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fanotify: fix double free of pending permission events

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Commit 8581679424 ("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: 8581679424
Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Douglas Leeder <douglas.leeder@sophos.com>
Tested-by: Douglas Leeder <douglas.leeder@sophos.com>
Reported-by: Heinrich Schuchard <xypron.glpk@gmx.de>
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:
Jan Kara 2014-08-06 16:03:28 -07:00 committed by Linus Torvalds
parent 8ba8fa9170
commit 5838d4442b
4 changed files with 39 additions and 2 deletions
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9
fs/notify/fanotify/fanotify.c
View File

@ -70,8 +70,15 @@ static int fanotify_get_response(struct fsnotify_group *group,
wait_event(group->fanotify_data.access_waitq, event->response ||
atomic_read(&group->fanotify_data.bypass_perm));
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) {

12
fs/notify/fanotify/fanotify_user.c
View File

@ -359,6 +359,11 @@ static int fanotify_release(struct inode *ignored, struct file *file)
#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
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.
*/
spin_lock(&group->fanotify_data.access_lock);
atomic_inc(&group->fanotify_data.bypass_perm);
@ -373,6 +378,13 @@ static int fanotify_release(struct inode *ignored, struct file *file)
}
spin_unlock(&group->fanotify_data.access_lock);
/*
* 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.
*/
wake_up(&group->fanotify_data.access_waitq);
#endif

18
fs/notify/notification.c
View File

@ -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)
return;
/* If the event is still queued, we have a problem... */
WARN_ON(!list_empty(&event->list));
group->ops->free_event(event);
}
@ -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)
{
mutex_lock(&group->notification_mutex);
if (!list_empty(&event->list)) {
list_del_init(&event->list);
group->q_len--;
}
mutex_unlock(&group->notification_mutex);
}
/*
* Remove and return the first event from the notification list. It is the
* responsibility of the caller to destroy the obtained event

2
include/linux/fsnotify_backend.h
View File

@ -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 */