_FS_WRITE_FILE | \
309 LANDLOCK_ACCESS_FS_READ_FILE | \
310 LANDLOCK_ACCESS_FS_TRUNCATE | \
311 LANDLOCK_ACCESS_FS_IOCTL_DEV)
312 /* clang-format on */
313
314 /*
315 * @path: Should have been checked by get_path_from_fd().
316 */
landlock_append_fs_rule(struct landlock_ruleset * const ruleset,const struct path * const path,access_mask_t access_rights)317 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
318 const struct path *const path,
319 access_mask_t access_rights)
320 {
321 int err;
322 struct landlock_id id = {
323 .type = LANDLOCK_KEY_INODE,
324 };
325
326 /* Files only get access rights that make sense. */
327 if (!d_is_dir(path->dentry) &&
328 (access_rights | ACCESS_FILE) != ACCESS_FILE)
329 return -EINVAL;
330 if (WARN_ON_ONCE(ruleset->num_layers != 1))
331 return -EINVAL;
332
333 /* Transforms relative access rights to absolute ones. */
334 access_rights |= LANDLOCK_MASK_ACCESS_FS &
335 ~landlock_get_fs_access_mask(ruleset, 0);
336 id.key.object = get_inode_object(d_backing_inode(path->dentry));
337 if (IS_ERR(id.key.object))
338 return PTR_ERR(id.key.object);
339 mutex_lock(&ruleset->lock);
340 err = landlock_insert_rule(ruleset, id, access_rights);
341 mutex_unlock(&ruleset->lock);
342 /*
343 * No need to check for an error because landlock_insert_rule()
344 * increments the refcount for the new object if needed.
345 */
346 landlock_put_object(id.key.object);
347 return err;
348 }
349
350 /* Access-control management */
351
352 /*
353 * The lifetime of the returned rule is tied to @domain.
354 *
355 * Returns NULL if no rule is found or if @dentry is negative.
356 */
357 static const struct landlock_rule *
find_rule(const struct landlock_ruleset * const domain,const struct dentry * const dentry)358 find_rule(const struct landlock_ruleset *const domain,
359 const struct dentry *const dentry)
360 {
361 const struct landlock_rule *rule;
362 const struct inode *inode;
363 struct landlock_id id = {
364 .type = LANDLOCK_KEY_INODE,
365 };
366
367 /* Ignores nonexistent leafs. */
368 if (d_is_negative(dentry))
369 return NULL;
370
371 inode = d_backing_inode(dentry);
372 rcu_read_lock();
373 id.key.object = rcu_dereference(landlock_inode(inode)->object);
374 rule = landlock_find_rule(domain, id);
375 rcu_read_unlock();
376 return rule;
377 }
378
379 /*
380 * Allows access to pseudo filesystems that will never be mountable (e.g.
381 * sockfs, pipefs), but can still be reachable through
382 * /proc/<pid>/fd/<file-descriptor>
383 */
is_nouser_or_private(const struct dentry * dentry)384 static bool is_nouser_or_private(const struct dentry *dentry)
385 {
386 return (dentry->d_sb->s_flags & SB_NOUSER) ||
387 (d_is_positive(dentry) &&
388 unlikely(IS_PRIVATE(d_backing_inode(dentry))));
389 }
390
391 static access_mask_t
get_raw_handled_fs_accesses(const struct landlock_ruleset * const domain)392 get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
393 {
394 access_mask_t access_dom = 0;
395 size_t layer_level;
396
397 for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
398 access_dom |=
399 landlock_get_raw_fs_access_mask(domain, layer_level);
400 return access_dom;
401 }
402
403 static access_mask_t
get_handled_fs_accesses(const struct landlock_ruleset * const domain)404 get_handled_fs_accesses(const struct landlock_ruleset *const domain)
405 {
406 /* Handles all initially denied by default access rights. */
407 return get_raw_handled_fs_accesses(domain) |
408 LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
409 }
410
411 static const struct landlock_ruleset *
get_fs_domain(const struct landlock_ruleset * const domain)412 get_fs_domain(const struct landlock_ruleset *const domain)
413 {
414 if (!domain || !get_raw_handled_fs_accesses(domain))
415 return NULL;
416
417 return domain;
418 }
419
get_current_fs_domain(void)420 static const struct landlock_ruleset *get_current_fs_domain(void)
421 {
422 return get_fs_domain(landlock_get_current_domain());
423 }
424
425 /*
426 * Check that a destination file hierarchy has more restrictions than a source
427 * file hierarchy. This is only used for link and rename actions.
428 *
429 * @layer_masks_child2: Optional child masks.
430 */
no_more_access(const layer_mask_t (* const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],const layer_mask_t (* const layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS],const bool child1_is_directory,const layer_mask_t (* const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],const layer_mask_t (* const layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS],const bool child2_is_directory)431 static bool no_more_access(
432 const layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],
433 const layer_mask_t (*const layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS],
434 const bool child1_is_directory,
435 const layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],
436 const layer_mask_t (*const layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS],
437 const bool child2_is_directory)
438 {
439 unsigned long access_bit;
440
441 for (access_bit = 0; access_bit < ARRAY_SIZE(*layer_masks_parent2);
442 access_bit++) {
443 /* Ignores accesses that only make sense for directories. */
444 const bool is_file_access =
445 !!(BIT_ULL(access_bit) & ACCESS_FILE);
446
447 if (child1_is_directory || is_file_access) {
448 /*
449 * Checks if the destination restrictions are a
450 * superset of the source ones (i.e. inherited access
451 * rights without child exceptions):
452 * restrictions(parent2) >= restrictions(child1)
453 */
454 if ((((*layer_masks_parent1)[access_bit] &
455 (*layer_masks_child1)[access_bit]) |
456 (*layer_masks_parent2)[access_bit]) !=
457 (*layer_masks_parent2)[access_bit])
458 return false;
459 }
460
461 if (!layer_masks_child2)
462 continue;
463 if (child2_is_directory || is_file_access) {
464 /*
465 * Checks inverted restrictions for RENAME_EXCHANGE:
466 * restrictions(parent1) >= restrictions(child2)
467 */
468 if ((((*layer_masks_parent2)[access_bit] &
469 (*layer_masks_child2)[access_bit]) |
470 (*layer_masks_parent1)[access_bit]) !=
471 (*layer_masks_parent1)[access_bit])
472 return false;
473 }
474 }
475 return true;
476 }
477
478 #define NMA_TRUE(...) KUNIT_EXPECT_TRUE(test, no_more_access(__VA_ARGS__))
479 #define NMA_FALSE(...) KUNIT_EXPECT_FALSE(test, no_more_access(__VA_ARGS__))
480
481 #ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
482
test_no_more_access(struct kunit * const test)483 static void test_no_more_access(struct kunit *const test)
484 {
485 const layer_mask_t rx0[LANDLOCK_NUM_ACCESS_FS] = {
486 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0),
487 [BIT_INDEX(LANDLOCK_ACCESS_FS_READ_FILE)] = BIT_ULL(0),
488 };
489 const layer_mask_t mx0[LANDLOCK_NUM_ACCESS_FS] = {
490 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0),
491 [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_REG)] = BIT_ULL(0),
492 };
493 const layer_mask_t x0[LANDLOCK_NUM_ACCESS_FS] = {
494 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0),
495 };
496 const layer_mask_t x1[LANDLOCK_NUM_ACCESS_FS] = {
497 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(1),
498 };
499 const layer_mask_t x01[LANDLOCK_NUM_ACCESS_FS] = {
500 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0) |
501 BIT_ULL(1),
502 };
503 const layer_mask_t allows_all[LANDLOCK_NUM_ACCESS_FS] = {};
504
505 /* Checks without restriction. */
506 NMA_TRUE(&x0, &allows_all, false, &allows_all, NULL, false);
507 NMA_TRUE(&allows_all, &x0, false, &allows_all, NULL, false);
508 NMA_FALSE(&x0, &x0, false, &allows_all, NULL, false);
509
510 /*
511 * Checks that we can only refer a file if no more access could be
512 * inherited.
513 */
514 NMA_TRUE(&x0, &x0, false, &rx0, NULL, false);
515 NMA_TRUE(&rx0, &rx0, false, &rx0, NULL, false);
516 NMA_FALSE(&rx0, &rx0, false, &x0, NULL, false);
517 NMA_FALSE(&rx0, &rx0, false, &x1, NULL, false);
518
519 /* Checks allowed referring with different nested domains. */
520 NMA_TRUE(&x0, &x1, false, &x0, NULL, false);
521 NMA_TRUE(&x1, &x0, false, &x0, NULL, false);
522 NMA_TRUE(&x0, &x01, false, &x0, NULL, false);
523 NMA_TRUE(&x0, &x01, false, &rx0, NULL, false);
524 NMA_TRUE(&x01, &x0, false, &x0, NULL, false);
525 NMA_TRUE(&x01, &x0, false, &rx0, NULL, false);
526 NMA_FALSE(&x01, &x01, false, &x0, NULL, false);
527
528 /* Checks that file access rights are also enforced for a directory. */
529 NMA_FALSE(&rx0, &rx0, true, &x0, NULL, false);
530
531 /* Checks that directory access rights don't impact file referring... */
532 NMA_TRUE(&mx0, &mx0, false, &x0, NULL, false);
533 /* ...but only directory referring. */
534 NMA_FALSE(&mx0, &mx0, true, &x0, NULL, false);
535
536 /* Checks directory exchange. */
537 NMA_TRUE(&mx0, &mx0, true, &mx0, &mx0, true);
538 NMA_TRUE(&mx0, &mx0, true, &mx0, &x0, true);
539 NMA_FALSE(&mx0, &mx0, true, &x0, &mx0, true);
540 NMA_FALSE(&mx0, &mx0, true, &x0, &x0, true);
541 NMA_FALSE(&mx0, &mx0, true, &x1, &x1, true);
542
543 /* Checks file exchange with directory access rights... */
544 NMA_TRUE(&mx0, &mx0, false, &mx0, &mx0, false);
545 NMA_TRUE(&mx0, &mx0, false, &mx0, &x0, false);
546 NMA_TRUE(&mx0, &mx0, false, &x0, &mx0, false);
547 NMA_TRUE(&mx0, &mx0, false, &x0, &x0, false);
548 /* ...and with file access rights. */
549 NMA_TRUE(&rx0, &rx0, false, &rx0, &rx0, false);
550 NMA_TRUE(&rx0, &rx0, false, &rx0, &x0, false);
551 NMA_FALSE(&rx0, &rx0, false, &x0, &rx0, false);
552 NMA_FALSE(&rx0, &rx0, false, &x0, &x0, false);
553 NMA_FALSE(&rx0, &rx0, false, &x1, &x1, false);
554
555 /*
556 * Allowing the following requests should not be a security risk
557 * because domain 0 denies execute access, and domain 1 is always
558 * nested with domain 0. However, adding an exception for this case
559 * would mean to check all nested domains to make sure none can get
560 * more privileges (e.g. processes only sandboxed by domain 0).
561 * Moreover, this behavior (i.e. composition of N domains) could then
562 * be inconsistent compared to domain 1's ruleset alone (e.g. it might
563 * be denied to link/rename with domain 1's ruleset, whereas it would
564 * be allowed if nested on top of domain 0). Another drawback would be
565 * to create a cover channel that could enable sandboxed processes to
566 * infer most of the filesystem restrictions from their domain. To
567 * make it simple, efficient, safe, and more consistent, this case is
568 * always denied.
569 */
570 NMA_FALSE(&x1, &x1, false, &x0, NULL, false);
571 NMA_FALSE(&x1, &x1, false, &rx0, NULL, false);
572 NMA_FALSE(&x1, &x1, true, &x0, NULL, false);
573 NMA_FALSE(&x1, &x1, true, &rx0, NULL, false);
574
575 /* Checks the same case of exclusive domains with a file... */
576 NMA_TRUE(&x1, &x1, false, &x01, NULL, false);
577 NMA_FALSE(&x1, &x1, false, &x01, &x0, false);
578 NMA_FALSE(&x1, &x1, false, &x01, &x01, false);
579 NMA_FALSE(&x1, &x1, false, &x0, &x0, false);
580 /* ...and with a directory. */
581 NMA_FALSE(&x1, &x1, false, &x0, &x0, true);
582 NMA_FALSE(&x1, &x1, true, &x0, &x0, false);
583 NMA_FALSE(&x1, &x1, true, &x0, &x0, true);
584 }
585
586 #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
587
588 #undef NMA_TRUE
589 #undef NMA_FALSE
590
591 /*
592 * Removes @layer_masks accesses that are not requested.
593 *
594 * Returns true if the request is allowed, false otherwise.
595 */
596 static bool
scope_to_request(const access_mask_t access_request,layer_mask_t (* const layer_masks)[LANDLOCK_NUM_ACCESS_FS])597 scope_to_request(const access_mask_t access_request,
598 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
599 {
600 const unsigned long access_req = access_request;
601 unsigned long access_bit;
602
603 if (WARN_ON_ONCE(!layer_masks))
604 return true;
605
606 for_each_clear_bit(access_bit, &access_req, ARRAY_SIZE(*layer_masks))
607 (*layer_masks)[access_bit] = 0;
608 return !memchr_inv(layer_masks, 0, sizeof(*layer_masks));
609 }
610
611 #ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
612
test_scope_to_request_with_exec_none(struct kunit * const test)613 static void test_scope_to_request_with_exec_none(struct kunit *const test)
614 {
615 /* Allows everything. */
616 layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
617
618 /* Checks and scopes with execute. */
619 KUNIT_EXPECT_TRUE(test, scope_to_request(LANDLOCK_ACCESS_FS_EXECUTE,
620 &layer_masks));
621 KUNIT_EXPECT_EQ(test, 0,
622 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)]);
623 KUNIT_EXPECT_EQ(test, 0,
624 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)]);
625 }
626
test_scope_to_request_with_exec_some(struct kunit * const test)627 static void test_scope_to_request_with_exec_some(struct kunit *const test)
628 {
629 /* Denies execute and write. */
630 layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {
631 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0),
632 [BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)] = BIT_ULL(1),
633 };
634
635 /* Checks and scopes with execute. */
636 KUNIT_EXPECT_FALSE(test, scope_to_request(LANDLOCK_ACCESS_FS_EXECUTE,
637 &layer_masks));
638 KUNIT_EXPECT_EQ(test, BIT_ULL(0),
639 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)]);
640 KUNIT_EXPECT_EQ(test, 0,
641 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)]);
642 }
643
test_scope_to_request_without_access(struct kunit * const test)644 static void test_scope_to_request_without_access(struct kunit *const test)
645 {
646 /* Denies execute and write. */
647 layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {
648 [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0),
649 [BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)] = BIT_ULL(1),
650 };
651
652 /* Checks and scopes without access request. */
653 KUNIT_EXPECT_TRUE(test, scope_to_request(0, &layer_masks));
654 KUNIT_EXPECT_EQ(test, 0,
655 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)]);
656 KUNIT_EXPECT_EQ(test, 0,
657 layer_masks[BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)]);
658 }
659
660 #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
661
662 /*
663 * Returns true if there is at least one access right different than
664 * LANDLOCK_ACCESS_FS_REFER.
665 */
666 static bool
is_eacces(const layer_mask_t (* const layer_masks)[LANDLOCK_NUM_ACCESS_FS],const access_mask_t access_request)667 is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS],
668 const access_mask_t access_request)
669 {
670 unsigned long access_bit;
671 /* LANDLOCK_ACCESS_FS_REFER alone must return -EXDEV. */
672 const unsigned long access_check = access_request &
673 ~LANDLOCK_ACCESS_FS_REFER;
674
675 if (!layer_masks)
676 return false;
677
678 for_each_set_bit(access_bit, &access_check, ARRAY_SIZE(*layer_masks)) {
679 if ((*layer_masks)[access_bit])
680 return true;
681 }
682 return false;
683 }
684
685 #define IE_TRUE(...) KUNIT_EXPECT_TRUE(test, is_eacces(__VA_ARGS__))
686 #define IE_FALSE(...) KUNIT_EXPECT_FALSE(test, is_eacces(__VA_ARGS__))
687
688 #ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
689
test_is_eacces_with_none(struct kunit * const test)690 static void test_is_eacces_with_none(struct kunit *const test)
691 {
692 const layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
693
694 IE_FALSE(&layer_masks, 0);
695 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_REFER);
696 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_EXECUTE);
697 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
698 }
699
test_is_eacces_with_refer(struct kunit * const test)700 static void test_is_eacces_with_refer(struct kunit *const test)
701 {
702 const layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {
703 [BIT_INDEX(LANDLOCK_ACCESS_FS_REFER)] = BIT_ULL(0),
704 };
705
706 IE_FALSE(&layer_masks, 0);
707 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_REFER);
708 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_EXECUTE);
709 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
710 }
711
test_is_eacces_with_write(struct kunit * const test)712 static void test_is_eacces_with_write(struct kunit *const test)
713 {
714 const layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {
715 [BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)] = BIT_ULL(0),
716 };
717
718 IE_FALSE(&layer_masks, 0);
719 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_REFER);
720 IE_FALSE(&layer_masks, LANDLOCK_ACCESS_FS_EXECUTE);
721
722 IE_TRUE(&layer_masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
723 }
724
725 #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
726
727 #undef IE_TRUE
728 #undef IE_FALSE
729
730 /**
731 * is_access_to_paths_allowed - Check accesses for requests with a common path
732 *
733 * @domain: Domain to check against.
734 * @path: File hierarchy to walk through.
735 * @access_request_parent1: Accesses to check, once @layer_masks_parent1 is
736 * equal to @layer_masks_parent2 (if any). This is tied to the unique
737 * requested path for most actions, or the source in case of a refer action
738 * (i.e. rename or link), or the source and destination in case of
739 * RENAME_EXCHANGE.
740 * @layer_masks_parent1: Pointer to a matrix of layer masks per access
741 * masks, identifying the layers that forbid a specific access. Bits from
742 * this matrix can be unset according to the @path walk. An empty matrix
743 * means that @domain allows all possible Landlock accesses (i.e. not only
744 * those identified by @access_request_parent1). This matrix can
745 * initially refer to domain layer masks and, when the accesses for the
746 * destination and source are the same, to requested layer masks.
747 * @dentry_child1: Dentry to the initial child of the parent1 path. This
748 * pointer must be NULL for non-refer actions (i.e. not link nor rename).
749 * @access_request_parent2: Similar to @access_request_parent1 but for a
750 * request involving a source and a destination. This refers to the
751 * destination, except in case of RENAME_EXCHANGE where it also refers to
752 * the source. Must be set to 0 when using a simple path request.
753 * @layer_masks_parent2: Similar to @layer_masks_parent1 but for a refer
754 * action. This must be NULL otherwise.
755 * @dentry_child2: Dentry to the initial child of the parent2 path. This
756 * pointer is only set for RENAME_EXCHANGE actions and must be NULL
757 * otherwise.
758 *
759 * This helper first checks that the destination has a superset of restrictions
760 * compared to the source (if any) for a common path. Because of
761 * RENAME_EXCHANGE actions, source and destinations may be swapped. It then
762 * checks that the collected accesses and the remaining ones are enough to
763 * allow the request.
764 *
765 * Returns:
766 * - true if the access request is granted;
767 * - false otherwise.
768 */
is_access_to_paths_allowed(const struct landlock_ruleset * const domain,const struct path * const path,const access_mask_t access_request_parent1,layer_mask_t (* const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],const struct dentry * const dentry_child1,const access_mask_t access_request_parent2,layer_mask_t (* const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],const struct dentry * const dentry_child2)769 static bool is_access_to_paths_allowed(
770 const struct landlock_ruleset *const domain,
771 const struct path *const path,
772 const access_mask_t access_request_parent1,
773 layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],
774 const struct dentry *const dentry_child1,
775 const access_mask_t access_request_parent2,
776 layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],
777 const struct dentry *const dentry_child2)
778 {
779 bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check,
780 child1_is_directory = true, child2_is_directory = true;
781 struct path walker_path;
782 access_mask_t access_masked_parent1, access_masked_parent2;
783 layer_mask_t _layer_masks_child1[LANDLOCK_NUM_ACCESS_FS],
784 _layer_masks_child2[LANDLOCK_NUM_ACCESS_FS];
785 layer_mask_t(*layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS] = NULL,
786 (*layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS] = NULL;
787
788 if (!access_request_parent1 && !access_request_parent2)
789 return true;
790 if (WARN_ON_ONCE(!domain || !path))
791 return true;
792 if (is_nouser_or_private(path->dentry))
793 return true;
794 if (WARN_ON_ONCE(domain->num_layers < 1 || !layer_masks_parent1))
795 return false;
796
797 if (unlikely(layer_masks_parent2)) {
798 if (WARN_ON_ONCE(!dentry_child1))
799 return false;
800 /*
801 * For a double request, first check for potential privilege
802 * escalation by looking at domain handled accesses (which are
803 * a superset of the meaningful requested accesses).
804 */
805 access_masked_parent1 = access_masked_parent2 =
806 get_handled_fs_accesses(domain);
807 is_dom_check = true;
808 } else {
809 if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
810 return false;
811 /* For a simple request, only check for requested accesses. */
812 access_masked_parent1 = access_request_parent1;
813 access_masked_parent2 = access_request_parent2;
814 is_dom_check = false;
815 }
816
817 if (unlikely(dentry_child1)) {
818 landlock_unmask_layers(
819 find_rule(domain, dentry_child1),
820 landlock_init_layer_masks(
821 domain, LANDLOCK_MASK_ACCESS_FS,
822 &_layer_masks_child1, LANDLOCK_KEY_INODE),
823 &_layer_masks_child1, ARRAY_SIZE(_layer_masks_child1));
824 layer_masks_child1 = &_layer_masks_child1;
825 child1_is_directory = d_is_dir(dentry_child1);
826 }
827 if (unlikely(dentry_child2)) {
828 landlock_unmask_layers(
829 find_rule(domain, dentry_child2),
830 landlock_init_layer_masks(
831 domain, LANDLOCK_MASK_ACCESS_FS,
832 &_layer_masks_child2, LANDLOCK_KEY_INODE),
833 &_layer_masks_child2, ARRAY_SIZE(_layer_masks_child2));
834 layer_masks_child2 = &_layer_masks_child2;
835 child2_is_directory = d_is_dir(dentry_child2);
836 }
837
838 walker_path = *path;
839 path_get(&walker_path);
840 /*
841 * We need to walk through all the hierarchy to not miss any relevant
842 * restriction.
843 */
844 while (true) {
845 struct dentry *parent_dentry;
846 const struct landlock_rule *rule;
847
848 /*
849 * If at least all accesses allowed on the destination are
850 * already allowed on the source, respectively if there is at
851 * least as much as restrictions on the destination than on the
852 * source, then we can safely refer files from the source to
853 * the destination without risking a privilege escalation.
854 * This also applies in the case of RENAME_EXCHANGE, which
855 * implies checks on both direction. This is crucial for
856 * standalone multilayered security policies. Furthermore,
857 * this helps avoid policy writers to shoot themselves in the
858 * foot.
859 */
860 if (unlikely(is_dom_check &&
861 no_more_access(
862 layer_masks_parent1, layer_masks_child1,
863 child1_is_directory, layer_masks_parent2,
864 layer_masks_child2,
865 child2_is_directory))) {
866 allowed_parent1 = scope_to_request(
867 access_request_parent1, layer_masks_parent1);
868 allowed_parent2 = scope_to_request(
869 access_request_parent2, layer_masks_parent2);
870
871 /* Stops when all accesses are granted. */
872 if (allowed_parent1 && allowed_parent2)
873 break;
874
875 /*
876 * Now, downgrades the remaining checks from domain
877 * handled accesses to requested accesses.
878 */
879 is_dom_check = false;
880 access_masked_parent1 = access_request_parent1;
881 access_masked_parent2 = access_request_parent2;
882 }
883
884 rule = find_rule(domain, walker_path.dentry);
885 allowed_parent1 = landlock_unmask_layers(
886 rule, access_masked_parent1, layer_masks_parent1,
887 ARRAY_SIZE(*layer_masks_parent1));
888 allowed_parent2 = landlock_unmask_layers(
889 rule, access_masked_parent2, layer_masks_parent2,
890 ARRAY_SIZE(*layer_masks_parent2));
891
892 /* Stops when a rule from each layer grants access. */
893 if (allowed_parent1 && allowed_parent2)
894 break;
895 jump_up:
896 if (walker_path.dentry == walker_path.mnt->mnt_root) {
897 if (follow_up(&walker_path)) {
898 /* Ignores hidden mount points. */
899 goto jump_up;
900 } else {
901 /*
902 * Stops at the real root. Denies access
903 * because not all layers have granted access.
904 */
905 break;
906 }
907 }
908 if (unlikely(IS_ROOT(walker_path.dentry))) {
909 /*
910 * Stops at disconnected root directories. Only allows
911 * access to internal filesystems (e.g. nsfs, which is
912 * reachable through /proc/<pid>/ns/<namespace>).
913 */
914 allowed_parent1 = allowed_parent2 =
915 !!(walker_path.mnt->mnt_flags & MNT_INTERNAL);
916 break;
917 }
918 parent_dentry = dget_parent(walker_path.dentry);
919 dput(walker_path.dentry);
920 walker_path.dentry = parent_dentry;
921 }
922 path_put(&walker_path);
923
924 return allowed_parent1 && allowed_parent2;
925 }
926
check_access_path(const struct landlock_ruleset * const domain,const struct path * const path,access_mask_t access_request)927 static int check_access_path(const struct landlock_ruleset *const domain,
928 const struct path *const path,
929 access_mask_t access_request)
930 {
931 layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
932
933 access_request = landlock_init_layer_masks(
934 domain, access_request, &layer_masks, LANDLOCK_KEY_INODE);
935 if (is_access_to_paths_allowed(domain, path, access_request,
936 &layer_masks, NULL, 0, NULL, NULL))
937 return 0;
938 return -EACCES;
939 }
940
current_check_access_path(const struct path * const path,const access_mask_t access_request)941 static int current_check_access_path(const struct path *const path,
942 const access_mask_t access_request)
943 {
944 const struct landlock_ruleset *const dom = get_current_fs_domain();
945
946 if (!dom)
947 return 0;
948 return check_access_path(dom, path, access_request);
949 }
950
get_mode_access(const umode_t mode)951 static access_mask_t get_mode_access(const umode_t mode)
952 {
953 switch (mode & S_IFMT) {
954 case S_IFLNK:
955 return LANDLOCK_ACCESS_FS_MAKE_SYM;
956 case 0:
957 /* A zero mode translates to S_IFREG. */
958 case S_IFREG:
959 return LANDLOCK_ACCESS_FS_MAKE_REG;
960 case S_IFDIR:
961 return LANDLOCK_ACCESS_FS_MAKE_DIR;
962 case S_IFCHR:
963 return LANDLOCK_ACCESS_FS_MAKE_CHAR;
964 case S_IFBLK:
965 return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
966 case S_IFIFO:
967 return LANDLOCK_ACCESS_FS_MAKE_FIFO;
968 case S_IFSOCK:
969 return LANDLOCK_ACCESS_FS_MAKE_SOCK;
970 default:
971 WARN_ON_ONCE(1);
972 return 0;
973 }
974 }
975
maybe_remove(const struct dentry * const dentry)976 static access_mask_t maybe_remove(const struct dentry *const dentry)
977 {
978 if (d_is_negative(dentry))
979 return 0;
980 return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
981 LANDLOCK_ACCESS_FS_REMOVE_FILE;
982 }
983
984 /**
985 * collect_domain_accesses - Walk through a file path and collect accesses
986 *
987 * @domain: Domain to check against.
988 * @mnt_root: Last directory to check.
989 * @dir: Directory to start the walk from.
990 * @layer_masks_dom: Where to store the collected accesses.
991 *
992 * This helper is useful to begin a path walk from the @dir directory to a
993 * @mnt_root directory used as a mount point. This mount point is the common
994 * ancestor between the source and the destination of a renamed and linked
995 * file. While walking from @dir to @mnt_root, we record all the domain's
996 * allowed accesses in @layer_masks_dom.
997 *
998 * This is similar to is_access_to_paths_allowed() but much simpler because it
999 * only handles walking on the same mount point and only checks one set of
1000 * accesses.
1001 *
1002 * Returns:
1003 * - true if all the domain access rights are allowed for @dir;
1004 * - false if the walk reached @mnt_root.
1005 */
collect_domain_accesses(const struct landlock_ruleset * const domain,const struct dentry * const mnt_root,struct dentry * dir,layer_mask_t (* const layer_masks_dom)[LANDLOCK_NUM_ACCESS_FS])1006 static bool collect_domain_accesses(
1007 const struct landlock_ruleset *const domain,
1008 const struct dentry *const mnt_root, struct dentry *dir,
1009 layer_mask_t (*const layer_masks_dom)[LANDLOCK_NUM_ACCESS_FS])
1010 {
1011 unsigned long access_dom;
1012 bool ret = false;
1013
1014 if (WARN_ON_ONCE(!domain || !mnt_root || !dir || !layer_masks_dom))
1015 return true;
1016 if (is_nouser_or_private(dir))
1017 return true;
1018
1019 access_dom = landlock_init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
1020 layer_masks_dom,
1021 LANDLOCK_KEY_INODE);
1022
1023 dget(dir);
1024 while (true) {
1025 struct dentry *parent_dentry;
1026
1027 /* Gets all layers allowing all domain accesses. */
1028 if (landlock_unmask_layers(find_rule(domain, dir), access_dom,
1029 layer_masks_dom,
1030 ARRAY_SIZE(*layer_masks_dom))) {
1031 /*
1032 * Stops when all handled accesses are allowed by at
1033 * least one rule in each layer.
1034 */
1035 ret = true;
1036 break;
1037 }
1038
1039 /* We should not reach a root other than @mnt_root. */
1040 if (dir == mnt_root || WARN_ON_ONCE(IS_ROOT(dir)))
1041 break;
1042
1043 parent_dentry = dget_parent(dir);
1044 dput(dir);
1045 dir = parent_dentry;
1046 }
1047 dput(dir);
1048 return ret;
1049 }
1050
1051 /**
1052 * current_check_refer_path - Check if a rename or link action is allowed
1053 *
1054 * @old_dentry: File or directory requested to be moved or linked.
1055 * @new_dir: Destination parent directory.
1056 * @new_dentry: Destination file or directory.
1057 * @removable: Sets to true if it is a rename operation.
1058 * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE.
1059 *
1060 * Because of its unprivileged constraints, Landlock relies on file hierarchies
1061 * (and not only inodes) to tie access rights to files. Being able to link or
1062 * rename a file hierarchy brings some challenges. Indeed, moving or linking a
1063 * file (i.e. creating a new reference to an inode) can have an impact on the
1064 * actions allowed for a set of files if it would change its parent directory
1065 * (i.e. reparenting).
1066 *
1067 * To avoid trivial access right bypasses, Landlock first checks if the file or
1068 * directory requested to be moved would gain new access rights inherited from
1069 * its new hierarchy. Before returning any error, Landlock then checks that
1070 * the parent source hierarchy and the destination hierarchy would allow the
1071 * link or rename action. If it is not the case, an error with EACCES is
1072 * returned to inform user space that there is no way to remove or create the
1073 * requested source file type. If it should be allowed but the new inherited
1074 * access rights would be greater than the source access rights, then the
1075 * kernel returns an error with EXDEV. Prioritizing EACCES over EXDEV enables
1076 * user space to abort the whole operation if there is no way to do it, or to
1077 * manually copy the source to the destination if this remains allowed, e.g.
1078 * because file creation is allowed on the destination directory but not direct
1079 * linking.
1080 *
1081 * To achieve this goal, the kernel needs to compare two file hierarchies: the
1082 * one identifying the source file or directory (including itself), and the
1083 * destination one. This can be seen as a multilayer partial ordering problem.
1084 * The kernel walks through these paths and collects in a matrix the access
1085 * rights that are denied per layer. These matrices are then compared to see
1086 * if the destination one has more (or the same) restrictions as the source
1087 * one. If this is the case, the requested action will not return EXDEV, which
1088 * doesn't mean the action is allowed. The parent hierarchy of the source
1089 * (i.e. parent directory), and the destination hierarchy must also be checked
1090 * to verify that they explicitly allow such action (i.e. referencing,
1091 * creation and potentially removal rights). The kernel implementation is then
1092 * required to rely on potentially four matrices of access rights: one for the
1093 * source file or directory (i.e. the child), a potentially other one for the
1094 * other source/destination (in case of RENAME_EXCHANGE), one for the source
1095 * parent hierarchy and a last one for the destination hierarchy. These
1096 * ephemeral matrices take some space on the stack, which limits the number of
1097 * layers to a deemed reasonable number: 16.
1098 *
1099 * Returns:
1100 * - 0 if access is allowed;
1101 * - -EXDEV if @old_dentry would inherit new access rights from @new_dir;
1102 * - -EACCES if file removal or creation is denied.
1103 */
current_check_refer_path(struct dentry * const old_dentry,const struct path * const new_dir,struct dentry * const new_dentry,const bool removable,const bool exchange)1104 static int current_check_refer_path(struct dentry *const old_dentry,
1105 const struct path *const new_dir,
1106 struct dentry *const new_dentry,
1107 const bool removable, const bool exchange)
1108 {
1109 const struct landlock_ruleset *const dom = get_current_fs_domain();
1110 bool allow_parent1, allow_parent2;
1111 access_mask_t access_request_parent1, access_request_parent2;
1112 struct path mnt_dir;
1113 struct dentry *old_parent;
1114 layer_mask_t layer_masks_parent1[LANDLOCK_NUM_ACCESS_FS] = {},
1115 layer_masks_parent2[LANDLOCK_NUM_ACCESS_FS] = {};
1116
1117 if (!dom)
1118 return 0;
1119 if (WARN_ON_ONCE(dom->num_layers < 1))
1120 return -EACCES;
1121 if (unlikely(d_is_negative(old_dentry)))
1122 return -ENOENT;
1123 if (exchange) {
1124 if (unlikely(d_is_negative(new_dentry)))
1125 return -ENOENT;
1126 access_request_parent1 =
1127 get_mode_access(d_backing_inode(new_dentry)->i_mode);
1128 } else {
1129 access_request_parent1 = 0;
1130 }
1131 access_request_parent2 =
1132 get_mode_access(d_backing_inode(old_dentry)->i_mode);
1133 if (removable) {
1134 access_request_parent1 |= maybe_remove(old_dentry);
1135 access_request_parent2 |= maybe_remove(new_dentry);
1136 }
1137
1138 /* The mount points are the same for old and new paths, cf. EXDEV. */
1139 if (old_dentry->d_parent == new_dir->dentry) {
1140 /*
1141 * The LANDLOCK_ACCESS_FS_REFER access right is not required
1142 * for same-directory referer (i.e. no reparenting).
1143 */
1144 access_request_parent1 = landlock_init_layer_masks(
1145 dom, access_request_parent1 | access_request_parent2,
1146 &layer_masks_parent1, LANDLOCK_KEY_INODE);
1147 if (is_access_to_paths_allowed(
1148 dom, new_dir, access_request_parent1,
1149 &layer_masks_parent1, NULL, 0, NULL, NULL))
1150 return 0;
1151 return -EACCES;
1152 }
1153
1154 access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
1155 access_request_parent2 |= LANDLOCK_ACCESS_FS_REFER;
1156
1157 /* Saves the common mount point. */
1158 mnt_dir.mnt = new_dir->mnt;
1159 mnt_dir.dentry = new_dir->mnt->mnt_root;
1160
1161 /*
1162 * old_dentry may be the root of the common mount point and
1163 * !IS_ROOT(old_dentry) at the same time (e.g. with open_tree() and
1164 * OPEN_TREE_CLONE). We do not need to call dget(old_parent) because
1165 * we keep a reference to old_dentry.
1166 */
1167 old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry :
1168 old_dentry->d_parent;
1169
1170 /* new_dir->dentry is equal to new_dentry->d_parent */
1171 allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry, old_parent,
1172 &layer_masks_parent1);
1173 allow_parent2 = collect_domain_accesses(
1174 dom, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2);
1175
1176 if (allow_parent1 && allow_parent2)
1177 return 0;
1178
1179 /*
1180 * To be able to compare source and destination domain access rights,
1181 * take into account the @old_dentry access rights aggregated with its
1182 * parent access rights. This will be useful to compare with the
1183 * destination parent access rights.
1184 */
1185 if (is_access_to_paths_allowed(
1186 dom, &mnt_dir, access_request_parent1, &layer_masks_parent1,
1187 old_dentry, access_request_parent2, &layer_masks_parent2,
1188 exchange ? new_dentry : NULL))
1189 return 0;
1190
1191 /*
1192 * This prioritizes EACCES over EXDEV for all actions, including
1193 * renames with RENAME_EXCHANGE.
1194 */
1195 if (likely(is_eacces(&layer_masks_parent1, access_request_parent1) ||
1196 is_eacces(&layer_masks_parent2, access_request_parent2)))
1197 return -EACCES;
1198
1199 /*
1200 * Gracefully forbids reparenting if the destination directory
1201 * hierarchy is not a superset of restrictions of the source directory
1202 * hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the
1203 * source or the destination.
1204 */
1205 return -EXDEV;
1206 }
1207
1208 /* Inode hooks */
1209
hook_inode_free_security(struct inode * const inode)1210 static void hook_inode_free_security(struct inode *const inode)
1211 {
1212 /*
1213 * All inodes must already have been untied from their object by
1214 * release_inode() or hook_sb_delete().
1215 */
1216 WARN_ON_ONCE(landlock_inode(inode)->object);
1217 }
1218
1219 /* Super-block hooks */
1220
1221 /*
1222 * Release the inodes used in a security policy.
1223 *
1224 * Cf. fsnotify_unmount_inodes() and invalidate_inodes()
1225 */
hook_sb_delete(struct super_block * const sb)1226 static void hook_sb_delete(struct super_block *const sb)
1227 {
1228 struct inode *inode, *prev_inode = NULL;
1229
1230 if (!landlock_initialized)
1231 return;
1232
1233 spin_lock(&sb->s_inode_list_lock);
1234 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1235 struct landlock_object *object;
1236
1237 /* Only handles referenced inodes. */
1238 if (!atomic_read(&inode->i_count))
1239 continue;
1240
1241 /*
1242 * Protects against concurrent modification of inode (e.g.
1243 * from get_inode_object()).
1244 */
1245 spin_lock(&inode->i_lock);
1246 /*
1247 * Checks I_FREEING and I_WILL_FREE to protect against a race
1248 * condition when release_inode() just called iput(), which
1249 * could lead to a NULL dereference of inode->security or a
1250 * second call to iput() for the same Landlock object. Also
1251 * checks I_NEW because such inode cannot be tied to an object.
1252 */
1253 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
1254 spin_unlock(&inode->i_lock);
1255 continue;
1256 }
1257
1258 rcu_read_lock();
1259 object = rcu_dereference(landlock_inode(inode)->object);
1260 if (!object) {
1261 rcu_read_unlock();
1262 spin_unlock(&inode->i_lock);
1263 continue;
1264 }
1265 /* Keeps a reference to this inode until the next loop walk. */
1266 __iget(inode);
1267 spin_unlock(&inode->i_lock);
1268
1269 /*
1270 * If there is no concurrent release_inode() ongoing, then we
1271 * are in charge of calling iput() on this inode, otherwise we
1272 * will just wait for it to finish.
1273 */
1274 spin_lock(&object->lock);
1275 if (object->underobj == inode) {
1276 object->underobj = NULL;
1277 spin_unlock(&object->lock);
1278 rcu_read_unlock();
1279
1280 /*
1281 * Because object->underobj was not NULL,
1282 * release_inode() and get_inode_object() guarantee
1283 * that it is safe to reset
1284 * landlock_inode(inode)->object while it is not NULL.
1285 * It is therefore not necessary to lock inode->i_lock.
1286 */
1287 rcu_assign_pointer(landlock_inode(inode)->object, NULL);
1288 /*
1289 * At this point, we own the ihold() reference that was
1290 * originally set up by get_inode_object() and the
1291 * __iget() reference that we just set in this loop
1292 * walk. Therefore the following call to iput() will
1293 * not sleep nor drop the inode because there is now at
1294 * least two references to it.
1295 */
1296 iput(inode);
1297 } else {
1298 spin_unlock(&object->lock);
1299 rcu_read_unlock();
1300 }
1301
1302 if (prev_inode) {
1303 /*
1304 * At this point, we still own the __iget() reference
1305 * that we just set in this loop walk. Therefore we
1306 * can drop the list lock and know that the inode won't
1307 * disappear from under us until the next loop walk.
1308 */
1309 spin_unlock(&sb->s_inode_list_lock);
1310 /*
1311 * We can now actually put the inode reference from the
1312 * previous loop walk, which is not needed anymore.
1313 */
1314 iput(prev_inode);
1315 cond_resched();
1316 spin_lock(&sb->s_inode_list_lock);
1317 }
1318 prev_inode = inode;
1319 }
1320 spin_unlock(&sb->s_inode_list_lock);
1321
1322 /* Puts the inode reference from the last loop walk, if any. */
1323 if (prev_inode)
1324 iput(prev_inode);
1325 /* Waits for pending iput() in release_inode(). */
1326 wait_var_event(&landlock_superblock(sb)->inode_refs,
1327 !atomic_long_read(&landlock_superblock(sb)->inode_refs));
1328 }
1329
1330 /*
1331 * Because a Landlock security policy is defined according to the filesystem
1332 * topology (i.e. the mount namespace), changing it may grant access to files
1333 * not previously allowed.
1334 *
1335 * To make it simple, deny any filesystem topology modification by landlocked
1336 * processes. Non-landlocked processes may still change the namespace of a
1337 * landlocked process, but this kind of threat must be handled by a system-wide
1338 * access-control security policy.
1339 *
1340 * This could be lifted in the future if Landlock can safely handle mount
1341 * namespace updates requested by a landlocked process. Indeed, we could
1342 * update the current domain (which is currently read-only) by taking into
1343 * account the accesses of the source and the destination of a new mount point.
1344 * However, it would also require to make all the child domains dynamically
1345 * inherit these new constraints. Anyway, for backward compatibility reasons,
1346 * a dedicated user space option would be required (e.g. as a ruleset flag).
1347 */
hook_sb_mount(const char * const dev_name,const struct path * const path,const char * const type,const unsigned long flags,void * const data)1348 static int hook_sb_mount(const char *const dev_name,
1349 const struct path *const path, const char *const type,
1350 const unsigned long flags, void *const data)
1351 {
1352 if (!get_current_fs_domain())
1353 return 0;
1354 return -EPERM;
1355 }
1356
hook_move_mount(const struct path * const from_path,const struct path * const to_path)1357 static int hook_move_mount(const struct path *const from_path,
1358 const struct path *const to_path)
1359 {
1360 if (!get_current_fs_domain())
1361 return 0;
1362 return -EPERM;
1363 }
1364
1365 /*
1366 * Removing a mount point may reveal a previously hidden file hierarchy, which
1367 * may then grant access to files, which may have previously been forbidden.
1368 */
hook_sb_umount(struct vfsmount * const mnt,const int flags)1369 static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
1370 {
1371 if (!get_current_fs_domain())
1372 return 0;
1373 return -EPERM;
1374 }
1375
hook_sb_remount(struct super_block * const sb,void * const mnt_opts)1376 static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
1377 {
1378 if (!get_current_fs_domain())
1379 return 0;
1380 return -EPERM;
1381 }
1382
1383 /*
1384 * pivot_root(2), like mount(2), changes the current mount namespace. It must
1385 * then be forbidden for a landlocked process.
1386 *
1387 * However, chroot(2) may be allowed because it only changes the relative root
1388 * directory of the current process. Moreover, it can be used to restrict the
1389 * view of the filesystem.
1390 */
hook_sb_pivotroot(const struct path * const old_path,const struct path * const new_path)1391 static int hook_sb_pivotroot(const struct path *const old_path,
1392 const struct path *const new_path)
1393 {
1394 if (!get_current_fs_domain())
1395 return 0;
1396 return -EPERM;
1397 }
1398
1399 /* Path hooks */
1400
hook_path_link(struct dentry * const old_dentry,const struct path * const new_dir,struct dentry * const new_dentry)1401 static int hook_path_link(struct dentry *const old_dentry,
1402 const struct path *const new_dir,
1403 struct dentry *const new_dentry)
1404 {
1405 return current_check_refer_path(old_dentry, new_dir, new_dentry, false,
1406 false);
1407 }
1408
hook_path_rename(const struct path * const old_dir,struct dentry * const old_dentry,const struct path * const new_dir,struct dentry * const new_dentry,const unsigned int flags)1409 static int hook_path_rename(const struct path *const old_dir,
1410 struct dentry *const old_dentry,
1411 const struct path *const new_dir,
1412 struct dentry *const new_dentry,
1413 const unsigned int flags)
1414 {
1415 /* old_dir refers to old_dentry->d_parent and new_dir->mnt */
1416 return current_check_refer_path(old_dentry, new_dir, new_dentry, true,
1417 !!(flags & RENAME_EXCHANGE));
1418 }
1419
hook_path_mkdir(const struct path * const dir,struct dentry * const dentry,const umode_t mode)1420 static int hook_path_mkdir(const struct path *const dir,
1421 struct dentry *const dentry, const umode_t mode)
1422 {
1423 return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR);
1424 }
1425
hook_path_mknod(const struct path * const dir,struct dentry * const dentry,const umode_t mode,const unsigned int dev)1426 static int hook_path_mknod(const struct path *const dir,
1427 struct dentry *const dentry, const umode_t mode,
1428 const unsigned int dev)
1429 {
1430 const struct landlock_ruleset *const dom = get_current_fs_domain();
1431
1432 if (!dom)
1433 return 0;
1434 return check_access_path(dom, dir, get_mode_access(mode));
1435 }
1436
hook_path_symlink(const struct path * const dir,struct dentry * const dentry,const char * const old_name)1437 static int hook_path_symlink(const struct path *const dir,
1438 struct dentry *const dentry,
1439 const char *const old_name)
1440 {
1441 return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM);
1442 }
1443
hook_path_unlink(const struct path * const dir,struct dentry * const dentry)1444 static int hook_path_unlink(const struct path *const dir,
1445 struct dentry *const dentry)
1446 {
1447 return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE);
1448 }
1449
hook_path_rmdir(const struct path * const dir,struct dentry * const dentry)1450 static int hook_path_rmdir(const struct path *const dir,
1451 struct dentry *const dentry)
1452 {
1453 return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR);
1454 }
1455
hook_path_truncate(const struct path * const path)1456 static int hook_path_truncate(const struct path *const path)
1457 {
1458 return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
1459 }
1460
1461 /* File hooks */
1462
1463 /**
1464 * get_required_file_open_access - Get access needed to open a file
1465 *
1466 * @file: File being opened.
1467 *
1468 * Returns the access rights that are required for opening the given file,
1469 * depending on the file type and open mode.
1470 */
1471 static access_mask_t
get_required_file_open_access(const struct file * const file)1472 get_required_file_open_access(const struct file *const file)
1473 {
1474 access_mask_t access = 0;
1475
1476 if (file->f_mode & FMODE_READ) {
1477 /* A directory can only be opened in read mode. */
1478 if (S_ISDIR(file_inode(file)->i_mode))
1479 return LANDLOCK_ACCESS_FS_READ_DIR;
1480 access = LANDLOCK_ACCESS_FS_READ_FILE;
1481 }
1482 if (file->f_mode & FMODE_WRITE)
1483 access |= LANDLOCK_ACCESS_FS_WRITE_FILE;
1484 /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */
1485 if (file->f_flags & __FMODE_EXEC)
1486 access |= LANDLOCK_ACCESS_FS_EXECUTE;
1487 return access;
1488 }
1489
hook_file_alloc_security(struct file * const file)1490 static int hook_file_alloc_security(struct file *const file)
1491 {
1492 /*
1493 * Grants all access rights, even if most of them are not checked later
1494 * on. It is more consistent.
1495 *
1496 * Notably, file descriptors for regular files can also be acquired
1497 * without going through the file_open hook, for example when using
1498 * memfd_create(2).
1499 */
1500 landlock_file(file)->allowed_access = LANDLOCK_MASK_ACCESS_FS;
1501 return 0;
1502 }
1503
is_device(const struct file * const file)1504 static bool is_device(const struct file *const file)
1505 {
1506 const struct inode *inode = file_inode(file);
1507
1508 return S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode);
1509 }
1510
hook_file_open(struct file * const file)1511 static int hook_file_open(struct file *const file)
1512 {
1513 layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
1514 access_mask_t open_access_request, full_access_request, allowed_access,
1515 optional_access;
1516 const struct landlock_ruleset *const dom =
1517 get_fs_domain(landlock_cred(file->f_cred)->domain);
1518
1519 if (!dom)
1520 return 0;
1521
1522 /*
1523 * Because a file may be opened with O_PATH, get_required_file_open_access()
1524 * may return 0. This case will be handled with a future Landlock
1525 * evolution.
1526 */
1527 open_access_request = get_required_file_open_access(file);
1528
1529 /*
1530 * We look up more access than what we immediately need for open(), so
1531 * that we can later authorize operations on opened files.
1532 */
1533 optional_access = LANDLOCK_ACCESS_FS_TRUNCATE;
1534 if (is_device(file))
1535 optional_access |= LANDLOCK_ACCESS_FS_IOCTL_DEV;
1536
1537 full_access_request = open_access_request | optional_access;
1538
1539 if (is_access_to_paths_allowed(
1540 dom, &file->f_path,
1541 landlock_init_layer_masks(dom, full_access_request,
1542 &layer_masks, LANDLOCK_KEY_INODE),
1543 &layer_masks, NULL, 0, NULL, NULL)) {
1544 allowed_access = full_access_request;
1545 } else {
1546 unsigned long access_bit;
1547 const unsigned long access_req = full_access_request;
1548
1549 /*
1550 * Calculate the actual allowed access rights from layer_masks.
1551 * Add each access right to allowed_access which has not been
1552 * vetoed by any layer.
1553 */
1554 allowed_access = 0;
1555 for_each_set_bit(access_bit, &access_req,
1556 ARRAY_SIZE(layer_masks)) {
1557 if (!layer_masks[access_bit])
1558 allowed_access |= BIT_ULL(access_bit);
1559 }
1560 }
1561
1562 /*
1563 * For operations on already opened files (i.e. ftruncate()), it is the
1564 * access rights at the time of open() which decide whether the
1565 * operation is permitted. Therefore, we record the relevant subset of
1566 * file access rights in the opened struct file.
1567 */
1568 landlock_file(file)->allowed_access = allowed_access;
1569
1570 if ((open_access_request & allowed_access) == open_access_request)
1571 return 0;
1572
1573 return -EACCES;
1574 }
1575
hook_file_truncate(struct file * const file)1576 static int hook_file_truncate(struct file *const file)
1577 {
1578 /*
1579 * Allows truncation if the truncate right was available at the time of
1580 * opening the file, to get a consistent access check as for read, write
1581 * and execute operations.
1582 *
1583 * Note: For checks done based on the file's Landlock allowed access, we
1584 * enforce them independently of whether the current thread is in a
1585 * Landlock domain, so that open files passed between independent
1586 * processes retain their behaviour.
1587 */
1588 if (landlock_file(file)->allowed_access & LANDLOCK_ACCESS_FS_TRUNCATE)
1589 return 0;
1590 return -EACCES;
1591 }
1592
hook_file_ioctl(struct file * file,unsigned int cmd,unsigned long arg)1593 static int hook_file_ioctl(struct file *file, unsigned int cmd,
1594 unsigned long arg)
1595 {
1596 access_mask_t allowed_access = landlock_file(file)->allowed_access;
1597
1598 /*
1599 * It is the access rights at the time of opening the file which
1600 * determine whether IOCTL can be used on the opened file later.
1601 *
1602 * The access right is attached to the opened file in hook_file_open().
1603 */
1604 if (allowed_access & LANDLOCK_ACCESS_FS_IOCTL_DEV)
1605 return 0;
1606
1607 if (!is_device(file))
1608 return 0;
1609
1610 if (is_masked_device_ioctl(cmd))
1611 return 0;
1612
1613 return -EACCES;
1614 }
1615
hook_file_ioctl_compat(struct file * file,unsigned int cmd,unsigned long arg)1616 static int hook_file_ioctl_compat(struct file *file, unsigned int cmd,
1617 unsigned long arg)
1618 {
1619 access_mask_t allowed_access = landlock_file(file)->allowed_access;
1620
1621 /*
1622 * It is the access rights at the time of opening the file which
1623 * determine whether IOCTL can be used on the opened file later.
1624 *
1625 * The access right is attached to the opened file in hook_file_open().
1626 */
1627 if (allowed_access & LANDLOCK_ACCESS_FS_IOCTL_DEV)
1628 return 0;
1629
1630 if (!is_device(file))
1631 return 0;
1632
1633 if (is_masked_device_ioctl_compat(cmd))
1634 return 0;
1635
1636 return -EACCES;
1637 }
1638
1639 static struct security_hook_list landlock_hooks[] __ro_after_init = {
1640 LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
1641
1642 LSM_HOOK_INIT(sb_delete, hook_sb_delete),
1643 LSM_HOOK_INIT(sb_mount, hook_sb_mount),
1644 LSM_HOOK_INIT(move_mount, hook_move_mount),
1645 LSM_HOOK_INIT(sb_umount, hook_sb_umount),
1646 LSM_HOOK_INIT(sb_remount, hook_sb_remount),
1647 LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot),
1648
1649 LSM_HOOK_INIT(path_link, hook_path_link),
1650 LSM_HOOK_INIT(path_rename, hook_path_rename),
1651 LSM_HOOK_INIT(path_mkdir, hook_path_mkdir),
1652 LSM_HOOK_INIT(path_mknod, hook_path_mknod),
1653 LSM_HOOK_INIT(path_symlink, hook_path_symlink),
1654 LSM_HOOK_INIT(path_unlink, hook_path_unlink),
1655 LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
1656 LSM_HOOK_INIT(path_truncate, hook_path_truncate),
1657
1658 LSM_HOOK_INIT(file_alloc_security, hook_file_alloc_security),
1659 LSM_HOOK_INIT(file_open, hook_file_open),
1660 LSM_HOOK_INIT(file_truncate, hook_file_truncate),
1661 LSM_HOOK_INIT(file_ioctl, hook_file_ioctl),
1662 LSM_HOOK_INIT(file_ioctl_compat, hook_file_ioctl_compat),
1663 };
1664
landlock_add_fs_hooks(void)1665 __init void landlock_add_fs_hooks(void)
1666 {
1667 security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
1668 &landlock_lsmid);
1669 }
1670
1671 #ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
1672
1673 /* clang-format off */
1674 static struct kunit_case test_cases[] = {
1675 KUNIT_CASE(test_no_more_access),
1676 KUNIT_CASE(test_scope_to_request_with_exec_none),
1677 KUNIT_CASE(test_scope_to_request_with_exec_some),
1678 KUNIT_CASE(test_scope_to_request_without_access),
1679 KUNIT_CASE(test_is_eacces_with_none),
1680 KUNIT_CASE(test_is_eacces_with_refer),
1681 KUNIT_CASE(test_is_eacces_with_write),
1682 {}
1683 };
1684 /* clang-format on */
1685
1686 static struct kunit_suite test_suite = {
1687 .name = "landlock_fs",
1688 .test_cases = test_cases,
1689 };
1690
1691 kunit_test_suite(test_suite);
1692
1693 #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
1694