linux-kernel - [patch] fsnotify: potential use after free

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Message-ID: <20130722065327.GA14617@longonot.mountain>
Date:	Mon, 22 Jul 2013 09:53:27 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Lino Sanfilippo <LinoSanfilippo@....de>
Cc:	Eric Paris <eparis@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch] fsnotify: potential use after free

My static checker complains that if we drop the last reference then it
would be a use after free.  I don't know if it's possible, but really
the atomic_dec(&group->num_marks); should be done while we are holding a
reference to "group".

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 923fe4a..27e357e 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -262,9 +262,9 @@ int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
 err:
 	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
 	list_del_init(&mark->g_list);
+	atomic_dec(&group->num_marks);
 	fsnotify_put_group(group);
 	mark->group = NULL;
-	atomic_dec(&group->num_marks);
 
 	spin_unlock(&mark->lock);
 
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