sys/netgraph/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  * $FreeBSD$
  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_info ng_vjc_config_type_info
 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_info
 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 #if _MACHINE_ARCH == i386
 111 #define NG_VJC_TSTATE_PTR_TYPE  &ng_parse_uint32_type
 112 #elif _MACHINE_ARCH == alpha
 113 #define NG_VJC_TSTATE_PTR_TYPE  &ng_parse_uint64_type
 114 #else
 115 #error Unspported _MACHINE_ARCH
 116 #endif
 117
 118 /* Parse type for the 'cs_hdr' field in a struct cstate. Ideally we would
 119    like to use a 'struct ip' type instead of a simple array of bytes. */
 120 static const struct ng_parse_fixedarray_info ng_vjc_cs_hdr_type_info = {
 121         &ng_parse_hint8_type,
 122         MAX_HDR
 123 };
 124 static const struct ng_parse_type ng_vjc_cs_hdr_type = {
 125         &ng_parse_fixedarray_type,
 126         &ng_vjc_cs_hdr_type_info
 127 };
 128
 129 /* Parse type for a struct cstate */
 130 static const struct ng_parse_struct_info ng_vjc_cstate_type_info = {
 131     {
 132         { "cs_next",            NG_VJC_TSTATE_PTR_TYPE          },
 133         { "cs_hlen",            &ng_parse_uint16_type           },
 134         { "cs_id",              &ng_parse_uint8_type            },
 135         { "cs_filler",          &ng_parse_uint8_type            },
 136         { "cs_hdr",             &ng_vjc_cs_hdr_type             },
 137         { NULL },
 138     }
 139 };
 140 static const struct ng_parse_type ng_vjc_cstate_type = {
 141         &ng_parse_struct_type,
 142         &ng_vjc_cstate_type_info
 143 };
 144
 145 /* Parse type for an array of MAX_STATES struct cstate's, ie, tstate & rstate */
 146 static const struct ng_parse_fixedarray_info ng_vjc_cstatearray_type_info = {
 147         &ng_vjc_cstate_type,
 148         MAX_STATES
 149 };
 150 static const struct ng_parse_type ng_vjc_cstatearray_type = {
 151         &ng_parse_fixedarray_type,
 152         &ng_vjc_cstatearray_type_info
 153 };
 154
 155 /* Parse type for struct slcompress. Keep this in sync with the
 156    definition of struct slcompress defined in <net/slcompress.h> */
 157 static const struct ng_parse_struct_info ng_vjc_slcompress_type_info = {
 158     {
 159         { "last_cs",            NG_VJC_TSTATE_PTR_TYPE          },
 160         { "last_recv",          &ng_parse_uint8_type            },
 161         { "last_xmit",          &ng_parse_uint8_type            },
 162         { "flags",              &ng_parse_hint16_type           },
 163 #ifndef SL_NO_STATS
 164         { "sls_packets",        &ng_parse_uint32_type           },
 165         { "sls_compressed",     &ng_parse_uint32_type           },
 166         { "sls_searches",       &ng_parse_uint32_type           },
 167         { "sls_misses",         &ng_parse_uint32_type           },
 168         { "sls_uncompressedin", &ng_parse_uint32_type           },
 169         { "sls_compressedin",   &ng_parse_uint32_type           },
 170         { "sls_errorin",        &ng_parse_uint32_type           },
 171         { "sls_tossed",         &ng_parse_uint32_type           },
 172 #endif
 173         { "tstate",             &ng_vjc_cstatearray_type        },
 174         { "rstate",             &ng_vjc_cstatearray_type        },
 175         { NULL },
 176     }
 177 };
 178 static const struct ng_parse_type ng_vjc_slcompress_type = {
 179         &ng_parse_struct_type,
 180         &ng_vjc_slcompress_type_info
 181 };
 182
 183 /* List of commands and how to convert arguments to/from ASCII */
 184 static const struct ng_cmdlist ng_vjc_cmds[] = {
 185         {
 186           NGM_VJC_COOKIE,
 187           NGM_VJC_SET_CONFIG,
 188           "setconfig",
 189           &ng_vjc_config_type,
 190           NULL
 191         },
 192         {
 193           NGM_VJC_COOKIE,
 194           NGM_VJC_GET_CONFIG,
 195           "getconfig",
 196           NULL,
 197           &ng_vjc_config_type,
 198         },
 199         {
 200           NGM_VJC_COOKIE,
 201           NGM_VJC_GET_STATE,
 202           "getstate",
 203           NULL,
 204           &ng_vjc_slcompress_type,
 205         },
 206         {
 207           NGM_VJC_COOKIE,
 208           NGM_VJC_CLR_STATS,
 209           "clrstats",
 210           NULL,
 211           NULL,
 212         },
 213         {
 214           NGM_VJC_COOKIE,
 215           NGM_VJC_RECV_ERROR,
 216           "recverror",
 217           NULL,
 218           NULL,
 219         },
 220         { 0 }
 221 };
 222
 223 /* Node type descriptor */
 224 static struct ng_type ng_vjc_typestruct = {
 225         NG_ABI_VERSION,
 226         NG_VJC_NODE_TYPE,
 227         NULL,
 228         ng_vjc_constructor,
 229         ng_vjc_rcvmsg,
 230         ng_vjc_shutdown,
 231         ng_vjc_newhook,
 232         NULL,
 233         NULL,
 234         ng_vjc_rcvdata,
 235         ng_vjc_disconnect,
 236         ng_vjc_cmds
 237 };
 238 NETGRAPH_INIT(vjc, &ng_vjc_typestruct);
 239
 240 /************************************************************************
 241                         NETGRAPH NODE METHODS
 242  ************************************************************************/
 243
 244 /*
 245  * Create a new node
 246  */
 247 static int
 248 ng_vjc_constructor(node_p node)
 249 {
 250         priv_p priv;
 251
 252         /* Allocate private structure */
 253         MALLOC(priv, priv_p, sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
 254         if (priv == NULL)
 255                 return (ENOMEM);
 256
 257         NG_NODE_SET_PRIVATE(node, 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 = NG_NODE_PRIVATE(node);
 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, item_p item, hook_p lasthook)
 298 {
 299         const priv_p priv = NG_NODE_PRIVATE(node);
 300         struct ng_mesg *resp = NULL;
 301         int error = 0;
 302         struct ng_mesg *msg;
 303
 304         NGI_GET_MSG(item, msg);
 305         /* Check type cookie */
 306         switch (msg->header.typecookie) {
 307         case NGM_VJC_COOKIE:
 308                 switch (msg->header.cmd) {
 309                 case NGM_VJC_SET_CONFIG:
 310                     {
 311                         struct ngm_vjc_config *const c =
 312                                 (struct ngm_vjc_config *) msg->data;
 313
 314                         if (msg->header.arglen != sizeof(*c))
 315                                 ERROUT(EINVAL);
 316                         if ((priv->conf.enableComp || priv->conf.enableDecomp)
 317                             && (c->enableComp || c->enableDecomp))
 318                                 ERROUT(EALREADY);
 319                         if (c->enableComp) {
 320                                 if (c->maxChannel > NG_VJC_MAX_CHANNELS - 1
 321                                     || c->maxChannel < NG_VJC_MIN_CHANNELS - 1)
 322                                         ERROUT(EINVAL);
 323                         } else
 324                                 c->maxChannel = NG_VJC_MAX_CHANNELS - 1;
 325                         if (c->enableComp != 0 || c->enableDecomp != 0) {
 326                                 bzero(&priv->slc, sizeof(priv->slc));
 327                                 sl_compress_init(&priv->slc, c->maxChannel);
 328                         }
 329                         priv->conf = *c;
 330                         break;
 331                     }
 332                 case NGM_VJC_GET_CONFIG:
 333                     {
 334                         struct ngm_vjc_config *conf;
 335
 336                         NG_MKRESPONSE(resp, msg, sizeof(*conf), M_NOWAIT);
 337                         if (resp == NULL)
 338                                 ERROUT(ENOMEM);
 339                         conf = (struct ngm_vjc_config *)resp->data;
 340                         *conf = priv->conf;
 341                         break;
 342                     }
 343                 case NGM_VJC_GET_STATE:
 344                     {
 345                         const struct slcompress *const sl0 = &priv->slc;
 346                         struct slcompress *sl;
 347                         u_int16_t index;
 348                         int i;
 349
 350                         /* Get response structure */
 351                         NG_MKRESPONSE(resp, msg, sizeof(*sl), M_NOWAIT);
 352                         if (resp == NULL)
 353                                 ERROUT(ENOMEM);
 354                         sl = (struct slcompress *)resp->data;
 355                         *sl = *sl0;
 356
 357                         /* Replace pointers with integer indicies */
 358                         if (sl->last_cs != NULL) {
 359                                 index = sl0->last_cs - sl0->tstate;
 360                                 bzero(&sl->last_cs, sizeof(sl->last_cs));
 361                                 *((u_int16_t *)&sl->last_cs) = index;
 362                         }
 363                         for (i = 0; i < MAX_STATES; i++) {
 364                                 struct cstate *const cs = &sl->tstate[i];
 365
 366                                 index = sl0->tstate[i].cs_next - sl0->tstate;
 367                                 bzero(&cs->cs_next, sizeof(cs->cs_next));
 368                                 *((u_int16_t *)&cs->cs_next) = index;
 369                         }
 370                         break;
 371                     }
 372                 case NGM_VJC_CLR_STATS:
 373                         priv->slc.sls_packets = 0;
 374                         priv->slc.sls_compressed = 0;
 375                         priv->slc.sls_searches = 0;
 376                         priv->slc.sls_misses = 0;
 377                         priv->slc.sls_uncompressedin = 0;
 378                         priv->slc.sls_compressedin = 0;
 379                         priv->slc.sls_errorin = 0;
 380                         priv->slc.sls_tossed = 0;
 381                         break;
 382                 case NGM_VJC_RECV_ERROR:
 383                         sl_uncompress_tcp(NULL, 0, TYPE_ERROR, &priv->slc);
 384                         break;
 385                 default:
 386                         error = EINVAL;
 387                         break;
 388                 }
 389                 break;
 390         default:
 391                 error = EINVAL;
 392                 break;
 393         }
 394 done:
 395         NG_RESPOND_MSG(error, node, item, resp);
 396         NG_FREE_MSG(msg);
 397         return (error);
 398 }
 399
 400 /*
 401  * Receive data
 402  */
 403 static int
 404 ng_vjc_rcvdata(hook_p hook, item_p item)
 405 {
 406         const node_p node = NG_HOOK_NODE(hook);
 407         const priv_p priv = NG_NODE_PRIVATE(node);
 408         int error = 0;
 409         struct mbuf *m;
 410
 411         NGI_GET_M(item, m);
 412         if (hook == priv->ip) {                 /* outgoing packet */
 413                 u_int type = TYPE_IP;
 414
 415                 /* Compress packet if enabled and proto is TCP */
 416                 if (priv->conf.enableComp) {
 417                         struct ip *ip;
 418
 419                         if ((m = ng_vjc_pulluphdrs(m, 0)) == NULL) {
 420                                 NG_FREE_ITEM(item);
 421                                 return (ENOBUFS);
 422                         }
 423                         ip = mtod(m, struct ip *);
 424                         if (ip->ip_p == IPPROTO_TCP) {
 425                                 const int origLen = m->m_len;
 426
 427                                 type = sl_compress_tcp(m, ip,
 428                                     &priv->slc, priv->conf.compressCID);
 429                                 m->m_pkthdr.len += m->m_len - origLen;
 430                         }
 431                 }
 432
 433                 /* Dispatch to the appropriate outgoing hook */
 434                 switch (type) {
 435                 case TYPE_IP:
 436                         hook = priv->vjip;
 437                         break;
 438                 case TYPE_UNCOMPRESSED_TCP:
 439                         hook = priv->vjuncomp;
 440                         break;
 441                 case TYPE_COMPRESSED_TCP:
 442                         hook = priv->vjcomp;
 443                         break;
 444                 default:
 445                         panic("%s: type=%d", __func__, type);
 446                 }
 447         } else if (hook == priv->vjcomp) {      /* incoming compressed packet */
 448                 int vjlen, need2pullup;
 449                 struct mbuf *hm;
 450                 u_char *hdr;
 451                 u_int hlen;
 452
 453                 /* Are we decompressing? */
 454                 if (!priv->conf.enableDecomp) {
 455                         NG_FREE_M(m);
 456                         NG_FREE_ITEM(item);
 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_ITEM(item);
 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_M(m);
 477                         NG_FREE_ITEM(item);
 478                         return (EINVAL);
 479                 }
 480                 m_adj(m, vjlen);
 481
 482                 /* Copy the reconstructed TCP/IP headers into a new mbuf */
 483                 MGETHDR(hm, M_DONTWAIT, MT_DATA);
 484                 if (hm == NULL) {
 485                         priv->slc.sls_errorin++;
 486                         NG_FREE_M(m);
 487                         NG_FREE_ITEM(item);
 488                         return (ENOBUFS);
 489                 }
 490                 hm->m_len = 0;
 491                 hm->m_pkthdr.rcvif = NULL;
 492                 if (hlen > MHLEN) {             /* unlikely, but can happen */
 493                         MCLGET(hm, M_DONTWAIT);
 494                         if ((hm->m_flags & M_EXT) == 0) {
 495                                 m_freem(hm);
 496                                 priv->slc.sls_errorin++;
 497                                 NG_FREE_M(m);
 498                                 NG_FREE_ITEM(item);
 499                                 return (ENOBUFS);
 500                         }
 501                 }
 502                 bcopy(hdr, mtod(hm, u_char *), hlen);
 503                 hm->m_len = hlen;
 504
 505                 /* Glue TCP/IP headers and rest of packet together */
 506                 hm->m_next = m;
 507                 hm->m_pkthdr.len = hlen + m->m_pkthdr.len;
 508                 m = hm;
 509                 hook = priv->ip;
 510         } else if (hook == priv->vjuncomp) {    /* incoming uncompressed pkt */
 511                 u_char *hdr;
 512                 u_int hlen;
 513
 514                 /* Are we decompressing? */
 515                 if (!priv->conf.enableDecomp) {
 516                         NG_FREE_M(m);
 517                         NG_FREE_ITEM(item);
 518                         return (ENXIO);
 519                 }
 520
 521                 /* Pull up IP+TCP headers */
 522                 if ((m = ng_vjc_pulluphdrs(m, 1)) == NULL) {
 523                         NG_FREE_ITEM(item);
 524                         return (ENOBUFS);
 525                 }
 526
 527                 /* Run packet through uncompressor */
 528                 if (sl_uncompress_tcp_core(mtod(m, u_char *),
 529                     m->m_len, m->m_pkthdr.len, TYPE_UNCOMPRESSED_TCP,
 530                     &priv->slc, &hdr, &hlen) < 0) {
 531                         NG_FREE_M(m);
 532                         NG_FREE_ITEM(item);
 533                         return (EINVAL);
 534                 }
 535                 hook = priv->ip;
 536         } else if (hook == priv->vjip)  /* incoming regular packet (bypass) */
 537                 hook = priv->ip;
 538         else
 539                 panic("%s: unknown hook", __func__);
 540
 541         /* Send result back out */
 542         NG_FWD_NEW_DATA(error, item, hook, m);
 543         return (error);
 544 }
 545
 546 /*
 547  * Shutdown node
 548  */
 549 static int
 550 ng_vjc_shutdown(node_p node)
 551 {
 552         const priv_p priv = NG_NODE_PRIVATE(node);
 553
 554         bzero(priv, sizeof(*priv));
 555         FREE(priv, M_NETGRAPH);
 556         NG_NODE_SET_PRIVATE(node, NULL);
 557         NG_NODE_UNREF(node);
 558         return (0);
 559 }
 560
 561 /*
 562  * Hook disconnection
 563  */
 564 static int
 565 ng_vjc_disconnect(hook_p hook)
 566 {
 567         const node_p node = NG_HOOK_NODE(hook);
 568         const priv_p priv = NG_NODE_PRIVATE(node);
 569
 570         /* Zero out hook pointer */
 571         if (hook == priv->ip)
 572                 priv->ip = NULL;
 573         else if (hook == priv->vjcomp)
 574                 priv->vjcomp = NULL;
 575         else if (hook == priv->vjuncomp)
 576                 priv->vjuncomp = NULL;
 577         else if (hook == priv->vjip)
 578                 priv->vjip = NULL;
 579         else
 580                 panic("%s: unknown hook", __func__);
 581
 582         /* Go away if no hooks left */
 583         if ((NG_NODE_NUMHOOKS(node) == 0)
 584         && (NG_NODE_IS_VALID(node)))
 585                 ng_rmnode_self(node);
 586         return (0);
 587 }
 588
 589 /************************************************************************
 590                         HELPER STUFF
 591  ************************************************************************/
 592
 593 /*
 594  * Pull up the full IP and TCP headers of a packet. If packet is not
 595  * a TCP packet, just pull up the IP header.
 596  */
 597 static struct mbuf *
 598 ng_vjc_pulluphdrs(struct mbuf *m, int knownTCP)
 599 {
 600         struct ip *ip;
 601         struct tcphdr *tcp;
 602         int ihlen, thlen;
 603
 604         if (m->m_len < sizeof(*ip) && (m = m_pullup(m, sizeof(*ip))) == NULL)
 605                 return (NULL);
 606         ip = mtod(m, struct ip *);
 607         if (!knownTCP && ip->ip_p != IPPROTO_TCP)
 608                 return (m);
 609         ihlen = ip->ip_hl << 2;
 610         if (m->m_len < ihlen + sizeof(*tcp)) {
 611                 if ((m = m_pullup(m, ihlen + sizeof(*tcp))) == NULL)
 612                         return (NULL);
 613                 ip = mtod(m, struct ip *);
 614         }
 615         tcp = (struct tcphdr *)((u_char *)ip + ihlen);
 616         thlen = tcp->th_off << 2;
 617         if (m->m_len < ihlen + thlen)
 618                 m = m_pullup(m, ihlen + thlen);
 619         return (m);
 620 }
 621