Commit 5838d444 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds

fanotify: fix double free of pending permission events

Commit 85816794 ("fanotify: Fix use after free for permission
events") introduced a double free issue for permission events which are
pending in group's notification queue while group is being destroyed.
These events are freed from fanotify_handle_event() but they are not
removed from groups notification queue and thus they get freed again
from fsnotify_flush_notify().

Fix the problem by removing permission events from notification queue
before freeing them if we skip processing access response.  Also expand
comments in fanotify_release() to explain group shutdown in detail.

Fixes: 85816794Signed-off-by: default avatarJan Kara <>
Reported-by: default avatarDouglas Leeder <>
Tested-by: default avatarDouglas Leeder <>
Reported-by: default avatarHeinrich Schuchard <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 8ba8fa91
......@@ -70,8 +70,15 @@ static int fanotify_get_response(struct fsnotify_group *group,
wait_event(group->fanotify_data.access_waitq, event->response ||
if (!event->response) /* bypass_perm set */
if (!event->response) { /* bypass_perm set */
* Event was canceled because group is being destroyed. Remove
* it from group's event list because we are responsible for
* freeing the permission event.
fsnotify_remove_event(group, &event->fae.fse);
return 0;
/* userspace responded, convert to something usable */
switch (event->response) {
......@@ -359,6 +359,11 @@ static int fanotify_release(struct inode *ignored, struct file *file)
struct fanotify_perm_event_info *event, *next;
* There may be still new events arriving in the notification queue
* but since userspace cannot use fanotify fd anymore, no event can
* enter or leave access_list by now.
......@@ -373,6 +378,13 @@ static int fanotify_release(struct inode *ignored, struct file *file)
* Since bypass_perm is set, newly queued events will not wait for
* access response. Wake up the already sleeping ones now.
* synchronize_srcu() in fsnotify_destroy_group() will wait for all
* processes sleeping in fanotify_handle_event() waiting for access
* response and thus also for all permission events to be freed.
......@@ -73,7 +73,8 @@ void fsnotify_destroy_event(struct fsnotify_group *group,
/* Overflow events are per-group and we don't want to free them */
if (!event || event->mask == FS_Q_OVERFLOW)
/* If the event is still queued, we have a problem... */
......@@ -124,6 +125,21 @@ int fsnotify_add_event(struct fsnotify_group *group,
return ret;
* Remove @event from group's notification queue. It is the responsibility of
* the caller to destroy the event.
void fsnotify_remove_event(struct fsnotify_group *group,
struct fsnotify_event *event)
if (!list_empty(&event->list)) {
* Remove and return the first event from the notification list. It is the
* responsibility of the caller to destroy the obtained event
......@@ -326,6 +326,8 @@ extern int fsnotify_add_event(struct fsnotify_group *group,
struct fsnotify_event *event,
int (*merge)(struct list_head *,
struct fsnotify_event *));
/* Remove passed event from groups notification queue */
extern void fsnotify_remove_event(struct fsnotify_group *group, struct fsnotify_event *event);
/* true if the group notification queue is empty */
extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
/* return, but do not dequeue the first event on the notification queue */
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