summaryrefslogtreecommitdiff
path: root/fs/notify/fanotify/fanotify.c
blob: b428c295d13f8cf311431a2ece7bb72f3a44d242 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/sched/signal.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <linux/audit.h>
#include <linux/sched/mm.h>
#include <linux/statfs.h>

#include "fanotify.h"

static bool should_merge(struct fsnotify_event *old_fsn,
			 struct fsnotify_event *new_fsn)
{
	struct fanotify_event *old, *new;

	pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
	old = FANOTIFY_E(old_fsn);
	new = FANOTIFY_E(new_fsn);

	if (old_fsn->inode != new_fsn->inode || old->pid != new->pid ||
	    old->fh_type != new->fh_type || old->fh_len != new->fh_len)
		return false;

	if (fanotify_event_has_path(old)) {
		return old->path.mnt == new->path.mnt &&
			old->path.dentry == new->path.dentry;
	} else if (fanotify_event_has_fid(old)) {
		/*
		 * We want to merge many dirent events in the same dir (i.e.
		 * creates/unlinks/renames), but we do not want to merge dirent
		 * events referring to subdirs with dirent events referring to
		 * non subdirs, otherwise, user won't be able to tell from a
		 * mask FAN_CREATE|FAN_DELETE|FAN_ONDIR if it describes mkdir+
		 * unlink pair or rmdir+create pair of events.
		 */
		return (old->mask & FS_ISDIR) == (new->mask & FS_ISDIR) &&
			fanotify_fid_equal(&old->fid, &new->fid, old->fh_len);
	}

	/* Do not merge events if we failed to encode fid */
	return false;
}

/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
	struct fsnotify_event *test_event;
	struct fanotify_event *new;

	pr_debug("%s: list=%p event=%p\n", __func__, list, event);
	new = FANOTIFY_E(event);

	/*
	 * Don't merge a permission event with any other event so that we know
	 * the event structure we have created in fanotify_handle_event() is the
	 * one we should check for permission response.
	 */
	if (fanotify_is_perm_event(new->mask))
		return 0;

	list_for_each_entry_reverse(test_event, list, list) {
		if (should_merge(test_event, event)) {
			FANOTIFY_E(test_event)->mask |= new->mask;
			return 1;
		}
	}

	return 0;
}

/*
 * Wait for response to permission event. The function also takes care of
 * freeing the permission event (or offloads that in case the wait is canceled
 * by a signal). The function returns 0 in case access got allowed by userspace,
 * -EPERM in case userspace disallowed the access, and -ERESTARTSYS in case
 * the wait got interrupted by a signal.
 */
static int fanotify_get_response(struct fsnotify_group *group,
				 struct fanotify_perm_event *event,
				 struct fsnotify_iter_info *iter_info)
{
	int ret;

	pr_debug("%s: group=%p event=%p\n", __func__, group, event);

	ret = wait_event_killable(group->fanotify_data.access_waitq,
				  event->state == FAN_EVENT_ANSWERED);
	/* Signal pending? */
	if (ret < 0) {
		spin_lock(&group->notification_lock);
		/* Event reported to userspace and no answer yet? */
		if (event->state == FAN_EVENT_REPORTED) {
			/* Event will get freed once userspace answers to it */
			event->state = FAN_EVENT_CANCELED;
			spin_unlock(&group->notification_lock);
			return ret;
		}
		/* Event not yet reported? Just remove it. */
		if (event->state == FAN_EVENT_INIT)
			fsnotify_remove_queued_event(group, &event->fae.fse);
		/*
		 * Event may be also answered in case signal delivery raced
		 * with wakeup. In that case we have nothing to do besides
		 * freeing the event and reporting error.
		 */
		spin_unlock(&group->notification_lock);
		goto out;
	}

	/* userspace responded, convert to something usable */
	switch (event->response & ~FAN_AUDIT) {
	case FAN_ALLOW:
		ret = 0;
		break;
	case FAN_DENY:
	default:
		ret = -EPERM;
	}

	/* Check if the response should be audited */
	if (event->response & FAN_AUDIT)
		audit_fanotify(event->response & ~FAN_AUDIT);

	pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
		 group, event, ret);
out:
	fsnotify_destroy_event(group, &event->fae.fse);

	return ret;
}

/*
 * This function returns a mask for an event that only contains the flags
 * that have been specifically requested by the user. Flags that may have
 * been included within the event mask, but have not been explicitly
 * requested by the user, will not be present in the returned mask.
 */
static u32 fanotify_group_event_mask(struct fsnotify_group *group,
				     struct fsnotify_iter_info *iter_info,
				     u32 event_mask, const void *data,
				     int data_type)
{
	__u32 marks_mask = 0, marks_ignored_mask = 0;
	__u32 test_mask, user_mask = FANOTIFY_OUTGOING_EVENTS;
	const struct path *path = data;
	struct fsnotify_mark *mark;
	int type;

	pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
		 __func__, iter_info->report_mask, event_mask, data, data_type);

	if (!FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
		/* Do we have path to open a file descriptor? */
		if (data_type != FSNOTIFY_EVENT_PATH)
			return 0;
		/* Path type events are only relevant for files and dirs */
		if (!d_is_reg(path->dentry) && !d_can_lookup(path->dentry))
			return 0;
	}

	fsnotify_foreach_obj_type(type) {
		if (!fsnotify_iter_should_report_type(iter_info, type))
			continue;
		mark = iter_info->marks[type];
		/*
		 * If the event is for a child and this mark doesn't care about
		 * events on a child, don't send it!
		 */
		if (event_mask & FS_EVENT_ON_CHILD &&
		    (type != FSNOTIFY_OBJ_TYPE_INODE ||
		     !(mark->mask & FS_EVENT_ON_CHILD)))
			continue;

		marks_mask |= mark->mask;
		marks_ignored_mask |= mark->ignored_mask;
	}

	test_mask = event_mask & marks_mask & ~marks_ignored_mask;

	/*
	 * dirent modification events (create/delete/move) do not carry the
	 * child entry name/inode information. Instead, we report FAN_ONDIR
	 * for mkdir/rmdir so user can differentiate them from creat/unlink.
	 *
	 * For backward compatibility and consistency, do not report FAN_ONDIR
	 * to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
	 * to user in FAN_REPORT_FID mode for all event types.
	 */
	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
		/* Do not report FAN_ONDIR without any event */
		if (!(test_mask & ~FAN_ONDIR))
			return 0;
	} else {
		user_mask &= ~FAN_ONDIR;
	}

	if (event_mask & FS_ISDIR &&
	    !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
		return 0;

	return test_mask & user_mask;
}

static int fanotify_encode_fid(struct fanotify_event *event,
			       struct inode *inode, gfp_t gfp,
			       __kernel_fsid_t *fsid)
{
	struct fanotify_fid *fid = &event->fid;
	int dwords, bytes = 0;
	int err, type;

	fid->ext_fh = NULL;
	dwords = 0;
	err = -ENOENT;
	type = exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
	if (!dwords)
		goto out_err;

	bytes = dwords << 2;
	if (bytes > FANOTIFY_INLINE_FH_LEN) {
		/* Treat failure to allocate fh as failure to allocate event */
		err = -ENOMEM;
		fid->ext_fh = kmalloc(bytes, gfp);
		if (!fid->ext_fh)
			goto out_err;
	}

	type = exportfs_encode_inode_fh(inode, fanotify_fid_fh(fid, bytes),
					&dwords, NULL);
	err = -EINVAL;
	if (!type || type == FILEID_INVALID || bytes != dwords << 2)
		goto out_err;

	fid->fsid = *fsid;
	event->fh_len = bytes;

	return type;

out_err:
	pr_warn_ratelimited("fanotify: failed to encode fid (fsid=%x.%x, "
			    "type=%d, bytes=%d, err=%i)\n",
			    fsid->val[0], fsid->val[1], type, bytes, err);
	kfree(fid->ext_fh);
	fid->ext_fh = NULL;
	event->fh_len = 0;

	return FILEID_INVALID;
}

/*
 * The inode to use as identifier when reporting fid depends on the event.
 * Report the modified directory inode on dirent modification events.
 * Report the "victim" inode otherwise.
 * For example:
 * FS_ATTRIB reports the child inode even if reported on a watched parent.
 * FS_CREATE reports the modified dir inode and not the created inode.
 */
static struct inode *fanotify_fid_inode(struct inode *to_tell, u32 event_mask,
					const void *data, int data_type)
{
	if (event_mask & ALL_FSNOTIFY_DIRENT_EVENTS)
		return to_tell;
	else if (data_type == FSNOTIFY_EVENT_INODE)
		return (struct inode *)data;
	else if (data_type == FSNOTIFY_EVENT_PATH)
		return d_inode(((struct path *)data)->dentry);
	return NULL;
}

struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
					    struct inode *inode, u32 mask,
					    const void *data, int data_type,
					    __kernel_fsid_t *fsid)
{
	struct fanotify_event *event = NULL;
	gfp_t gfp = GFP_KERNEL_ACCOUNT;
	struct inode *id = fanotify_fid_inode(inode, mask, data, data_type);

	/*
	 * For queues with unlimited length lost events are not expected and
	 * can possibly have security implications. Avoid losing events when
	 * memory is short.
	 */
	if (group->max_events == UINT_MAX)
		gfp |= __GFP_NOFAIL;

	/* Whoever is interested in the event, pays for the allocation. */
	memalloc_use_memcg(group->memcg);

	if (fanotify_is_perm_event(mask)) {
		struct fanotify_perm_event *pevent;

		pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
		if (!pevent)
			goto out;
		event = &pevent->fae;
		pevent->response = 0;
		pevent->state = FAN_EVENT_INIT;
		goto init;
	}
	event = kmem_cache_alloc(fanotify_event_cachep, gfp);
	if (!event)
		goto out;
init: __maybe_unused
	fsnotify_init_event(&event->fse, inode);
	event->mask = mask;
	if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
		event->pid = get_pid(task_pid(current));
	else
		event->pid = get_pid(task_tgid(current));
	event->fh_len = 0;
	if (id && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
		/* Report the event without a file identifier on encode error */
		event->fh_type = fanotify_encode_fid(event, id, gfp, fsid);
	} else if (data_type == FSNOTIFY_EVENT_PATH) {
		event->fh_type = FILEID_ROOT;
		event->path = *((struct path *)data);
		path_get(&event->path);
	} else {
		event->fh_type = FILEID_INVALID;
		event->path.mnt = NULL;
		event->path.dentry = NULL;
	}
out:
	memalloc_unuse_memcg();
	return event;
}

/*
 * Get cached fsid of the filesystem containing the object from any connector.
 * All connectors are supposed to have the same fsid, but we do not verify that
 * here.
 */
static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
{
	int type;
	__kernel_fsid_t fsid = {};

	fsnotify_foreach_obj_type(type) {
		struct fsnotify_mark_connector *conn;

		if (!fsnotify_iter_should_report_type(iter_info, type))
			continue;

		conn = READ_ONCE(iter_info->marks[type]->connector);
		/* Mark is just getting destroyed or created? */
		if (!conn)
			continue;
		if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID))
			continue;
		/* Pairs with smp_wmb() in fsnotify_add_mark_list() */
		smp_rmb();
		fsid = conn->fsid;
		if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
			continue;
		return fsid;
	}

	return fsid;
}

static int fanotify_handle_event(struct fsnotify_group *group,
				 struct inode *inode,
				 u32 mask, const void *data, int data_type,
				 const struct qstr *file_name, u32 cookie,
				 struct fsnotify_iter_info *iter_info)
{
	int ret = 0;
	struct fanotify_event *event;
	struct fsnotify_event *fsn_event;
	__kernel_fsid_t fsid = {};

	BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
	BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
	BUILD_BUG_ON(FAN_ATTRIB != FS_ATTRIB);
	BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
	BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
	BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
	BUILD_BUG_ON(FAN_MOVED_TO != FS_MOVED_TO);
	BUILD_BUG_ON(FAN_MOVED_FROM != FS_MOVED_FROM);
	BUILD_BUG_ON(FAN_CREATE != FS_CREATE);
	BUILD_BUG_ON(FAN_DELETE != FS_DELETE);
	BUILD_BUG_ON(FAN_DELETE_SELF != FS_DELETE_SELF);
	BUILD_BUG_ON(FAN_MOVE_SELF != FS_MOVE_SELF);
	BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
	BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
	BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
	BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
	BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
	BUILD_BUG_ON(FAN_OPEN_EXEC != FS_OPEN_EXEC);
	BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);

	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 19);

	mask = fanotify_group_event_mask(group, iter_info, mask, data,
					 data_type);
	if (!mask)
		return 0;

	pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
		 mask);

	if (fanotify_is_perm_event(mask)) {
		/*
		 * fsnotify_prepare_user_wait() fails if we race with mark
		 * deletion.  Just let the operation pass in that case.
		 */
		if (!fsnotify_prepare_user_wait(iter_info))
			return 0;
	}

	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
		fsid = fanotify_get_fsid(iter_info);
		/* Racing with mark destruction or creation? */
		if (!fsid.val[0] && !fsid.val[1])
			return 0;
	}

	event = fanotify_alloc_event(group, inode, mask, data, data_type,
				     &fsid);
	ret = -ENOMEM;
	if (unlikely(!event)) {
		/*
		 * We don't queue overflow events for permission events as
		 * there the access is denied and so no event is in fact lost.
		 */
		if (!fanotify_is_perm_event(mask))
			fsnotify_queue_overflow(group);
		goto finish;
	}

	fsn_event = &event->fse;
	ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
	if (ret) {
		/* Permission events shouldn't be merged */
		BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
		/* Our event wasn't used in the end. Free it. */
		fsnotify_destroy_event(group, fsn_event);

		ret = 0;
	} else if (fanotify_is_perm_event(mask)) {
		ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
					    iter_info);
	}
finish:
	if (fanotify_is_perm_event(mask))
		fsnotify_finish_user_wait(iter_info);

	return ret;
}

static void fanotify_free_group_priv(struct fsnotify_group *group)
{
	struct user_struct *user;

	user = group->fanotify_data.user;
	atomic_dec(&user->fanotify_listeners);
	free_uid(user);
}

static void fanotify_free_event(struct fsnotify_event *fsn_event)
{
	struct fanotify_event *event;

	event = FANOTIFY_E(fsn_event);
	if (fanotify_event_has_path(event))
		path_put(&event->path);
	else if (fanotify_event_has_ext_fh(event))
		kfree(event->fid.ext_fh);
	put_pid(event->pid);
	if (fanotify_is_perm_event(event->mask)) {
		kmem_cache_free(fanotify_perm_event_cachep,
				FANOTIFY_PE(fsn_event));
		return;
	}
	kmem_cache_free(fanotify_event_cachep, event);
}

static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
{
	kmem_cache_free(fanotify_mark_cache, fsn_mark);
}

const struct fsnotify_ops fanotify_fsnotify_ops = {
	.handle_event = fanotify_handle_event,
	.free_group_priv = fanotify_free_group_priv,
	.free_event = fanotify_free_event,
	.free_mark = fanotify_free_mark,
};