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/fsnotify_backend.h>
20
21static int dir_notify_enable __read_mostly = 1;
22#ifdef CONFIG_SYSCTL
23static const struct ctl_table dnotify_sysctls[] = {
24 {
25 .procname = "dir-notify-enable",
26 .data = &dir_notify_enable,
27 .maxlen = sizeof(int),
28 .mode = 0644,
29 .proc_handler = proc_dointvec,
30 },
31};
32static void __init dnotify_sysctl_init(void)
33{
34 register_sysctl_init("fs", dnotify_sysctls);
35}
36#else
37#define dnotify_sysctl_init() do { } while (0)
38#endif
39
40static struct kmem_cache *dnotify_struct_cache __ro_after_init;
41static struct kmem_cache *dnotify_mark_cache __ro_after_init;
42static struct fsnotify_group *dnotify_group __ro_after_init;
43
44/*
45 * dnotify will attach one of these to each inode (i_fsnotify_marks) which
46 * is being watched by dnotify. If multiple userspace applications are watching
47 * the same directory with dnotify their information is chained in dn
48 */
49struct dnotify_mark {
50 struct fsnotify_mark fsn_mark;
51 struct dnotify_struct *dn;
52};
53
54/*
55 * When a process starts or stops watching an inode the set of events which
56 * dnotify cares about for that inode may change. This function runs the
57 * list of everything receiving dnotify events about this directory and calculates
58 * the set of all those events. After it updates what dnotify is interested in
59 * it calls the fsnotify function so it can update the set of all events relevant
60 * to this inode.
61 */
62static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
63{
64 __u32 new_mask = 0;
65 struct dnotify_struct *dn;
66 struct dnotify_mark *dn_mark = container_of(fsn_mark,
67 struct dnotify_mark,
68 fsn_mark);
69
70 assert_spin_locked(&fsn_mark->lock);
71
72 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
73 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
74 if (fsn_mark->mask == new_mask)
75 return;
76 fsn_mark->mask = new_mask;
77
78 fsnotify_recalc_mask(conn: fsn_mark->connector);
79}
80
81/*
82 * Mains fsnotify call where events are delivered to dnotify.
83 * Find the dnotify mark on the relevant inode, run the list of dnotify structs
84 * on that mark and determine which of them has expressed interest in receiving
85 * events of this type. When found send the correct process and signal and
86 * destroy the dnotify struct if it was not registered to receive multiple
87 * events.
88 */
89static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
90 struct inode *inode, struct inode *dir,
91 const struct qstr *name, u32 cookie)
92{
93 struct dnotify_mark *dn_mark;
94 struct dnotify_struct *dn;
95 struct dnotify_struct **prev;
96 struct fown_struct *fown;
97 __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
98
99 /* not a dir, dnotify doesn't care */
100 if (!dir && !(mask & FS_ISDIR))
101 return 0;
102
103 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
104
105 spin_lock(lock: &inode_mark->lock);
106 prev = &dn_mark->dn;
107 while ((dn = *prev) != NULL) {
108 if ((dn->dn_mask & test_mask) == 0) {
109 prev = &dn->dn_next;
110 continue;
111 }
112 fown = file_f_owner(file: dn->dn_filp);
113 send_sigio(fown, fd: dn->dn_fd, POLL_MSG);
114 if (dn->dn_mask & FS_DN_MULTISHOT)
115 prev = &dn->dn_next;
116 else {
117 *prev = dn->dn_next;
118 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
119 dnotify_recalc_inode_mask(fsn_mark: inode_mark);
120 }
121 }
122
123 spin_unlock(lock: &inode_mark->lock);
124
125 return 0;
126}
127
128static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
129{
130 struct dnotify_mark *dn_mark = container_of(fsn_mark,
131 struct dnotify_mark,
132 fsn_mark);
133
134 BUG_ON(dn_mark->dn);
135
136 kmem_cache_free(s: dnotify_mark_cache, objp: dn_mark);
137}
138
139static const struct fsnotify_ops dnotify_fsnotify_ops = {
140 .handle_inode_event = dnotify_handle_event,
141 .free_mark = dnotify_free_mark,
142};
143
144/*
145 * Called every time a file is closed. Looks first for a dnotify mark on the
146 * inode. If one is found run all of the ->dn structures attached to that
147 * mark for one relevant to this process closing the file and remove that
148 * dnotify_struct. If that was the last dnotify_struct also remove the
149 * fsnotify_mark.
150 */
151void dnotify_flush(struct file *filp, fl_owner_t id)
152{
153 struct fsnotify_mark *fsn_mark;
154 struct dnotify_mark *dn_mark;
155 struct dnotify_struct *dn;
156 struct dnotify_struct **prev;
157 struct inode *inode;
158 bool free = false;
159
160 inode = file_inode(f: filp);
161 if (!S_ISDIR(inode->i_mode))
162 return;
163
164 fsn_mark = fsnotify_find_inode_mark(inode, group: dnotify_group);
165 if (!fsn_mark)
166 return;
167 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
168
169 fsnotify_group_lock(group: dnotify_group);
170
171 spin_lock(lock: &fsn_mark->lock);
172 prev = &dn_mark->dn;
173 while ((dn = *prev) != NULL) {
174 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
175 *prev = dn->dn_next;
176 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
177 dnotify_recalc_inode_mask(fsn_mark);
178 break;
179 }
180 prev = &dn->dn_next;
181 }
182
183 spin_unlock(lock: &fsn_mark->lock);
184
185 /* nothing else could have found us thanks to the dnotify_groups
186 mark_mutex */
187 if (dn_mark->dn == NULL) {
188 fsnotify_detach_mark(mark: fsn_mark);
189 free = true;
190 }
191
192 fsnotify_group_unlock(group: dnotify_group);
193
194 if (free)
195 fsnotify_free_mark(mark: fsn_mark);
196 fsnotify_put_mark(mark: fsn_mark);
197}
198
199/* this conversion is done only at watch creation */
200static __u32 convert_arg(unsigned int arg)
201{
202 __u32 new_mask = FS_EVENT_ON_CHILD;
203
204 if (arg & DN_MULTISHOT)
205 new_mask |= FS_DN_MULTISHOT;
206 if (arg & DN_DELETE)
207 new_mask |= (FS_DELETE | FS_MOVED_FROM);
208 if (arg & DN_MODIFY)
209 new_mask |= FS_MODIFY;
210 if (arg & DN_ACCESS)
211 new_mask |= FS_ACCESS;
212 if (arg & DN_ATTRIB)
213 new_mask |= FS_ATTRIB;
214 if (arg & DN_RENAME)
215 new_mask |= FS_RENAME;
216 if (arg & DN_CREATE)
217 new_mask |= (FS_CREATE | FS_MOVED_TO);
218
219 return new_mask;
220}
221
222/*
223 * If multiple processes watch the same inode with dnotify there is only one
224 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
225 * onto that mark. This function either attaches the new dnotify_struct onto
226 * that list, or it |= the mask onto an existing dnofiy_struct.
227 */
228static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
229 fl_owner_t id, int fd, struct file *filp, __u32 mask)
230{
231 struct dnotify_struct *odn;
232
233 odn = dn_mark->dn;
234 while (odn != NULL) {
235 /* adding more events to existing dnofiy_struct? */
236 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
237 odn->dn_fd = fd;
238 odn->dn_mask |= mask;
239 return -EEXIST;
240 }
241 odn = odn->dn_next;
242 }
243
244 dn->dn_mask = mask;
245 dn->dn_fd = fd;
246 dn->dn_filp = filp;
247 dn->dn_owner = id;
248 dn->dn_next = dn_mark->dn;
249 dn_mark->dn = dn;
250
251 return 0;
252}
253
254/*
255 * When a process calls fcntl to attach a dnotify watch to a directory it ends
256 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
257 * attached to the fsnotify_mark.
258 */
259int fcntl_dirnotify(int fd, struct file *filp, unsigned int arg)
260{
261 struct dnotify_mark *new_dn_mark, *dn_mark;
262 struct fsnotify_mark *new_fsn_mark, *fsn_mark;
263 struct dnotify_struct *dn;
264 struct inode *inode;
265 fl_owner_t id = current->files;
266 struct file *f = NULL;
267 int destroy = 0, error = 0;
268 __u32 mask;
269
270 /* we use these to tell if we need to kfree */
271 new_fsn_mark = NULL;
272 dn = NULL;
273
274 if (!dir_notify_enable) {
275 error = -EINVAL;
276 goto out_err;
277 }
278
279 /* a 0 mask means we are explicitly removing the watch */
280 if ((arg & ~DN_MULTISHOT) == 0) {
281 dnotify_flush(filp, id);
282 error = 0;
283 goto out_err;
284 }
285
286 /* dnotify only works on directories */
287 inode = file_inode(f: filp);
288 if (!S_ISDIR(inode->i_mode)) {
289 error = -ENOTDIR;
290 goto out_err;
291 }
292
293 /*
294 * convert the userspace DN_* "arg" to the internal FS_*
295 * defined in fsnotify
296 */
297 mask = convert_arg(arg);
298
299 error = security_path_notify(path: &filp->f_path, mask,
300 obj_type: FSNOTIFY_OBJ_TYPE_INODE);
301 if (error)
302 goto out_err;
303
304 /* expect most fcntl to add new rather than augment old */
305 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
306 if (!dn) {
307 error = -ENOMEM;
308 goto out_err;
309 }
310
311 error = file_f_owner_allocate(file: filp);
312 if (error)
313 goto out_err;
314
315 /* new fsnotify mark, we expect most fcntl calls to add a new mark */
316 new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
317 if (!new_dn_mark) {
318 error = -ENOMEM;
319 goto out_err;
320 }
321
322 /* set up the new_fsn_mark and new_dn_mark */
323 new_fsn_mark = &new_dn_mark->fsn_mark;
324 fsnotify_init_mark(mark: new_fsn_mark, group: dnotify_group);
325 new_fsn_mark->mask = mask;
326 new_dn_mark->dn = NULL;
327
328 /* this is needed to prevent the fcntl/close race described below */
329 fsnotify_group_lock(group: dnotify_group);
330
331 /* add the new_fsn_mark or find an old one. */
332 fsn_mark = fsnotify_find_inode_mark(inode, group: dnotify_group);
333 if (fsn_mark) {
334 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
335 spin_lock(lock: &fsn_mark->lock);
336 } else {
337 error = fsnotify_add_inode_mark_locked(mark: new_fsn_mark, inode, add_flags: 0);
338 if (error) {
339 fsnotify_group_unlock(group: dnotify_group);
340 goto out_err;
341 }
342 spin_lock(lock: &new_fsn_mark->lock);
343 fsn_mark = new_fsn_mark;
344 dn_mark = new_dn_mark;
345 /* we used new_fsn_mark, so don't free it */
346 new_fsn_mark = NULL;
347 }
348
349 f = fget_raw(fd);
350
351 /* if (f != filp) means that we lost a race and another task/thread
352 * actually closed the fd we are still playing with before we grabbed
353 * the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the
354 * fd is the only time we clean up the marks we need to get our mark
355 * off the list. */
356 if (f != filp) {
357 /* if we added ourselves, shoot ourselves, it's possible that
358 * the flush actually did shoot this fsn_mark. That's fine too
359 * since multiple calls to destroy_mark is perfectly safe, if
360 * we found a dn_mark already attached to the inode, just sod
361 * off silently as the flush at close time dealt with it.
362 */
363 if (dn_mark == new_dn_mark)
364 destroy = 1;
365 error = 0;
366 goto out;
367 }
368
369 __f_setown(filp, task_pid(current), PIDTYPE_TGID, force: 0);
370
371 error = attach_dn(dn, dn_mark, id, fd, filp, mask);
372 /* !error means that we attached the dn to the dn_mark, so don't free it */
373 if (!error)
374 dn = NULL;
375 /* -EEXIST means that we didn't add this new dn and used an old one.
376 * that isn't an error (and the unused dn should be freed) */
377 else if (error == -EEXIST)
378 error = 0;
379
380 dnotify_recalc_inode_mask(fsn_mark);
381out:
382 spin_unlock(lock: &fsn_mark->lock);
383
384 if (destroy)
385 fsnotify_detach_mark(mark: fsn_mark);
386 fsnotify_group_unlock(group: dnotify_group);
387 if (destroy)
388 fsnotify_free_mark(mark: fsn_mark);
389 fsnotify_put_mark(mark: fsn_mark);
390out_err:
391 if (new_fsn_mark)
392 fsnotify_put_mark(mark: new_fsn_mark);
393 if (dn)
394 kmem_cache_free(s: dnotify_struct_cache, objp: dn);
395 if (f)
396 fput(f);
397 return error;
398}
399
400static int __init dnotify_init(void)
401{
402 dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
403 SLAB_PANIC|SLAB_ACCOUNT);
404 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
405
406 dnotify_group = fsnotify_alloc_group(ops: &dnotify_fsnotify_ops, flags: 0);
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