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