1 /* $NetBSD: slcompress.c,v 1.26 2004/12/06 02:59:23 christos Exp $ */ 2 /* Id: slcompress.c,v 1.3 1996/05/24 07:04:47 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. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 33 */ 34 35 /* 36 * Routines to compress and uncompess tcp packets (for transmission 37 * over low speed serial lines. 38 * 39 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 40 * - Initial distribution. 41 */ 42 43 #include <sys/cdefs.h> 44 __KERNEL_RCSID(0, "$NetBSD: slcompress.c,v 1.26 2004/12/06 02:59:23 christos Exp $"); 45 46 #include "opt_inet.h" 47 #ifdef INET 48 #include <sys/param.h> 49 #include <sys/mbuf.h> 50 #include <sys/systm.h> 51 52 #include <netinet/in.h> 53 #include <netinet/in_systm.h> 54 #include <netinet/ip.h> 55 #include <netinet/tcp.h> 56 57 #include <net/slcompress.h> 58 59 #ifndef SL_NO_STATS 60 #define INCR(counter) ++comp->counter; 61 #else 62 #define INCR(counter) 63 #endif 64 65 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 66 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 67 68 69 void 70 sl_compress_init(comp) 71 struct slcompress *comp; 72 { 73 u_int i; 74 struct cstate *tstate = comp->tstate; 75 76 memset((char *)comp, 0, sizeof(*comp)); 77 for (i = MAX_STATES - 1; i > 0; --i) { 78 tstate[i].cs_id = i; 79 tstate[i].cs_next = &tstate[i - 1]; 80 } 81 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 82 tstate[0].cs_id = 0; 83 comp->last_cs = &tstate[0]; 84 comp->last_recv = 255; 85 comp->last_xmit = 255; 86 comp->flags = SLF_TOSS; 87 } 88 89 90 /* 91 * Like sl_compress_init, but we get to specify the maximum connection 92 * ID to use on transmission. 93 */ 94 void 95 sl_compress_setup(comp, max_state) 96 struct slcompress *comp; 97 int max_state; 98 { 99 u_int i; 100 struct cstate *tstate = comp->tstate; 101 102 if (max_state == -1) { 103 max_state = MAX_STATES - 1; 104 memset((char *)comp, 0, sizeof(*comp)); 105 } else { 106 /* Don't reset statistics */ 107 memset((char *)comp->tstate, 0, sizeof(comp->tstate)); 108 memset((char *)comp->rstate, 0, sizeof(comp->rstate)); 109 } 110 for (i = max_state; i > 0; --i) { 111 tstate[i].cs_id = i; 112 tstate[i].cs_next = &tstate[i - 1]; 113 } 114 tstate[0].cs_next = &tstate[max_state]; 115 tstate[0].cs_id = 0; 116 comp->last_cs = &tstate[0]; 117 comp->last_recv = 255; 118 comp->last_xmit = 255; 119 comp->flags = SLF_TOSS; 120 } 121 122 123 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 124 * checks for zero (since zero has to be encoded in the long, 3 byte 125 * form). 126 */ 127 #define ENCODE(n) { \ 128 if ((u_int16_t)(n) >= 256) { \ 129 *cp++ = 0; \ 130 cp[1] = (n); \ 131 cp[0] = (n) >> 8; \ 132 cp += 2; \ 133 } else { \ 134 *cp++ = (n); \ 135 } \ 136 } 137 #define ENCODEZ(n) { \ 138 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 139 *cp++ = 0; \ 140 cp[1] = (n); \ 141 cp[0] = (n) >> 8; \ 142 cp += 2; \ 143 } else { \ 144 *cp++ = (n); \ 145 } \ 146 } 147 148 #define DECODEL(f) { \ 149 if (*cp == 0) {\ 150 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 151 cp += 3; \ 152 } else { \ 153 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 154 } \ 155 } 156 157 #define DECODES(f) { \ 158 if (*cp == 0) {\ 159 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 160 cp += 3; \ 161 } else { \ 162 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 163 } \ 164 } 165 166 #define DECODEU(f) { \ 167 if (*cp == 0) {\ 168 (f) = htons((cp[1] << 8) | cp[2]); \ 169 cp += 3; \ 170 } else { \ 171 (f) = htons((u_int32_t)*cp++); \ 172 } \ 173 } 174 175 u_int 176 sl_compress_tcp(m, ip, comp, compress_cid) 177 struct mbuf *m; 178 struct ip *ip; 179 struct slcompress *comp; 180 int compress_cid; 181 { 182 struct cstate *cs = comp->last_cs->cs_next; 183 u_int hlen = ip->ip_hl; 184 struct tcphdr *oth; 185 struct tcphdr *th; 186 u_int deltaS, deltaA; 187 u_int changes = 0; 188 u_char new_seq[16]; 189 u_char *cp = new_seq; 190 191 /* 192 * Bail if this is an IP fragment or if the TCP packet isn't 193 * `compressible' (i.e., ACK isn't set or some other control bit is 194 * set). (We assume that the caller has already made sure the 195 * packet is IP proto TCP). 196 */ 197 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 198 return (TYPE_IP); 199 200 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 201 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 202 return (TYPE_IP); 203 /* 204 * Packet is compressible -- we're going to send either a 205 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 206 * to locate (or create) the connection state. Special case the 207 * most recently used connection since it's most likely to be used 208 * again & we don't have to do any reordering if it's used. 209 */ 210 INCR(sls_packets) 211 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 212 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 213 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 214 /* 215 * Wasn't the first -- search for it. 216 * 217 * States are kept in a circularly linked list with 218 * last_cs pointing to the end of the list. The 219 * list is kept in lru order by moving a state to the 220 * head of the list whenever it is referenced. Since 221 * the list is short and, empirically, the connection 222 * we want is almost always near the front, we locate 223 * states via linear search. If we don't find a state 224 * for the datagram, the oldest state is (re-)used. 225 */ 226 struct cstate *lcs; 227 struct cstate *lastcs = comp->last_cs; 228 229 do { 230 lcs = cs; cs = cs->cs_next; 231 INCR(sls_searches) 232 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 233 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 234 && *(int32_t *)th == 235 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 236 goto found; 237 } while (cs != lastcs); 238 239 /* 240 * Didn't find it -- re-use oldest cstate. Send an 241 * uncompressed packet that tells the other side what 242 * connection number we're using for this conversation. 243 * Note that since the state list is circular, the oldest 244 * state points to the newest and we only need to set 245 * last_cs to update the lru linkage. 246 */ 247 INCR(sls_misses) 248 comp->last_cs = lcs; 249 hlen += th->th_off; 250 hlen <<= 2; 251 if (hlen > m->m_len) 252 return (TYPE_IP); 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 if (hlen > m->m_len) 284 return (TYPE_IP); 285 286 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 287 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 288 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 289 th->th_off != oth->th_off || 290 (deltaS > 5 && 291 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 292 (th->th_off > 5 && 293 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 294 goto uncompressed; 295 296 /* 297 * Figure out which of the changing fields changed. The 298 * receiver expects changes in the order: urgent, window, 299 * ack, seq (the order minimizes the number of temporaries 300 * needed in this section of code). 301 */ 302 if (th->th_flags & TH_URG) { 303 deltaS = ntohs(th->th_urp); 304 ENCODEZ(deltaS); 305 changes |= NEW_U; 306 } else if (th->th_urp != oth->th_urp) 307 /* argh! URG not set but urp changed -- a sensible 308 * implementation should never do this but RFC793 309 * doesn't prohibit the change so we have to deal 310 * with it. */ 311 goto uncompressed; 312 313 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 314 if (deltaS) { 315 ENCODE(deltaS); 316 changes |= NEW_W; 317 } 318 319 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 320 if (deltaA) { 321 if (deltaA > 0xffff) 322 goto uncompressed; 323 ENCODE(deltaA); 324 changes |= NEW_A; 325 } 326 327 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 328 if (deltaS) { 329 if (deltaS > 0xffff) 330 goto uncompressed; 331 ENCODE(deltaS); 332 changes |= NEW_S; 333 } 334 335 switch (changes) { 336 337 case 0: 338 /* 339 * Nothing changed. If this packet contains data and the 340 * last one didn't, this is probably a data packet following 341 * an ack (normal on an interactive connection) and we send 342 * it compressed. Otherwise it's probably a retransmit, 343 * retransmitted ack or window probe. Send it uncompressed 344 * in case the other side missed the compressed version. 345 */ 346 if (ip->ip_len != cs->cs_ip.ip_len && 347 ntohs(cs->cs_ip.ip_len) == hlen) 348 break; 349 350 /* (fall through) */ 351 352 case SPECIAL_I: 353 case SPECIAL_D: 354 /* 355 * actual changes match one of our special case encodings -- 356 * send packet uncompressed. 357 */ 358 goto uncompressed; 359 360 case NEW_S|NEW_A: 361 if (deltaS == deltaA && 362 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 363 /* special case for echoed terminal traffic */ 364 changes = SPECIAL_I; 365 cp = new_seq; 366 } 367 break; 368 369 case NEW_S: 370 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 371 /* special case for data xfer */ 372 changes = SPECIAL_D; 373 cp = new_seq; 374 } 375 break; 376 } 377 378 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 379 if (deltaS != 1) { 380 ENCODEZ(deltaS); 381 changes |= NEW_I; 382 } 383 if (th->th_flags & TH_PUSH) 384 changes |= TCP_PUSH_BIT; 385 /* 386 * Grab the cksum before we overwrite it below. Then update our 387 * state with this packet's header. 388 */ 389 deltaA = ntohs(th->th_sum); 390 BCOPY(ip, &cs->cs_ip, hlen); 391 392 /* 393 * We want to use the original packet as our compressed packet. 394 * (cp - new_seq) is the number of bytes we need for compressed 395 * sequence numbers. In addition we need one byte for the change 396 * mask, one for the connection id and two for the tcp checksum. 397 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 398 * many bytes of the original packet to toss so subtract the two to 399 * get the new packet size. 400 */ 401 deltaS = cp - new_seq; 402 cp = (u_char *)ip; 403 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 404 comp->last_xmit = cs->cs_id; 405 hlen -= deltaS + 4; 406 cp += hlen; 407 *cp++ = changes | NEW_C; 408 *cp++ = cs->cs_id; 409 } else { 410 hlen -= deltaS + 3; 411 cp += hlen; 412 *cp++ = changes; 413 } 414 m->m_len -= hlen; 415 m->m_data += hlen; 416 *cp++ = deltaA >> 8; 417 *cp++ = deltaA; 418 BCOPY(new_seq, cp, deltaS); 419 INCR(sls_compressed) 420 return (TYPE_COMPRESSED_TCP); 421 422 /* 423 * Update connection state cs & send uncompressed packet ('uncompressed' 424 * means a regular ip/tcp packet but with the 'conversation id' we hope 425 * to use on future compressed packets in the protocol field). 426 */ 427 uncompressed: 428 BCOPY(ip, &cs->cs_ip, hlen); 429 ip->ip_p = cs->cs_id; 430 comp->last_xmit = cs->cs_id; 431 return (TYPE_UNCOMPRESSED_TCP); 432 } 433 434 435 int 436 sl_uncompress_tcp(bufp, len, type, comp) 437 u_char **bufp; 438 int len; 439 u_int type; 440 struct slcompress *comp; 441 { 442 u_char *hdr, *cp; 443 int vjlen; 444 u_int hlen; 445 446 cp = bufp? *bufp: NULL; 447 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 448 if (vjlen < 0) 449 return (0); /* error */ 450 if (vjlen == 0) 451 return (len); /* was uncompressed already */ 452 453 cp += vjlen; 454 len -= vjlen; 455 456 /* 457 * At this point, cp points to the first byte of data in the 458 * packet. If we're not aligned on a 4-byte boundary, copy the 459 * data down so the ip & tcp headers will be aligned. Then back up 460 * cp by the tcp/ip header length to make room for the reconstructed 461 * header (we assume the packet we were handed has enough space to 462 * prepend 128 bytes of header). 463 */ 464 if ((long)cp & 3) { 465 if (len > 0) 466 memmove((caddr_t)((long)cp &~ 3), cp, len); 467 cp = (u_char *)((long)cp &~ 3); 468 } 469 cp -= hlen; 470 len += hlen; 471 BCOPY(hdr, cp, hlen); 472 473 *bufp = cp; 474 return (len); 475 } 476 477 /* 478 * Uncompress a packet of total length total_len. The first buflen 479 * bytes are at buf; this must include the entire (compressed or 480 * uncompressed) TCP/IP header. This procedure returns the length 481 * of the VJ header, with a pointer to the uncompressed IP header 482 * in *hdrp and its length in *hlenp. 483 */ 484 int 485 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 486 u_char *buf; 487 int buflen, total_len; 488 u_int type; 489 struct slcompress *comp; 490 u_char **hdrp; 491 u_int *hlenp; 492 { 493 u_char *cp; 494 u_int hlen, changes; 495 struct tcphdr *th; 496 struct cstate *cs; 497 struct ip *ip; 498 u_int16_t *bp; 499 u_int vjlen; 500 501 switch (type) { 502 503 case TYPE_UNCOMPRESSED_TCP: 504 ip = (struct ip *) buf; 505 if (ip->ip_p >= MAX_STATES) 506 goto bad; 507 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 508 comp->flags &=~ SLF_TOSS; 509 ip->ip_p = IPPROTO_TCP; 510 /* 511 * Calculate the size of the TCP/IP header and make sure that 512 * we don't overflow the space we have available for it. 513 */ 514 hlen = ip->ip_hl << 2; 515 if (hlen + sizeof(struct tcphdr) > buflen) 516 goto bad; 517 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 518 if (hlen > MAX_HDR || hlen > buflen) 519 goto bad; 520 BCOPY(ip, &cs->cs_ip, hlen); 521 cs->cs_hlen = hlen; 522 INCR(sls_uncompressedin) 523 *hdrp = (u_char *) &cs->cs_ip; 524 *hlenp = hlen; 525 return (0); 526 527 default: 528 goto bad; 529 530 case TYPE_COMPRESSED_TCP: 531 break; 532 } 533 /* We've got a compressed packet. */ 534 INCR(sls_compressedin) 535 cp = buf; 536 changes = *cp++; 537 if (changes & NEW_C) { 538 /* Make sure the state index is in range, then grab the state. 539 * If we have a good state index, clear the 'discard' flag. */ 540 if (*cp >= MAX_STATES) 541 goto bad; 542 543 comp->flags &=~ SLF_TOSS; 544 comp->last_recv = *cp++; 545 } else { 546 /* this packet has an implicit state index. If we've 547 * had a line error since the last time we got an 548 * explicit state index, we have to toss the packet. */ 549 if (comp->flags & SLF_TOSS) { 550 INCR(sls_tossed) 551 return (-1); 552 } 553 } 554 cs = &comp->rstate[comp->last_recv]; 555 hlen = cs->cs_ip.ip_hl << 2; 556 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 557 th->th_sum = htons((*cp << 8) | cp[1]); 558 cp += 2; 559 if (changes & TCP_PUSH_BIT) 560 th->th_flags |= TH_PUSH; 561 else 562 th->th_flags &=~ TH_PUSH; 563 564 switch (changes & SPECIALS_MASK) { 565 case SPECIAL_I: 566 { 567 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 568 th->th_ack = htonl(ntohl(th->th_ack) + i); 569 th->th_seq = htonl(ntohl(th->th_seq) + i); 570 } 571 break; 572 573 case SPECIAL_D: 574 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 575 - cs->cs_hlen); 576 break; 577 578 default: 579 if (changes & NEW_U) { 580 th->th_flags |= TH_URG; 581 DECODEU(th->th_urp) 582 } else 583 th->th_flags &=~ TH_URG; 584 if (changes & NEW_W) 585 DECODES(th->th_win) 586 if (changes & NEW_A) 587 DECODEL(th->th_ack) 588 if (changes & NEW_S) 589 DECODEL(th->th_seq) 590 break; 591 } 592 if (changes & NEW_I) { 593 DECODES(cs->cs_ip.ip_id) 594 } else 595 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 596 597 /* 598 * At this point, cp points to the first byte of data in the 599 * packet. Fill in the IP total length and update the IP 600 * header checksum. 601 */ 602 vjlen = cp - buf; 603 buflen -= vjlen; 604 if (buflen < 0) 605 /* we must have dropped some characters (crc should detect 606 * this but the old slip framing won't) */ 607 goto bad; 608 609 total_len += cs->cs_hlen - vjlen; 610 cs->cs_ip.ip_len = htons(total_len); 611 612 /* recompute the ip header checksum */ 613 bp = (u_int16_t *) &cs->cs_ip; 614 cs->cs_ip.ip_sum = 0; 615 for (changes = 0; hlen > 0; hlen -= 2) 616 changes += *bp++; 617 changes = (changes & 0xffff) + (changes >> 16); 618 changes = (changes & 0xffff) + (changes >> 16); 619 cs->cs_ip.ip_sum = ~ changes; 620 621 *hdrp = (u_char *) &cs->cs_ip; 622 *hlenp = cs->cs_hlen; 623 return vjlen; 624 625 bad: 626 comp->flags |= SLF_TOSS; 627 INCR(sls_errorin) 628 return (-1); 629 } 630 #endif 631