net: avoid false positives in untrusted gso validation

GSO packets with vnet_hdr must conform to a small set of gso_types.
The below commit uses flow dissection to drop packets that do not.

But it has false positives when the skb is not fully initialized.
Dissection needs skb->protocol and skb->network_header.

Infer skb->protocol from gso_type as the two must agree.
SKB_GSO_UDP can use both ipv4 and ipv6, so try both.

Exclude callers for which network header offset is not known.

Fixes: d5be7f632bad ("net: validate untrusted gso packets without csum offload")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 71f2394..e0348cb 100644 (file)
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -61,10 +61,20 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
                /* gso packets without NEEDS_CSUM do not set transport_offset.
                 * probe and drop if does not match one of the above types.
                 */
-               if (gso_type) {
+               if (gso_type && skb->network_header) {
+                       if (!skb->protocol)
+                               virtio_net_hdr_set_proto(skb, hdr);
+retry:
                        skb_probe_transport_header(skb, -1);
-                       if (!skb_transport_header_was_set(skb))
+                       if (!skb_transport_header_was_set(skb)) {
+                               /* UFO does not specify ipv4 or 6: try both */
+                               if (gso_type & SKB_GSO_UDP &&
+                                   skb->protocol == htons(ETH_P_IP)) {
+                                       skb->protocol = htons(ETH_P_IPV6);
+                                       goto retry;
+                               }
                                return -EINVAL;
+                       }
                }
        }