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/*
 *	NET3:	Implementation of the ICMP protocol layer. 
 *	
 *		Alan Cox, <alan@redhat.com>
 *
 *	Version: $Id: icmp.c,v 1.1.1.1 2004-04-15 01:13:46 phoenix Exp $
 *
 *	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.
 *
 *	Some of the function names and the icmp unreach table for this
 *	module were derived from [icmp.c 1.0.11 06/02/93] by
 *	Ross Biro, Fred N. van Kempen, Mark Evans, Alan Cox, Gerhard Koerting.
 *	Other than that this module is a complete rewrite.
 *
 *	Fixes:
 *	Clemens Fruhwirth	:	introduce global icmp rate limiting
 *					with icmp type masking ability instead
 *					of broken per type icmp timeouts.
 *		Mike Shaver	:	RFC1122 checks.
 *		Alan Cox	:	Multicast ping reply as self.
 *		Alan Cox	:	Fix atomicity lockup in ip_build_xmit 
 *					call.
 *		Alan Cox	:	Added 216,128 byte paths to the MTU 
 *					code.
 *		Martin Mares	:	RFC1812 checks.
 *		Martin Mares	:	Can be configured to follow redirects 
 *					if acting as a router _without_ a
 *					routing protocol (RFC 1812).
 *		Martin Mares	:	Echo requests may be configured to 
 *					be ignored (RFC 1812).
 *		Martin Mares	:	Limitation of ICMP error message 
 *					transmit rate (RFC 1812).
 *		Martin Mares	:	TOS and Precedence set correctly 
 *					(RFC 1812).
 *		Martin Mares	:	Now copying as much data from the 
 *					original packet as we can without
 *					exceeding 576 bytes (RFC 1812).
 *	Willy Konynenberg	:	Transparent proxying support.
 *		Keith Owens	:	RFC1191 correction for 4.2BSD based 
 *					path MTU bug.
 *		Thomas Quinot	:	ICMP Dest Unreach codes up to 15 are
 *					valid (RFC 1812).
 *		Andi Kleen	:	Check all packet lengths properly
 *					and moved all kfree_skb() up to
 *					icmp_rcv.
 *		Andi Kleen	:	Move the rate limit bookkeeping
 *					into the dest entry and use a token
 *					bucket filter (thanks to ANK). Make
 *					the rates sysctl configurable.
 *		Yu Tianli	:	Fixed two ugly bugs in icmp_send
 *					- IP option length was accounted wrongly
 *					- ICMP header length was not accounted at all.
 *              Tristan Greaves :       Added sysctl option to ignore bogus broadcast
 *                                      responses from broken routers.
 *
 * To Fix:
 *
 *	- Should use skb_pull() instead of all the manual checking.
 *	  This would also greatly simply some upper layer error handlers. --AK
 *
 */
 
#include <linux/config.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/fcntl.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/string.h>
#include <linux/netfilter_ipv4.h>
#include <net/snmp.h>
#include <net/ip.h>
#include <net/route.h>
#include <net/protocol.h>
#include <net/icmp.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/raw.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/init.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <net/checksum.h>
 
/*
 *	Build xmit assembly blocks
 */
 
struct icmp_bxm
{
	struct sk_buff *skb;
	int offset;
	int data_len;
 
	unsigned int csum;
	struct {
		struct icmphdr icmph;
		__u32	       times[3];
	} data;
	int head_len;
	struct ip_options replyopts;
	unsigned char  optbuf[40];
};
 
/*
 *	Statistics
 */
 
struct icmp_mib icmp_statistics[NR_CPUS*2];
 
/* An array of errno for error messages from dest unreach. */
/* RFC 1122: 3.2.2.1 States that NET_UNREACH, HOS_UNREACH and SR_FAIELD MUST be considered 'transient errs'. */
 
struct icmp_err icmp_err_convert[] = {
  { ENETUNREACH,	0 },	/*	ICMP_NET_UNREACH	*/
  { EHOSTUNREACH,	0 },	/*	ICMP_HOST_UNREACH	*/
  { ENOPROTOOPT,	1 },	/*	ICMP_PROT_UNREACH	*/
  { ECONNREFUSED,	1 },	/*	ICMP_PORT_UNREACH	*/
  { EMSGSIZE,		0 },	/*	ICMP_FRAG_NEEDED	*/
  { EOPNOTSUPP,		0 },	/*	ICMP_SR_FAILED		*/
  { ENETUNREACH,	1 },	/* 	ICMP_NET_UNKNOWN	*/
  { EHOSTDOWN,		1 },	/*	ICMP_HOST_UNKNOWN	*/
  { ENONET,		1 },	/*	ICMP_HOST_ISOLATED	*/
  { ENETUNREACH,	1 },	/*	ICMP_NET_ANO		*/
  { EHOSTUNREACH,	1 },	/*	ICMP_HOST_ANO		*/
  { ENETUNREACH,	0 },	/*	ICMP_NET_UNR_TOS	*/
  { EHOSTUNREACH,	0 },	/*	ICMP_HOST_UNR_TOS	*/
  { EHOSTUNREACH,	1 },	/*	ICMP_PKT_FILTERED	*/
  { EHOSTUNREACH,	1 },	/*	ICMP_PREC_VIOLATION	*/
  { EHOSTUNREACH,	1 }	/*	ICMP_PREC_CUTOFF	*/
};
 
extern int sysctl_ip_default_ttl;
 
/* Control parameters for ECHO replies. */
int sysctl_icmp_echo_ignore_all;
int sysctl_icmp_echo_ignore_broadcasts;
 
/* Control parameter - ignore bogus broadcast responses? */
int sysctl_icmp_ignore_bogus_error_responses;
 
/* 
 * 	Configurable global rate limit.
 *
 *	ratelimit defines tokens/packet consumed for dst->rate_token bucket
 *	ratemask defines which icmp types are ratelimited by setting
 * 	it's bit position.
 *
 *	default: 
 *	dest unreachable (3), source quench (4),
 *	time exceeded (11), parameter problem (12)
 */
 
int sysctl_icmp_ratelimit = 1*HZ;
int sysctl_icmp_ratemask = 0x1818;
 
/*
 *	ICMP control array. This specifies what to do with each ICMP.
 */
 
struct icmp_control
{
	unsigned long *output;		/* Address to increment on output */
	unsigned long *input;		/* Address to increment on input */
	void (*handler)(struct sk_buff *skb);
	short	error;		/* This ICMP is classed as an error message */
};
 
static struct icmp_control icmp_pointers[NR_ICMP_TYPES+1];
 
/*
 *	The ICMP socket(s). This is the most convenient way to flow control
 *	our ICMP output as well as maintain a clean interface throughout
 *	all layers. All Socketless IP sends will soon be gone.
 */
 
static struct inode __icmp_inode[NR_CPUS];
#define icmp_socket (&__icmp_inode[smp_processor_id()].u.socket_i)
#define icmp_socket_cpu(X) (&__icmp_inode[(X)].u.socket_i)
 
static int icmp_xmit_lock(void)
{
	local_bh_disable();
	if (unlikely(!spin_trylock(&icmp_socket->sk->lock.slock))) {
		/* This can happen if the output path signals a
		 * dst_link_failure() for an outgoing ICMP packet.
		 */
		local_bh_enable();
		return 1;
	}
	return 0;
}
 
static void icmp_xmit_unlock(void)
{
	spin_unlock_bh(&icmp_socket->sk->lock.slock);
}
 
/*
 *	Send an ICMP frame.
 */
 
/*
 *	Check transmit rate limitation for given message.
 *	The rate information is held in the destination cache now.
 *	This function is generic and could be used for other purposes
 *	too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
 *
 *	Note that the same dst_entry fields are modified by functions in 
 *	route.c too, but these work for packet destinations while xrlim_allow
 *	works for icmp destinations. This means the rate limiting information
 *	for one "ip object" is shared - and these ICMPs are twice limited:
 *	by source and by destination.
 *
 *	RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
 *			  SHOULD allow setting of rate limits 
 *
 * 	Shared between ICMPv4 and ICMPv6.
 */
#define XRLIM_BURST_FACTOR 6
int xrlim_allow(struct dst_entry *dst, int timeout)
{
	unsigned long now;
 
	now = jiffies;
	dst->rate_tokens += now - dst->rate_last;
	dst->rate_last = now;
	if (dst->rate_tokens > XRLIM_BURST_FACTOR*timeout)
        	dst->rate_tokens = XRLIM_BURST_FACTOR*timeout;
	if (dst->rate_tokens >= timeout) {
		dst->rate_tokens -= timeout;
		return 1;
	}
	return 0; 
}
 
static inline int icmpv4_xrlim_allow(struct rtable *rt, int type, int code)
{
	struct dst_entry *dst = &rt->u.dst; 
 
	if (type > NR_ICMP_TYPES)
		return 1;
 
	/* Don't limit PMTU discovery. */
	if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED)
		return 1;
 
	/* No rate limit on loopback */
	if (dst->dev && (dst->dev->flags&IFF_LOOPBACK))
 		return 1;
 
	/* Limit if icmp type is enabled in ratemask. */
	if((1 << type) & sysctl_icmp_ratemask)
		return xrlim_allow(dst, sysctl_icmp_ratelimit);
	else
		return 1;
}
 
/*
 *	Maintain the counters used in the SNMP statistics for outgoing ICMP
 */
 
static void icmp_out_count(int type)
{
	if (type>NR_ICMP_TYPES)
		return;
	(icmp_pointers[type].output)[(smp_processor_id()*2+!in_softirq())*sizeof(struct icmp_mib)/sizeof(unsigned long)]++;
	ICMP_INC_STATS(IcmpOutMsgs);
}
 
/*
 *	Checksum each fragment, and on the first include the headers and final checksum.
 */
 
static int icmp_glue_bits(const void *p, char *to, unsigned int offset, unsigned int fraglen)
{
	struct icmp_bxm *icmp_param = (struct icmp_bxm *)p;
	struct icmphdr *icmph;
	unsigned int csum;
 
	if (offset) {
		icmp_param->csum=skb_copy_and_csum_bits(icmp_param->skb,
							icmp_param->offset+(offset-icmp_param->head_len), 
							to, fraglen,icmp_param->csum);
		return 0;
	}
 
	/*
	 *	First fragment includes header. Note that we've done
	 *	the other fragments first, so that we get the checksum
	 *	for the whole packet here.
	 */
	csum = csum_partial_copy_nocheck((void *)&icmp_param->data,
		to, icmp_param->head_len,
		icmp_param->csum);
	csum=skb_copy_and_csum_bits(icmp_param->skb,
				    icmp_param->offset, 
				    to+icmp_param->head_len,
				    fraglen-icmp_param->head_len,
				    csum);
	icmph=(struct icmphdr *)to;
	icmph->checksum = csum_fold(csum);
	return 0;
}
 
/*
 *	Driving logic for building and sending ICMP messages.
 */
 
static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
{
	struct sock *sk=icmp_socket->sk;
	struct ipcm_cookie ipc;
	struct rtable *rt = (struct rtable*)skb->dst;
	u32 daddr;
 
	if (ip_options_echo(&icmp_param->replyopts, skb))
		return;
 
	if (icmp_xmit_lock())
		return;
 
	icmp_param->data.icmph.checksum=0;
	icmp_param->csum=0;
	icmp_out_count(icmp_param->data.icmph.type);
 
	sk->protinfo.af_inet.tos = skb->nh.iph->tos;
	sk->protinfo.af_inet.ttl = sysctl_ip_default_ttl;
	daddr = ipc.addr = rt->rt_src;
	ipc.opt = NULL;
	if (icmp_param->replyopts.optlen) {
		ipc.opt = &icmp_param->replyopts;
		if (ipc.opt->srr)
			daddr = icmp_param->replyopts.faddr;
	}
	if (ip_route_output(&rt, daddr, rt->rt_spec_dst, RT_TOS(skb->nh.iph->tos), 0))
		goto out;
	if (icmpv4_xrlim_allow(rt, icmp_param->data.icmph.type, 
			       icmp_param->data.icmph.code)) { 
		ip_build_xmit(sk, icmp_glue_bits, icmp_param, 
			      icmp_param->data_len+icmp_param->head_len,
			      &ipc, rt, MSG_DONTWAIT);
	}
	ip_rt_put(rt);
out:
	icmp_xmit_unlock();
}
 
 
/*
 *	Send an ICMP message in response to a situation
 *
 *	RFC 1122: 3.2.2	MUST send at least the IP header and 8 bytes of header. MAY send more (we do).
 *			MUST NOT change this header information.
 *			MUST NOT reply to a multicast/broadcast IP address.
 *			MUST NOT reply to a multicast/broadcast MAC address.
 *			MUST reply to only the first fragment.
 */
 
void icmp_send(struct sk_buff *skb_in, int type, int code, u32 info)
{
	struct iphdr *iph;
	int room;
	struct icmp_bxm icmp_param;
	struct rtable *rt = (struct rtable*)skb_in->dst;
	struct ipcm_cookie ipc;
	u32 saddr;
	u8  tos;
 
	if (!rt)
		return;
 
	/*
	 *	Find the original header. It is expected to be valid, of course.
	 *	Check this, icmp_send is called from the most obscure devices
	 *	sometimes.
	 */
	iph = skb_in->nh.iph;
 
	if ((u8*)iph < skb_in->head || (u8*)(iph+1) > skb_in->tail)
		return;
 
	/*
	 *	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. We byte re-order the constant
	 *	mask for efficiency.
	 */
	if (iph->frag_off&htons(IP_OFFSET))
		return;
 
	/* 
	 *	If we send an ICMP error to an ICMP error a mess would result..
	 */
	if (icmp_pointers[type].error) {
		/*
		 *	We are an error, check if we are replying to an ICMP error
		 */
		if (iph->protocol==IPPROTO_ICMP) {
			u8 inner_type;
 
			if (skb_copy_bits(skb_in,
					  skb_in->nh.raw + (iph->ihl<<2)
					  + offsetof(struct icmphdr, type)
					  - skb_in->data,
					  &inner_type, 1))
				return;
 
			/*
			 *	Assume any unknown ICMP type is an error. This isn't
			 *	specified by the RFC, but think about it..
			 */
			if (inner_type>NR_ICMP_TYPES || icmp_pointers[inner_type].error)
				return;
		}
	}
 
	if (icmp_xmit_lock())
		return;
 
	/*
	 *	Construct source address and options.
	 */
 
#ifdef CONFIG_IP_ROUTE_NAT	
	/*
	 *	Restore original addresses if packet has been translated.
	 */
	if (rt->rt_flags&RTCF_NAT && IPCB(skb_in)->flags&IPSKB_TRANSLATED) {
		iph->daddr = rt->key.dst;
		iph->saddr = rt->key.src;
	}
#endif
 
	saddr = iph->daddr;
	if (!(rt->rt_flags & RTCF_LOCAL))
		saddr = 0;
 
	tos = icmp_pointers[type].error ?
		((iph->tos & IPTOS_TOS_MASK) | IPTOS_PREC_INTERNETCONTROL) :
			iph->tos;
 
	if (ip_route_output(&rt, iph->saddr, saddr, RT_TOS(tos), 0))
		goto out;
 
	if (ip_options_echo(&icmp_param.replyopts, skb_in)) 
		goto ende;
 
 
	/*
	 *	Prepare data for ICMP header.
	 */
 
	icmp_param.data.icmph.type=type;
	icmp_param.data.icmph.code=code;
	icmp_param.data.icmph.un.gateway = info;
	icmp_param.data.icmph.checksum=0;
	icmp_param.csum=0;
	icmp_param.skb=skb_in;
	icmp_param.offset=skb_in->nh.raw - skb_in->data;
	icmp_out_count(icmp_param.data.icmph.type);
	icmp_socket->sk->protinfo.af_inet.tos = tos;
	icmp_socket->sk->protinfo.af_inet.ttl = sysctl_ip_default_ttl;
	ipc.addr = iph->saddr;
	ipc.opt = &icmp_param.replyopts;
	if (icmp_param.replyopts.srr) {
		ip_rt_put(rt);
		if (ip_route_output(&rt, icmp_param.replyopts.faddr, saddr, RT_TOS(tos), 0))
			goto out;
	}
 
	if (!icmpv4_xrlim_allow(rt, type, code))
		goto ende;
 
	/* RFC says return as much as we can without exceeding 576 bytes. */
 
	room = rt->u.dst.pmtu;
	if (room > 576)
		room = 576;
	room -= sizeof(struct iphdr) + icmp_param.replyopts.optlen;
	room -= sizeof(struct icmphdr);
 
	icmp_param.data_len=skb_in->len-icmp_param.offset;
	if (icmp_param.data_len > room)
		icmp_param.data_len = room;
	icmp_param.head_len = sizeof(struct icmphdr);
 
	ip_build_xmit(icmp_socket->sk, icmp_glue_bits, &icmp_param, 
		icmp_param.data_len+sizeof(struct icmphdr),
		&ipc, rt, MSG_DONTWAIT);
 
ende:
	ip_rt_put(rt);
out:
	icmp_xmit_unlock();
}
 
 
/* 
 *	Handle ICMP_DEST_UNREACH, ICMP_TIME_EXCEED, and ICMP_QUENCH. 
 */
 
static void icmp_unreach(struct sk_buff *skb)
{
	struct iphdr *iph;
	struct icmphdr *icmph;
	int hash, protocol;
	struct inet_protocol *ipprot;
	struct sock *raw_sk;
	u32 info = 0;
 
	/*
	 *	Incomplete header ?
	 * 	Only checks for the IP header, there should be an
	 *	additional check for longer headers in upper levels.
	 */
 
	if (!pskb_may_pull(skb, sizeof(struct iphdr))) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}
 
	icmph = skb->h.icmph;
	iph = (struct iphdr *) skb->data;
 
	if (iph->ihl<5) {
		/* Mangled header, drop. */
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}
 
	if(icmph->type==ICMP_DEST_UNREACH) {
		switch(icmph->code & 15) {
			case ICMP_NET_UNREACH:
				break;
			case ICMP_HOST_UNREACH:
				break;
			case ICMP_PROT_UNREACH:
				break;
			case ICMP_PORT_UNREACH:
				break;
			case ICMP_FRAG_NEEDED:
				if (ipv4_config.no_pmtu_disc) {
					if (net_ratelimit())
						printk(KERN_INFO "ICMP: %u.%u.%u.%u: fragmentation needed and DF set.\n",
						       NIPQUAD(iph->daddr));
				} else {
					info = ip_rt_frag_needed(iph, ntohs(icmph->un.frag.mtu));
					if (!info) 
						goto out;
				}
				break;
			case ICMP_SR_FAILED:
				if (net_ratelimit())
					printk(KERN_INFO "ICMP: %u.%u.%u.%u: Source Route Failed.\n", NIPQUAD(iph->daddr));
				break;
			default:
				break;
		}
		if (icmph->code>NR_ICMP_UNREACH)
			goto out;
	} else if (icmph->type == ICMP_PARAMETERPROB) {
		info = ntohl(icmph->un.gateway)>>24;
	}
 
	/*
	 *	Throw it at our lower layers
	 *
	 *	RFC 1122: 3.2.2 MUST extract the protocol ID from the passed header.
	 *	RFC 1122: 3.2.2.1 MUST pass ICMP unreach messages to the transport layer.
	 *	RFC 1122: 3.2.2.2 MUST pass ICMP time expired messages to transport layer.
	 */
 
	/*
	 *	Check the other end isnt violating RFC 1122. Some routers send
	 *	bogus responses to broadcast frames. If you see this message
	 *	first check your netmask matches at both ends, if it does then
	 *	get the other vendor to fix their kit.
	 */
 
	if (!sysctl_icmp_ignore_bogus_error_responses)
	{
 
		if (inet_addr_type(iph->daddr) == RTN_BROADCAST)
		{
			if (net_ratelimit())
				printk(KERN_WARNING "%u.%u.%u.%u sent an invalid ICMP type %u, code %u error to a broadcast: %u.%u.%u.%u on %s\n",
					NIPQUAD(skb->nh.iph->saddr),
					icmph->type, icmph->code,
					NIPQUAD(iph->daddr),
					skb->dev->name);
			goto out;
		}
	}
 
	/* Checkin full IP header plus 8 bytes of protocol to
	 * avoid additional coding at protocol handlers.
	 */
	if (!pskb_may_pull(skb, iph->ihl*4+8))
		goto out;
 
	iph = (struct iphdr *) skb->data;
	protocol = iph->protocol;
 
	/*
	 *	Deliver ICMP message to raw sockets. Pretty useless feature?
	 */
 
	/* Note: See raw.c and net/raw.h, RAWV4_HTABLE_SIZE==MAX_INET_PROTOS */
	hash = protocol & (MAX_INET_PROTOS - 1);
	read_lock(&raw_v4_lock);
	if ((raw_sk = raw_v4_htable[hash]) != NULL) 
	{
		while ((raw_sk = __raw_v4_lookup(raw_sk, protocol, iph->daddr,
						 iph->saddr, skb->dev->ifindex)) != NULL) {
			raw_err(raw_sk, skb, info);
			raw_sk = raw_sk->next;
			iph = (struct iphdr *)skb->data;
		}
	}
	read_unlock(&raw_v4_lock);
 
	/*
	 *	This can't change while we are doing it. 
	 *	Callers have obtained BR_NETPROTO_LOCK so
	 *	we are OK.
	 */
 
	ipprot = (struct inet_protocol *) inet_protos[hash];
	while (ipprot) {
		struct inet_protocol *nextip;
 
		nextip = (struct inet_protocol *) ipprot->next;
 
		/* 
		 *	Pass it off to everyone who wants it. 
		 */
 
		/* RFC1122: OK. Passes appropriate ICMP errors to the */
		/* appropriate protocol layer (MUST), as per 3.2.2. */
 
		if (protocol == ipprot->protocol && ipprot->err_handler)
 			ipprot->err_handler(skb, info);
 
		ipprot = nextip;
  	}
out:;
}
 
 
/*
 *	Handle ICMP_REDIRECT. 
 */
 
static void icmp_redirect(struct sk_buff *skb)
{
	struct iphdr *iph;
	unsigned long ip;
 
	if (skb->len < sizeof(struct iphdr)) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return; 
	}
 
	/*
	 *	Get the copied header of the packet that caused the redirect
	 */
	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
		return;
 
	iph = (struct iphdr *) skb->data;
	ip = iph->daddr;
 
	switch (skb->h.icmph->code & 7) {
		case ICMP_REDIR_NET:
		case ICMP_REDIR_NETTOS:
			/*
			 *	As per RFC recommendations now handle it as
			 *	a host redirect.
			 */
 
		case ICMP_REDIR_HOST:
		case ICMP_REDIR_HOSTTOS:
			ip_rt_redirect(skb->nh.iph->saddr, ip, skb->h.icmph->un.gateway, iph->saddr, iph->tos, skb->dev);
			break;
		default:
			break;
  	}
}
 
/*
 *	Handle ICMP_ECHO ("ping") requests. 
 *
 *	RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo requests.
 *	RFC 1122: 3.2.2.6 Data received in the ICMP_ECHO request MUST be included in the reply.
 *	RFC 1812: 4.3.3.6 SHOULD have a config option for silently ignoring echo requests, MUST have default=NOT.
 *	See also WRT handling of options once they are done and working.
 */
 
static void icmp_echo(struct sk_buff *skb)
{
	if (!sysctl_icmp_echo_ignore_all) {
		struct icmp_bxm icmp_param;
 
		icmp_param.data.icmph=*skb->h.icmph;
		icmp_param.data.icmph.type=ICMP_ECHOREPLY;
		icmp_param.skb=skb;
		icmp_param.offset=0;
		icmp_param.data_len=skb->len;
		icmp_param.head_len=sizeof(struct icmphdr);
		icmp_reply(&icmp_param, skb);
	}
}
 
/*
 *	Handle ICMP Timestamp requests. 
 *	RFC 1122: 3.2.2.8 MAY implement ICMP timestamp requests.
 *		  SHOULD be in the kernel for minimum random latency.
 *		  MUST be accurate to a few minutes.
 *		  MUST be updated at least at 15Hz.
 */
 
static void icmp_timestamp(struct sk_buff *skb)
{
	struct timeval tv;
	struct icmp_bxm icmp_param;
 
	/*
	 *	Too short.
	 */
 
	if (skb->len < 4) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}
 
	/*
	 *	Fill in the current time as ms since midnight UT: 
	 */
	do_gettimeofday(&tv);
	icmp_param.data.times[1] = htonl((tv.tv_sec % 86400) * 1000 + tv.tv_usec / 1000);
	icmp_param.data.times[2] = icmp_param.data.times[1];
	if (skb_copy_bits(skb, 0, &icmp_param.data.times[0], 4))
		BUG();
	icmp_param.data.icmph=*skb->h.icmph;
	icmp_param.data.icmph.type=ICMP_TIMESTAMPREPLY;
	icmp_param.data.icmph.code=0;
	icmp_param.skb=skb;
	icmp_param.offset=0;
	icmp_param.data_len=0;
	icmp_param.head_len=sizeof(struct icmphdr)+12;
	icmp_reply(&icmp_param, skb);
}
 
 
/* 
 *	Handle ICMP_ADDRESS_MASK requests.  (RFC950)
 *
 * RFC1122 (3.2.2.9).  A host MUST only send replies to 
 * ADDRESS_MASK requests if it's been configured as an address mask 
 * agent.  Receiving a request doesn't constitute implicit permission to 
 * act as one. Of course, implementing this correctly requires (SHOULD) 
 * a way to turn the functionality on and off.  Another one for sysctl(), 
 * I guess. -- MS
 *
 * RFC1812 (4.3.3.9).	A router MUST implement it.
 *			A router SHOULD have switch turning it on/off.
 *		      	This switch MUST be ON by default.
 *
 * Gratuitous replies, zero-source replies are not implemented,
 * that complies with RFC. DO NOT implement them!!! All the idea
 * of broadcast addrmask replies as specified in RFC950 is broken.
 * The problem is that it is not uncommon to have several prefixes
 * on one physical interface. Moreover, addrmask agent can even be
 * not aware of existing another prefixes.
 * If source is zero, addrmask agent cannot choose correct prefix.
 * Gratuitous mask announcements suffer from the same problem.
 * RFC1812 explains it, but still allows to use ADDRMASK,
 * that is pretty silly. --ANK
 *
 * All these rules are so bizarre, that I removed kernel addrmask
 * support at all. It is wrong, it is obsolete, nobody uses it in
 * any case. --ANK
 *
 * Furthermore you can do it with a usermode address agent program
 * anyway...
 */
 
static void icmp_address(struct sk_buff *skb)
{
#if 0
	if (net_ratelimit())
		printk(KERN_DEBUG "a guy asks for address mask. Who is it?\n");
#endif		
}
 
/*
 * RFC1812 (4.3.3.9).	A router SHOULD listen all replies, and complain
 *			loudly if an inconsistency is found.
 */
 
static void icmp_address_reply(struct sk_buff *skb)
{
	struct rtable *rt = (struct rtable*)skb->dst;
	struct net_device *dev = skb->dev;
	struct in_device *in_dev;
	struct in_ifaddr *ifa;
	u32 mask;
 
	if (skb->len < 4 || !(rt->rt_flags&RTCF_DIRECTSRC))
		return;
 
	in_dev = in_dev_get(dev);
	if (!in_dev)
		return;
	read_lock(&in_dev->lock);
	if (in_dev->ifa_list &&
	    IN_DEV_LOG_MARTIANS(in_dev) &&
	    IN_DEV_FORWARD(in_dev)) {
		if (skb_copy_bits(skb, 0, &mask, 4))
			BUG();
		for (ifa=in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
			if (mask == ifa->ifa_mask && inet_ifa_match(rt->rt_src, ifa))
				break;
		}
		if (!ifa && net_ratelimit()) {
			printk(KERN_INFO "Wrong address mask %u.%u.%u.%u from %s/%u.%u.%u.%u\n",
			       NIPQUAD(mask), dev->name, NIPQUAD(rt->rt_src));
		}
	}
	read_unlock(&in_dev->lock);
	in_dev_put(in_dev);
}
 
static void icmp_discard(struct sk_buff *skb)
{
}
 
/* 
 *	Deal with incoming ICMP packets.
 */
 
int icmp_rcv(struct sk_buff *skb)
{
	struct icmphdr *icmph;
	struct rtable *rt = (struct rtable*)skb->dst;
 
	ICMP_INC_STATS_BH(IcmpInMsgs);
 
	switch (skb->ip_summed) {
	case CHECKSUM_HW:
		if ((u16)csum_fold(skb->csum) == 0)
			break;
		NETDEBUG(if (net_ratelimit()) printk(KERN_DEBUG "icmp v4 hw csum failure\n"));
	case CHECKSUM_NONE:
		if ((u16)csum_fold(skb_checksum(skb, 0, skb->len, 0)))
			goto error;
	default:;
	}
 
	if (!pskb_pull(skb, sizeof(struct icmphdr)))
		goto error;
 
	icmph = skb->h.icmph;
 
	/*
	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
	 *
	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently discarded.
	 */
	if (icmph->type > NR_ICMP_TYPES)
		goto error;
 
 
	/*
	 *	Parse the ICMP message 
	 */
 
 	if (rt->rt_flags&(RTCF_BROADCAST|RTCF_MULTICAST)) {
		/*
		 *	RFC 1122: 3.2.2.6 An ICMP_ECHO to broadcast MAY be
		 *	  silently ignored (we let user decide with a sysctl).
		 *	RFC 1122: 3.2.2.8 An ICMP_TIMESTAMP MAY be silently
		 *	  discarded if to broadcast/multicast.
		 */
		if (icmph->type == ICMP_ECHO &&
		    sysctl_icmp_echo_ignore_broadcasts) {
			goto error;
		}
		if (icmph->type != ICMP_ECHO &&
		    icmph->type != ICMP_TIMESTAMP &&
		    icmph->type != ICMP_ADDRESS &&
		    icmph->type != ICMP_ADDRESSREPLY) {
			goto error;
  		}
	}
 
	icmp_pointers[icmph->type].input[smp_processor_id()*2*sizeof(struct icmp_mib)/sizeof(unsigned long)]++;
	(icmp_pointers[icmph->type].handler)(skb);
 
drop:
	kfree_skb(skb);
	return 0;
error:
	ICMP_INC_STATS_BH(IcmpInErrors);
	goto drop;
}
 
/*
 *	This table is the definition of how we handle ICMP.
 */
 
static struct icmp_control icmp_pointers[NR_ICMP_TYPES+1] = {
/* ECHO REPLY (0) */
 { &icmp_statistics[0].IcmpOutEchoReps, &icmp_statistics[0].IcmpInEchoReps, icmp_discard, 0 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* DEST UNREACH (3) */
 { &icmp_statistics[0].IcmpOutDestUnreachs, &icmp_statistics[0].IcmpInDestUnreachs, icmp_unreach, 1 },
/* SOURCE QUENCH (4) */
 { &icmp_statistics[0].IcmpOutSrcQuenchs, &icmp_statistics[0].IcmpInSrcQuenchs, icmp_unreach, 1 },
/* REDIRECT (5) */
 { &icmp_statistics[0].IcmpOutRedirects, &icmp_statistics[0].IcmpInRedirects, icmp_redirect, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* ECHO (8) */
 { &icmp_statistics[0].IcmpOutEchos, &icmp_statistics[0].IcmpInEchos, icmp_echo, 0 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* TIME EXCEEDED (11) */
 { &icmp_statistics[0].IcmpOutTimeExcds, &icmp_statistics[0].IcmpInTimeExcds, icmp_unreach, 1 },
/* PARAMETER PROBLEM (12) */
 { &icmp_statistics[0].IcmpOutParmProbs, &icmp_statistics[0].IcmpInParmProbs, icmp_unreach, 1 },
/* TIMESTAMP (13) */
 { &icmp_statistics[0].IcmpOutTimestamps, &icmp_statistics[0].IcmpInTimestamps, icmp_timestamp, 0  },
/* TIMESTAMP REPLY (14) */
 { &icmp_statistics[0].IcmpOutTimestampReps, &icmp_statistics[0].IcmpInTimestampReps, icmp_discard, 0 },
/* INFO (15) */
 { &icmp_statistics[0].dummy, &icmp_statistics[0].dummy, icmp_discard, 0 },
/* INFO REPLY (16) */
 { &icmp_statistics[0].dummy, &icmp_statistics[0].dummy, icmp_discard, 0 },
/* ADDR MASK (17) */
 { &icmp_statistics[0].IcmpOutAddrMasks, &icmp_statistics[0].IcmpInAddrMasks, icmp_address, 0  },
/* ADDR MASK REPLY (18) */
 { &icmp_statistics[0].IcmpOutAddrMaskReps, &icmp_statistics[0].IcmpInAddrMaskReps, icmp_address_reply, 0 }
};
 
void __init icmp_init(struct net_proto_family *ops)
{
	int err, i;
 
	for (i = 0; i < NR_CPUS; i++) {
		__icmp_inode[i].i_mode = S_IFSOCK;
		__icmp_inode[i].i_sock = 1;
		__icmp_inode[i].i_uid = 0;
		__icmp_inode[i].i_gid = 0;
		init_waitqueue_head(&__icmp_inode[i].i_wait);
		init_waitqueue_head(&__icmp_inode[i].u.socket_i.wait);
 
		icmp_socket_cpu(i)->inode = &__icmp_inode[i];
		icmp_socket_cpu(i)->state = SS_UNCONNECTED;
		icmp_socket_cpu(i)->type = SOCK_RAW;
 
		if ((err=ops->create(icmp_socket_cpu(i), IPPROTO_ICMP)) < 0)
			panic("Failed to create the ICMP control socket.\n");
 
		icmp_socket_cpu(i)->sk->allocation=GFP_ATOMIC;
 
		/* Enough space for 2 64K ICMP packets, including
		 * sk_buff struct overhead.
		 */
		icmp_socket_cpu(i)->sk->sndbuf =
			(2 * ((64 * 1024) + sizeof(struct sk_buff)));
 
		icmp_socket_cpu(i)->sk->protinfo.af_inet.ttl = MAXTTL;
		icmp_socket_cpu(i)->sk->protinfo.af_inet.pmtudisc = IP_PMTUDISC_DONT;
 
		/* Unhash it so that IP input processing does not even
		 * see it, we do not wish this socket to see incoming
		 * packets.
		 */
		icmp_socket_cpu(i)->sk->prot->unhash(icmp_socket_cpu(i)->sk);
	}
}