[NET]: Introducing socket mark socket option.

A userspace program may wish to set the mark for each packets its send
without using the netfilter MARK target. Changing the mark can be used
for mark based routing without netfilter or for packet filtering.

It requires CAP_NET_ADMIN capability.

Signed-off-by: Laszlo Attila Toth <panther@balabit.hu>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 6e4d5f4..341779e 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -168,6 +168,7 @@
 	}
 
 	skb->priority = sk->sk_priority;
+	skb->mark = sk->sk_mark;
 
 	/* Send it out. */
 	return ip_local_out(skb);
@@ -385,6 +386,7 @@
 			     (skb_shinfo(skb)->gso_segs ?: 1) - 1);
 
 	skb->priority = sk->sk_priority;
+	skb->mark = sk->sk_mark;
 
 	return ip_local_out(skb);
 
@@ -1286,6 +1288,7 @@
 	iph->daddr = rt->rt_dst;
 
 	skb->priority = sk->sk_priority;
+	skb->mark = sk->sk_mark;
 	skb->dst = dst_clone(&rt->u.dst);
 
 	if (iph->protocol == IPPROTO_ICMP)
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 85c0869..f863c3d 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -352,6 +352,7 @@
 	skb_reserve(skb, hh_len);
 
 	skb->priority = sk->sk_priority;
+	skb->mark = sk->sk_mark;
 	skb->dst = dst_clone(&rt->u.dst);
 
 	skb_reset_network_header(skb);
@@ -544,6 +545,7 @@
 
 	{
 		struct flowi fl = { .oif = ipc.oif,
+				    .mark = sk->sk_mark,
 				    .nl_u = { .ip4_u =
 					      { .daddr = daddr,
 						.saddr = saddr,