slcompress.c revision 26778
1/*- 2 * Copyright (c) 1989, 1993, 1994 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 34 * $Id: slcompress.c,v 1.9 1997/02/22 09:41:16 peter Exp $ 35 */ 36 37/* 38 * Routines to compress and uncompess tcp packets (for transmission 39 * over low speed serial lines. 40 * 41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 42 * - Initial distribution. 43 * 44 */ 45 46#include <sys/param.h> 47#include <sys/systm.h> 48#include <sys/mbuf.h> 49 50#include <netinet/in.h> 51#include <netinet/in_systm.h> 52#include <netinet/ip.h> 53#include <netinet/tcp.h> 54 55#include <net/slcompress.h> 56 57#ifndef SL_NO_STATS 58#define INCR(counter) ++comp->counter; 59#else 60#define INCR(counter) 61#endif 62 63#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 64#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 65#ifndef KERNEL 66#define ovbcopy bcopy 67#endif 68 69void 70sl_compress_init(comp, max_state) 71 struct slcompress *comp; 72 int max_state; 73{ 74 register u_int i; 75 register struct cstate *tstate = comp->tstate; 76 77 if (max_state == -1) 78 max_state = MAX_STATES - 1; 79 bzero((char *)comp, sizeof(*comp)); 80 for (i = max_state; i > 0; --i) { 81 tstate[i].cs_id = i; 82 tstate[i].cs_next = &tstate[i - 1]; 83 } 84 tstate[0].cs_next = &tstate[max_state]; 85 tstate[0].cs_id = 0; 86 comp->last_cs = &tstate[0]; 87 comp->last_recv = 255; 88 comp->last_xmit = 255; 89 comp->flags = SLF_TOSS; 90} 91 92 93/* ENCODE encodes a number that is known to be non-zero. ENCODEZ 94 * checks for zero (since zero has to be encoded in the long, 3 byte 95 * form). 96 */ 97#define ENCODE(n) { \ 98 if ((u_short)(n) >= 256) { \ 99 *cp++ = 0; \ 100 cp[1] = (n); \ 101 cp[0] = (n) >> 8; \ 102 cp += 2; \ 103 } else { \ 104 *cp++ = (n); \ 105 } \ 106} 107#define ENCODEZ(n) { \ 108 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 109 *cp++ = 0; \ 110 cp[1] = (n); \ 111 cp[0] = (n) >> 8; \ 112 cp += 2; \ 113 } else { \ 114 *cp++ = (n); \ 115 } \ 116} 117 118#define DECODEL(f) { \ 119 if (*cp == 0) {\ 120 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 121 cp += 3; \ 122 } else { \ 123 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 124 } \ 125} 126 127#define DECODES(f) { \ 128 if (*cp == 0) {\ 129 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 130 cp += 3; \ 131 } else { \ 132 (f) = htons(ntohs(f) + (u_long)*cp++); \ 133 } \ 134} 135 136#define DECODEU(f) { \ 137 if (*cp == 0) {\ 138 (f) = htons((cp[1] << 8) | cp[2]); \ 139 cp += 3; \ 140 } else { \ 141 (f) = htons((u_long)*cp++); \ 142 } \ 143} 144 145u_int 146sl_compress_tcp(m, ip, comp, compress_cid) 147 struct mbuf *m; 148 register struct ip *ip; 149 struct slcompress *comp; 150 int compress_cid; 151{ 152 register struct cstate *cs = comp->last_cs->cs_next; 153 register u_int hlen = ip->ip_hl; 154 register struct tcphdr *oth; 155 register struct tcphdr *th; 156 register u_int deltaS, deltaA; 157 register u_int changes = 0; 158 u_char new_seq[16]; 159 register u_char *cp = new_seq; 160 161 /* 162 * Bail if this is an IP fragment or if the TCP packet isn't 163 * `compressible' (i.e., ACK isn't set or some other control bit is 164 * set). (We assume that the caller has already made sure the 165 * packet is IP proto TCP). 166 */ 167 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 168 return (TYPE_IP); 169 170 th = (struct tcphdr *)&((int *)ip)[hlen]; 171 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 172 return (TYPE_IP); 173 /* 174 * Packet is compressible -- we're going to send either a 175 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 176 * to locate (or create) the connection state. Special case the 177 * most recently used connection since it's most likely to be used 178 * again & we don't have to do any reordering if it's used. 179 */ 180 INCR(sls_packets) 181 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 182 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 183 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 184 /* 185 * Wasn't the first -- search for it. 186 * 187 * States are kept in a circularly linked list with 188 * last_cs pointing to the end of the list. The 189 * list is kept in lru order by moving a state to the 190 * head of the list whenever it is referenced. Since 191 * the list is short and, empirically, the connection 192 * we want is almost always near the front, we locate 193 * states via linear search. If we don't find a state 194 * for the datagram, the oldest state is (re-)used. 195 */ 196 register struct cstate *lcs; 197 register struct cstate *lastcs = comp->last_cs; 198 199 do { 200 lcs = cs; cs = cs->cs_next; 201 INCR(sls_searches) 202 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 203 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 204 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 205 goto found; 206 } while (cs != lastcs); 207 208 /* 209 * Didn't find it -- re-use oldest cstate. Send an 210 * uncompressed packet that tells the other side what 211 * connection number we're using for this conversation. 212 * Note that since the state list is circular, the oldest 213 * state points to the newest and we only need to set 214 * last_cs to update the lru linkage. 215 */ 216 INCR(sls_misses) 217 comp->last_cs = lcs; 218 hlen += th->th_off; 219 hlen <<= 2; 220 if (hlen > m->m_len) 221 return TYPE_IP; 222 goto uncompressed; 223 224 found: 225 /* 226 * Found it -- move to the front on the connection list. 227 */ 228 if (cs == lastcs) 229 comp->last_cs = lcs; 230 else { 231 lcs->cs_next = cs->cs_next; 232 cs->cs_next = lastcs->cs_next; 233 lastcs->cs_next = cs; 234 } 235 } 236 237 /* 238 * Make sure that only what we expect to change changed. The first 239 * line of the `if' checks the IP protocol version, header length & 240 * type of service. The 2nd line checks the "Don't fragment" bit. 241 * The 3rd line checks the time-to-live and protocol (the protocol 242 * check is unnecessary but costless). The 4th line checks the TCP 243 * header length. The 5th line checks IP options, if any. The 6th 244 * line checks TCP options, if any. If any of these things are 245 * different between the previous & current datagram, we send the 246 * current datagram `uncompressed'. 247 */ 248 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 249 deltaS = hlen; 250 hlen += th->th_off; 251 hlen <<= 2; 252 if (hlen > m->m_len) 253 return TYPE_IP; 254 255 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 256 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 257 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 258 th->th_off != oth->th_off || 259 (deltaS > 5 && 260 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 261 (th->th_off > 5 && 262 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 263 goto uncompressed; 264 265 /* 266 * Figure out which of the changing fields changed. The 267 * receiver expects changes in the order: urgent, window, 268 * ack, seq (the order minimizes the number of temporaries 269 * needed in this section of code). 270 */ 271 if (th->th_flags & TH_URG) { 272 deltaS = ntohs(th->th_urp); 273 ENCODEZ(deltaS); 274 changes |= NEW_U; 275 } else if (th->th_urp != oth->th_urp) 276 /* argh! URG not set but urp changed -- a sensible 277 * implementation should never do this but RFC793 278 * doesn't prohibit the change so we have to deal 279 * with it. */ 280 goto uncompressed; 281 282 deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win)); 283 if (deltaS) { 284 ENCODE(deltaS); 285 changes |= NEW_W; 286 } 287 288 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 289 if (deltaA) { 290 if (deltaA > 0xffff) 291 goto uncompressed; 292 ENCODE(deltaA); 293 changes |= NEW_A; 294 } 295 296 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 297 if (deltaS) { 298 if (deltaS > 0xffff) 299 goto uncompressed; 300 ENCODE(deltaS); 301 changes |= NEW_S; 302 } 303 304 switch(changes) { 305 306 case 0: 307 /* 308 * Nothing changed. If this packet contains data and the 309 * last one didn't, this is probably a data packet following 310 * an ack (normal on an interactive connection) and we send 311 * it compressed. Otherwise it's probably a retransmit, 312 * retransmitted ack or window probe. Send it uncompressed 313 * in case the other side missed the compressed version. 314 */ 315 if (ip->ip_len != cs->cs_ip.ip_len && 316 ntohs(cs->cs_ip.ip_len) == hlen) 317 break; 318 319 /* (fall through) */ 320 321 case SPECIAL_I: 322 case SPECIAL_D: 323 /* 324 * actual changes match one of our special case encodings -- 325 * send packet uncompressed. 326 */ 327 goto uncompressed; 328 329 case NEW_S|NEW_A: 330 if (deltaS == deltaA && 331 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 332 /* special case for echoed terminal traffic */ 333 changes = SPECIAL_I; 334 cp = new_seq; 335 } 336 break; 337 338 case NEW_S: 339 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 340 /* special case for data xfer */ 341 changes = SPECIAL_D; 342 cp = new_seq; 343 } 344 break; 345 } 346 347 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 348 if (deltaS != 1) { 349 ENCODEZ(deltaS); 350 changes |= NEW_I; 351 } 352 if (th->th_flags & TH_PUSH) 353 changes |= TCP_PUSH_BIT; 354 /* 355 * Grab the cksum before we overwrite it below. Then update our 356 * state with this packet's header. 357 */ 358 deltaA = ntohs(th->th_sum); 359 BCOPY(ip, &cs->cs_ip, hlen); 360 361 /* 362 * We want to use the original packet as our compressed packet. 363 * (cp - new_seq) is the number of bytes we need for compressed 364 * sequence numbers. In addition we need one byte for the change 365 * mask, one for the connection id and two for the tcp checksum. 366 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 367 * many bytes of the original packet to toss so subtract the two to 368 * get the new packet size. 369 */ 370 deltaS = cp - new_seq; 371 cp = (u_char *)ip; 372 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 373 comp->last_xmit = cs->cs_id; 374 hlen -= deltaS + 4; 375 cp += hlen; 376 *cp++ = changes | NEW_C; 377 *cp++ = cs->cs_id; 378 } else { 379 hlen -= deltaS + 3; 380 cp += hlen; 381 *cp++ = changes; 382 } 383 m->m_len -= hlen; 384 m->m_data += hlen; 385 *cp++ = deltaA >> 8; 386 *cp++ = deltaA; 387 BCOPY(new_seq, cp, deltaS); 388 INCR(sls_compressed) 389 return (TYPE_COMPRESSED_TCP); 390 391 /* 392 * Update connection state cs & send uncompressed packet ('uncompressed' 393 * means a regular ip/tcp packet but with the 'conversation id' we hope 394 * to use on future compressed packets in the protocol field). 395 */ 396uncompressed: 397 BCOPY(ip, &cs->cs_ip, hlen); 398 ip->ip_p = cs->cs_id; 399 comp->last_xmit = cs->cs_id; 400 return (TYPE_UNCOMPRESSED_TCP); 401} 402 403 404int 405sl_uncompress_tcp(bufp, len, type, comp) 406 u_char **bufp; 407 int len; 408 u_int type; 409 struct slcompress *comp; 410{ 411 u_char *hdr, *cp; 412 int hlen, vjlen; 413 414 cp = bufp? *bufp: NULL; 415 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 416 if (vjlen < 0) 417 return (0); /* error */ 418 if (vjlen == 0) 419 return (len); /* was uncompressed already */ 420 421 cp += vjlen; 422 len -= vjlen; 423 424 /* 425 * At this point, cp points to the first byte of data in the 426 * packet. If we're not aligned on a 4-byte boundary, copy the 427 * data down so the ip & tcp headers will be aligned. Then back up 428 * cp by the tcp/ip header length to make room for the reconstructed 429 * header (we assume the packet we were handed has enough space to 430 * prepend 128 bytes of header). 431 */ 432 if ((int)cp & 3) { 433 if (len > 0) 434 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 435 cp = (u_char *)((int)cp &~ 3); 436 } 437 cp -= hlen; 438 len += hlen; 439 BCOPY(hdr, cp, hlen); 440 441 *bufp = cp; 442 return (len); 443} 444 445/* 446 * Uncompress a packet of total length total_len. The first buflen 447 * bytes are at buf; this must include the entire (compressed or 448 * uncompressed) TCP/IP header. This procedure returns the length 449 * of the VJ header, with a pointer to the uncompressed IP header 450 * in *hdrp and its length in *hlenp. 451 */ 452int 453sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 454 u_char *buf; 455 int buflen, total_len; 456 u_int type; 457 struct slcompress *comp; 458 u_char **hdrp; 459 u_int *hlenp; 460{ 461 register u_char *cp; 462 register u_int hlen, changes; 463 register struct tcphdr *th; 464 register struct cstate *cs; 465 register struct ip *ip; 466 register u_short *bp; 467 register u_int vjlen; 468 469 switch (type) { 470 471 case TYPE_UNCOMPRESSED_TCP: 472 ip = (struct ip *) buf; 473 if (ip->ip_p >= MAX_STATES) 474 goto bad; 475 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 476 comp->flags &=~ SLF_TOSS; 477 ip->ip_p = IPPROTO_TCP; 478 /* 479 * Calculate the size of the TCP/IP header and make sure that 480 * we don't overflow the space we have available for it. 481 */ 482 hlen = ip->ip_hl << 2; 483 if (hlen + sizeof(struct tcphdr) > buflen) 484 goto bad; 485 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 486 if (hlen > MAX_HDR) 487 goto bad; 488 BCOPY(ip, &cs->cs_ip, hlen); 489 cs->cs_hlen = hlen; 490 INCR(sls_uncompressedin) 491 *hdrp = (u_char *) &cs->cs_ip; 492 *hlenp = hlen; 493 return (0); 494 495 default: 496 goto bad; 497 498 case TYPE_COMPRESSED_TCP: 499 break; 500 } 501 /* We've got a compressed packet. */ 502 INCR(sls_compressedin) 503 cp = buf; 504 changes = *cp++; 505 if (changes & NEW_C) { 506 /* Make sure the state index is in range, then grab the state. 507 * If we have a good state index, clear the 'discard' flag. */ 508 if (*cp >= MAX_STATES) 509 goto bad; 510 511 comp->flags &=~ SLF_TOSS; 512 comp->last_recv = *cp++; 513 } else { 514 /* this packet has an implicit state index. If we've 515 * had a line error since the last time we got an 516 * explicit state index, we have to toss the packet. */ 517 if (comp->flags & SLF_TOSS) { 518 INCR(sls_tossed) 519 return (-1); 520 } 521 } 522 cs = &comp->rstate[comp->last_recv]; 523 hlen = cs->cs_ip.ip_hl << 2; 524 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 525 th->th_sum = htons((*cp << 8) | cp[1]); 526 cp += 2; 527 if (changes & TCP_PUSH_BIT) 528 th->th_flags |= TH_PUSH; 529 else 530 th->th_flags &=~ TH_PUSH; 531 532 switch (changes & SPECIALS_MASK) { 533 case SPECIAL_I: 534 { 535 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 536 th->th_ack = htonl(ntohl(th->th_ack) + i); 537 th->th_seq = htonl(ntohl(th->th_seq) + i); 538 } 539 break; 540 541 case SPECIAL_D: 542 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 543 - cs->cs_hlen); 544 break; 545 546 default: 547 if (changes & NEW_U) { 548 th->th_flags |= TH_URG; 549 DECODEU(th->th_urp) 550 } else 551 th->th_flags &=~ TH_URG; 552 if (changes & NEW_W) 553 DECODES(th->th_win) 554 if (changes & NEW_A) 555 DECODEL(th->th_ack) 556 if (changes & NEW_S) 557 DECODEL(th->th_seq) 558 break; 559 } 560 if (changes & NEW_I) { 561 DECODES(cs->cs_ip.ip_id) 562 } else 563 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 564 565 /* 566 * At this point, cp points to the first byte of data in the 567 * packet. Fill in the IP total length and update the IP 568 * header checksum. 569 */ 570 vjlen = cp - buf; 571 buflen -= vjlen; 572 if (buflen < 0) 573 /* we must have dropped some characters (crc should detect 574 * this but the old slip framing won't) */ 575 goto bad; 576 577 total_len += cs->cs_hlen - vjlen; 578 cs->cs_ip.ip_len = htons(total_len); 579 580 /* recompute the ip header checksum */ 581 bp = (u_short *) &cs->cs_ip; 582 cs->cs_ip.ip_sum = 0; 583 for (changes = 0; hlen > 0; hlen -= 2) 584 changes += *bp++; 585 changes = (changes & 0xffff) + (changes >> 16); 586 changes = (changes & 0xffff) + (changes >> 16); 587 cs->cs_ip.ip_sum = ~ changes; 588 589 *hdrp = (u_char *) &cs->cs_ip; 590 *hlenp = cs->cs_hlen; 591 return vjlen; 592 593bad: 594 comp->flags |= SLF_TOSS; 595 INCR(sls_errorin) 596 return (-1); 597} 598