netdev - [PATCH net] vhost/net: fix heads usage of ubuf

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Message-ID: <20130317124609.GA25967@redhat.com>
Date:	Sun, 17 Mar 2013 14:46:09 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	stable@...nel.org, Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>,
	Basil Gor <basil.gor@...il.com>,
	"Nicholas A. Bellinger" <nab@...ingtidesystems.com>,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] vhost/net: fix heads usage of ubuf_info

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>
Cc: stable@...nel.org
---

Rusty's working on switching to allocating ubufs dynamically
but that's not 3.9 material.
This patch is against latest net master,
needed for 3.9-rc2 and older kernels.

 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 959b1cd..ec6fb3f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -339,7 +339,8 @@ 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 =
 					VHOST_DMA_IN_PROGRESS;
-- 
MST
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