1 /* $NetBSD: slcompress.c,v 1.28 2005/12/11 23:05:25 thorpej 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 1.28 2005/12/11 23:05:25 thorpej 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(struct slcompress *comp) 71 { 72 u_int i; 73 struct cstate *tstate = comp->tstate; 74 75 memset((char *)comp, 0, sizeof(*comp)); 76 for (i = MAX_STATES - 1; i > 0; --i) { 77 tstate[i].cs_id = i; 78 tstate[i].cs_next = &tstate[i - 1]; 79 } 80 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 81 tstate[0].cs_id = 0; 82 comp->last_cs = &tstate[0]; 83 comp->last_recv = 255; 84 comp->last_xmit = 255; 85 comp->flags = SLF_TOSS; 86 } 87 88 89 /* 90 * Like sl_compress_init, but we get to specify the maximum connection 91 * ID to use on transmission. 92 */ 93 void 94 sl_compress_setup(struct slcompress *comp, int max_state) 95 { 96 u_int i; 97 struct cstate *tstate = comp->tstate; 98 99 if (max_state == -1) { 100 max_state = MAX_STATES - 1; 101 memset((char *)comp, 0, sizeof(*comp)); 102 } else { 103 /* Don't reset statistics */ 104 memset((char *)comp->tstate, 0, sizeof(comp->tstate)); 105 memset((char *)comp->rstate, 0, sizeof(comp->rstate)); 106 } 107 for (i = max_state; i > 0; --i) { 108 tstate[i].cs_id = i; 109 tstate[i].cs_next = &tstate[i - 1]; 110 } 111 tstate[0].cs_next = &tstate[max_state]; 112 tstate[0].cs_id = 0; 113 comp->last_cs = &tstate[0]; 114 comp->last_recv = 255; 115 comp->last_xmit = 255; 116 comp->flags = SLF_TOSS; 117 } 118 119 120 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 121 * checks for zero (since zero has to be encoded in the long, 3 byte 122 * form). 123 */ 124 #define ENCODE(n) { \ 125 if ((u_int16_t)(n) >= 256) { \ 126 *cp++ = 0; \ 127 cp[1] = (n); \ 128 cp[0] = (n) >> 8; \ 129 cp += 2; \ 130 } else { \ 131 *cp++ = (n); \ 132 } \ 133 } 134 #define ENCODEZ(n) { \ 135 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 136 *cp++ = 0; \ 137 cp[1] = (n); \ 138 cp[0] = (n) >> 8; \ 139 cp += 2; \ 140 } else { \ 141 *cp++ = (n); \ 142 } \ 143 } 144 145 #define DECODEL(f) { \ 146 if (*cp == 0) {\ 147 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 148 cp += 3; \ 149 } else { \ 150 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 151 } \ 152 } 153 154 #define DECODES(f) { \ 155 if (*cp == 0) {\ 156 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 157 cp += 3; \ 158 } else { \ 159 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 160 } \ 161 } 162 163 #define DECODEU(f) { \ 164 if (*cp == 0) {\ 165 (f) = htons((cp[1] << 8) | cp[2]); \ 166 cp += 3; \ 167 } else { \ 168 (f) = htons((u_int32_t)*cp++); \ 169 } \ 170 } 171 172 u_int 173 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 174 int compress_cid) 175 { 176 struct cstate *cs = comp->last_cs->cs_next; 177 u_int hlen = ip->ip_hl; 178 struct tcphdr *oth; 179 struct tcphdr *th; 180 u_int deltaS, deltaA; 181 u_int changes = 0; 182 u_char new_seq[16]; 183 u_char *cp = new_seq; 184 185 /* 186 * Bail if this is an IP fragment or if the TCP packet isn't 187 * `compressible' (i.e., ACK isn't set or some other control bit is 188 * set). (We assume that the caller has already made sure the 189 * packet is IP proto TCP). 190 */ 191 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 192 return (TYPE_IP); 193 194 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 195 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 196 return (TYPE_IP); 197 /* 198 * Packet is compressible -- we're going to send either a 199 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 200 * to locate (or create) the connection state. Special case the 201 * most recently used connection since it's most likely to be used 202 * again & we don't have to do any reordering if it's used. 203 */ 204 INCR(sls_packets) 205 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 206 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 207 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 208 /* 209 * Wasn't the first -- search for it. 210 * 211 * States are kept in a circularly linked list with 212 * last_cs pointing to the end of the list. The 213 * list is kept in lru order by moving a state to the 214 * head of the list whenever it is referenced. Since 215 * the list is short and, empirically, the connection 216 * we want is almost always near the front, we locate 217 * states via linear search. If we don't find a state 218 * for the datagram, the oldest state is (re-)used. 219 */ 220 struct cstate *lcs; 221 struct cstate *lastcs = comp->last_cs; 222 223 do { 224 lcs = cs; cs = cs->cs_next; 225 INCR(sls_searches) 226 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 227 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 228 && *(int32_t *)th == 229 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 230 goto found; 231 } while (cs != lastcs); 232 233 /* 234 * Didn't find it -- re-use oldest cstate. Send an 235 * uncompressed packet that tells the other side what 236 * connection number we're using for this conversation. 237 * Note that since the state list is circular, the oldest 238 * state points to the newest and we only need to set 239 * last_cs to update the lru linkage. 240 */ 241 INCR(sls_misses) 242 comp->last_cs = lcs; 243 hlen += th->th_off; 244 hlen <<= 2; 245 if (hlen > m->m_len) 246 return (TYPE_IP); 247 goto uncompressed; 248 249 found: 250 /* 251 * Found it -- move to the front on the connection list. 252 */ 253 if (cs == lastcs) 254 comp->last_cs = lcs; 255 else { 256 lcs->cs_next = cs->cs_next; 257 cs->cs_next = lastcs->cs_next; 258 lastcs->cs_next = cs; 259 } 260 } 261 262 /* 263 * Make sure that only what we expect to change changed. The first 264 * line of the `if' checks the IP protocol version, header length & 265 * type of service. The 2nd line checks the "Don't fragment" bit. 266 * The 3rd line checks the time-to-live and protocol (the protocol 267 * check is unnecessary but costless). The 4th line checks the TCP 268 * header length. The 5th line checks IP options, if any. The 6th 269 * line checks TCP options, if any. If any of these things are 270 * different between the previous & current datagram, we send the 271 * current datagram `uncompressed'. 272 */ 273 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 274 deltaS = hlen; 275 hlen += th->th_off; 276 hlen <<= 2; 277 if (hlen > m->m_len) 278 return (TYPE_IP); 279 280 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 281 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 282 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 283 th->th_off != oth->th_off || 284 (deltaS > 5 && 285 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 286 (th->th_off > 5 && 287 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 288 goto uncompressed; 289 290 /* 291 * Figure out which of the changing fields changed. The 292 * receiver expects changes in the order: urgent, window, 293 * ack, seq (the order minimizes the number of temporaries 294 * needed in this section of code). 295 */ 296 if (th->th_flags & TH_URG) { 297 deltaS = ntohs(th->th_urp); 298 ENCODEZ(deltaS); 299 changes |= NEW_U; 300 } else if (th->th_urp != oth->th_urp) 301 /* argh! URG not set but urp changed -- a sensible 302 * implementation should never do this but RFC793 303 * doesn't prohibit the change so we have to deal 304 * with it. */ 305 goto uncompressed; 306 307 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 308 if (deltaS) { 309 ENCODE(deltaS); 310 changes |= NEW_W; 311 } 312 313 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 314 if (deltaA) { 315 if (deltaA > 0xffff) 316 goto uncompressed; 317 ENCODE(deltaA); 318 changes |= NEW_A; 319 } 320 321 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 322 if (deltaS) { 323 if (deltaS > 0xffff) 324 goto uncompressed; 325 ENCODE(deltaS); 326 changes |= NEW_S; 327 } 328 329 switch (changes) { 330 331 case 0: 332 /* 333 * Nothing changed. If this packet contains data and the 334 * last one didn't, this is probably a data packet following 335 * an ack (normal on an interactive connection) and we send 336 * it compressed. Otherwise it's probably a retransmit, 337 * retransmitted ack or window probe. Send it uncompressed 338 * in case the other side missed the compressed version. 339 */ 340 if (ip->ip_len != cs->cs_ip.ip_len && 341 ntohs(cs->cs_ip.ip_len) == hlen) 342 break; 343 344 /* (fall through) */ 345 346 case SPECIAL_I: 347 case SPECIAL_D: 348 /* 349 * actual changes match one of our special case encodings -- 350 * send packet uncompressed. 351 */ 352 goto uncompressed; 353 354 case NEW_S|NEW_A: 355 if (deltaS == deltaA && 356 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 357 /* special case for echoed terminal traffic */ 358 changes = SPECIAL_I; 359 cp = new_seq; 360 } 361 break; 362 363 case NEW_S: 364 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 365 /* special case for data xfer */ 366 changes = SPECIAL_D; 367 cp = new_seq; 368 } 369 break; 370 } 371 372 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 373 if (deltaS != 1) { 374 ENCODEZ(deltaS); 375 changes |= NEW_I; 376 } 377 if (th->th_flags & TH_PUSH) 378 changes |= TCP_PUSH_BIT; 379 /* 380 * Grab the cksum before we overwrite it below. Then update our 381 * state with this packet's header. 382 */ 383 deltaA = ntohs(th->th_sum); 384 BCOPY(ip, &cs->cs_ip, hlen); 385 386 /* 387 * We want to use the original packet as our compressed packet. 388 * (cp - new_seq) is the number of bytes we need for compressed 389 * sequence numbers. In addition we need one byte for the change 390 * mask, one for the connection id and two for the tcp checksum. 391 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 392 * many bytes of the original packet to toss so subtract the two to 393 * get the new packet size. 394 */ 395 deltaS = cp - new_seq; 396 cp = (u_char *)ip; 397 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 398 comp->last_xmit = cs->cs_id; 399 hlen -= deltaS + 4; 400 cp += hlen; 401 *cp++ = changes | NEW_C; 402 *cp++ = cs->cs_id; 403 } else { 404 hlen -= deltaS + 3; 405 cp += hlen; 406 *cp++ = changes; 407 } 408 m->m_len -= hlen; 409 m->m_data += hlen; 410 *cp++ = deltaA >> 8; 411 *cp++ = deltaA; 412 BCOPY(new_seq, cp, deltaS); 413 INCR(sls_compressed) 414 return (TYPE_COMPRESSED_TCP); 415 416 /* 417 * Update connection state cs & send uncompressed packet ('uncompressed' 418 * means a regular ip/tcp packet but with the 'conversation id' we hope 419 * to use on future compressed packets in the protocol field). 420 */ 421 uncompressed: 422 BCOPY(ip, &cs->cs_ip, hlen); 423 ip->ip_p = cs->cs_id; 424 comp->last_xmit = cs->cs_id; 425 return (TYPE_UNCOMPRESSED_TCP); 426 } 427 428 429 int 430 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 431 { 432 u_char *hdr, *cp; 433 int vjlen; 434 u_int hlen; 435 436 cp = bufp? *bufp: NULL; 437 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 438 if (vjlen < 0) 439 return (0); /* error */ 440 if (vjlen == 0) 441 return (len); /* was uncompressed already */ 442 443 cp += vjlen; 444 len -= vjlen; 445 446 /* 447 * At this point, cp points to the first byte of data in the 448 * packet. If we're not aligned on a 4-byte boundary, copy the 449 * data down so the ip & tcp headers will be aligned. Then back up 450 * cp by the tcp/ip header length to make room for the reconstructed 451 * header (we assume the packet we were handed has enough space to 452 * prepend 128 bytes of header). 453 */ 454 if ((long)cp & 3) { 455 if (len > 0) 456 memmove((caddr_t)((long)cp &~ 3), cp, len); 457 cp = (u_char *)((long)cp &~ 3); 458 } 459 cp -= hlen; 460 len += hlen; 461 BCOPY(hdr, cp, hlen); 462 463 *bufp = cp; 464 return (len); 465 } 466 467 /* 468 * Uncompress a packet of total length total_len. The first buflen 469 * bytes are at buf; this must include the entire (compressed or 470 * uncompressed) TCP/IP header. This procedure returns the length 471 * of the VJ header, with a pointer to the uncompressed IP header 472 * in *hdrp and its length in *hlenp. 473 */ 474 int 475 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 476 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 477 { 478 u_char *cp; 479 u_int hlen, changes; 480 struct tcphdr *th; 481 struct cstate *cs; 482 struct ip *ip; 483 u_int16_t *bp; 484 u_int vjlen; 485 486 switch (type) { 487 488 case TYPE_UNCOMPRESSED_TCP: 489 ip = (struct ip *) buf; 490 if (ip->ip_p >= MAX_STATES) 491 goto bad; 492 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 493 comp->flags &=~ SLF_TOSS; 494 ip->ip_p = IPPROTO_TCP; 495 /* 496 * Calculate the size of the TCP/IP header and make sure that 497 * we don't overflow the space we have available for it. 498 */ 499 hlen = ip->ip_hl << 2; 500 if (hlen + sizeof(struct tcphdr) > buflen) 501 goto bad; 502 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 503 if (hlen > MAX_HDR || hlen > buflen) 504 goto bad; 505 BCOPY(ip, &cs->cs_ip, hlen); 506 cs->cs_hlen = hlen; 507 INCR(sls_uncompressedin) 508 *hdrp = (u_char *) &cs->cs_ip; 509 *hlenp = hlen; 510 return (0); 511 512 default: 513 goto bad; 514 515 case TYPE_COMPRESSED_TCP: 516 break; 517 } 518 /* We've got a compressed packet. */ 519 INCR(sls_compressedin) 520 cp = buf; 521 changes = *cp++; 522 if (changes & NEW_C) { 523 /* Make sure the state index is in range, then grab the state. 524 * If we have a good state index, clear the 'discard' flag. */ 525 if (*cp >= MAX_STATES) 526 goto bad; 527 528 comp->flags &=~ SLF_TOSS; 529 comp->last_recv = *cp++; 530 } else { 531 /* this packet has an implicit state index. If we've 532 * had a line error since the last time we got an 533 * explicit state index, we have to toss the packet. */ 534 if (comp->flags & SLF_TOSS) { 535 INCR(sls_tossed) 536 return (-1); 537 } 538 } 539 cs = &comp->rstate[comp->last_recv]; 540 hlen = cs->cs_ip.ip_hl << 2; 541 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 542 th->th_sum = htons((*cp << 8) | cp[1]); 543 cp += 2; 544 if (changes & TCP_PUSH_BIT) 545 th->th_flags |= TH_PUSH; 546 else 547 th->th_flags &=~ TH_PUSH; 548 549 switch (changes & SPECIALS_MASK) { 550 case SPECIAL_I: 551 { 552 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 553 th->th_ack = htonl(ntohl(th->th_ack) + i); 554 th->th_seq = htonl(ntohl(th->th_seq) + i); 555 } 556 break; 557 558 case SPECIAL_D: 559 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 560 - cs->cs_hlen); 561 break; 562 563 default: 564 if (changes & NEW_U) { 565 th->th_flags |= TH_URG; 566 DECODEU(th->th_urp) 567 } else 568 th->th_flags &=~ TH_URG; 569 if (changes & NEW_W) 570 DECODES(th->th_win) 571 if (changes & NEW_A) 572 DECODEL(th->th_ack) 573 if (changes & NEW_S) 574 DECODEL(th->th_seq) 575 break; 576 } 577 if (changes & NEW_I) { 578 DECODES(cs->cs_ip.ip_id) 579 } else 580 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 581 582 /* 583 * At this point, cp points to the first byte of data in the 584 * packet. Fill in the IP total length and update the IP 585 * header checksum. 586 */ 587 vjlen = cp - buf; 588 buflen -= vjlen; 589 if (buflen < 0) 590 /* we must have dropped some characters (crc should detect 591 * this but the old slip framing won't) */ 592 goto bad; 593 594 total_len += cs->cs_hlen - vjlen; 595 cs->cs_ip.ip_len = htons(total_len); 596 597 /* recompute the ip header checksum */ 598 bp = (u_int16_t *) &cs->cs_ip; 599 cs->cs_ip.ip_sum = 0; 600 for (changes = 0; hlen > 0; hlen -= 2) 601 changes += *bp++; 602 changes = (changes & 0xffff) + (changes >> 16); 603 changes = (changes & 0xffff) + (changes >> 16); 604 cs->cs_ip.ip_sum = ~ changes; 605 606 *hdrp = (u_char *) &cs->cs_ip; 607 *hlenp = cs->cs_hlen; 608 return vjlen; 609 610 bad: 611 comp->flags |= SLF_TOSS; 612 INCR(sls_errorin) 613 return (-1); 614 } 615 #endif 616