Commit d996573e authored Feb 18, 2019 by Willem de Bruijn Committed by Greg Kroah-Hartman Feb 27, 2019

net: avoid false positives in untrusted gso validation



commit 9e8db5913264d3967b93c765a6a9e464d9c473db upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent dac7d443

include/linux/virtio_net.h

+12 −2

Original line number	Diff line number	Diff line
		@@ -61,12 +61,22 @@ 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;
		}
		}
		}

		if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
		u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);