ip_frag.c

00001 /**
00002  * @file
00003  * This is the IPv4 packet segmentation and reassembly implementation.
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: Jani Monoses <jani@iv.ro> 
00036  *         Simon Goldschmidt
00037  * original reassembly code by Adam Dunkels <adam@sics.se>
00038  * 
00039  */
00040 
00041 #include "lwip/opt.h"
00042 #include "lwip/ip_frag.h"
00043 #include "lwip/ip.h"
00044 #include "lwip/inet.h"
00045 #include "lwip/inet_chksum.h"
00046 #include "lwip/netif.h"
00047 #include "lwip/snmp.h"
00048 #include "lwip/stats.h"
00049 #include "lwip/icmp.h"
00050 
00051 #include <string.h>
00052 
00053 #if IP_REASSEMBLY
00054 /**
00055  * The IP reassembly code currently has the following limitations:
00056  * - IP header options are not supported
00057  * - fragments must not overlap (e.g. due to different routes),
00058  *   currently, overlapping or duplicate fragments are thrown away
00059  *   if IP_REASS_CHECK_OVERLAP=1 (the default)!
00060  *
00061  * @todo: work with IP header options
00062  */
00063 
00064 /** Setting this to 0, you can turn off checking the fragments for overlapping
00065  * regions. The code gets a little smaller. Only use this if you know that
00066  * overlapping won't occur on your network! */
00067 #ifndef IP_REASS_CHECK_OVERLAP
00068 #define IP_REASS_CHECK_OVERLAP 1
00069 #endif /* IP_REASS_CHECK_OVERLAP */
00070 
00071 /** Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is
00072  * full (IP_REASS_MAX_PBUFS pbufs are enqueued). The code gets a little smaller.
00073  * Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA
00074  * is set to 1, so one datagram can be reassembled at a time, only. */
00075 #ifndef IP_REASS_FREE_OLDEST
00076 #define IP_REASS_FREE_OLDEST 1
00077 #endif /* IP_REASS_FREE_OLDEST */
00078 
00079 #define IP_REASS_FLAG_LASTFRAG 0x01
00080 
00081 /** This is a helper struct which holds the starting
00082  * offset and the ending offset of this fragment to
00083  * easily chain the fragments.
00084  * It has to be packed since it has to fit inside the IP header.
00085  */
00086 // XXX: For armcc
00087 struct ip_reass_helper {
00088   struct pbuf *next_pbuf;
00089   u16_t start;
00090   u16_t end;
00091 };
00092 
00093 /*
00094 #ifdef PACK_STRUCT_USE_INCLUDES
00095 #  include "arch/bpstruct.h"
00096 #endif
00097 PACK_STRUCT_BEGIN
00098 struct ip_reass_helper {
00099   PACK_STRUCT_FIELD(struct pbuf *next_pbuf);
00100   PACK_STRUCT_FIELD(u16_t start);
00101   PACK_STRUCT_FIELD(u16_t end);
00102 } PACK_STRUCT_STRUCT;
00103 PACK_STRUCT_END
00104 #ifdef PACK_STRUCT_USE_INCLUDES
00105 #  include "arch/epstruct.h"
00106 #endif
00107 */
00108 #define IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)  \
00109   (ip_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \
00110    ip_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \
00111    IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0
00112 
00113 /* global variables */
00114 static struct ip_reassdata *reassdatagrams;
00115 static u16_t ip_reass_pbufcount;
00116 
00117 /* function prototypes */
00118 static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00119 static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00120 
00121 /**
00122  * Reassembly timer base function
00123  * for both NO_SYS == 0 and 1 (!).
00124  *
00125  * Should be called every 1000 msec (defined by IP_TMR_INTERVAL).
00126  */
00127 void
00128 ip_reass_tmr(void)
00129 {
00130   struct ip_reassdata *r, *prev = NULL;
00131 
00132   r = reassdatagrams;
00133   while (r != NULL) {
00134     /* Decrement the timer. Once it reaches 0,
00135      * clean up the incomplete fragment assembly */
00136     if (r->timer > 0) {
00137       r->timer--;
00138       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n",(u16_t)r->timer));
00139       prev = r;
00140       r = r->next;
00141     } else {
00142       /* reassembly timed out */
00143       struct ip_reassdata *tmp;
00144       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer timed out\n"));
00145       tmp = r;
00146       /* get the next pointer before freeing */
00147       r = r->next;
00148       /* free the helper struct and all enqueued pbufs */
00149       ip_reass_free_complete_datagram(tmp, prev);
00150      }
00151    }
00152 }
00153 
00154 /**
00155  * Free a datagram (struct ip_reassdata) and all its pbufs.
00156  * Updates the total count of enqueued pbufs (ip_reass_pbufcount),
00157  * SNMP counters and sends an ICMP time exceeded packet.
00158  *
00159  * @param ipr datagram to free
00160  * @param prev the previous datagram in the linked list
00161  * @return the number of pbufs freed
00162  */
00163 static int
00164 ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00165 {
00166   int pbufs_freed = 0;
00167   struct pbuf *p;
00168   struct ip_reass_helper *iprh;
00169 
00170   LWIP_ASSERT("prev != ipr", prev != ipr);
00171   if (prev != NULL) {
00172     LWIP_ASSERT("prev->next == ipr", prev->next == ipr);
00173   }
00174 
00175   snmp_inc_ipreasmfails();
00176 #if LWIP_ICMP
00177   iprh = (struct ip_reass_helper *)ipr->p->payload;
00178   if (iprh->start == 0) {
00179     /* The first fragment was received, send ICMP time exceeded. */
00180     /* First, de-queue the first pbuf from r->p. */
00181     p = ipr->p;
00182     ipr->p = iprh->next_pbuf;
00183     /* Then, copy the original header into it. */
00184     SMEMCPY(p->payload, &ipr->iphdr, IP_HLEN);
00185     icmp_time_exceeded(p, ICMP_TE_FRAG);
00186     pbufs_freed += pbuf_clen(p);
00187     pbuf_free(p);
00188   }
00189 #endif /* LWIP_ICMP */
00190 
00191   /* First, free all received pbufs.  The individual pbufs need to be released 
00192      separately as they have not yet been chained */
00193   p = ipr->p;
00194   while (p != NULL) {
00195     struct pbuf *pcur;
00196     iprh = (struct ip_reass_helper *)p->payload;
00197     pcur = p;
00198     /* get the next pointer before freeing */
00199     p = iprh->next_pbuf;
00200     pbufs_freed += pbuf_clen(pcur);
00201     pbuf_free(pcur);    
00202   }
00203   /* Then, unchain the struct ip_reassdata from the list and free it. */
00204   ip_reass_dequeue_datagram(ipr, prev);
00205   LWIP_ASSERT("ip_reass_pbufcount >= clen", ip_reass_pbufcount >= pbufs_freed);
00206   ip_reass_pbufcount -= pbufs_freed;
00207 
00208   return pbufs_freed;
00209 }
00210 
00211 #if IP_REASS_FREE_OLDEST
00212 /**
00213  * Free the oldest datagram to make room for enqueueing new fragments.
00214  * The datagram 'fraghdr' belongs to is not freed!
00215  *
00216  * @param fraghdr IP header of the current fragment
00217  * @param pbufs_needed number of pbufs needed to enqueue
00218  *        (used for freeing other datagrams if not enough space)
00219  * @return the number of pbufs freed
00220  */
00221 static int
00222 ip_reass_remove_oldest_datagram(struct ip_hdr *fraghdr, int pbufs_needed)
00223 {
00224   /* @todo Can't we simply remove the last datagram in the
00225    *       linked list behind reassdatagrams?
00226    */
00227   struct ip_reassdata *r, *oldest, *prev;
00228   int pbufs_freed = 0, pbufs_freed_current;
00229   int other_datagrams;
00230 
00231   /* Free datagrams until being allowed to enqueue 'pbufs_needed' pbufs,
00232    * but don't free the datagram that 'fraghdr' belongs to! */
00233   do {
00234     oldest = NULL;
00235     prev = NULL;
00236     other_datagrams = 0;
00237     r = reassdatagrams;
00238     while (r != NULL) {
00239       if (!IP_ADDRESSES_AND_ID_MATCH(&r->iphdr, fraghdr)) {
00240         /* Not the same datagram as fraghdr */
00241         other_datagrams++;
00242         if (oldest == NULL) {
00243           oldest = r;
00244         } else if (r->timer <= oldest->timer) {
00245           /* older than the previous oldest */
00246           oldest = r;
00247         }
00248       }
00249       if (r->next != NULL) {
00250         prev = r;
00251       }
00252       r = r->next;
00253     }
00254     if (oldest != NULL) {
00255       pbufs_freed_current = ip_reass_free_complete_datagram(oldest, prev);
00256       pbufs_freed += pbufs_freed_current;
00257     }
00258   } while ((pbufs_freed < pbufs_needed) && (other_datagrams > 1));
00259   return pbufs_freed;
00260 }
00261 #endif /* IP_REASS_FREE_OLDEST */
00262 
00263 /**
00264  * Enqueues a new fragment into the fragment queue
00265  * @param fraghdr points to the new fragments IP hdr
00266  * @param clen number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)
00267  * @return A pointer to the queue location into which the fragment was enqueued
00268  */
00269 static struct ip_reassdata*
00270 ip_reass_enqueue_new_datagram(struct ip_hdr *fraghdr, int clen)
00271 {
00272   struct ip_reassdata* ipr;
00273   /* No matching previous fragment found, allocate a new reassdata struct */
00274   ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00275   if (ipr == NULL) {
00276 #if IP_REASS_FREE_OLDEST
00277     if (ip_reass_remove_oldest_datagram(fraghdr, clen) >= clen) {
00278       ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00279     }
00280     if (ipr == NULL)
00281 #endif /* IP_REASS_FREE_OLDEST */
00282     {
00283       IPFRAG_STATS_INC(ip_frag.memerr);
00284       LWIP_DEBUGF(IP_REASS_DEBUG,("Failed to alloc reassdata struct\n"));
00285       return NULL;
00286     }
00287   }
00288   memset(ipr, 0, sizeof(struct ip_reassdata));
00289   ipr->timer = IP_REASS_MAXAGE;
00290 
00291   /* enqueue the new structure to the front of the list */
00292   ipr->next = reassdatagrams;
00293   reassdatagrams = ipr;
00294   /* copy the ip header for later tests and input */
00295   /* @todo: no ip options supported? */
00296   SMEMCPY(&(ipr->iphdr), fraghdr, IP_HLEN);
00297   return ipr;
00298 }
00299 
00300 /**
00301  * Dequeues a datagram from the datagram queue. Doesn't deallocate the pbufs.
00302  * @param ipr points to the queue entry to dequeue
00303  */
00304 static void
00305 ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00306 {
00307   
00308   /* dequeue the reass struct  */
00309   if (reassdatagrams == ipr) {
00310     /* it was the first in the list */
00311     reassdatagrams = ipr->next;
00312   } else {
00313     /* it wasn't the first, so it must have a valid 'prev' */
00314     LWIP_ASSERT("sanity check linked list", prev != NULL);
00315     prev->next = ipr->next;
00316   }
00317 
00318   /* now we can free the ip_reass struct */
00319   memp_free(MEMP_REASSDATA, ipr);
00320 }
00321 
00322 /**
00323  * Chain a new pbuf into the pbuf list that composes the datagram.  The pbuf list
00324  * will grow over time as  new pbufs are rx.
00325  * Also checks that the datagram passes basic continuity checks (if the last
00326  * fragment was received at least once).
00327  * @param root_p points to the 'root' pbuf for the current datagram being assembled.
00328  * @param new_p points to the pbuf for the current fragment
00329  * @return 0 if invalid, >0 otherwise
00330  */
00331 static int
00332 ip_reass_chain_frag_into_datagram_and_validate(struct ip_reassdata *ipr, struct pbuf *new_p)
00333 {
00334   struct ip_reass_helper *iprh, *iprh_tmp, *iprh_prev=NULL;
00335   struct pbuf *q;
00336   u16_t offset,len;
00337   struct ip_hdr *fraghdr;
00338   int valid = 1;
00339 
00340   /* Extract length and fragment offset from current fragment */
00341   fraghdr = (struct ip_hdr*)new_p->payload; 
00342   len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00343   offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00344 
00345   /* overwrite the fragment's ip header from the pbuf with our helper struct,
00346    * and setup the embedded helper structure. */
00347   /* make sure the struct ip_reass_helper fits into the IP header */
00348   LWIP_ASSERT("sizeof(struct ip_reass_helper) <= IP_HLEN",
00349               sizeof(struct ip_reass_helper) <= IP_HLEN);
00350   iprh = (struct ip_reass_helper*)new_p->payload;
00351   iprh->next_pbuf = NULL;
00352   iprh->start = offset;
00353   iprh->end = offset + len;
00354 
00355   /* Iterate through until we either get to the end of the list (append),
00356    * or we find on with a larger offset (insert). */
00357   for (q = ipr->p; q != NULL;) {
00358     iprh_tmp = (struct ip_reass_helper*)q->payload;
00359     if (iprh->start < iprh_tmp->start) {
00360       /* the new pbuf should be inserted before this */
00361       iprh->next_pbuf = q;
00362       if (iprh_prev != NULL) {
00363         /* not the fragment with the lowest offset */
00364 #if IP_REASS_CHECK_OVERLAP
00365         if ((iprh->start < iprh_prev->end) || (iprh->end > iprh_tmp->start)) {
00366           /* fragment overlaps with previous or following, throw away */
00367           goto freepbuf;
00368         }
00369 #endif /* IP_REASS_CHECK_OVERLAP */
00370         iprh_prev->next_pbuf = new_p;
00371       } else {
00372         /* fragment with the lowest offset */
00373         ipr->p = new_p;
00374       }
00375       break;
00376     } else if(iprh->start == iprh_tmp->start) {
00377       /* received the same datagram twice: no need to keep the datagram */
00378       goto freepbuf;
00379 #if IP_REASS_CHECK_OVERLAP
00380     } else if(iprh->start < iprh_tmp->end) {
00381       /* overlap: no need to keep the new datagram */
00382       goto freepbuf;
00383 #endif /* IP_REASS_CHECK_OVERLAP */
00384     } else {
00385       /* Check if the fragments received so far have no wholes. */
00386       if (iprh_prev != NULL) {
00387         if (iprh_prev->end != iprh_tmp->start) {
00388           /* There is a fragment missing between the current
00389            * and the previous fragment */
00390           valid = 0;
00391         }
00392       }
00393     }
00394     q = iprh_tmp->next_pbuf;
00395     iprh_prev = iprh_tmp;
00396   }
00397 
00398   /* If q is NULL, then we made it to the end of the list. Determine what to do now */
00399   if (q == NULL) {
00400     if (iprh_prev != NULL) {
00401       /* this is (for now), the fragment with the highest offset:
00402        * chain it to the last fragment */
00403 #if IP_REASS_CHECK_OVERLAP
00404       LWIP_ASSERT("check fragments don't overlap", iprh_prev->end <= iprh->start);
00405 #endif /* IP_REASS_CHECK_OVERLAP */
00406       iprh_prev->next_pbuf = new_p;
00407       if (iprh_prev->end != iprh->start) {
00408         valid = 0;
00409       }
00410     } else {
00411 #if IP_REASS_CHECK_OVERLAP
00412       LWIP_ASSERT("no previous fragment, this must be the first fragment!",
00413         ipr->p == NULL);
00414 #endif /* IP_REASS_CHECK_OVERLAP */
00415       /* this is the first fragment we ever received for this ip datagram */
00416       ipr->p = new_p;
00417     }
00418   }
00419 
00420   /* At this point, the validation part begins: */
00421   /* If we already received the last fragment */
00422   if ((ipr->flags & IP_REASS_FLAG_LASTFRAG) != 0) {
00423     /* and had no wholes so far */
00424     if (valid) {
00425       /* then check if the rest of the fragments is here */
00426       /* Check if the queue starts with the first datagram */
00427       if (((struct ip_reass_helper*)ipr->p->payload)->start != 0) {
00428         valid = 0;
00429       } else {
00430         /* and check that there are no wholes after this datagram */
00431         iprh_prev = iprh;
00432         q = iprh->next_pbuf;
00433         while (q != NULL) {
00434           iprh = (struct ip_reass_helper*)q->payload;
00435           if (iprh_prev->end != iprh->start) {
00436             valid = 0;
00437             break;
00438           }
00439           iprh_prev = iprh;
00440           q = iprh->next_pbuf;
00441         }
00442         /* if still valid, all fragments are received
00443          * (because to the MF==0 already arrived */
00444         if (valid) {
00445           LWIP_ASSERT("sanity check", ipr->p != NULL);
00446           LWIP_ASSERT("sanity check",
00447             ((struct ip_reass_helper*)ipr->p->payload) != iprh);
00448           LWIP_ASSERT("validate_datagram:next_pbuf!=NULL",
00449             iprh->next_pbuf == NULL);
00450           LWIP_ASSERT("validate_datagram:datagram end!=datagram len",
00451             iprh->end == ipr->datagram_len);
00452         }
00453       }
00454     }
00455     /* If valid is 0 here, there are some fragments missing in the middle
00456      * (since MF == 0 has already arrived). Such datagrams simply time out if
00457      * no more fragments are received... */
00458     return valid;
00459   }
00460   /* If we come here, not all fragments were received, yet! */
00461   return 0; /* not yet valid! */
00462 #if IP_REASS_CHECK_OVERLAP
00463 freepbuf:
00464   ip_reass_pbufcount -= pbuf_clen(new_p);
00465   pbuf_free(new_p);
00466   return 0;
00467 #endif /* IP_REASS_CHECK_OVERLAP */
00468 }
00469 
00470 /**
00471  * Reassembles incoming IP fragments into an IP datagram.
00472  *
00473  * @param p points to a pbuf chain of the fragment
00474  * @return NULL if reassembly is incomplete, ? otherwise
00475  */
00476 struct pbuf *
00477 ip_reass(struct pbuf *p)
00478 {
00479   struct pbuf *r;
00480   struct ip_hdr *fraghdr;
00481   struct ip_reassdata *ipr;
00482   struct ip_reass_helper *iprh;
00483   u16_t offset, len;
00484   u8_t clen;
00485   struct ip_reassdata *ipr_prev = NULL;
00486 
00487   IPFRAG_STATS_INC(ip_frag.recv);
00488   snmp_inc_ipreasmreqds();
00489 
00490   fraghdr = (struct ip_hdr*)p->payload;
00491 
00492   if ((IPH_HL(fraghdr) * 4) != IP_HLEN) {
00493     LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: IP options currently not supported!\n"));
00494     IPFRAG_STATS_INC(ip_frag.err);
00495     goto nullreturn;
00496   }
00497 
00498   offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00499   len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00500 
00501   /* Check if we are allowed to enqueue more datagrams. */
00502   clen = pbuf_clen(p);
00503   if ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS) {
00504 #if IP_REASS_FREE_OLDEST
00505     if (!ip_reass_remove_oldest_datagram(fraghdr, clen) ||
00506         ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS))
00507 #endif /* IP_REASS_FREE_OLDEST */
00508     {
00509       /* No datagram could be freed and still too many pbufs enqueued */
00510       LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: Overflow condition: pbufct=%d, clen=%d, MAX=%d\n",
00511         ip_reass_pbufcount, clen, IP_REASS_MAX_PBUFS));
00512       IPFRAG_STATS_INC(ip_frag.memerr);
00513       /* @todo: send ICMP time exceeded here? */
00514       /* drop this pbuf */
00515       goto nullreturn;
00516     }
00517   }
00518 
00519   /* Look for the datagram the fragment belongs to in the current datagram queue,
00520    * remembering the previous in the queue for later dequeueing. */
00521   for (ipr = reassdatagrams; ipr != NULL; ipr = ipr->next) {
00522     /* Check if the incoming fragment matches the one currently present
00523        in the reassembly buffer. If so, we proceed with copying the
00524        fragment into the buffer. */
00525     if (IP_ADDRESSES_AND_ID_MATCH(&ipr->iphdr, fraghdr)) {
00526       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass: matching previous fragment ID=%"X16_F"\n",
00527         ntohs(IPH_ID(fraghdr))));
00528       IPFRAG_STATS_INC(ip_frag.cachehit);
00529       break;
00530     }
00531     ipr_prev = ipr;
00532   }
00533 
00534   if (ipr == NULL) {
00535   /* Enqueue a new datagram into the datagram queue */
00536     ipr = ip_reass_enqueue_new_datagram(fraghdr, clen);
00537     /* Bail if unable to enqueue */
00538     if(ipr == NULL) {
00539       goto nullreturn;
00540     }
00541   } else {
00542     if (((ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) == 0) && 
00543       ((ntohs(IPH_OFFSET(&ipr->iphdr)) & IP_OFFMASK) != 0)) {
00544       /* ipr->iphdr is not the header from the first fragment, but fraghdr is
00545        * -> copy fraghdr into ipr->iphdr since we want to have the header
00546        * of the first fragment (for ICMP time exceeded and later, for copying
00547        * all options, if supported)*/
00548       SMEMCPY(&ipr->iphdr, fraghdr, IP_HLEN);
00549     }
00550   }
00551   /* Track the current number of pbufs current 'in-flight', in order to limit 
00552   the number of fragments that may be enqueued at any one time */
00553   ip_reass_pbufcount += clen;
00554 
00555   /* At this point, we have either created a new entry or pointing 
00556    * to an existing one */
00557 
00558   /* check for 'no more fragments', and update queue entry*/
00559   if ((ntohs(IPH_OFFSET(fraghdr)) & IP_MF) == 0) {
00560     ipr->flags |= IP_REASS_FLAG_LASTFRAG;
00561     ipr->datagram_len = offset + len;
00562     LWIP_DEBUGF(IP_REASS_DEBUG,
00563      ("ip_reass: last fragment seen, total len %"S16_F"\n",
00564       ipr->datagram_len));
00565   }
00566   /* find the right place to insert this pbuf */
00567   /* @todo: trim pbufs if fragments are overlapping */
00568   if (ip_reass_chain_frag_into_datagram_and_validate(ipr, p)) {
00569     /* the totally last fragment (flag more fragments = 0) was received at least
00570      * once AND all fragments are received */
00571     ipr->datagram_len += IP_HLEN;
00572 
00573     /* save the second pbuf before copying the header over the pointer */
00574     r = ((struct ip_reass_helper*)ipr->p->payload)->next_pbuf;
00575 
00576     /* copy the original ip header back to the first pbuf */
00577     fraghdr = (struct ip_hdr*)(ipr->p->payload);
00578     SMEMCPY(fraghdr, &ipr->iphdr, IP_HLEN);
00579     IPH_LEN_SET(fraghdr, htons(ipr->datagram_len));
00580     IPH_OFFSET_SET(fraghdr, 0);
00581     IPH_CHKSUM_SET(fraghdr, 0);
00582     /* @todo: do we need to set calculate the correct checksum? */
00583     IPH_CHKSUM_SET(fraghdr, inet_chksum(fraghdr, IP_HLEN));
00584 
00585     p = ipr->p;
00586 
00587     /* chain together the pbufs contained within the reass_data list. */
00588     while(r != NULL) {
00589       iprh = (struct ip_reass_helper*)r->payload;
00590 
00591       /* hide the ip header for every succeding fragment */
00592       pbuf_header(r, -IP_HLEN);
00593       pbuf_cat(p, r);
00594       r = iprh->next_pbuf;
00595     }
00596     /* release the sources allocate for the fragment queue entry */
00597     ip_reass_dequeue_datagram(ipr, ipr_prev);
00598 
00599     /* and adjust the number of pbufs currently queued for reassembly. */
00600     ip_reass_pbufcount -= pbuf_clen(p);
00601 
00602     /* Return the pbuf chain */
00603     return p;
00604   }
00605   /* the datagram is not (yet?) reassembled completely */
00606   LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass_pbufcount: %d out\n", ip_reass_pbufcount));
00607   return NULL;
00608 
00609 nullreturn:
00610   LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: nullreturn\n"));
00611   IPFRAG_STATS_INC(ip_frag.drop);
00612   pbuf_free(p);
00613   return NULL;
00614 }
00615 #endif /* IP_REASSEMBLY */
00616 
00617 #if IP_FRAG
00618 #if IP_FRAG_USES_STATIC_BUF
00619 static u8_t buf[LWIP_MEM_ALIGN_SIZE(IP_FRAG_MAX_MTU + MEM_ALIGNMENT - 1)];
00620 #endif /* IP_FRAG_USES_STATIC_BUF */
00621 
00622 /**
00623  * Fragment an IP datagram if too large for the netif.
00624  *
00625  * Chop the datagram in MTU sized chunks and send them in order
00626  * by using a fixed size static memory buffer (PBUF_REF) or
00627  * point PBUF_REFs into p (depending on IP_FRAG_USES_STATIC_BUF).
00628  *
00629  * @param p ip packet to send
00630  * @param netif the netif on which to send
00631  * @param dest destination ip address to which to send
00632  *
00633  * @return ERR_OK if sent successfully, err_t otherwise
00634  */
00635 err_t 
00636 ip_frag(struct pbuf *p, struct netif *netif, struct ip_addr *dest)
00637 {
00638   struct pbuf *rambuf;
00639 #if IP_FRAG_USES_STATIC_BUF
00640   struct pbuf *header;
00641 #else
00642   struct pbuf *newpbuf;
00643   struct ip_hdr *original_iphdr;
00644 #endif
00645   struct ip_hdr *iphdr;
00646   u16_t nfb;
00647   u16_t left, cop;
00648   u16_t mtu = netif->mtu;
00649   u16_t ofo, omf;
00650   u16_t last;
00651   u16_t poff = IP_HLEN;
00652   u16_t tmp;
00653 #if !IP_FRAG_USES_STATIC_BUF
00654   u16_t newpbuflen = 0;
00655   u16_t left_to_copy;
00656 #endif
00657 
00658   /* Get a RAM based MTU sized pbuf */
00659 #if IP_FRAG_USES_STATIC_BUF
00660   /* When using a static buffer, we use a PBUF_REF, which we will
00661    * use to reference the packet (without link header).
00662    * Layer and length is irrelevant.
00663    */
00664   rambuf = pbuf_alloc(PBUF_LINK, 0, PBUF_REF);
00665   if (rambuf == NULL) {
00666     LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_frag: pbuf_alloc(PBUF_LINK, 0, PBUF_REF) failed\n"));
00667     return ERR_MEM;
00668   }
00669   rambuf->tot_len = rambuf->len = mtu;
00670   rambuf->payload = LWIP_MEM_ALIGN((void *)buf);
00671 
00672   /* Copy the IP header in it */
00673   iphdr = rambuf->payload;
00674   SMEMCPY(iphdr, p->payload, IP_HLEN);
00675 #else /* IP_FRAG_USES_STATIC_BUF */
00676   original_iphdr = (struct ip_hdr *)p->payload;
00677   iphdr = original_iphdr;
00678 #endif /* IP_FRAG_USES_STATIC_BUF */
00679 
00680   /* Save original offset */
00681   tmp = ntohs(IPH_OFFSET(iphdr));
00682   ofo = tmp & IP_OFFMASK;
00683   omf = tmp & IP_MF;
00684 
00685   left = p->tot_len - IP_HLEN;
00686 
00687   nfb = (mtu - IP_HLEN) / 8;
00688 
00689   while (left) {
00690     last = (left <= mtu - IP_HLEN);
00691 
00692     /* Set new offset and MF flag */
00693     tmp = omf | (IP_OFFMASK & (ofo));
00694     if (!last)
00695       tmp = tmp | IP_MF;
00696 
00697     /* Fill this fragment */
00698     cop = last ? left : nfb * 8;
00699 
00700 #if IP_FRAG_USES_STATIC_BUF
00701     poff += pbuf_copy_partial(p, (u8_t*)iphdr + IP_HLEN, cop, poff);
00702 #else /* IP_FRAG_USES_STATIC_BUF */
00703     /* When not using a static buffer, create a chain of pbufs.
00704      * The first will be a PBUF_RAM holding the link and IP header.
00705      * The rest will be PBUF_REFs mirroring the pbuf chain to be fragged,
00706      * but limited to the size of an mtu.
00707      */
00708     rambuf = pbuf_alloc(PBUF_LINK, IP_HLEN, PBUF_RAM);
00709     if (rambuf == NULL) {
00710       return ERR_MEM;
00711     }
00712     LWIP_ASSERT("this needs a pbuf in one piece!",
00713                 (p->len >= (IP_HLEN)));
00714     SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);
00715     iphdr = (struct ip_hdr *)rambuf->payload;
00716 
00717     /* Can just adjust p directly for needed offset. */
00718     p->payload = (u8_t *)p->payload + poff;
00719     p->len -= poff;
00720 
00721     left_to_copy = cop;
00722     while (left_to_copy) {
00723       newpbuflen = (left_to_copy < p->len) ? left_to_copy : p->len;
00724       /* Is this pbuf already empty? */
00725       if (!newpbuflen) {
00726         p = p->next;
00727         continue;
00728       }
00729       newpbuf = pbuf_alloc(PBUF_RAW, 0, PBUF_REF);
00730       if (newpbuf == NULL) {
00731         pbuf_free(rambuf);
00732         return ERR_MEM;
00733       }
00734       /* Mirror this pbuf, although we might not need all of it. */
00735       newpbuf->payload = p->payload;
00736       newpbuf->len = newpbuf->tot_len = newpbuflen;
00737       /* Add it to end of rambuf's chain, but using pbuf_cat, not pbuf_chain
00738        * so that it is removed when pbuf_dechain is later called on rambuf.
00739        */
00740       pbuf_cat(rambuf, newpbuf);
00741       left_to_copy -= newpbuflen;
00742       if (left_to_copy)
00743         p = p->next;
00744     }
00745     poff = newpbuflen;
00746 #endif /* IP_FRAG_USES_STATIC_BUF */
00747 
00748     /* Correct header */
00749     IPH_OFFSET_SET(iphdr, htons(tmp));
00750     IPH_LEN_SET(iphdr, htons(cop + IP_HLEN));
00751     IPH_CHKSUM_SET(iphdr, 0);
00752     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
00753 
00754 #if IP_FRAG_USES_STATIC_BUF
00755     if (last)
00756       pbuf_realloc(rambuf, left + IP_HLEN);
00757 
00758     /* This part is ugly: we alloc a RAM based pbuf for 
00759      * the link level header for each chunk and then 
00760      * free it.A PBUF_ROM style pbuf for which pbuf_header
00761      * worked would make things simpler.
00762      */
00763     header = pbuf_alloc(PBUF_LINK, 0, PBUF_RAM);
00764     if (header != NULL) {
00765       pbuf_chain(header, rambuf);
00766       netif->output(netif, header, dest);
00767       IPFRAG_STATS_INC(ip_frag.xmit);
00768       snmp_inc_ipfragcreates();
00769       pbuf_free(header);
00770     } else {
00771       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_frag: pbuf_alloc() for header failed\n"));
00772       pbuf_free(rambuf);
00773       return ERR_MEM;
00774     }
00775 #else /* IP_FRAG_USES_STATIC_BUF */
00776     /* No need for separate header pbuf - we allowed room for it in rambuf
00777      * when allocated.
00778      */
00779     netif->output(netif, rambuf, dest);
00780     IPFRAG_STATS_INC(ip_frag.xmit);
00781 
00782     /* Unfortunately we can't reuse rambuf - the hardware may still be
00783      * using the buffer. Instead we free it (and the ensuing chain) and
00784      * recreate it next time round the loop. If we're lucky the hardware
00785      * will have already sent the packet, the free will really free, and
00786      * there will be zero memory penalty.
00787      */
00788     
00789     pbuf_free(rambuf);
00790 #endif /* IP_FRAG_USES_STATIC_BUF */
00791     left -= cop;
00792     ofo += nfb;
00793   }
00794 #if IP_FRAG_USES_STATIC_BUF
00795   pbuf_free(rambuf);
00796 #endif /* IP_FRAG_USES_STATIC_BUF */
00797   snmp_inc_ipfragoks();
00798   return ERR_OK;
00799 }
00800 #endif /* IP_FRAG */