ip: support SO_MARK cmsg

Enable setting skb->mark for UDP and RAW sockets using cmsg.

This is analogous to existing support for TOS, TTL, txtime, etc.

Packet sockets already support this as of commit c7d39e32632e
("packet: support per-packet fwmark for af_packet sendmsg").

Similar to other fields, implement by
1. initialize the sockcm_cookie.mark from socket option sk_mark
2. optionally overwrite this in ip_cmsg_send/ip6_datagram_send_ctl
3. initialize inet_cork.mark from sockcm_cookie.mark
4. initialize each (usually just one) skb->mark from inet_cork.mark

Step 1 is handled in one location for most protocols by ipcm_init_sk
as of commit 351782067b6b ("ipv4: ipcm_cookie initializers").

Signed-off-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/inet_sock.h

···
 	char			priority;
 	__u16			gso_size;
 	u64			transmit_time;
+	u32			mark;
 };
 
 struct inet_cork_full {

include/net/ip.h

···
 {
 	ipcm_init(ipcm);
 
+	ipcm->sockc.mark = inet->sk.sk_mark;
 	ipcm->sockc.tsflags = inet->sk.sk_tsflags;
 	ipcm->oif = inet->sk.sk_bound_dev_if;
 	ipcm->addr = inet->inet_saddr;

net/ipv4/ip_output.c

···
 	cork->length = 0;
 	cork->ttl = ipc->ttl;
 	cork->tos = ipc->tos;
+	cork->mark = ipc->sockc.mark;
 	cork->priority = ipc->priority;
 	cork->transmit_time = ipc->sockc.transmit_time;
 	cork->tx_flags = 0;
···
 	}
 
 	skb->priority = (cork->tos != -1) ? cork->priority: sk->sk_priority;
-	skb->mark = sk->sk_mark;
+	skb->mark = cork->mark;
 	skb->tstamp = cork->transmit_time;
 	/*
 	 * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec

net/ipv4/ping.c

···
 	} else if (!ipc.oif)
 		ipc.oif = inet->uc_index;
 
-	flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
+	flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos,
 			   RT_SCOPE_UNIVERSE, sk->sk_protocol,
 			   inet_sk_flowi_flags(sk), faddr, saddr, 0, 0,
 			   sk->sk_uid);

net/ipv4/raw.c

···
 	skb_reserve(skb, hlen);
 
 	skb->priority = sk->sk_priority;
-	skb->mark = sk->sk_mark;
+	skb->mark = sockc->mark;
 	skb->tstamp = sockc->transmit_time;
 	skb_dst_set(skb, &rt->dst);
 	*rtp = NULL;
···
 		}
 	}
 
-	flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
+	flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos,
 			   RT_SCOPE_UNIVERSE,
 			   hdrincl ? IPPROTO_RAW : sk->sk_protocol,
 			   inet_sk_flowi_flags(sk) |

net/ipv4/udp.c

···
 
 		fl4 = &fl4_stack;
 
-		flowi4_init_output(fl4, ipc.oif, sk->sk_mark, tos,
+		flowi4_init_output(fl4, ipc.oif, ipc.sockc.mark, tos,
 				   RT_SCOPE_UNIVERSE, sk->sk_protocol,
 				   flow_flags,
 				   faddr, saddr, dport, inet->inet_sport,

net/ipv6/ip6_output.c

···
 	cork->base.fragsize = mtu;
 	cork->base.gso_size = ipc6->gso_size;
 	cork->base.tx_flags = 0;
+	cork->base.mark = ipc6->sockc.mark;
 	sock_tx_timestamp(sk, ipc6->sockc.tsflags, &cork->base.tx_flags);
 
 	if (dst_allfrag(xfrm_dst_path(&rt->dst)))
···
 	hdr->daddr = *final_dst;
 
 	skb->priority = sk->sk_priority;
-	skb->mark = sk->sk_mark;
+	skb->mark = cork->base.mark;
 
 	skb->tstamp = cork->base.transmit_time;
 

net/ipv6/raw.c

···
 
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->priority = sk->sk_priority;
-	skb->mark = sk->sk_mark;
+	skb->mark = sockc->mark;
 	skb->tstamp = sockc->transmit_time;
 
 	skb_put(skb, length);
···
 
 	ipcm6_init(&ipc6);
 	ipc6.sockc.tsflags = sk->sk_tsflags;
+	ipc6.sockc.mark = sk->sk_mark;
 
 	if (sin6) {
 		if (addr_len < SIN6_LEN_RFC2133)
···
 	opt = ipv6_fixup_options(&opt_space, opt);
 
 	fl6.flowi6_proto = proto;
+	fl6.flowi6_mark = ipc6.sockc.mark;
 
 	if (!hdrincl) {
 		rfv.msg = msg;

net/ipv6/udp.c

···
 	ipcm6_init(&ipc6);
 	ipc6.gso_size = up->gso_size;
 	ipc6.sockc.tsflags = sk->sk_tsflags;
+	ipc6.sockc.mark = sk->sk_mark;
 
 	/* destination address check */
 	if (sin6) {
···
 	if (!fl6.flowi6_oif)
 		fl6.flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
 
-	fl6.flowi6_mark = sk->sk_mark;
+	fl6.flowi6_mark = ipc6.sockc.mark;
 	fl6.flowi6_uid = sk->sk_uid;
 
 	if (msg->msg_controllen) {