xref: /openbmc/linux/fs/notify/fsnotify.c (revision 2540d3c9)
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  #include <linux/dcache.h>
7  #include <linux/fs.h>
8  #include <linux/gfp.h>
9  #include <linux/init.h>
10  #include <linux/module.h>
11  #include <linux/mount.h>
12  #include <linux/srcu.h>
13  
14  #include <linux/fsnotify_backend.h>
15  #include "fsnotify.h"
16  
17  /*
18   * Clear all of the marks on an inode when it is being evicted from core
19   */
20  void __fsnotify_inode_delete(struct inode *inode)
21  {
22  	fsnotify_clear_marks_by_inode(inode);
23  }
24  EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
25  
26  void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
27  {
28  	fsnotify_clear_marks_by_mount(mnt);
29  }
30  
31  /**
32   * fsnotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
33   * @sb: superblock being unmounted.
34   *
35   * Called during unmount with no locks held, so needs to be safe against
36   * concurrent modifiers. We temporarily drop sb->s_inode_list_lock and CAN block.
37   */
38  static void fsnotify_unmount_inodes(struct super_block *sb)
39  {
40  	struct inode *inode, *iput_inode = NULL;
41  
42  	spin_lock(&sb->s_inode_list_lock);
43  	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
44  		/*
45  		 * We cannot __iget() an inode in state I_FREEING,
46  		 * I_WILL_FREE, or I_NEW which is fine because by that point
47  		 * the inode cannot have any associated watches.
48  		 */
49  		spin_lock(&inode->i_lock);
50  		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
51  			spin_unlock(&inode->i_lock);
52  			continue;
53  		}
54  
55  		/*
56  		 * If i_count is zero, the inode cannot have any watches and
57  		 * doing an __iget/iput with SB_ACTIVE clear would actually
58  		 * evict all inodes with zero i_count from icache which is
59  		 * unnecessarily violent and may in fact be illegal to do.
60  		 * However, we should have been called /after/ evict_inodes
61  		 * removed all zero refcount inodes, in any case.  Test to
62  		 * be sure.
63  		 */
64  		if (!atomic_read(&inode->i_count)) {
65  			spin_unlock(&inode->i_lock);
66  			continue;
67  		}
68  
69  		__iget(inode);
70  		spin_unlock(&inode->i_lock);
71  		spin_unlock(&sb->s_inode_list_lock);
72  
73  		iput(iput_inode);
74  
75  		/* for each watch, send FS_UNMOUNT and then remove it */
76  		fsnotify_inode(inode, FS_UNMOUNT);
77  
78  		fsnotify_inode_delete(inode);
79  
80  		iput_inode = inode;
81  
82  		cond_resched();
83  		spin_lock(&sb->s_inode_list_lock);
84  	}
85  	spin_unlock(&sb->s_inode_list_lock);
86  
87  	iput(iput_inode);
88  }
89  
90  void fsnotify_sb_delete(struct super_block *sb)
91  {
92  	fsnotify_unmount_inodes(sb);
93  	fsnotify_clear_marks_by_sb(sb);
94  	/* Wait for outstanding object references from connectors */
95  	wait_var_event(&sb->s_fsnotify_connectors,
96  		       !atomic_long_read(&sb->s_fsnotify_connectors));
97  }
98  
99  /*
100   * Given an inode, first check if we care what happens to our children.  Inotify
101   * and dnotify both tell their parents about events.  If we care about any event
102   * on a child we run all of our children and set a dentry flag saying that the
103   * parent cares.  Thus when an event happens on a child it can quickly tell if
104   * if there is a need to find a parent and send the event to the parent.
105   */
106  void __fsnotify_update_child_dentry_flags(struct inode *inode)
107  {
108  	struct dentry *alias;
109  	int watched;
110  
111  	if (!S_ISDIR(inode->i_mode))
112  		return;
113  
114  	/* determine if the children should tell inode about their events */
115  	watched = fsnotify_inode_watches_children(inode);
116  
117  	spin_lock(&inode->i_lock);
118  	/* run all of the dentries associated with this inode.  Since this is a
119  	 * directory, there damn well better only be one item on this list */
120  	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
121  		struct dentry *child;
122  
123  		/* run all of the children of the original inode and fix their
124  		 * d_flags to indicate parental interest (their parent is the
125  		 * original inode) */
126  		spin_lock(&alias->d_lock);
127  		list_for_each_entry(child, &alias->d_subdirs, d_child) {
128  			if (!child->d_inode)
129  				continue;
130  
131  			spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
132  			if (watched)
133  				child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
134  			else
135  				child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
136  			spin_unlock(&child->d_lock);
137  		}
138  		spin_unlock(&alias->d_lock);
139  	}
140  	spin_unlock(&inode->i_lock);
141  }
142  
143  /* Are inode/sb/mount interested in parent and name info with this event? */
144  static bool fsnotify_event_needs_parent(struct inode *inode, struct mount *mnt,
145  					__u32 mask)
146  {
147  	__u32 marks_mask = 0;
148  
149  	/* We only send parent/name to inode/sb/mount for events on non-dir */
150  	if (mask & FS_ISDIR)
151  		return false;
152  
153  	/*
154  	 * All events that are possible on child can also may be reported with
155  	 * parent/name info to inode/sb/mount.  Otherwise, a watching parent
156  	 * could result in events reported with unexpected name info to sb/mount.
157  	 */
158  	BUILD_BUG_ON(FS_EVENTS_POSS_ON_CHILD & ~FS_EVENTS_POSS_TO_PARENT);
159  
160  	/* Did either inode/sb/mount subscribe for events with parent/name? */
161  	marks_mask |= fsnotify_parent_needed_mask(inode->i_fsnotify_mask);
162  	marks_mask |= fsnotify_parent_needed_mask(inode->i_sb->s_fsnotify_mask);
163  	if (mnt)
164  		marks_mask |= fsnotify_parent_needed_mask(mnt->mnt_fsnotify_mask);
165  
166  	/* Did they subscribe for this event with parent/name info? */
167  	return mask & marks_mask;
168  }
169  
170  /*
171   * Notify this dentry's parent about a child's events with child name info
172   * if parent is watching or if inode/sb/mount are interested in events with
173   * parent and name info.
174   *
175   * Notify only the child without name info if parent is not watching and
176   * inode/sb/mount are not interested in events with parent and name info.
177   */
178  int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
179  		      int data_type)
180  {
181  	const struct path *path = fsnotify_data_path(data, data_type);
182  	struct mount *mnt = path ? real_mount(path->mnt) : NULL;
183  	struct inode *inode = d_inode(dentry);
184  	struct dentry *parent;
185  	bool parent_watched = dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED;
186  	bool parent_needed, parent_interested;
187  	__u32 p_mask;
188  	struct inode *p_inode = NULL;
189  	struct name_snapshot name;
190  	struct qstr *file_name = NULL;
191  	int ret = 0;
192  
193  	/*
194  	 * Do inode/sb/mount care about parent and name info on non-dir?
195  	 * Do they care about any event at all?
196  	 */
197  	if (!inode->i_fsnotify_marks && !inode->i_sb->s_fsnotify_marks &&
198  	    (!mnt || !mnt->mnt_fsnotify_marks) && !parent_watched)
199  		return 0;
200  
201  	parent = NULL;
202  	parent_needed = fsnotify_event_needs_parent(inode, mnt, mask);
203  	if (!parent_watched && !parent_needed)
204  		goto notify;
205  
206  	/* Does parent inode care about events on children? */
207  	parent = dget_parent(dentry);
208  	p_inode = parent->d_inode;
209  	p_mask = fsnotify_inode_watches_children(p_inode);
210  	if (unlikely(parent_watched && !p_mask))
211  		__fsnotify_update_child_dentry_flags(p_inode);
212  
213  	/*
214  	 * Include parent/name in notification either if some notification
215  	 * groups require parent info or the parent is interested in this event.
216  	 */
217  	parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS;
218  	if (parent_needed || parent_interested) {
219  		/* When notifying parent, child should be passed as data */
220  		WARN_ON_ONCE(inode != fsnotify_data_inode(data, data_type));
221  
222  		/* Notify both parent and child with child name info */
223  		take_dentry_name_snapshot(&name, dentry);
224  		file_name = &name.name;
225  		if (parent_interested)
226  			mask |= FS_EVENT_ON_CHILD;
227  	}
228  
229  notify:
230  	ret = fsnotify(mask, data, data_type, p_inode, file_name, inode, 0);
231  
232  	if (file_name)
233  		release_dentry_name_snapshot(&name);
234  	dput(parent);
235  
236  	return ret;
237  }
238  EXPORT_SYMBOL_GPL(__fsnotify_parent);
239  
240  static int fsnotify_handle_inode_event(struct fsnotify_group *group,
241  				       struct fsnotify_mark *inode_mark,
242  				       u32 mask, const void *data, int data_type,
243  				       struct inode *dir, const struct qstr *name,
244  				       u32 cookie)
245  {
246  	const struct path *path = fsnotify_data_path(data, data_type);
247  	struct inode *inode = fsnotify_data_inode(data, data_type);
248  	const struct fsnotify_ops *ops = group->ops;
249  
250  	if (WARN_ON_ONCE(!ops->handle_inode_event))
251  		return 0;
252  
253  	if (WARN_ON_ONCE(!inode && !dir))
254  		return 0;
255  
256  	if ((inode_mark->flags & FSNOTIFY_MARK_FLAG_EXCL_UNLINK) &&
257  	    path && d_unlinked(path->dentry))
258  		return 0;
259  
260  	/* Check interest of this mark in case event was sent with two marks */
261  	if (!(mask & inode_mark->mask & ALL_FSNOTIFY_EVENTS))
262  		return 0;
263  
264  	return ops->handle_inode_event(inode_mark, mask, inode, dir, name, cookie);
265  }
266  
267  static int fsnotify_handle_event(struct fsnotify_group *group, __u32 mask,
268  				 const void *data, int data_type,
269  				 struct inode *dir, const struct qstr *name,
270  				 u32 cookie, struct fsnotify_iter_info *iter_info)
271  {
272  	struct fsnotify_mark *inode_mark = fsnotify_iter_inode_mark(iter_info);
273  	struct fsnotify_mark *parent_mark = fsnotify_iter_parent_mark(iter_info);
274  	int ret;
275  
276  	if (WARN_ON_ONCE(fsnotify_iter_sb_mark(iter_info)) ||
277  	    WARN_ON_ONCE(fsnotify_iter_vfsmount_mark(iter_info)))
278  		return 0;
279  
280  	/*
281  	 * For FS_RENAME, 'dir' is old dir and 'data' is new dentry.
282  	 * The only ->handle_inode_event() backend that supports FS_RENAME is
283  	 * dnotify, where it means file was renamed within same parent.
284  	 */
285  	if (mask & FS_RENAME) {
286  		struct dentry *moved = fsnotify_data_dentry(data, data_type);
287  
288  		if (dir != moved->d_parent->d_inode)
289  			return 0;
290  	}
291  
292  	if (parent_mark) {
293  		ret = fsnotify_handle_inode_event(group, parent_mark, mask,
294  						  data, data_type, dir, name, 0);
295  		if (ret)
296  			return ret;
297  	}
298  
299  	if (!inode_mark)
300  		return 0;
301  
302  	if (mask & FS_EVENT_ON_CHILD) {
303  		/*
304  		 * Some events can be sent on both parent dir and child marks
305  		 * (e.g. FS_ATTRIB).  If both parent dir and child are
306  		 * watching, report the event once to parent dir with name (if
307  		 * interested) and once to child without name (if interested).
308  		 * The child watcher is expecting an event without a file name
309  		 * and without the FS_EVENT_ON_CHILD flag.
310  		 */
311  		mask &= ~FS_EVENT_ON_CHILD;
312  		dir = NULL;
313  		name = NULL;
314  	}
315  
316  	return fsnotify_handle_inode_event(group, inode_mark, mask, data, data_type,
317  					   dir, name, cookie);
318  }
319  
320  static int send_to_group(__u32 mask, const void *data, int data_type,
321  			 struct inode *dir, const struct qstr *file_name,
322  			 u32 cookie, struct fsnotify_iter_info *iter_info)
323  {
324  	struct fsnotify_group *group = NULL;
325  	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
326  	__u32 marks_mask = 0;
327  	__u32 marks_ignored_mask = 0;
328  	struct fsnotify_mark *mark;
329  	int type;
330  
331  	if (!iter_info->report_mask)
332  		return 0;
333  
334  	/* clear ignored on inode modification */
335  	if (mask & FS_MODIFY) {
336  		fsnotify_foreach_iter_mark_type(iter_info, mark, type) {
337  			if (!(mark->flags &
338  			      FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
339  				mark->ignored_mask = 0;
340  		}
341  	}
342  
343  	/* Are any of the group marks interested in this event? */
344  	fsnotify_foreach_iter_mark_type(iter_info, mark, type) {
345  		group = mark->group;
346  		marks_mask |= mark->mask;
347  		marks_ignored_mask |= mark->ignored_mask;
348  	}
349  
350  	pr_debug("%s: group=%p mask=%x marks_mask=%x marks_ignored_mask=%x data=%p data_type=%d dir=%p cookie=%d\n",
351  		 __func__, group, mask, marks_mask, marks_ignored_mask,
352  		 data, data_type, dir, cookie);
353  
354  	if (!(test_mask & marks_mask & ~marks_ignored_mask))
355  		return 0;
356  
357  	if (group->ops->handle_event) {
358  		return group->ops->handle_event(group, mask, data, data_type, dir,
359  						file_name, cookie, iter_info);
360  	}
361  
362  	return fsnotify_handle_event(group, mask, data, data_type, dir,
363  				     file_name, cookie, iter_info);
364  }
365  
366  static struct fsnotify_mark *fsnotify_first_mark(struct fsnotify_mark_connector **connp)
367  {
368  	struct fsnotify_mark_connector *conn;
369  	struct hlist_node *node = NULL;
370  
371  	conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
372  	if (conn)
373  		node = srcu_dereference(conn->list.first, &fsnotify_mark_srcu);
374  
375  	return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
376  }
377  
378  static struct fsnotify_mark *fsnotify_next_mark(struct fsnotify_mark *mark)
379  {
380  	struct hlist_node *node = NULL;
381  
382  	if (mark)
383  		node = srcu_dereference(mark->obj_list.next,
384  					&fsnotify_mark_srcu);
385  
386  	return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
387  }
388  
389  /*
390   * iter_info is a multi head priority queue of marks.
391   * Pick a subset of marks from queue heads, all with the same group
392   * and set the report_mask to a subset of the selected marks.
393   * Returns false if there are no more groups to iterate.
394   */
395  static bool fsnotify_iter_select_report_types(
396  		struct fsnotify_iter_info *iter_info)
397  {
398  	struct fsnotify_group *max_prio_group = NULL;
399  	struct fsnotify_mark *mark;
400  	int type;
401  
402  	/* Choose max prio group among groups of all queue heads */
403  	fsnotify_foreach_iter_type(type) {
404  		mark = iter_info->marks[type];
405  		if (mark &&
406  		    fsnotify_compare_groups(max_prio_group, mark->group) > 0)
407  			max_prio_group = mark->group;
408  	}
409  
410  	if (!max_prio_group)
411  		return false;
412  
413  	/* Set the report mask for marks from same group as max prio group */
414  	iter_info->current_group = max_prio_group;
415  	iter_info->report_mask = 0;
416  	fsnotify_foreach_iter_type(type) {
417  		mark = iter_info->marks[type];
418  		if (mark && mark->group == iter_info->current_group) {
419  			/*
420  			 * FSNOTIFY_ITER_TYPE_PARENT indicates that this inode
421  			 * is watching children and interested in this event,
422  			 * which is an event possible on child.
423  			 * But is *this mark* watching children?
424  			 */
425  			if (type == FSNOTIFY_ITER_TYPE_PARENT &&
426  			    !(mark->mask & FS_EVENT_ON_CHILD))
427  				continue;
428  
429  			fsnotify_iter_set_report_type(iter_info, type);
430  		}
431  	}
432  
433  	return true;
434  }
435  
436  /*
437   * Pop from iter_info multi head queue, the marks that belong to the group of
438   * current iteration step.
439   */
440  static void fsnotify_iter_next(struct fsnotify_iter_info *iter_info)
441  {
442  	struct fsnotify_mark *mark;
443  	int type;
444  
445  	/*
446  	 * We cannot use fsnotify_foreach_iter_mark_type() here because we
447  	 * may need to advance a mark of type X that belongs to current_group
448  	 * but was not selected for reporting.
449  	 */
450  	fsnotify_foreach_iter_type(type) {
451  		mark = iter_info->marks[type];
452  		if (mark && mark->group == iter_info->current_group)
453  			iter_info->marks[type] =
454  				fsnotify_next_mark(iter_info->marks[type]);
455  	}
456  }
457  
458  /*
459   * fsnotify - This is the main call to fsnotify.
460   *
461   * The VFS calls into hook specific functions in linux/fsnotify.h.
462   * Those functions then in turn call here.  Here will call out to all of the
463   * registered fsnotify_group.  Those groups can then use the notification event
464   * in whatever means they feel necessary.
465   *
466   * @mask:	event type and flags
467   * @data:	object that event happened on
468   * @data_type:	type of object for fanotify_data_XXX() accessors
469   * @dir:	optional directory associated with event -
470   *		if @file_name is not NULL, this is the directory that
471   *		@file_name is relative to
472   * @file_name:	optional file name associated with event
473   * @inode:	optional inode associated with event -
474   *		If @dir and @inode are both non-NULL, event may be
475   *		reported to both.
476   * @cookie:	inotify rename cookie
477   */
478  int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
479  	     const struct qstr *file_name, struct inode *inode, u32 cookie)
480  {
481  	const struct path *path = fsnotify_data_path(data, data_type);
482  	struct super_block *sb = fsnotify_data_sb(data, data_type);
483  	struct fsnotify_iter_info iter_info = {};
484  	struct mount *mnt = NULL;
485  	struct inode *inode2 = NULL;
486  	struct dentry *moved;
487  	int inode2_type;
488  	int ret = 0;
489  	__u32 test_mask, marks_mask;
490  
491  	if (path)
492  		mnt = real_mount(path->mnt);
493  
494  	if (!inode) {
495  		/* Dirent event - report on TYPE_INODE to dir */
496  		inode = dir;
497  		/* For FS_RENAME, inode is old_dir and inode2 is new_dir */
498  		if (mask & FS_RENAME) {
499  			moved = fsnotify_data_dentry(data, data_type);
500  			inode2 = moved->d_parent->d_inode;
501  			inode2_type = FSNOTIFY_ITER_TYPE_INODE2;
502  		}
503  	} else if (mask & FS_EVENT_ON_CHILD) {
504  		/*
505  		 * Event on child - report on TYPE_PARENT to dir if it is
506  		 * watching children and on TYPE_INODE to child.
507  		 */
508  		inode2 = dir;
509  		inode2_type = FSNOTIFY_ITER_TYPE_PARENT;
510  	}
511  
512  	/*
513  	 * Optimization: srcu_read_lock() has a memory barrier which can
514  	 * be expensive.  It protects walking the *_fsnotify_marks lists.
515  	 * However, if we do not walk the lists, we do not have to do
516  	 * SRCU because we have no references to any objects and do not
517  	 * need SRCU to keep them "alive".
518  	 */
519  	if (!sb->s_fsnotify_marks &&
520  	    (!mnt || !mnt->mnt_fsnotify_marks) &&
521  	    (!inode || !inode->i_fsnotify_marks) &&
522  	    (!inode2 || !inode2->i_fsnotify_marks))
523  		return 0;
524  
525  	marks_mask = sb->s_fsnotify_mask;
526  	if (mnt)
527  		marks_mask |= mnt->mnt_fsnotify_mask;
528  	if (inode)
529  		marks_mask |= inode->i_fsnotify_mask;
530  	if (inode2)
531  		marks_mask |= inode2->i_fsnotify_mask;
532  
533  
534  	/*
535  	 * If this is a modify event we may need to clear some ignored masks.
536  	 * In that case, the object with ignored masks will have the FS_MODIFY
537  	 * event in its mask.
538  	 * Otherwise, return if none of the marks care about this type of event.
539  	 */
540  	test_mask = (mask & ALL_FSNOTIFY_EVENTS);
541  	if (!(test_mask & marks_mask))
542  		return 0;
543  
544  	iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
545  
546  	iter_info.marks[FSNOTIFY_ITER_TYPE_SB] =
547  		fsnotify_first_mark(&sb->s_fsnotify_marks);
548  	if (mnt) {
549  		iter_info.marks[FSNOTIFY_ITER_TYPE_VFSMOUNT] =
550  			fsnotify_first_mark(&mnt->mnt_fsnotify_marks);
551  	}
552  	if (inode) {
553  		iter_info.marks[FSNOTIFY_ITER_TYPE_INODE] =
554  			fsnotify_first_mark(&inode->i_fsnotify_marks);
555  	}
556  	if (inode2) {
557  		iter_info.marks[inode2_type] =
558  			fsnotify_first_mark(&inode2->i_fsnotify_marks);
559  	}
560  
561  	/*
562  	 * We need to merge inode/vfsmount/sb mark lists so that e.g. inode mark
563  	 * ignore masks are properly reflected for mount/sb mark notifications.
564  	 * That's why this traversal is so complicated...
565  	 */
566  	while (fsnotify_iter_select_report_types(&iter_info)) {
567  		ret = send_to_group(mask, data, data_type, dir, file_name,
568  				    cookie, &iter_info);
569  
570  		if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
571  			goto out;
572  
573  		fsnotify_iter_next(&iter_info);
574  	}
575  	ret = 0;
576  out:
577  	srcu_read_unlock(&fsnotify_mark_srcu, iter_info.srcu_idx);
578  
579  	return ret;
580  }
581  EXPORT_SYMBOL_GPL(fsnotify);
582  
583  static __init int fsnotify_init(void)
584  {
585  	int ret;
586  
587  	BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 23);
588  
589  	ret = init_srcu_struct(&fsnotify_mark_srcu);
590  	if (ret)
591  		panic("initializing fsnotify_mark_srcu");
592  
593  	fsnotify_mark_connector_cachep = KMEM_CACHE(fsnotify_mark_connector,
594  						    SLAB_PANIC);
595  
596  	return 0;
597  }
598  core_initcall(fsnotify_init);
599