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_chksum.h"
00048 #include "lwip/ip.h"
00049 #include "lwip/def.h"
00050 #include "lwip/stats.h"
00051 #include "lwip/snmp.h"
00052 
00053 #include <string.h>
00054 
00055 /** Small optimization: set to 0 if incoming PBUF_POOL pbuf always can be
00056  * used to modify and send a response packet (and to 1 if this is not the case,
00057  * e.g. when link header is stripped of when receiving) */
00058 #ifndef LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00059 #define LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN 1
00060 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00061 
00062 /* The amount of data from the original packet to return in a dest-unreachable */
00063 #define ICMP_DEST_UNREACH_DATASIZE 8
00064 
00065 static void icmp_send_response(struct pbuf *p, u8_t type, u8_t code);
00066 
00067 /**
00068  * Processes ICMP input packets, called from ip_input().
00069  *
00070  * Currently only processes icmp echo requests and sends
00071  * out the echo response.
00072  *
00073  * @param p the icmp echo request packet, p->payload pointing to the ip header
00074  * @param inp the netif on which this packet was received
00075  */
00076 void
00077 icmp_input(struct pbuf *p, struct netif *inp)
00078 {
00079   u8_t type;
00080 #ifdef LWIP_DEBUG
00081   u8_t code;
00082 #endif /* LWIP_DEBUG */
00083   struct icmp_echo_hdr *iecho;
00084   struct ip_hdr *iphdr;
00085   ip_addr_t tmpaddr;
00086   s16_t hlen;
00087 
00088   ICMP_STATS_INC(icmp.recv);
00089   snmp_inc_icmpinmsgs();
00090 
00091 
00092   iphdr = (struct ip_hdr *)p->payload;
00093   hlen = IPH_HL(iphdr) * 4;
00094   if (pbuf_header(p, -hlen) || (p->tot_len < sizeof(u16_t)*2)) {
00095     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
00096     goto lenerr;
00097   }
00098 
00099   type = *((u8_t *)p->payload);
00100 #ifdef LWIP_DEBUG
00101   code = *(((u8_t *)p->payload)+1);
00102 #endif /* LWIP_DEBUG */
00103   switch (type) {
00104   case ICMP_ER:
00105     /* This is OK, echo reply might have been parsed by a raw PCB
00106        (as obviously, an echo request has been sent, too). */
00107     break; 
00108   case ICMP_ECHO:
00109 #if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
00110     {
00111       int accepted = 1;
00112 #if !LWIP_MULTICAST_PING
00113       /* multicast destination address? */
00114       if (ip_addr_ismulticast(&iphdr->dest)) {
00115         accepted = 0;
00116       }
00117 #endif /* LWIP_MULTICAST_PING */
00118 #if !LWIP_BROADCAST_PING
00119       /* broadcast destination address? */
00120       if (ip_addr_isbroadcast(&iphdr->dest, inp)) {
00121         accepted = 0;
00122       }
00123 #endif /* LWIP_BROADCAST_PING */
00124       /* broadcast or multicast destination address not acceptd? */
00125       if (!accepted) {
00126         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
00127         ICMP_STATS_INC(icmp.err);
00128         pbuf_free(p);
00129         return;
00130       }
00131     }
00132 #endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
00133     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
00134     if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
00135       LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
00136       goto lenerr;
00137     }
00138     if (inet_chksum_pbuf(p) != 0) {
00139       LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
00140       pbuf_free(p);
00141       ICMP_STATS_INC(icmp.chkerr);
00142       snmp_inc_icmpinerrors();
00143       return;
00144     }
00145 #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00146     if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
00147       /* p is not big enough to contain link headers
00148        * allocate a new one and copy p into it
00149        */
00150       struct pbuf *r;
00151       /* switch p->payload to ip header */
00152       if (pbuf_header(p, hlen)) {
00153         LWIP_ASSERT("icmp_input: moving p->payload to ip header failed\n", 0);
00154         goto memerr;
00155       }
00156       /* allocate new packet buffer with space for link headers */
00157       r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);
00158       if (r == NULL) {
00159         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
00160         goto memerr;
00161       }
00162       LWIP_ASSERT("check that first pbuf can hold struct the ICMP header",
00163                   (r->len >= hlen + sizeof(struct icmp_echo_hdr)));
00164       /* copy the whole packet including ip header */
00165       if (pbuf_copy(r, p) != ERR_OK) {
00166         LWIP_ASSERT("icmp_input: copying to new pbuf failed\n", 0);
00167         goto memerr;
00168       }
00169       iphdr = (struct ip_hdr *)r->payload;
00170       /* switch r->payload back to icmp header */
00171       if (pbuf_header(r, -hlen)) {
00172         LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
00173         goto memerr;
00174       }
00175       /* free the original p */
00176       pbuf_free(p);
00177       /* we now have an identical copy of p that has room for link headers */
00178       p = r;
00179     } else {
00180       /* restore p->payload to point to icmp header */
00181       if (pbuf_header(p, -(s16_t)(PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
00182         LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
00183         goto memerr;
00184       }
00185     }
00186 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00187     /* At this point, all checks are OK. */
00188     /* We generate an answer by switching the dest and src ip addresses,
00189      * setting the icmp type to ECHO_RESPONSE and updating the checksum. */
00190     iecho = (struct icmp_echo_hdr *)p->payload;
00191     ip_addr_copy(tmpaddr, iphdr->src);
00192     ip_addr_copy(iphdr->src, iphdr->dest);
00193     ip_addr_copy(iphdr->dest, tmpaddr);
00194     ICMPH_TYPE_SET(iecho, ICMP_ER);
00195     /* adjust the checksum */
00196     if (iecho->chksum >= htons(0xffff - (ICMP_ECHO << 8))) {
00197       iecho->chksum += htons(ICMP_ECHO << 8) + 1;
00198     } else {
00199       iecho->chksum += htons(ICMP_ECHO << 8);
00200     }
00201 
00202     /* Set the correct TTL and recalculate the header checksum. */
00203     IPH_TTL_SET(iphdr, ICMP_TTL);
00204     IPH_CHKSUM_SET(iphdr, 0);
00205 #if CHECKSUM_GEN_IP
00206     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
00207 #endif /* CHECKSUM_GEN_IP */
00208 
00209     ICMP_STATS_INC(icmp.xmit);
00210     /* increase number of messages attempted to send */
00211     snmp_inc_icmpoutmsgs();
00212     /* increase number of echo replies attempted to send */
00213     snmp_inc_icmpoutechoreps();
00214 
00215     if(pbuf_header(p, hlen)) {
00216       LWIP_ASSERT("Can't move over header in packet", 0);
00217     } else {
00218       err_t ret;
00219       ret = ip_output_if(p, &(iphdr->src), IP_HDRINCL,
00220                    ICMP_TTL, 0, IP_PROTO_ICMP, inp);
00221       if (ret != ERR_OK) {
00222         LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ip_output_if returned an error: %c.\n", ret));
00223       }
00224     }
00225     break;
00226   default:
00227     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" code %"S16_F" not supported.\n", 
00228                 (s16_t)type, (s16_t)code));
00229     ICMP_STATS_INC(icmp.proterr);
00230     ICMP_STATS_INC(icmp.drop);
00231   }
00232   pbuf_free(p);
00233   return;
00234 lenerr:
00235   pbuf_free(p);
00236   ICMP_STATS_INC(icmp.lenerr);
00237   snmp_inc_icmpinerrors();
00238   return;
00239 #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
00240 memerr:
00241   pbuf_free(p);
00242   ICMP_STATS_INC(icmp.err);
00243   snmp_inc_icmpinerrors();
00244   return;
00245 #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
00246 }
00247 
00248 /**
00249  * Send an icmp 'destination unreachable' packet, called from ip_input() if
00250  * the transport layer protocol is unknown and from udp_input() if the local
00251  * port is not bound.
00252  *
00253  * @param p the input packet for which the 'unreachable' should be sent,
00254  *          p->payload pointing to the IP header
00255  * @param t type of the 'unreachable' packet
00256  */
00257 void
00258 icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
00259 {
00260   icmp_send_response(p, ICMP_DUR, t);
00261 }
00262 
00263 #if IP_FORWARD || IP_REASSEMBLY
00264 /**
00265  * Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
00266  *
00267  * @param p the input packet for which the 'time exceeded' should be sent,
00268  *          p->payload pointing to the IP header
00269  * @param t type of the 'time exceeded' packet
00270  */
00271 void
00272 icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
00273 {
00274   icmp_send_response(p, ICMP_TE, t);
00275 }
00276 
00277 #endif /* IP_FORWARD || IP_REASSEMBLY */
00278 
00279 /**
00280  * Send an icmp packet in response to an incoming packet.
00281  *
00282  * @param p the input packet for which the 'unreachable' should be sent,
00283  *          p->payload pointing to the IP header
00284  * @param type Type of the ICMP header
00285  * @param code Code of the ICMP header
00286  */
00287 static void
00288 icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
00289 {
00290   struct pbuf *q;
00291   struct ip_hdr *iphdr;
00292   /* we can use the echo header here */
00293   struct icmp_echo_hdr *icmphdr;
00294 
00295   /* ICMP header + IP header + 8 bytes of data */
00296   q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
00297                  PBUF_RAM);
00298   if (q == NULL) {
00299     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
00300     return;
00301   }
00302   LWIP_ASSERT("check that first pbuf can hold icmp message",
00303              (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
00304 
00305   iphdr = (struct ip_hdr *)p->payload;
00306   LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
00307   ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
00308   LWIP_DEBUGF(ICMP_DEBUG, (" to "));
00309   ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
00310   LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
00311 
00312   icmphdr = (struct icmp_echo_hdr *)q->payload;
00313   icmphdr->type = type;
00314   icmphdr->code = code;
00315   icmphdr->id = 0;
00316   icmphdr->seqno = 0;
00317 
00318   /* copy fields from original packet */
00319   SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
00320           IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
00321 
00322   /* calculate checksum */
00323   icmphdr->chksum = 0;
00324   icmphdr->chksum = inet_chksum(icmphdr, q->len);
00325   ICMP_STATS_INC(icmp.xmit);
00326   /* increase number of messages attempted to send */
00327   snmp_inc_icmpoutmsgs();
00328   /* increase number of destination unreachable messages attempted to send */
00329   snmp_inc_icmpouttimeexcds();
00330   ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
00331   pbuf_free(q);
00332 }
00333 
00334 #endif /* LWIP_ICMP */