linux-kernel - [ 51/61] 9p: BUG before corrupting memory

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Date:	Wed, 20 Jun 2012 10:31:11 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Sasha Levin <levinsasha928@...il.com>,
	Eric Van Hensbergen <ericvh@...il.com>
Subject: [ 51/61] 9p: BUG before corrupting memory

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sasha Levin <levinsasha928@...il.com>

commit 5fcb08befaf57faa1b00e514915c1660252b8c26 upstream.

The BUG_ON() in pack_sg_list() would get triggered only one time after we've
corrupted some memory by sg_set_buf() into an invalid sg buffer.

I'm still working on figuring out why I manage to trigger that bug...

Signed-off-by: Sasha Levin <levinsasha928@...il.com>
Signed-off-by: Eric Van Hensbergen <ericvh@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/9p/trans_virtio.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -192,10 +192,10 @@ static int pack_sg_list(struct scatterli
 		s = rest_of_page(data);
 		if (s > count)
 			s = count;
+		BUG_ON(index > limit);
 		sg_set_buf(&sg[index++], data, s);
 		count -= s;
 		data += s;
-		BUG_ON(index > limit);
 	}
 
 	return index-start;


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