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/def.h"
00044 #include "lwip/inet_chksum.h"
00045 #include "lwip/netif.h"
00046 #include "lwip/snmp.h"
00047 #include "lwip/stats.h"
00048 #include "lwip/icmp.h"
00049 
00050 #include <string.h>
00051 
00052 #if IP_REASSEMBLY
00053 /**
00054  * The IP reassembly code currently has the following limitations:
00055  * - IP header options are not supported
00056  * - fragments must not overlap (e.g. due to different routes),
00057  *   currently, overlapping or duplicate fragments are thrown away
00058  *   if IP_REASS_CHECK_OVERLAP=1 (the default)!
00059  *
00060  * @todo: work with IP header options
00061  */
00062 
00063 /** Setting this to 0, you can turn off checking the fragments for overlapping
00064  * regions. The code gets a little smaller. Only use this if you know that
00065  * overlapping won't occur on your network! */
00066 #ifndef IP_REASS_CHECK_OVERLAP
00067 #define IP_REASS_CHECK_OVERLAP 1
00068 #endif /* IP_REASS_CHECK_OVERLAP */
00069 
00070 /** Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is
00071  * full (IP_REASS_MAX_PBUFS pbufs are enqueued). The code gets a little smaller.
00072  * Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA
00073  * is set to 1, so one datagram can be reassembled at a time, only. */
00074 #ifndef IP_REASS_FREE_OLDEST
00075 #define IP_REASS_FREE_OLDEST 1
00076 #endif /* IP_REASS_FREE_OLDEST */
00077 
00078 #define IP_REASS_FLAG_LASTFRAG 0x01
00079 
00080 /** This is a helper struct which holds the starting
00081  * offset and the ending offset of this fragment to
00082  * easily chain the fragments.
00083  * It has the same packing requirements as the IP header, since it replaces
00084  * the IP header in memory in incoming fragments (after copying it) to keep
00085  * track of the various fragments. (-> If the IP header doesn't need packing,
00086  * this struct doesn't need packing, too.)
00087  */
00088 #ifdef PACK_STRUCT_USE_INCLUDES
00089 #  include "arch/bpstruct.h"
00090 #endif
00091 PACK_STRUCT_BEGIN
00092 struct ip_reass_helper {
00093   PACK_STRUCT_FIELD(struct pbuf *next_pbuf);
00094   PACK_STRUCT_FIELD(u16_t start);
00095   PACK_STRUCT_FIELD(u16_t end);
00096 } PACK_STRUCT_STRUCT;
00097 PACK_STRUCT_END
00098 #ifdef PACK_STRUCT_USE_INCLUDES
00099 #  include "arch/epstruct.h"
00100 #endif
00101 
00102 #define IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)  \
00103   (ip_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \
00104    ip_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \
00105    IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0
00106 
00107 /* global variables */
00108 static struct ip_reassdata *reassdatagrams;
00109 static u16_t ip_reass_pbufcount;
00110 
00111 /* function prototypes */
00112 static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00113 static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00114 
00115 /**
00116  * Reassembly timer base function
00117  * for both NO_SYS == 0 and 1 (!).
00118  *
00119  * Should be called every 1000 msec (defined by IP_TMR_INTERVAL).
00120  */
00121 void
00122 ip_reass_tmr(void)
00123 {
00124   struct ip_reassdata *r, *prev = NULL;
00125 
00126   r = reassdatagrams;
00127   while (r != NULL) {
00128     /* Decrement the timer. Once it reaches 0,
00129      * clean up the incomplete fragment assembly */
00130     if (r->timer > 0) {
00131       r->timer--;
00132       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n",(u16_t)r->timer));
00133       prev = r;
00134       r = r->next;
00135     } else {
00136       /* reassembly timed out */
00137       struct ip_reassdata *tmp;
00138       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer timed out\n"));
00139       tmp = r;
00140       /* get the next pointer before freeing */
00141       r = r->next;
00142       /* free the helper struct and all enqueued pbufs */
00143       ip_reass_free_complete_datagram(tmp, prev);
00144      }
00145    }
00146 }
00147 
00148 /**
00149  * Free a datagram (struct ip_reassdata) and all its pbufs.
00150  * Updates the total count of enqueued pbufs (ip_reass_pbufcount),
00151  * SNMP counters and sends an ICMP time exceeded packet.
00152  *
00153  * @param ipr datagram to free
00154  * @param prev the previous datagram in the linked list
00155  * @return the number of pbufs freed
00156  */
00157 static int
00158 ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00159 {
00160   u16_t pbufs_freed = 0;
00161   u8_t clen;
00162   struct pbuf *p;
00163   struct ip_reass_helper *iprh;
00164 
00165   LWIP_ASSERT("prev != ipr", prev != ipr);
00166   if (prev != NULL) {
00167     LWIP_ASSERT("prev->next == ipr", prev->next == ipr);
00168   }
00169 
00170   snmp_inc_ipreasmfails();
00171 #if LWIP_ICMP
00172   iprh = (struct ip_reass_helper *)ipr->p->payload;
00173   if (iprh->start == 0) {
00174     /* The first fragment was received, send ICMP time exceeded. */
00175     /* First, de-queue the first pbuf from r->p. */
00176     p = ipr->p;
00177     ipr->p = iprh->next_pbuf;
00178     /* Then, copy the original header into it. */
00179     SMEMCPY(p->payload, &ipr->iphdr, IP_HLEN);
00180     icmp_time_exceeded(p, ICMP_TE_FRAG);
00181     clen = pbuf_clen(p);
00182     LWIP_ASSERT("pbufs_freed + clen <= 0xffff", pbufs_freed + clen <= 0xffff);
00183     pbufs_freed += clen;
00184     pbuf_free(p);
00185   }
00186 #endif /* LWIP_ICMP */
00187 
00188   /* First, free all received pbufs.  The individual pbufs need to be released 
00189      separately as they have not yet been chained */
00190   p = ipr->p;
00191   while (p != NULL) {
00192     struct pbuf *pcur;
00193     iprh = (struct ip_reass_helper *)p->payload;
00194     pcur = p;
00195     /* get the next pointer before freeing */
00196     p = iprh->next_pbuf;
00197     clen = pbuf_clen(pcur);
00198     LWIP_ASSERT("pbufs_freed + clen <= 0xffff", pbufs_freed + clen <= 0xffff);
00199     pbufs_freed += clen;
00200     pbuf_free(pcur);
00201   }
00202   /* Then, unchain the struct ip_reassdata from the list and free it. */
00203   ip_reass_dequeue_datagram(ipr, prev);
00204   LWIP_ASSERT("ip_reass_pbufcount >= clen", ip_reass_pbufcount >= pbufs_freed);
00205   ip_reass_pbufcount -= pbufs_freed;
00206 
00207   return pbufs_freed;
00208 }
00209 
00210 #if IP_REASS_FREE_OLDEST
00211 /**
00212  * Free the oldest datagram to make room for enqueueing new fragments.
00213  * The datagram 'fraghdr' belongs to is not freed!
00214  *
00215  * @param fraghdr IP header of the current fragment
00216  * @param pbufs_needed number of pbufs needed to enqueue
00217  *        (used for freeing other datagrams if not enough space)
00218  * @return the number of pbufs freed
00219  */
00220 static int
00221 ip_reass_remove_oldest_datagram(struct ip_hdr *fraghdr, int pbufs_needed)
00222 {
00223   /* @todo Can't we simply remove the last datagram in the
00224    *       linked list behind reassdatagrams?
00225    */
00226   struct ip_reassdata *r, *oldest, *prev;
00227   int pbufs_freed = 0, pbufs_freed_current;
00228   int other_datagrams;
00229 
00230   /* Free datagrams until being allowed to enqueue 'pbufs_needed' pbufs,
00231    * but don't free the datagram that 'fraghdr' belongs to! */
00232   do {
00233     oldest = NULL;
00234     prev = NULL;
00235     other_datagrams = 0;
00236     r = reassdatagrams;
00237     while (r != NULL) {
00238       if (!IP_ADDRESSES_AND_ID_MATCH(&r->iphdr, fraghdr)) {
00239         /* Not the same datagram as fraghdr */
00240         other_datagrams++;
00241         if (oldest == NULL) {
00242           oldest = r;
00243         } else if (r->timer <= oldest->timer) {
00244           /* older than the previous oldest */
00245           oldest = r;
00246         }
00247       }
00248       if (r->next != NULL) {
00249         prev = r;
00250       }
00251       r = r->next;
00252     }
00253     if (oldest != NULL) {
00254       pbufs_freed_current = ip_reass_free_complete_datagram(oldest, prev);
00255       pbufs_freed += pbufs_freed_current;
00256     }
00257   } while ((pbufs_freed < pbufs_needed) && (other_datagrams > 1));
00258   return pbufs_freed;
00259 }
00260 #endif /* IP_REASS_FREE_OLDEST */
00261 
00262 /**
00263  * Enqueues a new fragment into the fragment queue
00264  * @param fraghdr points to the new fragments IP hdr
00265  * @param clen number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)
00266  * @return A pointer to the queue location into which the fragment was enqueued
00267  */
00268 static struct ip_reassdata*
00269 ip_reass_enqueue_new_datagram(struct ip_hdr *fraghdr, int clen)
00270 {
00271   struct ip_reassdata* ipr;
00272   /* No matching previous fragment found, allocate a new reassdata struct */
00273   ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00274   if (ipr == NULL) {
00275 #if IP_REASS_FREE_OLDEST
00276     if (ip_reass_remove_oldest_datagram(fraghdr, clen) >= clen) {
00277       ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00278     }
00279     if (ipr == NULL)
00280 #endif /* IP_REASS_FREE_OLDEST */
00281     {
00282       IPFRAG_STATS_INC(ip_frag.memerr);
00283       LWIP_DEBUGF(IP_REASS_DEBUG,("Failed to alloc reassdata struct\n"));
00284       return NULL;
00285     }
00286   }
00287   memset(ipr, 0, sizeof(struct ip_reassdata));
00288   ipr->timer = IP_REASS_MAXAGE;
00289 
00290   /* enqueue the new structure to the front of the list */
00291   ipr->next = reassdatagrams;
00292   reassdatagrams = ipr;
00293   /* copy the ip header for later tests and input */
00294   /* @todo: no ip options supported? */
00295   SMEMCPY(&(ipr->iphdr), fraghdr, IP_HLEN);
00296   return ipr;
00297 }
00298 
00299 /**
00300  * Dequeues a datagram from the datagram queue. Doesn't deallocate the pbufs.
00301  * @param ipr points to the queue entry to dequeue
00302  */
00303 static void
00304 ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00305 {
00306   
00307   /* dequeue the reass struct  */
00308   if (reassdatagrams == ipr) {
00309     /* it was the first in the list */
00310     reassdatagrams = ipr->next;
00311   } else {
00312     /* it wasn't the first, so it must have a valid 'prev' */
00313     LWIP_ASSERT("sanity check linked list", prev != NULL);
00314     prev->next = ipr->next;
00315   }
00316 
00317   /* now we can free the ip_reass struct */
00318   memp_free(MEMP_REASSDATA, ipr);
00319 }
00320 
00321 /**
00322  * Chain a new pbuf into the pbuf list that composes the datagram.  The pbuf list
00323  * will grow over time as  new pbufs are rx.
00324  * Also checks that the datagram passes basic continuity checks (if the last
00325  * fragment was received at least once).
00326  * @param root_p points to the 'root' pbuf for the current datagram being assembled.
00327  * @param new_p points to the pbuf for the current fragment
00328  * @return 0 if invalid, >0 otherwise
00329  */
00330 static int
00331 ip_reass_chain_frag_into_datagram_and_validate(struct ip_reassdata *ipr, struct pbuf *new_p)
00332 {
00333   struct ip_reass_helper *iprh, *iprh_tmp, *iprh_prev=NULL;
00334   struct pbuf *q;
00335   u16_t offset,len;
00336   struct ip_hdr *fraghdr;
00337   int valid = 1;
00338 
00339   /* Extract length and fragment offset from current fragment */
00340   fraghdr = (struct ip_hdr*)new_p->payload; 
00341   len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00342   offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00343 
00344   /* overwrite the fragment's ip header from the pbuf with our helper struct,
00345    * and setup the embedded helper structure. */
00346   /* make sure the struct ip_reass_helper fits into the IP header */
00347   LWIP_ASSERT("sizeof(struct ip_reass_helper) <= IP_HLEN",
00348               sizeof(struct ip_reass_helper) <= IP_HLEN);
00349   iprh = (struct ip_reass_helper*)new_p->payload;
00350   iprh->next_pbuf = NULL;
00351   iprh->start = offset;
00352   iprh->end = offset + len;
00353 
00354   /* Iterate through until we either get to the end of the list (append),
00355    * or we find on with a larger offset (insert). */
00356   for (q = ipr->p; q != NULL;) {
00357     iprh_tmp = (struct ip_reass_helper*)q->payload;
00358     if (iprh->start < iprh_tmp->start) {
00359       /* the new pbuf should be inserted before this */
00360       iprh->next_pbuf = q;
00361       if (iprh_prev != NULL) {
00362         /* not the fragment with the lowest offset */
00363 #if IP_REASS_CHECK_OVERLAP
00364         if ((iprh->start < iprh_prev->end) || (iprh->end > iprh_tmp->start)) {
00365           /* fragment overlaps with previous or following, throw away */
00366           goto freepbuf;
00367         }
00368 #endif /* IP_REASS_CHECK_OVERLAP */
00369         iprh_prev->next_pbuf = new_p;
00370       } else {
00371         /* fragment with the lowest offset */
00372         ipr->p = new_p;
00373       }
00374       break;
00375     } else if(iprh->start == iprh_tmp->start) {
00376       /* received the same datagram twice: no need to keep the datagram */
00377       goto freepbuf;
00378 #if IP_REASS_CHECK_OVERLAP
00379     } else if(iprh->start < iprh_tmp->end) {
00380       /* overlap: no need to keep the new datagram */
00381       goto freepbuf;
00382 #endif /* IP_REASS_CHECK_OVERLAP */
00383     } else {
00384       /* Check if the fragments received so far have no wholes. */
00385       if (iprh_prev != NULL) {
00386         if (iprh_prev->end != iprh_tmp->start) {
00387           /* There is a fragment missing between the current
00388            * and the previous fragment */
00389           valid = 0;
00390         }
00391       }
00392     }
00393     q = iprh_tmp->next_pbuf;
00394     iprh_prev = iprh_tmp;
00395   }
00396 
00397   /* If q is NULL, then we made it to the end of the list. Determine what to do now */
00398   if (q == NULL) {
00399     if (iprh_prev != NULL) {
00400       /* this is (for now), the fragment with the highest offset:
00401        * chain it to the last fragment */
00402 #if IP_REASS_CHECK_OVERLAP
00403       LWIP_ASSERT("check fragments don't overlap", iprh_prev->end <= iprh->start);
00404 #endif /* IP_REASS_CHECK_OVERLAP */
00405       iprh_prev->next_pbuf = new_p;
00406       if (iprh_prev->end != iprh->start) {
00407         valid = 0;
00408       }
00409     } else {
00410 #if IP_REASS_CHECK_OVERLAP
00411       LWIP_ASSERT("no previous fragment, this must be the first fragment!",
00412         ipr->p == NULL);
00413 #endif /* IP_REASS_CHECK_OVERLAP */
00414       /* this is the first fragment we ever received for this ip datagram */
00415       ipr->p = new_p;
00416     }
00417   }
00418 
00419   /* At this point, the validation part begins: */
00420   /* If we already received the last fragment */
00421   if ((ipr->flags & IP_REASS_FLAG_LASTFRAG) != 0) {
00422     /* and had no wholes so far */
00423     if (valid) {
00424       /* then check if the rest of the fragments is here */
00425       /* Check if the queue starts with the first datagram */
00426       if (((struct ip_reass_helper*)ipr->p->payload)->start != 0) {
00427         valid = 0;
00428       } else {
00429         /* and check that there are no wholes after this datagram */
00430         iprh_prev = iprh;
00431         q = iprh->next_pbuf;
00432         while (q != NULL) {
00433           iprh = (struct ip_reass_helper*)q->payload;
00434           if (iprh_prev->end != iprh->start) {
00435             valid = 0;
00436             break;
00437           }
00438           iprh_prev = iprh;
00439           q = iprh->next_pbuf;
00440         }
00441         /* if still valid, all fragments are received
00442          * (because to the MF==0 already arrived */
00443         if (valid) {
00444           LWIP_ASSERT("sanity check", ipr->p != NULL);
00445           LWIP_ASSERT("sanity check",
00446             ((struct ip_reass_helper*)ipr->p->payload) != iprh);
00447           LWIP_ASSERT("validate_datagram:next_pbuf!=NULL",
00448             iprh->next_pbuf == NULL);
00449           LWIP_ASSERT("validate_datagram:datagram end!=datagram len",
00450             iprh->end == ipr->datagram_len);
00451         }
00452       }
00453     }
00454     /* If valid is 0 here, there are some fragments missing in the middle
00455      * (since MF == 0 has already arrived). Such datagrams simply time out if
00456      * no more fragments are received... */
00457     return valid;
00458   }
00459   /* If we come here, not all fragments were received, yet! */
00460   return 0; /* not yet valid! */
00461 #if IP_REASS_CHECK_OVERLAP
00462 freepbuf:
00463   ip_reass_pbufcount -= pbuf_clen(new_p);
00464   pbuf_free(new_p);
00465   return 0;
00466 #endif /* IP_REASS_CHECK_OVERLAP */
00467 }
00468 
00469 /**
00470  * Reassembles incoming IP fragments into an IP datagram.
00471  *
00472  * @param p points to a pbuf chain of the fragment
00473  * @return NULL if reassembly is incomplete, ? otherwise
00474  */
00475 struct pbuf *
00476 ip_reass(struct pbuf *p)
00477 {
00478   struct pbuf *r;
00479   struct ip_hdr *fraghdr;
00480   struct ip_reassdata *ipr;
00481   struct ip_reass_helper *iprh;
00482   u16_t offset, len;
00483   u8_t clen;
00484   struct ip_reassdata *ipr_prev = NULL;
00485 
00486   IPFRAG_STATS_INC(ip_frag.recv);
00487   snmp_inc_ipreasmreqds();
00488 
00489   fraghdr = (struct ip_hdr*)p->payload;
00490 
00491   if ((IPH_HL(fraghdr) * 4) != IP_HLEN) {
00492     LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: IP options currently not supported!\n"));
00493     IPFRAG_STATS_INC(ip_frag.err);
00494     goto nullreturn;
00495   }
00496 
00497   offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00498   len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00499 
00500   /* Check if we are allowed to enqueue more datagrams. */
00501   clen = pbuf_clen(p);
00502   if ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS) {
00503 #if IP_REASS_FREE_OLDEST
00504     if (!ip_reass_remove_oldest_datagram(fraghdr, clen) ||
00505         ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS))
00506 #endif /* IP_REASS_FREE_OLDEST */
00507     {
00508       /* No datagram could be freed and still too many pbufs enqueued */
00509       LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: Overflow condition: pbufct=%d, clen=%d, MAX=%d\n",
00510         ip_reass_pbufcount, clen, IP_REASS_MAX_PBUFS));
00511       IPFRAG_STATS_INC(ip_frag.memerr);
00512       /* @todo: send ICMP time exceeded here? */
00513       /* drop this pbuf */
00514       goto nullreturn;
00515     }
00516   }
00517 
00518   /* Look for the datagram the fragment belongs to in the current datagram queue,
00519    * remembering the previous in the queue for later dequeueing. */
00520   for (ipr = reassdatagrams; ipr != NULL; ipr = ipr->next) {
00521     /* Check if the incoming fragment matches the one currently present
00522        in the reassembly buffer. If so, we proceed with copying the
00523        fragment into the buffer. */
00524     if (IP_ADDRESSES_AND_ID_MATCH(&ipr->iphdr, fraghdr)) {
00525       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass: matching previous fragment ID=%"X16_F"\n",
00526         ntohs(IPH_ID(fraghdr))));
00527       IPFRAG_STATS_INC(ip_frag.cachehit);
00528       break;
00529     }
00530     ipr_prev = ipr;
00531   }
00532 
00533   if (ipr == NULL) {
00534   /* Enqueue a new datagram into the datagram queue */
00535     ipr = ip_reass_enqueue_new_datagram(fraghdr, clen);
00536     /* Bail if unable to enqueue */
00537     if(ipr == NULL) {
00538       goto nullreturn;
00539     }
00540   } else {
00541     if (((ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) == 0) && 
00542       ((ntohs(IPH_OFFSET(&ipr->iphdr)) & IP_OFFMASK) != 0)) {
00543       /* ipr->iphdr is not the header from the first fragment, but fraghdr is
00544        * -> copy fraghdr into ipr->iphdr since we want to have the header
00545        * of the first fragment (for ICMP time exceeded and later, for copying
00546        * all options, if supported)*/
00547       SMEMCPY(&ipr->iphdr, fraghdr, IP_HLEN);
00548     }
00549   }
00550   /* Track the current number of pbufs current 'in-flight', in order to limit 
00551   the number of fragments that may be enqueued at any one time */
00552   ip_reass_pbufcount += clen;
00553 
00554   /* At this point, we have either created a new entry or pointing 
00555    * to an existing one */
00556 
00557   /* check for 'no more fragments', and update queue entry*/
00558   if ((IPH_OFFSET(fraghdr) & PP_NTOHS(IP_MF)) == 0) {
00559     ipr->flags |= IP_REASS_FLAG_LASTFRAG;
00560     ipr->datagram_len = offset + len;
00561     LWIP_DEBUGF(IP_REASS_DEBUG,
00562      ("ip_reass: last fragment seen, total len %"S16_F"\n",
00563       ipr->datagram_len));
00564   }
00565   /* find the right place to insert this pbuf */
00566   /* @todo: trim pbufs if fragments are overlapping */
00567   if (ip_reass_chain_frag_into_datagram_and_validate(ipr, p)) {
00568     /* the totally last fragment (flag more fragments = 0) was received at least
00569      * once AND all fragments are received */
00570     ipr->datagram_len += IP_HLEN;
00571 
00572     /* save the second pbuf before copying the header over the pointer */
00573     r = ((struct ip_reass_helper*)ipr->p->payload)->next_pbuf;
00574 
00575     /* copy the original ip header back to the first pbuf */
00576     fraghdr = (struct ip_hdr*)(ipr->p->payload);
00577     SMEMCPY(fraghdr, &ipr->iphdr, IP_HLEN);
00578     IPH_LEN_SET(fraghdr, htons(ipr->datagram_len));
00579     IPH_OFFSET_SET(fraghdr, 0);
00580     IPH_CHKSUM_SET(fraghdr, 0);
00581     /* @todo: do we need to set calculate the correct checksum? */
00582     IPH_CHKSUM_SET(fraghdr, inet_chksum(fraghdr, IP_HLEN));
00583 
00584     p = ipr->p;
00585 
00586     /* chain together the pbufs contained within the reass_data list. */
00587     while(r != NULL) {
00588       iprh = (struct ip_reass_helper*)r->payload;
00589 
00590       /* hide the ip header for every succeding fragment */
00591       pbuf_header(r, -IP_HLEN);
00592       pbuf_cat(p, r);
00593       r = iprh->next_pbuf;
00594     }
00595     /* release the sources allocate for the fragment queue entry */
00596     ip_reass_dequeue_datagram(ipr, ipr_prev);
00597 
00598     /* and adjust the number of pbufs currently queued for reassembly. */
00599     ip_reass_pbufcount -= pbuf_clen(p);
00600 
00601     /* Return the pbuf chain */
00602     return p;
00603   }
00604   /* the datagram is not (yet?) reassembled completely */
00605   LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass_pbufcount: %d out\n", ip_reass_pbufcount));
00606   return NULL;
00607 
00608 nullreturn:
00609   LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: nullreturn\n"));
00610   IPFRAG_STATS_INC(ip_frag.drop);
00611   pbuf_free(p);
00612   return NULL;
00613 }
00614 #endif /* IP_REASSEMBLY */
00615 
00616 #if IP_FRAG
00617 #if IP_FRAG_USES_STATIC_BUF
00618 static u8_t buf[LWIP_MEM_ALIGN_SIZE(IP_FRAG_MAX_MTU + MEM_ALIGNMENT - 1)];
00619 #else /* IP_FRAG_USES_STATIC_BUF */
00620 
00621 #if !LWIP_NETIF_TX_SINGLE_PBUF
00622 /** Allocate a new struct pbuf_custom_ref */
00623 static struct pbuf_custom_ref*
00624 ip_frag_alloc_pbuf_custom_ref(void)
00625 {
00626   return (struct pbuf_custom_ref*)memp_malloc(MEMP_FRAG_PBUF);
00627 }
00628 
00629 /** Free a struct pbuf_custom_ref */
00630 static void
00631 ip_frag_free_pbuf_custom_ref(struct pbuf_custom_ref* p)
00632 {
00633   LWIP_ASSERT("p != NULL", p != NULL);
00634   memp_free(MEMP_FRAG_PBUF, p);
00635 }
00636 
00637 /** Free-callback function to free a 'struct pbuf_custom_ref', called by
00638  * pbuf_free. */
00639 static void
00640 ipfrag_free_pbuf_custom(struct pbuf *p)
00641 {
00642   struct pbuf_custom_ref *pcr = (struct pbuf_custom_ref*)p;
00643   LWIP_ASSERT("pcr != NULL", pcr != NULL);
00644   LWIP_ASSERT("pcr == p", (void*)pcr == (void*)p);
00645   if (pcr->original != NULL) {
00646     pbuf_free(pcr->original);
00647   }
00648   ip_frag_free_pbuf_custom_ref(pcr);
00649 }
00650 #endif /* !LWIP_NETIF_TX_SINGLE_PBUF */
00651 #endif /* IP_FRAG_USES_STATIC_BUF */
00652 
00653 /**
00654  * Fragment an IP datagram if too large for the netif.
00655  *
00656  * Chop the datagram in MTU sized chunks and send them in order
00657  * by using a fixed size static memory buffer (PBUF_REF) or
00658  * point PBUF_REFs into p (depending on IP_FRAG_USES_STATIC_BUF).
00659  *
00660  * @param p ip packet to send
00661  * @param netif the netif on which to send
00662  * @param dest destination ip address to which to send
00663  *
00664  * @return ERR_OK if sent successfully, err_t otherwise
00665  */
00666 err_t 
00667 ip_frag(struct pbuf *p, struct netif *netif, ip_addr_t *dest)
00668 {
00669   struct pbuf *rambuf;
00670 #if IP_FRAG_USES_STATIC_BUF
00671   struct pbuf *header;
00672 #else
00673 #if !LWIP_NETIF_TX_SINGLE_PBUF
00674   struct pbuf *newpbuf;
00675 #endif
00676   struct ip_hdr *original_iphdr;
00677 #endif
00678   struct ip_hdr *iphdr;
00679   u16_t nfb;
00680   u16_t left, cop;
00681   u16_t mtu = netif->mtu;
00682   u16_t ofo, omf;
00683   u16_t last;
00684   u16_t poff = IP_HLEN;
00685   u16_t tmp;
00686 #if !IP_FRAG_USES_STATIC_BUF && !LWIP_NETIF_TX_SINGLE_PBUF
00687   u16_t newpbuflen = 0;
00688   u16_t left_to_copy;
00689 #endif
00690 
00691   /* Get a RAM based MTU sized pbuf */
00692 #if IP_FRAG_USES_STATIC_BUF
00693   /* When using a static buffer, we use a PBUF_REF, which we will
00694    * use to reference the packet (without link header).
00695    * Layer and length is irrelevant.
00696    */
00697   rambuf = pbuf_alloc(PBUF_LINK, 0, PBUF_REF);
00698   if (rambuf == NULL) {
00699     LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_frag: pbuf_alloc(PBUF_LINK, 0, PBUF_REF) failed\n"));
00700     return ERR_MEM;
00701   }
00702   rambuf->tot_len = rambuf->len = mtu;
00703   rambuf->payload = LWIP_MEM_ALIGN((void *)buf);
00704 
00705   /* Copy the IP header in it */
00706   iphdr = (struct ip_hdr *)rambuf->payload;
00707   SMEMCPY(iphdr, p->payload, IP_HLEN);
00708 #else /* IP_FRAG_USES_STATIC_BUF */
00709   original_iphdr = (struct ip_hdr *)p->payload;
00710   iphdr = original_iphdr;
00711 #endif /* IP_FRAG_USES_STATIC_BUF */
00712 
00713   /* Save original offset */
00714   tmp = ntohs(IPH_OFFSET(iphdr));
00715   ofo = tmp & IP_OFFMASK;
00716   omf = tmp & IP_MF;
00717 
00718   left = p->tot_len - IP_HLEN;
00719 
00720   nfb = (mtu - IP_HLEN) / 8;
00721 
00722   while (left) {
00723     last = (left <= mtu - IP_HLEN);
00724 
00725     /* Set new offset and MF flag */
00726     tmp = omf | (IP_OFFMASK & (ofo));
00727     if (!last) {
00728       tmp = tmp | IP_MF;
00729     }
00730 
00731     /* Fill this fragment */
00732     cop = last ? left : nfb * 8;
00733 
00734 #if IP_FRAG_USES_STATIC_BUF
00735     poff += pbuf_copy_partial(p, (u8_t*)iphdr + IP_HLEN, cop, poff);
00736 #else /* IP_FRAG_USES_STATIC_BUF */
00737 #if LWIP_NETIF_TX_SINGLE_PBUF
00738     rambuf = pbuf_alloc(PBUF_IP, cop, PBUF_RAM);
00739     if (rambuf == NULL) {
00740       return ERR_MEM;
00741     }
00742     LWIP_ASSERT("this needs a pbuf in one piece!",
00743       (rambuf->len == rambuf->tot_len) && (rambuf->next == NULL));
00744     poff += pbuf_copy_partial(p, rambuf->payload, cop, poff);
00745     /* make room for the IP header */
00746     if(pbuf_header(rambuf, IP_HLEN)) {
00747       pbuf_free(rambuf);
00748       return ERR_MEM;
00749     }
00750     /* fill in the IP header */
00751     SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);
00752     iphdr = rambuf->payload;
00753 #else /* LWIP_NETIF_TX_SINGLE_PBUF */
00754     /* When not using a static buffer, create a chain of pbufs.
00755      * The first will be a PBUF_RAM holding the link and IP header.
00756      * The rest will be PBUF_REFs mirroring the pbuf chain to be fragged,
00757      * but limited to the size of an mtu.
00758      */
00759     rambuf = pbuf_alloc(PBUF_LINK, IP_HLEN, PBUF_RAM);
00760     if (rambuf == NULL) {
00761       return ERR_MEM;
00762     }
00763     LWIP_ASSERT("this needs a pbuf in one piece!",
00764                 (p->len >= (IP_HLEN)));
00765     SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);
00766     iphdr = (struct ip_hdr *)rambuf->payload;
00767 
00768     /* Can just adjust p directly for needed offset. */
00769     p->payload = (u8_t *)p->payload + poff;
00770     p->len -= poff;
00771 
00772     left_to_copy = cop;
00773     while (left_to_copy) {
00774       struct pbuf_custom_ref *pcr;
00775       newpbuflen = (left_to_copy < p->len) ? left_to_copy : p->len;
00776       /* Is this pbuf already empty? */
00777       if (!newpbuflen) {
00778         p = p->next;
00779         continue;
00780       }
00781       pcr = ip_frag_alloc_pbuf_custom_ref();
00782       if (pcr == NULL) {
00783         pbuf_free(rambuf);
00784         return ERR_MEM;
00785       }
00786       /* Mirror this pbuf, although we might not need all of it. */
00787       newpbuf = pbuf_alloced_custom(PBUF_RAW, newpbuflen, PBUF_REF, &pcr->pc, p->payload, newpbuflen);
00788       if (newpbuf == NULL) {
00789         ip_frag_free_pbuf_custom_ref(pcr);
00790         pbuf_free(rambuf);
00791         return ERR_MEM;
00792       }
00793       pbuf_ref(p);
00794       pcr->original = p;
00795       pcr->pc.custom_free_function = ipfrag_free_pbuf_custom;
00796 
00797       /* Add it to end of rambuf's chain, but using pbuf_cat, not pbuf_chain
00798        * so that it is removed when pbuf_dechain is later called on rambuf.
00799        */
00800       pbuf_cat(rambuf, newpbuf);
00801       left_to_copy -= newpbuflen;
00802       if (left_to_copy) {
00803         p = p->next;
00804       }
00805     }
00806     poff = newpbuflen;
00807 #endif /* LWIP_NETIF_TX_SINGLE_PBUF */
00808 #endif /* IP_FRAG_USES_STATIC_BUF */
00809 
00810     /* Correct header */
00811     IPH_OFFSET_SET(iphdr, htons(tmp));
00812     IPH_LEN_SET(iphdr, htons(cop + IP_HLEN));
00813     IPH_CHKSUM_SET(iphdr, 0);
00814     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
00815 
00816 #if IP_FRAG_USES_STATIC_BUF
00817     if (last) {
00818       pbuf_realloc(rambuf, left + IP_HLEN);
00819     }
00820 
00821     /* This part is ugly: we alloc a RAM based pbuf for 
00822      * the link level header for each chunk and then 
00823      * free it.A PBUF_ROM style pbuf for which pbuf_header
00824      * worked would make things simpler.
00825      */
00826     header = pbuf_alloc(PBUF_LINK, 0, PBUF_RAM);
00827     if (header != NULL) {
00828       pbuf_chain(header, rambuf);
00829       netif->output(netif, header, dest);
00830       IPFRAG_STATS_INC(ip_frag.xmit);
00831       snmp_inc_ipfragcreates();
00832       pbuf_free(header);
00833     } else {
00834       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_frag: pbuf_alloc() for header failed\n"));
00835       pbuf_free(rambuf);
00836       return ERR_MEM;
00837     }
00838 #else /* IP_FRAG_USES_STATIC_BUF */
00839     /* No need for separate header pbuf - we allowed room for it in rambuf
00840      * when allocated.
00841      */
00842     netif->output(netif, rambuf, dest);
00843     IPFRAG_STATS_INC(ip_frag.xmit);
00844 
00845     /* Unfortunately we can't reuse rambuf - the hardware may still be
00846      * using the buffer. Instead we free it (and the ensuing chain) and
00847      * recreate it next time round the loop. If we're lucky the hardware
00848      * will have already sent the packet, the free will really free, and
00849      * there will be zero memory penalty.
00850      */
00851     
00852     pbuf_free(rambuf);
00853 #endif /* IP_FRAG_USES_STATIC_BUF */
00854     left -= cop;
00855     ofo += nfb;
00856   }
00857 #if IP_FRAG_USES_STATIC_BUF
00858   pbuf_free(rambuf);
00859 #endif /* IP_FRAG_USES_STATIC_BUF */
00860   snmp_inc_ipfragoks();
00861   return ERR_OK;
00862 }
00863 #endif /* IP_FRAG */