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 "../../include/lwip/opt.h"
  
  #if LWIP_IPV4 && LWIP_ICMP /* don't build if not configured for use in lwipopts.h */
  
  #include "../../include/lwip/icmp.h"
  #include "../../include/lwip/inet_chksum.h"
  #include "../../include/lwip/ip.h"
  #include "../../include/lwip/def.h"
  #include "../../include/lwip/stats.h"
  
  #include <string.h>
  
  #ifdef LWIP_HOOK_FILENAME
  #include LWIP_HOOK_FILENAME
  #endif
  
  /** 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 off 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;
  	const struct ip_hdr *iphdr_in;
  	u16_t hlen;
  	const ip4_addr_t *src;
  
  	ICMP_STATS_INC(icmp.recv);
  	MIB2_STATS_INC(mib2.icmpinmsgs);
  
  	iphdr_in = ip4_current_header();
  	hlen = IPH_HL_BYTES(iphdr_in);
  	if(hlen < IP_HLEN) {
  		LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short IP header (%"
  				S16_F
  				" bytes) received\n", hlen));
  		goto lenerr;
  	}
  	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);
  	/* if debug is enabled but debug statement below is somehow disabled: */
  	LWIP_UNUSED_ARG(code);
  #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). */
  			MIB2_STATS_INC(mib2.icmpinechoreps);
  			break;
  		case ICMP_ECHO:
  			MIB2_STATS_INC(mib2.icmpinechos);
  			src = ip4_current_dest_addr();
  			/* multicast destination address? */
  			if(ip4_addr_ismulticast(ip4_current_dest_addr())) {
  #if LWIP_MULTICAST_PING
  				/* For multicast, use address of receiving interface as source address */
  				src = netif_ip4_addr(inp);
  #else /* LWIP_MULTICAST_PING */
  				LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast pings\n"));
  				goto icmperr;
  #endif /* LWIP_MULTICAST_PING */
  			}
  			/* broadcast destination address? */
  			if(ip4_addr_isbroadcast(ip4_current_dest_addr(), ip_current_netif())) {
  #if LWIP_BROADCAST_PING
  				/* For broadcast, use address of receiving interface as source address */
  				src = netif_ip4_addr(inp);
  #else /* LWIP_BROADCAST_PING */
  				LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to broadcast pings\n"));
  				goto icmperr;
  #endif /* 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__NETIF_CHECKSUM_ENABLED(inp, NETIF_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);
  			MIB2_STATS_INC(mib2.icmpinerrors);
  			return;
  		}
  	}
  #endif
  #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
  			if(pbuf_add_header(p, hlen + PBUF_LINK_HLEN + PBUF_LINK_ENCAPSULATION_HLEN)) {
  				/* p is not big enough to contain link headers
  				 * allocate a new one and copy p into it
  				 */
  				struct pbuf *r;
  				u16_t alloc_len = (u16_t) (p->tot_len + hlen);
  				if(alloc_len < p->tot_len) {
  					LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed (tot_len overflow)\n"));
  					goto icmperr;
  				}
  				/* allocate new packet buffer with space for link headers */
  				r = pbuf_alloc(PBUF_LINK, alloc_len, PBUF_RAM);
  				if(r == NULL) {
  					LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
  					goto icmperr;
  				}
  				if(r->len < hlen + sizeof(struct icmp_echo_hdr)) {
  					LWIP_DEBUGF(ICMP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("first pbuf cannot hold the ICMP header"));
  					pbuf_free(r);
  					goto icmperr;
  				}
  				/* copy the ip header */
  				MEMCPY(r->payload, iphdr_in, hlen);
  				/* switch r->payload back to icmp header (cannot fail) */
  				if(pbuf_remove_header(r, hlen)) {
  					LWIP_ASSERT("icmp_input: moving r->payload to icmp header failed\n", 0);
  					pbuf_free(r);
  					goto icmperr;
  				}
  				/* copy the rest of the packet without ip header */
  				if(pbuf_copy(r, p) != ERR_OK) {
  					LWIP_DEBUGF(ICMP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("icmp_input: copying to new pbuf failed"));
  					pbuf_free(r);
  					goto icmperr;
  				}
  				/* 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 (cannot fail) */
  				if(pbuf_remove_header(p, hlen + PBUF_LINK_HLEN + PBUF_LINK_ENCAPSULATION_HLEN)) {
  					LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
  					goto icmperr;
  				}
  			}
  #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;
  			if(pbuf_add_header(p, hlen)) {
  				LWIP_DEBUGF(ICMP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("Can't move over header in packet"));
  			} else {
  				err_t ret;
  				struct ip_hdr *iphdr = (struct ip_hdr *) p->payload;
  				ip4_addr_copy(iphdr->src, *src);
  				ip4_addr_copy(iphdr->dest, *ip4_current_src_addr());
  				ICMPH_TYPE_SET(iecho, ICMP_ER);
  #if CHECKSUM_GEN_ICMP
  				IF__NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_ICMP) {
  					/* adjust the checksum */
  					if(iecho->chksum > PP_HTONS(0xffffU - (ICMP_ECHO << 8))) {
  						iecho->chksum = (u16_t) (iecho->chksum + PP_HTONS((u16_t) (ICMP_ECHO << 8)) + 1);
  					} else {
  						iecho->chksum = (u16_t) (iecho->chksum + PP_HTONS(ICMP_ECHO << 8));
  					}
  				}
  #if LWIP_CHECKSUM_CTRL_PER_NETIF
  				else {
  				  iecho->chksum = 0;
  				}
  #endif /* LWIP_CHECKSUM_CTRL_PER_NETIF */
  #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
  				IF__NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_IP) {
  					IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, hlen));
  				}
  #endif /* CHECKSUM_GEN_IP */
  
  				ICMP_STATS_INC(icmp.xmit);
  				/* increase number of messages attempted to send */
  				MIB2_STATS_INC(mib2.icmpoutmsgs);
  				/* increase number of echo replies attempted to send */
  				MIB2_STATS_INC(mib2.icmpoutechoreps);
  
  				/* send an ICMP packet */
  				ret = ip4_output_if(p, src, LWIP_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: %s\n", lwip_strerr(ret)));
  				}
  			}
  			break;
  		default:
  			if(type == ICMP_DUR) {
  				MIB2_STATS_INC(mib2.icmpindestunreachs);
  			} else if(type == ICMP_TE) {
  				MIB2_STATS_INC(mib2.icmpintimeexcds);
  			} else if(type == ICMP_PP) {
  				MIB2_STATS_INC(mib2.icmpinparmprobs);
  			} else if(type == ICMP_SQ) {
  				MIB2_STATS_INC(mib2.icmpinsrcquenchs);
  			} else if(type == ICMP_RD) {
  				MIB2_STATS_INC(mib2.icmpinredirects);
  			} else if(type == ICMP_TS) {
  				MIB2_STATS_INC(mib2.icmpintimestamps);
  			} else if(type == ICMP_TSR) {
  				MIB2_STATS_INC(mib2.icmpintimestampreps);
  			} else if(type == ICMP_AM) {
  				MIB2_STATS_INC(mib2.icmpinaddrmasks);
  			} else if(type == ICMP_AMR) {
  				MIB2_STATS_INC(mib2.icmpinaddrmaskreps);
  			}
  			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);
  	MIB2_STATS_INC(mib2.icmpinerrors);
  	return;
  #if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN || !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
  	icmperr:
  	pbuf_free(p);
  	ICMP_STATS_INC(icmp.err);
  	MIB2_STATS_INC(mib2.icmpinerrors);
  	return;
  #endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN || !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
  }
  
  /**
   * 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) {
  	MIB2_STATS_INC(mib2.icmpoutdestunreachs);
  	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) {
  	MIB2_STATS_INC(mib2.icmpouttimeexcds);
  	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;
  	ip4_addr_t iphdr_src;
  	struct netif *netif;
  
  	/* increase number of messages attempted to send */
  	MIB2_STATS_INC(mib2.icmpoutmsgs);
  
  	/* 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"));
  		MIB2_STATS_INC(mib2.icmpouterrors);
  		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 "));
  	ip4_addr_debug_print_val(ICMP_DEBUG, iphdr->src);
  	LWIP_DEBUGF(ICMP_DEBUG, (" to "));
  	ip4_addr_debug_print_val(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);
  
  	ip4_addr_copy(iphdr_src, iphdr->src);
  #ifdef LWIP_HOOK_IP4_ROUTE_SRC
  	{
  	  ip4_addr_t iphdr_dst;
  	  ip4_addr_copy(iphdr_dst, iphdr->dest);
  	  netif = ip4_route_src(&iphdr_dst, &iphdr_src);
  	}
  #else
  	netif = ip4_route(&iphdr_src);
  #endif
  	if(netif != NULL) {
  		/* calculate checksum */
  		icmphdr->chksum = 0;
  #if CHECKSUM_GEN_ICMP
  		IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_ICMP) {
  			icmphdr->chksum = inet_chksum(icmphdr, q->len);
  		}
  #endif
  		ICMP_STATS_INC(icmp.xmit);
  		ip4_output_if(q, NULL, &iphdr_src, ICMP_TTL, 0, IP_PROTO_ICMP, netif);
  	}
  	pbuf_free(q);
  }
  
  #endif /* LWIP_IPV4 && LWIP_ICMP */
  