slcompress.c revision 53192
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 * $FreeBSD: head/sys/net/slcompress.c 53192 1999-11-15 20:17:04Z archie $ 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/mbuf.h> 48#include <sys/systm.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 } else { 81 /* Don't reset statistics */ 82 bzero((char *)comp->tstate, sizeof(comp->tstate)); 83 bzero((char *)comp->rstate, sizeof(comp->rstate)); 84 } 85 for (i = max_state; i > 0; --i) { 86 tstate[i].cs_id = i; 87 tstate[i].cs_next = &tstate[i - 1]; 88 } 89 tstate[0].cs_next = &tstate[max_state]; 90 tstate[0].cs_id = 0; 91 comp->last_cs = &tstate[0]; 92 comp->last_recv = 255; 93 comp->last_xmit = 255; 94 comp->flags = SLF_TOSS; 95} 96 97 98/* ENCODE encodes a number that is known to be non-zero. ENCODEZ 99 * checks for zero (since zero has to be encoded in the long, 3 byte 100 * form). 101 */ 102#define ENCODE(n) { \ 103 if ((u_int16_t)(n) >= 256) { \ 104 *cp++ = 0; \ 105 cp[1] = (n); \ 106 cp[0] = (n) >> 8; \ 107 cp += 2; \ 108 } else { \ 109 *cp++ = (n); \ 110 } \ 111} 112#define ENCODEZ(n) { \ 113 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 114 *cp++ = 0; \ 115 cp[1] = (n); \ 116 cp[0] = (n) >> 8; \ 117 cp += 2; \ 118 } else { \ 119 *cp++ = (n); \ 120 } \ 121} 122 123#define DECODEL(f) { \ 124 if (*cp == 0) {\ 125 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 126 cp += 3; \ 127 } else { \ 128 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 129 } \ 130} 131 132#define DECODES(f) { \ 133 if (*cp == 0) {\ 134 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 135 cp += 3; \ 136 } else { \ 137 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 138 } \ 139} 140 141#define DECODEU(f) { \ 142 if (*cp == 0) {\ 143 (f) = htons((cp[1] << 8) | cp[2]); \ 144 cp += 3; \ 145 } else { \ 146 (f) = htons((u_int32_t)*cp++); \ 147 } \ 148} 149 150/* 151 * Attempt to compress an outgoing TCP packet and return the type of 152 * the result. The caller must have already verified that the protocol 153 * is TCP. The first mbuf must contain the complete IP and TCP headers, 154 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 155 * compression state, and "compress_cid" tells us whether it is OK 156 * to leave out the CID field when feasible. 157 * 158 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 159 * if m is an M_PKTHDR mbuf. 160 */ 161u_int 162sl_compress_tcp(m, ip, comp, compress_cid) 163 struct mbuf *m; 164 register struct ip *ip; 165 struct slcompress *comp; 166 int compress_cid; 167{ 168 register struct cstate *cs = comp->last_cs->cs_next; 169 register u_int hlen = ip->ip_hl; 170 register struct tcphdr *oth; 171 register struct tcphdr *th; 172 register u_int deltaS, deltaA; 173 register u_int changes = 0; 174 u_char new_seq[16]; 175 register u_char *cp = new_seq; 176 177 /* 178 * Bail if this is an IP fragment or if the TCP packet isn't 179 * `compressible' (i.e., ACK isn't set or some other control bit is 180 * set). (We assume that the caller has already made sure the 181 * packet is IP proto TCP). 182 */ 183 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 184 return (TYPE_IP); 185 186 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 187 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 188 return (TYPE_IP); 189 /* 190 * Packet is compressible -- we're going to send either a 191 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 192 * to locate (or create) the connection state. Special case the 193 * most recently used connection since it's most likely to be used 194 * again & we don't have to do any reordering if it's used. 195 */ 196 INCR(sls_packets) 197 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 198 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 199 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 200 /* 201 * Wasn't the first -- search for it. 202 * 203 * States are kept in a circularly linked list with 204 * last_cs pointing to the end of the list. The 205 * list is kept in lru order by moving a state to the 206 * head of the list whenever it is referenced. Since 207 * the list is short and, empirically, the connection 208 * we want is almost always near the front, we locate 209 * states via linear search. If we don't find a state 210 * for the datagram, the oldest state is (re-)used. 211 */ 212 register struct cstate *lcs; 213 register struct cstate *lastcs = comp->last_cs; 214 215 do { 216 lcs = cs; cs = cs->cs_next; 217 INCR(sls_searches) 218 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 219 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 220 && *(int32_t *)th == 221 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 222 goto found; 223 } while (cs != lastcs); 224 225 /* 226 * Didn't find it -- re-use oldest cstate. Send an 227 * uncompressed packet that tells the other side what 228 * connection number we're using for this conversation. 229 * Note that since the state list is circular, the oldest 230 * state points to the newest and we only need to set 231 * last_cs to update the lru linkage. 232 */ 233 INCR(sls_misses) 234 comp->last_cs = lcs; 235 hlen += th->th_off; 236 hlen <<= 2; 237 if (hlen > m->m_len) 238 return TYPE_IP; 239 goto uncompressed; 240 241 found: 242 /* 243 * Found it -- move to the front on the connection list. 244 */ 245 if (cs == lastcs) 246 comp->last_cs = lcs; 247 else { 248 lcs->cs_next = cs->cs_next; 249 cs->cs_next = lastcs->cs_next; 250 lastcs->cs_next = cs; 251 } 252 } 253 254 /* 255 * Make sure that only what we expect to change changed. The first 256 * line of the `if' checks the IP protocol version, header length & 257 * type of service. The 2nd line checks the "Don't fragment" bit. 258 * The 3rd line checks the time-to-live and protocol (the protocol 259 * check is unnecessary but costless). The 4th line checks the TCP 260 * header length. The 5th line checks IP options, if any. The 6th 261 * line checks TCP options, if any. If any of these things are 262 * different between the previous & current datagram, we send the 263 * current datagram `uncompressed'. 264 */ 265 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 266 deltaS = hlen; 267 hlen += th->th_off; 268 hlen <<= 2; 269 if (hlen > m->m_len) 270 return TYPE_IP; 271 272 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 273 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 274 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 275 th->th_off != oth->th_off || 276 (deltaS > 5 && 277 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 278 (th->th_off > 5 && 279 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 280 goto uncompressed; 281 282 /* 283 * Figure out which of the changing fields changed. The 284 * receiver expects changes in the order: urgent, window, 285 * ack, seq (the order minimizes the number of temporaries 286 * needed in this section of code). 287 */ 288 if (th->th_flags & TH_URG) { 289 deltaS = ntohs(th->th_urp); 290 ENCODEZ(deltaS); 291 changes |= NEW_U; 292 } else if (th->th_urp != oth->th_urp) 293 /* argh! URG not set but urp changed -- a sensible 294 * implementation should never do this but RFC793 295 * doesn't prohibit the change so we have to deal 296 * with it. */ 297 goto uncompressed; 298 299 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 300 if (deltaS) { 301 ENCODE(deltaS); 302 changes |= NEW_W; 303 } 304 305 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 306 if (deltaA) { 307 if (deltaA > 0xffff) 308 goto uncompressed; 309 ENCODE(deltaA); 310 changes |= NEW_A; 311 } 312 313 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 314 if (deltaS) { 315 if (deltaS > 0xffff) 316 goto uncompressed; 317 ENCODE(deltaS); 318 changes |= NEW_S; 319 } 320 321 switch(changes) { 322 323 case 0: 324 /* 325 * Nothing changed. If this packet contains data and the 326 * last one didn't, this is probably a data packet following 327 * an ack (normal on an interactive connection) and we send 328 * it compressed. Otherwise it's probably a retransmit, 329 * retransmitted ack or window probe. Send it uncompressed 330 * in case the other side missed the compressed version. 331 */ 332 if (ip->ip_len != cs->cs_ip.ip_len && 333 ntohs(cs->cs_ip.ip_len) == hlen) 334 break; 335 336 /* (fall through) */ 337 338 case SPECIAL_I: 339 case SPECIAL_D: 340 /* 341 * actual changes match one of our special case encodings -- 342 * send packet uncompressed. 343 */ 344 goto uncompressed; 345 346 case NEW_S|NEW_A: 347 if (deltaS == deltaA && 348 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 349 /* special case for echoed terminal traffic */ 350 changes = SPECIAL_I; 351 cp = new_seq; 352 } 353 break; 354 355 case NEW_S: 356 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 357 /* special case for data xfer */ 358 changes = SPECIAL_D; 359 cp = new_seq; 360 } 361 break; 362 } 363 364 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 365 if (deltaS != 1) { 366 ENCODEZ(deltaS); 367 changes |= NEW_I; 368 } 369 if (th->th_flags & TH_PUSH) 370 changes |= TCP_PUSH_BIT; 371 /* 372 * Grab the cksum before we overwrite it below. Then update our 373 * state with this packet's header. 374 */ 375 deltaA = ntohs(th->th_sum); 376 BCOPY(ip, &cs->cs_ip, hlen); 377 378 /* 379 * We want to use the original packet as our compressed packet. 380 * (cp - new_seq) is the number of bytes we need for compressed 381 * sequence numbers. In addition we need one byte for the change 382 * mask, one for the connection id and two for the tcp checksum. 383 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 384 * many bytes of the original packet to toss so subtract the two to 385 * get the new packet size. 386 */ 387 deltaS = cp - new_seq; 388 cp = (u_char *)ip; 389 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 390 comp->last_xmit = cs->cs_id; 391 hlen -= deltaS + 4; 392 cp += hlen; 393 *cp++ = changes | NEW_C; 394 *cp++ = cs->cs_id; 395 } else { 396 hlen -= deltaS + 3; 397 cp += hlen; 398 *cp++ = changes; 399 } 400 m->m_len -= hlen; 401 m->m_data += hlen; 402 *cp++ = deltaA >> 8; 403 *cp++ = deltaA; 404 BCOPY(new_seq, cp, deltaS); 405 INCR(sls_compressed) 406 return (TYPE_COMPRESSED_TCP); 407 408 /* 409 * Update connection state cs & send uncompressed packet ('uncompressed' 410 * means a regular ip/tcp packet but with the 'conversation id' we hope 411 * to use on future compressed packets in the protocol field). 412 */ 413uncompressed: 414 BCOPY(ip, &cs->cs_ip, hlen); 415 ip->ip_p = cs->cs_id; 416 comp->last_xmit = cs->cs_id; 417 return (TYPE_UNCOMPRESSED_TCP); 418} 419 420 421int 422sl_uncompress_tcp(bufp, len, type, comp) 423 u_char **bufp; 424 int len; 425 u_int type; 426 struct slcompress *comp; 427{ 428 u_char *hdr, *cp; 429 int hlen, vjlen; 430 431 cp = bufp? *bufp: NULL; 432 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 433 if (vjlen < 0) 434 return (0); /* error */ 435 if (vjlen == 0) 436 return (len); /* was uncompressed already */ 437 438 cp += vjlen; 439 len -= vjlen; 440 441 /* 442 * At this point, cp points to the first byte of data in the 443 * packet. If we're not aligned on a 4-byte boundary, copy the 444 * data down so the ip & tcp headers will be aligned. Then back up 445 * cp by the tcp/ip header length to make room for the reconstructed 446 * header (we assume the packet we were handed has enough space to 447 * prepend 128 bytes of header). 448 */ 449 if ((intptr_t)cp & 3) { 450 if (len > 0) 451 (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 452 cp = (u_char *)((intptr_t)cp &~ 3); 453 } 454 cp -= hlen; 455 len += hlen; 456 BCOPY(hdr, cp, hlen); 457 458 *bufp = cp; 459 return (len); 460} 461 462/* 463 * Uncompress a packet of total length total_len. The first buflen 464 * bytes are at buf; this must include the entire (compressed or 465 * uncompressed) TCP/IP header. This procedure returns the length 466 * of the VJ header, with a pointer to the uncompressed IP header 467 * in *hdrp and its length in *hlenp. 468 */ 469int 470sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 471 u_char *buf; 472 int buflen, total_len; 473 u_int type; 474 struct slcompress *comp; 475 u_char **hdrp; 476 u_int *hlenp; 477{ 478 register u_char *cp; 479 register u_int hlen, changes; 480 register struct tcphdr *th; 481 register struct cstate *cs; 482 register struct ip *ip; 483 register u_int16_t *bp; 484 register 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 register 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 610bad: 611 comp->flags |= SLF_TOSS; 612 INCR(sls_errorin) 613 return (-1); 614} 615