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 1.8 2008/01/05 14:02:40 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 | M_ZERO);
 251         if (priv == NULL)
 252                 return (ENOMEM);
 253
 254         /* Call generic node constructor */
 255         if ((error = ng_make_node_common(&ng_vjc_typestruct, nodep))) {
 256                 FREE(priv, M_NETGRAPH);
 257                 return (error);
 258         }
 259         (*nodep)->private = priv;
 260
 261         /* Done */
 262         return (0);
 263 }
 264
 265 /*
 266  * Add a new hook
 267  */
 268 static int
 269 ng_vjc_newhook(node_p node, hook_p hook, const char *name)
 270 {
 271         const priv_p priv = (priv_p) node->private;
 272         hook_p *hookp;
 273
 274         /* Get hook */
 275         if (strcmp(name, NG_VJC_HOOK_IP) == 0)
 276                 hookp = &priv->ip;
 277         else if (strcmp(name, NG_VJC_HOOK_VJCOMP) == 0)
 278                 hookp = &priv->vjcomp;
 279         else if (strcmp(name, NG_VJC_HOOK_VJUNCOMP) == 0)
 280                 hookp = &priv->vjuncomp;
 281         else if (strcmp(name, NG_VJC_HOOK_VJIP) == 0)
 282                 hookp = &priv->vjip;
 283         else
 284                 return (EINVAL);
 285
 286         /* See if already connected */
 287         if (*hookp)
 288                 return (EISCONN);
 289
 290         /* OK */
 291         *hookp = hook;
 292         return (0);
 293 }
 294
 295 /*
 296  * Receive a control message
 297  */
 298 static int
 299 ng_vjc_rcvmsg(node_p node, struct ng_mesg *msg,
 300               const char *raddr, struct ng_mesg **rptr)
 301 {
 302         const priv_p priv = (priv_p) node->private;
 303         struct ng_mesg *resp = NULL;
 304         int error = 0;
 305
 306         /* Check type cookie */
 307         switch (msg->header.typecookie) {
 308         case NGM_VJC_COOKIE:
 309                 switch (msg->header.cmd) {
 310                 case NGM_VJC_SET_CONFIG:
 311                     {
 312                         struct ngm_vjc_config *const c =
 313                                 (struct ngm_vjc_config *) msg->data;
 314
 315                         if (msg->header.arglen != sizeof(*c))
 316                                 ERROUT(EINVAL);
 317                         if ((priv->conf.enableComp || priv->conf.enableDecomp)
 318                             && (c->enableComp || c->enableDecomp))
 319                                 ERROUT(EALREADY);
 320                         if (c->enableComp) {
 321                                 if (c->maxChannel > NG_VJC_MAX_CHANNELS - 1
 322                                     || c->maxChannel < NG_VJC_MIN_CHANNELS - 1)
 323                                         ERROUT(EINVAL);
 324                         } else
 325                                 c->maxChannel = NG_VJC_MAX_CHANNELS - 1;
 326                         if (c->enableComp != 0 || c->enableDecomp != 0) {
 327                                 bzero(&priv->slc, sizeof(priv->slc));
 328                                 sl_compress_init(&priv->slc, c->maxChannel);
 329                         }
 330                         priv->conf = *c;
 331                         break;
 332                     }
 333                 case NGM_VJC_GET_CONFIG:
 334                     {
 335                         struct ngm_vjc_config *conf;
 336
 337                         NG_MKRESPONSE(resp, msg, sizeof(*conf), M_NOWAIT);
 338                         if (resp == NULL)
 339                                 ERROUT(ENOMEM);
 340                         conf = (struct ngm_vjc_config *)resp->data;
 341                         *conf = priv->conf;
 342                         break;
 343                     }
 344                 case NGM_VJC_GET_STATE:
 345                     {
 346                         const struct slcompress *const sl0 = &priv->slc;
 347                         struct slcompress *sl;
 348                         u_int16_t index;
 349                         int i;
 350
 351                         /* Get response structure */
 352                         NG_MKRESPONSE(resp, msg, sizeof(*sl), M_NOWAIT);
 353                         if (resp == NULL)
 354                                 ERROUT(ENOMEM);
 355                         sl = (struct slcompress *)resp->data;
 356                         *sl = *sl0;
 357
 358                         /* Replace pointers with integer indicies */
 359                         if (sl->last_cs != NULL) {
 360                                 index = sl0->last_cs - sl0->tstate;
 361                                 bzero(&sl->last_cs, sizeof(sl->last_cs));
 362                                 *((u_int16_t *)&sl->last_cs) = index;
 363                         }
 364                         for (i = 0; i < MAX_STATES; i++) {
 365                                 struct cstate *const cs = &sl->tstate[i];
 366
 367                                 index = sl0->tstate[i].cs_next - sl0->tstate;
 368                                 bzero(&cs->cs_next, sizeof(cs->cs_next));
 369                                 *((u_int16_t *)&cs->cs_next) = index;
 370                         }
 371                         break;
 372                     }
 373                 case NGM_VJC_CLR_STATS:
 374                         priv->slc.sls_packets = 0;
 375                         priv->slc.sls_compressed = 0;
 376                         priv->slc.sls_searches = 0;
 377                         priv->slc.sls_misses = 0;
 378                         priv->slc.sls_uncompressedin = 0;
 379                         priv->slc.sls_compressedin = 0;
 380                         priv->slc.sls_errorin = 0;
 381                         priv->slc.sls_tossed = 0;
 382                         break;
 383                 case NGM_VJC_RECV_ERROR:
 384                         sl_uncompress_tcp(NULL, 0, TYPE_ERROR, &priv->slc);
 385                         break;
 386                 default:
 387                         error = EINVAL;
 388                         break;
 389                 }
 390                 break;
 391         default:
 392                 error = EINVAL;
 393                 break;
 394         }
 395         if (rptr)
 396                 *rptr = resp;
 397         else if (resp)
 398                 FREE(resp, M_NETGRAPH);
 399
 400 done:
 401         FREE(msg, M_NETGRAPH);
 402         return (error);
 403 }
 404
 405 /*
 406  * Receive data
 407  */
 408 static int
 409 ng_vjc_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
 410 {
 411         const node_p node = hook->node;
 412         const priv_p priv = (priv_p) node->private;
 413         int error = 0;
 414
 415         if (hook == priv->ip) {                 /* outgoing packet */
 416                 u_int type = TYPE_IP;
 417
 418                 /* Compress packet if enabled and proto is TCP */
 419                 if (priv->conf.enableComp) {
 420                         struct ip *ip;
 421
 422                         if ((m = ng_vjc_pulluphdrs(m, 0)) == NULL) {
 423                                 NG_FREE_META(meta);
 424                                 return (ENOBUFS);
 425                         }
 426                         ip = mtod(m, struct ip *);
 427                         if (ip->ip_p == IPPROTO_TCP) {
 428                                 const int origLen = m->m_len;
 429
 430                                 type = sl_compress_tcp(m, ip,
 431                                     &priv->slc, priv->conf.compressCID);
 432                                 m->m_pkthdr.len += m->m_len - origLen;
 433                         }
 434                 }
 435
 436                 /* Dispatch to the appropriate outgoing hook */
 437                 switch (type) {
 438                 case TYPE_IP:
 439                         hook = priv->vjip;
 440                         break;
 441                 case TYPE_UNCOMPRESSED_TCP:
 442                         hook = priv->vjuncomp;
 443                         break;
 444                 case TYPE_COMPRESSED_TCP:
 445                         hook = priv->vjcomp;
 446                         break;
 447                 default:
 448                         panic("%s: type=%d", __func__, type);
 449                 }
 450         } else if (hook == priv->vjcomp) {      /* incoming compressed packet */
 451                 int vjlen, need2pullup;
 452                 struct mbuf *hm;
 453                 u_char *hdr;
 454                 u_int hlen;
 455
 456                 /* Are we decompressing? */
 457                 if (!priv->conf.enableDecomp) {
 458                         NG_FREE_DATA(m, meta);
 459                         return (ENXIO);
 460                 }
 461
 462                 /* Pull up the necessary amount from the mbuf */
 463                 need2pullup = MAX_VJHEADER;
 464                 if (need2pullup > m->m_pkthdr.len)
 465                         need2pullup = m->m_pkthdr.len;
 466                 if (m->m_len < need2pullup
 467                     && (m = m_pullup(m, need2pullup)) == NULL) {
 468                         priv->slc.sls_errorin++;
 469                         NG_FREE_META(meta);
 470                         return (ENOBUFS);
 471                 }
 472
 473                 /* Uncompress packet to reconstruct TCP/IP header */
 474                 vjlen = sl_uncompress_tcp_core(mtod(m, u_char *),
 475                     m->m_len, m->m_pkthdr.len, TYPE_COMPRESSED_TCP,
 476                     &priv->slc, &hdr, &hlen);
 477                 if (vjlen <= 0) {
 478                         NG_FREE_DATA(m, meta);
 479                         return (EINVAL);
 480                 }
 481                 m_adj(m, vjlen);
 482
 483                 /* Copy the reconstructed TCP/IP headers into a new mbuf */
 484                 MGETHDR(hm, MB_DONTWAIT, MT_DATA);
 485                 if (hm == NULL) {
 486                         priv->slc.sls_errorin++;
 487                         NG_FREE_DATA(m, meta);
 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, MB_DONTWAIT);
 494                         if ((hm->m_flags & M_EXT) == 0) {
 495                                 m_freem(hm);
 496                                 priv->slc.sls_errorin++;
 497                                 NG_FREE_DATA(m, meta);
 498                                 return (ENOBUFS);
 499                         }
 500                 }
 501                 bcopy(hdr, mtod(hm, u_char *), hlen);
 502                 hm->m_len = hlen;
 503
 504                 /* Glue TCP/IP headers and rest of packet together */
 505                 hm->m_next = m;
 506                 hm->m_pkthdr.len = hlen + m->m_pkthdr.len;
 507                 m = hm;
 508                 hook = priv->ip;
 509         } else if (hook == priv->vjuncomp) {    /* incoming uncompressed pkt */
 510                 u_char *hdr;
 511                 u_int hlen;
 512
 513                 /* Are we decompressing? */
 514                 if (!priv->conf.enableDecomp) {
 515                         NG_FREE_DATA(m, meta);
 516                         return (ENXIO);
 517                 }
 518
 519                 /* Pull up IP+TCP headers */
 520                 if ((m = ng_vjc_pulluphdrs(m, 1)) == NULL) {
 521                         NG_FREE_META(meta);
 522                         return (ENOBUFS);
 523                 }
 524
 525                 /* Run packet through uncompressor */
 526                 if (sl_uncompress_tcp_core(mtod(m, u_char *),
 527                     m->m_len, m->m_pkthdr.len, TYPE_UNCOMPRESSED_TCP,
 528                     &priv->slc, &hdr, &hlen) < 0) {
 529                         NG_FREE_DATA(m, meta);
 530                         return (EINVAL);
 531                 }
 532                 hook = priv->ip;
 533         } else if (hook == priv->vjip)  /* incoming regular packet (bypass) */
 534                 hook = priv->ip;
 535         else
 536                 panic("%s: unknown hook", __func__);
 537
 538         /* Send result back out */
 539         NG_SEND_DATA(error, hook, m, meta);
 540         return (error);
 541 }
 542
 543 /*
 544  * Shutdown node
 545  */
 546 static int
 547 ng_vjc_rmnode(node_p node)
 548 {
 549         const priv_p priv = (priv_p) node->private;
 550
 551         node->flags |= NG_INVALID;
 552         ng_cutlinks(node);
 553         ng_unname(node);
 554         bzero(priv, sizeof(*priv));
 555         FREE(priv, M_NETGRAPH);
 556         node->private = NULL;
 557         ng_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 = hook->node;
 568         const priv_p priv = node->private;
 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 (node->numhooks == 0)
 584                 ng_rmnode(node);
 585         return (0);
 586 }
 587
 588 /************************************************************************
 589                         HELPER STUFF
 590  ************************************************************************/
 591
 592 /*
 593  * Pull up the full IP and TCP headers of a packet. If packet is not
 594  * a TCP packet, just pull up the IP header.
 595  */
 596 static struct mbuf *
 597 ng_vjc_pulluphdrs(struct mbuf *m, int knownTCP)
 598 {
 599         struct ip *ip;
 600         struct tcphdr *tcp;
 601         int ihlen, thlen;
 602
 603         if (m->m_len < sizeof(*ip) && (m = m_pullup(m, sizeof(*ip))) == NULL)
 604                 return (NULL);
 605         ip = mtod(m, struct ip *);
 606         if (!knownTCP && ip->ip_p != IPPROTO_TCP)
 607                 return (m);
 608         ihlen = ip->ip_hl << 2;
 609         if (m->m_len < ihlen + sizeof(*tcp)) {
 610                 if ((m = m_pullup(m, ihlen + sizeof(*tcp))) == NULL)
 611                         return (NULL);
 612                 ip = mtod(m, struct ip *);
 613         }
 614         tcp = (struct tcphdr *)((u_char *)ip + ihlen);
 615         thlen = tcp->th_off << 2;
 616         if (m->m_len < ihlen + thlen)
 617                 m = m_pullup(m, ihlen + thlen);
 618         return (m);
 619 }
 620