/* @file * * This is the IP layer implementation for incoming and outgoing IP traffic. *  * @see ip_frag.c * *//* * 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> * */#include "lwip/opt.h"#include "lwip/def.h"#include "lwip/mem.h"#include "lwip/ip.h"#include "lwip/ip_frag.h"#include "lwip/inet.h"#include "lwip/netif.h"#include "lwip/icmp.h"#include "lwip/raw.h"#include "lwip/udp.h"#include "lwip/tcp.h"#include "lwip/stats.h"#include "arch/perf.h"#include "lwip/snmp.h"#if LWIP_DHCP#  include "lwip/dhcp.h"#endif /* LWIP_DHCP *//** * Initializes the IP layer. */voidip_init(void){  /* no initializations as of yet */}/** * Finds the appropriate network interface for a given IP address. It * searches the list of network interfaces linearly. A match is found * if the masked IP address of the network interface equals the masked * IP address given to the function. */struct netif *ip_route(struct ip_addr *dest){  struct netif *netif;  /* iterate through netifs */  for(netif = netif_list; netif != NULL; netif = netif->next) {    /* network mask matches? */    if (ip_addr_maskcmp(dest, &(netif->ip_addr), &(netif->netmask))) {      /* return netif on which to forward IP packet */      return netif;    }  }  /* no matching netif found, use default netif */  return netif_default;}#if IP_FORWARD/** * Forwards an IP packet. It finds an appropriate route for the * packet, decrements the TTL value of the packet, adjusts the * checksum and outputs the packet on the appropriate interface. */static struct netif *ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp){  struct netif *netif;  PERF_START;  /* Find network interface where to forward this IP packet to. */  netif = ip_route((struct ip_addr *)&(iphdr->dest));  if (netif == NULL) {    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%lx found\n",                      iphdr->dest.addr));    snmp_inc_ipnoroutes();    return (struct netif *)NULL;  }  /* Do not forward packets onto the same network interface on which   * they arrived. */  if (netif == inp) {    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));    snmp_inc_ipnoroutes();    return (struct netif *)NULL;  }  /* decrement TTL */  IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);  /* send ICMP if TTL == 0 */  if (IPH_TTL(iphdr) == 0) {    /* Don't send ICMP messages in response to ICMP messages */    if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {      icmp_time_exceeded(p, ICMP_TE_TTL);      snmp_inc_icmpouttimeexcds();    }    return (struct netif *)NULL;  }  /* Incrementally update the IP checksum. */  if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);  } else {    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));  }  LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%lx\n",                    iphdr->dest.addr));  IP_STATS_INC(ip.fw);  IP_STATS_INC(ip.xmit);    snmp_inc_ipforwdatagrams();  PERF_STOP("ip_forward");  /* transmit pbuf on chosen interface */  netif->output(netif, p, (struct ip_addr *)&(iphdr->dest));  return netif;}#endif /* IP_FORWARD *//** * This function is called by the network interface device driver when * an IP packet is received. The function does the basic checks of the * IP header such as packet size being at least larger than the header * size etc. If the packet was not destined for us, the packet is * forwarded (using ip_forward). The IP checksum is always checked. * * Finally, the packet is sent to the upper layer protocol input function. *  *  *  */err_tip_input(struct pbuf *p, struct netif *inp) {  struct ip_hdr *iphdr;  struct netif *netif;  u16_t iphdrlen;  IP_STATS_INC(ip.recv);  snmp_inc_ipinreceives();  /* identify the IP header */  iphdr = p->payload;  if (IPH_V(iphdr) != 4) {    LWIP_DEBUGF(IP_DEBUG | 1, ("IP packet dropped due to bad version number %u\n", IPH_V(iphdr)));    ip_debug_print(p);    pbuf_free(p);    IP_STATS_INC(ip.err);    IP_STATS_INC(ip.drop);    snmp_inc_ipunknownprotos();    return ERR_OK;  }  /* obtain IP header length in number of 32-bit words */  iphdrlen = IPH_HL(iphdr);  /* calculate IP header length in bytes */  iphdrlen *= 4;  /* header length exceeds first pbuf length? */  if (iphdrlen > p->len) {    LWIP_DEBUGF(IP_DEBUG | 2, ("IP header (len %u) does not fit in first pbuf (len %u), IP packet droppped.\n",      iphdrlen, p->len));    /* free (drop) packet pbufs */    pbuf_free(p);    IP_STATS_INC(ip.lenerr);    IP_STATS_INC(ip.drop);    snmp_inc_ipindiscards();    return ERR_OK;  }  /* verify checksum */#if CHECKSUM_CHECK_IP  if (inet_chksum(iphdr, iphdrlen) != 0) {    LWIP_DEBUGF(IP_DEBUG | 2, ("Checksum (0x%x) failed, IP packet dropped.\n", inet_chksum(iphdr, iphdrlen)));    ip_debug_print(p);    pbuf_free(p);    IP_STATS_INC(ip.chkerr);    IP_STATS_INC(ip.drop);    snmp_inc_ipindiscards();    return ERR_OK;  }#endif  /* Trim pbuf. This should have been done at the netif layer,   * but we'll do it anyway just to be sure that its done. */  pbuf_realloc(p, ntohs(IPH_LEN(iphdr)));  /* match packet against an interface, i.e. is this packet for us? */  for (netif = netif_list; netif != NULL; netif = netif->next) {    LWIP_DEBUGF(IP_DEBUG, ("ip_input: iphdr->dest 0x%lx netif->ip_addr 0x%lx (0x%lx, 0x%lx, 0x%lx)\n",      iphdr->dest.addr, netif->ip_addr.addr,      iphdr->dest.addr & netif->netmask.addr,      netif->ip_addr.addr & netif->netmask.addr,      iphdr->dest.addr & ~(netif->netmask.addr)));    /* interface is up and configured? */    if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr))))    {      /* unicast to this interface address? */      if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||        /* or broadcast matching this interface network address? */        (ip_addr_isbroadcast(&(iphdr->dest), netif) &&         ip_addr_maskcmp(&(iphdr->dest), &(netif->ip_addr), &(netif->netmask))) ||         /* or restricted broadcast? */         ip_addr_cmp(&(iphdr->dest), IP_ADDR_BROADCAST)) {        LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c\n",          netif->name[0], netif->name[1]));        /* break out of for loop */        break;      }    }  }#if LWIP_DHCP  /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed   * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.   * According to RFC 1542 section 3.1.1, referred by RFC 2131).