From: David Ahern <dsahern@gmail.com>
Date: Tue, 26 Feb 2019 09:00:02 -0800
Subject: ipv4: Return error for RTA_VIA attribute
Git-commit: b6e9e5df4ecf100f6a10ab2ade8e46d47a4b9779
Patch-mainline: v5.0
References: networking-stable-19_03_07

IPv4 currently does not support nexthops outside of the AF_INET family.
Specifically, it does not handle RTA_VIA attribute. If it is passed
in a route add request, the actual route added only uses the device
which is clearly not what the user intended:

  $ ip ro add 172.16.1.0/24 via inet6 2001:db8:1::1 dev eth0
  $ ip ro ls
  ...
  172.16.1.0/24 dev eth0

Catch this and fail the route add:
  $ ip ro add 172.16.1.0/24 via inet6 2001:db8:1::1 dev eth0
  Error: IPv4 does not support RTA_VIA attribute.

[js] no extack in 4.12 here yet.

Fixes: 03c0566542f4c ("mpls: Netlink commands to add, remove, and dump routes")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv4/fib_frontend.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -671,6 +671,9 @@ static int rtm_to_fib_config(struct net
 		case RTA_GATEWAY:
 			cfg->fc_gw = nla_get_be32(attr);
 			break;
+		case RTA_VIA:
+			err = -EINVAL;
+			goto errout;
 		case RTA_PRIORITY:
 			cfg->fc_priority = nla_get_u32(attr);
 			break;