linux-kernel - [PATCH] ext4: fix racy use-after-free in ext4_end_io

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Message-ID: <20111124194626.GA5260@google.com>
Date:	Thu, 24 Nov 2011 11:46:26 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kent Overstreet <koverstreet@...gle.com>, rickyb@...gle.com,
	aberkan@...gle.com
Subject: [PATCH] ext4: fix racy use-after-free in ext4_end_io_dio()

ext4_end_io_dio() queues io_end->work and then clears iocb->private;
however, io_end->work completes the iocb by calling aio_complete(),
which may happen before io_end->work clearing thus leading to
use-after-free.

Detected and tested with slab poisoning.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Kent Overstreet <koverstreet@...gle.com>
Tested-by: Kent Overstreet <koverstreet@...gle.com>
Cc: stable@...nel.org
---
I *think* this is the corret fix but am not too familiar with code
path, so please proceed with caution.

Thank you.

 fs/ext4/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 240f6e2..0f5583b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2806,8 +2806,8 @@ out:
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
 
 	/* queue the work to convert unwritten extents to written */
-	queue_work(wq, &io_end->work);
 	iocb->private = NULL;
+	queue_work(wq, &io_end->work);
 
 	/* XXX: probably should move into the real I/O completion handler */
 	inode_dio_done(inode);
--
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