/*
 *      NET3:   Implementation of the ICMP protocol layer.
 *
 *              Alan Cox, <alan@redhat.com>
 *
 *      Version: $Id: icmp.c,v 1.85 2002/02/01 22:01:03 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/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/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;

        struct {
                struct icmphdr icmph;
                __u32          times[3];
        } data;
        int head_len;
        struct ip_options replyopts;
        unsigned char  optbuf[40];
};

/*
 *      Statistics
 */
DEFINE_SNMP_STAT(struct icmp_mib, icmp_statistics);

/* 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,
        },
};

/* 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 {
        int output_off;         /* Field offset for increment on output */
        int input_off;          /* Field offset for 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.
 *
 *      On SMP we have one ICMP socket per-cpu.
 */
static DEFINE_PER_CPU(struct socket *, __icmp_socket) = NULL;
#define icmp_socket     __get_cpu_var(__icmp_socket)

static __inline__ int icmp_xmit_lock(void)
{
        local_bh_disable();

        if (unlikely(!spin_trylock(&icmp_socket->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 1;
        }
        return 0;
}

static void icmp_xmit_unlock(void)
{
        spin_unlock_bh(&icmp_socket->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;
        int rc = 0;

        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;
                rc = 1;
        }
        return rc;
}

static inline int icmpv4_xrlim_allow(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) & sysctl_icmp_ratemask)
                rc = xrlim_allow(dst, sysctl_icmp_ratelimit);
out:
        return rc;
}

/*
 *      Maintain the counters used in the SNMP statistics for outgoing ICMP
 */
static void icmp_out_count(int type)
{
        if (type <= NR_ICMP_TYPES) {
                ICMP_INC_STATS_FIELD(icmp_pointers[type].output_off);
                ICMP_INC_STATS(IcmpOutMsgs);
        }
}

/*
 *      Checksum each fragment, and on the first include the headers and final
 *      checksum.
 */
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;
        unsigned int 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);
        return 0;
}

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

        ip_append_data(icmp_socket->sk, icmp_glue_bits, icmp_param,
                       icmp_param->data_len+icmp_param->head_len,
                       icmp_param->head_len,
                       ipc, rt, MSG_DONTWAIT);

        if ((skb = skb_peek(&icmp_socket->sk->sk_write_queue)) != NULL) {
                struct icmphdr *icmph = skb->h.icmph;
                unsigned int csum = 0;
                struct sk_buff *skb1;

                skb_queue_walk(&icmp_socket->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(icmp_socket->sk);
        }
}

/*
 *      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 inet_opt *inet = inet_sk(sk);
        struct ipcm_cookie ipc;
        struct rtable *rt = (struct rtable *)skb->dst;
        u32 daddr;

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

        if (icmp_xmit_lock())
                return;

        icmp_param->data.icmph.checksum = 0;
        icmp_out_count(icmp_param->data.icmph.type);

        inet->tos = skb->nh.iph->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(skb->nh.iph->tos) } },
                                    .proto = IPPROTO_ICMP };
                if (ip_route_output_key(&rt, &fl))
                        goto out_unlock;
        }
        if (icmpv4_xrlim_allow(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();
out:;
}


/*
 *      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)
                goto out;

        /*
         *      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)
                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;

                        if (skb_copy_bits(skb_in,
                                          skb_in->nh.raw + (iph->ihl << 2) +
                                          offsetof(struct icmphdr, type) -
                                          skb_in->data, &inner_type, 1))
                                goto out;

                        /*
                         *      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)
                                goto out;
                }
        }

        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->fl.fl4_dst;
                iph->saddr = rt->fl.fl4_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;

        {
                struct flowi fl = { .nl_u = { .ip4_u = { .daddr = iph->saddr,
                                                         .saddr = saddr,
                                                         .tos = RT_TOS(tos) } },
                                    .proto = IPPROTO_ICMP };
                if (ip_route_output_key(&rt, &fl))
                    goto out_unlock;
        }
        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.skb    = skb_in;
        icmp_param.offset = skb_in->nh.raw - skb_in->data;
        icmp_out_count(icmp_param.data.icmph.type);
        inet_sk(icmp_socket->sk)->tos = tos;
        ipc.addr = iph->saddr;
        ipc.opt = &icmp_param.replyopts;
        if (icmp_param.replyopts.srr) {
                struct flowi fl = { .nl_u = { .ip4_u =
                                              { .daddr = icmp_param.replyopts.faddr,
                                                .saddr = saddr,
                                                .tos = RT_TOS(tos) } },
                                    .proto = IPPROTO_ICMP };
                ip_rt_put(rt);
                if (ip_route_output_key(&rt, &fl))
                        goto out_unlock;
        }

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

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

        room = dst_pmtu(&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();
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 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)))
                goto out_err;

        icmph = skb->h.icmph;
        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) {
                                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 &&
            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 = sk_head(&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 = sk_next(raw_sk);
                        iph = (struct iphdr *)skb->data;
                }
        }
        read_unlock(&raw_v4_lock);

        rcu_read_lock();
        ipprot = inet_protos[hash];
        smp_read_barrier_depends();
        if (ipprot && ipprot->err_handler)
                ipprot->err_handler(skb, info);
        rcu_read_unlock();

out:
        return;
out_err:
        ICMP_INC_STATS_BH(IcmpInErrors);
        goto out;
}


/*
 *      Handle ICMP_REDIRECT.
 */

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

        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;
        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;
        }
out:
        return;
out_err:
        ICMP_INC_STATS_BH(IcmpInErrors);
        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)
{
        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)
                goto out_err;

        /*
         *      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);
out:
        return;
out_err:
        ICMP_INC_STATS_BH(IcmpInErrors);
        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 = (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))
                goto out;

        in_dev = in_dev_get(dev);
        if (!in_dev)
                goto out;
        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);
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 = (struct rtable *)skb->dst;

        ICMP_INC_STATS_BH(IcmpInMsgs);

        switch (skb->ip_summed) {
        case CHECKSUM_HW:
                if (!(u16)csum_fold(skb->csum))
                        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_INC_STATS_BH_FIELD(icmp_pointers[icmph->type].input_off);
        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] = {
        [ICMP_ECHOREPLY] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutEchoReps),
                .input_off = offsetof(struct icmp_mib, IcmpInEchoReps),
                .handler = icmp_discard,
        },
        [1] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib,IcmpInErrors),
                .handler = icmp_discard,

                .error = 1,
        },
        [2] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib,IcmpInErrors),
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_DEST_UNREACH] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutDestUnreachs),
                .input_off = offsetof(struct icmp_mib, IcmpInDestUnreachs),
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_SOURCE_QUENCH] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutSrcQuenchs),
                .input_off = offsetof(struct icmp_mib, IcmpInSrcQuenchs),
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_REDIRECT] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutRedirects),
                .input_off = offsetof(struct icmp_mib, IcmpInRedirects),
                .handler = icmp_redirect,
                .error = 1,
        },
        [6] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, IcmpInErrors),
                .handler = icmp_discard,
                .error = 1,
        },
        [7] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, IcmpInErrors),
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_ECHO] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutEchos),
                .input_off = offsetof(struct icmp_mib, IcmpInEchos),
                .handler = icmp_echo,
        },
        [9] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, IcmpInErrors),
                .handler = icmp_discard,
                .error = 1,
        },
        [10] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, IcmpInErrors),
                .handler = icmp_discard,
                .error = 1,
        },
        [ICMP_TIME_EXCEEDED] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutTimeExcds),
                .input_off = offsetof(struct icmp_mib,IcmpInTimeExcds),
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_PARAMETERPROB] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutParmProbs),
                .input_off = offsetof(struct icmp_mib, IcmpInParmProbs),
                .handler = icmp_unreach,
                .error = 1,
        },
        [ICMP_TIMESTAMP] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutTimestamps),
                .input_off = offsetof(struct icmp_mib, IcmpInTimestamps),
                .handler = icmp_timestamp,
        },
        [ICMP_TIMESTAMPREPLY] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutTimestampReps),
                .input_off = offsetof(struct icmp_mib, IcmpInTimestampReps),
                .handler = icmp_discard,
        },
        [ICMP_INFO_REQUEST] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, dummy),
                .handler = icmp_discard,
        },
        [ICMP_INFO_REPLY] = {
                .output_off = offsetof(struct icmp_mib, dummy),
                .input_off = offsetof(struct icmp_mib, dummy),
                .handler = icmp_discard,
        },
        [ICMP_ADDRESS] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutAddrMasks),
                .input_off = offsetof(struct icmp_mib, IcmpInAddrMasks),
                .handler = icmp_address,
        },
        [ICMP_ADDRESSREPLY] = {
                .output_off = offsetof(struct icmp_mib, IcmpOutAddrMaskReps),
                .input_off = offsetof(struct icmp_mib, IcmpInAddrMaskReps),
                .handler = icmp_address_reply,
        },
};

void __init icmp_init(struct net_proto_family *ops)
{
        struct inet_opt *inet;
        int i;

        for (i = 0; i < NR_CPUS; i++) {
                int err;

                if (!cpu_possible(i))
                        continue;

                err = sock_create(PF_INET, SOCK_RAW, IPPROTO_ICMP,
                                  &per_cpu(__icmp_socket, i));

                if (err < 0)
                        panic("Failed to create the ICMP control socket.\n");

                per_cpu(__icmp_socket, i)->sk->sk_allocation = GFP_ATOMIC;
                per_cpu(__icmp_socket, i)->sk->sk_sndbuf = SK_WMEM_MAX * 2;
                inet = inet_sk(per_cpu(__icmp_socket, i)->sk);
                inet->uc_ttl = -1;
                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.
                 */
                per_cpu(__icmp_socket, i)->sk->sk_prot->unhash(per_cpu(__icmp_socket, i)->sk);
        }
}

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