/* * This is a module which is used for rejecting packets. * Added support for customized reject packets (Jozsef Kadlecsik). * Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812] *//* (C) 1999-2001 Paul `Rusty' Russell * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */#include <linux/config.h>#include <linux/module.h>#include <linux/skbuff.h>#include <linux/ip.h>#include <linux/udp.h>#include <linux/icmp.h>#include <net/icmp.h>#include <net/ip.h>#include <net/tcp.h>#include <net/route.h>#include <linux/netfilter_ipv4/ip_tables.h>#include <linux/netfilter_ipv4/ipt_REJECT.h>#ifdef CONFIG_BRIDGE_NETFILTER#include <linux/netfilter_bridge.h>#endifMODULE_LICENSE("GPL");MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");MODULE_DESCRIPTION("iptables REJECT target module");#if 0#define DEBUGP printk#else#define DEBUGP(format, args...)#endif/* If the original packet is part of a connection, but the connection   is not confirmed, our manufactured reply will not be associated   with it, so we need to do this manually. */static void connection_attach(struct sk_buff *new_skb, struct nf_ct_info *nfct){	void (*attach)(struct sk_buff *, struct nf_ct_info *);	/* Avoid module unload race with ip_ct_attach being NULLed out */	if (nfct && (attach = ip_ct_attach) != NULL) {		mb(); /* Just to be sure: must be read before executing this */		attach(new_skb, nfct);	}}static inline struct rtable *route_reverse(struct sk_buff *skb, int hook){	struct iphdr *iph = skb->nh.iph;	struct dst_entry *odst;	struct flowi fl = {};	struct rtable *rt;	/* We don't require ip forwarding to be enabled to be able to	 * send a RST reply for bridged traffic. */	if (hook != NF_IP_FORWARD#ifdef CONFIG_BRIDGE_NETFILTER	    || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)#endif	   ) {		fl.nl_u.ip4_u.daddr = iph->saddr;		if (hook == NF_IP_LOCAL_IN)			fl.nl_u.ip4_u.saddr = iph->daddr;		fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);		if (ip_route_output_key(&rt, &fl) != 0)			return NULL;	} else {		/* non-local src, find valid iif to satisfy		 * rp-filter when calling ip_route_input. */		fl.nl_u.ip4_u.daddr = iph->daddr;		if (ip_route_output_key(&rt, &fl) != 0)			return NULL;		odst = skb->dst;		if (ip_route_input(skb, iph->saddr, iph->daddr,		                   RT_TOS(iph->tos), rt->u.dst.dev) != 0) {			dst_release(&rt->u.dst);			return NULL;		}		dst_release(&rt->u.dst);		rt = (struct rtable *)skb->dst;		skb->dst = odst;	}	if (rt->u.dst.error) {		dst_release(&rt->u.dst);		rt = NULL;	}	return rt;}/* Send RST reply */static void send_reset(struct sk_buff *oldskb, int hook){	struct sk_buff *nskb;	struct tcphdr otcph, *tcph;	struct rtable *rt;	u_int16_t tmp_port;	u_int32_t tmp_addr;	int needs_ack;	int hh_len;	/* IP header checks: fragment. */	if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))		return;	if (skb_copy_bits(oldskb, oldskb->nh.iph->ihl*4,			  &otcph, sizeof(otcph)) < 0) 		return;	/* No RST for RST. */	if (otcph.rst)		return;	/* FIXME: Check checksum --RR */	if ((rt = route_reverse(oldskb, hook)) == NULL)		return;	hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);	/* We need a linear, writeable skb.  We also need to expand	   headroom in case hh_len of incoming interface < hh_len of	   outgoing interface */	nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),			       GFP_ATOMIC);	if (!nskb) {		dst_release(&rt->u.dst);		return;	}	dst_release(nskb->dst);	nskb->dst = &rt->u.dst;	/* This packet will not be the same as the other: clear nf fields */	nf_reset(nskb);	nskb->nfcache = 0;	nskb->nfmark = 0;#ifdef CONFIG_BRIDGE_NETFILTER	nf_bridge_put(nskb->nf_bridge);	nskb->nf_bridge = NULL;#endif	tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);	/* Swap source and dest */	tmp_addr = nskb->nh.iph->saddr;	nskb->nh.iph->saddr = nskb->nh.iph->daddr;	nskb->nh.iph->daddr = tmp_addr;	tmp_port = tcph->source;	tcph->source = tcph->dest;	tcph->dest = tmp_port;	/* Truncate to length (no data) */	tcph->doff = sizeof(struct tcphdr)/4;	skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));	nskb->nh.iph->tot_len = htons(nskb->len);	if (tcph->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				      + oldskb->len - oldskb->nh.iph->ihl*4				      - (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;	/* Adjust TCP checksum */	tcph->check = 0;	tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),				   nskb->nh.iph->saddr,				   nskb->nh.iph->daddr,				   csum_partial((char *)tcph,						sizeof(struct tcphdr), 0));	/* Adjust IP TTL, DF */	nskb->nh.iph->ttl = MAXTTL;	/* Set DF, id = 0 */	nskb->nh.iph->frag_off = htons(IP_DF);	nskb->nh.iph->id = 0;	/* Adjust IP checksum */	nskb->nh.iph->check = 0;	nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph, 					   nskb->nh.iph->ihl);	/* "Never happens" */	if (nskb->len > dst_pmtu(nskb->dst))		goto free_nskb;	connection_attach(nskb, oldskb->nfct);	NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,		ip_finish_output);	return; free_nskb:	kfree_skb(nskb);}static void send_unreach(struct sk_buff *skb_in, int code){	struct iphdr *iph;	struct udphdr *udph;	struct icmphdr *icmph;	struct sk_buff *nskb;	u32 saddr;	u8 tos;	int hh_len, length;	struct rtable *rt = (struct rtable*)skb_in->dst;	unsigned char *data;	if (!rt)		return;	/* FIXME: Use sysctl number. --RR */	if (!xrlim_allow(&rt->u.dst, 1*HZ))		return;	iph = skb_in->nh.iph;	/* No replies to physical multicast/broadcast */	if (skb_in->pkt_type!=PACKET_HOST)		return;	/* Now check at the protocol level */	if (rt->rt_flags&(RTCF_BROADCAST|RTCF_MULTICAST))		return;	/* Only reply to fragment 0. */	if (iph->frag_off&htons(IP_OFFSET))		return;	/* Ensure we have at least 8 bytes of proto header. */	if (skb_in->len < skb_in->nh.iph->ihl*4 + 8)		return;	/* if UDP checksum is set, verify it's correct */	if (iph->protocol == IPPROTO_UDP	    && skb_in->tail-(u8*)iph >= sizeof(struct udphdr)) {		int datalen = skb_in->len - (iph->ihl<<2);		udph = (struct udphdr *)((char *)iph + (iph->ihl<<2));		if (udph->check		    && csum_tcpudp_magic(iph->saddr, iph->daddr,		                         datalen, IPPROTO_UDP,		                         csum_partial((char *)udph, datalen,		                                      0)) != 0)			return;	}	/* If we send an ICMP error to an ICMP error a mess would result.. */	if (iph->protocol == IPPROTO_ICMP	    && skb_in->tail-(u8*)iph >= sizeof(struct icmphdr)) {		icmph = (struct icmphdr *)((char *)iph + (iph->ihl<<2));		if (skb_copy_bits(skb_in, skb_in->nh.iph->ihl*4,				  icmph, sizeof(*icmph)) < 0)			return;		/* Between echo-reply (0) and timestamp (13),		   everything except echo-request (8) is an error.		   Also, anything greater than NR_ICMP_TYPES is		   unknown, and hence should be treated as an error... */		if ((icmph->type < ICMP_TIMESTAMP		     && icmph->type != ICMP_ECHOREPLY		     && icmph->type != ICMP_ECHO)		    || icmph->type > NR_ICMP_TYPES)			return;	}	saddr = iph->daddr;	if (!(rt->rt_flags & RTCF_LOCAL))		saddr = 0;	tos = (iph->tos & IPTOS_TOS_MASK) | IPTOS_PREC_INTERNETCONTROL;	{		struct flowi fl = { .nl_u = { .ip4_u =					      { .daddr = skb_in->nh.iph->saddr,						.saddr = saddr,						.tos = RT_TOS(tos) } } };		if (ip_route_output_key(&rt, &fl))			return;	}	/* RFC says return as much as we can without exceeding 576 bytes. */	length = skb_in->len + sizeof(struct iphdr) + sizeof(struct icmphdr);	if (length > dst_pmtu(&rt->u.dst))		length = dst_pmtu(&rt->u.dst);	if (length > 576)		length = 576;	hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);	nskb = alloc_skb(hh_len + length, GFP_ATOMIC);	if (!nskb) {		ip_rt_put(rt);		return;	}	nskb->priority = 0;	nskb->dst = &rt->u.dst;	skb_reserve(nskb, hh_len);	/* Set up IP header */	iph = nskb->nh.iph		= (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));	iph->version=4;	iph->ihl=5;	iph->tos=tos;	iph->tot_len = htons(length);	/* PMTU discovery never applies to ICMP packets. */	iph->frag_off = 0;	iph->ttl = MAXTTL;	ip_select_ident(iph, &rt->u.dst, NULL);	iph->protocol=IPPROTO_ICMP;	iph->saddr=rt->rt_src;	iph->daddr=rt->rt_dst;	iph->check=0;	iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);	/* Set up ICMP header. */	icmph = nskb->h.icmph		= (struct icmphdr *)skb_put(nskb, sizeof(struct icmphdr));	icmph->type = ICMP_DEST_UNREACH;	icmph->code = code;		icmph->un.gateway = 0;	icmph->checksum = 0;		/* Copy as much of original packet as will fit */	data = skb_put(nskb,		       length - sizeof(struct iphdr) - sizeof(struct icmphdr));	skb_copy_bits(skb_in, 0, data,		      length - sizeof(struct iphdr) - sizeof(struct icmphdr));	icmph->checksum = ip_compute_csum((unsigned char *)icmph,					  length - sizeof(struct iphdr));	connection_attach(nskb, skb_in->nfct);	NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,		ip_finish_output);}	static unsigned int reject(struct sk_buff **pskb,			   const struct net_device *in,			   const struct net_device *out,			   unsigned int hooknum,			   const void *targinfo,			   void *userinfo){	const struct ipt_reject_info *reject = targinfo;	/* Our naive response construction doesn't deal with IP           options, and probably shouldn't try. */	if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))		return NF_DROP;	/* WARNING: This code causes reentry within iptables.	   This means that the iptables jump stack is now crap.  We	   must return an absolute verdict. --RR */    	switch (reject->with) {    	case IPT_ICMP_NET_UNREACHABLE:    		send_unreach(*pskb, ICMP_NET_UNREACH);    		break;    	case IPT_ICMP_HOST_UNREACHABLE:    		send_unreach(*pskb, ICMP_HOST_UNREACH);    		break;    	case IPT_ICMP_PROT_UNREACHABLE:    		send_unreach(*pskb, ICMP_PROT_UNREACH);    		break;    	case IPT_ICMP_PORT_UNREACHABLE:    		send_unreach(*pskb, ICMP_PORT_UNREACH);    		break;    	case IPT_ICMP_NET_PROHIBITED:    		send_unreach(*pskb, ICMP_NET_ANO);    		break;	case IPT_ICMP_HOST_PROHIBITED:    		send_unreach(*pskb, ICMP_HOST_ANO);    		break;    	case IPT_ICMP_ADMIN_PROHIBITED:		send_unreach(*pskb, ICMP_PKT_FILTERED);		break;	case IPT_TCP_RESET:		send_reset(*pskb, hooknum);	case IPT_ICMP_ECHOREPLY:		/* Doesn't happen. */		break;	}	return NF_DROP;}static int check(const char *tablename,		 const struct ipt_entry *e,		 void *targinfo,		 unsigned int targinfosize,		 unsigned int hook_mask){ 	const struct ipt_reject_info *rejinfo = targinfo; 	if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) {  		DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize);  		return 0;  	}	/* Only allow these for packet filtering. */	if (strcmp(tablename, "filter") != 0) {		DEBUGP("REJECT: bad table `%s'.\n", tablename);		return 0;	}	if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)			   | (1 << NF_IP_FORWARD)			   | (1 << NF_IP_LOCAL_OUT))) != 0) {		DEBUGP("REJECT: bad hook mask %X\n", hook_mask);		return 0;	}	if (rejinfo->with == IPT_ICMP_ECHOREPLY) {		printk("REJECT: ECHOREPLY no longer supported.\n");		return 0;	} else if (rejinfo->with == IPT_TCP_RESET) {		/* Must specify that it's a TCP packet */		if (e->ip.proto != IPPROTO_TCP		    || (e->ip.invflags & IPT_INV_PROTO)) {			DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");			return 0;		}	}	return 1;}static struct ipt_target ipt_reject_reg = {	.name		= "REJECT",	.target		= reject,	.checkentry	= check,	.me		= THIS_MODULE,};static int __init init(void){	return ipt_register_target(&ipt_reject_reg);}static void __exit fini(void){	ipt_unregister_target(&ipt_reject_reg);}module_init(init);module_exit(fini);