extensions: libipt_icmp: Add translation to nft

Add translation for icmp to nftables. Not supported types in nftables
are: any, network-unreachable, host-unreachable, protocol-unreachable, port-unreachable, fragmentation-needed, source-route-failed, network-unknown, host-unknown, network-prohibited, host-prohibited, TOS-network-unreachable, TOS-host-unreachable, communication-prohibited, host-precedence-violation, precedence-cutoff, network-redirect, host-redirect, TOS-network-redirect, TOS-host-redirect, router-advertisement, router-solicitation, ttl-zero-during-transit, ttl-zero-during-reassembly, ip-header-bad and required-option-missing.

Examples:

$ sudo iptables-translate -t filter -A INPUT -m icmp --icmp-type echo-reply -j ACCEPT
nft add rule ip filter INPUT icmp type echo-reply counter accept

$ sudo iptables-translate -t filter -A INPUT -m icmp --icmp-type 3 -j ACCEPT
nft add rule ip filter INPUT icmp type destination-unreachable counter accept

$ sudo iptables-translate -t filter -A INPUT -m icmp ! --icmp-type 3 -j ACCEPT
nft add rule ip filter INPUT icmp type != destination-unreachable counter accept

---
v2:
- Detection of not supported types in nftables, as Shivani suggested.
v3:
- Fix array iteration protection.
v4:
- icmp types router-advertisement and router-solicitation already supported in nft.

 extensions/libipt_icmp.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

index 666e7da..cc8e732 100644
@@ -249,6 +249,41 @@ static void icmp_save(const void *ip, const struct xt_entry_match *match)
 	}
 }
 
+static unsigned int type_xlate_print(struct xt_xlate *xl, unsigned int icmptype,
+				     unsigned int code_min,
+				     unsigned int code_max)
+{
+	unsigned int i;
+
+	if (code_min != code_max && icmptype != 0xFF) {
+		for (i = 0; i < ARRAY_SIZE(icmp_codes); ++i)
+			if (icmp_codes[i].type == icmptype &&
+			    icmp_codes[i].code_min == code_min &&
+			    icmp_codes[i].code_max == code_max) {
+				xt_xlate_add(xl, icmp_codes[i].name);
+				return 1;
+			}
+	}
+
+	return 0;
+}
+
+static int icmp_xlate(const struct xt_entry_match *match, struct xt_xlate *xl,
+		      int numeric)
+{
+	const struct ipt_icmp *info = (struct ipt_icmp *)match->data;
+
+	xt_xlate_add(xl, "icmp type%s ",
+		     (info->invflags & IPT_ICMP_INV) ? " !=" : "");
+
+	if (!type_xlate_print(xl, info->type, info->code[0], info->code[1]))
+		return 0;
+
+	xt_xlate_add(xl, " ");
+
+	return 1;
+}
+
 static struct xtables_match icmp_mt_reg = {
 	.name		= "icmp",
 	.version	= XTABLES_VERSION,

@@ -261,6 +296,7 @@ static struct xtables_match icmp_mt_reg = {
 	.save		= icmp_save,
 	.x6_parse	= icmp_parse,
 	.x6_options	= icmp_opts,
+	.xlate		= icmp_xlate,
 };
 
 void _init(void)

2.7.0