Use netmasks instead of prefix lengths internally

Iptables supports using non-continuous netmasks like FFFF::FFFF which would
match the first and last 16bit of an IPv6 address while ignoring the parts
in between which is useful fordeclaring rules targeting hosts on rotating
prefixes.

Instead of storing parsed netmasks as bitcount internally, use a full mask
which is passed to iptables as-is.

Also support a new shorthand notation "addr/-N" which will construct a mask
that matches the *last* N bits of an address - useful for matching the host
part only of an IPv4 address, e.g.

  option dest_ip '::c23f:eff:fe7a:a094/-64'

This will convert to a netmask of "::ffff:ffff:ffff:ffff".

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

1 files changed, 20 insertions, 44 deletions

diff --git a/iptables.c b/iptables.c
index 58ec752..03987af 100644
--- a/iptables.c
+++ b/iptables.c
@@ -606,34 +606,6 @@ fw3_ipt_rule_in_out(struct fw3_ipt_rule *r,
 }
 
 
-static void
-ip4prefix2mask(int prefix, struct in_addr *mask)
-{
-	if (prefix > 0)
-		mask->s_addr = htonl(~((1 << (32 - prefix)) - 1));
-	else
-		mask->s_addr = 0;
-}
-
-#ifndef DISABLE_IPV6
-static void
-ip6prefix2mask(int prefix, struct in6_addr *mask)
-{
-	char *p = (char *)mask;
-
-	if (prefix > 0)
-	{
-		memset(p, 0xff, prefix / 8);
-		memset(p + (prefix / 8) + 1, 0, (128 - prefix) / 8);
-		p[prefix / 8] = 0xff << (8 - (prefix & 7));
-	}
-	else
-	{
-		memset(mask, 0, sizeof(*mask));
-	}
-}
-#endif
-
 void
 fw3_ipt_rule_src_dest(struct fw3_ipt_rule *r,
                       struct fw3_address *src, struct fw3_address *dest)
@@ -648,13 +620,13 @@ fw3_ipt_rule_src_dest(struct fw3_ipt_rule *r,
 		if (src->range)
 		{
 			fw3_ipt_rule_addarg(r, src->invert, "--src-range",
-			                    fw3_address_to_string(src, false));
+			                    fw3_address_to_string(src, false, false));
 		}
 #ifndef DISABLE_IPV6
 		else if (r->h->family == FW3_FAMILY_V6)
 		{
 			r->e6.ipv6.src = src->address.v6;
-			ip6prefix2mask(src->mask, &r->e6.ipv6.smsk);
+			r->e6.ipv6.smsk = src->mask.v6;
 
 			int i;
 			for (i = 0; i < 4; i++)
@@ -667,7 +639,7 @@ fw3_ipt_rule_src_dest(struct fw3_ipt_rule *r,
 		else
 		{
 			r->e.ip.src = src->address.v4;
-			ip4prefix2mask(src->mask, &r->e.ip.smsk);
+			r->e.ip.smsk = src->mask.v4;
 
 			r->e.ip.src.s_addr &= r->e.ip.smsk.s_addr;
 
@@ -681,13 +653,13 @@ fw3_ipt_rule_src_dest(struct fw3_ipt_rule *r,
 		if (dest->range)
 		{
 			fw3_ipt_rule_addarg(r, dest->invert, "--dst-range",
-			                    fw3_address_to_string(dest, false));
+			                    fw3_address_to_string(dest, false, false));
 		}
 #ifndef DISABLE_IPV6
 		else if (r->h->family == FW3_FAMILY_V6)
 		{
 			r->e6.ipv6.dst = dest->address.v6;
-			ip6prefix2mask(dest->mask, &r->e6.ipv6.dmsk);
+			r->e6.ipv6.dmsk = dest->mask.v6;
 
 			int i;
 			for (i = 0; i < 4; i++)
@@ -700,7 +672,7 @@ fw3_ipt_rule_src_dest(struct fw3_ipt_rule *r,
 		else
 		{
 			r->e.ip.dst = dest->address.v4;
-			ip4prefix2mask(dest->mask, &r->e.ip.dmsk);
+			r->e.ip.dmsk = dest->mask.v4;
 
 			r->e.ip.dst.s_addr &= r->e.ip.dmsk.s_addr;
 
@@ -1003,7 +975,7 @@ fw3_ipt_rule_extra(struct fw3_ipt_rule *r, const char *extra)
 static void
 rule_print6(struct ip6t_entry *e)
 {
-	char buf[INET6_ADDRSTRLEN];
+	char buf1[INET6_ADDRSTRLEN], buf2[INET6_ADDRSTRLEN];
 	char *pname;
 
 	if (e->ipv6.flags & IP6T_F_PROTO)
@@ -1040,8 +1012,9 @@ rule_print6(struct ip6t_entry *e)
 		if (e->ipv6.flags & IP6T_INV_SRCIP)
 			printf(" !");
 
-		printf(" -s %s/%u", inet_ntop(AF_INET6, &e->ipv6.src, buf, sizeof(buf)),
-		                    xtables_ip6mask_to_cidr(&e->ipv6.smsk));
+		printf(" -s %s/%s",
+		       inet_ntop(AF_INET6, &e->ipv6.src, buf1, sizeof(buf1)),
+		       inet_ntop(AF_INET6, &e->ipv6.smsk, buf2, sizeof(buf2)));
 	}
 
 	if (memcmp(&e->ipv6.dst, &in6addr_any, sizeof(struct in6_addr)))
@@ -1049,8 +1022,9 @@ rule_print6(struct ip6t_entry *e)
 		if (e->ipv6.flags & IP6T_INV_DSTIP)
 			printf(" !");
 
-		printf(" -d %s/%u", inet_ntop(AF_INET6, &e->ipv6.dst, buf, sizeof(buf)),
-		                    xtables_ip6mask_to_cidr(&e->ipv6.dmsk));
+		printf(" -d %s/%s",
+		       inet_ntop(AF_INET6, &e->ipv6.dst, buf1, sizeof(buf1)),
+		       inet_ntop(AF_INET6, &e->ipv6.dmsk, buf2, sizeof(buf2)));
 	}
 }
 #endif
@@ -1059,7 +1033,7 @@ static void
 rule_print4(struct ipt_entry *e)
 {
 	struct in_addr in_zero = { 0 };
-	char buf[sizeof("255.255.255.255\0")];
+	char buf1[sizeof("255.255.255.255\0")], buf2[sizeof("255.255.255.255\0")];
 	char *pname;
 
 	if (e->ip.proto)
@@ -1096,8 +1070,9 @@ rule_print4(struct ipt_entry *e)
 		if (e->ip.flags & IPT_INV_SRCIP)
 			printf(" !");
 
-		printf(" -s %s/%u", inet_ntop(AF_INET, &e->ip.src, buf, sizeof(buf)),
-		                    xtables_ipmask_to_cidr(&e->ip.smsk));
+		printf(" -s %s/%s",
+		       inet_ntop(AF_INET, &e->ip.src, buf1, sizeof(buf1)),
+		       inet_ntop(AF_INET, &e->ip.smsk, buf2, sizeof(buf2)));
 	}
 
 	if (memcmp(&e->ip.dst, &in_zero, sizeof(struct in_addr)))
@@ -1105,8 +1080,9 @@ rule_print4(struct ipt_entry *e)
 		if (e->ip.flags & IPT_INV_DSTIP)
 			printf(" !");
 
-		printf(" -d %s/%u", inet_ntop(AF_INET, &e->ip.dst, buf, sizeof(buf)),
-		                    xtables_ipmask_to_cidr(&e->ip.dmsk));
+		printf(" -d %s/%s",
+		       inet_ntop(AF_INET, &e->ip.dst, buf1, sizeof(buf1)),
+		       inet_ntop(AF_INET, &e->ip.dmsk, buf2, sizeof(buf2)));
 	}
 }