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fanotify: fix list corruption in fanotify_get_response()
fanotify_get_response() calls fsnotify_remove_event() when it finds that
group is being released from fanotify_release() (bypass_perm is set).
However the event it removes need not be only in the group's notification
queue but it can have already moved to access_list (userspace read the
event before closing the fanotify instance fd) which is protected by a
different lock. Thus when fsnotify_remove_event() races with
fanotify_release() operating on access_list, the list can get corrupted.
Fix the problem by moving all the logic removing permission events from
the lists to one place - fanotify_release().
Fixes: 5838d4442b
("fanotify: fix double free of pending permission events")
Link: http://lkml.kernel.org/r/1473797711-14111-3-git-send-email-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Miklos Szeredi <mszeredi@redhat.com>
Tested-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
12703dbfeb
commit
96d41019e3
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@ -67,18 +67,7 @@ static int fanotify_get_response(struct fsnotify_group *group,
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pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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wait_event(group->fanotify_data.access_waitq, event->response ||
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atomic_read(&group->fanotify_data.bypass_perm));
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if (!event->response) { /* bypass_perm set */
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/*
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* Event was canceled because group is being destroyed. Remove
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* it from group's event list because we are responsible for
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* freeing the permission event.
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*/
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fsnotify_remove_event(group, &event->fae.fse);
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return 0;
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}
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wait_event(group->fanotify_data.access_waitq, event->response);
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/* userspace responded, convert to something usable */
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switch (event->response) {
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@ -358,16 +358,20 @@ static int fanotify_release(struct inode *ignored, struct file *file)
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#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
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struct fanotify_perm_event_info *event, *next;
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struct fsnotify_event *fsn_event;
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/*
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* There may be still new events arriving in the notification queue
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* but since userspace cannot use fanotify fd anymore, no event can
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* enter or leave access_list by now.
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* Stop new events from arriving in the notification queue. since
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* userspace cannot use fanotify fd anymore, no event can enter or
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* leave access_list by now either.
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*/
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fsnotify_group_stop_queueing(group);
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/*
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* Process all permission events on access_list and notification queue
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* and simulate reply from userspace.
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*/
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spin_lock(&group->fanotify_data.access_lock);
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atomic_inc(&group->fanotify_data.bypass_perm);
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list_for_each_entry_safe(event, next, &group->fanotify_data.access_list,
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fae.fse.list) {
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pr_debug("%s: found group=%p event=%p\n", __func__, group,
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@ -379,12 +383,21 @@ static int fanotify_release(struct inode *ignored, struct file *file)
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spin_unlock(&group->fanotify_data.access_lock);
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/*
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* Since bypass_perm is set, newly queued events will not wait for
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* access response. Wake up the already sleeping ones now.
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* synchronize_srcu() in fsnotify_destroy_group() will wait for all
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* processes sleeping in fanotify_handle_event() waiting for access
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* response and thus also for all permission events to be freed.
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* Destroy all non-permission events. For permission events just
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* dequeue them and set the response. They will be freed once the
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* response is consumed and fanotify_get_response() returns.
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*/
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mutex_lock(&group->notification_mutex);
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while (!fsnotify_notify_queue_is_empty(group)) {
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fsn_event = fsnotify_remove_first_event(group);
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if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS))
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fsnotify_destroy_event(group, fsn_event);
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else
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FANOTIFY_PE(fsn_event)->response = FAN_ALLOW;
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}
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mutex_unlock(&group->notification_mutex);
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/* Response for all permission events it set, wakeup waiters */
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wake_up(&group->fanotify_data.access_waitq);
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#endif
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@ -755,7 +768,6 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
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spin_lock_init(&group->fanotify_data.access_lock);
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init_waitqueue_head(&group->fanotify_data.access_waitq);
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INIT_LIST_HEAD(&group->fanotify_data.access_list);
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atomic_set(&group->fanotify_data.bypass_perm, 0);
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#endif
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switch (flags & FAN_ALL_CLASS_BITS) {
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case FAN_CLASS_NOTIF:
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@ -131,21 +131,6 @@ int fsnotify_add_event(struct fsnotify_group *group,
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return ret;
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}
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/*
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* Remove @event from group's notification queue. It is the responsibility of
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* the caller to destroy the event.
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*/
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void fsnotify_remove_event(struct fsnotify_group *group,
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struct fsnotify_event *event)
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{
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mutex_lock(&group->notification_mutex);
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if (!list_empty(&event->list)) {
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list_del_init(&event->list);
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group->q_len--;
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}
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mutex_unlock(&group->notification_mutex);
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}
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/*
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* Remove and return the first event from the notification list. It is the
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* responsibility of the caller to destroy the obtained event
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@ -180,7 +180,6 @@ struct fsnotify_group {
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spinlock_t access_lock;
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struct list_head access_list;
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wait_queue_head_t access_waitq;
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atomic_t bypass_perm;
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#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
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int f_flags;
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unsigned int max_marks;
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@ -307,8 +306,6 @@ extern int fsnotify_add_event(struct fsnotify_group *group,
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struct fsnotify_event *event,
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int (*merge)(struct list_head *,
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struct fsnotify_event *));
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/* Remove passed event from groups notification queue */
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extern void fsnotify_remove_event(struct fsnotify_group *group, struct fsnotify_event *event);
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/* true if the group notification queue is empty */
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extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
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/* return, but do not dequeue the first event on the notification queue */
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