ipv6: Set errno after ip_fib_metrics_init() in ip6_route_info_create().

While creating a new IPv6, we could get a weird -ENOMEM when
RTA_NH_ID is set and either of the conditions below is true:

  1) CONFIG_IPV6_SUBTREES is enabled and rtm_src_len is specified
  2) nexthop_get() fails

e.g.)

  # strace ip -6 route add fe80::dead:beef:dead:beef nhid 1 from ::
  recvmsg(3, {msg_iov=[{iov_base=[...[
    {error=-ENOMEM, msg=[... [...]]},
    [{nla_len=49, nla_type=NLMSGERR_ATTR_MSG}, "Nexthops can not be used with so"...]
  ]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 148

Let's set err explicitly after ip_fib_metrics_init() in
ip6_route_info_create().

Fixes: f88d8ea ("ipv6: Plumb support for nexthop object in a fib6_info")
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: q2ven

net/ipv6/route.c

@@ -3803,10 +3803,12 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
 	if (nh) {
 		if (rt->fib6_src.plen) {
 			NL_SET_ERR_MSG(extack, "Nexthops can not be used with source routing");
+			err = -EINVAL;
 			goto out_free;
 		}
 		if (!nexthop_get(nh)) {
 			NL_SET_ERR_MSG(extack, "Nexthop has been deleted");
+			err = -ENOENT;
 			goto out_free;
 		}
 		rt->nh = nh;