net: skip virtio_net_hdr_set_proto if protocol already set

stable inclusion
from linux-4.19.223
commit 5fefa884a55bd5995e77f4fdd89f0400f42b39f7

--------------------------------

[ Upstream commit 1ed1d592 ]

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: 9d2f67e4 ("net/packet: fix packet drop as of virtio gso")
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20211220145027.2784293-1-willemdebruijn.kernel@gmail.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: NLaibin Qiu <qiulaibin@huawei.com>

include/linux/virtio_net.h

@@ -10,6 +10,9 @@
 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: