ipv4: nexthop: Correctly update nexthop group when removing a nexthop

Each nexthop group contains an indication if it has IPv4 nexthops
('has_v4'). Its purpose is to prevent IPv6 routes from using groups with
IPv4 nexthops.

However, the indication is not updated when a nexthop is removed. This
results in the kernel wrongly rejecting IPv6 routes from pointing to
groups that only contain IPv6 nexthops. Example:

# ip nexthop replace id 1 via 192.0.2.2 dev dummy10
# ip nexthop replace id 2 via 2001:db8:1::2 dev dummy10
# ip nexthop replace id 10 group 1/2
# ip nexthop del id 1
# ip route replace 2001:db8:10::/64 nhid 10
Error: IPv6 routes can not use an IPv4 nexthop.

Solve this by updating the indication according to the new set of
member nexthops.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/nexthop.c

@@ -797,7 +797,7 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
 		return;
 	}
 
-	newg->has_v4 = nhg->has_v4;
+	newg->has_v4 = false;
 	newg->mpath = nhg->mpath;
 	newg->fdb_nh = nhg->fdb_nh;
 	newg->num_nh = nhg->num_nh;
@@ -806,12 +806,18 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
 	nhges = nhg->nh_entries;
 	new_nhges = newg->nh_entries;
 	for (i = 0, j = 0; i < nhg->num_nh; ++i) {
+		struct nh_info *nhi;
+
 		/* current nexthop getting removed */
 		if (nhg->nh_entries[i].nh == nh) {
 			newg->num_nh--;
 			continue;
 		}
 
+		nhi = rtnl_dereference(nhges[i].nh->nh_info);
+		if (nhi->family == AF_INET)
+			newg->has_v4 = true;
+
 		list_del(&nhges[i].nh_list);
 		new_nhges[j].nh_parent = nhges[i].nh_parent;
 		new_nhges[j].nh = nhges[i].nh;