Virtualization - Mar 2013 - [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 at rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Cc: stable at kernel.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

From: "Michael S. Tsirkin" <mst at redhat.com>
Date: Sun, 17 Mar 2013 14:46:09 +0200
> 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>
Applied and queued up for -stable, thanks.

And thankfully you got the stable URL wrong, please do not CC:
networking patches to stable, just make sure I apply them and in
your post-commit text explicitly ask me to queue it up to my
-stable queue.

Thanks.