sys/netgraph/vjc/ng_vjc.c

   1
   2 /*
   3  * ng_vjc.c
   4  *
   5  * Copyright (c) 1996-1999 Whistle Communications, Inc.
   6  * All rights reserved.
   7  *
   8  * Subject to the following obligations and disclaimer of warranty, use and
   9  * redistribution of this software, in source or object code forms, with or
  10  * without modifications are expressly permitted by Whistle Communications;
  11  * provided, however, that:
  12  * 1. Any and all reproductions of the source or object code must include the
  13  *    copyright notice above and the following disclaimer of warranties; and
  14  * 2. No rights are granted, in any manner or form, to use Whistle
  15  *    Communications, Inc. trademarks, including the mark "WHISTLE
  16  *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
  17  *    such appears in the above copyright notice or in the software.
  18  *
  19  * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
  20  * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
  21  * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
  22  * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
  23  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
  24  * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
  25  * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
  26  * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
  27  * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
  28  * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
  29  * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
  30  * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
  31  * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
  32  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  33  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  34  * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
  35  * OF SUCH DAMAGE.
  36  *
  37  * Author: Archie Cobbs <archie@freebsd.org>
  38  *
  39  * $FreeBSD: src/sys/netgraph/ng_vjc.c,v 1.9.2.5 2002/07/02 23:44:03 archie Exp $
  40  * $Whistle: ng_vjc.c,v 1.17 1999/11/01 09:24:52 julian Exp $
  41  */
  42
  43 /*
  44  * This node performs Van Jacobson IP header (de)compression.
  45  * You must have included net/slcompress.c in your kernel compilation.
  46  */
  47
  48 #include <sys/param.h>
  49 #include <sys/systm.h>
  50 #include <sys/errno.h>
  51 #include <sys/kernel.h>
  52 #include <sys/mbuf.h>
  53 #include <sys/malloc.h>
  54
  55 #include <netgraph/ng_message.h>
  56 #include <netgraph/netgraph.h>
  57 #include <netgraph/ng_parse.h>
  58 #include "ng_vjc.h"
  59
  60 #include <netinet/in.h>
  61 #include <netinet/in_systm.h>
  62 #include <netinet/ip.h>
  63 #include <netinet/tcp.h>
  64
  65 #include <net/slcompress.h>
  66
  67 /* Check agreement with slcompress.c */
  68 #if MAX_STATES != NG_VJC_MAX_CHANNELS
  69 #error NG_VJC_MAX_CHANNELS must be the same as MAX_STATES
  70 #endif
  71
  72 /* Maximum length of a compressed TCP VJ header */
  73 #define MAX_VJHEADER            19
  74
  75 /* Node private data */
  76 struct ng_vjc_private {
  77         struct  ngm_vjc_config conf;
  78         struct  slcompress slc;
  79         hook_p  ip;
  80         hook_p  vjcomp;
  81         hook_p  vjuncomp;
  82         hook_p  vjip;
  83 };
  84 typedef struct ng_vjc_private *priv_p;
  85
  86 #define ERROUT(x)       do { error = (x); goto done; } while (0)
  87
  88 /* Netgraph node methods */
  89 static ng_constructor_t ng_vjc_constructor;
  90 static ng_rcvmsg_t      ng_vjc_rcvmsg;
  91 static ng_shutdown_t    ng_vjc_rmnode;
  92 static ng_newhook_t     ng_vjc_newhook;
  93 static ng_rcvdata_t     ng_vjc_rcvdata;
  94 static ng_disconnect_t  ng_vjc_disconnect;
  95
  96 /* Helper stuff */
  97 static struct mbuf *ng_vjc_pulluphdrs(struct mbuf *m, int knownTCP);
  98
  99 /* Parse type for struct ngm_vjc_config */
 100 static const struct ng_parse_struct_field ng_vjc_config_type_fields[]
 101         = NG_VJC_CONFIG_TYPE_INFO;
 102 static const struct ng_parse_type ng_vjc_config_type = {
 103         &ng_parse_struct_type,
 104         &ng_vjc_config_type_fields
 105 };
 106
 107 /* Parse type for the 'last_cs' and 'cs_next' fields in struct slcompress,
 108    which are pointers converted to integer indices, so parse them that way. */
 109 #ifndef __LP64__
 110 #define NG_VJC_TSTATE_PTR_TYPE  &ng_parse_uint32_type
 111 #else
 112 #define NG_VJC_TSTATE_PTR_TYPE  &ng_parse_uint64_type
 113 #endif
 114
 115 /* Parse type for the 'cs_hdr' field in a struct cstate. Ideally we would
 116    like to use a 'struct ip' type instead of a simple array of bytes. */
 117 static const struct ng_parse_fixedarray_info ng_vjc_cs_hdr_type_info = {
 118         &ng_parse_hint8_type,
 119         MAX_HDR
 120 };
 121 static const struct ng_parse_type ng_vjc_cs_hdr_type = {
 122         &ng_parse_fixedarray_type,
 123         &ng_vjc_cs_hdr_type_info
 124 };
 125
 126 /* Parse type for a struct cstate */
 127 static const struct ng_parse_struct_field ng_vjc_cstate_type_fields[] = {
 128         { "cs_next",            NG_VJC_TSTATE_PTR_TYPE          },
 129         { "cs_hlen",            &ng_parse_uint16_type           },
 130         { "cs_id",              &ng_parse_uint8_type            },
 131         { "cs_filler",          &ng_parse_uint8_type            },
 132         { "cs_hdr",             &ng_vjc_cs_hdr_type             },
 133         { NULL }
 134 };
 135 static const struct ng_parse_type ng_vjc_cstate_type = {
 136         &ng_parse_struct_type,
 137         &ng_vjc_cstate_type_fields
 138 };
 139
 140 /* Parse type for an array of MAX_STATES struct cstate's, ie, tstate & rstate */
 141 static const struct ng_parse_fixedarray_info ng_vjc_cstatearray_type_info = {
 142         &ng_vjc_cstate_type,
 143         MAX_STATES
 144 };
 145 static const struct ng_parse_type ng_vjc_cstatearray_type = {
 146         &ng_parse_fixedarray_type,
 147         &ng_vjc_cstatearray_type_info
 148 };
 149
 150 /* Parse type for struct slcompress. Keep this in sync with the
 151    definition of struct slcompress defined in <net/slcompress.h> */
 152 static const struct ng_parse_struct_field ng_vjc_slcompress_type_fields[] = {
 153         { "last_cs",            NG_VJC_TSTATE_PTR_TYPE          },
 154         { "last_recv",          &ng_parse_uint8_type            },
 155         { "last_xmit",          &ng_parse_uint8_type            },
 156         { "flags",              &ng_parse_hint16_type           },
 157 #ifndef SL_NO_STATS
 158         { "sls_packets",        &ng_parse_uint32_type           },
 159         { "sls_compressed",     &ng_parse_uint32_type           },
 160         { "sls_searches",       &ng_parse_uint32_type           },
 161         { "sls_misses",         &ng_parse_uint32_type           },
 162         { "sls_uncompressedin", &ng_parse_uint32_type           },
 163         { "sls_compressedin",   &ng_parse_uint32_type           },
 164         { "sls_errorin",        &ng_parse_uint32_type           },
 165         { "sls_tossed",         &ng_parse_uint32_type           },
 166 #endif
 167         { "tstate",             &ng_vjc_cstatearray_type        },
 168         { "rstate",             &ng_vjc_cstatearray_type        },
 169         { NULL }
 170 };
 171 static const struct ng_parse_type ng_vjc_slcompress_type = {
 172         &ng_parse_struct_type,
 173         &ng_vjc_slcompress_type_fields
 174 };
 175
 176 /* List of commands and how to convert arguments to/from ASCII */
 177 static const struct ng_cmdlist ng_vjc_cmds[] = {
 178         {
 179           NGM_VJC_COOKIE,
 180           NGM_VJC_SET_CONFIG,
 181           "setconfig",
 182           &ng_vjc_config_type,
 183           NULL
 184         },
 185         {
 186           NGM_VJC_COOKIE,
 187           NGM_VJC_GET_CONFIG,
 188           "getconfig",
 189           NULL,
 190           &ng_vjc_config_type,
 191         },
 192         {
 193           NGM_VJC_COOKIE,
 194           NGM_VJC_GET_STATE,
 195           "getstate",
 196           NULL,
 197           &ng_vjc_slcompress_type,
 198         },
 199         {
 200           NGM_VJC_COOKIE,
 201           NGM_VJC_CLR_STATS,
 202           "clrstats",
 203           NULL,
 204           NULL,
 205         },
 206         {
 207           NGM_VJC_COOKIE,
 208           NGM_VJC_RECV_ERROR,
 209           "recverror",
 210           NULL,
 211           NULL,
 212         },
 213         { 0 }
 214 };
 215
 216 /* Node type descriptor */
 217 static struct ng_type ng_vjc_typestruct = {
 218         NG_VERSION,
 219         NG_VJC_NODE_TYPE,
 220         NULL,
 221         ng_vjc_constructor,
 222         ng_vjc_rcvmsg,
 223         ng_vjc_rmnode,
 224         ng_vjc_newhook,
 225         NULL,
 226         NULL,
 227         ng_vjc_rcvdata,
 228         ng_vjc_rcvdata,
 229         ng_vjc_disconnect,
 230         ng_vjc_cmds
 231 };
 232 NETGRAPH_INIT(vjc, &ng_vjc_typestruct);
 233
 234 /************************************************************************
 235                         NETGRAPH NODE METHODS
 236  ************************************************************************/
 237
 238 /*
 239  * Create a new node
 240  */
 241 static int
 242 ng_vjc_constructor(node_p *nodep)
 243 {
 244         priv_p priv;
 245         int error;
 246
 247         /* Allocate private structure */
 248         priv = kmalloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
 249         if (priv == NULL)
 250                 return (ENOMEM);
 251
 252         /* Call generic node constructor */
 253         if ((error = ng_make_node_common(&ng_vjc_typestruct, nodep))) {
 254                 kfree(priv, M_NETGRAPH);
 255                 return (error);
 256         }
 257         (*nodep)->private = priv;
 258
 259         /* Done */
 260         return (0);
 261 }
 262
 263 /*
 264  * Add a new hook
 265  */
 266 static int
 267 ng_vjc_newhook(node_p node, hook_p hook, const char *name)
 268 {
 269         const priv_p priv = (priv_p) node->private;
 270         hook_p *hookp;
 271
 272         /* Get hook */
 273         if (strcmp(name, NG_VJC_HOOK_IP) == 0)
 274                 hookp = &priv->ip;
 275         else if (strcmp(name, NG_VJC_HOOK_VJCOMP) == 0)
 276                 hookp = &priv->vjcomp;
 277         else if (strcmp(name, NG_VJC_HOOK_VJUNCOMP) == 0)
 278                 hookp = &priv->vjuncomp;
 279         else if (strcmp(name, NG_VJC_HOOK_VJIP) == 0)
 280                 hookp = &priv->vjip;
 281         else
 282                 return (EINVAL);
 283
 284         /* See if already connected */
 285         if (*hookp)
 286                 return (EISCONN);
 287
 288         /* OK */
 289         *hookp = hook;
 290         return (0);
 291 }
 292
 293 /*
 294  * Receive a control message
 295  */
 296 static int
 297 ng_vjc_rcvmsg(node_p node, struct ng_mesg *msg,
 298               const char *raddr, struct ng_mesg **rptr)
 299 {
 300         const priv_p priv = (priv_p) node->private;
 301         struct ng_mesg *resp = NULL;
 302         int error = 0;
 303
 304         /* Check type cookie */
 305         switch (msg->header.typecookie) {
 306         case NGM_VJC_COOKIE:
 307                 switch (msg->header.cmd) {
 308                 case NGM_VJC_SET_CONFIG:
 309                     {
 310                         struct ngm_vjc_config *const c =
 311                                 (struct ngm_vjc_config *) msg->data;
 312
 313                         if (msg->header.arglen != sizeof(*c))
 314                                 ERROUT(EINVAL);
 315                         if ((priv->conf.enableComp || priv->conf.enableDecomp)
 316                             && (c->enableComp || c->enableDecomp))
 317                                 ERROUT(EALREADY);
 318                         if (c->enableComp) {
 319                                 if (c->maxChannel > NG_VJC_MAX_CHANNELS - 1
 320                                     || c->maxChannel < NG_VJC_MIN_CHANNELS - 1)
 321                                         ERROUT(EINVAL);
 322                         } else
 323                                 c->maxChannel = NG_VJC_MAX_CHANNELS - 1;
 324                         if (c->enableComp != 0 || c->enableDecomp != 0) {
 325                                 bzero(&priv->slc, sizeof(priv->slc));
 326                                 sl_compress_init(&priv->slc, c->maxChannel);
 327                         }
 328                         priv->conf = *c;
 329                         break;
 330                     }
 331                 case NGM_VJC_GET_CONFIG:
 332                     {
 333                         struct ngm_vjc_config *conf;
 334
 335                         NG_MKRESPONSE(resp, msg, sizeof(*conf), M_NOWAIT);
 336                         if (resp == NULL)
 337                                 ERROUT(ENOMEM);
 338                         conf = (struct ngm_vjc_config *)resp->data;
 339                         *conf = priv->conf;
 340                         break;
 341                     }
 342                 case NGM_VJC_GET_STATE:
 343                     {
 344                         const struct slcompress *const sl0 = &priv->slc;
 345                         struct slcompress *sl;
 346                         u_int16_t index;
 347                         int i;
 348
 349                         /* Get response structure */
 350                         NG_MKRESPONSE(resp, msg, sizeof(*sl), M_NOWAIT);
 351                         if (resp == NULL)
 352                                 ERROUT(ENOMEM);
 353                         sl = (struct slcompress *)resp->data;
 354                         *sl = *sl0;
 355
 356                         /* Replace pointers with integer indicies */
 357                         if (sl->last_cs != NULL) {
 358                                 index = sl0->last_cs - sl0->tstate;
 359                                 bzero(&sl->last_cs, sizeof(sl->last_cs));
 360                                 *((u_int16_t *)&sl->last_cs) = index;
 361                         }
 362                         for (i = 0; i < MAX_STATES; i++) {
 363                                 struct cstate *const cs = &sl->tstate[i];
 364
 365                                 index = sl0->tstate[i].cs_next - sl0->tstate;
 366                                 bzero(&cs->cs_next, sizeof(cs->cs_next));
 367                                 *((u_int16_t *)&cs->cs_next) = index;
 368                         }
 369                         break;
 370                     }
 371                 case NGM_VJC_CLR_STATS:
 372                         priv->slc.sls_packets = 0;
 373                         priv->slc.sls_compressed = 0;
 374                         priv->slc.sls_searches = 0;
 375                         priv->slc.sls_misses = 0;
 376                         priv->slc.sls_uncompressedin = 0;
 377                         priv->slc.sls_compressedin = 0;
 378                         priv->slc.sls_errorin = 0;
 379                         priv->slc.sls_tossed = 0;
 380                         break;
 381                 case NGM_VJC_RECV_ERROR:
 382                         sl_uncompress_tcp(NULL, 0, TYPE_ERROR, &priv->slc);
 383                         break;
 384                 default:
 385                         error = EINVAL;
 386                         break;
 387                 }
 388                 break;
 389         default:
 390                 error = EINVAL;
 391                 break;
 392         }
 393         if (rptr)
 394                 *rptr = resp;
 395         else if (resp)
 396                 kfree(resp, M_NETGRAPH);
 397
 398 done:
 399         kfree(msg, M_NETGRAPH);
 400         return (error);
 401 }
 402
 403 /*
 404  * Receive data
 405  */
 406 static int
 407 ng_vjc_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
 408 {
 409         const node_p node = hook->node;
 410         const priv_p priv = (priv_p) node->private;
 411         int error = 0;
 412
 413         if (hook == priv->ip) {                 /* outgoing packet */
 414                 u_int type = TYPE_IP;
 415
 416                 /* Compress packet if enabled and proto is TCP */
 417                 if (priv->conf.enableComp) {
 418                         struct ip *ip;
 419
 420                         if ((m = ng_vjc_pulluphdrs(m, 0)) == NULL) {
 421                                 NG_FREE_META(meta);
 422                                 return (ENOBUFS);
 423                         }
 424                         ip = mtod(m, struct ip *);
 425                         if (ip->ip_p == IPPROTO_TCP) {
 426                                 const int origLen = m->m_len;
 427
 428                                 type = sl_compress_tcp(m, ip,
 429                                     &priv->slc, priv->conf.compressCID);
 430                                 m->m_pkthdr.len += m->m_len - origLen;
 431                         }
 432                 }
 433
 434                 /* Dispatch to the appropriate outgoing hook */
 435                 switch (type) {
 436                 case TYPE_IP:
 437                         hook = priv->vjip;
 438                         break;
 439                 case TYPE_UNCOMPRESSED_TCP:
 440                         hook = priv->vjuncomp;
 441                         break;
 442                 case TYPE_COMPRESSED_TCP:
 443                         hook = priv->vjcomp;
 444                         break;
 445                 default:
 446                         panic("%s: type=%d", __func__, type);
 447                 }
 448         } else if (hook == priv->vjcomp) {      /* incoming compressed packet */
 449                 int vjlen, need2pullup;
 450                 struct mbuf *hm;
 451                 u_char *hdr;
 452                 u_int hlen;
 453
 454                 /* Are we decompressing? */
 455                 if (!priv->conf.enableDecomp) {
 456                         NG_FREE_DATA(m, meta);
 457                         return (ENXIO);
 458                 }
 459
 460                 /* Pull up the necessary amount from the mbuf */
 461                 need2pullup = MAX_VJHEADER;
 462                 if (need2pullup > m->m_pkthdr.len)
 463                         need2pullup = m->m_pkthdr.len;
 464                 if (m->m_len < need2pullup
 465                     && (m = m_pullup(m, need2pullup)) == NULL) {
 466                         priv->slc.sls_errorin++;
 467                         NG_FREE_META(meta);
 468                         return (ENOBUFS);
 469                 }
 470
 471                 /* Uncompress packet to reconstruct TCP/IP header */
 472                 vjlen = sl_uncompress_tcp_core(mtod(m, u_char *),
 473                     m->m_len, m->m_pkthdr.len, TYPE_COMPRESSED_TCP,
 474                     &priv->slc, &hdr, &hlen);
 475                 if (vjlen <= 0) {
 476                         NG_FREE_DATA(m, meta);
 477                         return (EINVAL);
 478                 }
 479                 m_adj(m, vjlen);
 480
 481                 /* Copy the reconstructed TCP/IP headers into a new mbuf */
 482                 MGETHDR(hm, MB_DONTWAIT, MT_DATA);
 483                 if (hm == NULL) {
 484                         priv->slc.sls_errorin++;
 485                         NG_FREE_DATA(m, meta);
 486                         return (ENOBUFS);
 487                 }
 488                 hm->m_len = 0;
 489                 hm->m_pkthdr.rcvif = NULL;
 490                 if (hlen > MHLEN) {             /* unlikely, but can happen */
 491                         MCLGET(hm, MB_DONTWAIT);
 492                         if ((hm->m_flags & M_EXT) == 0) {
 493                                 m_freem(hm);
 494                                 priv->slc.sls_errorin++;
 495                                 NG_FREE_DATA(m, meta);
 496                                 return (ENOBUFS);
 497                         }
 498                 }
 499                 bcopy(hdr, mtod(hm, u_char *), hlen);
 500                 hm->m_len = hlen;
 501
 502                 /* Glue TCP/IP headers and rest of packet together */
 503                 hm->m_next = m;
 504                 hm->m_pkthdr.len = hlen + m->m_pkthdr.len;
 505                 m = hm;
 506                 hook = priv->ip;
 507         } else if (hook == priv->vjuncomp) {    /* incoming uncompressed pkt */
 508                 u_char *hdr;
 509                 u_int hlen;
 510
 511                 /* Are we decompressing? */
 512                 if (!priv->conf.enableDecomp) {
 513                         NG_FREE_DATA(m, meta);
 514                         return (ENXIO);
 515                 }
 516
 517                 /* Pull up IP+TCP headers */
 518                 if ((m = ng_vjc_pulluphdrs(m, 1)) == NULL) {
 519                         NG_FREE_META(meta);
 520                         return (ENOBUFS);
 521                 }
 522
 523                 /* Run packet through uncompressor */
 524                 if (sl_uncompress_tcp_core(mtod(m, u_char *),
 525                     m->m_len, m->m_pkthdr.len, TYPE_UNCOMPRESSED_TCP,
 526                     &priv->slc, &hdr, &hlen) < 0) {
 527                         NG_FREE_DATA(m, meta);
 528                         return (EINVAL);
 529                 }
 530                 hook = priv->ip;
 531         } else if (hook == priv->vjip)  /* incoming regular packet (bypass) */
 532                 hook = priv->ip;
 533         else
 534                 panic("%s: unknown hook", __func__);
 535
 536         /* Send result back out */
 537         NG_SEND_DATA(error, hook, m, meta);
 538         return (error);
 539 }
 540
 541 /*
 542  * Shutdown node
 543  */
 544 static int
 545 ng_vjc_rmnode(node_p node)
 546 {
 547         const priv_p priv = (priv_p) node->private;
 548
 549         node->flags |= NG_INVALID;
 550         ng_cutlinks(node);
 551         ng_unname(node);
 552         bzero(priv, sizeof(*priv));
 553         kfree(priv, M_NETGRAPH);
 554         node->private = NULL;
 555         ng_unref(node);
 556         return (0);
 557 }
 558
 559 /*
 560  * Hook disconnection
 561  */
 562 static int
 563 ng_vjc_disconnect(hook_p hook)
 564 {
 565         const node_p node = hook->node;
 566         const priv_p priv = node->private;
 567
 568         /* Zero out hook pointer */
 569         if (hook == priv->ip)
 570                 priv->ip = NULL;
 571         else if (hook == priv->vjcomp)
 572                 priv->vjcomp = NULL;
 573         else if (hook == priv->vjuncomp)
 574                 priv->vjuncomp = NULL;
 575         else if (hook == priv->vjip)
 576                 priv->vjip = NULL;
 577         else
 578                 panic("%s: unknown hook", __func__);
 579
 580         /* Go away if no hooks left */
 581         if (node->numhooks == 0)
 582                 ng_rmnode(node);
 583         return (0);
 584 }
 585
 586 /************************************************************************
 587                         HELPER STUFF
 588  ************************************************************************/
 589
 590 /*
 591  * Pull up the full IP and TCP headers of a packet. If packet is not
 592  * a TCP packet, just pull up the IP header.
 593  */
 594 static struct mbuf *
 595 ng_vjc_pulluphdrs(struct mbuf *m, int knownTCP)
 596 {
 597         struct ip *ip;
 598         struct tcphdr *tcp;
 599         int ihlen, thlen;
 600
 601         if (m->m_len < sizeof(*ip) && (m = m_pullup(m, sizeof(*ip))) == NULL)
 602                 return (NULL);
 603         ip = mtod(m, struct ip *);
 604         if (!knownTCP && ip->ip_p != IPPROTO_TCP)
 605                 return (m);
 606         ihlen = ip->ip_hl << 2;
 607         if (m->m_len < ihlen + sizeof(*tcp)) {
 608                 if ((m = m_pullup(m, ihlen + sizeof(*tcp))) == NULL)
 609                         return (NULL);
 610                 ip = mtod(m, struct ip *);
 611         }
 612         tcp = (struct tcphdr *)((u_char *)ip + ihlen);
 613         thlen = tcp->th_off << 2;
 614         if (m->m_len < ihlen + thlen)
 615                 m = m_pullup(m, ihlen + thlen);
 616         return (m);
 617 }
 618