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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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12
fs/notify/fanotify/fanotify_user.c
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@@ -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