gve: ignore nonrelevant GSO type bits when processing TSO headers

TSO currently fails when the skb's gso_type field has more than one bit
set.

TSO packets can be passed from userspace using PF_PACKET, TUNTAP and a
few others, using virtio_net_hdr (e.g., PACKET_VNET_HDR). This includes
virtualization, such as QEMU, a real use-case.

The gso_type and gso_size fields as passed from userspace in
virtio_net_hdr are not trusted blindly by the kernel. It adds gso_type
|= SKB_GSO_DODGY to force the packet to enter the software GSO stack
for verification.

This issue might similarly come up when the CWR bit is set in the TCP
header for congestion control, causing the SKB_GSO_TCP_ECN gso_type bit
to be set.

Fixes: a57e5de4 ("gve: DQO: Add TX path")
Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Acked-by: Andrei Vagin <avagin@gmail.com>

v2 - Remove unnecessary comments, remove line break between fixes tag
and signoffs.

v3 - Add back unrelated empty line removal.

Link: https://lore.kernel.org/r/20240610225729.2985343-1-joshwash@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/google/gve/gve_tx_dqo.c

@@ -555,28 +555,18 @@ static int gve_prep_tso(struct sk_buff *skb)
 	if (unlikely(skb_shinfo(skb)->gso_size < GVE_TX_MIN_TSO_MSS_DQO))
 		return -1;
 
+	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
+		return -EINVAL;
+
 	/* Needed because we will modify header. */
 	err = skb_cow_head(skb, 0);
 	if (err < 0)
 		return err;
 
 	tcp = tcp_hdr(skb);
-
-	/* Remove payload length from checksum. */
 	paylen = skb->len - skb_transport_offset(skb);
-
-	switch (skb_shinfo(skb)->gso_type) {
-	case SKB_GSO_TCPV4:
-	case SKB_GSO_TCPV6:
-		csum_replace_by_diff(&tcp->check,
-				     (__force __wsum)htonl(paylen));
-
-		/* Compute length of segmentation header. */
-		header_len = skb_tcp_all_headers(skb);
-		break;
-	default:
-		return -EINVAL;
-	}
+	csum_replace_by_diff(&tcp->check, (__force __wsum)htonl(paylen));
+	header_len = skb_tcp_all_headers(skb);
 
 	if (unlikely(header_len > GVE_TX_MAX_HDR_SIZE_DQO))
 		return -EINVAL;