diff options
Diffstat (limited to 'kernel/watch_queue.c')
| -rw-r--r-- | kernel/watch_queue.c | 700 |
1 files changed, 700 insertions, 0 deletions
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c new file mode 100644 index 000000000000..a6f9bdd956c3 --- /dev/null +++ b/kernel/watch_queue.c @@ -0,0 +1,700 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Watch queue and general notification mechanism, built on pipes + * + * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * See Documentation/core-api/watch_queue.rst + */ + +#define pr_fmt(fmt) "watchq: " fmt +#include <linux/module.h> +#include <linux/init.h> +#include <linux/sched.h> +#include <linux/slab.h> +#include <linux/printk.h> +#include <linux/miscdevice.h> +#include <linux/fs.h> +#include <linux/mm.h> +#include <linux/pagemap.h> +#include <linux/poll.h> +#include <linux/uaccess.h> +#include <linux/vmalloc.h> +#include <linux/file.h> +#include <linux/security.h> +#include <linux/cred.h> +#include <linux/sched/signal.h> +#include <linux/watch_queue.h> +#include <linux/pipe_fs_i.h> + +MODULE_DESCRIPTION("Watch queue"); +MODULE_AUTHOR("Red Hat, Inc."); +MODULE_LICENSE("GPL"); + +#define WATCH_QUEUE_NOTE_SIZE 128 +#define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE) + +/* + * This must be called under the RCU read-lock, which makes + * sure that the wqueue still exists. It can then take the lock, + * and check that the wqueue hasn't been destroyed, which in + * turn makes sure that the notification pipe still exists. + */ +static inline bool lock_wqueue(struct watch_queue *wqueue) +{ + spin_lock_bh(&wqueue->lock); + if (unlikely(wqueue->defunct)) { + spin_unlock_bh(&wqueue->lock); + return false; + } + return true; +} + +static inline void unlock_wqueue(struct watch_queue *wqueue) +{ + spin_unlock_bh(&wqueue->lock); +} + +static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, + struct pipe_buffer *buf) +{ + struct watch_queue *wqueue = (struct watch_queue *)buf->private; + struct page *page; + unsigned int bit; + + /* We need to work out which note within the page this refers to, but + * the note might have been maximum size, so merely ANDing the offset + * off doesn't work. OTOH, the note must've been more than zero size. + */ + bit = buf->offset + buf->len; + if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0) + bit -= WATCH_QUEUE_NOTE_SIZE; + bit /= WATCH_QUEUE_NOTE_SIZE; + + page = buf->page; + bit += page->index; + + set_bit(bit, wqueue->notes_bitmap); + generic_pipe_buf_release(pipe, buf); +} + +// No try_steal function => no stealing +#define watch_queue_pipe_buf_try_steal NULL + +/* New data written to a pipe may be appended to a buffer with this type. */ +static const struct pipe_buf_operations watch_queue_pipe_buf_ops = { + .release = watch_queue_pipe_buf_release, + .try_steal = watch_queue_pipe_buf_try_steal, + .get = generic_pipe_buf_get, +}; + +/* + * Post a notification to a watch queue. + * + * Must be called with the RCU lock for reading, and the + * watch_queue lock held, which guarantees that the pipe + * hasn't been released. + */ +static bool post_one_notification(struct watch_queue *wqueue, + struct watch_notification *n) +{ + void *p; + struct pipe_inode_info *pipe = wqueue->pipe; + struct pipe_buffer *buf; + struct page *page; + unsigned int head, tail, mask, note, offset, len; + bool done = false; + + if (!pipe) + return false; + + spin_lock_irq(&pipe->rd_wait.lock); + + mask = pipe->ring_size - 1; + head = pipe->head; + tail = pipe->tail; + if (pipe_full(head, tail, pipe->ring_size)) + goto lost; + + note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes); + if (note >= wqueue->nr_notes) + goto lost; + + page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE]; + offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE; + get_page(page); + len = n->info & WATCH_INFO_LENGTH; + p = kmap_atomic(page); + memcpy(p + offset, n, len); + kunmap_atomic(p); + + buf = &pipe->bufs[head & mask]; + buf->page = page; + buf->private = (unsigned long)wqueue; + buf->ops = &watch_queue_pipe_buf_ops; + buf->offset = offset; + buf->len = len; + buf->flags = PIPE_BUF_FLAG_WHOLE; + smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ + + if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { + spin_unlock_irq(&pipe->rd_wait.lock); + BUG(); + } + wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); + done = true; + +out: + spin_unlock_irq(&pipe->rd_wait.lock); + if (done) + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); + return done; + +lost: + buf = &pipe->bufs[(head - 1) & mask]; + buf->flags |= PIPE_BUF_FLAG_LOSS; + goto out; +} + +/* + * Apply filter rules to a notification. + */ +static bool filter_watch_notification(const struct watch_filter *wf, + const struct watch_notification *n) +{ + const struct watch_type_filter *wt; + unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8; + unsigned int st_index = n->subtype / st_bits; + unsigned int st_bit = 1U << (n->subtype % st_bits); + int i; + + if (!test_bit(n->type, wf->type_filter)) + return false; + + for (i = 0; i < wf->nr_filters; i++) { + wt = &wf->filters[i]; + if (n->type == wt->type && + (wt->subtype_filter[st_index] & st_bit) && + (n->info & wt->info_mask) == wt->info_filter) + return true; + } + + return false; /* If there is a filter, the default is to reject. */ +} + +/** + * __post_watch_notification - Post an event notification + * @wlist: The watch list to post the event to. + * @n: The notification record to post. + * @cred: The creds of the process that triggered the notification. + * @id: The ID to match on the watch. + * + * Post a notification of an event into a set of watch queues and let the users + * know. + * + * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and + * should be in units of sizeof(*n). + */ +void __post_watch_notification(struct watch_list *wlist, + struct watch_notification *n, + const struct cred *cred, + u64 id) +{ + const struct watch_filter *wf; + struct watch_queue *wqueue; + struct watch *watch; + + if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) { + WARN_ON(1); + return; + } + + rcu_read_lock(); + + hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) { + if (watch->id != id) + continue; + n->info &= ~WATCH_INFO_ID; + n->info |= watch->info_id; + + wqueue = rcu_dereference(watch->queue); + wf = rcu_dereference(wqueue->filter); + if (wf && !filter_watch_notification(wf, n)) + continue; + + if (security_post_notification(watch->cred, cred, n) < 0) + continue; + + if (lock_wqueue(wqueue)) { + post_one_notification(wqueue, n); + unlock_wqueue(wqueue); + } + } + + rcu_read_unlock(); +} +EXPORT_SYMBOL(__post_watch_notification); + +/* + * Allocate sufficient pages to preallocation for the requested number of + * notifications. + */ +long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) +{ + struct watch_queue *wqueue = pipe->watch_queue; + struct page **pages; + unsigned long *bitmap; + unsigned long user_bufs; + int ret, i, nr_pages; + + if (!wqueue) + return -ENODEV; + if (wqueue->notes) + return -EBUSY; + + if (nr_notes < 1 || + nr_notes > 512) /* TODO: choose a better hard limit */ + return -EINVAL; + + nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1); + nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE; + user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages); + + if (nr_pages > pipe->max_usage && + (too_many_pipe_buffers_hard(user_bufs) || + too_many_pipe_buffers_soft(user_bufs)) && + pipe_is_unprivileged_user()) { + ret = -EPERM; + goto error; + } + + nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; + ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes)); + if (ret < 0) + goto error; + + pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL); + if (!pages) + goto error; + + for (i = 0; i < nr_pages; i++) { + pages[i] = alloc_page(GFP_KERNEL); + if (!pages[i]) + goto error_p; + pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE; + } + + bitmap = bitmap_alloc(nr_notes, GFP_KERNEL); + if (!bitmap) + goto error_p; + + bitmap_fill(bitmap, nr_notes); + wqueue->notes = pages; + wqueue->notes_bitmap = bitmap; + wqueue->nr_pages = nr_pages; + wqueue->nr_notes = nr_notes; + return 0; + +error_p: + while (--i >= 0) + __free_page(pages[i]); + kfree(pages); +error: + (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted); + return ret; +} + +/* + * Set the filter on a watch queue. + */ +long watch_queue_set_filter(struct pipe_inode_info *pipe, + struct watch_notification_filter __user *_filter) +{ + struct watch_notification_type_filter *tf; + struct watch_notification_filter filter; + struct watch_type_filter *q; + struct watch_filter *wfilter; + struct watch_queue *wqueue = pipe->watch_queue; + int ret, nr_filter = 0, i; + + if (!wqueue) + return -ENODEV; + + if (!_filter) { + /* Remove the old filter */ + wfilter = NULL; + goto set; + } + + /* Grab the user's filter specification */ + if (copy_from_user(&filter, _filter, sizeof(filter)) != 0) + return -EFAULT; + if (filter.nr_filters == 0 || + filter.nr_filters > 16 || + filter.__reserved != 0) + return -EINVAL; + + tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf)); + if (IS_ERR(tf)) + return PTR_ERR(tf); + + ret = -EINVAL; + for (i = 0; i < filter.nr_filters; i++) { + if ((tf[i].info_filter & ~tf[i].info_mask) || + tf[i].info_mask & WATCH_INFO_LENGTH) + goto err_filter; + /* Ignore any unknown types */ + if (tf[i].type >= WATCH_TYPE__NR) + continue; + nr_filter++; + } + + /* Now we need to build the internal filter from only the relevant + * user-specified filters. + */ + ret = -ENOMEM; + wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL); + if (!wfilter) + goto err_filter; + wfilter->nr_filters = nr_filter; + + q = wfilter->filters; + for (i = 0; i < filter.nr_filters; i++) { + if (tf[i].type >= WATCH_TYPE__NR) + continue; + + q->type = tf[i].type; + q->info_filter = tf[i].info_filter; + q->info_mask = tf[i].info_mask; + q->subtype_filter[0] = tf[i].subtype_filter[0]; + __set_bit(q->type, wfilter->type_filter); + q++; + } + + kfree(tf); +set: + pipe_lock(pipe); + wfilter = rcu_replace_pointer(wqueue->filter, wfilter, + lockdep_is_held(&pipe->mutex)); + pipe_unlock(pipe); + if (wfilter) + kfree_rcu(wfilter, rcu); + return 0; + +err_filter: + kfree(tf); + return ret; +} + +static void __put_watch_queue(struct kref *kref) +{ + struct watch_queue *wqueue = + container_of(kref, struct watch_queue, usage); + struct watch_filter *wfilter; + int i; + + for (i = 0; i < wqueue->nr_pages; i++) + __free_page(wqueue->notes[i]); + kfree(wqueue->notes); + bitmap_free(wqueue->notes_bitmap); + + wfilter = rcu_access_pointer(wqueue->filter); + if (wfilter) + kfree_rcu(wfilter, rcu); + kfree_rcu(wqueue, rcu); +} + +/** + * put_watch_queue - Dispose of a ref on a watchqueue. + * @wqueue: The watch queue to unref. + */ +void put_watch_queue(struct watch_queue *wqueue) +{ + kref_put(&wqueue->usage, __put_watch_queue); +} +EXPORT_SYMBOL(put_watch_queue); + +static void free_watch(struct rcu_head *rcu) +{ + struct watch *watch = container_of(rcu, struct watch, rcu); + + put_watch_queue(rcu_access_pointer(watch->queue)); + atomic_dec(&watch->cred->user->nr_watches); + put_cred(watch->cred); + kfree(watch); +} + +static void __put_watch(struct kref *kref) +{ + struct watch *watch = container_of(kref, struct watch, usage); + + call_rcu(&watch->rcu, free_watch); +} + +/* + * Discard a watch. + */ +static void put_watch(struct watch *watch) +{ + kref_put(&watch->usage, __put_watch); +} + +/** + * init_watch - Initialise a watch + * @watch: The watch to initialise. + * @wqueue: The queue to assign. + * + * Initialise a watch and set the watch queue. + */ +void init_watch(struct watch *watch, struct watch_queue *wqueue) +{ + kref_init(&watch->usage); + INIT_HLIST_NODE(&watch->list_node); + INIT_HLIST_NODE(&watch->queue_node); + rcu_assign_pointer(watch->queue, wqueue); +} + +static int add_one_watch(struct watch *watch, struct watch_list *wlist, struct watch_queue *wqueue) +{ + const struct cred *cred; + struct watch *w; + + hlist_for_each_entry(w, &wlist->watchers, list_node) { + struct watch_queue *wq = rcu_access_pointer(w->queue); + if (wqueue == wq && watch->id == w->id) + return -EBUSY; + } + + cred = current_cred(); + if (atomic_inc_return(&cred->user->nr_watches) > task_rlimit(current, RLIMIT_NOFILE)) { + atomic_dec(&cred->user->nr_watches); + return -EAGAIN; + } + + watch->cred = get_cred(cred); + rcu_assign_pointer(watch->watch_list, wlist); + + kref_get(&wqueue->usage); + kref_get(&watch->usage); + hlist_add_head(&watch->queue_node, &wqueue->watches); + hlist_add_head_rcu(&watch->list_node, &wlist->watchers); + return 0; +} + +/** + * add_watch_to_object - Add a watch on an object to a watch list + * @watch: The watch to add + * @wlist: The watch list to add to + * + * @watch->queue must have been set to point to the queue to post notifications + * to and the watch list of the object to be watched. @watch->cred must also + * have been set to the appropriate credentials and a ref taken on them. + * + * The caller must pin the queue and the list both and must hold the list + * locked against racing watch additions/removals. + */ +int add_watch_to_object(struct watch *watch, struct watch_list *wlist) +{ + struct watch_queue *wqueue; + int ret = -ENOENT; + + rcu_read_lock(); + + wqueue = rcu_access_pointer(watch->queue); + if (lock_wqueue(wqueue)) { + spin_lock(&wlist->lock); + ret = add_one_watch(watch, wlist, wqueue); + spin_unlock(&wlist->lock); + unlock_wqueue(wqueue); + } + + rcu_read_unlock(); + return ret; +} +EXPORT_SYMBOL(add_watch_to_object); + +/** + * remove_watch_from_object - Remove a watch or all watches from an object. + * @wlist: The watch list to remove from + * @wq: The watch queue of interest (ignored if @all is true) + * @id: The ID of the watch to remove (ignored if @all is true) + * @all: True to remove all objects + * + * Remove a specific watch or all watches from an object. A notification is + * sent to the watcher to tell them that this happened. + */ +int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq, + u64 id, bool all) +{ + struct watch_notification_removal n; + struct watch_queue *wqueue; + struct watch *watch; + int ret = -EBADSLT; + + rcu_read_lock(); + +again: + spin_lock(&wlist->lock); + hlist_for_each_entry(watch, &wlist->watchers, list_node) { + if (all || + (watch->id == id && rcu_access_pointer(watch->queue) == wq)) + goto found; + } + spin_unlock(&wlist->lock); + goto out; + +found: + ret = 0; + hlist_del_init_rcu(&watch->list_node); + rcu_assign_pointer(watch->watch_list, NULL); + spin_unlock(&wlist->lock); + + /* We now own the reference on watch that used to belong to wlist. */ + + n.watch.type = WATCH_TYPE_META; + n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION; + n.watch.info = watch->info_id | watch_sizeof(n.watch); + n.id = id; + if (id != 0) + n.watch.info = watch->info_id | watch_sizeof(n); + + wqueue = rcu_dereference(watch->queue); + + if (lock_wqueue(wqueue)) { + post_one_notification(wqueue, &n.watch); + + if (!hlist_unhashed(&watch->queue_node)) { + hlist_del_init_rcu(&watch->queue_node); + put_watch(watch); + } + + unlock_wqueue(wqueue); + } + + if (wlist->release_watch) { + void (*release_watch)(struct watch *); + + release_watch = wlist->release_watch; + rcu_read_unlock(); + (*release_watch)(watch); + rcu_read_lock(); + } + put_watch(watch); + + if (all && !hlist_empty(&wlist->watchers)) + goto again; +out: + rcu_read_unlock(); + return ret; +} +EXPORT_SYMBOL(remove_watch_from_object); + +/* + * Remove all the watches that are contributory to a queue. This has the + * potential to race with removal of the watches by the destruction of the + * objects being watched or with the distribution of notifications. + */ +void watch_queue_clear(struct watch_queue *wqueue) +{ + struct watch_list *wlist; + struct watch *watch; + bool release; + + rcu_read_lock(); + spin_lock_bh(&wqueue->lock); + + /* Prevent new notifications from being stored. */ + wqueue->defunct = true; + + while (!hlist_empty(&wqueue->watches)) { + watch = hlist_entry(wqueue->watches.first, struct watch, queue_node); + hlist_del_init_rcu(&watch->queue_node); + /* We now own a ref on the watch. */ + spin_unlock_bh(&wqueue->lock); + + /* We can't do the next bit under the queue lock as we need to + * get the list lock - which would cause a deadlock if someone + * was removing from the opposite direction at the same time or + * posting a notification. + */ + wlist = rcu_dereference(watch->watch_list); + if (wlist) { + void (*release_watch)(struct watch *); + + spin_lock(&wlist->lock); + + release = !hlist_unhashed(&watch->list_node); + if (release) { + hlist_del_init_rcu(&watch->list_node); + rcu_assign_pointer(watch->watch_list, NULL); + + /* We now own a second ref on the watch. */ + } + + release_watch = wlist->release_watch; + spin_unlock(&wlist->lock); + + if (release) { + if (release_watch) { + rcu_read_unlock(); + /* This might need to call dput(), so + * we have to drop all the locks. + */ + (*release_watch)(watch); + rcu_read_lock(); + } + put_watch(watch); + } + } + + put_watch(watch); + spin_lock_bh(&wqueue->lock); + } + + spin_unlock_bh(&wqueue->lock); + rcu_read_unlock(); +} + +/** + * get_watch_queue - Get a watch queue from its file descriptor. + * @fd: The fd to query. + */ +struct watch_queue *get_watch_queue(int fd) +{ + struct pipe_inode_info *pipe; + struct watch_queue *wqueue = ERR_PTR(-EINVAL); + struct fd f; + + f = fdget(fd); + if (f.file) { + pipe = get_pipe_info(f.file, false); + if (pipe && pipe->watch_queue) { + wqueue = pipe->watch_queue; + kref_get(&wqueue->usage); + } + fdput(f); + } + + return wqueue; +} +EXPORT_SYMBOL(get_watch_queue); + +/* + * Initialise a watch queue + */ +int watch_queue_init(struct pipe_inode_info *pipe) +{ + struct watch_queue *wqueue; + + wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL); + if (!wqueue) + return -ENOMEM; + + wqueue->pipe = pipe; + kref_init(&wqueue->usage); + spin_lock_init(&wqueue->lock); + INIT_HLIST_HEAD(&wqueue->watches); + + pipe->watch_queue = wqueue; + return 0; +} |