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 : static void fsnotify_get_inode_ref(struct inode *inode)
120 : {
121 0 : ihold(inode);
122 0 : atomic_long_inc(&inode->i_sb->s_fsnotify_connectors);
123 : }
124 :
125 : /*
126 : * Grab or drop inode reference for the connector if needed.
127 : *
128 : * When it's time to drop the reference, we only clear the HAS_IREF flag and
129 : * return the inode object. fsnotify_drop_object() will be resonsible for doing
130 : * iput() outside of spinlocks. This happens when last mark that wanted iref is
131 : * detached.
132 : */
133 0 : static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn,
134 : bool want_iref)
135 : {
136 0 : bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF;
137 0 : struct inode *inode = NULL;
138 :
139 0 : if (conn->type != FSNOTIFY_OBJ_TYPE_INODE ||
140 : want_iref == has_iref)
141 : return NULL;
142 :
143 0 : if (want_iref) {
144 : /* Pin inode if any mark wants inode refcount held */
145 0 : fsnotify_get_inode_ref(fsnotify_conn_inode(conn));
146 0 : conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF;
147 : } else {
148 : /* Unpin inode after detach of last mark that wanted iref */
149 0 : inode = fsnotify_conn_inode(conn);
150 0 : conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF;
151 : }
152 :
153 : return inode;
154 : }
155 :
156 0 : static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
157 : {
158 0 : u32 new_mask = 0;
159 0 : bool want_iref = false;
160 : struct fsnotify_mark *mark;
161 :
162 : assert_spin_locked(&conn->lock);
163 : /* We can get detached connector here when inode is getting unlinked. */
164 0 : if (!fsnotify_valid_obj_type(conn->type))
165 : return NULL;
166 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
167 0 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
168 0 : continue;
169 0 : new_mask |= fsnotify_calc_mask(mark);
170 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE &&
171 0 : !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF))
172 0 : want_iref = true;
173 : }
174 0 : *fsnotify_conn_mask_p(conn) = new_mask;
175 :
176 0 : return fsnotify_update_iref(conn, want_iref);
177 : }
178 :
179 : /*
180 : * Calculate mask of events for a list of marks. The caller must make sure
181 : * connector and connector->obj cannot disappear under us. Callers achieve
182 : * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
183 : * list.
184 : */
185 0 : void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
186 : {
187 0 : if (!conn)
188 : return;
189 :
190 0 : spin_lock(&conn->lock);
191 0 : __fsnotify_recalc_mask(conn);
192 0 : spin_unlock(&conn->lock);
193 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
194 0 : __fsnotify_update_child_dentry_flags(
195 : fsnotify_conn_inode(conn));
196 : }
197 :
198 : /* Free all connectors queued for freeing once SRCU period ends */
199 0 : static void fsnotify_connector_destroy_workfn(struct work_struct *work)
200 : {
201 : struct fsnotify_mark_connector *conn, *free;
202 :
203 0 : spin_lock(&destroy_lock);
204 0 : conn = connector_destroy_list;
205 0 : connector_destroy_list = NULL;
206 0 : spin_unlock(&destroy_lock);
207 :
208 0 : synchronize_srcu(&fsnotify_mark_srcu);
209 0 : while (conn) {
210 0 : free = conn;
211 0 : conn = conn->destroy_next;
212 0 : kmem_cache_free(fsnotify_mark_connector_cachep, free);
213 : }
214 0 : }
215 :
216 0 : static void fsnotify_put_inode_ref(struct inode *inode)
217 : {
218 0 : struct super_block *sb = inode->i_sb;
219 :
220 0 : iput(inode);
221 0 : if (atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
222 0 : wake_up_var(&sb->s_fsnotify_connectors);
223 0 : }
224 :
225 : static void fsnotify_get_sb_connectors(struct fsnotify_mark_connector *conn)
226 : {
227 0 : struct super_block *sb = fsnotify_connector_sb(conn);
228 :
229 0 : if (sb)
230 0 : atomic_long_inc(&sb->s_fsnotify_connectors);
231 : }
232 :
233 0 : static void fsnotify_put_sb_connectors(struct fsnotify_mark_connector *conn)
234 : {
235 0 : struct super_block *sb = fsnotify_connector_sb(conn);
236 :
237 0 : if (sb && atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
238 0 : wake_up_var(&sb->s_fsnotify_connectors);
239 0 : }
240 :
241 0 : static void *fsnotify_detach_connector_from_object(
242 : struct fsnotify_mark_connector *conn,
243 : unsigned int *type)
244 : {
245 0 : struct inode *inode = NULL;
246 :
247 0 : *type = conn->type;
248 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
249 : return NULL;
250 :
251 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
252 0 : inode = fsnotify_conn_inode(conn);
253 0 : inode->i_fsnotify_mask = 0;
254 :
255 : /* Unpin inode when detaching from connector */
256 0 : if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF))
257 0 : inode = NULL;
258 0 : } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
259 0 : fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
260 0 : } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
261 0 : fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
262 : }
263 :
264 0 : fsnotify_put_sb_connectors(conn);
265 0 : rcu_assign_pointer(*(conn->obj), NULL);
266 0 : conn->obj = NULL;
267 0 : conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
268 :
269 0 : return inode;
270 : }
271 :
272 0 : static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
273 : {
274 0 : struct fsnotify_group *group = mark->group;
275 :
276 0 : if (WARN_ON_ONCE(!group))
277 : return;
278 0 : group->ops->free_mark(mark);
279 0 : fsnotify_put_group(group);
280 : }
281 :
282 : /* Drop object reference originally held by a connector */
283 0 : static void fsnotify_drop_object(unsigned int type, void *objp)
284 : {
285 0 : if (!objp)
286 : return;
287 : /* Currently only inode references are passed to be dropped */
288 0 : if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
289 : return;
290 0 : fsnotify_put_inode_ref(objp);
291 : }
292 :
293 0 : void fsnotify_put_mark(struct fsnotify_mark *mark)
294 : {
295 0 : struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
296 0 : void *objp = NULL;
297 0 : unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
298 0 : bool free_conn = false;
299 :
300 : /* Catch marks that were actually never attached to object */
301 0 : if (!conn) {
302 0 : if (refcount_dec_and_test(&mark->refcnt))
303 0 : fsnotify_final_mark_destroy(mark);
304 0 : return;
305 : }
306 :
307 : /*
308 : * We have to be careful so that traversals of obj_list under lock can
309 : * safely grab mark reference.
310 : */
311 0 : if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
312 : return;
313 :
314 0 : hlist_del_init_rcu(&mark->obj_list);
315 0 : if (hlist_empty(&conn->list)) {
316 0 : objp = fsnotify_detach_connector_from_object(conn, &type);
317 0 : free_conn = true;
318 : } else {
319 0 : objp = __fsnotify_recalc_mask(conn);
320 0 : type = conn->type;
321 : }
322 0 : WRITE_ONCE(mark->connector, NULL);
323 0 : spin_unlock(&conn->lock);
324 :
325 0 : fsnotify_drop_object(type, objp);
326 :
327 0 : if (free_conn) {
328 0 : spin_lock(&destroy_lock);
329 0 : conn->destroy_next = connector_destroy_list;
330 0 : connector_destroy_list = conn;
331 0 : spin_unlock(&destroy_lock);
332 0 : queue_work(system_unbound_wq, &connector_reaper_work);
333 : }
334 : /*
335 : * Note that we didn't update flags telling whether inode cares about
336 : * what's happening with children. We update these flags from
337 : * __fsnotify_parent() lazily when next event happens on one of our
338 : * children.
339 : */
340 0 : spin_lock(&destroy_lock);
341 0 : list_add(&mark->g_list, &destroy_list);
342 0 : spin_unlock(&destroy_lock);
343 0 : queue_delayed_work(system_unbound_wq, &reaper_work,
344 : FSNOTIFY_REAPER_DELAY);
345 : }
346 : EXPORT_SYMBOL_GPL(fsnotify_put_mark);
347 :
348 : /*
349 : * Get mark reference when we found the mark via lockless traversal of object
350 : * list. Mark can be already removed from the list by now and on its way to be
351 : * destroyed once SRCU period ends.
352 : *
353 : * Also pin the group so it doesn't disappear under us.
354 : */
355 0 : static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
356 : {
357 0 : if (!mark)
358 : return true;
359 :
360 0 : if (refcount_inc_not_zero(&mark->refcnt)) {
361 0 : spin_lock(&mark->lock);
362 0 : if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
363 : /* mark is attached, group is still alive then */
364 0 : atomic_inc(&mark->group->user_waits);
365 0 : spin_unlock(&mark->lock);
366 0 : return true;
367 : }
368 0 : spin_unlock(&mark->lock);
369 0 : fsnotify_put_mark(mark);
370 : }
371 : return false;
372 : }
373 :
374 : /*
375 : * Puts marks and wakes up group destruction if necessary.
376 : *
377 : * Pairs with fsnotify_get_mark_safe()
378 : */
379 0 : static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
380 : {
381 0 : if (mark) {
382 0 : struct fsnotify_group *group = mark->group;
383 :
384 0 : fsnotify_put_mark(mark);
385 : /*
386 : * We abuse notification_waitq on group shutdown for waiting for
387 : * all marks pinned when waiting for userspace.
388 : */
389 0 : if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
390 0 : wake_up(&group->notification_waitq);
391 : }
392 0 : }
393 :
394 0 : bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
395 : __releases(&fsnotify_mark_srcu)
396 : {
397 : int type;
398 :
399 0 : fsnotify_foreach_iter_type(type) {
400 : /* This can fail if mark is being removed */
401 0 : if (!fsnotify_get_mark_safe(iter_info->marks[type])) {
402 : __release(&fsnotify_mark_srcu);
403 : goto fail;
404 : }
405 : }
406 :
407 : /*
408 : * Now that both marks are pinned by refcount in the inode / vfsmount
409 : * lists, we can drop SRCU lock, and safely resume the list iteration
410 : * once userspace returns.
411 : */
412 0 : srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
413 :
414 0 : return true;
415 :
416 : fail:
417 0 : for (type--; type >= 0; type--)
418 0 : fsnotify_put_mark_wake(iter_info->marks[type]);
419 : return false;
420 : }
421 :
422 0 : void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
423 : __acquires(&fsnotify_mark_srcu)
424 : {
425 : int type;
426 :
427 0 : iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
428 0 : fsnotify_foreach_iter_type(type)
429 0 : fsnotify_put_mark_wake(iter_info->marks[type]);
430 0 : }
431 :
432 : /*
433 : * Mark mark as detached, remove it from group list. Mark still stays in object
434 : * list until its last reference is dropped. Note that we rely on mark being
435 : * removed from group list before corresponding reference to it is dropped. In
436 : * particular we rely on mark->connector being valid while we hold
437 : * group->mark_mutex if we found the mark through g_list.
438 : *
439 : * Must be called with group->mark_mutex held. The caller must either hold
440 : * reference to the mark or be protected by fsnotify_mark_srcu.
441 : */
442 0 : void fsnotify_detach_mark(struct fsnotify_mark *mark)
443 : {
444 0 : fsnotify_group_assert_locked(mark->group);
445 0 : WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
446 : refcount_read(&mark->refcnt) < 1 +
447 : !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
448 :
449 0 : spin_lock(&mark->lock);
450 : /* something else already called this function on this mark */
451 0 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
452 0 : spin_unlock(&mark->lock);
453 : return;
454 : }
455 0 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
456 0 : list_del_init(&mark->g_list);
457 0 : spin_unlock(&mark->lock);
458 :
459 : /* Drop mark reference acquired in fsnotify_add_mark_locked() */
460 0 : fsnotify_put_mark(mark);
461 : }
462 :
463 : /*
464 : * Free fsnotify mark. The mark is actually only marked as being freed. The
465 : * freeing is actually happening only once last reference to the mark is
466 : * dropped from a workqueue which first waits for srcu period end.
467 : *
468 : * Caller must have a reference to the mark or be protected by
469 : * fsnotify_mark_srcu.
470 : */
471 0 : void fsnotify_free_mark(struct fsnotify_mark *mark)
472 : {
473 0 : struct fsnotify_group *group = mark->group;
474 :
475 0 : spin_lock(&mark->lock);
476 : /* something else already called this function on this mark */
477 0 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
478 0 : spin_unlock(&mark->lock);
479 : return;
480 : }
481 0 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
482 0 : spin_unlock(&mark->lock);
483 :
484 : /*
485 : * Some groups like to know that marks are being freed. This is a
486 : * callback to the group function to let it know that this mark
487 : * is being freed.
488 : */
489 0 : if (group->ops->freeing_mark)
490 0 : group->ops->freeing_mark(mark, group);
491 : }
492 :
493 0 : void fsnotify_destroy_mark(struct fsnotify_mark *mark,
494 : struct fsnotify_group *group)
495 : {
496 0 : fsnotify_group_lock(group);
497 0 : fsnotify_detach_mark(mark);
498 0 : fsnotify_group_unlock(group);
499 0 : fsnotify_free_mark(mark);
500 0 : }
501 : EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
502 :
503 : /*
504 : * Sorting function for lists of fsnotify marks.
505 : *
506 : * Fanotify supports different notification classes (reflected as priority of
507 : * notification group). Events shall be passed to notification groups in
508 : * decreasing priority order. To achieve this marks in notification lists for
509 : * inodes and vfsmounts are sorted so that priorities of corresponding groups
510 : * are descending.
511 : *
512 : * Furthermore correct handling of the ignore mask requires processing inode
513 : * and vfsmount marks of each group together. Using the group address as
514 : * further sort criterion provides a unique sorting order and thus we can
515 : * merge inode and vfsmount lists of marks in linear time and find groups
516 : * present in both lists.
517 : *
518 : * A return value of 1 signifies that b has priority over a.
519 : * A return value of 0 signifies that the two marks have to be handled together.
520 : * A return value of -1 signifies that a has priority over b.
521 : */
522 0 : int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
523 : {
524 0 : if (a == b)
525 : return 0;
526 0 : if (!a)
527 : return 1;
528 0 : if (!b)
529 : return -1;
530 0 : if (a->priority < b->priority)
531 : return 1;
532 0 : if (a->priority > b->priority)
533 : return -1;
534 0 : if (a < b)
535 : return 1;
536 0 : return -1;
537 : }
538 :
539 0 : static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
540 : unsigned int obj_type,
541 : __kernel_fsid_t *fsid)
542 : {
543 : struct fsnotify_mark_connector *conn;
544 :
545 0 : conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
546 0 : if (!conn)
547 : return -ENOMEM;
548 0 : spin_lock_init(&conn->lock);
549 0 : INIT_HLIST_HEAD(&conn->list);
550 0 : conn->flags = 0;
551 0 : conn->type = obj_type;
552 0 : conn->obj = connp;
553 : /* Cache fsid of filesystem containing the object */
554 0 : if (fsid) {
555 0 : conn->fsid = *fsid;
556 0 : conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
557 : } else {
558 0 : conn->fsid.val[0] = conn->fsid.val[1] = 0;
559 : conn->flags = 0;
560 : }
561 0 : fsnotify_get_sb_connectors(conn);
562 :
563 : /*
564 : * cmpxchg() provides the barrier so that readers of *connp can see
565 : * only initialized structure
566 : */
567 0 : if (cmpxchg(connp, NULL, conn)) {
568 : /* Someone else created list structure for us */
569 0 : fsnotify_put_sb_connectors(conn);
570 0 : kmem_cache_free(fsnotify_mark_connector_cachep, conn);
571 : }
572 :
573 : return 0;
574 : }
575 :
576 : /*
577 : * Get mark connector, make sure it is alive and return with its lock held.
578 : * This is for users that get connector pointer from inode or mount. Users that
579 : * hold reference to a mark on the list may directly lock connector->lock as
580 : * they are sure list cannot go away under them.
581 : */
582 20 : static struct fsnotify_mark_connector *fsnotify_grab_connector(
583 : fsnotify_connp_t *connp)
584 : {
585 : struct fsnotify_mark_connector *conn;
586 : int idx;
587 :
588 20 : idx = srcu_read_lock(&fsnotify_mark_srcu);
589 20 : conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
590 20 : if (!conn)
591 : goto out;
592 0 : spin_lock(&conn->lock);
593 0 : if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
594 0 : spin_unlock(&conn->lock);
595 0 : srcu_read_unlock(&fsnotify_mark_srcu, idx);
596 0 : return NULL;
597 : }
598 : out:
599 20 : srcu_read_unlock(&fsnotify_mark_srcu, idx);
600 20 : return conn;
601 : }
602 :
603 : /*
604 : * Add mark into proper place in given list of marks. These marks may be used
605 : * for the fsnotify backend to determine which event types should be delivered
606 : * to which group and for which inodes. These marks are ordered according to
607 : * priority, highest number first, and then by the group's location in memory.
608 : */
609 0 : static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
610 : fsnotify_connp_t *connp,
611 : unsigned int obj_type,
612 : int add_flags, __kernel_fsid_t *fsid)
613 : {
614 0 : struct fsnotify_mark *lmark, *last = NULL;
615 : struct fsnotify_mark_connector *conn;
616 : int cmp;
617 0 : int err = 0;
618 :
619 0 : if (WARN_ON(!fsnotify_valid_obj_type(obj_type)))
620 : return -EINVAL;
621 :
622 : /* Backend is expected to check for zero fsid (e.g. tmpfs) */
623 0 : if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1]))
624 : return -ENODEV;
625 :
626 : restart:
627 0 : spin_lock(&mark->lock);
628 0 : conn = fsnotify_grab_connector(connp);
629 0 : if (!conn) {
630 0 : spin_unlock(&mark->lock);
631 0 : err = fsnotify_attach_connector_to_object(connp, obj_type,
632 : fsid);
633 0 : if (err)
634 : return err;
635 : goto restart;
636 0 : } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
637 0 : conn->fsid = *fsid;
638 : /* Pairs with smp_rmb() in fanotify_get_fsid() */
639 0 : smp_wmb();
640 0 : conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
641 0 : } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
642 0 : (fsid->val[0] != conn->fsid.val[0] ||
643 0 : fsid->val[1] != conn->fsid.val[1])) {
644 : /*
645 : * Backend is expected to check for non uniform fsid
646 : * (e.g. btrfs), but maybe we missed something?
647 : * Only allow setting conn->fsid once to non zero fsid.
648 : * inotify and non-fid fanotify groups do not set nor test
649 : * conn->fsid.
650 : */
651 0 : pr_warn_ratelimited("%s: fsid mismatch on object of type %u: "
652 : "%x.%x != %x.%x\n", __func__, conn->type,
653 : fsid->val[0], fsid->val[1],
654 : conn->fsid.val[0], conn->fsid.val[1]);
655 : err = -EXDEV;
656 : goto out_err;
657 : }
658 :
659 : /* is mark the first mark? */
660 0 : if (hlist_empty(&conn->list)) {
661 0 : hlist_add_head_rcu(&mark->obj_list, &conn->list);
662 : goto added;
663 : }
664 :
665 : /* should mark be in the middle of the current list? */
666 0 : hlist_for_each_entry(lmark, &conn->list, obj_list) {
667 0 : last = lmark;
668 :
669 0 : if ((lmark->group == mark->group) &&
670 0 : (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
671 0 : !(mark->group->flags & FSNOTIFY_GROUP_DUPS)) {
672 : err = -EEXIST;
673 : goto out_err;
674 : }
675 :
676 0 : cmp = fsnotify_compare_groups(lmark->group, mark->group);
677 0 : if (cmp >= 0) {
678 0 : hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
679 : goto added;
680 : }
681 : }
682 :
683 0 : BUG_ON(last == NULL);
684 : /* mark should be the last entry. last is the current last entry */
685 0 : hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
686 : added:
687 : /*
688 : * Since connector is attached to object using cmpxchg() we are
689 : * guaranteed that connector initialization is fully visible by anyone
690 : * seeing mark->connector set.
691 : */
692 0 : WRITE_ONCE(mark->connector, conn);
693 : out_err:
694 0 : spin_unlock(&conn->lock);
695 0 : spin_unlock(&mark->lock);
696 : return err;
697 : }
698 :
699 : /*
700 : * Attach an initialized mark to a given group and fs object.
701 : * These marks may be used for the fsnotify backend to determine which
702 : * event types should be delivered to which group.
703 : */
704 0 : int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
705 : fsnotify_connp_t *connp, unsigned int obj_type,
706 : int add_flags, __kernel_fsid_t *fsid)
707 : {
708 0 : struct fsnotify_group *group = mark->group;
709 0 : int ret = 0;
710 :
711 0 : fsnotify_group_assert_locked(group);
712 :
713 : /*
714 : * LOCKING ORDER!!!!
715 : * group->mark_mutex
716 : * mark->lock
717 : * mark->connector->lock
718 : */
719 0 : spin_lock(&mark->lock);
720 0 : mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
721 :
722 0 : list_add(&mark->g_list, &group->marks_list);
723 0 : fsnotify_get_mark(mark); /* for g_list */
724 0 : spin_unlock(&mark->lock);
725 :
726 0 : ret = fsnotify_add_mark_list(mark, connp, obj_type, add_flags, fsid);
727 0 : if (ret)
728 : goto err;
729 :
730 0 : fsnotify_recalc_mask(mark->connector);
731 :
732 0 : return ret;
733 : err:
734 0 : spin_lock(&mark->lock);
735 0 : mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
736 : FSNOTIFY_MARK_FLAG_ATTACHED);
737 0 : list_del_init(&mark->g_list);
738 0 : spin_unlock(&mark->lock);
739 :
740 0 : fsnotify_put_mark(mark);
741 0 : return ret;
742 : }
743 :
744 0 : int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
745 : unsigned int obj_type, int add_flags,
746 : __kernel_fsid_t *fsid)
747 : {
748 : int ret;
749 0 : struct fsnotify_group *group = mark->group;
750 :
751 0 : fsnotify_group_lock(group);
752 0 : ret = fsnotify_add_mark_locked(mark, connp, obj_type, add_flags, fsid);
753 0 : fsnotify_group_unlock(group);
754 0 : return ret;
755 : }
756 : EXPORT_SYMBOL_GPL(fsnotify_add_mark);
757 :
758 : /*
759 : * Given a list of marks, find the mark associated with given group. If found
760 : * take a reference to that mark and return it, else return NULL.
761 : */
762 0 : struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
763 : struct fsnotify_group *group)
764 : {
765 : struct fsnotify_mark_connector *conn;
766 : struct fsnotify_mark *mark;
767 :
768 0 : conn = fsnotify_grab_connector(connp);
769 0 : if (!conn)
770 : return NULL;
771 :
772 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
773 0 : if (mark->group == group &&
774 0 : (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
775 0 : fsnotify_get_mark(mark);
776 0 : spin_unlock(&conn->lock);
777 0 : return mark;
778 : }
779 : }
780 0 : spin_unlock(&conn->lock);
781 0 : return NULL;
782 : }
783 : EXPORT_SYMBOL_GPL(fsnotify_find_mark);
784 :
785 : /* Clear any marks in a group with given type mask */
786 0 : void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
787 : unsigned int obj_type)
788 : {
789 : struct fsnotify_mark *lmark, *mark;
790 0 : LIST_HEAD(to_free);
791 0 : struct list_head *head = &to_free;
792 :
793 : /* Skip selection step if we want to clear all marks. */
794 0 : if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) {
795 0 : head = &group->marks_list;
796 0 : goto clear;
797 : }
798 : /*
799 : * We have to be really careful here. Anytime we drop mark_mutex, e.g.
800 : * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
801 : * to_free list so we have to use mark_mutex even when accessing that
802 : * list. And freeing mark requires us to drop mark_mutex. So we can
803 : * reliably free only the first mark in the list. That's why we first
804 : * move marks to free to to_free list in one go and then free marks in
805 : * to_free list one by one.
806 : */
807 0 : fsnotify_group_lock(group);
808 0 : list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
809 0 : if (mark->connector->type == obj_type)
810 0 : list_move(&mark->g_list, &to_free);
811 : }
812 0 : fsnotify_group_unlock(group);
813 :
814 : clear:
815 : while (1) {
816 0 : fsnotify_group_lock(group);
817 0 : if (list_empty(head)) {
818 0 : fsnotify_group_unlock(group);
819 : break;
820 : }
821 0 : mark = list_first_entry(head, struct fsnotify_mark, g_list);
822 0 : fsnotify_get_mark(mark);
823 0 : fsnotify_detach_mark(mark);
824 0 : fsnotify_group_unlock(group);
825 0 : fsnotify_free_mark(mark);
826 0 : fsnotify_put_mark(mark);
827 : }
828 0 : }
829 :
830 : /* Destroy all marks attached to an object via connector */
831 20 : void fsnotify_destroy_marks(fsnotify_connp_t *connp)
832 : {
833 : struct fsnotify_mark_connector *conn;
834 20 : struct fsnotify_mark *mark, *old_mark = NULL;
835 : void *objp;
836 : unsigned int type;
837 :
838 20 : conn = fsnotify_grab_connector(connp);
839 20 : if (!conn)
840 20 : return;
841 : /*
842 : * We have to be careful since we can race with e.g.
843 : * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
844 : * list can get modified. However we are holding mark reference and
845 : * thus our mark cannot be removed from obj_list so we can continue
846 : * iteration after regaining conn->lock.
847 : */
848 0 : hlist_for_each_entry(mark, &conn->list, obj_list) {
849 0 : fsnotify_get_mark(mark);
850 0 : spin_unlock(&conn->lock);
851 0 : if (old_mark)
852 0 : fsnotify_put_mark(old_mark);
853 0 : old_mark = mark;
854 0 : fsnotify_destroy_mark(mark, mark->group);
855 0 : spin_lock(&conn->lock);
856 : }
857 : /*
858 : * Detach list from object now so that we don't pin inode until all
859 : * mark references get dropped. It would lead to strange results such
860 : * as delaying inode deletion or blocking unmount.
861 : */
862 0 : objp = fsnotify_detach_connector_from_object(conn, &type);
863 0 : spin_unlock(&conn->lock);
864 0 : if (old_mark)
865 0 : fsnotify_put_mark(old_mark);
866 0 : fsnotify_drop_object(type, objp);
867 : }
868 :
869 : /*
870 : * Nothing fancy, just initialize lists and locks and counters.
871 : */
872 0 : void fsnotify_init_mark(struct fsnotify_mark *mark,
873 : struct fsnotify_group *group)
874 : {
875 0 : memset(mark, 0, sizeof(*mark));
876 0 : spin_lock_init(&mark->lock);
877 0 : refcount_set(&mark->refcnt, 1);
878 0 : fsnotify_get_group(group);
879 0 : mark->group = group;
880 0 : WRITE_ONCE(mark->connector, NULL);
881 0 : }
882 : EXPORT_SYMBOL_GPL(fsnotify_init_mark);
883 :
884 : /*
885 : * Destroy all marks in destroy_list, waits for SRCU period to finish before
886 : * actually freeing marks.
887 : */
888 0 : static void fsnotify_mark_destroy_workfn(struct work_struct *work)
889 : {
890 : struct fsnotify_mark *mark, *next;
891 : struct list_head private_destroy_list;
892 :
893 0 : spin_lock(&destroy_lock);
894 : /* exchange the list head */
895 0 : list_replace_init(&destroy_list, &private_destroy_list);
896 0 : spin_unlock(&destroy_lock);
897 :
898 0 : synchronize_srcu(&fsnotify_mark_srcu);
899 :
900 0 : list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
901 0 : list_del_init(&mark->g_list);
902 0 : fsnotify_final_mark_destroy(mark);
903 : }
904 0 : }
905 :
906 : /* Wait for all marks queued for destruction to be actually destroyed */
907 0 : void fsnotify_wait_marks_destroyed(void)
908 : {
909 0 : flush_delayed_work(&reaper_work);
910 0 : }
911 : EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);
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