1 /* $OpenBSD: slcompress.c,v 1.6 1997/09/05 04:27:04 millert Exp $ */ 2 /* $NetBSD: slcompress.c,v 1.17 1997/05/17 21:12:10 christos Exp $ */ 3 4 /* 5 * Copyright (c) 1989, 1993, 1994 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 37 */ 38 39 /* 40 * Routines to compress and uncompess tcp packets (for transmission 41 * over low speed serial lines. 42 * 43 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 44 * - Initial distribution. 45 */ 46 47 #include <sys/param.h> 48 #include <sys/mbuf.h> 49 #include <sys/systm.h> 50 51 #include <netinet/in.h> 52 #include <netinet/in_systm.h> 53 #include <netinet/ip.h> 54 #include <netinet/tcp.h> 55 56 #include <net/slcompress.h> 57 58 #ifndef SL_NO_STATS 59 #define INCR(counter) ++comp->counter; 60 #else 61 #define INCR(counter) 62 #endif 63 64 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 65 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 66 #ifndef _KERNEL 67 #define ovbcopy bcopy 68 #endif 69 70 71 void 72 sl_compress_init(comp) 73 struct slcompress *comp; 74 { 75 register u_int i; 76 register struct cstate *tstate = comp->tstate; 77 78 bzero((char *)comp, sizeof(*comp)); 79 for (i = MAX_STATES - 1; i > 0; --i) { 80 tstate[i].cs_id = i; 81 tstate[i].cs_next = &tstate[i - 1]; 82 } 83 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 84 tstate[0].cs_id = 0; 85 comp->last_cs = &tstate[0]; 86 comp->last_recv = 255; 87 comp->last_xmit = 255; 88 comp->flags = SLF_TOSS; 89 } 90 91 92 /* 93 * Like sl_compress_init, but we get to specify the maximum connection 94 * ID to use on transmission. 95 */ 96 void 97 sl_compress_setup(comp, max_state) 98 struct slcompress *comp; 99 int max_state; 100 { 101 register u_int i; 102 register struct cstate *tstate = comp->tstate; 103 104 if (max_state == -1) { 105 max_state = MAX_STATES - 1; 106 bzero((char *)comp, sizeof(*comp)); 107 } else { 108 /* Don't reset statistics */ 109 bzero((char *)comp->tstate, sizeof(comp->tstate)); 110 bzero((char *)comp->rstate, sizeof(comp->rstate)); 111 } 112 for (i = max_state; i > 0; --i) { 113 tstate[i].cs_id = i; 114 tstate[i].cs_next = &tstate[i - 1]; 115 } 116 tstate[0].cs_next = &tstate[max_state]; 117 tstate[0].cs_id = 0; 118 comp->last_cs = &tstate[0]; 119 comp->last_recv = 255; 120 comp->last_xmit = 255; 121 comp->flags = SLF_TOSS; 122 } 123 124 125 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 126 * checks for zero (since zero has to be encoded in the long, 3 byte 127 * form). 128 */ 129 #define ENCODE(n) { \ 130 if ((u_int16_t)(n) >= 256) { \ 131 *cp++ = 0; \ 132 cp[1] = (n); \ 133 cp[0] = (n) >> 8; \ 134 cp += 2; \ 135 } else { \ 136 *cp++ = (n); \ 137 } \ 138 } 139 #define ENCODEZ(n) { \ 140 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 141 *cp++ = 0; \ 142 cp[1] = (n); \ 143 cp[0] = (n) >> 8; \ 144 cp += 2; \ 145 } else { \ 146 *cp++ = (n); \ 147 } \ 148 } 149 150 #define DECODEL(f) { \ 151 if (*cp == 0) {\ 152 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 153 cp += 3; \ 154 } else { \ 155 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 156 } \ 157 } 158 159 #define DECODES(f) { \ 160 if (*cp == 0) {\ 161 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 162 cp += 3; \ 163 } else { \ 164 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 165 } \ 166 } 167 168 #define DECODEU(f) { \ 169 if (*cp == 0) {\ 170 (f) = htons((cp[1] << 8) | cp[2]); \ 171 cp += 3; \ 172 } else { \ 173 (f) = htons((u_int32_t)*cp++); \ 174 } \ 175 } 176 177 u_int 178 sl_compress_tcp(m, ip, comp, compress_cid) 179 struct mbuf *m; 180 register struct ip *ip; 181 struct slcompress *comp; 182 int compress_cid; 183 { 184 register struct cstate *cs = comp->last_cs->cs_next; 185 register u_int hlen = ip->ip_hl; 186 register struct tcphdr *oth; 187 register struct tcphdr *th; 188 register u_int deltaS, deltaA; 189 register u_int changes = 0; 190 u_char new_seq[16]; 191 register u_char *cp = new_seq; 192 193 /* 194 * Bail if this is an IP fragment or if the TCP packet isn't 195 * `compressible' (i.e., ACK isn't set or some other control bit is 196 * set). (We assume that the caller has already made sure the 197 * packet is IP proto TCP). 198 */ 199 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 200 return (TYPE_IP); 201 202 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 203 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 204 return (TYPE_IP); 205 /* 206 * Packet is compressible -- we're going to send either a 207 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 208 * to locate (or create) the connection state. Special case the 209 * most recently used connection since it's most likely to be used 210 * again & we don't have to do any reordering if it's used. 211 */ 212 INCR(sls_packets) 213 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 214 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 215 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 216 /* 217 * Wasn't the first -- search for it. 218 * 219 * States are kept in a circularly linked list with 220 * last_cs pointing to the end of the list. The 221 * list is kept in lru order by moving a state to the 222 * head of the list whenever it is referenced. Since 223 * the list is short and, empirically, the connection 224 * we want is almost always near the front, we locate 225 * states via linear search. If we don't find a state 226 * for the datagram, the oldest state is (re-)used. 227 */ 228 register struct cstate *lcs; 229 register struct cstate *lastcs = comp->last_cs; 230 231 do { 232 lcs = cs; cs = cs->cs_next; 233 INCR(sls_searches) 234 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 235 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 236 && *(int32_t *)th == 237 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 238 goto found; 239 } while (cs != lastcs); 240 241 /* 242 * Didn't find it -- re-use oldest cstate. Send an 243 * uncompressed packet that tells the other side what 244 * connection number we're using for this conversation. 245 * Note that since the state list is circular, the oldest 246 * state points to the newest and we only need to set 247 * last_cs to update the lru linkage. 248 */ 249 INCR(sls_misses) 250 comp->last_cs = lcs; 251 hlen += th->th_off; 252 hlen <<= 2; 253 goto uncompressed; 254 255 found: 256 /* 257 * Found it -- move to the front on the connection list. 258 */ 259 if (cs == lastcs) 260 comp->last_cs = lcs; 261 else { 262 lcs->cs_next = cs->cs_next; 263 cs->cs_next = lastcs->cs_next; 264 lastcs->cs_next = cs; 265 } 266 } 267 268 /* 269 * Make sure that only what we expect to change changed. The first 270 * line of the `if' checks the IP protocol version, header length & 271 * type of service. The 2nd line checks the "Don't fragment" bit. 272 * The 3rd line checks the time-to-live and protocol (the protocol 273 * check is unnecessary but costless). The 4th line checks the TCP 274 * header length. The 5th line checks IP options, if any. The 6th 275 * line checks TCP options, if any. If any of these things are 276 * different between the previous & current datagram, we send the 277 * current datagram `uncompressed'. 278 */ 279 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 280 deltaS = hlen; 281 hlen += th->th_off; 282 hlen <<= 2; 283 284 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 285 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 286 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 287 th->th_off != oth->th_off || 288 (deltaS > 5 && 289 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 290 (th->th_off > 5 && 291 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 292 goto uncompressed; 293 294 /* 295 * Figure out which of the changing fields changed. The 296 * receiver expects changes in the order: urgent, window, 297 * ack, seq (the order minimizes the number of temporaries 298 * needed in this section of code). 299 */ 300 if (th->th_flags & TH_URG) { 301 deltaS = ntohs(th->th_urp); 302 ENCODEZ(deltaS); 303 changes |= NEW_U; 304 } else if (th->th_urp != oth->th_urp) 305 /* argh! URG not set but urp changed -- a sensible 306 * implementation should never do this but RFC793 307 * doesn't prohibit the change so we have to deal 308 * with it. */ 309 goto uncompressed; 310 311 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 312 if (deltaS) { 313 ENCODE(deltaS); 314 changes |= NEW_W; 315 } 316 317 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 318 if (deltaA) { 319 if (deltaA > 0xffff) 320 goto uncompressed; 321 ENCODE(deltaA); 322 changes |= NEW_A; 323 } 324 325 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 326 if (deltaS) { 327 if (deltaS > 0xffff) 328 goto uncompressed; 329 ENCODE(deltaS); 330 changes |= NEW_S; 331 } 332 333 switch(changes) { 334 335 case 0: 336 /* 337 * Nothing changed. If this packet contains data and the 338 * last one didn't, this is probably a data packet following 339 * an ack (normal on an interactive connection) and we send 340 * it compressed. Otherwise it's probably a retransmit, 341 * retransmitted ack or window probe. Send it uncompressed 342 * in case the other side missed the compressed version. 343 */ 344 if (ip->ip_len != cs->cs_ip.ip_len && 345 ntohs(cs->cs_ip.ip_len) == hlen) 346 break; 347 348 /* (fall through) */ 349 350 case SPECIAL_I: 351 case SPECIAL_D: 352 /* 353 * actual changes match one of our special case encodings -- 354 * send packet uncompressed. 355 */ 356 goto uncompressed; 357 358 case NEW_S|NEW_A: 359 if (deltaS == deltaA && 360 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 361 /* special case for echoed terminal traffic */ 362 changes = SPECIAL_I; 363 cp = new_seq; 364 } 365 break; 366 367 case NEW_S: 368 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 369 /* special case for data xfer */ 370 changes = SPECIAL_D; 371 cp = new_seq; 372 } 373 break; 374 } 375 376 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 377 if (deltaS != 1) { 378 ENCODEZ(deltaS); 379 changes |= NEW_I; 380 } 381 if (th->th_flags & TH_PUSH) 382 changes |= TCP_PUSH_BIT; 383 /* 384 * Grab the cksum before we overwrite it below. Then update our 385 * state with this packet's header. 386 */ 387 deltaA = ntohs(th->th_sum); 388 BCOPY(ip, &cs->cs_ip, hlen); 389 390 /* 391 * We want to use the original packet as our compressed packet. 392 * (cp - new_seq) is the number of bytes we need for compressed 393 * sequence numbers. In addition we need one byte for the change 394 * mask, one for the connection id and two for the tcp checksum. 395 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 396 * many bytes of the original packet to toss so subtract the two to 397 * get the new packet size. 398 */ 399 deltaS = cp - new_seq; 400 cp = (u_char *)ip; 401 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 402 comp->last_xmit = cs->cs_id; 403 hlen -= deltaS + 4; 404 cp += hlen; 405 *cp++ = changes | NEW_C; 406 *cp++ = cs->cs_id; 407 } else { 408 hlen -= deltaS + 3; 409 cp += hlen; 410 *cp++ = changes; 411 } 412 m->m_len -= hlen; 413 m->m_data += hlen; 414 *cp++ = deltaA >> 8; 415 *cp++ = deltaA; 416 BCOPY(new_seq, cp, deltaS); 417 INCR(sls_compressed) 418 return (TYPE_COMPRESSED_TCP); 419 420 /* 421 * Update connection state cs & send uncompressed packet ('uncompressed' 422 * means a regular ip/tcp packet but with the 'conversation id' we hope 423 * to use on future compressed packets in the protocol field). 424 */ 425 uncompressed: 426 BCOPY(ip, &cs->cs_ip, hlen); 427 ip->ip_p = cs->cs_id; 428 comp->last_xmit = cs->cs_id; 429 return (TYPE_UNCOMPRESSED_TCP); 430 } 431 432 433 int 434 sl_uncompress_tcp(bufp, len, type, comp) 435 u_char **bufp; 436 int len; 437 u_int type; 438 struct slcompress *comp; 439 { 440 u_char *hdr, *cp; 441 int hlen, vjlen; 442 443 cp = bufp? *bufp: NULL; 444 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 445 if (vjlen < 0) 446 return (0); /* error */ 447 if (vjlen == 0) 448 return (len); /* was uncompressed already */ 449 450 cp += vjlen; 451 len -= vjlen; 452 453 /* 454 * At this point, cp points to the first byte of data in the 455 * packet. If we're not aligned on a 4-byte boundary, copy the 456 * data down so the ip & tcp headers will be aligned. Then back up 457 * cp by the tcp/ip header length to make room for the reconstructed 458 * header (we assume the packet we were handed has enough space to 459 * prepend 128 bytes of header). 460 */ 461 if ((long)cp & 3) { 462 if (len > 0) 463 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len); 464 cp = (u_char *)((long)cp &~ 3); 465 } 466 cp -= hlen; 467 len += hlen; 468 BCOPY(hdr, cp, hlen); 469 470 *bufp = cp; 471 return (len); 472 } 473 474 /* 475 * Uncompress a packet of total length total_len. The first buflen 476 * bytes are at buf; this must include the entire (compressed or 477 * uncompressed) TCP/IP header. This procedure returns the length 478 * of the VJ header, with a pointer to the uncompressed IP header 479 * in *hdrp and its length in *hlenp. 480 */ 481 int 482 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 483 u_char *buf; 484 int buflen, total_len; 485 u_int type; 486 struct slcompress *comp; 487 u_char **hdrp; 488 u_int *hlenp; 489 { 490 register u_char *cp; 491 register u_int hlen, changes; 492 register struct tcphdr *th; 493 register struct cstate *cs; 494 register struct ip *ip; 495 register u_int16_t *bp; 496 register u_int vjlen; 497 498 switch (type) { 499 500 case TYPE_UNCOMPRESSED_TCP: 501 ip = (struct ip *) buf; 502 if (ip->ip_p >= MAX_STATES) 503 goto bad; 504 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 505 comp->flags &=~ SLF_TOSS; 506 ip->ip_p = IPPROTO_TCP; 507 /* 508 * Calculate the size of the TCP/IP header and make sure that 509 * we don't overflow the space we have available for it. 510 */ 511 hlen = ip->ip_hl << 2; 512 if (hlen + sizeof(struct tcphdr) > buflen) 513 goto bad; 514 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 515 if (hlen > MAX_HDR || hlen > buflen) 516 goto bad; 517 BCOPY(ip, &cs->cs_ip, hlen); 518 cs->cs_hlen = hlen; 519 INCR(sls_uncompressedin) 520 *hdrp = (u_char *) &cs->cs_ip; 521 *hlenp = hlen; 522 return (0); 523 524 default: 525 goto bad; 526 527 case TYPE_COMPRESSED_TCP: 528 break; 529 } 530 /* We've got a compressed packet. */ 531 INCR(sls_compressedin) 532 cp = buf; 533 changes = *cp++; 534 if (changes & NEW_C) { 535 /* Make sure the state index is in range, then grab the state. 536 * If we have a good state index, clear the 'discard' flag. */ 537 if (*cp >= MAX_STATES) 538 goto bad; 539 540 comp->flags &=~ SLF_TOSS; 541 comp->last_recv = *cp++; 542 } else { 543 /* this packet has an implicit state index. If we've 544 * had a line error since the last time we got an 545 * explicit state index, we have to toss the packet. */ 546 if (comp->flags & SLF_TOSS) { 547 INCR(sls_tossed) 548 return (-1); 549 } 550 } 551 cs = &comp->rstate[comp->last_recv]; 552 hlen = cs->cs_ip.ip_hl << 2; 553 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 554 th->th_sum = htons((*cp << 8) | cp[1]); 555 cp += 2; 556 if (changes & TCP_PUSH_BIT) 557 th->th_flags |= TH_PUSH; 558 else 559 th->th_flags &=~ TH_PUSH; 560 561 switch (changes & SPECIALS_MASK) { 562 case SPECIAL_I: 563 { 564 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 565 th->th_ack = htonl(ntohl(th->th_ack) + i); 566 th->th_seq = htonl(ntohl(th->th_seq) + i); 567 } 568 break; 569 570 case SPECIAL_D: 571 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 572 - cs->cs_hlen); 573 break; 574 575 default: 576 if (changes & NEW_U) { 577 th->th_flags |= TH_URG; 578 DECODEU(th->th_urp) 579 } else 580 th->th_flags &=~ TH_URG; 581 if (changes & NEW_W) 582 DECODES(th->th_win) 583 if (changes & NEW_A) 584 DECODEL(th->th_ack) 585 if (changes & NEW_S) 586 DECODEL(th->th_seq) 587 break; 588 } 589 if (changes & NEW_I) { 590 DECODES(cs->cs_ip.ip_id) 591 } else 592 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 593 594 /* 595 * At this point, cp points to the first byte of data in the 596 * packet. Fill in the IP total length and update the IP 597 * header checksum. 598 */ 599 vjlen = cp - buf; 600 buflen -= vjlen; 601 if (buflen < 0) 602 /* we must have dropped some characters (crc should detect 603 * this but the old slip framing won't) */ 604 goto bad; 605 606 total_len += cs->cs_hlen - vjlen; 607 cs->cs_ip.ip_len = htons(total_len); 608 609 /* recompute the ip header checksum */ 610 bp = (u_int16_t *) &cs->cs_ip; 611 cs->cs_ip.ip_sum = 0; 612 for (changes = 0; hlen > 0; hlen -= 2) 613 changes += *bp++; 614 changes = (changes & 0xffff) + (changes >> 16); 615 changes = (changes & 0xffff) + (changes >> 16); 616 cs->cs_ip.ip_sum = ~ changes; 617 618 *hdrp = (u_char *) &cs->cs_ip; 619 *hlenp = cs->cs_hlen; 620 return vjlen; 621 622 bad: 623 comp->flags |= SLF_TOSS; 624 INCR(sls_errorin) 625 return (-1); 626 } 627