[NETFILTER]: Add IPv6 REJECT target

Originally written by Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>,
taken from netfilter patch-o-matic and fixed up to work with current
kernels.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv6/ip6t_REJECT.h

+#ifndef _IP6T_REJECT_H
+#define _IP6T_REJECT_H
+
+enum ip6t_reject_with {
+	IP6T_ICMP6_NO_ROUTE,
+	IP6T_ICMP6_ADM_PROHIBITED,
+	IP6T_ICMP6_NOT_NEIGHBOUR,
+	IP6T_ICMP6_ADDR_UNREACH,
+	IP6T_ICMP6_PORT_UNREACH,
+	IP6T_ICMP6_ECHOREPLY,
+	IP6T_TCP_RESET
+};
+
+struct ip6t_reject_info {
+	u_int32_t	with;	/* reject type */
+};
+
+#endif /*_IP6T_REJECT_H*/

net/ipv6/netfilter/Kconfig

@@ -199,6 +199,16 @@ config IP6_NF_TARGET_LOG
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config IP6_NF_TARGET_REJECT
+	tristate "REJECT target support"
+	depends on IP6_NF_FILTER
+	help
+	  The REJECT target allows a filtering rule to specify that an ICMPv6
+	  error should be issued in response to an incoming packet, rather
+	  than silently being dropped.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 #  if [ "$CONFIG_IP6_NF_FILTER" != "n" ]; then
 #    dep_tristate '    REJECT target support' CONFIG_IP6_NF_TARGET_REJECT $CONFIG_IP6_NF_FILTER
 #    if [ "$CONFIG_EXPERIMENTAL" = "y" ]; then

net/ipv6/netfilter/Makefile

@@ -24,4 +24,5 @@ obj-$(CONFIG_IP6_NF_QUEUE) += ip6_queue.o
 obj-$(CONFIG_IP6_NF_TARGET_LOG) += ip6t_LOG.o
 obj-$(CONFIG_IP6_NF_RAW) += ip6table_raw.o
 obj-$(CONFIG_IP6_NF_MATCH_HL) += ip6t_hl.o
+obj-$(CONFIG_IP6_NF_TARGET_REJECT) += ip6t_REJECT.o
 obj-$(CONFIG_NETFILTER_NETLINK_QUEUE) += ip6t_NFQUEUE.o

net/ipv6/netfilter/ip6t_REJECT.c

+/*
+ * IP6 tables REJECT target module
+ * Linux INET6 implementation
+ *
+ * Copyright (C)2003 USAGI/WIDE Project
+ *
+ * Authors:
+ *	Yasuyuki Kozakai	<yasuyuki.kozakai@toshiba.co.jp>
+ *
+ * Based on net/ipv4/netfilter/ipt_REJECT.c
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/icmpv6.h>
+#include <linux/netdevice.h>
+#include <net/ipv6.h>
+#include <net/tcp.h>
+#include <net/icmp.h>
+#include <net/ip6_checksum.h>
+#include <net/ip6_fib.h>
+#include <net/ip6_route.h>
+#include <net/flow.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter_ipv6/ip6t_REJECT.h>
+
+MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
+MODULE_DESCRIPTION("IP6 tables REJECT target module");
+MODULE_LICENSE("GPL");
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+/* Send RST reply */
+static void send_reset(struct sk_buff *oldskb)
+{
+	struct sk_buff *nskb;
+	struct tcphdr otcph, *tcph;
+	unsigned int otcplen, hh_len;
+	int tcphoff, needs_ack;
+	struct ipv6hdr *oip6h = oldskb->nh.ipv6h, *ip6h;
+	struct dst_entry *dst = NULL;
+	u8 proto;
+	struct flowi fl;
+
+	if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
+	    (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
+		DEBUGP("ip6t_REJECT: addr is not unicast.\n");
+		return;
+	}
+
+	proto = oip6h->nexthdr;
+	tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
+
+	if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
+		DEBUGP("ip6t_REJECT: Can't get TCP header.\n");
+		return;
+	}
+
+	otcplen = oldskb->len - tcphoff;
+
+	/* IP header checks: fragment, too short. */
+	if ((proto != IPPROTO_TCP) || (otcplen < sizeof(struct tcphdr))) {
+		DEBUGP("ip6t_REJECT: proto(%d) != IPPROTO_TCP, or too short. otcplen = %d\n",
+			proto, otcplen);
+		return;
+	}
+
+	if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
+		BUG();
+
+	/* No RST for RST. */
+	if (otcph.rst) {
+		DEBUGP("ip6t_REJECT: RST is set\n");
+		return;
+	}
+
+	/* Check checksum. */
+	if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
+			    skb_checksum(oldskb, tcphoff, otcplen, 0))) {
+		DEBUGP("ip6t_REJECT: TCP checksum is invalid\n");
+		return;
+	}
+
+	memset(&fl, 0, sizeof(fl));
+	fl.proto = IPPROTO_TCP;
+	ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
+	ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
+	fl.fl_ip_sport = otcph.dest;
+	fl.fl_ip_dport = otcph.source;
+	dst = ip6_route_output(NULL, &fl);
+	if (dst == NULL)
+		return;
+	if (dst->error ||
+	    xfrm_lookup(&dst, &fl, NULL, 0)) {
+		dst_release(dst);
+		return;
+	}
+
+	hh_len = (dst->dev->hard_header_len + 15)&~15;
+	nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
+			 + sizeof(struct tcphdr) + dst->trailer_len,
+			 GFP_ATOMIC);
+
+	if (!nskb) {
+		if (net_ratelimit())
+			printk("ip6t_REJECT: Can't alloc skb\n");
+		dst_release(dst);
+		return;
+	}
+
+	nskb->dst = dst;
+
+	skb_reserve(nskb, hh_len + dst->header_len);
+
+	ip6h = nskb->nh.ipv6h = (struct ipv6hdr *)
+					skb_put(nskb, sizeof(struct ipv6hdr));
+	ip6h->version = 6;
+	ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
+	ip6h->nexthdr = IPPROTO_TCP;
+	ip6h->payload_len = htons(sizeof(struct tcphdr));
+	ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
+	ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
+
+	tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
+	/* Truncate to length (no data) */
+	tcph->doff = sizeof(struct tcphdr)/4;
+	tcph->source = otcph.dest;
+	tcph->dest = otcph.source;
+
+	if (otcph.ack) {
+		needs_ack = 0;
+		tcph->seq = otcph.ack_seq;
+		tcph->ack_seq = 0;
+	} else {
+		needs_ack = 1;
+		tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
+				      + otcplen - (otcph.doff<<2));
+		tcph->seq = 0;
+	}
+
+	/* Reset flags */
+	((u_int8_t *)tcph)[13] = 0;
+	tcph->rst = 1;
+	tcph->ack = needs_ack;
+	tcph->window = 0;
+	tcph->urg_ptr = 0;
+	tcph->check = 0;
+
+	/* Adjust TCP checksum */
+	tcph->check = csum_ipv6_magic(&nskb->nh.ipv6h->saddr,
+				      &nskb->nh.ipv6h->daddr,
+				      sizeof(struct tcphdr), IPPROTO_TCP,
+				      csum_partial((char *)tcph,
+						   sizeof(struct tcphdr), 0));
+
+	NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
+		dst_output);
+}
+
+static inline void
+send_unreach(struct sk_buff *skb_in, unsigned char code, unsigned int hooknum)
+{
+	if (hooknum == NF_IP6_LOCAL_OUT && skb_in->dev == NULL)
+		skb_in->dev = &loopback_dev;
+
+	icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
+}
+
+static unsigned int reject6_target(struct sk_buff **pskb,
+			   const struct net_device *in,
+			   const struct net_device *out,
+			   unsigned int hooknum,
+			   const void *targinfo,
+			   void *userinfo)
+{
+	const struct ip6t_reject_info *reject = targinfo;
+
+	DEBUGP(KERN_DEBUG "%s: medium point\n", __FUNCTION__);
+	/* WARNING: This code causes reentry within ip6tables.
+	   This means that the ip6tables jump stack is now crap.  We
+	   must return an absolute verdict. --RR */
+    	switch (reject->with) {
+    	case IP6T_ICMP6_NO_ROUTE:
+    		send_unreach(*pskb, ICMPV6_NOROUTE, hooknum);
+    		break;
+    	case IP6T_ICMP6_ADM_PROHIBITED:
+    		send_unreach(*pskb, ICMPV6_ADM_PROHIBITED, hooknum);
+    		break;
+    	case IP6T_ICMP6_NOT_NEIGHBOUR:
+    		send_unreach(*pskb, ICMPV6_NOT_NEIGHBOUR, hooknum);
+    		break;
+    	case IP6T_ICMP6_ADDR_UNREACH:
+    		send_unreach(*pskb, ICMPV6_ADDR_UNREACH, hooknum);
+    		break;
+    	case IP6T_ICMP6_PORT_UNREACH:
+    		send_unreach(*pskb, ICMPV6_PORT_UNREACH, hooknum);
+    		break;
+    	case IP6T_ICMP6_ECHOREPLY:
+		/* Do nothing */
+		break;
+	case IP6T_TCP_RESET:
+		send_reset(*pskb);
+		break;
+	default:
+		if (net_ratelimit())
+			printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
+		break;
+	}
+
+	return NF_DROP;
+}
+
+static int check(const char *tablename,
+		 const struct ip6t_entry *e,
+		 void *targinfo,
+		 unsigned int targinfosize,
+		 unsigned int hook_mask)
+{
+ 	const struct ip6t_reject_info *rejinfo = targinfo;
+
+ 	if (targinfosize != IP6T_ALIGN(sizeof(struct ip6t_reject_info))) {
+  		DEBUGP("ip6t_REJECT: targinfosize %u != 0\n", targinfosize);
+  		return 0;
+  	}
+
+	/* Only allow these for packet filtering. */
+	if (strcmp(tablename, "filter") != 0) {
+		DEBUGP("ip6t_REJECT: bad table `%s'.\n", tablename);
+		return 0;
+	}
+
+	if ((hook_mask & ~((1 << NF_IP6_LOCAL_IN)
+			   | (1 << NF_IP6_FORWARD)
+			   | (1 << NF_IP6_LOCAL_OUT))) != 0) {
+		DEBUGP("ip6t_REJECT: bad hook mask %X\n", hook_mask);
+		return 0;
+	}
+
+	if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
+		printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
+		return 0;
+	} else if (rejinfo->with == IP6T_TCP_RESET) {
+		/* Must specify that it's a TCP packet */
+		if (e->ipv6.proto != IPPROTO_TCP
+		    || (e->ipv6.invflags & IP6T_INV_PROTO)) {
+			DEBUGP("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
+static struct ip6t_target ip6t_reject_reg = {
+	.name		= "REJECT",
+	.target		= reject6_target,
+	.checkentry	= check,
+	.me		= THIS_MODULE
+};
+
+static int __init init(void)
+{
+	if (ip6t_register_target(&ip6t_reject_reg))
+		return -EINVAL;
+	return 0;
+}
+
+static void __exit fini(void)
+{
+	ip6t_unregister_target(&ip6t_reject_reg);
+}
+
+module_init(init);
+module_exit(fini);