icmp.c

00001 /**
00002  * @file
00003  * ICMP - Internet Control Message Protocol
00004  *
00005  */
00006 
00007 /*
00008  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
00009  * All rights reserved.
00010  *
00011  * Redistribution and use in source and binary forms, with or without modification,
00012  * are permitted provided that the following conditions are met:
00013  *
00014  * 1. Redistributions of source code must retain the above copyright notice,
00015  *    this list of conditions and the following disclaimer.
00016  * 2. Redistributions in binary form must reproduce the above copyright notice,
00017  *    this list of conditions and the following disclaimer in the documentation
00018  *    and/or other materials provided with the distribution.
00019  * 3. The name of the author may not be used to endorse or promote products
00020  *    derived from this software without specific prior written permission.
00021  *
00022  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
00023  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
00024  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
00025  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
00026  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
00027  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00028  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
00029  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
00030  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
00031  * OF SUCH DAMAGE.
00032  *
00033  * This file is part of the lwIP TCP/IP stack.
00034  *
00035  * Author: Adam Dunkels <adam@sics.se>
00036  *
00037  */
00038 
00039 /* Some ICMP messages should be passed to the transport protocols. This
00040    is not implemented. */
00041 
00042 #include "lwip/opt.h"
00043 
00044 #if LWIP_ICMP /* don't build if not configured for use in lwipopts.h */
00045 
00046 #include "lwip/icmp.h"
00047 #include "lwip/inet.h"
00048 #include "lwip/inet_chksum.h"
00049 #include "lwip/ip.h"
00050 #include "lwip/def.h"
00051 #include "lwip/stats.h"
00052 #include "lwip/snmp.h"
00053 
00054 #include <string.h>
00055 
00056 /** Small optimization: set to 0 if incoming PBUF_POOL pbuf always can be
00057  * used to modify and send a response packet (and to 1 if this is not the case,
00058  * e.g. when link header is stripped of when receiving) */
00059 #ifndef LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00060 #define LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN 1
00061 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00062 
00063 /* The amount of data from the original packet to return in a dest-unreachable */
00064 #define ICMP_DEST_UNREACH_DATASIZE 8
00065 
00066 static void icmp_send_response(struct pbuf *p, u8_t type, u8_t code);
00067 
00068 /**
00069  * Processes ICMP input packets, called from ip_input().
00070  *
00071  * Currently only processes icmp echo requests and sends
00072  * out the echo response.
00073  *
00074  * @param p the icmp echo request packet, p->payload pointing to the ip header
00075  * @param inp the netif on which this packet was received
00076  */
00077 void
00078 icmp_input(struct pbuf *p, struct netif *inp)
00079 {
00080   u8_t type;
00081 #ifdef LWIP_DEBUG
00082   u8_t code;
00083 #endif /* LWIP_DEBUG */
00084   struct icmp_echo_hdr *iecho;
00085   struct ip_hdr *iphdr;
00086   struct ip_addr tmpaddr;
00087   s16_t hlen;
00088 
00089   ICMP_STATS_INC(icmp.recv);
00090   snmp_inc_icmpinmsgs();
00091 
00092 
00093   iphdr = (struct ip_hdr *)p->payload;
00094   hlen = IPH_HL(iphdr) * 4;
00095   if (pbuf_header(p, -hlen) || (p->tot_len < sizeof(u16_t)*2)) {
00096     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
00097     goto lenerr;
00098   }
00099 
00100   type = *((u8_t *)p->payload);
00101 #ifdef LWIP_DEBUG
00102   code = *(((u8_t *)p->payload)+1);
00103 #endif /* LWIP_DEBUG */
00104   switch (type) {
00105   case ICMP_ECHO:
00106 #if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
00107     {
00108       int accepted = 1;
00109 #if !LWIP_MULTICAST_PING
00110       /* multicast destination address? */
00111       if (ip_addr_ismulticast(&iphdr->dest)) {
00112         accepted = 0;
00113       }
00114 #endif /* LWIP_MULTICAST_PING */
00115 #if !LWIP_BROADCAST_PING
00116       /* broadcast destination address? */
00117       if (ip_addr_isbroadcast(&iphdr->dest, inp)) {
00118         accepted = 0;
00119       }
00120 #endif /* LWIP_BROADCAST_PING */
00121       /* broadcast or multicast destination address not acceptd? */
00122       if (!accepted) {
00123         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
00124         ICMP_STATS_INC(icmp.err);
00125         pbuf_free(p);
00126         return;
00127       }
00128     }
00129 #endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
00130     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
00131     if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
00132       LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
00133       goto lenerr;
00134     }
00135     if (inet_chksum_pbuf(p) != 0) {
00136       LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
00137       pbuf_free(p);
00138       ICMP_STATS_INC(icmp.chkerr);
00139       snmp_inc_icmpinerrors();
00140       return;
00141     }
00142 #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00143     if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
00144       /* p is not big enough to contain link headers
00145        * allocate a new one and copy p into it
00146        */
00147       struct pbuf *r;
00148       /* switch p->payload to ip header */
00149       if (pbuf_header(p, hlen)) {
00150         LWIP_ASSERT("icmp_input: moving p->payload to ip header failed\n", 0);
00151         goto memerr;
00152       }
00153       /* allocate new packet buffer with space for link headers */
00154       r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);
00155       if (r == NULL) {
00156         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
00157         goto memerr;
00158       }
00159       LWIP_ASSERT("check that first pbuf can hold struct the ICMP header",
00160                   (r->len >= hlen + sizeof(struct icmp_echo_hdr)));
00161       /* copy the whole packet including ip header */
00162       if (pbuf_copy(r, p) != ERR_OK) {
00163         LWIP_ASSERT("icmp_input: copying to new pbuf failed\n", 0);
00164         goto memerr;
00165       }
00166       iphdr = (struct ip_hdr *)r->payload;
00167       /* switch r->payload back to icmp header */
00168       if (pbuf_header(r, -hlen)) {
00169         LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
00170         goto memerr;
00171       }
00172       /* free the original p */
00173       pbuf_free(p);
00174       /* we now have an identical copy of p that has room for link headers */
00175       p = r;
00176     } else {
00177       /* restore p->payload to point to icmp header */
00178       if (pbuf_header(p, -(s16_t)(PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
00179         LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
00180         goto memerr;
00181       }
00182     }
00183 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00184     /* At this point, all checks are OK. */
00185     /* We generate an answer by switching the dest and src ip addresses,
00186      * setting the icmp type to ECHO_RESPONSE and updating the checksum. */
00187     iecho = (struct icmp_echo_hdr *)p->payload;
00188     tmpaddr.addr = iphdr->src.addr;
00189     iphdr->src.addr = iphdr->dest.addr;
00190     iphdr->dest.addr = tmpaddr.addr;
00191     ICMPH_TYPE_SET(iecho, ICMP_ER);
00192     /* adjust the checksum */
00193     if (iecho->chksum >= htons(0xffff - (ICMP_ECHO << 8))) {
00194       iecho->chksum += htons(ICMP_ECHO << 8) + 1;
00195     } else {
00196       iecho->chksum += htons(ICMP_ECHO << 8);
00197     }
00198 
00199     /* Set the correct TTL and recalculate the header checksum. */
00200     IPH_TTL_SET(iphdr, ICMP_TTL);
00201     IPH_CHKSUM_SET(iphdr, 0);
00202 #if CHECKSUM_GEN_IP
00203     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
00204 #endif /* CHECKSUM_GEN_IP */
00205 
00206     ICMP_STATS_INC(icmp.xmit);
00207     /* increase number of messages attempted to send */
00208     snmp_inc_icmpoutmsgs();
00209     /* increase number of echo replies attempted to send */
00210     snmp_inc_icmpoutechoreps();
00211 
00212     if(pbuf_header(p, hlen)) {
00213       LWIP_ASSERT("Can't move over header in packet", 0);
00214     } else {
00215       err_t ret;
00216       ret = ip_output_if(p, &(iphdr->src), IP_HDRINCL,
00217                    ICMP_TTL, 0, IP_PROTO_ICMP, inp);
00218       if (ret != ERR_OK) {
00219         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ip_output_if returned an error: %c.\n", ret));
00220       }
00221     }
00222     break;
00223   default:
00224     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" code %"S16_F" not supported.\n", 
00225                 (s16_t)type, (s16_t)code));
00226     ICMP_STATS_INC(icmp.proterr);
00227     ICMP_STATS_INC(icmp.drop);
00228   }
00229   pbuf_free(p);
00230   return;
00231 lenerr:
00232   pbuf_free(p);
00233   ICMP_STATS_INC(icmp.lenerr);
00234   snmp_inc_icmpinerrors();
00235   return;
00236 #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00237 memerr:
00238   pbuf_free(p);
00239   ICMP_STATS_INC(icmp.err);
00240   snmp_inc_icmpinerrors();
00241   return;
00242 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00243 }
00244 
00245 /**
00246  * Send an icmp 'destination unreachable' packet, called from ip_input() if
00247  * the transport layer protocol is unknown and from udp_input() if the local
00248  * port is not bound.
00249  *
00250  * @param p the input packet for which the 'unreachable' should be sent,
00251  *          p->payload pointing to the IP header
00252  * @param t type of the 'unreachable' packet
00253  */
00254 void
00255 icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
00256 {
00257   icmp_send_response(p, ICMP_DUR, t);
00258 }
00259 
00260 #if IP_FORWARD || IP_REASSEMBLY
00261 /**
00262  * Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
00263  *
00264  * @param p the input packet for which the 'time exceeded' should be sent,
00265  *          p->payload pointing to the IP header
00266  * @param t type of the 'time exceeded' packet
00267  */
00268 void
00269 icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
00270 {
00271   icmp_send_response(p, ICMP_TE, t);
00272 }
00273 
00274 #endif /* IP_FORWARD || IP_REASSEMBLY */
00275 
00276 /**
00277  * Send an icmp packet in response to an incoming packet.
00278  *
00279  * @param p the input packet for which the 'unreachable' should be sent,
00280  *          p->payload pointing to the IP header
00281  * @param type Type of the ICMP header
00282  * @param code Code of the ICMP header
00283  */
00284 static void
00285 icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
00286 {
00287   struct pbuf *q;
00288   struct ip_hdr *iphdr;
00289   /* we can use the echo header here */
00290   struct icmp_echo_hdr *icmphdr;
00291 
00292   /* ICMP header + IP header + 8 bytes of data */
00293   q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
00294                  PBUF_RAM);
00295   if (q == NULL) {
00296     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
00297     return;
00298   }
00299   LWIP_ASSERT("check that first pbuf can hold icmp message",
00300              (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
00301 
00302   iphdr = (struct ip_hdr *)p->payload;
00303   LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
00304   ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
00305   LWIP_DEBUGF(ICMP_DEBUG, (" to "));
00306   ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
00307   LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
00308 
00309   icmphdr = (struct icmp_echo_hdr *)q->payload;
00310   icmphdr->type = type;
00311   icmphdr->code = code;
00312   icmphdr->id = 0;
00313   icmphdr->seqno = 0;
00314 
00315   /* copy fields from original packet */
00316   SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
00317           IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
00318 
00319   /* calculate checksum */
00320   icmphdr->chksum = 0;
00321   icmphdr->chksum = inet_chksum(icmphdr, q->len);
00322   ICMP_STATS_INC(icmp.xmit);
00323   /* increase number of messages attempted to send */
00324   snmp_inc_icmpoutmsgs();
00325   /* increase number of destination unreachable messages attempted to send */
00326   snmp_inc_icmpouttimeexcds();
00327   ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
00328   pbuf_free(q);
00329 }
00330 
00331 #endif /* LWIP_ICMP */