lwip_ip4_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 
00043 #if LWIP_IPV4
00044 
00045 #include "lwip/ip4_frag.h"
00046 #include "lwip/def.h"
00047 #include "lwip/inet_chksum.h"
00048 #include "lwip/netif.h"
00049 #include "lwip/stats.h"
00050 #include "lwip/icmp.h"
00051 
00052 #include <string.h>
00053 
00054 #if IP_REASSEMBLY
00055 /**
00056  * The IP reassembly code currently has the following limitations:
00057  * - IP header options are not supported
00058  * - fragments must not overlap (e.g. due to different routes),
00059  *   currently, overlapping or duplicate fragments are thrown away
00060  *   if IP_REASS_CHECK_OVERLAP=1 (the default)!
00061  *
00062  * @todo: work with IP header options
00063  */
00064 
00065 /** Setting this to 0, you can turn off checking the fragments for overlapping
00066  * regions. The code gets a little smaller. Only use this if you know that
00067  * overlapping won't occur on your network! */
00068 #ifndef IP_REASS_CHECK_OVERLAP
00069 #define IP_REASS_CHECK_OVERLAP 1
00070 #endif /* IP_REASS_CHECK_OVERLAP */
00071 
00072 /** Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is
00073  * full (IP_REASS_MAX_PBUFS pbufs are enqueued). The code gets a little smaller.
00074  * Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA
00075  * is set to 1, so one datagram can be reassembled at a time, only. */
00076 #ifndef IP_REASS_FREE_OLDEST
00077 #define IP_REASS_FREE_OLDEST 1
00078 #endif /* IP_REASS_FREE_OLDEST */
00079 
00080 #define IP_REASS_FLAG_LASTFRAG 0x01
00081 
00082 /** This is a helper struct which holds the starting
00083  * offset and the ending offset of this fragment to
00084  * easily chain the fragments.
00085  * It has the same packing requirements as the IP header, since it replaces
00086  * the IP header in memory in incoming fragments (after copying it) to keep
00087  * track of the various fragments. (-> If the IP header doesn't need packing,
00088  * this struct doesn't need packing, too.)
00089  */
00090 #ifdef PACK_STRUCT_USE_INCLUDES
00091 #  include "arch/bpstruct.h"
00092 #endif
00093 PACK_STRUCT_BEGIN
00094 struct ip_reass_helper {
00095   PACK_STRUCT_FIELD(struct pbuf *next_pbuf);
00096   PACK_STRUCT_FIELD(u16_t start);
00097   PACK_STRUCT_FIELD(u16_t end);
00098 } PACK_STRUCT_STRUCT;
00099 PACK_STRUCT_END
00100 #ifdef PACK_STRUCT_USE_INCLUDES
00101 #  include "arch/epstruct.h"
00102 #endif
00103 
00104 #define IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)  \
00105   (ip4_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \
00106    ip4_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \
00107    IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0
00108 
00109 /* global variables */
00110 static struct ip_reassdata *reassdatagrams;
00111 static u16_t ip_reass_pbufcount;
00112 
00113 /* function prototypes */
00114 static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00115 static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
00116 
00117 /**
00118  * Reassembly timer base function
00119  * for both NO_SYS == 0 and 1 (!).
00120  *
00121  * Should be called every 1000 msec (defined by IP_TMR_INTERVAL).
00122  */
00123 void
00124 ip_reass_tmr(void)
00125 {
00126   struct ip_reassdata *r, *prev = NULL;
00127 
00128   r = reassdatagrams;
00129   while (r != NULL) {
00130     /* Decrement the timer. Once it reaches 0,
00131      * clean up the incomplete fragment assembly */
00132     if (r->timer > 0) {
00133       r->timer--;
00134       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n",(u16_t)r->timer));
00135       prev = r;
00136       r = r->next;
00137     } else {
00138       /* reassembly timed out */
00139       struct ip_reassdata *tmp;
00140       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer timed out\n"));
00141       tmp = r;
00142       /* get the next pointer before freeing */
00143       r = r->next;
00144       /* free the helper struct and all enqueued pbufs */
00145       ip_reass_free_complete_datagram(tmp, prev);
00146      }
00147    }
00148 }
00149 
00150 /**
00151  * Free a datagram (struct ip_reassdata) and all its pbufs.
00152  * Updates the total count of enqueued pbufs (ip_reass_pbufcount),
00153  * SNMP counters and sends an ICMP time exceeded packet.
00154  *
00155  * @param ipr datagram to free
00156  * @param prev the previous datagram in the linked list
00157  * @return the number of pbufs freed
00158  */
00159 static int
00160 ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00161 {
00162   u16_t pbufs_freed = 0;
00163   u16_t clen;
00164   struct pbuf *p;
00165   struct ip_reass_helper *iprh;
00166 
00167   LWIP_ASSERT("prev != ipr", prev != ipr);
00168   if (prev != NULL) {
00169     LWIP_ASSERT("prev->next == ipr", prev->next == ipr);
00170   }
00171 
00172   MIB2_STATS_INC(mib2.ipreasmfails);
00173 #if LWIP_ICMP
00174   iprh = (struct ip_reass_helper *)ipr->p->payload;
00175   if (iprh->start == 0) {
00176     /* The first fragment was received, send ICMP time exceeded. */
00177     /* First, de-queue the first pbuf from r->p. */
00178     p = ipr->p;
00179     ipr->p = iprh->next_pbuf;
00180     /* Then, copy the original header into it. */
00181     SMEMCPY(p->payload, &ipr->iphdr, IP_HLEN);
00182     icmp_time_exceeded(p, ICMP_TE_FRAG);
00183     clen = pbuf_clen(p);
00184     LWIP_ASSERT("pbufs_freed + clen <= 0xffff", pbufs_freed + clen <= 0xffff);
00185     pbufs_freed += clen;
00186     pbuf_free(p);
00187   }
00188 #endif /* LWIP_ICMP */
00189 
00190   /* First, free all received pbufs.  The individual pbufs need to be released
00191      separately as they have not yet been chained */
00192   p = ipr->p;
00193   while (p != NULL) {
00194     struct pbuf *pcur;
00195     iprh = (struct ip_reass_helper *)p->payload;
00196     pcur = p;
00197     /* get the next pointer before freeing */
00198     p = iprh->next_pbuf;
00199     clen = pbuf_clen(pcur);
00200     LWIP_ASSERT("pbufs_freed + clen <= 0xffff", pbufs_freed + clen <= 0xffff);
00201     pbufs_freed += clen;
00202     pbuf_free(pcur);
00203   }
00204   /* Then, unchain the struct ip_reassdata from the list and free it. */
00205   ip_reass_dequeue_datagram(ipr, prev);
00206   LWIP_ASSERT("ip_reass_pbufcount >= clen", ip_reass_pbufcount >= pbufs_freed);
00207   ip_reass_pbufcount -= pbufs_freed;
00208 
00209   return pbufs_freed;
00210 }
00211 
00212 #if IP_REASS_FREE_OLDEST
00213 /**
00214  * Free the oldest datagram to make room for enqueueing new fragments.
00215  * The datagram 'fraghdr' belongs to is not freed!
00216  *
00217  * @param fraghdr IP header of the current fragment
00218  * @param pbufs_needed number of pbufs needed to enqueue
00219  *        (used for freeing other datagrams if not enough space)
00220  * @return the number of pbufs freed
00221  */
00222 static int
00223 ip_reass_remove_oldest_datagram(struct ip_hdr *fraghdr, int pbufs_needed)
00224 {
00225   /* @todo Can't we simply remove the last datagram in the
00226    *       linked list behind reassdatagrams?
00227    */
00228   struct ip_reassdata *r, *oldest, *prev, *oldest_prev;
00229   int pbufs_freed = 0, pbufs_freed_current;
00230   int other_datagrams;
00231 
00232   /* Free datagrams until being allowed to enqueue 'pbufs_needed' pbufs,
00233    * but don't free the datagram that 'fraghdr' belongs to! */
00234   do {
00235     oldest = NULL;
00236     prev = NULL;
00237     oldest_prev = NULL;
00238     other_datagrams = 0;
00239     r = reassdatagrams;
00240     while (r != NULL) {
00241       if (!IP_ADDRESSES_AND_ID_MATCH(&r->iphdr, fraghdr)) {
00242         /* Not the same datagram as fraghdr */
00243         other_datagrams++;
00244         if (oldest == NULL) {
00245           oldest = r;
00246           oldest_prev = prev;
00247         } else if (r->timer <= oldest->timer) {
00248           /* older than the previous oldest */
00249           oldest = r;
00250           oldest_prev = prev;
00251         }
00252       }
00253       if (r->next != NULL) {
00254         prev = r;
00255       }
00256       r = r->next;
00257     }
00258     if (oldest != NULL) {
00259       pbufs_freed_current = ip_reass_free_complete_datagram(oldest, oldest_prev);
00260       pbufs_freed += pbufs_freed_current;
00261     }
00262   } while ((pbufs_freed < pbufs_needed) && (other_datagrams > 1));
00263   return pbufs_freed;
00264 }
00265 #endif /* IP_REASS_FREE_OLDEST */
00266 
00267 /**
00268  * Enqueues a new fragment into the fragment queue
00269  * @param fraghdr points to the new fragments IP hdr
00270  * @param clen number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)
00271  * @return A pointer to the queue location into which the fragment was enqueued
00272  */
00273 static struct ip_reassdata*
00274 ip_reass_enqueue_new_datagram(struct ip_hdr *fraghdr, int clen)
00275 {
00276   struct ip_reassdata* ipr;
00277 #if ! IP_REASS_FREE_OLDEST
00278   LWIP_UNUSED_ARG(clen);
00279 #endif
00280 
00281   /* No matching previous fragment found, allocate a new reassdata struct */
00282   ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00283   if (ipr == NULL) {
00284 #if IP_REASS_FREE_OLDEST
00285     if (ip_reass_remove_oldest_datagram(fraghdr, clen) >= clen) {
00286       ipr = (struct ip_reassdata *)memp_malloc(MEMP_REASSDATA);
00287     }
00288     if (ipr == NULL)
00289 #endif /* IP_REASS_FREE_OLDEST */
00290     {
00291       IPFRAG_STATS_INC(ip_frag.memerr);
00292       LWIP_DEBUGF(IP_REASS_DEBUG,("Failed to alloc reassdata struct\n"));
00293       return NULL;
00294     }
00295   }
00296   memset(ipr, 0, sizeof(struct ip_reassdata));
00297   ipr->timer = IP_REASS_MAXAGE;
00298 
00299   /* enqueue the new structure to the front of the list */
00300   ipr->next = reassdatagrams;
00301   reassdatagrams = ipr;
00302   /* copy the ip header for later tests and input */
00303   /* @todo: no ip options supported? */
00304   SMEMCPY(&(ipr->iphdr), fraghdr, IP_HLEN);
00305   return ipr;
00306 }
00307 
00308 /**
00309  * Dequeues a datagram from the datagram queue. Doesn't deallocate the pbufs.
00310  * @param ipr points to the queue entry to dequeue
00311  */
00312 static void
00313 ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)
00314 {
00315   /* dequeue the reass struct  */
00316   if (reassdatagrams == ipr) {
00317     /* it was the first in the list */
00318     reassdatagrams = ipr->next;
00319   } else {
00320     /* it wasn't the first, so it must have a valid 'prev' */
00321     LWIP_ASSERT("sanity check linked list", prev != NULL);
00322     prev->next = ipr->next;
00323   }
00324 
00325   /* now we can free the ip_reassdata struct */
00326   memp_free(MEMP_REASSDATA, ipr);
00327 }
00328 
00329 /**
00330  * Chain a new pbuf into the pbuf list that composes the datagram.  The pbuf list
00331  * will grow over time as  new pbufs are rx.
00332  * Also checks that the datagram passes basic continuity checks (if the last
00333  * fragment was received at least once).
00334  * @param ipr points to the reassembly state
00335  * @param new_p points to the pbuf for the current fragment
00336  * @return 0 if invalid, >0 otherwise
00337  */
00338 static int
00339 ip_reass_chain_frag_into_datagram_and_validate(struct ip_reassdata *ipr, struct pbuf *new_p)
00340 {
00341   struct ip_reass_helper *iprh, *iprh_tmp, *iprh_prev=NULL;
00342   struct pbuf *q;
00343   u16_t offset, len;
00344   struct ip_hdr *fraghdr;
00345   int valid = 1;
00346 
00347   /* Extract length and fragment offset from current fragment */
00348   fraghdr = (struct ip_hdr*)new_p->payload;
00349   len = lwip_ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00350   offset = (lwip_ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00351 
00352   /* overwrite the fragment's ip header from the pbuf with our helper struct,
00353    * and setup the embedded helper structure. */
00354   /* make sure the struct ip_reass_helper fits into the IP header */
00355   LWIP_ASSERT("sizeof(struct ip_reass_helper) <= IP_HLEN",
00356               sizeof(struct ip_reass_helper) <= IP_HLEN);
00357   iprh = (struct ip_reass_helper*)new_p->payload;
00358   iprh->next_pbuf = NULL;
00359   iprh->start = offset;
00360   iprh->end = offset + len;
00361 
00362   /* Iterate through until we either get to the end of the list (append),
00363    * or we find one with a larger offset (insert). */
00364   for (q = ipr->p; q != NULL;) {
00365     iprh_tmp = (struct ip_reass_helper*)q->payload;
00366     if (iprh->start < iprh_tmp->start) {
00367       /* the new pbuf should be inserted before this */
00368       iprh->next_pbuf = q;
00369       if (iprh_prev != NULL) {
00370         /* not the fragment with the lowest offset */
00371 #if IP_REASS_CHECK_OVERLAP
00372         if ((iprh->start < iprh_prev->end) || (iprh->end > iprh_tmp->start)) {
00373           /* fragment overlaps with previous or following, throw away */
00374           goto freepbuf;
00375         }
00376 #endif /* IP_REASS_CHECK_OVERLAP */
00377         iprh_prev->next_pbuf = new_p;
00378       } else {
00379         /* fragment with the lowest offset */
00380         ipr->p = new_p;
00381       }
00382       break;
00383     } else if (iprh->start == iprh_tmp->start) {
00384       /* received the same datagram twice: no need to keep the datagram */
00385       goto freepbuf;
00386 #if IP_REASS_CHECK_OVERLAP
00387     } else if (iprh->start < iprh_tmp->end) {
00388       /* overlap: no need to keep the new datagram */
00389       goto freepbuf;
00390 #endif /* IP_REASS_CHECK_OVERLAP */
00391     } else {
00392       /* Check if the fragments received so far have no holes. */
00393       if (iprh_prev != NULL) {
00394         if (iprh_prev->end != iprh_tmp->start) {
00395           /* There is a fragment missing between the current
00396            * and the previous fragment */
00397           valid = 0;
00398         }
00399       }
00400     }
00401     q = iprh_tmp->next_pbuf;
00402     iprh_prev = iprh_tmp;
00403   }
00404 
00405   /* If q is NULL, then we made it to the end of the list. Determine what to do now */
00406   if (q == NULL) {
00407     if (iprh_prev != NULL) {
00408       /* this is (for now), the fragment with the highest offset:
00409        * chain it to the last fragment */
00410 #if IP_REASS_CHECK_OVERLAP
00411       LWIP_ASSERT("check fragments don't overlap", iprh_prev->end <= iprh->start);
00412 #endif /* IP_REASS_CHECK_OVERLAP */
00413       iprh_prev->next_pbuf = new_p;
00414       if (iprh_prev->end != iprh->start) {
00415         valid = 0;
00416       }
00417     } else {
00418 #if IP_REASS_CHECK_OVERLAP
00419       LWIP_ASSERT("no previous fragment, this must be the first fragment!",
00420         ipr->p == NULL);
00421 #endif /* IP_REASS_CHECK_OVERLAP */
00422       /* this is the first fragment we ever received for this ip datagram */
00423       ipr->p = new_p;
00424     }
00425   }
00426 
00427   /* At this point, the validation part begins: */
00428   /* If we already received the last fragment */
00429   if ((ipr->flags & IP_REASS_FLAG_LASTFRAG) != 0) {
00430     /* and had no holes so far */
00431     if (valid) {
00432       /* then check if the rest of the fragments is here */
00433       /* Check if the queue starts with the first datagram */
00434       if ((ipr->p == NULL) || (((struct ip_reass_helper*)ipr->p->payload)->start != 0)) {
00435         valid = 0;
00436       } else {
00437         /* and check that there are no holes after this datagram */
00438         iprh_prev = iprh;
00439         q = iprh->next_pbuf;
00440         while (q != NULL) {
00441           iprh = (struct ip_reass_helper*)q->payload;
00442           if (iprh_prev->end != iprh->start) {
00443             valid = 0;
00444             break;
00445           }
00446           iprh_prev = iprh;
00447           q = iprh->next_pbuf;
00448         }
00449         /* if still valid, all fragments are received
00450          * (because to the MF==0 already arrived */
00451         if (valid) {
00452           LWIP_ASSERT("sanity check", ipr->p != NULL);
00453           LWIP_ASSERT("sanity check",
00454             ((struct ip_reass_helper*)ipr->p->payload) != iprh);
00455           LWIP_ASSERT("validate_datagram:next_pbuf!=NULL",
00456             iprh->next_pbuf == NULL);
00457           LWIP_ASSERT("validate_datagram:datagram end!=datagram len",
00458             iprh->end == ipr->datagram_len);
00459         }
00460       }
00461     }
00462     /* If valid is 0 here, there are some fragments missing in the middle
00463      * (since MF == 0 has already arrived). Such datagrams simply time out if
00464      * no more fragments are received... */
00465     return valid;
00466   }
00467   /* If we come here, not all fragments were received, yet! */
00468   return 0; /* not yet valid! */
00469 #if IP_REASS_CHECK_OVERLAP
00470 freepbuf:
00471   ip_reass_pbufcount -= pbuf_clen(new_p);
00472   pbuf_free(new_p);
00473   return 0;
00474 #endif /* IP_REASS_CHECK_OVERLAP */
00475 }
00476 
00477 /**
00478  * Reassembles incoming IP fragments into an IP datagram.
00479  *
00480  * @param p points to a pbuf chain of the fragment
00481  * @return NULL if reassembly is incomplete, ? otherwise
00482  */
00483 struct pbuf *
00484 ip4_reass(struct pbuf *p)
00485 {
00486   struct pbuf *r;
00487   struct ip_hdr *fraghdr;
00488   struct ip_reassdata *ipr;
00489   struct ip_reass_helper *iprh;
00490   u16_t offset, len, clen;
00491 
00492   IPFRAG_STATS_INC(ip_frag.recv);
00493   MIB2_STATS_INC(mib2.ipreasmreqds);
00494 
00495   fraghdr = (struct ip_hdr*)p->payload;
00496 
00497   if ((IPH_HL(fraghdr) * 4) != IP_HLEN) {
00498     LWIP_DEBUGF(IP_REASS_DEBUG,("ip4_reass: IP options currently not supported!\n"));
00499     IPFRAG_STATS_INC(ip_frag.err);
00500     goto nullreturn;
00501   }
00502 
00503   offset = (lwip_ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;
00504   len = lwip_ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;
00505 
00506   /* Check if we are allowed to enqueue more datagrams. */
00507   clen = pbuf_clen(p);
00508   if ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS) {
00509 #if IP_REASS_FREE_OLDEST
00510     if (!ip_reass_remove_oldest_datagram(fraghdr, clen) ||
00511         ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS))
00512 #endif /* IP_REASS_FREE_OLDEST */
00513     {
00514       /* No datagram could be freed and still too many pbufs enqueued */
00515       LWIP_DEBUGF(IP_REASS_DEBUG,("ip4_reass: Overflow condition: pbufct=%d, clen=%d, MAX=%d\n",
00516         ip_reass_pbufcount, clen, IP_REASS_MAX_PBUFS));
00517       IPFRAG_STATS_INC(ip_frag.memerr);
00518       /* @todo: send ICMP time exceeded here? */
00519       /* drop this pbuf */
00520       goto nullreturn;
00521     }
00522   }
00523 
00524   /* Look for the datagram the fragment belongs to in the current datagram queue,
00525    * remembering the previous in the queue for later dequeueing. */
00526   for (ipr = reassdatagrams; ipr != NULL; ipr = ipr->next) {
00527     /* Check if the incoming fragment matches the one currently present
00528        in the reassembly buffer. If so, we proceed with copying the
00529        fragment into the buffer. */
00530     if (IP_ADDRESSES_AND_ID_MATCH(&ipr->iphdr, fraghdr)) {
00531       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip4_reass: matching previous fragment ID=%"X16_F"\n",
00532         lwip_ntohs(IPH_ID(fraghdr))));
00533       IPFRAG_STATS_INC(ip_frag.cachehit);
00534       break;
00535     }
00536   }
00537 
00538   if (ipr == NULL) {
00539   /* Enqueue a new datagram into the datagram queue */
00540     ipr = ip_reass_enqueue_new_datagram(fraghdr, clen);
00541     /* Bail if unable to enqueue */
00542     if (ipr == NULL) {
00543       goto nullreturn;
00544     }
00545   } else {
00546     if (((lwip_ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) == 0) &&
00547       ((lwip_ntohs(IPH_OFFSET(&ipr->iphdr)) & IP_OFFMASK) != 0)) {
00548       /* ipr->iphdr is not the header from the first fragment, but fraghdr is
00549        * -> copy fraghdr into ipr->iphdr since we want to have the header
00550        * of the first fragment (for ICMP time exceeded and later, for copying
00551        * all options, if supported)*/
00552       SMEMCPY(&ipr->iphdr, fraghdr, IP_HLEN);
00553     }
00554   }
00555   /* Track the current number of pbufs current 'in-flight', in order to limit
00556   the number of fragments that may be enqueued at any one time */
00557   ip_reass_pbufcount += clen;
00558 
00559   /* At this point, we have either created a new entry or pointing
00560    * to an existing one */
00561 
00562   /* check for 'no more fragments', and update queue entry*/
00563   if ((IPH_OFFSET(fraghdr) & PP_NTOHS(IP_MF)) == 0) {
00564     ipr->flags |= IP_REASS_FLAG_LASTFRAG;
00565     ipr->datagram_len = offset + len;
00566     LWIP_DEBUGF(IP_REASS_DEBUG,
00567      ("ip4_reass: last fragment seen, total len %"S16_F"\n",
00568       ipr->datagram_len));
00569   }
00570   /* find the right place to insert this pbuf */
00571   /* @todo: trim pbufs if fragments are overlapping */
00572   if (ip_reass_chain_frag_into_datagram_and_validate(ipr, p)) {
00573     struct ip_reassdata *ipr_prev;
00574     /* the totally last fragment (flag more fragments = 0) was received at least
00575      * once AND all fragments are received */
00576     ipr->datagram_len += IP_HLEN;
00577 
00578     /* save the second pbuf before copying the header over the pointer */
00579     r = ((struct ip_reass_helper*)ipr->p->payload)->next_pbuf;
00580 
00581     /* copy the original ip header back to the first pbuf */
00582     fraghdr = (struct ip_hdr*)(ipr->p->payload);
00583     SMEMCPY(fraghdr, &ipr->iphdr, IP_HLEN);
00584     IPH_LEN_SET(fraghdr, lwip_htons(ipr->datagram_len));
00585     IPH_OFFSET_SET(fraghdr, 0);
00586     IPH_CHKSUM_SET(fraghdr, 0);
00587     /* @todo: do we need to set/calculate the correct checksum? */
00588 #if CHECKSUM_GEN_IP
00589     IF__NETIF_CHECKSUM_ENABLED(ip_current_input_netif(), NETIF_CHECKSUM_GEN_IP) {
00590       IPH_CHKSUM_SET(fraghdr, inet_chksum(fraghdr, IP_HLEN));
00591     }
00592 #endif /* CHECKSUM_GEN_IP */
00593 
00594     p = ipr->p;
00595 
00596     /* chain together the pbufs contained within the reass_data list. */
00597     while (r != NULL) {
00598       iprh = (struct ip_reass_helper*)r->payload;
00599 
00600       /* hide the ip header for every succeeding fragment */
00601       pbuf_header(r, -IP_HLEN);
00602       pbuf_cat(p, r);
00603       r = iprh->next_pbuf;
00604     }
00605 
00606     /* find the previous entry in the linked list */
00607     if (ipr == reassdatagrams) {
00608       ipr_prev = NULL;
00609     } else {
00610       for (ipr_prev = reassdatagrams; ipr_prev != NULL; ipr_prev = ipr_prev->next) {
00611         if (ipr_prev->next == ipr) {
00612           break;
00613         }
00614       }
00615     }
00616 
00617     /* release the sources allocate for the fragment queue entry */
00618     ip_reass_dequeue_datagram(ipr, ipr_prev);
00619 
00620     /* and adjust the number of pbufs currently queued for reassembly. */
00621     ip_reass_pbufcount -= pbuf_clen(p);
00622 
00623     MIB2_STATS_INC(mib2.ipreasmoks);
00624 
00625     /* Return the pbuf chain */
00626     return p;
00627   }
00628   /* the datagram is not (yet?) reassembled completely */
00629   LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass_pbufcount: %d out\n", ip_reass_pbufcount));
00630   return NULL;
00631 
00632 nullreturn:
00633   LWIP_DEBUGF(IP_REASS_DEBUG,("ip4_reass: nullreturn\n"));
00634   IPFRAG_STATS_INC(ip_frag.drop);
00635   pbuf_free(p);
00636   return NULL;
00637 }
00638 #endif /* IP_REASSEMBLY */
00639 
00640 #if IP_FRAG
00641 #if !LWIP_NETIF_TX_SINGLE_PBUF
00642 /** Allocate a new struct pbuf_custom_ref */
00643 static struct pbuf_custom_ref*
00644 ip_frag_alloc_pbuf_custom_ref(void)
00645 {
00646   return (struct pbuf_custom_ref*)memp_malloc(MEMP_FRAG_PBUF);
00647 }
00648 
00649 /** Free a struct pbuf_custom_ref */
00650 static void
00651 ip_frag_free_pbuf_custom_ref(struct pbuf_custom_ref* p)
00652 {
00653   LWIP_ASSERT("p != NULL", p != NULL);
00654   memp_free(MEMP_FRAG_PBUF, p);
00655 }
00656 
00657 /** Free-callback function to free a 'struct pbuf_custom_ref', called by
00658  * pbuf_free. */
00659 static void
00660 ipfrag_free_pbuf_custom(struct pbuf *p)
00661 {
00662   struct pbuf_custom_ref *pcr = (struct pbuf_custom_ref*)p;
00663   LWIP_ASSERT("pcr != NULL", pcr != NULL);
00664   LWIP_ASSERT("pcr == p", (void*)pcr == (void*)p);
00665   if (pcr->original != NULL) {
00666     pbuf_free(pcr->original);
00667   }
00668   ip_frag_free_pbuf_custom_ref(pcr);
00669 }
00670 #endif /* !LWIP_NETIF_TX_SINGLE_PBUF */
00671 
00672 /**
00673  * Fragment an IP datagram if too large for the netif.
00674  *
00675  * Chop the datagram in MTU sized chunks and send them in order
00676  * by pointing PBUF_REFs into p.
00677  *
00678  * @param p ip packet to send
00679  * @param netif the netif on which to send
00680  * @param dest destination ip address to which to send
00681  *
00682  * @return ERR_OK if sent successfully, err_t otherwise
00683  */
00684 err_t
00685 ip4_frag(struct pbuf *p, struct netif *netif, const ip4_addr_t *dest)
00686 {
00687   struct pbuf *rambuf;
00688 #if !LWIP_NETIF_TX_SINGLE_PBUF
00689   struct pbuf *newpbuf;
00690   u16_t newpbuflen = 0;
00691   u16_t left_to_copy;
00692 #endif
00693   struct ip_hdr *original_iphdr;
00694   struct ip_hdr *iphdr;
00695   const u16_t nfb = (netif->mtu - IP_HLEN) / 8;
00696   u16_t left, fragsize;
00697   u16_t ofo;
00698   int last;
00699   u16_t poff = IP_HLEN;
00700   u16_t tmp;
00701 
00702   original_iphdr = (struct ip_hdr *)p->payload;
00703   iphdr = original_iphdr;
00704   LWIP_ERROR("ip4_frag() does not support IP options", IPH_HL(iphdr) * 4 == IP_HLEN, return ERR_VAL);
00705 
00706   /* Save original offset */
00707   tmp = lwip_ntohs(IPH_OFFSET(iphdr));
00708   ofo = tmp & IP_OFFMASK;
00709   LWIP_ERROR("ip_frag(): MF already set", (tmp & IP_MF) == 0, return ERR_VAL);
00710 
00711   left = p->tot_len - IP_HLEN;
00712 
00713   while (left) {
00714     /* Fill this fragment */
00715     fragsize = LWIP_MIN(left, nfb * 8);
00716 
00717 #if LWIP_NETIF_TX_SINGLE_PBUF
00718     rambuf = pbuf_alloc(PBUF_IP, fragsize, PBUF_RAM);
00719     if (rambuf == NULL) {
00720       goto memerr;
00721     }
00722     LWIP_ASSERT("this needs a pbuf in one piece!",
00723       (rambuf->len == rambuf->tot_len) && (rambuf->next == NULL));
00724     poff += pbuf_copy_partial(p, rambuf->payload, fragsize, poff);
00725     /* make room for the IP header */
00726     if (pbuf_header(rambuf, IP_HLEN)) {
00727       pbuf_free(rambuf);
00728       goto memerr;
00729     }
00730     /* fill in the IP header */
00731     SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);
00732     iphdr = (struct ip_hdr*)rambuf->payload;
00733 #else /* LWIP_NETIF_TX_SINGLE_PBUF */
00734     /* When not using a static buffer, create a chain of pbufs.
00735      * The first will be a PBUF_RAM holding the link and IP header.
00736      * The rest will be PBUF_REFs mirroring the pbuf chain to be fragged,
00737      * but limited to the size of an mtu.
00738      */
00739     rambuf = pbuf_alloc(PBUF_LINK, IP_HLEN, PBUF_RAM);
00740     if (rambuf == NULL) {
00741       goto memerr;
00742     }
00743     LWIP_ASSERT("this needs a pbuf in one piece!",
00744                 (p->len >= (IP_HLEN)));
00745     SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);
00746     iphdr = (struct ip_hdr *)rambuf->payload;
00747 
00748     left_to_copy = fragsize;
00749     while (left_to_copy) {
00750       struct pbuf_custom_ref *pcr;
00751       u16_t plen = p->len - poff;
00752       newpbuflen = LWIP_MIN(left_to_copy, plen);
00753       /* Is this pbuf already empty? */
00754       if (!newpbuflen) {
00755         poff = 0;
00756         p = p->next;
00757         continue;
00758       }
00759       pcr = ip_frag_alloc_pbuf_custom_ref();
00760       if (pcr == NULL) {
00761         pbuf_free(rambuf);
00762         goto memerr;
00763       }
00764       /* Mirror this pbuf, although we might not need all of it. */
00765       newpbuf = pbuf_alloced_custom(PBUF_RAW, newpbuflen, PBUF_REF, &pcr->pc,
00766         (u8_t*)p->payload + poff, newpbuflen);
00767       if (newpbuf == NULL) {
00768         ip_frag_free_pbuf_custom_ref(pcr);
00769         pbuf_free(rambuf);
00770         goto memerr;
00771       }
00772       pbuf_ref(p);
00773       pcr->original = p;
00774       pcr->pc.custom_free_function = ipfrag_free_pbuf_custom;
00775 
00776       /* Add it to end of rambuf's chain, but using pbuf_cat, not pbuf_chain
00777        * so that it is removed when pbuf_dechain is later called on rambuf.
00778        */
00779       pbuf_cat(rambuf, newpbuf);
00780       left_to_copy -= newpbuflen;
00781       if (left_to_copy) {
00782         poff = 0;
00783         p = p->next;
00784       }
00785     }
00786     poff += newpbuflen;
00787 #endif /* LWIP_NETIF_TX_SINGLE_PBUF */
00788 
00789     /* Correct header */
00790     last = (left <= netif->mtu - IP_HLEN);
00791 
00792     /* Set new offset and MF flag */
00793     tmp = (IP_OFFMASK & (ofo));
00794     if (!last) {
00795       tmp = tmp | IP_MF;
00796     }
00797     IPH_OFFSET_SET(iphdr, lwip_htons(tmp));
00798     IPH_LEN_SET(iphdr, lwip_htons(fragsize + IP_HLEN));
00799     IPH_CHKSUM_SET(iphdr, 0);
00800 #if CHECKSUM_GEN_IP
00801     IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_IP) {
00802       IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
00803     }
00804 #endif /* CHECKSUM_GEN_IP */
00805 
00806     /* No need for separate header pbuf - we allowed room for it in rambuf
00807      * when allocated.
00808      */
00809     netif->output(netif, rambuf, dest);
00810     IPFRAG_STATS_INC(ip_frag.xmit);
00811 
00812     /* Unfortunately we can't reuse rambuf - the hardware may still be
00813      * using the buffer. Instead we free it (and the ensuing chain) and
00814      * recreate it next time round the loop. If we're lucky the hardware
00815      * will have already sent the packet, the free will really free, and
00816      * there will be zero memory penalty.
00817      */
00818 
00819     pbuf_free(rambuf);
00820     left -= fragsize;
00821     ofo += nfb;
00822   }
00823   MIB2_STATS_INC(mib2.ipfragoks);
00824   return ERR_OK;
00825 memerr:
00826   MIB2_STATS_INC(mib2.ipfragfails);
00827   return ERR_MEM;
00828 }
00829 #endif /* IP_FRAG */
00830 
00831 #endif /* LWIP_IPV4 */