sys/netgraph/ng_vjc.c

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