ip6_tunnel: add optional fwmark inherit

Add IP6_TNL_F_USE_ORIG_FWMARK to ip6_tunnel, so that ip6_tnl_xmit2()
makes a route lookup taking into account skb->fwmark and doesnt cache
lookup result.

This permits more flexibility in policies and firewall setups.

To setup such a tunnel, "fwmark inherit" option should be added to "ip
-f inet6 tunnel" command.

Reported-by: Anders Franzen <[e-mail]>
CC: Hans Schillström <[e-mail]>
Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/ip6_tunnel.h

···
 #define IP6_TNL_F_MIP6_DEV 0x8
 /* copy DSCP from the outer packet */
 #define IP6_TNL_F_RCV_DSCP_COPY 0x10
+/* copy fwmark from inner packet */
+#define IP6_TNL_F_USE_ORIG_FWMARK 0x20
 
 struct ip6_tnl_parm {
 	char name[IFNAMSIZ];	/* name of tunnel device */

net/ipv6/ip6_tunnel.c

···
 	struct net_device_stats *stats = &t->dev->stats;
 	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
 	struct ipv6_tel_txoption opt;
-	struct dst_entry *dst, *ndst = NULL;
+	struct dst_entry *dst = NULL, *ndst = NULL;
 	struct net_device *tdev;
 	int mtu;
 	unsigned int max_headroom = sizeof(struct ipv6hdr);
···
 	int err = -1;
 	int pkt_len;
 
-	dst = ip6_tnl_dst_check(t);
+	if (!fl6->flowi6_mark)
+		dst = ip6_tnl_dst_check(t);
 	if (!dst) {
 		ndst = ip6_route_output(net, NULL, fl6);
 
···
 		skb = new_skb;
 	}
 	skb_dst_drop(skb);
-	skb_dst_set_noref(skb, dst);
-
+	if (fl6->flowi6_mark) {
+		skb_dst_set(skb, dst);
+		ndst = NULL;
+	} else {
+		skb_dst_set_noref(skb, dst);
+	}
 	skb->transport_header = skb->network_header;
 
 	proto = fl6->flowi6_proto;
···
 
 	dsfield = ipv4_get_dsfield(iph);
 
-	if ((t->parms.flags & IP6_TNL_F_USE_ORIG_TCLASS))
+	if (t->parms.flags & IP6_TNL_F_USE_ORIG_TCLASS)
 		fl6.flowlabel |= htonl((__u32)iph->tos << IPV6_TCLASS_SHIFT)
 					  & IPV6_TCLASS_MASK;
+	if (t->parms.flags & IP6_TNL_F_USE_ORIG_FWMARK)
+		fl6.flowi6_mark = skb->mark;
 
 	err = ip6_tnl_xmit2(skb, dev, dsfield, &fl6, encap_limit, &mtu);
 	if (err != 0) {
···
 	fl6.flowi6_proto = IPPROTO_IPV6;
 
 	dsfield = ipv6_get_dsfield(ipv6h);
-	if ((t->parms.flags & IP6_TNL_F_USE_ORIG_TCLASS))
+	if (t->parms.flags & IP6_TNL_F_USE_ORIG_TCLASS)
 		fl6.flowlabel |= (*(__be32 *) ipv6h & IPV6_TCLASS_MASK);
-	if ((t->parms.flags & IP6_TNL_F_USE_ORIG_FLOWLABEL))
+	if (t->parms.flags & IP6_TNL_F_USE_ORIG_FLOWLABEL)
 		fl6.flowlabel |= (*(__be32 *) ipv6h & IPV6_FLOWLABEL_MASK);
+	if (t->parms.flags & IP6_TNL_F_USE_ORIG_FWMARK)
+		fl6.flowi6_mark = skb->mark;
 
 	err = ip6_tnl_xmit2(skb, dev, dsfield, &fl6, encap_limit, &mtu);
 	if (err != 0) {