text: /**
   * @file
   * ICMP - Internet Control Message Protocol
   *
   */
  
  /*
   * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification,
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
   * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   *
   * This file is part of the lwIP TCP/IP stack.
   *
   * Author: Adam Dunkels <adam@sics.se>
   *
   */
  
  /* Some ICMP messages should be passed to the transport protocols. This
     is not implemented. */
  
  #include "lwip/opt.h"
  
  #if LWIP_ICMP /* don't build if not configured for use in lwipopts.h */
  
  #include "lwip/icmp.h"
  #include "lwip/inet_chksum.h"
  #include "lwip/lwip_ip.h"
  #include "lwip/def.h"
  #include "lwip/stats.h"
  #include "lwip/snmp.h"
  
  #include <string.h>
  
  /** Small optimization: set to 0 if incoming PBUF_POOL pbuf always can be
   * used to modify and send a response packet (and to 1 if this is not the case,
   * e.g. when link header is stripped of when receiving) */
  #ifndef LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
  #define LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN 1
  #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
  
  /* The amount of data from the original packet to return in a dest-unreachable */
  #define ICMP_DEST_UNREACH_DATASIZE 8
  
  static void icmp_send_response(struct pbuf *p, u8_t type, u8_t code);
  
  /**
   * Processes ICMP input packets, called from ip_input().
   *
   * Currently only processes icmp echo requests and sends
   * out the echo response.
   *
   * @param p the icmp echo request packet, p->payload pointing to the icmp header
   * @param inp the netif on which this packet was received
   */
  void
  icmp_input(struct pbuf *p, struct netif *inp)
  {
    u8_t type;
  #ifdef LWIP_DEBUG
    u8_t code;
  #endif /* LWIP_DEBUG */
    struct icmp_echo_hdr *iecho;
    struct ip_hdr *iphdr;
    s16_t hlen;
  
    ICMP_STATS_INC(icmp.recv);
    snmp_inc_icmpinmsgs();
  
    iphdr = (struct ip_hdr *)ip_current_header();
    hlen = IPH_HL(iphdr) * 4;
    if (p->len < sizeof(u16_t)*2) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
      goto lenerr;
    }
  
    type = *((u8_t *)p->payload);
  #ifdef LWIP_DEBUG
    code = *(((u8_t *)p->payload)+1);
  #endif /* LWIP_DEBUG */
    switch (type) {
    case ICMP_ER:
      /* This is OK, echo reply might have been parsed by a raw PCB
         (as obviously, an echo request has been sent, too). */
      break; 
    case ICMP_ECHO:
  #if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
      {
        int accepted = 1;
  #if !LWIP_MULTICAST_PING
        /* multicast destination address? */
        if (ip_addr_ismulticast(ip_current_dest_addr())) {
          accepted = 0;
        }
  #endif /* LWIP_MULTICAST_PING */
  #if !LWIP_BROADCAST_PING
        /* broadcast destination address? */
        if (ip_addr_isbroadcast(ip_current_dest_addr(), inp)) {
          accepted = 0;
        }
  #endif /* LWIP_BROADCAST_PING */
        /* broadcast or multicast destination address not accepted? */
        if (!accepted) {
          LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
          ICMP_STATS_INC(icmp.err);
          pbuf_free(p);
          return;
        }
      }
  #endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
      if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
        goto lenerr;
      }
  #if CHECKSUM_CHECK_ICMP
      if (inet_chksum_pbuf(p) != 0) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
        pbuf_free(p);
        ICMP_STATS_INC(icmp.chkerr);
        snmp_inc_icmpinerrors();
        return;
      }
  #endif
  #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
      if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
        /* p is not big enough to contain link headers
         * allocate a new one and copy p into it
         */
        struct pbuf *r;
        /* allocate new packet buffer with space for link headers */
        r = pbuf_alloc(PBUF_LINK, p->tot_len + hlen, PBUF_RAM);
        if (r == NULL) {
          LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
          goto memerr;
        }
        LWIP_ASSERT("check that first pbuf can hold struct the ICMP header",
                    (r->len >= hlen + sizeof(struct icmp_echo_hdr)));
        /* copy the ip header */
        MEMCPY(r->payload, iphdr, hlen);
        iphdr = (struct ip_hdr *)r->payload;
        /* switch r->payload back to icmp header */
        if (pbuf_header(r, -hlen)) {
          LWIP_ASSERT("icmp_input: moving r->payload to icmp header failed\n", 0);
          goto memerr;
        }
        /* copy the rest of the packet without ip header */
        if (pbuf_copy(r, p) != ERR_OK) {
          LWIP_ASSERT("icmp_input: copying to new pbuf failed\n", 0);
          goto memerr;
        }
        /* free the original p */
        pbuf_free(p);
        /* we now have an identical copy of p that has room for link headers */
        p = r;
      } else {
        /* restore p->payload to point to icmp header */
        if (pbuf_header(p, -(s16_t)(PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
          LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
          goto memerr;
        }
      }
  #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
      /* At this point, all checks are OK. */
      /* We generate an answer by switching the dest and src ip addresses,
       * setting the icmp type to ECHO_RESPONSE and updating the checksum. */
      iecho = (struct icmp_echo_hdr *)p->payload;
      ip_addr_copy(iphdr->src, *ip_current_dest_addr());
      ip_addr_copy(iphdr->dest, *ip_current_src_addr());
      ICMPH_TYPE_SET(iecho, ICMP_ER);
  #if CHECKSUM_GEN_ICMP
      /* adjust the checksum */
      if (iecho->chksum >= PP_HTONS(0xffffU - (ICMP_ECHO << 8))) {
        iecho->chksum += PP_HTONS(ICMP_ECHO << 8) + 1;
      } else {
        iecho->chksum += PP_HTONS(ICMP_ECHO << 8);
      }
  #else /* CHECKSUM_GEN_ICMP */
      iecho->chksum = 0;
  #endif /* CHECKSUM_GEN_ICMP */
  
      /* Set the correct TTL and recalculate the header checksum. */
      IPH_TTL_SET(iphdr, ICMP_TTL);
      IPH_CHKSUM_SET(iphdr, 0);
  #if CHECKSUM_GEN_IP
      IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
  #endif /* CHECKSUM_GEN_IP */
  
      ICMP_STATS_INC(icmp.xmit);
      /* increase number of messages attempted to send */
      snmp_inc_icmpoutmsgs();
      /* increase number of echo replies attempted to send */
      snmp_inc_icmpoutechoreps();
  
      if(pbuf_header(p, hlen)) {
        LWIP_ASSERT("Can't move over header in packet", 0);
      } else {
        err_t ret;
        /* send an ICMP packet, src addr is the dest addr of the current packet */
        ret = ip_output_if(p, ip_current_dest_addr(), IP_HDRINCL,
                     ICMP_TTL, 0, IP_PROTO_ICMP, inp);
        if (ret != ERR_OK) {
          LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ip_output_if returned an error: %c.\n", ret));
        }
      }
      break;
    default:
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" code %"S16_F" not supported.\n", 
                  (s16_t)type, (s16_t)code));
      ICMP_STATS_INC(icmp.proterr);
      ICMP_STATS_INC(icmp.drop);
    }
    pbuf_free(p);
    return;
  lenerr:
    pbuf_free(p);
    ICMP_STATS_INC(icmp.lenerr);
    snmp_inc_icmpinerrors();
    return;
  #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
  memerr:
    pbuf_free(p);
    ICMP_STATS_INC(icmp.err);
    snmp_inc_icmpinerrors();
    return;
  #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
  }
  
  /**
   * Send an icmp 'destination unreachable' packet, called from ip_input() if
   * the transport layer protocol is unknown and from udp_input() if the local
   * port is not bound.
   *
   * @param p the input packet for which the 'unreachable' should be sent,
   *          p->payload pointing to the IP header
   * @param t type of the 'unreachable' packet
   */
  void
  icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
  {
    icmp_send_response(p, ICMP_DUR, t);
  }
  
  #if IP_FORWARD || IP_REASSEMBLY
  /**
   * Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
   *
   * @param p the input packet for which the 'time exceeded' should be sent,
   *          p->payload pointing to the IP header
   * @param t type of the 'time exceeded' packet
   */
  void
  icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
  {
    icmp_send_response(p, ICMP_TE, t);
  }
  
  #endif /* IP_FORWARD || IP_REASSEMBLY */
  
  /**
   * Send an icmp packet in response to an incoming packet.
   *
   * @param p the input packet for which the 'unreachable' should be sent,
   *          p->payload pointing to the IP header
   * @param type Type of the ICMP header
   * @param code Code of the ICMP header
   */
  static void
  icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
  {
    struct pbuf *q;
    struct ip_hdr *iphdr;
    /* we can use the echo header here */
    struct icmp_echo_hdr *icmphdr;
    ip_addr_t iphdr_src;
  
    /* ICMP header + IP header + 8 bytes of data */
    q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
                   PBUF_RAM);
    if (q == NULL) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
      return;
    }
    LWIP_ASSERT("check that first pbuf can hold icmp message",
               (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
  
    iphdr = (struct ip_hdr *)p->payload;
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
    ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
    LWIP_DEBUGF(ICMP_DEBUG, (" to "));
    ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
    LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
  
    icmphdr = (struct icmp_echo_hdr *)q->payload;
    icmphdr->type = type;
    icmphdr->code = code;
    icmphdr->id = 0;
    icmphdr->seqno = 0;
  
    /* copy fields from original packet */
    SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
            IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
  
    /* calculate checksum */
    icmphdr->chksum = 0;
  #if CHECKSUM_GEN_ICMP
    icmphdr->chksum = inet_chksum(icmphdr, q->len);
  #endif
    ICMP_STATS_INC(icmp.xmit);
    /* increase number of messages attempted to send */
    snmp_inc_icmpoutmsgs();
    /* increase number of destination unreachable messages attempted to send */
    snmp_inc_icmpouttimeexcds();
    ip_addr_copy(iphdr_src, iphdr->src);
    ip_output(q, NULL, &iphdr_src, ICMP_TTL, 0, IP_PROTO_ICMP);
    pbuf_free(q);
  }
  
  #endif /* LWIP_ICMP */
  