/** * @file * This is the IPv4 packet segmentation and reassembly implementation. * *//* * 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: Jani Monoses <jani@iv.ro>  *         Simon Goldschmidt * original reassembly code by Adam Dunkels <adam@sics.se> *  */#include "lwip/opt.h"#include "lwip/ip_frag.h"#include "lwip/ip.h"#include "lwip/inet.h"#include "lwip/inet_chksum.h"#include "lwip/netif.h"#include "lwip/snmp.h"#include "lwip/stats.h"#include "lwip/icmp.h"#include <string.h>#if IP_REASSEMBLY/** * The IP reassembly code currently has the following limitations: * - IP header options are not supported * - fragments must not overlap (e.g. due to different routes), *   currently, overlapping or duplicate fragments are thrown away *   if IP_REASS_CHECK_OVERLAP=1 (the default)! * * @todo: work with IP header options *//** Setting this to 0, you can turn off checking the fragments for overlapping * regions. The code gets a little smaller. Only use this if you know that * overlapping won't occur on your network! */#ifndef IP_REASS_CHECK_OVERLAP#define IP_REASS_CHECK_OVERLAP 1#endif /* IP_REASS_CHECK_OVERLAP *//** Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is * full (IP_REASS_MAX_PBUFS pbufs are enqueued). The code gets a little smaller. * Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA * is set to 1, so one datagram can be reassembled at a time, only. */#ifndef IP_REASS_FREE_OLDEST#define IP_REASS_FREE_OLDEST 1#endif /* IP_REASS_FREE_OLDEST */#define IP_REASS_FLAG_LASTFRAG 0x01/** This is a helper struct which holds the starting * offset and the ending offset of this fragment to * easily chain the fragments. * It has to be packed since it has to fit inside the IP header. */#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/bpstruct.h"#endifPACK_STRUCT_BEGINstruct ip_reass_helper {  PACK_STRUCT_FIELD(struct pbuf *next_pbuf);  PACK_STRUCT_FIELD(u16_t start);  PACK_STRUCT_FIELD(u16_t end);} PACK_STRUCT_STRUCT;PACK_STRUCT_END#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/epstruct.h"#endif#define IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)  \  (ip_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \   ip_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \   IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0/* global variables */static struct ip_reassdata *reassdatagrams;static u16_t ip_reass_pbufcount;/* function prototypes */static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);/** * Reassembly timer base function * for both NO_SYS == 0 and 1 (!). * * Should be called every 1000 msec (defined by IP_TMR_INTERVAL). */voidip_reass_tmr(void){  struct ip_reassdata *r, *prev = NULL;  r = reassdatagrams;  while (r != NULL) {    /* Decrement the timer. Once it reaches 0,     * clean up the incomplete fragment assembly */    if (r->timer > 0) {      r->timer--;      LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n",(u16_t)r->timer));      prev = r;      r = r->next;    } else {      /* reassembly timed out */      struct ip_reassdata *tmp;      LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer timed out\n"));      tmp = r;      /* get the next pointer before freeing */      r = r->next;      /* free the helper struct and all enqueued pbufs */      ip_reass_free_complete_datagram(tmp, prev);     }   }}/** * Free a datagram (struct ip_reassdata) and all its pbufs. * Updates the total count of enqueued pbufs (ip_reass_pbufcount), * SNMP counters and sends an ICMP time exceeded packet. * * @param ipr datagram to free * @param prev the previous datagram in the linked list * @return the number of pbufs freed */static intip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev){  int pbufs_freed = 0;  struct pbuf *p;  struct ip_reass_helper *iprh;  LWIP_ASSERT("prev != ipr", prev != ipr);  if (prev != NULL) {    LWIP_ASSERT("prev->next == ipr", prev->next == ipr);  }  snmp_inc_ipreasmfails();#if LWIP_ICMP  iprh = (struct ip_reass_helper *)ipr->p->payload;  if (iprh->start == 0) {    /* The first fragment was received, send ICMP time exceeded. */    /* First, de-queue the first pbuf from r->p. */    p = ipr->p;    ipr->p = iprh->next_pbuf;    /* Then, copy the original header into it. */    SMEMCPY(p->payload, &ipr->iphdr, IP_HLEN);    icmp_time_exceeded(p, ICMP_TE_FRAG);    pbufs_freed += pbuf_clen(p);    pbuf_free(p);  }#endif /* LWIP_ICMP */  /* First, free all received pbufs.  The individual pbufs need to be released      separately as they have not yet been chained */  p = ipr->p;  while (p != NULL) {    struct pbuf *pcur;    iprh = (struct ip_reass_helper *)p->payload;    pcur = p;    /* get the next pointer before freeing */    p = iprh->next_pbuf;    pbufs_freed += pbuf_clen(pcur);    pbuf_free(pcur);      }  /* Then, unchain the struct ip_reassdata from the list and free it. */  ip_reass_dequeue_datagram(ipr, prev);  LWIP_ASSERT("ip_reass_pbufcount >= clen", ip_reass_pbufcount >= pbufs_freed);  ip_reass_pbufcount -= pbufs_freed;  return pbufs_freed;}#if IP_REASS_FREE_OLDEST/** * Free the oldest datagram to make room for enqueueing new fragments. * The datagram 'fraghdr' belongs to is not freed! * * @param fraghdr IP header of the current fragment * @param pbufs_needed number of pbufs needed to enqueue *        (used for freeing other datagrams if not enough space) * @return the number of pbufs freed */static intip_reass_remove_oldest_datagram(struct ip_hdr *fraghdr, int pbufs_needed){  /* @todo Can't we simply remove the last datagram in the   *       linked list behind reassdatagrams?   */  struct ip_reassdata *r, *oldest, *prev;  int pbufs_freed = 0, pbufs_freed_current;  int other_datagrams;  /* Free datagrams until being allowed to enqueue 'pbufs_needed' pbufs,   * but don't free the datagram that 'fraghdr' belongs to! */  do {    oldest = NULL;    prev = NULL;    other_datagrams = 0;    r = reassdatagrams;    while (r != NULL) {      if (!IP_ADDRESSES_AND_ID_MATCH(&r->iphdr, fraghdr)) {        /* Not the same datagram as fraghdr */        other_datagrams++;        if (oldest == NULL) {          oldest = r;        } else if (r->timer <= oldest->timer) {          /* older than the previous oldest */          oldest = r;        }      }      if (r->next != NULL) {        prev = r;      }      r = r->next;    }    if (oldest != NULL) {      pbufs_freed_current = ip_reass_free_complete_datagram(oldest, prev);      pbufs_freed += pbufs_freed_current;    }  } while ((pbufs_freed < pbufs_needed) && (other_datagrams > 1));  return pbufs_freed;}#endif /* IP_REASS_FREE_OLDEST *//** * Enqueues a new fragment into the fragment queue * @param fraghdr points to the new fragments IP hdr * @param clen number of pbufs needed to enqueue (used for freeing other datagrams if not enough space) * @return A pointer to the queue location into which the fragment was enqueued */static struct ip_reassdata*ip_reass_enqueue_new_datagram(struct ip_hdr *fraghdr, int clen){  struct ip_reassdata* ipr;  /* No matching previous fragment found, allocate a new reassdata struct */  ipr = memp_malloc(MEMP_REASSDATA);  if (ipr == NULL) {#if IP_REASS_FREE_OLDEST    if (ip_reass_remove_oldest_datagram(fraghdr, clen) >= clen) {      ipr = memp_malloc(MEMP_REASSDATA);    }    if (ipr == NULL)#endif /* IP_REASS_FREE_OLDEST */    {      IPFRAG_STATS_INC(ip_frag.memerr);      LWIP_DEBUGF(IP_REASS_DEBUG,("Failed to alloc reassdata struct\n"));      return NULL;    }  }  memset(ipr, 0, sizeof(struct ip_reassdata));  ipr->timer = IP_REASS_MAXAGE;  /* enqueue the new structure to the front of the list */  ipr->next = reassdatagrams;  reassdatagrams = ipr;  /* copy the ip header for later tests and input */  /* @todo: no ip options supported? */  SMEMCPY(&(ipr->iphdr), fraghdr, IP_HLEN);  return ipr;}/** * Dequeues a datagram from the datagram queue. Doesn't deallocate the pbufs. * @param ipr points to the queue entry to dequeue */static voidip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev){    /* dequeue the reass struct  */  if (reassdatagrams == ipr) {    /* it was the first in the list */    reassdatagrams = ipr->next;  } else {    /* it wasn't the first, so it must have a valid 'prev' */    LWIP_ASSERT("sanity check linked list", prev != NULL);    prev->next = ipr->next;  }  /* now we can free the ip_reass struct */  memp_free(MEMP_REASSDATA, ipr);}/** * Chain a new pbuf into the pbuf list that composes the datagram.  The pbuf list * will grow over time as  new pbufs are rx. * Also checks that the datagram passes basic continuity checks (if the last * fragment was received at least once). * @param root_p points to the 'root' pbuf for the current datagram being assembled. * @param new_p points to the pbuf for the current fragment * @return 0 if invalid, >0 otherwise */static intip_reass_chain_frag_into_datagram_and_validate(struct ip_reassdata *ipr, struct pbuf *new_p){  struct ip_reass_helper *iprh, *iprh_tmp, *iprh_prev=NULL;  struct pbuf *q;  u16_t offset,len;  struct ip_hdr *fraghdr;  int valid = 1;  /* Extract length and fragment offset from current fragment */  fraghdr = (struct ip_hdr*)new_p->payload;   len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;  offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;  /* overwrite the fragment's ip header from the pbuf with our helper struct,   * and setup the embedded helper structure. */  /* make sure the struct ip_reass_helper fits into the IP header */  LWIP_ASSERT("sizeof(struct ip_reass_helper) <= IP_HLEN",              sizeof(struct ip_reass_helper) <= IP_HLEN);  iprh = (struct ip_reass_helper*)new_p->payload;  iprh->next_pbuf = NULL;  iprh->start = offset;  iprh->end = offset + len;  /* Iterate through until we either get to the end of the list (append),   * or we find on with a larger offset (insert). */  for (q = ipr->p; q != NULL;) {    iprh_tmp = (struct ip_reass_helper*)q->payload;    if (iprh->start < iprh_tmp->start) {      /* the new pbuf should be inserted before this */      iprh->next_pbuf = q;      if (iprh_prev != NULL) {        /* not the fragment with the lowest offset */#if IP_REASS_CHECK_OVERLAP        if ((iprh->start < iprh_prev->end) || (iprh->end > iprh_tmp->start)) {          /* fragment overlaps with previous or following, throw away */          goto freepbuf;        }#endif /* IP_REASS_CHECK_OVERLAP */        iprh_prev->next_pbuf = new_p;      } else {        /* fragment with the lowest offset */        ipr->p = new_p;      }      break;    } else if(iprh->start == iprh_tmp->start) {      /* received the same datagram twice: no need to keep the datagram */      goto freepbuf;#if IP_REASS_CHECK_OVERLAP    } else if(iprh->start < iprh_tmp->end) {      /* overlap: no need to keep the new datagram */      goto freepbuf;#endif /* IP_REASS_CHECK_OVERLAP */    } else {      /* Check if the fragments received so far have no wholes. */      if (iprh_prev != NULL) {        if (iprh_prev->end != iprh_tmp->start) {          /* There is a fragment missing between the current           * and the previous fragment */          valid = 0;        }      }    }    q = iprh_tmp->next_pbuf;    iprh_prev = iprh_tmp;  }  /* If q is NULL, then we made it to the end of the list. Determine what to do now */  if (q == NULL) {    if (iprh_prev != NULL) {      /* this is (for now), the fragment with the highest offset:       * chain it to the last fragment */#if IP_REASS_CHECK_OVERLAP      LWIP_ASSERT("check fragments don't overlap", iprh_prev->end <= iprh->start);#endif /* IP_REASS_CHECK_OVERLAP */