af_packet: fix the tx skb protocol in raw sockets with ETH_P_ALL

I am using "protocol ip" filters in TC to manipulate TC flower
classifiers, which are only available with "protocol ip". However,
I faced an issue that packets sent via raw sockets with ETH_P_ALL
did not match the ip filters even if they did satisfy the condition
(e.g., DHCP offer from dhcpd).

I have determined that the behavior was caused by an unexpected
value stored in skb->protocol, namely, ETH_P_ALL instead of ETH_P_IP,
when packets were sent via raw sockets with ETH_P_ALL set.

IMHO, storing ETH_P_ALL in skb->protocol is not appropriate for
packets sent via raw sockets because ETH_P_ALL is not a real ether
type used on wire, but a virtual one.

This patch fixes the tx protocol selection in cases of transmission
via raw sockets created with ETH_P_ALL so that it asks the driver to
extract protocol from the Ethernet header.

Fixes: 75c6577 ("net/packet: Ask driver for protocol if not provided by user")
Signed-off-by: Yoshiki Komachi <[email protected]>
Acked-by: Willem de Bruijn <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

net/packet/af_packet.c

@@ -1852,7 +1852,8 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,
 
 static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
 {
-	if (!skb->protocol && sock->type == SOCK_RAW) {
+	if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) &&
+	    sock->type == SOCK_RAW) {
 		skb_reset_mac_header(skb);
 		skb->protocol = dev_parse_header_protocol(skb);
 	}