net: ipv4: Fix rtnexthop len when RTA_FLOW is present

Multipath RTA_FLOW is embedded in nexthop. Dump it in fib_add_nexthop()
to get the length of rtnexthop correct.

Fixes: b0f60193632e ("ipv4: Refactor nexthop attributes in fib_dump_info")
Signed-off-by: Xiao Liang <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ip_fib.h

···
 int fib_nexthop_info(struct sk_buff *skb, const struct fib_nh_common *nh,
 		     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, u8 rt_family);
+		    int nh_weight, u8 rt_family, u32 nh_tclassid);
 #endif  /* _NET_FIB_H */

include/net/nexthop.h

···
 		struct fib_nh_common *nhc = &nhi->fib_nhc;
 		int weight = nhg->nh_entries[i].weight;
 
-		if (fib_add_nexthop(skb, nhc, weight, rt_family) < 0)
+		if (fib_add_nexthop(skb, nhc, weight, rt_family, 0) < 0)
 			return -EMSGSIZE;
 	}
 

net/ipv4/fib_semantics.c

···
 
 #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, u8 rt_family)
+		    int nh_weight, u8 rt_family, u32 nh_tclassid)
 {
 	const struct net_device *dev = nhc->nhc_dev;
 	struct rtnexthop *rtnh;
···
 		goto nla_put_failure;
 
 	rtnh->rtnh_flags = flags;
+
+	if (nh_tclassid && nla_put_u32(skb, RTA_FLOW, nh_tclassid))
+		goto nla_put_failure;
 
 	/* length of rtnetlink header + attributes */
 	rtnh->rtnh_len = nlmsg_get_pos(skb) - (void *)rtnh;
···
 	}
 
 	for_nexthops(fi) {
-		if (fib_add_nexthop(skb, &nh->nh_common, nh->fib_nh_weight,
-				    AF_INET) < 0)
-			goto nla_put_failure;
+		u32 nh_tclassid = 0;
 #ifdef CONFIG_IP_ROUTE_CLASSID
-		if (nh->nh_tclassid &&
-		    nla_put_u32(skb, RTA_FLOW, nh->nh_tclassid))
-			goto nla_put_failure;
+		nh_tclassid = nh->nh_tclassid;
 #endif
+		if (fib_add_nexthop(skb, &nh->nh_common, nh->fib_nh_weight,
+				    AF_INET, nh_tclassid) < 0)
+			goto nla_put_failure;
 	} endfor_nexthops(fi);
 
 mp_end:

net/ipv6/route.c

···
 			goto nla_put_failure;
 
 		if (fib_add_nexthop(skb, &rt->fib6_nh->nh_common,
-				    rt->fib6_nh->fib_nh_weight, AF_INET6) < 0)
+				    rt->fib6_nh->fib_nh_weight, AF_INET6,
+				    0) < 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,
-					    AF_INET6) < 0)
+					    AF_INET6, 0) < 0)
 				goto nla_put_failure;
 		}