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