ovpn: propagate socket mark to skb in UDP

OpenVPN allows users to configure a FW mark on sockets used to
communicate with other peers. The mark is set by means of the
`SO_MARK` Linux socket option.

However, in the ovpn UDP code path, the socket's `sk_mark` value is
currently ignored and it is not propagated to outgoing `skbs`.

This commit ensures proper inheritance of the field by setting
`skb->mark` to `sk->sk_mark` before handing the `skb` to the network
stack for transmission.

Fixes: 08857b5 ("ovpn: implement basic TX path (UDP)")
Reviewed-by: Sabrina Dubroca <[email protected]>
Signed-off-by: Ralf Lici <[email protected]>
Link: https://www.mail-archive.com/[email protected]/msg31877.html
Signed-off-by: Antonio Quartulli <[email protected]>

Author: ralflici

drivers/net/ovpn/udp.c

@@ -344,6 +344,7 @@ void ovpn_udp_send_skb(struct ovpn_peer *peer, struct sock *sk,
 	int ret;
 
 	skb->dev = peer->ovpn->dev;
+	skb->mark = READ_ONCE(sk->sk_mark);
 	/* no checksum performed at this layer */
 	skb->ip_summed = CHECKSUM_NONE;