1 /* $OpenBSD: slcompress.c,v 1.5 1996/07/25 14:20:52 joshd Exp $ */ 2 /* $NetBSD: slcompress.c,v 1.15 1996/03/15 02:28:12 paulus 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 void 71 sl_compress_init(comp, max_state) 72 struct slcompress *comp; 73 int max_state; 74 { 75 register u_int i; 76 register struct cstate *tstate = comp->tstate; 77 78 if (max_state == -1) { 79 max_state = MAX_STATES - 1; 80 bzero((char *)comp, sizeof(*comp)); 81 } else { 82 /* Don't reset statistics */ 83 bzero((char *)comp->tstate, sizeof(comp->tstate)); 84 bzero((char *)comp->rstate, sizeof(comp->rstate)); 85 } 86 for (i = max_state; i > 0; --i) { 87 tstate[i].cs_id = i; 88 tstate[i].cs_next = &tstate[i - 1]; 89 } 90 tstate[0].cs_next = &tstate[max_state]; 91 tstate[0].cs_id = 0; 92 comp->last_cs = &tstate[0]; 93 comp->last_recv = 255; 94 comp->last_xmit = 255; 95 comp->flags = SLF_TOSS; 96 } 97 98 99 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 100 * checks for zero (since zero has to be encoded in the long, 3 byte 101 * form). 102 */ 103 #define ENCODE(n) { \ 104 if ((u_int16_t)(n) >= 256) { \ 105 *cp++ = 0; \ 106 cp[1] = (n); \ 107 cp[0] = (n) >> 8; \ 108 cp += 2; \ 109 } else { \ 110 *cp++ = (n); \ 111 } \ 112 } 113 #define ENCODEZ(n) { \ 114 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 115 *cp++ = 0; \ 116 cp[1] = (n); \ 117 cp[0] = (n) >> 8; \ 118 cp += 2; \ 119 } else { \ 120 *cp++ = (n); \ 121 } \ 122 } 123 124 #define DECODEL(f) { \ 125 if (*cp == 0) {\ 126 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 127 cp += 3; \ 128 } else { \ 129 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 130 } \ 131 } 132 133 #define DECODES(f) { \ 134 if (*cp == 0) {\ 135 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 136 cp += 3; \ 137 } else { \ 138 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 139 } \ 140 } 141 142 #define DECODEU(f) { \ 143 if (*cp == 0) {\ 144 (f) = htons((cp[1] << 8) | cp[2]); \ 145 cp += 3; \ 146 } else { \ 147 (f) = htons((u_int32_t)*cp++); \ 148 } \ 149 } 150 151 u_int 152 sl_compress_tcp(m, ip, comp, compress_cid) 153 struct mbuf *m; 154 register struct ip *ip; 155 struct slcompress *comp; 156 int compress_cid; 157 { 158 register struct cstate *cs = comp->last_cs->cs_next; 159 register u_int hlen = ip->ip_hl; 160 register struct tcphdr *oth; 161 register struct tcphdr *th; 162 register u_int deltaS, deltaA; 163 register u_int changes = 0; 164 u_char new_seq[16]; 165 register u_char *cp = new_seq; 166 167 /* 168 * Bail if this is an IP fragment or if the TCP packet isn't 169 * `compressible' (i.e., ACK isn't set or some other control bit is 170 * set). (We assume that the caller has already made sure the 171 * packet is IP proto TCP). 172 */ 173 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 174 return (TYPE_IP); 175 176 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 177 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 178 return (TYPE_IP); 179 /* 180 * Packet is compressible -- we're going to send either a 181 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 182 * to locate (or create) the connection state. Special case the 183 * most recently used connection since it's most likely to be used 184 * again & we don't have to do any reordering if it's used. 185 */ 186 INCR(sls_packets) 187 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 188 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 189 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 190 /* 191 * Wasn't the first -- search for it. 192 * 193 * States are kept in a circularly linked list with 194 * last_cs pointing to the end of the list. The 195 * list is kept in lru order by moving a state to the 196 * head of the list whenever it is referenced. Since 197 * the list is short and, empirically, the connection 198 * we want is almost always near the front, we locate 199 * states via linear search. If we don't find a state 200 * for the datagram, the oldest state is (re-)used. 201 */ 202 register struct cstate *lcs; 203 register struct cstate *lastcs = comp->last_cs; 204 205 do { 206 lcs = cs; cs = cs->cs_next; 207 INCR(sls_searches) 208 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 209 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 210 && *(int32_t *)th == 211 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 212 goto found; 213 } while (cs != lastcs); 214 215 /* 216 * Didn't find it -- re-use oldest cstate. Send an 217 * uncompressed packet that tells the other side what 218 * connection number we're using for this conversation. 219 * Note that since the state list is circular, the oldest 220 * state points to the newest and we only need to set 221 * last_cs to update the lru linkage. 222 */ 223 INCR(sls_misses) 224 comp->last_cs = lcs; 225 hlen += th->th_off; 226 hlen <<= 2; 227 goto uncompressed; 228 229 found: 230 /* 231 * Found it -- move to the front on the connection list. 232 */ 233 if (cs == lastcs) 234 comp->last_cs = lcs; 235 else { 236 lcs->cs_next = cs->cs_next; 237 cs->cs_next = lastcs->cs_next; 238 lastcs->cs_next = cs; 239 } 240 } 241 242 /* 243 * Make sure that only what we expect to change changed. The first 244 * line of the `if' checks the IP protocol version, header length & 245 * type of service. The 2nd line checks the "Don't fragment" bit. 246 * The 3rd line checks the time-to-live and protocol (the protocol 247 * check is unnecessary but costless). The 4th line checks the TCP 248 * header length. The 5th line checks IP options, if any. The 6th 249 * line checks TCP options, if any. If any of these things are 250 * different between the previous & current datagram, we send the 251 * current datagram `uncompressed'. 252 */ 253 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 254 deltaS = hlen; 255 hlen += th->th_off; 256 hlen <<= 2; 257 258 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 259 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 260 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 261 th->th_off != oth->th_off || 262 (deltaS > 5 && 263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 264 (th->th_off > 5 && 265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 266 goto uncompressed; 267 268 /* 269 * Figure out which of the changing fields changed. The 270 * receiver expects changes in the order: urgent, window, 271 * ack, seq (the order minimizes the number of temporaries 272 * needed in this section of code). 273 */ 274 if (th->th_flags & TH_URG) { 275 deltaS = ntohs(th->th_urp); 276 ENCODEZ(deltaS); 277 changes |= NEW_U; 278 } else if (th->th_urp != oth->th_urp) 279 /* argh! URG not set but urp changed -- a sensible 280 * implementation should never do this but RFC793 281 * doesn't prohibit the change so we have to deal 282 * with it. */ 283 goto uncompressed; 284 285 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 286 if (deltaS) { 287 ENCODE(deltaS); 288 changes |= NEW_W; 289 } 290 291 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 292 if (deltaA) { 293 if (deltaA > 0xffff) 294 goto uncompressed; 295 ENCODE(deltaA); 296 changes |= NEW_A; 297 } 298 299 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 300 if (deltaS) { 301 if (deltaS > 0xffff) 302 goto uncompressed; 303 ENCODE(deltaS); 304 changes |= NEW_S; 305 } 306 307 switch(changes) { 308 309 case 0: 310 /* 311 * Nothing changed. If this packet contains data and the 312 * last one didn't, this is probably a data packet following 313 * an ack (normal on an interactive connection) and we send 314 * it compressed. Otherwise it's probably a retransmit, 315 * retransmitted ack or window probe. Send it uncompressed 316 * in case the other side missed the compressed version. 317 */ 318 if (ip->ip_len != cs->cs_ip.ip_len && 319 ntohs(cs->cs_ip.ip_len) == hlen) 320 break; 321 322 /* (fall through) */ 323 324 case SPECIAL_I: 325 case SPECIAL_D: 326 /* 327 * actual changes match one of our special case encodings -- 328 * send packet uncompressed. 329 */ 330 goto uncompressed; 331 332 case NEW_S|NEW_A: 333 if (deltaS == deltaA && 334 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 335 /* special case for echoed terminal traffic */ 336 changes = SPECIAL_I; 337 cp = new_seq; 338 } 339 break; 340 341 case NEW_S: 342 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 343 /* special case for data xfer */ 344 changes = SPECIAL_D; 345 cp = new_seq; 346 } 347 break; 348 } 349 350 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 351 if (deltaS != 1) { 352 ENCODEZ(deltaS); 353 changes |= NEW_I; 354 } 355 if (th->th_flags & TH_PUSH) 356 changes |= TCP_PUSH_BIT; 357 /* 358 * Grab the cksum before we overwrite it below. Then update our 359 * state with this packet's header. 360 */ 361 deltaA = ntohs(th->th_sum); 362 BCOPY(ip, &cs->cs_ip, hlen); 363 364 /* 365 * We want to use the original packet as our compressed packet. 366 * (cp - new_seq) is the number of bytes we need for compressed 367 * sequence numbers. In addition we need one byte for the change 368 * mask, one for the connection id and two for the tcp checksum. 369 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 370 * many bytes of the original packet to toss so subtract the two to 371 * get the new packet size. 372 */ 373 deltaS = cp - new_seq; 374 cp = (u_char *)ip; 375 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 376 comp->last_xmit = cs->cs_id; 377 hlen -= deltaS + 4; 378 cp += hlen; 379 *cp++ = changes | NEW_C; 380 *cp++ = cs->cs_id; 381 } else { 382 hlen -= deltaS + 3; 383 cp += hlen; 384 *cp++ = changes; 385 } 386 m->m_len -= hlen; 387 m->m_data += hlen; 388 *cp++ = deltaA >> 8; 389 *cp++ = deltaA; 390 BCOPY(new_seq, cp, deltaS); 391 INCR(sls_compressed) 392 return (TYPE_COMPRESSED_TCP); 393 394 /* 395 * Update connection state cs & send uncompressed packet ('uncompressed' 396 * means a regular ip/tcp packet but with the 'conversation id' we hope 397 * to use on future compressed packets in the protocol field). 398 */ 399 uncompressed: 400 BCOPY(ip, &cs->cs_ip, hlen); 401 ip->ip_p = cs->cs_id; 402 comp->last_xmit = cs->cs_id; 403 return (TYPE_UNCOMPRESSED_TCP); 404 } 405 406 407 int 408 sl_uncompress_tcp(bufp, len, type, comp) 409 u_char **bufp; 410 int len; 411 u_int type; 412 struct slcompress *comp; 413 { 414 u_char *hdr, *cp; 415 int hlen, vjlen; 416 417 cp = bufp? *bufp: NULL; 418 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 419 if (vjlen < 0) 420 return (0); /* error */ 421 if (vjlen == 0) 422 return (len); /* was uncompressed already */ 423 424 cp += vjlen; 425 len -= vjlen; 426 427 /* 428 * At this point, cp points to the first byte of data in the 429 * packet. If we're not aligned on a 4-byte boundary, copy the 430 * data down so the ip & tcp headers will be aligned. Then back up 431 * cp by the tcp/ip header length to make room for the reconstructed 432 * header (we assume the packet we were handed has enough space to 433 * prepend 128 bytes of header). 434 */ 435 if ((long)cp & 3) { 436 if (len > 0) 437 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len); 438 cp = (u_char *)((long)cp &~ 3); 439 } 440 cp -= hlen; 441 len += hlen; 442 BCOPY(hdr, cp, hlen); 443 444 *bufp = cp; 445 return (len); 446 } 447 448 /* 449 * Uncompress a packet of total length total_len. The first buflen 450 * bytes are at buf; this must include the entire (compressed or 451 * uncompressed) TCP/IP header. This procedure returns the length 452 * of the VJ header, with a pointer to the uncompressed IP header 453 * in *hdrp and its length in *hlenp. 454 */ 455 int 456 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 457 u_char *buf; 458 int buflen, total_len; 459 u_int type; 460 struct slcompress *comp; 461 u_char **hdrp; 462 u_int *hlenp; 463 { 464 register u_char *cp; 465 register u_int hlen, changes; 466 register struct tcphdr *th; 467 register struct cstate *cs; 468 register struct ip *ip; 469 register u_int16_t *bp; 470 register u_int vjlen; 471 472 switch (type) { 473 474 case TYPE_UNCOMPRESSED_TCP: 475 ip = (struct ip *) buf; 476 if (ip->ip_p >= MAX_STATES) 477 goto bad; 478 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 479 comp->flags &=~ SLF_TOSS; 480 ip->ip_p = IPPROTO_TCP; 481 /* 482 * Calculate the size of the TCP/IP header and make sure that 483 * we don't overflow the space we have available for it. 484 */ 485 hlen = ip->ip_hl << 2; 486 if (hlen + sizeof(struct tcphdr) > buflen) 487 goto bad; 488 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 489 if (hlen > MAX_HDR || hlen > buflen) 490 goto bad; 491 492 BCOPY(ip, &cs->cs_ip, hlen); 493 cs->cs_hlen = hlen; 494 INCR(sls_uncompressedin) 495 *hdrp = (u_char *) &cs->cs_ip; 496 *hlenp = hlen; 497 return (0); 498 499 default: 500 goto bad; 501 502 case TYPE_COMPRESSED_TCP: 503 break; 504 } 505 /* We've got a compressed packet. */ 506 INCR(sls_compressedin) 507 cp = buf; 508 changes = *cp++; 509 if (changes & NEW_C) { 510 /* Make sure the state index is in range, then grab the state. 511 * If we have a good state index, clear the 'discard' flag. */ 512 if (*cp >= MAX_STATES) 513 goto bad; 514 515 comp->flags &=~ SLF_TOSS; 516 comp->last_recv = *cp++; 517 } else { 518 /* this packet has an implicit state index. If we've 519 * had a line error since the last time we got an 520 * explicit state index, we have to toss the packet. */ 521 if (comp->flags & SLF_TOSS) { 522 INCR(sls_tossed) 523 return (-1); 524 } 525 } 526 cs = &comp->rstate[comp->last_recv]; 527 hlen = cs->cs_ip.ip_hl << 2; 528 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 529 th->th_sum = htons((*cp << 8) | cp[1]); 530 cp += 2; 531 if (changes & TCP_PUSH_BIT) 532 th->th_flags |= TH_PUSH; 533 else 534 th->th_flags &=~ TH_PUSH; 535 536 switch (changes & SPECIALS_MASK) { 537 case SPECIAL_I: 538 { 539 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 540 th->th_ack = htonl(ntohl(th->th_ack) + i); 541 th->th_seq = htonl(ntohl(th->th_seq) + i); 542 } 543 break; 544 545 case SPECIAL_D: 546 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 547 - cs->cs_hlen); 548 break; 549 550 default: 551 if (changes & NEW_U) { 552 th->th_flags |= TH_URG; 553 DECODEU(th->th_urp) 554 } else 555 th->th_flags &=~ TH_URG; 556 if (changes & NEW_W) 557 DECODES(th->th_win) 558 if (changes & NEW_A) 559 DECODEL(th->th_ack) 560 if (changes & NEW_S) 561 DECODEL(th->th_seq) 562 break; 563 } 564 if (changes & NEW_I) { 565 DECODES(cs->cs_ip.ip_id) 566 } else 567 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 568 569 /* 570 * At this point, cp points to the first byte of data in the 571 * packet. Fill in the IP total length and update the IP 572 * header checksum. 573 */ 574 vjlen = cp - buf; 575 buflen -= vjlen; 576 if (buflen < 0) 577 /* we must have dropped some characters (crc should detect 578 * this but the old slip framing won't) */ 579 goto bad; 580 581 total_len += cs->cs_hlen - vjlen; 582 cs->cs_ip.ip_len = htons(total_len); 583 584 /* recompute the ip header checksum */ 585 bp = (u_int16_t *) &cs->cs_ip; 586 cs->cs_ip.ip_sum = 0; 587 for (changes = 0; hlen > 0; hlen -= 2) 588 changes += *bp++; 589 changes = (changes & 0xffff) + (changes >> 16); 590 changes = (changes & 0xffff) + (changes >> 16); 591 cs->cs_ip.ip_sum = ~ changes; 592 593 *hdrp = (u_char *) &cs->cs_ip; 594 *hlenp = cs->cs_hlen; 595 return vjlen; 596 597 bad: 598 comp->flags |= SLF_TOSS; 599 INCR(sls_errorin) 600 return (-1); 601 } 602