icmp.c

Go to the documentation of this file.

/*
 *      NET3:   Implementation of the ICMP protocol layer. 
 *      
 *              Alan Cox, <alan@redhat.com>
 *
 *      Version: $Id: icmp.c,v 1.82.2.1 2001/12/13 08:59:27 davem 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;
}

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(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;
                icmp_socket_cpu(i)->sk->sndbuf = SK_WMEM_MAX*2;
                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);
        }
}

---