linux-kernel - [ 025/104] vhost/net: fix heads usage of ubuf

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Message-Id: <20130325010526.795498363@decadent.org.uk>
Date:	Mon, 25 Mar 2013 01:05:49 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, "Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 025/104] vhost/net: fix heads usage of ubuf_info

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

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

From: "Michael S. Tsirkin" <mst@...hat.com>

commit 46aa92d1ba162b4b3d6b7102440e459d4e4ee255 upstream.

ubuf info allocator uses guest controlled head as an index,
so a malicious guest could put the same head entry in the ring twice,
and we will get two callbacks on the same value.
To fix use upend_idx which is guaranteed to be unique.

Reported-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/vhost/net.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -234,7 +234,8 @@ static void handle_tx(struct vhost_net *
 				msg.msg_controllen = 0;
 				ubufs = NULL;
 			} else {
-				struct ubuf_info *ubuf = &vq->ubuf_info[head];
+				struct ubuf_info *ubuf;
+				ubuf = vq->ubuf_info + vq->upend_idx;
 
 				vq->heads[vq->upend_idx].len = len;
 				ubuf->callback = vhost_zerocopy_callback;


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