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  * $DragonFly: src/sys/netgraph/vjc/ng_vjc.c,v 1.7 2007/05/13 18:33:58 swildner Exp $
  41  * $Whistle: ng_vjc.c,v 1.17 1999/11/01 09:24:52 julian Exp $
  42  */
  43
  44 /*
  45  * This node performs Van Jacobson IP header (de)compression.
  46  * You must have included net/slcompress.c in your kernel compilation.
  47  */
  48
  49 #include <sys/param.h>
  50 #include <sys/systm.h>
  51 #include <sys/errno.h>
  52 #include <sys/kernel.h>
  53 #include <sys/mbuf.h>
  54 #include <sys/malloc.h>
  55 #include <sys/errno.h>
  56
  57 #include <netgraph/ng_message.h>
  58 #include <netgraph/netgraph.h>
  59 #include <netgraph/ng_parse.h>
  60 #include "ng_vjc.h"
  61
  62 #include <netinet/in.h>
  63 #include <netinet/in_systm.h>
  64 #include <netinet/ip.h>
  65 #include <netinet/tcp.h>
  66
  67 #include <net/slcompress.h>
  68
  69 /* Check agreement with slcompress.c */
  70 #if MAX_STATES != NG_VJC_MAX_CHANNELS
  71 #error NG_VJC_MAX_CHANNELS must be the same as MAX_STATES
  72 #endif
  73
  74 /* Maximum length of a compressed TCP VJ header */
  75 #define MAX_VJHEADER            19
  76
  77 /* Node private data */
  78 struct ng_vjc_private {
  79         struct  ngm_vjc_config conf;
  80         struct  slcompress slc;
  81         hook_p  ip;
  82         hook_p  vjcomp;
  83         hook_p  vjuncomp;
  84         hook_p  vjip;
  85 };
  86 typedef struct ng_vjc_private *priv_p;
  87
  88 #define ERROUT(x)       do { error = (x); goto done; } while (0)
  89
  90 /* Netgraph node methods */
  91 static ng_constructor_t ng_vjc_constructor;
  92 static ng_rcvmsg_t      ng_vjc_rcvmsg;
  93 static ng_shutdown_t    ng_vjc_rmnode;
  94 static ng_newhook_t     ng_vjc_newhook;
  95 static ng_rcvdata_t     ng_vjc_rcvdata;
  96 static ng_disconnect_t  ng_vjc_disconnect;
  97
  98 /* Helper stuff */
  99 static struct mbuf *ng_vjc_pulluphdrs(struct mbuf *m, int knownTCP);
 100
 101 /* Parse type for struct ngm_vjc_config */
 102 static const struct ng_parse_struct_field ng_vjc_config_type_fields[]
 103         = NG_VJC_CONFIG_TYPE_INFO;
 104 static const struct ng_parse_type ng_vjc_config_type = {
 105         &ng_parse_struct_type,
 106         &ng_vjc_config_type_fields
 107 };
 108
 109 /* Parse type for the 'last_cs' and 'cs_next' fields in struct slcompress,
 110    which are pointers converted to integer indices, so parse them that way. */
 111 #if _MACHINE_ARCH == i386
 112 #define NG_VJC_TSTATE_PTR_TYPE  &ng_parse_uint32_type
 113 #else
 114 #error Unsupported _MACHINE_ARCH
 115 #endif
 116
 117 /* Parse type for the 'cs_hdr' field in a struct cstate. Ideally we would
 118    like to use a 'struct ip' type instead of a simple array of bytes. */
 119 static const struct ng_parse_fixedarray_info ng_vjc_cs_hdr_type_info = {
 120         &ng_parse_hint8_type,
 121         MAX_HDR
 122 };
 123 static const struct ng_parse_type ng_vjc_cs_hdr_type = {
 124         &ng_parse_fixedarray_type,
 125         &ng_vjc_cs_hdr_type_info
 126 };
 127
 128 /* Parse type for a struct cstate */
 129 static const struct ng_parse_struct_field ng_vjc_cstate_type_fields[] = {
 130         { "cs_next",            NG_VJC_TSTATE_PTR_TYPE          },
 131         { "cs_hlen",            &ng_parse_uint16_type           },
 132         { "cs_id",              &ng_parse_uint8_type            },
 133         { "cs_filler",          &ng_parse_uint8_type            },
 134         { "cs_hdr",             &ng_vjc_cs_hdr_type             },
 135         { NULL }
 136 };
 137 static const struct ng_parse_type ng_vjc_cstate_type = {
 138         &ng_parse_struct_type,
 139         &ng_vjc_cstate_type_fields
 140 };
 141
 142 /* Parse type for an array of MAX_STATES struct cstate's, ie, tstate & rstate */
 143 static const struct ng_parse_fixedarray_info ng_vjc_cstatearray_type_info = {
 144         &ng_vjc_cstate_type,
 145         MAX_STATES
 146 };
 147 static const struct ng_parse_type ng_vjc_cstatearray_type = {
 148         &ng_parse_fixedarray_type,
 149         &ng_vjc_cstatearray_type_info
 150 };
 151
 152 /* Parse type for struct slcompress. Keep this in sync with the
 153    definition of struct slcompress defined in <net/slcompress.h> */
 154 static const struct ng_parse_struct_field ng_vjc_slcompress_type_fields[] = {
 155         { "last_cs",            NG_VJC_TSTATE_PTR_TYPE          },
 156         { "last_recv",          &ng_parse_uint8_type            },
 157         { "last_xmit",          &ng_parse_uint8_type            },
 158         { "flags",              &ng_parse_hint16_type           },
 159 #ifndef SL_NO_STATS
 160         { "sls_packets",        &ng_parse_uint32_type           },
 161         { "sls_compressed",     &ng_parse_uint32_type           },
 162         { "sls_searches",       &ng_parse_uint32_type           },
 163         { "sls_misses",         &ng_parse_uint32_type           },
 164         { "sls_uncompressedin", &ng_parse_uint32_type           },
 165         { "sls_compressedin",   &ng_parse_uint32_type           },
 166         { "sls_errorin",        &ng_parse_uint32_type           },
 167         { "sls_tossed",         &ng_parse_uint32_type           },
 168 #endif
 169         { "tstate",             &ng_vjc_cstatearray_type        },
 170         { "rstate",             &ng_vjc_cstatearray_type        },
 171         { NULL }
 172 };
 173 static const struct ng_parse_type ng_vjc_slcompress_type = {
 174         &ng_parse_struct_type,
 175         &ng_vjc_slcompress_type_fields
 176 };
 177
 178 /* List of commands and how to convert arguments to/from ASCII */
 179 static const struct ng_cmdlist ng_vjc_cmds[] = {
 180         {
 181           NGM_VJC_COOKIE,
 182           NGM_VJC_SET_CONFIG,
 183           "setconfig",
 184           &ng_vjc_config_type,
 185           NULL
 186         },
 187         {
 188           NGM_VJC_COOKIE,
 189           NGM_VJC_GET_CONFIG,
 190           "getconfig",
 191           NULL,
 192           &ng_vjc_config_type,
 193         },
 194         {
 195           NGM_VJC_COOKIE,
 196           NGM_VJC_GET_STATE,
 197           "getstate",
 198           NULL,
 199           &ng_vjc_slcompress_type,
 200         },
 201         {
 202           NGM_VJC_COOKIE,
 203           NGM_VJC_CLR_STATS,
 204           "clrstats",
 205           NULL,
 206           NULL,
 207         },
 208         {
 209           NGM_VJC_COOKIE,
 210           NGM_VJC_RECV_ERROR,
 211           "recverror",
 212           NULL,
 213           NULL,
 214         },
 215         { 0 }
 216 };
 217
 218 /* Node type descriptor */
 219 static struct ng_type ng_vjc_typestruct = {
 220         NG_VERSION,
 221         NG_VJC_NODE_TYPE,
 222         NULL,
 223         ng_vjc_constructor,
 224         ng_vjc_rcvmsg,
 225         ng_vjc_rmnode,
 226         ng_vjc_newhook,
 227         NULL,
 228         NULL,
 229         ng_vjc_rcvdata,
 230         ng_vjc_rcvdata,
 231         ng_vjc_disconnect,
 232         ng_vjc_cmds
 233 };
 234 NETGRAPH_INIT(vjc, &ng_vjc_typestruct);
 235
 236 /************************************************************************
 237                         NETGRAPH NODE METHODS
 238  ************************************************************************/
 239
 240 /*
 241  * Create a new node
 242  */
 243 static int
 244 ng_vjc_constructor(node_p *nodep)
 245 {
 246         priv_p priv;
 247         int error;
 248
 249         /* Allocate private structure */
 250         MALLOC(priv, priv_p, sizeof(*priv), M_NETGRAPH, M_NOWAIT);
 251         if (priv == NULL)
 252                 return (ENOMEM);
 253         bzero(priv, sizeof(*priv));
 254
 255         /* Call generic node constructor */
 256         if ((error = ng_make_node_common(&ng_vjc_typestruct, nodep))) {
 257                 FREE(priv, M_NETGRAPH);
 258                 return (error);
 259         }
 260         (*nodep)->private = priv;
 261
 262         /* Done */
 263         return (0);
 264 }
 265
 266 /*
 267  * Add a new hook
 268  */
 269 static int
 270 ng_vjc_newhook(node_p node, hook_p hook, const char *name)
 271 {
 272         const priv_p priv = (priv_p) node->private;
 273         hook_p *hookp;
 274
 275         /* Get hook */
 276         if (strcmp(name, NG_VJC_HOOK_IP) == 0)
 277                 hookp = &priv->ip;
 278         else if (strcmp(name, NG_VJC_HOOK_VJCOMP) == 0)
 279                 hookp = &priv->vjcomp;
 280         else if (strcmp(name, NG_VJC_HOOK_VJUNCOMP) == 0)
 281                 hookp = &priv->vjuncomp;
 282         else if (strcmp(name, NG_VJC_HOOK_VJIP) == 0)
 283                 hookp = &priv->vjip;
 284         else
 285                 return (EINVAL);
 286
 287         /* See if already connected */
 288         if (*hookp)
 289                 return (EISCONN);
 290
 291         /* OK */
 292         *hookp = hook;
 293         return (0);
 294 }
 295
 296 /*
 297  * Receive a control message
 298  */
 299 static int
 300 ng_vjc_rcvmsg(node_p node, struct ng_mesg *msg,
 301               const char *raddr, struct ng_mesg **rptr)
 302 {
 303         const priv_p priv = (priv_p) node->private;
 304         struct ng_mesg *resp = NULL;
 305         int error = 0;
 306
 307         /* Check type cookie */
 308         switch (msg->header.typecookie) {
 309         case NGM_VJC_COOKIE:
 310                 switch (msg->header.cmd) {
 311                 case NGM_VJC_SET_CONFIG:
 312                     {
 313                         struct ngm_vjc_config *const c =
 314                                 (struct ngm_vjc_config *) msg->data;
 315
 316                         if (msg->header.arglen != sizeof(*c))
 317                                 ERROUT(EINVAL);
 318                         if ((priv->conf.enableComp || priv->conf.enableDecomp)
 319                             && (c->enableComp || c->enableDecomp))
 320                                 ERROUT(EALREADY);
 321                         if (c->enableComp) {
 322                                 if (c->maxChannel > NG_VJC_MAX_CHANNELS - 1
 323                                     || c->maxChannel < NG_VJC_MIN_CHANNELS - 1)
 324                                         ERROUT(EINVAL);
 325                         } else
 326                                 c->maxChannel = NG_VJC_MAX_CHANNELS - 1;
 327                         if (c->enableComp != 0 || c->enableDecomp != 0) {
 328                                 bzero(&priv->slc, sizeof(priv->slc));
 329                                 sl_compress_init(&priv->slc, c->maxChannel);
 330                         }
 331                         priv->conf = *c;
 332                         break;
 333                     }
 334                 case NGM_VJC_GET_CONFIG:
 335                     {
 336                         struct ngm_vjc_config *conf;
 337
 338                         NG_MKRESPONSE(resp, msg, sizeof(*conf), M_NOWAIT);
 339                         if (resp == NULL)
 340                                 ERROUT(ENOMEM);
 341                         conf = (struct ngm_vjc_config *)resp->data;
 342                         *conf = priv->conf;
 343                         break;
 344                     }
 345                 case NGM_VJC_GET_STATE:
 346                     {
 347                         const struct slcompress *const sl0 = &priv->slc;
 348                         struct slcompress *sl;
 349                         u_int16_t index;
 350                         int i;
 351
 352                         /* Get response structure */
 353                         NG_MKRESPONSE(resp, msg, sizeof(*sl), M_NOWAIT);
 354                         if (resp == NULL)
 355                                 ERROUT(ENOMEM);
 356                         sl = (struct slcompress *)resp->data;
 357                         *sl = *sl0;
 358
 359                         /* Replace pointers with integer indicies */
 360                         if (sl->last_cs != NULL) {
 361                                 index = sl0->last_cs - sl0->tstate;
 362                                 bzero(&sl->last_cs, sizeof(sl->last_cs));
 363                                 *((u_int16_t *)&sl->last_cs) = index;
 364                         }
 365                         for (i = 0; i < MAX_STATES; i++) {
 366                                 struct cstate *const cs = &sl->tstate[i];
 367
 368                                 index = sl0->tstate[i].cs_next - sl0->tstate;
 369                                 bzero(&cs->cs_next, sizeof(cs->cs_next));
 370                                 *((u_int16_t *)&cs->cs_next) = index;
 371                         }
 372                         break;
 373                     }
 374                 case NGM_VJC_CLR_STATS:
 375                         priv->slc.sls_packets = 0;
 376                         priv->slc.sls_compressed = 0;
 377                         priv->slc.sls_searches = 0;
 378                         priv->slc.sls_misses = 0;
 379                         priv->slc.sls_uncompressedin = 0;
 380                         priv->slc.sls_compressedin = 0;
 381                         priv->slc.sls_errorin = 0;
 382                         priv->slc.sls_tossed = 0;
 383                         break;
 384                 case NGM_VJC_RECV_ERROR:
 385                         sl_uncompress_tcp(NULL, 0, TYPE_ERROR, &priv->slc);
 386                         break;
 387                 default:
 388                         error = EINVAL;
 389                         break;
 390                 }
 391                 break;
 392         default:
 393                 error = EINVAL;
 394                 break;
 395         }
 396         if (rptr)
 397                 *rptr = resp;
 398         else if (resp)
 399                 FREE(resp, M_NETGRAPH);
 400
 401 done:
 402         FREE(msg, M_NETGRAPH);
 403         return (error);
 404 }
 405
 406 /*
 407  * Receive data
 408  */
 409 static int
 410 ng_vjc_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
 411 {
 412         const node_p node = hook->node;
 413         const priv_p priv = (priv_p) node->private;
 414         int error = 0;
 415
 416         if (hook == priv->ip) {                 /* outgoing packet */
 417                 u_int type = TYPE_IP;
 418
 419                 /* Compress packet if enabled and proto is TCP */
 420                 if (priv->conf.enableComp) {
 421                         struct ip *ip;
 422
 423                         if ((m = ng_vjc_pulluphdrs(m, 0)) == NULL) {
 424                                 NG_FREE_META(meta);
 425                                 return (ENOBUFS);
 426                         }
 427                         ip = mtod(m, struct ip *);
 428                         if (ip->ip_p == IPPROTO_TCP) {
 429                                 const int origLen = m->m_len;
 430
 431                                 type = sl_compress_tcp(m, ip,
 432                                     &priv->slc, priv->conf.compressCID);
 433                                 m->m_pkthdr.len += m->m_len - origLen;
 434                         }
 435                 }
 436
 437                 /* Dispatch to the appropriate outgoing hook */
 438                 switch (type) {
 439                 case TYPE_IP:
 440                         hook = priv->vjip;
 441                         break;
 442                 case TYPE_UNCOMPRESSED_TCP:
 443                         hook = priv->vjuncomp;
 444                         break;
 445                 case TYPE_COMPRESSED_TCP:
 446                         hook = priv->vjcomp;
 447                         break;
 448                 default:
 449                         panic("%s: type=%d", __func__, type);
 450                 }
 451         } else if (hook == priv->vjcomp) {      /* incoming compressed packet */
 452                 int vjlen, need2pullup;
 453                 struct mbuf *hm;
 454                 u_char *hdr;
 455                 u_int hlen;
 456
 457                 /* Are we decompressing? */
 458                 if (!priv->conf.enableDecomp) {
 459                         NG_FREE_DATA(m, meta);
 460                         return (ENXIO);
 461                 }
 462
 463                 /* Pull up the necessary amount from the mbuf */
 464                 need2pullup = MAX_VJHEADER;
 465                 if (need2pullup > m->m_pkthdr.len)
 466                         need2pullup = m->m_pkthdr.len;
 467                 if (m->m_len < need2pullup
 468                     && (m = m_pullup(m, need2pullup)) == NULL) {
 469                         priv->slc.sls_errorin++;
 470                         NG_FREE_META(meta);
 471                         return (ENOBUFS);
 472                 }
 473
 474                 /* Uncompress packet to reconstruct TCP/IP header */
 475                 vjlen = sl_uncompress_tcp_core(mtod(m, u_char *),
 476                     m->m_len, m->m_pkthdr.len, TYPE_COMPRESSED_TCP,
 477                     &priv->slc, &hdr, &hlen);
 478                 if (vjlen <= 0) {
 479                         NG_FREE_DATA(m, meta);
 480                         return (EINVAL);
 481                 }
 482                 m_adj(m, vjlen);
 483
 484                 /* Copy the reconstructed TCP/IP headers into a new mbuf */
 485                 MGETHDR(hm, MB_DONTWAIT, MT_DATA);
 486                 if (hm == NULL) {
 487                         priv->slc.sls_errorin++;
 488                         NG_FREE_DATA(m, meta);
 489                         return (ENOBUFS);
 490                 }
 491                 hm->m_len = 0;
 492                 hm->m_pkthdr.rcvif = NULL;
 493                 if (hlen > MHLEN) {             /* unlikely, but can happen */
 494                         MCLGET(hm, MB_DONTWAIT);
 495                         if ((hm->m_flags & M_EXT) == 0) {
 496                                 m_freem(hm);
 497                                 priv->slc.sls_errorin++;
 498                                 NG_FREE_DATA(m, meta);
 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_DATA(m, meta);
 517                         return (ENXIO);
 518                 }
 519
 520                 /* Pull up IP+TCP headers */
 521                 if ((m = ng_vjc_pulluphdrs(m, 1)) == NULL) {
 522                         NG_FREE_META(meta);
 523                         return (ENOBUFS);
 524                 }
 525
 526                 /* Run packet through uncompressor */
 527                 if (sl_uncompress_tcp_core(mtod(m, u_char *),
 528                     m->m_len, m->m_pkthdr.len, TYPE_UNCOMPRESSED_TCP,
 529                     &priv->slc, &hdr, &hlen) < 0) {
 530                         NG_FREE_DATA(m, meta);
 531                         return (EINVAL);
 532                 }
 533                 hook = priv->ip;
 534         } else if (hook == priv->vjip)  /* incoming regular packet (bypass) */
 535                 hook = priv->ip;
 536         else
 537                 panic("%s: unknown hook", __func__);
 538
 539         /* Send result back out */
 540         NG_SEND_DATA(error, hook, m, meta);
 541         return (error);
 542 }
 543
 544 /*
 545  * Shutdown node
 546  */
 547 static int
 548 ng_vjc_rmnode(node_p node)
 549 {
 550         const priv_p priv = (priv_p) node->private;
 551
 552         node->flags |= NG_INVALID;
 553         ng_cutlinks(node);
 554         ng_unname(node);
 555         bzero(priv, sizeof(*priv));
 556         FREE(priv, M_NETGRAPH);
 557         node->private = NULL;
 558         ng_unref(node);
 559         return (0);
 560 }
 561
 562 /*
 563  * Hook disconnection
 564  */
 565 static int
 566 ng_vjc_disconnect(hook_p hook)
 567 {
 568         const node_p node = hook->node;
 569         const priv_p priv = node->private;
 570
 571         /* Zero out hook pointer */
 572         if (hook == priv->ip)
 573                 priv->ip = NULL;
 574         else if (hook == priv->vjcomp)
 575                 priv->vjcomp = NULL;
 576         else if (hook == priv->vjuncomp)
 577                 priv->vjuncomp = NULL;
 578         else if (hook == priv->vjip)
 579                 priv->vjip = NULL;
 580         else
 581                 panic("%s: unknown hook", __func__);
 582
 583         /* Go away if no hooks left */
 584         if (node->numhooks == 0)
 585                 ng_rmnode(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