xref: /linux/fs/notify/dnotify/dnotify.c (revision 3fd6c59042dbba50391e30862beac979491145fe)
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 
21 static int dir_notify_enable __read_mostly = 1;
22 #ifdef CONFIG_SYSCTL
23 static 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 };
dnotify_sysctl_init(void)32 static 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 
40 static struct kmem_cache *dnotify_struct_cache __ro_after_init;
41 static struct kmem_cache *dnotify_mark_cache __ro_after_init;
42 static 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  */
49 struct 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  */
dnotify_recalc_inode_mask(struct fsnotify_mark * fsn_mark)62 static 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(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  */
dnotify_handle_event(struct fsnotify_mark * inode_mark,u32 mask,struct inode * inode,struct inode * dir,const struct qstr * name,u32 cookie)89 static 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(&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(dn->dn_filp);
113 		send_sigio(fown, 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(dnotify_struct_cache, dn);
119 			dnotify_recalc_inode_mask(inode_mark);
120 		}
121 	}
122 
123 	spin_unlock(&inode_mark->lock);
124 
125 	return 0;
126 }
127 
dnotify_free_mark(struct fsnotify_mark * fsn_mark)128 static 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(dnotify_mark_cache, dn_mark);
137 }
138 
139 static 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  */
dnotify_flush(struct file * filp,fl_owner_t id)151 void 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(filp);
161 	if (!S_ISDIR(inode->i_mode))
162 		return;
163 
164 	fsn_mark = fsnotify_find_inode_mark(inode, 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(dnotify_group);
170 
171 	spin_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(dnotify_struct_cache, dn);
177 			dnotify_recalc_inode_mask(fsn_mark);
178 			break;
179 		}
180 		prev = &dn->dn_next;
181 	}
182 
183 	spin_unlock(&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(fsn_mark);
189 		free = true;
190 	}
191 
192 	fsnotify_group_unlock(dnotify_group);
193 
194 	if (free)
195 		fsnotify_free_mark(fsn_mark);
196 	fsnotify_put_mark(fsn_mark);
197 }
198 
199 /* this conversion is done only at watch creation */
convert_arg(unsigned int arg)200 static __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  */
attach_dn(struct dnotify_struct * dn,struct dnotify_mark * dn_mark,fl_owner_t id,int fd,struct file * filp,__u32 mask)228 static 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  */
fcntl_dirnotify(int fd,struct file * filp,unsigned int arg)259 int 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(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(&filp->f_path, mask,
300 			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 	/* new fsnotify mark, we expect most fcntl calls to add a new mark */
312 	new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
313 	if (!new_dn_mark) {
314 		error = -ENOMEM;
315 		goto out_err;
316 	}
317 
318 	error = file_f_owner_allocate(filp);
319 	if (error)
320 		goto out_err;
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(new_fsn_mark, 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(dnotify_group);
330 
331 	/* add the new_fsn_mark or find an old one. */
332 	fsn_mark = fsnotify_find_inode_mark(inode, dnotify_group);
333 	if (fsn_mark) {
334 		dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
335 		spin_lock(&fsn_mark->lock);
336 	} else {
337 		error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
338 		if (error) {
339 			fsnotify_group_unlock(dnotify_group);
340 			goto out_err;
341 		}
342 		spin_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, 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);
381 out:
382 	spin_unlock(&fsn_mark->lock);
383 
384 	if (destroy)
385 		fsnotify_detach_mark(fsn_mark);
386 	fsnotify_group_unlock(dnotify_group);
387 	if (destroy)
388 		fsnotify_free_mark(fsn_mark);
389 	fsnotify_put_mark(fsn_mark);
390 out_err:
391 	if (new_fsn_mark)
392 		fsnotify_put_mark(new_fsn_mark);
393 	if (dn)
394 		kmem_cache_free(dnotify_struct_cache, dn);
395 	if (f)
396 		fput(f);
397 	return error;
398 }
399 
dnotify_init(void)400 static 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(&dnotify_fsnotify_ops, 0);
407 	if (IS_ERR(dnotify_group))
408 		panic("unable to allocate fsnotify group for dnotify\n");
409 	dnotify_sysctl_init();
410 	return 0;
411 }
412 
413 module_init(dnotify_init)
414