1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Directory notifications for Linux.
4 *
5 * Copyright (C) 2000,2001,2002 Stephen Rothwell
6 *
7 * Copyright (C) 2009 Eric Paris <Red Hat Inc>
8 * dnotify was largly rewritten to use the new fsnotify infrastructure
9 */
10#include <linux/fs.h>
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>
21
22static int dir_notify_enable __read_mostly = 1;
23#ifdef CONFIG_SYSCTL
24static struct ctl_table dnotify_sysctls[] = {
25 {
26 .procname = "dir-notify-enable",
27 .data = &dir_notify_enable,
28 .maxlen = sizeof(int),
29 .mode = 0644,
30 .proc_handler = proc_dointvec,
31 },
32};
33static void __init dnotify_sysctl_init(void)
34{
35 register_sysctl_init("fs", dnotify_sysctls);
36}
37#else
38#define dnotify_sysctl_init() do { } while (0)
39#endif
40
41static struct kmem_cache *dnotify_struct_cache __ro_after_init;
42static struct kmem_cache *dnotify_mark_cache __ro_after_init;
43static struct fsnotify_group *dnotify_group __ro_after_init;
44
45/*
46 * dnotify will attach one of these to each inode (i_fsnotify_marks) which
47 * is being watched by dnotify. If multiple userspace applications are watching
48 * the same directory with dnotify their information is chained in dn
49 */
50struct dnotify_mark {
51 struct fsnotify_mark fsn_mark;
52 struct dnotify_struct *dn;
53};
54
55/*
56 * When a process starts or stops watching an inode the set of events which
57 * dnotify cares about for that inode may change. This function runs the
58 * list of everything receiving dnotify events about this directory and calculates
59 * the set of all those events. After it updates what dnotify is interested in
60 * it calls the fsnotify function so it can update the set of all events relevant
61 * to this inode.
62 */
63static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
64{
65 __u32 new_mask = 0;
66 struct dnotify_struct *dn;
67 struct dnotify_mark *dn_mark = container_of(fsn_mark,
68 struct dnotify_mark,
69 fsn_mark);
70
71 assert_spin_locked(&fsn_mark->lock);
72
73 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
74 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
75 if (fsn_mark->mask == new_mask)
76 return;
77 fsn_mark->mask = new_mask;
78
79 fsnotify_recalc_mask(conn: fsn_mark->connector);
80}
81
82/*
83 * Mains fsnotify call where events are delivered to dnotify.
84 * Find the dnotify mark on the relevant inode, run the list of dnotify structs
85 * on that mark and determine which of them has expressed interest in receiving
86 * events of this type. When found send the correct process and signal and
87 * destroy the dnotify struct if it was not registered to receive multiple
88 * events.
89 */
90static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
91 struct inode *inode, struct inode *dir,
92 const struct qstr *name, u32 cookie)
93{
94 struct dnotify_mark *dn_mark;
95 struct dnotify_struct *dn;
96 struct dnotify_struct **prev;
97 struct fown_struct *fown;
98 __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
99
100 /* not a dir, dnotify doesn't care */
101 if (!dir && !(mask & FS_ISDIR))
102 return 0;
103
104 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
105
106 spin_lock(lock: &inode_mark->lock);
107 prev = &dn_mark->dn;
108 while ((dn = *prev) != NULL) {
109 if ((dn->dn_mask & test_mask) == 0) {
110 prev = &dn->dn_next;
111 continue;
112 }
113 fown = &dn->dn_filp->f_owner;
114 send_sigio(fown, fd: dn->dn_fd, POLL_MSG);
115 if (dn->dn_mask & FS_DN_MULTISHOT)
116 prev = &dn->dn_next;
117 else {
118 *prev = dn->dn_next;
119 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
120 dnotify_recalc_inode_mask(fsn_mark: inode_mark);
121 }
122 }
123
124 spin_unlock(lock: &inode_mark->lock);
125
126 return 0;
127}
128
129static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
130{
131 struct dnotify_mark *dn_mark = container_of(fsn_mark,
132 struct dnotify_mark,
133 fsn_mark);
134
135 BUG_ON(dn_mark->dn);
136
137 kmem_cache_free(s: dnotify_mark_cache, objp: dn_mark);
138}
139
140static const struct fsnotify_ops dnotify_fsnotify_ops = {
141 .handle_inode_event = dnotify_handle_event,
142 .free_mark = dnotify_free_mark,
143};
144
145/*
146 * Called every time a file is closed. Looks first for a dnotify mark on the
147 * inode. If one is found run all of the ->dn structures attached to that
148 * mark for one relevant to this process closing the file and remove that
149 * dnotify_struct. If that was the last dnotify_struct also remove the
150 * fsnotify_mark.
151 */
152void dnotify_flush(struct file *filp, fl_owner_t id)
153{
154 struct fsnotify_mark *fsn_mark;
155 struct dnotify_mark *dn_mark;
156 struct dnotify_struct *dn;
157 struct dnotify_struct **prev;
158 struct inode *inode;
159 bool free = false;
160
161 inode = file_inode(f: filp);
162 if (!S_ISDIR(inode->i_mode))
163 return;
164
165 fsn_mark = fsnotify_find_mark(connp: &inode->i_fsnotify_marks, group: dnotify_group);
166 if (!fsn_mark)
167 return;
168 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
169
170 fsnotify_group_lock(group: dnotify_group);
171
172 spin_lock(lock: &fsn_mark->lock);
173 prev = &dn_mark->dn;
174 while ((dn = *prev) != NULL) {
175 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
176 *prev = dn->dn_next;
177 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
178 dnotify_recalc_inode_mask(fsn_mark);
179 break;
180 }
181 prev = &dn->dn_next;
182 }
183
184 spin_unlock(lock: &fsn_mark->lock);
185
186 /* nothing else could have found us thanks to the dnotify_groups
187 mark_mutex */
188 if (dn_mark->dn == NULL) {
189 fsnotify_detach_mark(mark: fsn_mark);
190 free = true;
191 }
192
193 fsnotify_group_unlock(group: dnotify_group);
194
195 if (free)
196 fsnotify_free_mark(mark: fsn_mark);
197 fsnotify_put_mark(mark: fsn_mark);
198}
199
200/* this conversion is done only at watch creation */
201static __u32 convert_arg(unsigned int arg)
202{
203 __u32 new_mask = FS_EVENT_ON_CHILD;
204
205 if (arg & DN_MULTISHOT)
206 new_mask |= FS_DN_MULTISHOT;
207 if (arg & DN_DELETE)
208 new_mask |= (FS_DELETE | FS_MOVED_FROM);
209 if (arg & DN_MODIFY)
210 new_mask |= FS_MODIFY;
211 if (arg & DN_ACCESS)
212 new_mask |= FS_ACCESS;
213 if (arg & DN_ATTRIB)
214 new_mask |= FS_ATTRIB;
215 if (arg & DN_RENAME)
216 new_mask |= FS_RENAME;
217 if (arg & DN_CREATE)
218 new_mask |= (FS_CREATE | FS_MOVED_TO);
219
220 return new_mask;
221}
222
223/*
224 * If multiple processes watch the same inode with dnotify there is only one
225 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
226 * onto that mark. This function either attaches the new dnotify_struct onto
227 * that list, or it |= the mask onto an existing dnofiy_struct.
228 */
229static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
230 fl_owner_t id, int fd, struct file *filp, __u32 mask)
231{
232 struct dnotify_struct *odn;
233
234 odn = dn_mark->dn;
235 while (odn != NULL) {
236 /* adding more events to existing dnofiy_struct? */
237 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
238 odn->dn_fd = fd;
239 odn->dn_mask |= mask;
240 return -EEXIST;
241 }
242 odn = odn->dn_next;
243 }
244
245 dn->dn_mask = mask;
246 dn->dn_fd = fd;
247 dn->dn_filp = filp;
248 dn->dn_owner = id;
249 dn->dn_next = dn_mark->dn;
250 dn_mark->dn = dn;
251
252 return 0;
253}
254
255/*
256 * When a process calls fcntl to attach a dnotify watch to a directory it ends
257 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
258 * attached to the fsnotify_mark.
259 */
260int fcntl_dirnotify(int fd, struct file *filp, unsigned int arg)
261{
262 struct dnotify_mark *new_dn_mark, *dn_mark;
263 struct fsnotify_mark *new_fsn_mark, *fsn_mark;
264 struct dnotify_struct *dn;
265 struct inode *inode;
266 fl_owner_t id = current->files;
267 struct file *f = NULL;
268 int destroy = 0, error = 0;
269 __u32 mask;
270
271 /* we use these to tell if we need to kfree */
272 new_fsn_mark = NULL;
273 dn = NULL;
274
275 if (!dir_notify_enable) {
276 error = -EINVAL;
277 goto out_err;
278 }
279
280 /* a 0 mask means we are explicitly removing the watch */
281 if ((arg & ~DN_MULTISHOT) == 0) {
282 dnotify_flush(filp, id);
283 error = 0;
284 goto out_err;
285 }
286
287 /* dnotify only works on directories */
288 inode = file_inode(f: filp);
289 if (!S_ISDIR(inode->i_mode)) {
290 error = -ENOTDIR;
291 goto out_err;
292 }
293
294 /*
295 * convert the userspace DN_* "arg" to the internal FS_*
296 * defined in fsnotify
297 */
298 mask = convert_arg(arg);
299
300 error = security_path_notify(path: &filp->f_path, mask,
301 obj_type: FSNOTIFY_OBJ_TYPE_INODE);
302 if (error)
303 goto out_err;
304
305 /* expect most fcntl to add new rather than augment old */
306 dn = kmem_cache_alloc(cachep: dnotify_struct_cache, GFP_KERNEL);
307 if (!dn) {
308 error = -ENOMEM;
309 goto out_err;
310 }
311
312 /* new fsnotify mark, we expect most fcntl calls to add a new mark */
313 new_dn_mark = kmem_cache_alloc(cachep: dnotify_mark_cache, GFP_KERNEL);
314 if (!new_dn_mark) {
315 error = -ENOMEM;
316 goto out_err;
317 }
318
319 /* set up the new_fsn_mark and new_dn_mark */
320 new_fsn_mark = &new_dn_mark->fsn_mark;
321 fsnotify_init_mark(mark: new_fsn_mark, group: dnotify_group);
322 new_fsn_mark->mask = mask;
323 new_dn_mark->dn = NULL;
324
325 /* this is needed to prevent the fcntl/close race described below */
326 fsnotify_group_lock(group: dnotify_group);
327
328 /* add the new_fsn_mark or find an old one. */
329 fsn_mark = fsnotify_find_mark(connp: &inode->i_fsnotify_marks, group: dnotify_group);
330 if (fsn_mark) {
331 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
332 spin_lock(lock: &fsn_mark->lock);
333 } else {
334 error = fsnotify_add_inode_mark_locked(mark: new_fsn_mark, inode, add_flags: 0);
335 if (error) {
336 fsnotify_group_unlock(group: dnotify_group);
337 goto out_err;
338 }
339 spin_lock(lock: &new_fsn_mark->lock);
340 fsn_mark = new_fsn_mark;
341 dn_mark = new_dn_mark;
342 /* we used new_fsn_mark, so don't free it */
343 new_fsn_mark = NULL;
344 }
345
346 rcu_read_lock();
347 f = lookup_fdget_rcu(fd);
348 rcu_read_unlock();
349
350 /* if (f != filp) means that we lost a race and another task/thread
351 * actually closed the fd we are still playing with before we grabbed
352 * the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the
353 * fd is the only time we clean up the marks we need to get our mark
354 * off the list. */
355 if (f != filp) {
356 /* if we added ourselves, shoot ourselves, it's possible that
357 * the flush actually did shoot this fsn_mark. That's fine too
358 * since multiple calls to destroy_mark is perfectly safe, if
359 * we found a dn_mark already attached to the inode, just sod
360 * off silently as the flush at close time dealt with it.
361 */
362 if (dn_mark == new_dn_mark)
363 destroy = 1;
364 error = 0;
365 goto out;
366 }
367
368 __f_setown(filp, task_pid(current), PIDTYPE_TGID, force: 0);
369
370 error = attach_dn(dn, dn_mark, id, fd, filp, mask);
371 /* !error means that we attached the dn to the dn_mark, so don't free it */
372 if (!error)
373 dn = NULL;
374 /* -EEXIST means that we didn't add this new dn and used an old one.
375 * that isn't an error (and the unused dn should be freed) */
376 else if (error == -EEXIST)
377 error = 0;
378
379 dnotify_recalc_inode_mask(fsn_mark);
380out:
381 spin_unlock(lock: &fsn_mark->lock);
382
383 if (destroy)
384 fsnotify_detach_mark(mark: fsn_mark);
385 fsnotify_group_unlock(group: dnotify_group);
386 if (destroy)
387 fsnotify_free_mark(mark: fsn_mark);
388 fsnotify_put_mark(mark: fsn_mark);
389out_err:
390 if (new_fsn_mark)
391 fsnotify_put_mark(mark: new_fsn_mark);
392 if (dn)
393 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
394 if (f)
395 fput(f);
396 return error;
397}
398
399static int __init dnotify_init(void)
400{
401 dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
402 SLAB_PANIC|SLAB_ACCOUNT);
403 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
404
405 dnotify_group = fsnotify_alloc_group(ops: &dnotify_fsnotify_ops,
406 FSNOTIFY_GROUP_NOFS);
407 if (IS_ERR(ptr: dnotify_group))
408 panic(fmt: "unable to allocate fsnotify group for dnotify\n");
409 dnotify_sysctl_init();
410 return 0;
411}
412
413module_init(dnotify_init)
414

source code of linux/fs/notify/dnotify/dnotify.c