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@rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Cc: stable@kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 959b1cd89e6a..ec6fb3fa59bb 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;