proxy.cgi: Correctly validate domain lists

Fixes: #12925 - JVN#15411362 Inquiry on vulnerability found in IPFire
Reported-by: Noriko Totsuka <vuls@jpcert.or.jp>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

config/cfgroot/general-functions.pl

@@ -756,6 +756,17 @@ sub validdomainname
 	return 1;
 }
 
+sub validwildcarddomainname($) {
+	my $domainname = shift;
+
+	# Ignore any leading dots
+	if ($domainname =~ m/^\*\.(.*)/) {
+		$domainname = $1;
+	}
+
+	return &validdomainname($domainname);
+}
+
 sub validfqdn
 {
 	# Checks a fully qualified domain name against RFC1035 and RFC2181