Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0-or-later
2 : /*
3 : * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
4 : */
5 :
6 : /*
7 : * fsnotify inode mark locking/lifetime/and refcnting
8 : *
9 : * REFCNT:
10 : * The group->recnt and mark->refcnt tell how many "things" in the kernel
11 : * currently are referencing the objects. Both kind of objects typically will
12 : * live inside the kernel with a refcnt of 2, one for its creation and one for
13 : * the reference a group and a mark hold to each other.
14 : * If you are holding the appropriate locks, you can take a reference and the
15 : * object itself is guaranteed to survive until the reference is dropped.
16 : *
17 : * LOCKING:
18 : * There are 3 locks involved with fsnotify inode marks and they MUST be taken
19 : * in order as follows:
20 : *
21 : * group->mark_mutex
22 : * mark->lock
23 : * mark->connector->lock
24 : *
25 : * group->mark_mutex protects the marks_list anchored inside a given group and
26 : * each mark is hooked via the g_list. It also protects the groups private
27 : * data (i.e group limits).
28 :
29 : * mark->lock protects the marks attributes like its masks and flags.
30 : * Furthermore it protects the access to a reference of the group that the mark
31 : * is assigned to as well as the access to a reference of the inode/vfsmount
32 : * that is being watched by the mark.
33 : *
34 : * mark->connector->lock protects the list of marks anchored inside an
35 : * inode / vfsmount and each mark is hooked via the i_list.
36 : *
37 : * A list of notification marks relating to inode / mnt is contained in
38 : * fsnotify_mark_connector. That structure is alive as long as there are any
39 : * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
40 : * detached from fsnotify_mark_connector when last reference to the mark is
41 : * dropped. Thus having mark reference is enough to protect mark->connector
42 : * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
43 : * because we remove mark from g_list before dropping mark reference associated
44 : * with that, any mark found through g_list is guaranteed to have
45 : * mark->connector set until we drop group->mark_mutex.
46 : *
47 : * LIFETIME:
48 : * Inode marks survive between when they are added to an inode and when their
49 : * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
50 : *
51 : * The inode mark can be cleared for a number of different reasons including:
52 : * - The inode is unlinked for the last time. (fsnotify_inode_remove)
53 : * - The inode is being evicted from cache. (fsnotify_inode_delete)
54 : * - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
55 : * - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
56 : * - The fsnotify_group associated with the mark is going away and all such marks
57 : * need to be cleaned up. (fsnotify_clear_marks_by_group)
58 : *
59 : * This has the very interesting property of being able to run concurrently with
60 : * any (or all) other directions.
61 : */
62 :
63 : #include <linux/fs.h>
64 : #include <linux/init.h>
65 : #include <linux/kernel.h>
66 : #include <linux/kthread.h>
67 : #include <linux/module.h>
68 : #include <linux/mutex.h>
69 : #include <linux/slab.h>
70 : #include <linux/spinlock.h>
71 : #include <linux/srcu.h>
72 : #include <linux/ratelimit.h>
73 :
74 : #include <linux/atomic.h>
75 :
76 : #include <linux/fsnotify_backend.h>
77 : #include "fsnotify.h"
78 :
79 : #define FSNOTIFY_REAPER_DELAY (1) /* 1 jiffy */
80 :
81 : struct srcu_struct fsnotify_mark_srcu;
82 : struct kmem_cache *fsnotify_mark_connector_cachep;
83 :
84 : static DEFINE_SPINLOCK(destroy_lock);
85 : static LIST_HEAD(destroy_list);
86 : static struct fsnotify_mark_connector *connector_destroy_list;
87 :
88 : static void fsnotify_mark_destroy_workfn(struct work_struct *work);
89 : static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);
90 :
91 : static void fsnotify_connector_destroy_workfn(struct work_struct *work);
92 : static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
93 :
94 0 : void fsnotify_get_mark(struct fsnotify_mark *mark)
95 : {
96 0 : WARN_ON_ONCE(!refcount_read(&mark->refcnt));
97 0 : refcount_inc(&mark->refcnt);
98 0 : }
99 :
100 : static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
101 : {
102 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
103 0 : return &fsnotify_conn_inode(conn)->i_fsnotify_mask;
104 0 : else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
105 0 : return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask;
106 0 : else if (conn->type == FSNOTIFY_OBJ_TYPE_SB)
107 0 : return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
108 : return NULL;
109 : }
110 :
111 0 : __u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn)
112 : {
113 0 : if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
114 : return 0;
115 :
116 0 : return *fsnotify_conn_mask_p(conn);
117 : }
118 :
119 0 : static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
120 : {
121 0 : u32 new_mask = 0;
122 : struct fsnotify_mark *mark;
123 :
124 : assert_spin_locked(&conn->lock);
125 : /* We can get detached connector here when inode is getting unlinked. */
126 0 : if (!fsnotify_valid_obj_type(conn->type))
127 : return;
128 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
129 0 : if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
130 0 : new_mask |= fsnotify_calc_mask(mark);
131 : }
132 0 : *fsnotify_conn_mask_p(conn) = new_mask;
133 : }
134 :
135 : /*
136 : * Calculate mask of events for a list of marks. The caller must make sure
137 : * connector and connector->obj cannot disappear under us. Callers achieve
138 : * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
139 : * list.
140 : */
141 0 : void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
142 : {
143 0 : if (!conn)
144 : return;
145 :
146 0 : spin_lock(&conn->lock);
147 0 : __fsnotify_recalc_mask(conn);
148 0 : spin_unlock(&conn->lock);
149 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
150 0 : __fsnotify_update_child_dentry_flags(
151 : fsnotify_conn_inode(conn));
152 : }
153 :
154 : /* Free all connectors queued for freeing once SRCU period ends */
155 0 : static void fsnotify_connector_destroy_workfn(struct work_struct *work)
156 : {
157 : struct fsnotify_mark_connector *conn, *free;
158 :
159 0 : spin_lock(&destroy_lock);
160 0 : conn = connector_destroy_list;
161 0 : connector_destroy_list = NULL;
162 0 : spin_unlock(&destroy_lock);
163 :
164 0 : synchronize_srcu(&fsnotify_mark_srcu);
165 0 : while (conn) {
166 0 : free = conn;
167 0 : conn = conn->destroy_next;
168 0 : kmem_cache_free(fsnotify_mark_connector_cachep, free);
169 : }
170 0 : }
171 :
172 : static void fsnotify_get_inode_ref(struct inode *inode)
173 : {
174 0 : ihold(inode);
175 0 : atomic_long_inc(&inode->i_sb->s_fsnotify_connectors);
176 : }
177 :
178 0 : static void fsnotify_put_inode_ref(struct inode *inode)
179 : {
180 0 : struct super_block *sb = inode->i_sb;
181 :
182 0 : iput(inode);
183 0 : if (atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
184 0 : wake_up_var(&sb->s_fsnotify_connectors);
185 0 : }
186 :
187 : static void fsnotify_get_sb_connectors(struct fsnotify_mark_connector *conn)
188 : {
189 0 : struct super_block *sb = fsnotify_connector_sb(conn);
190 :
191 0 : if (sb)
192 0 : atomic_long_inc(&sb->s_fsnotify_connectors);
193 : }
194 :
195 0 : static void fsnotify_put_sb_connectors(struct fsnotify_mark_connector *conn)
196 : {
197 0 : struct super_block *sb = fsnotify_connector_sb(conn);
198 :
199 0 : if (sb && atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
200 0 : wake_up_var(&sb->s_fsnotify_connectors);
201 0 : }
202 :
203 0 : static void *fsnotify_detach_connector_from_object(
204 : struct fsnotify_mark_connector *conn,
205 : unsigned int *type)
206 : {
207 0 : struct inode *inode = NULL;
208 :
209 0 : *type = conn->type;
210 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
211 : return NULL;
212 :
213 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
214 0 : inode = fsnotify_conn_inode(conn);
215 0 : inode->i_fsnotify_mask = 0;
216 0 : } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
217 0 : fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
218 0 : } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
219 0 : fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
220 : }
221 :
222 0 : fsnotify_put_sb_connectors(conn);
223 0 : rcu_assign_pointer(*(conn->obj), NULL);
224 0 : conn->obj = NULL;
225 0 : conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
226 :
227 0 : return inode;
228 : }
229 :
230 0 : static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
231 : {
232 0 : struct fsnotify_group *group = mark->group;
233 :
234 0 : if (WARN_ON_ONCE(!group))
235 : return;
236 0 : group->ops->free_mark(mark);
237 0 : fsnotify_put_group(group);
238 : }
239 :
240 : /* Drop object reference originally held by a connector */
241 0 : static void fsnotify_drop_object(unsigned int type, void *objp)
242 : {
243 0 : if (!objp)
244 : return;
245 : /* Currently only inode references are passed to be dropped */
246 0 : if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
247 : return;
248 0 : fsnotify_put_inode_ref(objp);
249 : }
250 :
251 0 : void fsnotify_put_mark(struct fsnotify_mark *mark)
252 : {
253 0 : struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
254 0 : void *objp = NULL;
255 0 : unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
256 0 : bool free_conn = false;
257 :
258 : /* Catch marks that were actually never attached to object */
259 0 : if (!conn) {
260 0 : if (refcount_dec_and_test(&mark->refcnt))
261 0 : fsnotify_final_mark_destroy(mark);
262 0 : return;
263 : }
264 :
265 : /*
266 : * We have to be careful so that traversals of obj_list under lock can
267 : * safely grab mark reference.
268 : */
269 0 : if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
270 : return;
271 :
272 0 : hlist_del_init_rcu(&mark->obj_list);
273 0 : if (hlist_empty(&conn->list)) {
274 0 : objp = fsnotify_detach_connector_from_object(conn, &type);
275 0 : free_conn = true;
276 : } else {
277 0 : __fsnotify_recalc_mask(conn);
278 : }
279 0 : WRITE_ONCE(mark->connector, NULL);
280 0 : spin_unlock(&conn->lock);
281 :
282 0 : fsnotify_drop_object(type, objp);
283 :
284 0 : if (free_conn) {
285 0 : spin_lock(&destroy_lock);
286 0 : conn->destroy_next = connector_destroy_list;
287 0 : connector_destroy_list = conn;
288 0 : spin_unlock(&destroy_lock);
289 0 : queue_work(system_unbound_wq, &connector_reaper_work);
290 : }
291 : /*
292 : * Note that we didn't update flags telling whether inode cares about
293 : * what's happening with children. We update these flags from
294 : * __fsnotify_parent() lazily when next event happens on one of our
295 : * children.
296 : */
297 0 : spin_lock(&destroy_lock);
298 0 : list_add(&mark->g_list, &destroy_list);
299 0 : spin_unlock(&destroy_lock);
300 0 : queue_delayed_work(system_unbound_wq, &reaper_work,
301 : FSNOTIFY_REAPER_DELAY);
302 : }
303 : EXPORT_SYMBOL_GPL(fsnotify_put_mark);
304 :
305 : /*
306 : * Get mark reference when we found the mark via lockless traversal of object
307 : * list. Mark can be already removed from the list by now and on its way to be
308 : * destroyed once SRCU period ends.
309 : *
310 : * Also pin the group so it doesn't disappear under us.
311 : */
312 0 : static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
313 : {
314 0 : if (!mark)
315 : return true;
316 :
317 0 : if (refcount_inc_not_zero(&mark->refcnt)) {
318 0 : spin_lock(&mark->lock);
319 0 : if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
320 : /* mark is attached, group is still alive then */
321 0 : atomic_inc(&mark->group->user_waits);
322 0 : spin_unlock(&mark->lock);
323 0 : return true;
324 : }
325 0 : spin_unlock(&mark->lock);
326 0 : fsnotify_put_mark(mark);
327 : }
328 : return false;
329 : }
330 :
331 : /*
332 : * Puts marks and wakes up group destruction if necessary.
333 : *
334 : * Pairs with fsnotify_get_mark_safe()
335 : */
336 0 : static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
337 : {
338 0 : if (mark) {
339 0 : struct fsnotify_group *group = mark->group;
340 :
341 0 : fsnotify_put_mark(mark);
342 : /*
343 : * We abuse notification_waitq on group shutdown for waiting for
344 : * all marks pinned when waiting for userspace.
345 : */
346 0 : if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
347 0 : wake_up(&group->notification_waitq);
348 : }
349 0 : }
350 :
351 0 : bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
352 : __releases(&fsnotify_mark_srcu)
353 : {
354 : int type;
355 :
356 0 : fsnotify_foreach_iter_type(type) {
357 : /* This can fail if mark is being removed */
358 0 : if (!fsnotify_get_mark_safe(iter_info->marks[type])) {
359 : __release(&fsnotify_mark_srcu);
360 : goto fail;
361 : }
362 : }
363 :
364 : /*
365 : * Now that both marks are pinned by refcount in the inode / vfsmount
366 : * lists, we can drop SRCU lock, and safely resume the list iteration
367 : * once userspace returns.
368 : */
369 0 : srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
370 :
371 0 : return true;
372 :
373 : fail:
374 0 : for (type--; type >= 0; type--)
375 0 : fsnotify_put_mark_wake(iter_info->marks[type]);
376 : return false;
377 : }
378 :
379 0 : void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
380 : __acquires(&fsnotify_mark_srcu)
381 : {
382 : int type;
383 :
384 0 : iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
385 0 : fsnotify_foreach_iter_type(type)
386 0 : fsnotify_put_mark_wake(iter_info->marks[type]);
387 0 : }
388 :
389 : /*
390 : * Mark mark as detached, remove it from group list. Mark still stays in object
391 : * list until its last reference is dropped. Note that we rely on mark being
392 : * removed from group list before corresponding reference to it is dropped. In
393 : * particular we rely on mark->connector being valid while we hold
394 : * group->mark_mutex if we found the mark through g_list.
395 : *
396 : * Must be called with group->mark_mutex held. The caller must either hold
397 : * reference to the mark or be protected by fsnotify_mark_srcu.
398 : */
399 0 : void fsnotify_detach_mark(struct fsnotify_mark *mark)
400 : {
401 0 : struct fsnotify_group *group = mark->group;
402 :
403 0 : WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
404 0 : WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
405 : refcount_read(&mark->refcnt) < 1 +
406 : !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
407 :
408 0 : spin_lock(&mark->lock);
409 : /* something else already called this function on this mark */
410 0 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
411 0 : spin_unlock(&mark->lock);
412 : return;
413 : }
414 0 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
415 0 : list_del_init(&mark->g_list);
416 0 : spin_unlock(&mark->lock);
417 :
418 : /* Drop mark reference acquired in fsnotify_add_mark_locked() */
419 0 : fsnotify_put_mark(mark);
420 : }
421 :
422 : /*
423 : * Free fsnotify mark. The mark is actually only marked as being freed. The
424 : * freeing is actually happening only once last reference to the mark is
425 : * dropped from a workqueue which first waits for srcu period end.
426 : *
427 : * Caller must have a reference to the mark or be protected by
428 : * fsnotify_mark_srcu.
429 : */
430 0 : void fsnotify_free_mark(struct fsnotify_mark *mark)
431 : {
432 0 : struct fsnotify_group *group = mark->group;
433 :
434 0 : spin_lock(&mark->lock);
435 : /* something else already called this function on this mark */
436 0 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
437 0 : spin_unlock(&mark->lock);
438 : return;
439 : }
440 0 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
441 0 : spin_unlock(&mark->lock);
442 :
443 : /*
444 : * Some groups like to know that marks are being freed. This is a
445 : * callback to the group function to let it know that this mark
446 : * is being freed.
447 : */
448 0 : if (group->ops->freeing_mark)
449 0 : group->ops->freeing_mark(mark, group);
450 : }
451 :
452 0 : void fsnotify_destroy_mark(struct fsnotify_mark *mark,
453 : struct fsnotify_group *group)
454 : {
455 0 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
456 0 : fsnotify_detach_mark(mark);
457 0 : mutex_unlock(&group->mark_mutex);
458 0 : fsnotify_free_mark(mark);
459 0 : }
460 : EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
461 :
462 : /*
463 : * Sorting function for lists of fsnotify marks.
464 : *
465 : * Fanotify supports different notification classes (reflected as priority of
466 : * notification group). Events shall be passed to notification groups in
467 : * decreasing priority order. To achieve this marks in notification lists for
468 : * inodes and vfsmounts are sorted so that priorities of corresponding groups
469 : * are descending.
470 : *
471 : * Furthermore correct handling of the ignore mask requires processing inode
472 : * and vfsmount marks of each group together. Using the group address as
473 : * further sort criterion provides a unique sorting order and thus we can
474 : * merge inode and vfsmount lists of marks in linear time and find groups
475 : * present in both lists.
476 : *
477 : * A return value of 1 signifies that b has priority over a.
478 : * A return value of 0 signifies that the two marks have to be handled together.
479 : * A return value of -1 signifies that a has priority over b.
480 : */
481 0 : int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
482 : {
483 0 : if (a == b)
484 : return 0;
485 0 : if (!a)
486 : return 1;
487 0 : if (!b)
488 : return -1;
489 0 : if (a->priority < b->priority)
490 : return 1;
491 0 : if (a->priority > b->priority)
492 : return -1;
493 0 : if (a < b)
494 : return 1;
495 0 : return -1;
496 : }
497 :
498 0 : static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
499 : unsigned int obj_type,
500 : __kernel_fsid_t *fsid)
501 : {
502 0 : struct inode *inode = NULL;
503 : struct fsnotify_mark_connector *conn;
504 :
505 0 : conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
506 0 : if (!conn)
507 : return -ENOMEM;
508 0 : spin_lock_init(&conn->lock);
509 0 : INIT_HLIST_HEAD(&conn->list);
510 0 : conn->type = obj_type;
511 0 : conn->obj = connp;
512 : /* Cache fsid of filesystem containing the object */
513 0 : if (fsid) {
514 0 : conn->fsid = *fsid;
515 0 : conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
516 : } else {
517 0 : conn->fsid.val[0] = conn->fsid.val[1] = 0;
518 0 : conn->flags = 0;
519 : }
520 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
521 0 : inode = fsnotify_conn_inode(conn);
522 : fsnotify_get_inode_ref(inode);
523 : }
524 0 : fsnotify_get_sb_connectors(conn);
525 :
526 : /*
527 : * cmpxchg() provides the barrier so that readers of *connp can see
528 : * only initialized structure
529 : */
530 0 : if (cmpxchg(connp, NULL, conn)) {
531 : /* Someone else created list structure for us */
532 0 : if (inode)
533 0 : fsnotify_put_inode_ref(inode);
534 0 : fsnotify_put_sb_connectors(conn);
535 0 : kmem_cache_free(fsnotify_mark_connector_cachep, conn);
536 : }
537 :
538 : return 0;
539 : }
540 :
541 : /*
542 : * Get mark connector, make sure it is alive and return with its lock held.
543 : * This is for users that get connector pointer from inode or mount. Users that
544 : * hold reference to a mark on the list may directly lock connector->lock as
545 : * they are sure list cannot go away under them.
546 : */
547 0 : static struct fsnotify_mark_connector *fsnotify_grab_connector(
548 : fsnotify_connp_t *connp)
549 : {
550 : struct fsnotify_mark_connector *conn;
551 : int idx;
552 :
553 0 : idx = srcu_read_lock(&fsnotify_mark_srcu);
554 0 : conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
555 0 : if (!conn)
556 : goto out;
557 0 : spin_lock(&conn->lock);
558 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
559 0 : spin_unlock(&conn->lock);
560 0 : srcu_read_unlock(&fsnotify_mark_srcu, idx);
561 0 : return NULL;
562 : }
563 : out:
564 0 : srcu_read_unlock(&fsnotify_mark_srcu, idx);
565 0 : return conn;
566 : }
567 :
568 : /*
569 : * Add mark into proper place in given list of marks. These marks may be used
570 : * for the fsnotify backend to determine which event types should be delivered
571 : * to which group and for which inodes. These marks are ordered according to
572 : * priority, highest number first, and then by the group's location in memory.
573 : */
574 0 : static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
575 : fsnotify_connp_t *connp,
576 : unsigned int obj_type,
577 : int allow_dups, __kernel_fsid_t *fsid)
578 : {
579 0 : struct fsnotify_mark *lmark, *last = NULL;
580 : struct fsnotify_mark_connector *conn;
581 : int cmp;
582 0 : int err = 0;
583 :
584 0 : if (WARN_ON(!fsnotify_valid_obj_type(obj_type)))
585 : return -EINVAL;
586 :
587 : /* Backend is expected to check for zero fsid (e.g. tmpfs) */
588 0 : if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1]))
589 : return -ENODEV;
590 :
591 : restart:
592 0 : spin_lock(&mark->lock);
593 0 : conn = fsnotify_grab_connector(connp);
594 0 : if (!conn) {
595 0 : spin_unlock(&mark->lock);
596 0 : err = fsnotify_attach_connector_to_object(connp, obj_type,
597 : fsid);
598 0 : if (err)
599 : return err;
600 : goto restart;
601 0 : } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
602 0 : conn->fsid = *fsid;
603 : /* Pairs with smp_rmb() in fanotify_get_fsid() */
604 0 : smp_wmb();
605 0 : conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
606 0 : } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
607 0 : (fsid->val[0] != conn->fsid.val[0] ||
608 0 : fsid->val[1] != conn->fsid.val[1])) {
609 : /*
610 : * Backend is expected to check for non uniform fsid
611 : * (e.g. btrfs), but maybe we missed something?
612 : * Only allow setting conn->fsid once to non zero fsid.
613 : * inotify and non-fid fanotify groups do not set nor test
614 : * conn->fsid.
615 : */
616 0 : pr_warn_ratelimited("%s: fsid mismatch on object of type %u: "
617 : "%x.%x != %x.%x\n", __func__, conn->type,
618 : fsid->val[0], fsid->val[1],
619 : conn->fsid.val[0], conn->fsid.val[1]);
620 : err = -EXDEV;
621 : goto out_err;
622 : }
623 :
624 : /* is mark the first mark? */
625 0 : if (hlist_empty(&conn->list)) {
626 0 : hlist_add_head_rcu(&mark->obj_list, &conn->list);
627 : goto added;
628 : }
629 :
630 : /* should mark be in the middle of the current list? */
631 0 : hlist_for_each_entry(lmark, &conn->list, obj_list) {
632 0 : last = lmark;
633 :
634 0 : if ((lmark->group == mark->group) &&
635 0 : (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
636 : !allow_dups) {
637 : err = -EEXIST;
638 : goto out_err;
639 : }
640 :
641 0 : cmp = fsnotify_compare_groups(lmark->group, mark->group);
642 0 : if (cmp >= 0) {
643 0 : hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
644 : goto added;
645 : }
646 : }
647 :
648 0 : BUG_ON(last == NULL);
649 : /* mark should be the last entry. last is the current last entry */
650 0 : hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
651 : added:
652 : /*
653 : * Since connector is attached to object using cmpxchg() we are
654 : * guaranteed that connector initialization is fully visible by anyone
655 : * seeing mark->connector set.
656 : */
657 0 : WRITE_ONCE(mark->connector, conn);
658 : out_err:
659 0 : spin_unlock(&conn->lock);
660 0 : spin_unlock(&mark->lock);
661 0 : return err;
662 : }
663 :
664 : /*
665 : * Attach an initialized mark to a given group and fs object.
666 : * These marks may be used for the fsnotify backend to determine which
667 : * event types should be delivered to which group.
668 : */
669 0 : int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
670 : fsnotify_connp_t *connp, unsigned int obj_type,
671 : int allow_dups, __kernel_fsid_t *fsid)
672 : {
673 0 : struct fsnotify_group *group = mark->group;
674 0 : int ret = 0;
675 :
676 0 : BUG_ON(!mutex_is_locked(&group->mark_mutex));
677 :
678 : /*
679 : * LOCKING ORDER!!!!
680 : * group->mark_mutex
681 : * mark->lock
682 : * mark->connector->lock
683 : */
684 0 : spin_lock(&mark->lock);
685 0 : mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
686 :
687 0 : list_add(&mark->g_list, &group->marks_list);
688 0 : fsnotify_get_mark(mark); /* for g_list */
689 0 : spin_unlock(&mark->lock);
690 :
691 0 : ret = fsnotify_add_mark_list(mark, connp, obj_type, allow_dups, fsid);
692 0 : if (ret)
693 : goto err;
694 :
695 0 : if (mark->mask || mark->ignored_mask)
696 0 : fsnotify_recalc_mask(mark->connector);
697 :
698 : return ret;
699 : err:
700 0 : spin_lock(&mark->lock);
701 0 : mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
702 : FSNOTIFY_MARK_FLAG_ATTACHED);
703 0 : list_del_init(&mark->g_list);
704 0 : spin_unlock(&mark->lock);
705 :
706 0 : fsnotify_put_mark(mark);
707 0 : return ret;
708 : }
709 :
710 0 : int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
711 : unsigned int obj_type, int allow_dups,
712 : __kernel_fsid_t *fsid)
713 : {
714 : int ret;
715 0 : struct fsnotify_group *group = mark->group;
716 :
717 0 : mutex_lock(&group->mark_mutex);
718 0 : ret = fsnotify_add_mark_locked(mark, connp, obj_type, allow_dups, fsid);
719 0 : mutex_unlock(&group->mark_mutex);
720 0 : return ret;
721 : }
722 : EXPORT_SYMBOL_GPL(fsnotify_add_mark);
723 :
724 : /*
725 : * Given a list of marks, find the mark associated with given group. If found
726 : * take a reference to that mark and return it, else return NULL.
727 : */
728 0 : struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
729 : struct fsnotify_group *group)
730 : {
731 : struct fsnotify_mark_connector *conn;
732 : struct fsnotify_mark *mark;
733 :
734 0 : conn = fsnotify_grab_connector(connp);
735 0 : if (!conn)
736 : return NULL;
737 :
738 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
739 0 : if (mark->group == group &&
740 0 : (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
741 0 : fsnotify_get_mark(mark);
742 0 : spin_unlock(&conn->lock);
743 0 : return mark;
744 : }
745 : }
746 0 : spin_unlock(&conn->lock);
747 0 : return NULL;
748 : }
749 : EXPORT_SYMBOL_GPL(fsnotify_find_mark);
750 :
751 : /* Clear any marks in a group with given type mask */
752 0 : void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
753 : unsigned int obj_type)
754 : {
755 : struct fsnotify_mark *lmark, *mark;
756 0 : LIST_HEAD(to_free);
757 0 : struct list_head *head = &to_free;
758 :
759 : /* Skip selection step if we want to clear all marks. */
760 0 : if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) {
761 0 : head = &group->marks_list;
762 0 : goto clear;
763 : }
764 : /*
765 : * We have to be really careful here. Anytime we drop mark_mutex, e.g.
766 : * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
767 : * to_free list so we have to use mark_mutex even when accessing that
768 : * list. And freeing mark requires us to drop mark_mutex. So we can
769 : * reliably free only the first mark in the list. That's why we first
770 : * move marks to free to to_free list in one go and then free marks in
771 : * to_free list one by one.
772 : */
773 0 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
774 0 : list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
775 0 : if (mark->connector->type == obj_type)
776 0 : list_move(&mark->g_list, &to_free);
777 : }
778 0 : mutex_unlock(&group->mark_mutex);
779 :
780 : clear:
781 : while (1) {
782 0 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
783 0 : if (list_empty(head)) {
784 0 : mutex_unlock(&group->mark_mutex);
785 : break;
786 : }
787 0 : mark = list_first_entry(head, struct fsnotify_mark, g_list);
788 0 : fsnotify_get_mark(mark);
789 0 : fsnotify_detach_mark(mark);
790 0 : mutex_unlock(&group->mark_mutex);
791 0 : fsnotify_free_mark(mark);
792 0 : fsnotify_put_mark(mark);
793 : }
794 0 : }
795 :
796 : /* Destroy all marks attached to an object via connector */
797 0 : void fsnotify_destroy_marks(fsnotify_connp_t *connp)
798 : {
799 : struct fsnotify_mark_connector *conn;
800 0 : struct fsnotify_mark *mark, *old_mark = NULL;
801 : void *objp;
802 : unsigned int type;
803 :
804 0 : conn = fsnotify_grab_connector(connp);
805 0 : if (!conn)
806 0 : return;
807 : /*
808 : * We have to be careful since we can race with e.g.
809 : * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
810 : * list can get modified. However we are holding mark reference and
811 : * thus our mark cannot be removed from obj_list so we can continue
812 : * iteration after regaining conn->lock.
813 : */
814 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
815 0 : fsnotify_get_mark(mark);
816 0 : spin_unlock(&conn->lock);
817 0 : if (old_mark)
818 0 : fsnotify_put_mark(old_mark);
819 0 : old_mark = mark;
820 0 : fsnotify_destroy_mark(mark, mark->group);
821 0 : spin_lock(&conn->lock);
822 : }
823 : /*
824 : * Detach list from object now so that we don't pin inode until all
825 : * mark references get dropped. It would lead to strange results such
826 : * as delaying inode deletion or blocking unmount.
827 : */
828 0 : objp = fsnotify_detach_connector_from_object(conn, &type);
829 0 : spin_unlock(&conn->lock);
830 0 : if (old_mark)
831 0 : fsnotify_put_mark(old_mark);
832 0 : fsnotify_drop_object(type, objp);
833 : }
834 :
835 : /*
836 : * Nothing fancy, just initialize lists and locks and counters.
837 : */
838 0 : void fsnotify_init_mark(struct fsnotify_mark *mark,
839 : struct fsnotify_group *group)
840 : {
841 0 : memset(mark, 0, sizeof(*mark));
842 0 : spin_lock_init(&mark->lock);
843 0 : refcount_set(&mark->refcnt, 1);
844 0 : fsnotify_get_group(group);
845 0 : mark->group = group;
846 0 : WRITE_ONCE(mark->connector, NULL);
847 0 : }
848 : EXPORT_SYMBOL_GPL(fsnotify_init_mark);
849 :
850 : /*
851 : * Destroy all marks in destroy_list, waits for SRCU period to finish before
852 : * actually freeing marks.
853 : */
854 0 : static void fsnotify_mark_destroy_workfn(struct work_struct *work)
855 : {
856 : struct fsnotify_mark *mark, *next;
857 : struct list_head private_destroy_list;
858 :
859 0 : spin_lock(&destroy_lock);
860 : /* exchange the list head */
861 0 : list_replace_init(&destroy_list, &private_destroy_list);
862 0 : spin_unlock(&destroy_lock);
863 :
864 0 : synchronize_srcu(&fsnotify_mark_srcu);
865 :
866 0 : list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
867 0 : list_del_init(&mark->g_list);
868 0 : fsnotify_final_mark_destroy(mark);
869 : }
870 0 : }
871 :
872 : /* Wait for all marks queued for destruction to be actually destroyed */
873 0 : void fsnotify_wait_marks_destroyed(void)
874 : {
875 0 : flush_delayed_work(&reaper_work);
876 0 : }
877 : EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);
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