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products/sources/formale Sprachen/C/Linux/kernel/ (Open Source Betriebssystem Version 6.17.9^©) Datei vom 24.10.2025 mit Größe 17 kB

Quelle watch_queue.c Sprache: C

// 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.");

#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->pipe)) {
  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->private;

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, note, offset, len;
bool done = false;

spin_lock_irq(&pipe->rd_wait.lock);

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_buf(pipe, head);
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_buf(pipe, head - 1);
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;

/*
* pipe_resize_ring() does not update nr_accounted for watch_queue
* pipes, because the above vastly overprovisions. Set nr_accounted on
* and max_usage this pipe to the number that was actually charged to
* the user above via account_pipe_buffers.
*/
pipe->max_usage = nr_pages;
pipe->nr_accounted = nr_pages;

ret = -ENOMEM;
pages = kcalloc(nr_pages, sizeof(struct page *), 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]->private = 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_array_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);

/*
* This pipe can be freed by callers like free_pipe_info().
* Removing this reference also prevents new notifications.
*/
wqueue->pipe = NULL;

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);
CLASS(fd, f)(fd);

if (!fd_empty(f)) {
  pipe = get_pipe_info(fd_file(f), false);
  if (pipe && pipe->watch_queue) {
   wqueue = pipe->watch_queue;
   kref_get(&wqueue->usage);
  }
}

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;
}

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