/*
 *      NET3:   Implementation of the ICMP protocol layer.
 *
 *              Alan Cox, <alan@redhat.com>
 *
 *      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/module.h>
#include <linux/types.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/fcntl.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/inetdevice.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>
#include <net/xfrm.h>
#include <net/inet_common.h>

/*
 *      Build xmit assembly blocks
 */

struct icmp_bxm {
        struct sk_buff *skb;
        int offset;
        int data_len;

        struct {
                struct icmphdr icmph;
                __be32         times[3];
        } data;
        int head_len;
        struct ip_options replyopts;
        unsigned char  optbuf[40];
};

/* An array of errno for error messages from dest unreach. */
/* RFC 1122: 3.2.2.1 States that NET_UNREACH, HOST_UNREACH and SR_FAILED MUST be considered 'transient errs'. */

struct icmp_err icmp_err_convert[] = {
        {
                .errno = ENETUNREACH,   /* ICMP_NET_UNREACH */
                .fatal = 0,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_HOST_UNREACH */
                .fatal = 0,
        },
        {
                .errno = ENOPROTOOPT    /* ICMP_PROT_UNREACH */,
                .fatal = 1,
        },
        {
                .errno = ECONNREFUSED,  /* ICMP_PORT_UNREACH */
                .fatal = 1,
        },
        {
                .errno = EMSGSIZE,      /* ICMP_FRAG_NEEDED */
                .fatal = 0,
        },
        {
                .errno = EOPNOTSUPP,    /* ICMP_SR_FAILED */
                .fatal = 0,
        },
        {
                .errno = ENETUNREACH,   /* ICMP_NET_UNKNOWN */
                .fatal = 1,
        },
        {
                .errno = EHOSTDOWN,     /* ICMP_HOST_UNKNOWN */
                .fatal = 1,
        },
        {
                .errno = ENONET,        /* ICMP_HOST_ISOLATED */
                .fatal = 1,
        },
        {
                .errno = ENETUNREACH,   /* ICMP_NET_ANO */
                .fatal = 1,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_HOST_ANO */
                .fatal = 1,
        },
        {
                .errno = ENETUNREACH,   /* ICMP_NET_UNR_TOS */
                .fatal = 0,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_HOST_UNR_TOS */
                .fatal = 0,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_PKT_FILTERED */
                .fatal = 1,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_PREC_VIOLATION */
                .fatal = 1,
        },
        {
                .errno = EHOSTUNREACH,  /* ICMP_PREC_CUTOFF */
                .fatal = 1,
        },
};

/*
 *      ICMP control array. This specifies what to do with each ICMP.
 */

struct icmp_control {
        void (*handler)(struct sk_buff *skb);
        short   error;          /* This ICMP is classed as an error message */
};

static const 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.
 *
 *      On SMP we have one ICMP socket per-cpu.
 */
static struct sock *icmp_sk(struct net *net)
{
        return net->ipv4.icmp_sk[smp_processor_id()];
}

static inline struct sock *icmp_xmit_lock(struct net *net)
{
        struct sock *sk;

        local_bh_disable();

        sk = icmp_sk(net);

        if (unlikely(!spin_trylock(&sk->sk_lock.slock))) {
                /* This can happen if the output path signals a
                 * dst_link_failure() for an outgoing ICMP packet.
                 */
                local_bh_enable();
                return NULL;
        }
        return sk;
}

static inline void icmp_xmit_unlock(struct sock *sk)
{
        spin_unlock_bh(&sk->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, token = dst->rate_tokens;
        int rc = 0;

        now = jiffies;
        token += now - dst->rate_last;
        dst->rate_last = now;
        if (token > XRLIM_BURST_FACTOR * timeout)
                token = XRLIM_BURST_FACTOR * timeout;
        if (token >= timeout) {
                token -= timeout;
                rc = 1;
        }
        dst->rate_tokens = token;
        return rc;
}

static inline int icmpv4_xrlim_allow(struct net *net, struct rtable *rt,
                int type, int code)
{
        struct dst_entry *dst = &rt->u.dst;
        int rc = 1;

        if (type > NR_ICMP_TYPES)
                goto out;

        /* Don't limit PMTU discovery. */
        if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED)
                goto out;

        /* No rate limit on loopback */
        if (dst->dev && (dst->dev->flags&IFF_LOOPBACK))
                goto out;

        /* Limit if icmp type is enabled in ratemask. */
        if ((1 << type) & net->ipv4.sysctl_icmp_ratemask)
                rc = xrlim_allow(dst, net->ipv4.sysctl_icmp_ratelimit);
out:
        return rc;
}

/*
 *      Maintain the counters used in the SNMP statistics for outgoing ICMP
 */
void icmp_out_count(struct net *net, unsigned char type)
{
        ICMPMSGOUT_INC_STATS(net, type);
        ICMP_INC_STATS(net, ICMP_MIB_OUTMSGS);
}

/*
 *      Checksum each fragment, and on the first include the headers and final
 *      checksum.
 */
static int icmp_glue_bits(void *from, char *to, int offset, int len, int odd,
                          struct sk_buff *skb)
{
        struct icmp_bxm *icmp_param = (struct icmp_bxm *)from;
        __wsum csum;

        csum = skb_copy_and_csum_bits(icmp_param->skb,
                                      icmp_param->offset + offset,
                                      to, len, 0);

        skb->csum = csum_block_add(skb->csum, csum, odd);
        if (icmp_pointers[icmp_param->data.icmph.type].error)
                nf_ct_attach(skb, icmp_param->skb);
        return 0;
}

static void icmp_push_reply(struct icmp_bxm *icmp_param,
                            struct ipcm_cookie *ipc, struct rtable *rt)
{
        struct sock *sk;
        struct sk_buff *skb;

        sk = icmp_sk(dev_net(rt->u.dst.dev));
        if (ip_append_data(sk, icmp_glue_bits, icmp_param,
                           icmp_param->data_len+icmp_param->head_len,
                           icmp_param->head_len,
                           ipc, rt, MSG_DONTWAIT) < 0)
                ip_flush_pending_frames(sk);
        else if ((skb = skb_peek(&sk->sk_write_queue)) != NULL) {
                struct icmphdr *icmph = icmp_hdr(skb);
                __wsum csum = 0;
                struct sk_buff *skb1;

                skb_queue_walk(&sk->sk_write_queue, skb1) {
                        csum = csum_add(csum, skb1->csum);
                }
                csum = csum_partial_copy_nocheck((void *)&icmp_param->data,
                                                 (char *)icmph,
                                                 icmp_param->head_len, csum);
                icmph->checksum = csum_fold(csum);
                skb->ip_summed = CHECKSUM_NONE;
                ip_push_pending_frames(sk);
        }
}

/*
 *      Driving logic for building and sending ICMP messages.
 */

static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
{
        struct ipcm_cookie ipc;
        struct rtable *rt = skb->rtable;
        struct net *net = dev_net(rt->u.dst.dev);
        struct sock *sk;
        struct inet_sock *inet;
        __be32 daddr;

        if (ip_options_echo(&icmp_param->replyopts, skb))
                return;

        sk = icmp_xmit_lock(net);
        if (sk == NULL)
                return;
        inet = inet_sk(sk);

        icmp_param->data.icmph.checksum = 0;

        inet->tos = ip_hdr(skb)->tos;
        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;
        }
        {
                struct flowi fl = { .nl_u = { .ip4_u =
                                              { .daddr = daddr,
                                                .saddr = rt->rt_spec_dst,
                                                .tos = RT_TOS(ip_hdr(skb)->tos) } },
                                    .proto = IPPROTO_ICMP };
                security_skb_classify_flow(skb, &fl);
                if (ip_route_output_key(net, &rt, &fl))
                        goto out_unlock;
        }
        if (icmpv4_xrlim_allow(net, rt, icmp_param->data.icmph.type,
                               icmp_param->data.icmph.code))
                icmp_push_reply(icmp_param, &ipc, rt);
        ip_rt_put(rt);
out_unlock:
        icmp_xmit_unlock(sk);
}


/*
 *      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, __be32 info)
{
        struct iphdr *iph;
        int room;
        struct icmp_bxm icmp_param;
        struct rtable *rt = skb_in->rtable;
        struct ipcm_cookie ipc;
        __be32 saddr;
        u8  tos;
        struct net *net;
        struct sock *sk;

        if (!rt)
                goto out;
        net = dev_net(rt->u.dst.dev);

        /*
         *      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 = ip_hdr(skb_in);

        if ((u8 *)iph < skb_in->head ||
            (skb_in->network_header + sizeof(*iph)) > skb_in->tail)
                goto out;

        /*
         *      No replies to physical multicast/broadcast
         */
        if (skb_in->pkt_type != PACKET_HOST)
                goto out;

        /*
         *      Now check at the protocol level
         */
        if (rt->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
                goto out;

        /*
         *      Only reply to fragment 0. We byte re-order the constant
         *      mask for efficiency.
         */
        if (iph->frag_off & htons(IP_OFFSET))
                goto out;

        /*
         *      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, *itp;

                        itp = skb_header_pointer(skb_in,
                                                 skb_network_header(skb_in) +
                                                 (iph->ihl << 2) +
                                                 offsetof(struct icmphdr,
                                                          type) -
                                                 skb_in->data,
                                                 sizeof(_inner_type),
                                                 &_inner_type);
                        if (itp == NULL)
                                goto out;

                        /*
                         *      Assume any unknown ICMP type is an error. This
                         *      isn't specified by the RFC, but think about it..
                         */
                        if (*itp > NR_ICMP_TYPES ||
                            icmp_pointers[*itp].error)
                                goto out;
                }
        }

        sk = icmp_xmit_lock(net);
        if (sk == NULL)
                return;

        /*
         *      Construct source address and options.
         */

        saddr = iph->daddr;
        if (!(rt->rt_flags & RTCF_LOCAL)) {
                struct net_device *dev = NULL;

                if (rt->fl.iif &&
                        net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr)
                        dev = dev_get_by_index(net, rt->fl.iif);

                if (dev) {
                        saddr = inet_select_addr(dev, 0, RT_SCOPE_LINK);
                        dev_put(dev);
                } else
                        saddr = 0;
        }

        tos = icmp_pointers[type].error ? ((iph->tos & IPTOS_TOS_MASK) |
                                           IPTOS_PREC_INTERNETCONTROL) :
                                          iph->tos;

        if (ip_options_echo(&icmp_param.replyopts, skb_in))
                goto out_unlock;


        /*
         *      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.skb    = skb_in;
        icmp_param.offset = skb_network_offset(skb_in);
        inet_sk(sk)->tos = tos;
        ipc.addr = iph->saddr;
        ipc.opt = &icmp_param.replyopts;

        {
                struct flowi fl = {
                        .nl_u = {
                                .ip4_u = {
                                        .daddr = icmp_param.replyopts.srr ?
                                                icmp_param.replyopts.faddr :
                                                iph->saddr,
                                        .saddr = saddr,
                                        .tos = RT_TOS(tos)
                                }
                        },
                        .proto = IPPROTO_ICMP,
                        .uli_u = {
                                .icmpt = {
                                        .type = type,
                                        .code = code
                                }
                        }
                };
                int err;
                struct rtable *rt2;

                security_skb_classify_flow(skb_in, &fl);
                if (__ip_route_output_key(net, &rt, &fl))
                        goto out_unlock;

                /* No need to clone since we're just using its address. */
                rt2 = rt;

                err = xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
                switch (err) {
                case 0:
                        if (rt != rt2)
                                goto route_done;
                        break;
                case -EPERM:
                        rt = NULL;
                        break;
                default:
                        goto out_unlock;
                }

                if (xfrm_decode_session_reverse(skb_in, &fl, AF_INET))
                        goto relookup_failed;

                if (inet_addr_type(net, fl.fl4_src) == RTN_LOCAL)
                        err = __ip_route_output_key(net, &rt2, &fl);
                else {
                        struct flowi fl2 = {};
                        struct dst_entry *odst;

                        fl2.fl4_dst = fl.fl4_src;
                        if (ip_route_output_key(net, &rt2, &fl2))
                                goto relookup_failed;

                        /* Ugh! */
                        odst = skb_in->dst;
                        err = ip_route_input(skb_in, fl.fl4_dst, fl.fl4_src,
                                             RT_TOS(tos), rt2->u.dst.dev);

                        dst_release(&rt2->u.dst);
                        rt2 = skb_in->rtable;
                        skb_in->dst = odst;
                }

                if (err)
                        goto relookup_failed;

                err = xfrm_lookup((struct dst_entry **)&rt2, &fl, NULL,
                                  XFRM_LOOKUP_ICMP);
                switch (err) {
                case 0:
                        dst_release(&rt->u.dst);
                        rt = rt2;
                        break;
                case -EPERM:
                        goto ende;
                default:
relookup_failed:
                        if (!rt)
                                goto out_unlock;
                        break;
                }
        }

route_done:
        if (!icmpv4_xrlim_allow(net, rt, type, code))
                goto ende;

        /* RFC says return as much as we can without exceeding 576 bytes. */

        room = dst_mtu(&rt->u.dst);
        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);

        icmp_push_reply(&icmp_param, &ipc, rt);
ende:
        ip_rt_put(rt);
out_unlock:
        icmp_xmit_unlock(sk);
out:;
}


/*
 *      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 net_protocol *ipprot;
        u32 info = 0;
        struct net *net;

        net = dev_net(skb->dst->dev);

        /*
         *      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)))
                goto out_err;

        icmph = icmp_hdr(skb);
        iph   = (struct iphdr *)skb->data;

        if (iph->ihl < 5) /* Mangled header, drop. */
                goto out_err;

        if (icmph->type == ICMP_DEST_UNREACH) {
                switch (icmph->code & 15) {
                case ICMP_NET_UNREACH:
                case ICMP_HOST_UNREACH:
                case ICMP_PROT_UNREACH:
                case ICMP_PORT_UNREACH:
                        break;
                case ICMP_FRAG_NEEDED:
                        if (ipv4_config.no_pmtu_disc) {
                                LIMIT_NETDEBUG(KERN_INFO "ICMP: " NIPQUAD_FMT ": "
                                                         "fragmentation needed "
                                                         "and DF set.\n",
                                               NIPQUAD(iph->daddr));
                        } else {
                                info = ip_rt_frag_needed(net, iph,
                                                         ntohs(icmph->un.frag.mtu),
                                                         skb->dev);
                                if (!info)
                                        goto out;
                        }
                        break;
                case ICMP_SR_FAILED:
                        LIMIT_NETDEBUG(KERN_INFO "ICMP: " NIPQUAD_FMT ": 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 (!net->ipv4.sysctl_icmp_ignore_bogus_error_responses &&
            inet_addr_type(net, iph->daddr) == RTN_BROADCAST) {
                if (net_ratelimit())
                        printk(KERN_WARNING NIPQUAD_FMT " sent an invalid ICMP "
                                            "type %u, code %u "
                                            "error to a broadcast: " NIPQUAD_FMT " on %s\n",
                               NIPQUAD(ip_hdr(skb)->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?
         */
        raw_icmp_error(skb, protocol, info);

        hash = protocol & (MAX_INET_PROTOS - 1);
        rcu_read_lock();
        ipprot = rcu_dereference(inet_protos[hash]);
        if (ipprot && ipprot->err_handler)
                ipprot->err_handler(skb, info);
        rcu_read_unlock();

out:
        return;
out_err:
        ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
        goto out;
}


/*
 *      Handle ICMP_REDIRECT.
 */

static void icmp_redirect(struct sk_buff *skb)
{
        struct iphdr *iph;

        if (skb->len < sizeof(struct iphdr))
                goto out_err;

        /*
         *      Get the copied header of the packet that caused the redirect
         */
        if (!pskb_may_pull(skb, sizeof(struct iphdr)))
                goto out;

        iph = (struct iphdr *)skb->data;

        switch (icmp_hdr(skb)->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(ip_hdr(skb)->saddr, iph->daddr,
                               icmp_hdr(skb)->un.gateway,
                               iph->saddr, skb->dev);
                break;
        }
out:
        return;
out_err:
        ICMP_INC_STATS_BH(dev_net(skb->dev), ICMP_MIB_INERRORS);
        goto out;
}

/*
 *      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)
{
        struct net *net;

        net = dev_net(skb->dst->dev);
        if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
                struct icmp_bxm icmp_param;

                icmp_param.data.icmph      = *icmp_hdr(skb);
                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 timespec tv;
        struct icmp_bxm icmp_param;
        /*
         *      Too short.
         */
        if (skb->len < 4)
                goto out_err;

        /*
         *      Fill in the current time as ms since midnight UT:
         */
        getnstimeofday(&tv);
        icmp_param.data.times[1] = htonl((tv.tv_sec % 86400) * MSEC_PER_SEC +
                                         tv.tv_nsec / NSEC_PER_MSEC);
        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      = *icmp_hdr(skb);
        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);
out:
        return;
out_err:
        ICMP_INC_STATS_BH(dev_net(skb->dst->dev), ICMP_MIB_INERRORS);
        goto out;
}


/*
 *      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 = skb->rtable;
        struct net_device *dev = skb->dev;
        struct in_device *in_dev;
        struct in_ifaddr *ifa;

        if (skb->len < 4 || !(rt->rt_flags&RTCF_DIRECTSRC))
                goto out;

        in_dev = in_dev_get(dev);
        if (!in_dev)
                goto out;
        rcu_read_lock();
        if (in_dev->ifa_list &&
            IN_DEV_LOG_MARTIANS(in_dev) &&
            IN_DEV_FORWARD(in_dev)) {
                __be32 _mask, *mp;

                mp = skb_header_pointer(skb, 0, sizeof(_mask), &_mask);
                BUG_ON(mp == NULL);
                for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
                        if (*mp == ifa->ifa_mask &&
                            inet_ifa_match(rt->rt_src, ifa))
                                break;
                }
                if (!ifa && net_ratelimit()) {
                        printk(KERN_INFO "Wrong address mask " NIPQUAD_FMT " from "
                                         "%s/" NIPQUAD_FMT "\n",
                               NIPQUAD(*mp), dev->name, NIPQUAD(rt->rt_src));
                }
        }
        rcu_read_unlock();
        in_dev_put(in_dev);
out:;
}

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 = skb->rtable;
        struct net *net = dev_net(rt->u.dst.dev);

        if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
                int nh;

                if (!(skb->sp && skb->sp->xvec[skb->sp->len - 1]->props.flags &
                                 XFRM_STATE_ICMP))
                        goto drop;

                if (!pskb_may_pull(skb, sizeof(*icmph) + sizeof(struct iphdr)))
                        goto drop;

                nh = skb_network_offset(skb);
                skb_set_network_header(skb, sizeof(*icmph));

                if (!xfrm4_policy_check_reverse(NULL, XFRM_POLICY_IN, skb))
                        goto drop;

                skb_set_network_header(skb, nh);
        }

        ICMP_INC_STATS_BH(net, ICMP_MIB_INMSGS);

        switch (skb->ip_summed) {
        case CHECKSUM_COMPLETE:

                if (!csum_fold(skb->csum))
                        break;
                /* fall through */
        case CHECKSUM_NONE:
                skb->csum = 0;
                if (__skb_checksum_complete(skb))
                        goto error;
        }

        if (!pskb_pull(skb, sizeof(*icmph)))
                goto error;

        icmph = icmp_hdr(skb);

        ICMPMSGIN_INC_STATS_BH(net, icmph->type);
        /*
         *      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 ||
                     icmph->type == ICMP_TIMESTAMP) &&
                    net->ipv4.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].handler(skb);

drop:
        kfree_skb(skb);
        return 0;
error:
        ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
        goto drop;
}

/*
 *      This table is the definition of how we handle ICMP.
 */
static const struct icmp_control icmp_pointers[NR_ICMP_TYPES + 1] = {
        [ICMP_ECHOREPLY] = {
                .handler = icmp_discard,
        },
        [1] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [2] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_DEST_UNREACH] = {
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_SOURCE_QUENCH] = {
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_REDIRECT] = {
                .handler = icmp_redirect,
                .error = 1,
        },
        [6] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [7] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_ECHO] = {
                .handler = icmp_echo,
        },
        [9] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [10] = {
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_TIME_EXCEEDED] = {
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_PARAMETERPROB] = {
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_TIMESTAMP] = {
                .handler = icmp_timestamp,
        },
        [ICMP_TIMESTAMPREPLY] = {
                .handler = icmp_discard,
        },
        [ICMP_INFO_REQUEST] = {
                .handler = icmp_discard,
        },
        [ICMP_INFO_REPLY] = {
                .handler = icmp_discard,
        },
        [ICMP_ADDRESS] = {
                .handler = icmp_address,
        },
        [ICMP_ADDRESSREPLY] = {
                .handler = icmp_address_reply,
        },
};

static void __net_exit icmp_sk_exit(struct net *net)
{
        int i;

        for_each_possible_cpu(i)
                inet_ctl_sock_destroy(net->ipv4.icmp_sk[i]);
        kfree(net->ipv4.icmp_sk);
        net->ipv4.icmp_sk = NULL;
}

static int __net_init icmp_sk_init(struct net *net)
{
        int i, err;

        net->ipv4.icmp_sk =
                kzalloc(nr_cpu_ids * sizeof(struct sock *), GFP_KERNEL);
        if (net->ipv4.icmp_sk == NULL)
                return -ENOMEM;

        for_each_possible_cpu(i) {
                struct sock *sk;

                err = inet_ctl_sock_create(&sk, PF_INET,
                                           SOCK_RAW, IPPROTO_ICMP, net);
                if (err < 0)
                        goto fail;

                net->ipv4.icmp_sk[i] = sk;

                /* Enough space for 2 64K ICMP packets, including
                 * sk_buff struct overhead.
                 */
                sk->sk_sndbuf =
                        (2 * ((64 * 1024) + sizeof(struct sk_buff)));

                inet_sk(sk)->pmtudisc = IP_PMTUDISC_DONT;
        }

        /* Control parameters for ECHO replies. */
        net->ipv4.sysctl_icmp_echo_ignore_all = 0;
        net->ipv4.sysctl_icmp_echo_ignore_broadcasts = 1;

        /* Control parameter - ignore bogus broadcast responses? */
        net->ipv4.sysctl_icmp_ignore_bogus_error_responses = 1;

        /*
         *      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)
         */

        net->ipv4.sysctl_icmp_ratelimit = 1 * HZ;
        net->ipv4.sysctl_icmp_ratemask = 0x1818;
        net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr = 0;

        return 0;

fail:
        for_each_possible_cpu(i)
                inet_ctl_sock_destroy(net->ipv4.icmp_sk[i]);
        kfree(net->ipv4.icmp_sk);
        return err;
}

static struct pernet_operations __net_initdata icmp_sk_ops = {
       .init = icmp_sk_init,
       .exit = icmp_sk_exit,
};

int __init icmp_init(void)
{
        return register_pernet_device(&icmp_sk_ops);
}

EXPORT_SYMBOL(icmp_err_convert);
EXPORT_SYMBOL(icmp_send);
EXPORT_SYMBOL(xrlim_allow);