libxtables: properly reject empty hostnames

An empty hostname in the address list of an -s/-d argument, which may
be the result of a typo, is interpreted as 0/0, which, when combined
with -j ACCEPT, leads to an undesired opening of the firewall.

References: http://bugzilla.netfilter.org/show_bug.cgi?id=727
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
1 file changed