vhost/net: fix heads usage of ubuf_info

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@rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index b76071e..5c58128 100644 (file)
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -234,7 +234,8 @@ 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;