net: skip virtio_net_hdr_set_proto if protocol already set

virtio_net_hdr_set_proto infers skb->protocol from the virtio_net_hdr
gso_type, to avoid packets getting dropped for lack of a proto type.

Its protocol choice is a guess, especially in the case of UFO, where
the single VIRTIO_NET_HDR_GSO_UDP label covers both UFOv4 and UFOv6.

Skip this best effort if the field is already initialized. Whether
explicitly from userspace, or implicitly based on an earlier call to
dev_parse_header_protocol (which is more robust, but was introduced
after this patch).

Fixes: 4b69b91dea15 ("net/packet: fix packet drop as of virtio gso")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20211220145027.2784293-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 22dd48c8256006ae7e7f7ecb3c3ece81ea974bb7..a960de68ac69ee12939a95729e36513312e41a68 100644 (file)
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -25,6 +25,9 @@ static inline bool virtio_net_hdr_match_proto(__be16 protocol, __u8 gso_type)
 static inline int virtio_net_hdr_set_proto(struct sk_buff *skb,
                                           const struct virtio_net_hdr *hdr)
 {
+       if (skb->protocol)
+               return 0;
+
        switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
        case VIRTIO_NET_HDR_GSO_TCPV4:
        case VIRTIO_NET_HDR_GSO_UDP: