net: vrf: do not allow table id 0

Frank reported that vrf devices can be created with a table id of 0.
This breaks many of the run time table id checks and should not be
allowed. Detect this condition at create time and fail with EINVAL.

Fixes: 193125db ("net: Introduce VRF device driver")
Reported-by: NFrank Kellermann <frank.kellermann@atos.net>
Signed-off-by: NDavid Ahern <dsa@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/vrf.c

@@ -1252,6 +1252,8 @@ static int vrf_newlink(struct net *src_net, struct net_device *dev,
 		return -EINVAL;
 
 	vrf->tb_id = nla_get_u32(data[IFLA_VRF_TABLE]);
+	if (vrf->tb_id == RT_TABLE_UNSPEC)
+		return -EINVAL;
 
 	dev->priv_flags |= IFF_L3MDEV_MASTER;