[PATCH 059/150] vhost/net: fix heads usage of ubuf_info

[Luis Henriques]

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

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

From: "Michael S. Tsirkin" <mst at redhat.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 at rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/vhost/net.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 3c4dcc3d9..f2e8236 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -235,7 +235,8 @@ static void handle_tx(struct vhost_net *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;
-- 
1.8.1.2