net: Fix the arp error in some cases

BugLink: https://bugs.launchpad.net/bugs/1885932

[ Upstream commit 5eea3a63 ]

ie.,
$ ifconfig eth0 6.6.6.6 netmask 255.255.255.0

$ ip rule add from 6.6.6.6 table 6666

$ ip route add 9.9.9.9 via 6.6.6.6

$ ping -I 6.6.6.6 9.9.9.9
PING 9.9.9.9 (9.9.9.9) from 6.6.6.6 : 56(84) bytes of data.

3 packets transmitted, 0 received, 100% packet loss, time 2079ms

$ arp
Address     HWtype  HWaddress           Flags Mask            Iface
6.6.6.6             (incomplete)                              eth0

The arp request address is error, this is because fib_table_lookup in
fib_check_nh lookup the destnation 9.9.9.9 nexthop, the scope of
the fib result is RT_SCOPE_LINK,the correct scope is RT_SCOPE_HOST.
Here I add a check of whether this is RT_TABLE_MAIN to solve this problem.

Fixes: 3bfd8472 ("net: Use passed in table for nexthop lookups")
Signed-off-by: guodeqing <geffrey.guo@huawei.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/ipv4/fib_semantics.c

@@ -776,7 +776,7 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_info *fi,
 			if (fl4.flowi4_scope < RT_SCOPE_LINK)
 				fl4.flowi4_scope = RT_SCOPE_LINK;
 
-			if (cfg->fc_table)
+			if (cfg->fc_table && cfg->fc_table != RT_TABLE_MAIN)
 				tbl = fib_get_table(net, cfg->fc_table);
 
 			if (tbl)