net: Properly update v4 routes with v6 nexthop

When creating a v4 route that uses a v6 nexthop from a nexthop group.
Allow the kernel to properly send the nexthop as v6 via the RTA_VIA
attribute.

Broken behavior:

$ ip nexthop add via fe80::9 dev eth0
$ ip nexthop show
id 1 via fe80::9 dev eth0 scope link
$ ip route add 4.5.6.7/32 nhid 1
$ ip route show
default via 10.0.2.2 dev eth0
4.5.6.7 nhid 1 via 254.128.0.0 dev eth0
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
$

Fixed behavior:

$ ip nexthop add via fe80::9 dev eth0
$ ip nexthop show
id 1 via fe80::9 dev eth0 scope link
$ ip route add 4.5.6.7/32 nhid 1
$ ip route show
default via 10.0.2.2 dev eth0
4.5.6.7 nhid 1 via inet6 fe80::9 dev eth0
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
$

v2, v3: Addresses code review comments from David Ahern

Fixes: dcb1ecb50edf (“ipv4: Prepare for fib6_nh from a nexthop object”)
Signed-off-by: Donald Sharp <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ip_fib.h

···
 			  struct netlink_callback *cb);
 
 int fib_nexthop_info(struct sk_buff *skb, const struct fib_nh_common *nh,
-		     unsigned char *flags, bool skip_oif);
+		     u8 rt_family, unsigned char *flags, bool skip_oif);
 int fib_add_nexthop(struct sk_buff *skb, const struct fib_nh_common *nh,
-		    int nh_weight);
+		    int nh_weight, u8 rt_family);
 #endif  /* _NET_FIB_H */

include/net/nexthop.h

···
 }
 
 static inline
-int nexthop_mpath_fill_node(struct sk_buff *skb, struct nexthop *nh)
+int nexthop_mpath_fill_node(struct sk_buff *skb, struct nexthop *nh,
+			    u8 rt_family)
 {
 	struct nh_group *nhg = rtnl_dereference(nh->nh_grp);
 	int i;
···
 		struct fib_nh_common *nhc = &nhi->fib_nhc;
 		int weight = nhg->nh_entries[i].weight;
 
-		if (fib_add_nexthop(skb, nhc, weight) < 0)
+		if (fib_add_nexthop(skb, nhc, weight, rt_family) < 0)
 			return -EMSGSIZE;
 	}
 

net/ipv4/fib_semantics.c

···
 }
 
 int fib_nexthop_info(struct sk_buff *skb, const struct fib_nh_common *nhc,
-		     unsigned char *flags, bool skip_oif)
+		     u8 rt_family, unsigned char *flags, bool skip_oif)
 {
 	if (nhc->nhc_flags & RTNH_F_DEAD)
 		*flags |= RTNH_F_DEAD;
···
 		/* if gateway family does not match nexthop family
 		 * gateway is encoded as RTA_VIA
 		 */
-		if (nhc->nhc_gw_family != nhc->nhc_family) {
+		if (rt_family != nhc->nhc_gw_family) {
 			int alen = sizeof(struct in6_addr);
 			struct nlattr *nla;
 			struct rtvia *via;
···
 
 #if IS_ENABLED(CONFIG_IP_ROUTE_MULTIPATH) || IS_ENABLED(CONFIG_IPV6)
 int fib_add_nexthop(struct sk_buff *skb, const struct fib_nh_common *nhc,
-		    int nh_weight)
+		    int nh_weight, u8 rt_family)
 {
 	const struct net_device *dev = nhc->nhc_dev;
 	struct rtnexthop *rtnh;
···
 	rtnh->rtnh_hops = nh_weight - 1;
 	rtnh->rtnh_ifindex = dev ? dev->ifindex : 0;
 
-	if (fib_nexthop_info(skb, nhc, &flags, true) < 0)
+	if (fib_nexthop_info(skb, nhc, rt_family, &flags, true) < 0)
 		goto nla_put_failure;
 
 	rtnh->rtnh_flags = flags;
···
 		goto nla_put_failure;
 
 	if (unlikely(fi->nh)) {
-		if (nexthop_mpath_fill_node(skb, fi->nh) < 0)
+		if (nexthop_mpath_fill_node(skb, fi->nh, AF_INET) < 0)
 			goto nla_put_failure;
 		goto mp_end;
 	}
 
 	for_nexthops(fi) {
-		if (fib_add_nexthop(skb, &nh->nh_common, nh->fib_nh_weight) < 0)
+		if (fib_add_nexthop(skb, &nh->nh_common, nh->fib_nh_weight,
+				    AF_INET) < 0)
 			goto nla_put_failure;
 #ifdef CONFIG_IP_ROUTE_CLASSID
 		if (nh->nh_tclassid &&
···
 		const struct fib_nh_common *nhc = fib_info_nhc(fi, 0);
 		unsigned char flags = 0;
 
-		if (fib_nexthop_info(skb, nhc, &flags, false) < 0)
+		if (fib_nexthop_info(skb, nhc, AF_INET, &flags, false) < 0)
 			goto nla_put_failure;
 
 		rtm->rtm_flags = flags;

net/ipv6/route.c

···
 		if (!mp)
 			goto nla_put_failure;
 
-		if (nexthop_mpath_fill_node(skb, nh))
+		if (nexthop_mpath_fill_node(skb, nh, AF_INET6))
 			goto nla_put_failure;
 
 		nla_nest_end(skb, mp);
···
 		struct fib6_nh *fib6_nh;
 
 		fib6_nh = nexthop_fib6_nh(nh);
-		if (fib_nexthop_info(skb, &fib6_nh->nh_common,
+		if (fib_nexthop_info(skb, &fib6_nh->nh_common, AF_INET6,
 				     flags, false) < 0)
 			goto nla_put_failure;
 	}
···
 			goto nla_put_failure;
 
 		if (fib_add_nexthop(skb, &rt->fib6_nh->nh_common,
-				    rt->fib6_nh->fib_nh_weight) < 0)
+				    rt->fib6_nh->fib_nh_weight, AF_INET6) < 0)
 			goto nla_put_failure;
 
 		list_for_each_entry_safe(sibling, next_sibling,
 					 &rt->fib6_siblings, fib6_siblings) {
 			if (fib_add_nexthop(skb, &sibling->fib6_nh->nh_common,
-					    sibling->fib6_nh->fib_nh_weight) < 0)
+					    sibling->fib6_nh->fib_nh_weight,
+					    AF_INET6) < 0)
 				goto nla_put_failure;
 		}
 
···
 
 		rtm->rtm_flags |= nh_flags;
 	} else {
-		if (fib_nexthop_info(skb, &rt->fib6_nh->nh_common,
+		if (fib_nexthop_info(skb, &rt->fib6_nh->nh_common, AF_INET6,
 				     &nh_flags, false) < 0)
 			goto nla_put_failure;