1 // SPDX-License-Identifier: GPL-2.0
2 /* Watch queue and general notification mechanism, built on pipes
3 *
4 * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 *
7 * See Documentation/watch_queue.rst
8 */
9
10 #define pr_fmt(fmt) "watchq: " fmt
11 #include <linux/module.h>
12 #include <linux/init.h>
13 #include <linux/sched.h>
14 #include <linux/slab.h>
15 #include <linux/printk.h>
16 #include <linux/miscdevice.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/pagemap.h>
20 #include <linux/poll.h>
21 #include <linux/uaccess.h>
22 #include <linux/vmalloc.h>
23 #include <linux/file.h>
24 #include <linux/security.h>
25 #include <linux/cred.h>
26 #include <linux/sched/signal.h>
27 #include <linux/watch_queue.h>
28 #include <linux/pipe_fs_i.h>
29
30 MODULE_DESCRIPTION("Watch queue");
31 MODULE_AUTHOR("Red Hat, Inc.");
32 MODULE_LICENSE("GPL");
33
34 #define WATCH_QUEUE_NOTE_SIZE 128
35 #define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE)
36
watch_queue_pipe_buf_release(struct pipe_inode_info * pipe,struct pipe_buffer * buf)37 static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe,
38 struct pipe_buffer *buf)
39 {
40 struct watch_queue *wqueue = (struct watch_queue *)buf->private;
41 struct page *page;
42 unsigned int bit;
43
44 /* We need to work out which note within the page this refers to, but
45 * the note might have been maximum size, so merely ANDing the offset
46 * off doesn't work. OTOH, the note must've been more than zero size.
47 */
48 bit = buf->offset + buf->len;
49 if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0)
50 bit -= WATCH_QUEUE_NOTE_SIZE;
51 bit /= WATCH_QUEUE_NOTE_SIZE;
52
53 page = buf->page;
54 bit += page->index;
55
56 set_bit(bit, wqueue->notes_bitmap);
57 }
58
59 // No try_steal function => no stealing
60 #define watch_queue_pipe_buf_try_steal NULL
61
62 /* New data written to a pipe may be appended to a buffer with this type. */
63 static const struct pipe_buf_operations watch_queue_pipe_buf_ops = {
64 .release = watch_queue_pipe_buf_release,
65 .try_steal = watch_queue_pipe_buf_try_steal,
66 .get = generic_pipe_buf_get,
67 };
68
69 /*
70 * Post a notification to a watch queue.
71 */
post_one_notification(struct watch_queue * wqueue,struct watch_notification * n)72 static bool post_one_notification(struct watch_queue *wqueue,
73 struct watch_notification *n)
74 {
75 void *p;
76 struct pipe_inode_info *pipe = wqueue->pipe;
77 struct pipe_buffer *buf;
78 struct page *page;
79 unsigned int head, tail, mask, note, offset, len;
80 bool done = false;
81
82 if (!pipe)
83 return false;
84
85 spin_lock_irq(&pipe->rd_wait.lock);
86
87 if (wqueue->defunct)
88 goto out;
89
90 mask = pipe->ring_size - 1;
91 head = pipe->head;
92 tail = pipe->tail;
93 if (pipe_full(head, tail, pipe->ring_size))
94 goto lost;
95
96 note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
97 if (note >= wqueue->nr_notes)
98 goto lost;
99
100 page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
101 offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE;
102 get_page(page);
103 len = n->info & WATCH_INFO_LENGTH;
104 p = kmap_atomic(page);
105 memcpy(p + offset, n, len);
106 kunmap_atomic(p);
107
108 buf = &pipe->bufs[head & mask];
109 buf->page = page;
110 buf->private = (unsigned long)wqueue;
111 buf->ops = &watch_queue_pipe_buf_ops;
112 buf->offset = offset;
113 buf->len = len;
114 buf->flags = PIPE_BUF_FLAG_WHOLE;
115 pipe->head = head + 1;
116
117 if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
118 spin_unlock_irq(&pipe->rd_wait.lock);
119 BUG();
120 }
121 wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
122 done = true;
123
124 out:
125 spin_unlock_irq(&pipe->rd_wait.lock);
126 if (done)
127 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
128 return done;
129
130 lost:
131 buf = &pipe->bufs[(head - 1) & mask];
132 buf->flags |= PIPE_BUF_FLAG_LOSS;
133 goto out;
134 }
135
136 /*
137 * Apply filter rules to a notification.
138 */
filter_watch_notification(const struct watch_filter * wf,const struct watch_notification * n)139 static bool filter_watch_notification(const struct watch_filter *wf,
140 const struct watch_notification *n)
141 {
142 const struct watch_type_filter *wt;
143 unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8;
144 unsigned int st_index = n->subtype / st_bits;
145 unsigned int st_bit = 1U << (n->subtype % st_bits);
146 int i;
147
148 if (!test_bit(n->type, wf->type_filter))
149 return false;
150
151 for (i = 0; i < wf->nr_filters; i++) {
152 wt = &wf->filters[i];
153 if (n->type == wt->type &&
154 (wt->subtype_filter[st_index] & st_bit) &&
155 (n->info & wt->info_mask) == wt->info_filter)
156 return true;
157 }
158
159 return false; /* If there is a filter, the default is to reject. */
160 }
161
162 /**
163 * __post_watch_notification - Post an event notification
164 * @wlist: The watch list to post the event to.
165 * @n: The notification record to post.
166 * @cred: The creds of the process that triggered the notification.
167 * @id: The ID to match on the watch.
168 *
169 * Post a notification of an event into a set of watch queues and let the users
170 * know.
171 *
172 * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and
173 * should be in units of sizeof(*n).
174 */
__post_watch_notification(struct watch_list * wlist,struct watch_notification * n,const struct cred * cred,u64 id)175 void __post_watch_notification(struct watch_list *wlist,
176 struct watch_notification *n,
177 const struct cred *cred,
178 u64 id)
179 {
180 const struct watch_filter *wf;
181 struct watch_queue *wqueue;
182 struct watch *watch;
183
184 if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) {
185 WARN_ON(1);
186 return;
187 }
188
189 rcu_read_lock();
190
191 hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
192 if (watch->id != id)
193 continue;
194 n->info &= ~WATCH_INFO_ID;
195 n->info |= watch->info_id;
196
197 wqueue = rcu_dereference(watch->queue);
198 wf = rcu_dereference(wqueue->filter);
199 if (wf && !filter_watch_notification(wf, n))
200 continue;
201
202 if (security_post_notification(watch->cred, cred, n) < 0)
203 continue;
204
205 post_one_notification(wqueue, n);
206 }
207
208 rcu_read_unlock();
209 }
210 EXPORT_SYMBOL(__post_watch_notification);
211
212 /*
213 * Allocate sufficient pages to preallocation for the requested number of
214 * notifications.
215 */
watch_queue_set_size(struct pipe_inode_info * pipe,unsigned int nr_notes)216 long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
217 {
218 struct watch_queue *wqueue = pipe->watch_queue;
219 struct page **pages;
220 unsigned long *bitmap;
221 unsigned long user_bufs;
222 unsigned int bmsize;
223 int ret, i, nr_pages;
224
225 if (!wqueue)
226 return -ENODEV;
227 if (wqueue->notes)
228 return -EBUSY;
229
230 if (nr_notes < 1 ||
231 nr_notes > 512) /* TODO: choose a better hard limit */
232 return -EINVAL;
233
234 nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1);
235 nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE;
236 user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages);
237
238 if (nr_pages > pipe->max_usage &&
239 (too_many_pipe_buffers_hard(user_bufs) ||
240 too_many_pipe_buffers_soft(user_bufs)) &&
241 pipe_is_unprivileged_user()) {
242 ret = -EPERM;
243 goto error;
244 }
245
246 ret = pipe_resize_ring(pipe, nr_notes);
247 if (ret < 0)
248 goto error;
249
250 pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL);
251 if (!pages)
252 goto error;
253
254 for (i = 0; i < nr_pages; i++) {
255 pages[i] = alloc_page(GFP_KERNEL);
256 if (!pages[i])
257 goto error_p;
258 pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE;
259 }
260
261 bmsize = (nr_notes + BITS_PER_LONG - 1) / BITS_PER_LONG;
262 bmsize *= sizeof(unsigned long);
263 bitmap = kmalloc(bmsize, GFP_KERNEL);
264 if (!bitmap)
265 goto error_p;
266
267 memset(bitmap, 0xff, bmsize);
268 wqueue->notes = pages;
269 wqueue->notes_bitmap = bitmap;
270 wqueue->nr_pages = nr_pages;
271 wqueue->nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE;
272 return 0;
273
274 error_p:
275 for (i = 0; i < nr_pages; i++)
276 __free_page(pages[i]);
277 kfree(pages);
278 error:
279 (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);
280 return ret;
281 }
282
283 /*
284 * Set the filter on a watch queue.
285 */
watch_queue_set_filter(struct pipe_inode_info * pipe,struct watch_notification_filter __user * _filter)286 long watch_queue_set_filter(struct pipe_inode_info *pipe,
287 struct watch_notification_filter __user *_filter)
288 {
289 struct watch_notification_type_filter *tf;
290 struct watch_notification_filter filter;
291 struct watch_type_filter *q;
292 struct watch_filter *wfilter;
293 struct watch_queue *wqueue = pipe->watch_queue;
294 int ret, nr_filter = 0, i;
295
296 if (!wqueue)
297 return -ENODEV;
298
299 if (!_filter) {
300 /* Remove the old filter */
301 wfilter = NULL;
302 goto set;
303 }
304
305 /* Grab the user's filter specification */
306 if (copy_from_user(&filter, _filter, sizeof(filter)) != 0)
307 return -EFAULT;
308 if (filter.nr_filters == 0 ||
309 filter.nr_filters > 16 ||
310 filter.__reserved != 0)
311 return -EINVAL;
312
313 tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf));
314 if (IS_ERR(tf))
315 return PTR_ERR(tf);
316
317 ret = -EINVAL;
318 for (i = 0; i < filter.nr_filters; i++) {
319 if ((tf[i].info_filter & ~tf[i].info_mask) ||
320 tf[i].info_mask & WATCH_INFO_LENGTH)
321 goto err_filter;
322 /* Ignore any unknown types */
323 if (tf[i].type >= sizeof(wfilter->type_filter) * 8)
324 continue;
325 nr_filter++;
326 }
327
328 /* Now we need to build the internal filter from only the relevant
329 * user-specified filters.
330 */
331 ret = -ENOMEM;
332 wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL);
333 if (!wfilter)
334 goto err_filter;
335 wfilter->nr_filters = nr_filter;
336
337 q = wfilter->filters;
338 for (i = 0; i < filter.nr_filters; i++) {
339 if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG)
340 continue;
341
342 q->type = tf[i].type;
343 q->info_filter = tf[i].info_filter;
344 q->info_mask = tf[i].info_mask;
345 q->subtype_filter[0] = tf[i].subtype_filter[0];
346 __set_bit(q->type, wfilter->type_filter);
347 q++;
348 }
349
350 kfree(tf);
351 set:
352 pipe_lock(pipe);
353 wfilter = rcu_replace_pointer(wqueue->filter, wfilter,
354 lockdep_is_held(&pipe->mutex));
355 pipe_unlock(pipe);
356 if (wfilter)
357 kfree_rcu(wfilter, rcu);
358 return 0;
359
360 err_filter:
361 kfree(tf);
362 return ret;
363 }
364
__put_watch_queue(struct kref * kref)365 static void __put_watch_queue(struct kref *kref)
366 {
367 struct watch_queue *wqueue =
368 container_of(kref, struct watch_queue, usage);
369 struct watch_filter *wfilter;
370 int i;
371
372 for (i = 0; i < wqueue->nr_pages; i++)
373 __free_page(wqueue->notes[i]);
374
375 wfilter = rcu_access_pointer(wqueue->filter);
376 if (wfilter)
377 kfree_rcu(wfilter, rcu);
378 kfree_rcu(wqueue, rcu);
379 }
380
381 /**
382 * put_watch_queue - Dispose of a ref on a watchqueue.
383 * @wqueue: The watch queue to unref.
384 */
put_watch_queue(struct watch_queue * wqueue)385 void put_watch_queue(struct watch_queue *wqueue)
386 {
387 kref_put(&wqueue->usage, __put_watch_queue);
388 }
389 EXPORT_SYMBOL(put_watch_queue);
390
free_watch(struct rcu_head * rcu)391 static void free_watch(struct rcu_head *rcu)
392 {
393 struct watch *watch = container_of(rcu, struct watch, rcu);
394
395 put_watch_queue(rcu_access_pointer(watch->queue));
396 atomic_dec(&watch->cred->user->nr_watches);
397 put_cred(watch->cred);
398 }
399
__put_watch(struct kref * kref)400 static void __put_watch(struct kref *kref)
401 {
402 struct watch *watch = container_of(kref, struct watch, usage);
403
404 call_rcu(&watch->rcu, free_watch);
405 }
406
407 /*
408 * Discard a watch.
409 */
put_watch(struct watch * watch)410 static void put_watch(struct watch *watch)
411 {
412 kref_put(&watch->usage, __put_watch);
413 }
414
415 /**
416 * init_watch_queue - Initialise a watch
417 * @watch: The watch to initialise.
418 * @wqueue: The queue to assign.
419 *
420 * Initialise a watch and set the watch queue.
421 */
init_watch(struct watch * watch,struct watch_queue * wqueue)422 void init_watch(struct watch *watch, struct watch_queue *wqueue)
423 {
424 kref_init(&watch->usage);
425 INIT_HLIST_NODE(&watch->list_node);
426 INIT_HLIST_NODE(&watch->queue_node);
427 rcu_assign_pointer(watch->queue, wqueue);
428 }
429
430 /**
431 * add_watch_to_object - Add a watch on an object to a watch list
432 * @watch: The watch to add
433 * @wlist: The watch list to add to
434 *
435 * @watch->queue must have been set to point to the queue to post notifications
436 * to and the watch list of the object to be watched. @watch->cred must also
437 * have been set to the appropriate credentials and a ref taken on them.
438 *
439 * The caller must pin the queue and the list both and must hold the list
440 * locked against racing watch additions/removals.
441 */
add_watch_to_object(struct watch * watch,struct watch_list * wlist)442 int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
443 {
444 struct watch_queue *wqueue = rcu_access_pointer(watch->queue);
445 struct watch *w;
446
447 hlist_for_each_entry(w, &wlist->watchers, list_node) {
448 struct watch_queue *wq = rcu_access_pointer(w->queue);
449 if (wqueue == wq && watch->id == w->id)
450 return -EBUSY;
451 }
452
453 watch->cred = get_current_cred();
454 rcu_assign_pointer(watch->watch_list, wlist);
455
456 if (atomic_inc_return(&watch->cred->user->nr_watches) >
457 task_rlimit(current, RLIMIT_NOFILE)) {
458 atomic_dec(&watch->cred->user->nr_watches);
459 put_cred(watch->cred);
460 return -EAGAIN;
461 }
462
463 spin_lock_bh(&wqueue->lock);
464 kref_get(&wqueue->usage);
465 kref_get(&watch->usage);
466 hlist_add_head(&watch->queue_node, &wqueue->watches);
467 spin_unlock_bh(&wqueue->lock);
468
469 hlist_add_head(&watch->list_node, &wlist->watchers);
470 return 0;
471 }
472 EXPORT_SYMBOL(add_watch_to_object);
473
474 /**
475 * remove_watch_from_object - Remove a watch or all watches from an object.
476 * @wlist: The watch list to remove from
477 * @wq: The watch queue of interest (ignored if @all is true)
478 * @id: The ID of the watch to remove (ignored if @all is true)
479 * @all: True to remove all objects
480 *
481 * Remove a specific watch or all watches from an object. A notification is
482 * sent to the watcher to tell them that this happened.
483 */
remove_watch_from_object(struct watch_list * wlist,struct watch_queue * wq,u64 id,bool all)484 int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
485 u64 id, bool all)
486 {
487 struct watch_notification_removal n;
488 struct watch_queue *wqueue;
489 struct watch *watch;
490 int ret = -EBADSLT;
491
492 rcu_read_lock();
493
494 again:
495 spin_lock(&wlist->lock);
496 hlist_for_each_entry(watch, &wlist->watchers, list_node) {
497 if (all ||
498 (watch->id == id && rcu_access_pointer(watch->queue) == wq))
499 goto found;
500 }
501 spin_unlock(&wlist->lock);
502 goto out;
503
504 found:
505 ret = 0;
506 hlist_del_init_rcu(&watch->list_node);
507 rcu_assign_pointer(watch->watch_list, NULL);
508 spin_unlock(&wlist->lock);
509
510 /* We now own the reference on watch that used to belong to wlist. */
511
512 n.watch.type = WATCH_TYPE_META;
513 n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION;
514 n.watch.info = watch->info_id | watch_sizeof(n.watch);
515 n.id = id;
516 if (id != 0)
517 n.watch.info = watch->info_id | watch_sizeof(n);
518
519 wqueue = rcu_dereference(watch->queue);
520
521 /* We don't need the watch list lock for the next bit as RCU is
522 * protecting *wqueue from deallocation.
523 */
524 if (wqueue) {
525 post_one_notification(wqueue, &n.watch);
526
527 spin_lock_bh(&wqueue->lock);
528
529 if (!hlist_unhashed(&watch->queue_node)) {
530 hlist_del_init_rcu(&watch->queue_node);
531 put_watch(watch);
532 }
533
534 spin_unlock_bh(&wqueue->lock);
535 }
536
537 if (wlist->release_watch) {
538 void (*release_watch)(struct watch *);
539
540 release_watch = wlist->release_watch;
541 rcu_read_unlock();
542 (*release_watch)(watch);
543 rcu_read_lock();
544 }
545 put_watch(watch);
546
547 if (all && !hlist_empty(&wlist->watchers))
548 goto again;
549 out:
550 rcu_read_unlock();
551 return ret;
552 }
553 EXPORT_SYMBOL(remove_watch_from_object);
554
555 /*
556 * Remove all the watches that are contributory to a queue. This has the
557 * potential to race with removal of the watches by the destruction of the
558 * objects being watched or with the distribution of notifications.
559 */
watch_queue_clear(struct watch_queue * wqueue)560 void watch_queue_clear(struct watch_queue *wqueue)
561 {
562 struct watch_list *wlist;
563 struct watch *watch;
564 bool release;
565
566 rcu_read_lock();
567 spin_lock_bh(&wqueue->lock);
568
569 /* Prevent new additions and prevent notifications from happening */
570 wqueue->defunct = true;
571
572 while (!hlist_empty(&wqueue->watches)) {
573 watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
574 hlist_del_init_rcu(&watch->queue_node);
575 /* We now own a ref on the watch. */
576 spin_unlock_bh(&wqueue->lock);
577
578 /* We can't do the next bit under the queue lock as we need to
579 * get the list lock - which would cause a deadlock if someone
580 * was removing from the opposite direction at the same time or
581 * posting a notification.
582 */
583 wlist = rcu_dereference(watch->watch_list);
584 if (wlist) {
585 void (*release_watch)(struct watch *);
586
587 spin_lock(&wlist->lock);
588
589 release = !hlist_unhashed(&watch->list_node);
590 if (release) {
591 hlist_del_init_rcu(&watch->list_node);
592 rcu_assign_pointer(watch->watch_list, NULL);
593
594 /* We now own a second ref on the watch. */
595 }
596
597 release_watch = wlist->release_watch;
598 spin_unlock(&wlist->lock);
599
600 if (release) {
601 if (release_watch) {
602 rcu_read_unlock();
603 /* This might need to call dput(), so
604 * we have to drop all the locks.
605 */
606 (*release_watch)(watch);
607 rcu_read_lock();
608 }
609 put_watch(watch);
610 }
611 }
612
613 put_watch(watch);
614 spin_lock_bh(&wqueue->lock);
615 }
616
617 spin_unlock_bh(&wqueue->lock);
618 rcu_read_unlock();
619 }
620
621 /**
622 * get_watch_queue - Get a watch queue from its file descriptor.
623 * @fd: The fd to query.
624 */
get_watch_queue(int fd)625 struct watch_queue *get_watch_queue(int fd)
626 {
627 struct pipe_inode_info *pipe;
628 struct watch_queue *wqueue = ERR_PTR(-EINVAL);
629 struct fd f;
630
631 f = fdget(fd);
632 if (f.file) {
633 pipe = get_pipe_info(f.file, false);
634 if (pipe && pipe->watch_queue) {
635 wqueue = pipe->watch_queue;
636 kref_get(&wqueue->usage);
637 }
638 fdput(f);
639 }
640
641 return wqueue;
642 }
643 EXPORT_SYMBOL(get_watch_queue);
644
645 /*
646 * Initialise a watch queue
647 */
watch_queue_init(struct pipe_inode_info * pipe)648 int watch_queue_init(struct pipe_inode_info *pipe)
649 {
650 struct watch_queue *wqueue;
651
652 wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL);
653 if (!wqueue)
654 return -ENOMEM;
655
656 wqueue->pipe = pipe;
657 kref_init(&wqueue->usage);
658 spin_lock_init(&wqueue->lock);
659 INIT_HLIST_HEAD(&wqueue->watches);
660
661 pipe->watch_queue = wqueue;
662 return 0;
663 }
664
