1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Directory notifications for Linux.
5 * Copyright (C) 2000,2001,2002 Stephen Rothwell
7 * Copyright (C) 2009 Eric Paris <Red Hat Inc>
8 * dnotify was largly rewritten to use the new fsnotify infrastructure
11 #include <linux/module.h>
12 #include <linux/sched.h>
13 #include <linux/sched/signal.h>
14 #include <linux/dnotify.h>
15 #include <linux/init.h>
16 #include <linux/security.h>
17 #include <linux/spinlock.h>
18 #include <linux/slab.h>
19 #include <linux/fdtable.h>
20 #include <linux/fsnotify_backend.h>
22 int dir_notify_enable __read_mostly = 1;
24 static struct kmem_cache *dnotify_struct_cache __read_mostly;
25 static struct kmem_cache *dnotify_mark_cache __read_mostly;
26 static struct fsnotify_group *dnotify_group __read_mostly;
29 * dnotify will attach one of these to each inode (i_fsnotify_marks) which
30 * is being watched by dnotify. If multiple userspace applications are watching
31 * the same directory with dnotify their information is chained in dn
34 struct fsnotify_mark fsn_mark;
35 struct dnotify_struct *dn;
39 * When a process starts or stops watching an inode the set of events which
40 * dnotify cares about for that inode may change. This function runs the
41 * list of everything receiving dnotify events about this directory and calculates
42 * the set of all those events. After it updates what dnotify is interested in
43 * it calls the fsnotify function so it can update the set of all events relevant
46 static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
49 struct dnotify_struct *dn;
50 struct dnotify_mark *dn_mark = container_of(fsn_mark,
54 assert_spin_locked(&fsn_mark->lock);
56 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
57 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
58 if (fsn_mark->mask == new_mask)
60 fsn_mark->mask = new_mask;
62 fsnotify_recalc_mask(fsn_mark->connector);
66 * Mains fsnotify call where events are delivered to dnotify.
67 * Find the dnotify mark on the relevant inode, run the list of dnotify structs
68 * on that mark and determine which of them has expressed interest in receiving
69 * events of this type. When found send the correct process and signal and
70 * destroy the dnotify struct if it was not registered to receive multiple
73 static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
74 struct inode *inode, struct inode *dir,
75 const struct qstr *name, u32 cookie)
77 struct dnotify_mark *dn_mark;
78 struct dnotify_struct *dn;
79 struct dnotify_struct **prev;
80 struct fown_struct *fown;
81 __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
83 /* not a dir, dnotify doesn't care */
84 if (!dir && !(mask & FS_ISDIR))
87 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
89 spin_lock(&inode_mark->lock);
91 while ((dn = *prev) != NULL) {
92 if ((dn->dn_mask & test_mask) == 0) {
96 fown = &dn->dn_filp->f_owner;
97 send_sigio(fown, dn->dn_fd, POLL_MSG);
98 if (dn->dn_mask & FS_DN_MULTISHOT)
102 kmem_cache_free(dnotify_struct_cache, dn);
103 dnotify_recalc_inode_mask(inode_mark);
107 spin_unlock(&inode_mark->lock);
112 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
114 struct dnotify_mark *dn_mark = container_of(fsn_mark,
120 kmem_cache_free(dnotify_mark_cache, dn_mark);
123 static const struct fsnotify_ops dnotify_fsnotify_ops = {
124 .handle_inode_event = dnotify_handle_event,
125 .free_mark = dnotify_free_mark,
129 * Called every time a file is closed. Looks first for a dnotify mark on the
130 * inode. If one is found run all of the ->dn structures attached to that
131 * mark for one relevant to this process closing the file and remove that
132 * dnotify_struct. If that was the last dnotify_struct also remove the
135 void dnotify_flush(struct file *filp, fl_owner_t id)
137 struct fsnotify_mark *fsn_mark;
138 struct dnotify_mark *dn_mark;
139 struct dnotify_struct *dn;
140 struct dnotify_struct **prev;
144 inode = file_inode(filp);
145 if (!S_ISDIR(inode->i_mode))
148 fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
151 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
153 mutex_lock(&dnotify_group->mark_mutex);
155 spin_lock(&fsn_mark->lock);
157 while ((dn = *prev) != NULL) {
158 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
160 kmem_cache_free(dnotify_struct_cache, dn);
161 dnotify_recalc_inode_mask(fsn_mark);
167 spin_unlock(&fsn_mark->lock);
169 /* nothing else could have found us thanks to the dnotify_groups
171 if (dn_mark->dn == NULL) {
172 fsnotify_detach_mark(fsn_mark);
176 mutex_unlock(&dnotify_group->mark_mutex);
179 fsnotify_free_mark(fsn_mark);
180 fsnotify_put_mark(fsn_mark);
183 /* this conversion is done only at watch creation */
184 static __u32 convert_arg(unsigned long arg)
186 __u32 new_mask = FS_EVENT_ON_CHILD;
188 if (arg & DN_MULTISHOT)
189 new_mask |= FS_DN_MULTISHOT;
191 new_mask |= (FS_DELETE | FS_MOVED_FROM);
193 new_mask |= FS_MODIFY;
195 new_mask |= FS_ACCESS;
197 new_mask |= FS_ATTRIB;
199 new_mask |= FS_DN_RENAME;
201 new_mask |= (FS_CREATE | FS_MOVED_TO);
207 * If multiple processes watch the same inode with dnotify there is only one
208 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
209 * onto that mark. This function either attaches the new dnotify_struct onto
210 * that list, or it |= the mask onto an existing dnofiy_struct.
212 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
213 fl_owner_t id, int fd, struct file *filp, __u32 mask)
215 struct dnotify_struct *odn;
218 while (odn != NULL) {
219 /* adding more events to existing dnofiy_struct? */
220 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
222 odn->dn_mask |= mask;
232 dn->dn_next = dn_mark->dn;
239 * When a process calls fcntl to attach a dnotify watch to a directory it ends
240 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
241 * attached to the fsnotify_mark.
243 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
245 struct dnotify_mark *new_dn_mark, *dn_mark;
246 struct fsnotify_mark *new_fsn_mark, *fsn_mark;
247 struct dnotify_struct *dn;
249 fl_owner_t id = current->files;
251 int destroy = 0, error = 0;
254 /* we use these to tell if we need to kfree */
258 if (!dir_notify_enable) {
263 /* a 0 mask means we are explicitly removing the watch */
264 if ((arg & ~DN_MULTISHOT) == 0) {
265 dnotify_flush(filp, id);
270 /* dnotify only works on directories */
271 inode = file_inode(filp);
272 if (!S_ISDIR(inode->i_mode)) {
278 * convert the userspace DN_* "arg" to the internal FS_*
279 * defined in fsnotify
281 mask = convert_arg(arg);
283 error = security_path_notify(&filp->f_path, mask,
284 FSNOTIFY_OBJ_TYPE_INODE);
288 /* expect most fcntl to add new rather than augment old */
289 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
295 /* new fsnotify mark, we expect most fcntl calls to add a new mark */
296 new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
302 /* set up the new_fsn_mark and new_dn_mark */
303 new_fsn_mark = &new_dn_mark->fsn_mark;
304 fsnotify_init_mark(new_fsn_mark, dnotify_group);
305 new_fsn_mark->mask = mask;
306 new_dn_mark->dn = NULL;
308 /* this is needed to prevent the fcntl/close race described below */
309 mutex_lock(&dnotify_group->mark_mutex);
311 /* add the new_fsn_mark or find an old one. */
312 fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
314 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
315 spin_lock(&fsn_mark->lock);
317 error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
319 mutex_unlock(&dnotify_group->mark_mutex);
322 spin_lock(&new_fsn_mark->lock);
323 fsn_mark = new_fsn_mark;
324 dn_mark = new_dn_mark;
325 /* we used new_fsn_mark, so don't free it */
330 f = lookup_fd_rcu(fd);
333 /* if (f != filp) means that we lost a race and another task/thread
334 * actually closed the fd we are still playing with before we grabbed
335 * the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the
336 * fd is the only time we clean up the marks we need to get our mark
339 /* if we added ourselves, shoot ourselves, it's possible that
340 * the flush actually did shoot this fsn_mark. That's fine too
341 * since multiple calls to destroy_mark is perfectly safe, if
342 * we found a dn_mark already attached to the inode, just sod
343 * off silently as the flush at close time dealt with it.
345 if (dn_mark == new_dn_mark)
351 __f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
353 error = attach_dn(dn, dn_mark, id, fd, filp, mask);
354 /* !error means that we attached the dn to the dn_mark, so don't free it */
357 /* -EEXIST means that we didn't add this new dn and used an old one.
358 * that isn't an error (and the unused dn should be freed) */
359 else if (error == -EEXIST)
362 dnotify_recalc_inode_mask(fsn_mark);
364 spin_unlock(&fsn_mark->lock);
367 fsnotify_detach_mark(fsn_mark);
368 mutex_unlock(&dnotify_group->mark_mutex);
370 fsnotify_free_mark(fsn_mark);
371 fsnotify_put_mark(fsn_mark);
374 fsnotify_put_mark(new_fsn_mark);
376 kmem_cache_free(dnotify_struct_cache, dn);
380 static int __init dnotify_init(void)
382 dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
383 SLAB_PANIC|SLAB_ACCOUNT);
384 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
386 dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
387 if (IS_ERR(dnotify_group))
388 panic("unable to allocate fsnotify group for dnotify\n");
392 module_init(dnotify_init)