[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>

3 files changed, 295 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index cd1551983c63..8a10c2d0d154 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/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
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index 847651dbcd2a..70f6ba610102 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/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
diff --git a/net/ipv6/netfilter/ip6t_REJECT.c b/net/ipv6/netfilter/ip6t_REJECT.c
new file mode 100644
index 000000000000..14316c3ebde4
--- /dev/null
+++ b/net/ipv6/netfilter/ip6t_REJECT.c
@@ -0,0 +1,284 @@
+/*
+ * 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);