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 * $FreeBSD$ 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((void *)(p1), (void *)(p2), (int)(n)) 64 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n)) 65 66 void 67 sl_compress_init(comp, max_state) 68 struct slcompress *comp; 69 int max_state; 70 { 71 register u_int i; 72 register struct cstate *tstate = comp->tstate; 73 74 if (max_state == -1) { 75 max_state = MAX_STATES - 1; 76 bzero((char *)comp, sizeof(*comp)); 77 } else { 78 /* Don't reset statistics */ 79 bzero((char *)comp->tstate, sizeof(comp->tstate)); 80 bzero((char *)comp->rstate, sizeof(comp->rstate)); 81 } 82 for (i = max_state; i > 0; --i) { 83 tstate[i].cs_id = i; 84 tstate[i].cs_next = &tstate[i - 1]; 85 } 86 tstate[0].cs_next = &tstate[max_state]; 87 tstate[0].cs_id = 0; 88 comp->last_cs = &tstate[0]; 89 comp->last_recv = 255; 90 comp->last_xmit = 255; 91 comp->flags = SLF_TOSS; 92 } 93 94 95 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 96 * checks for zero (since zero has to be encoded in the long, 3 byte 97 * form). 98 */ 99 #define ENCODE(n) { \ 100 if ((u_int16_t)(n) >= 256) { \ 101 *cp++ = 0; \ 102 cp[1] = (n); \ 103 cp[0] = (n) >> 8; \ 104 cp += 2; \ 105 } else { \ 106 *cp++ = (n); \ 107 } \ 108 } 109 #define ENCODEZ(n) { \ 110 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 111 *cp++ = 0; \ 112 cp[1] = (n); \ 113 cp[0] = (n) >> 8; \ 114 cp += 2; \ 115 } else { \ 116 *cp++ = (n); \ 117 } \ 118 } 119 120 #define DECODEL(f) { \ 121 if (*cp == 0) {\ 122 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 123 cp += 3; \ 124 } else { \ 125 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 126 } \ 127 } 128 129 #define DECODES(f) { \ 130 if (*cp == 0) {\ 131 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 132 cp += 3; \ 133 } else { \ 134 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 135 } \ 136 } 137 138 #define DECODEU(f) { \ 139 if (*cp == 0) {\ 140 (f) = htons((cp[1] << 8) | cp[2]); \ 141 cp += 3; \ 142 } else { \ 143 (f) = htons((u_int32_t)*cp++); \ 144 } \ 145 } 146 147 /* 148 * Attempt to compress an outgoing TCP packet and return the type of 149 * the result. The caller must have already verified that the protocol 150 * is TCP. The first mbuf must contain the complete IP and TCP headers, 151 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 152 * compression state, and "compress_cid" tells us whether it is OK 153 * to leave out the CID field when feasible. 154 * 155 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 156 * if m is an M_PKTHDR mbuf. 157 */ 158 u_int 159 sl_compress_tcp(m, ip, comp, compress_cid) 160 struct mbuf *m; 161 register struct ip *ip; 162 struct slcompress *comp; 163 int compress_cid; 164 { 165 register struct cstate *cs = comp->last_cs->cs_next; 166 register u_int hlen = ip->ip_hl; 167 register struct tcphdr *oth; 168 register struct tcphdr *th; 169 register u_int deltaS, deltaA; 170 register u_int changes = 0; 171 u_char new_seq[16]; 172 register u_char *cp = new_seq; 173 174 /* 175 * Bail if this is an IP fragment or if the TCP packet isn't 176 * `compressible' (i.e., ACK isn't set or some other control bit is 177 * set). (We assume that the caller has already made sure the 178 * packet is IP proto TCP). 179 */ 180 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 181 return (TYPE_IP); 182 183 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 184 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 185 return (TYPE_IP); 186 /* 187 * Packet is compressible -- we're going to send either a 188 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 189 * to locate (or create) the connection state. Special case the 190 * most recently used connection since it's most likely to be used 191 * again & we don't have to do any reordering if it's used. 192 */ 193 INCR(sls_packets) 194 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 195 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 196 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 197 /* 198 * Wasn't the first -- search for it. 199 * 200 * States are kept in a circularly linked list with 201 * last_cs pointing to the end of the list. The 202 * list is kept in lru order by moving a state to the 203 * head of the list whenever it is referenced. Since 204 * the list is short and, empirically, the connection 205 * we want is almost always near the front, we locate 206 * states via linear search. If we don't find a state 207 * for the datagram, the oldest state is (re-)used. 208 */ 209 register struct cstate *lcs; 210 register struct cstate *lastcs = comp->last_cs; 211 212 do { 213 lcs = cs; cs = cs->cs_next; 214 INCR(sls_searches) 215 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 216 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 217 && *(int32_t *)th == 218 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 219 goto found; 220 } while (cs != lastcs); 221 222 /* 223 * Didn't find it -- re-use oldest cstate. Send an 224 * uncompressed packet that tells the other side what 225 * connection number we're using for this conversation. 226 * Note that since the state list is circular, the oldest 227 * state points to the newest and we only need to set 228 * last_cs to update the lru linkage. 229 */ 230 INCR(sls_misses) 231 comp->last_cs = lcs; 232 hlen += th->th_off; 233 hlen <<= 2; 234 if (hlen > m->m_len) 235 return TYPE_IP; 236 goto uncompressed; 237 238 found: 239 /* 240 * Found it -- move to the front on the connection list. 241 */ 242 if (cs == lastcs) 243 comp->last_cs = lcs; 244 else { 245 lcs->cs_next = cs->cs_next; 246 cs->cs_next = lastcs->cs_next; 247 lastcs->cs_next = cs; 248 } 249 } 250 251 /* 252 * Make sure that only what we expect to change changed. The first 253 * line of the `if' checks the IP protocol version, header length & 254 * type of service. The 2nd line checks the "Don't fragment" bit. 255 * The 3rd line checks the time-to-live and protocol (the protocol 256 * check is unnecessary but costless). The 4th line checks the TCP 257 * header length. The 5th line checks IP options, if any. The 6th 258 * line checks TCP options, if any. If any of these things are 259 * different between the previous & current datagram, we send the 260 * current datagram `uncompressed'. 261 */ 262 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 263 deltaS = hlen; 264 hlen += th->th_off; 265 hlen <<= 2; 266 if (hlen > m->m_len) 267 return TYPE_IP; 268 269 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 270 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 271 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 272 th->th_off != oth->th_off || 273 (deltaS > 5 && 274 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 275 (th->th_off > 5 && 276 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 277 goto uncompressed; 278 279 /* 280 * Figure out which of the changing fields changed. The 281 * receiver expects changes in the order: urgent, window, 282 * ack, seq (the order minimizes the number of temporaries 283 * needed in this section of code). 284 */ 285 if (th->th_flags & TH_URG) { 286 deltaS = ntohs(th->th_urp); 287 ENCODEZ(deltaS); 288 changes |= NEW_U; 289 } else if (th->th_urp != oth->th_urp) 290 /* argh! URG not set but urp changed -- a sensible 291 * implementation should never do this but RFC793 292 * doesn't prohibit the change so we have to deal 293 * with it. */ 294 goto uncompressed; 295 296 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 297 if (deltaS) { 298 ENCODE(deltaS); 299 changes |= NEW_W; 300 } 301 302 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 303 if (deltaA) { 304 if (deltaA > 0xffff) 305 goto uncompressed; 306 ENCODE(deltaA); 307 changes |= NEW_A; 308 } 309 310 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 311 if (deltaS) { 312 if (deltaS > 0xffff) 313 goto uncompressed; 314 ENCODE(deltaS); 315 changes |= NEW_S; 316 } 317 318 switch(changes) { 319 320 case 0: 321 /* 322 * Nothing changed. If this packet contains data and the 323 * last one didn't, this is probably a data packet following 324 * an ack (normal on an interactive connection) and we send 325 * it compressed. Otherwise it's probably a retransmit, 326 * retransmitted ack or window probe. Send it uncompressed 327 * in case the other side missed the compressed version. 328 */ 329 if (ip->ip_len != cs->cs_ip.ip_len && 330 ntohs(cs->cs_ip.ip_len) == hlen) 331 break; 332 333 /* FALLTHROUGH */ 334 335 case SPECIAL_I: 336 case SPECIAL_D: 337 /* 338 * actual changes match one of our special case encodings -- 339 * send packet uncompressed. 340 */ 341 goto uncompressed; 342 343 case NEW_S|NEW_A: 344 if (deltaS == deltaA && 345 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 346 /* special case for echoed terminal traffic */ 347 changes = SPECIAL_I; 348 cp = new_seq; 349 } 350 break; 351 352 case NEW_S: 353 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 354 /* special case for data xfer */ 355 changes = SPECIAL_D; 356 cp = new_seq; 357 } 358 break; 359 } 360 361 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 362 if (deltaS != 1) { 363 ENCODEZ(deltaS); 364 changes |= NEW_I; 365 } 366 if (th->th_flags & TH_PUSH) 367 changes |= TCP_PUSH_BIT; 368 /* 369 * Grab the cksum before we overwrite it below. Then update our 370 * state with this packet's header. 371 */ 372 deltaA = ntohs(th->th_sum); 373 BCOPY(ip, &cs->cs_ip, hlen); 374 375 /* 376 * We want to use the original packet as our compressed packet. 377 * (cp - new_seq) is the number of bytes we need for compressed 378 * sequence numbers. In addition we need one byte for the change 379 * mask, one for the connection id and two for the tcp checksum. 380 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 381 * many bytes of the original packet to toss so subtract the two to 382 * get the new packet size. 383 */ 384 deltaS = cp - new_seq; 385 cp = (u_char *)ip; 386 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 387 comp->last_xmit = cs->cs_id; 388 hlen -= deltaS + 4; 389 cp += hlen; 390 *cp++ = changes | NEW_C; 391 *cp++ = cs->cs_id; 392 } else { 393 hlen -= deltaS + 3; 394 cp += hlen; 395 *cp++ = changes; 396 } 397 m->m_len -= hlen; 398 m->m_data += hlen; 399 *cp++ = deltaA >> 8; 400 *cp++ = deltaA; 401 BCOPY(new_seq, cp, deltaS); 402 INCR(sls_compressed) 403 return (TYPE_COMPRESSED_TCP); 404 405 /* 406 * Update connection state cs & send uncompressed packet ('uncompressed' 407 * means a regular ip/tcp packet but with the 'conversation id' we hope 408 * to use on future compressed packets in the protocol field). 409 */ 410 uncompressed: 411 BCOPY(ip, &cs->cs_ip, hlen); 412 ip->ip_p = cs->cs_id; 413 comp->last_xmit = cs->cs_id; 414 return (TYPE_UNCOMPRESSED_TCP); 415 } 416 417 418 int 419 sl_uncompress_tcp(bufp, len, type, comp) 420 u_char **bufp; 421 int len; 422 u_int type; 423 struct slcompress *comp; 424 { 425 u_char *hdr, *cp; 426 int hlen, vjlen; 427 428 cp = bufp? *bufp: NULL; 429 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 430 if (vjlen < 0) 431 return (0); /* error */ 432 if (vjlen == 0) 433 return (len); /* was uncompressed already */ 434 435 cp += vjlen; 436 len -= vjlen; 437 438 /* 439 * At this point, cp points to the first byte of data in the 440 * packet. If we're not aligned on a 4-byte boundary, copy the 441 * data down so the ip & tcp headers will be aligned. Then back up 442 * cp by the tcp/ip header length to make room for the reconstructed 443 * header (we assume the packet we were handed has enough space to 444 * prepend 128 bytes of header). 445 */ 446 if ((intptr_t)cp & 3) { 447 if (len > 0) 448 BCOPY(cp, ((intptr_t)cp &~ 3), len); 449 cp = (u_char *)((intptr_t)cp &~ 3); 450 } 451 cp -= hlen; 452 len += hlen; 453 BCOPY(hdr, cp, hlen); 454 455 *bufp = cp; 456 return (len); 457 } 458 459 /* 460 * Uncompress a packet of total length total_len. The first buflen 461 * bytes are at buf; this must include the entire (compressed or 462 * uncompressed) TCP/IP header. This procedure returns the length 463 * of the VJ header, with a pointer to the uncompressed IP header 464 * in *hdrp and its length in *hlenp. 465 */ 466 int 467 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 468 u_char *buf; 469 int buflen, total_len; 470 u_int type; 471 struct slcompress *comp; 472 u_char **hdrp; 473 u_int *hlenp; 474 { 475 register u_char *cp; 476 register u_int hlen, changes; 477 register struct tcphdr *th; 478 register struct cstate *cs; 479 register struct ip *ip; 480 register u_int16_t *bp; 481 register u_int vjlen; 482 483 switch (type) { 484 485 case TYPE_UNCOMPRESSED_TCP: 486 ip = (struct ip *) buf; 487 if (ip->ip_p >= MAX_STATES) 488 goto bad; 489 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 490 comp->flags &=~ SLF_TOSS; 491 ip->ip_p = IPPROTO_TCP; 492 /* 493 * Calculate the size of the TCP/IP header and make sure that 494 * we don't overflow the space we have available for it. 495 */ 496 hlen = ip->ip_hl << 2; 497 if (hlen + sizeof(struct tcphdr) > buflen) 498 goto bad; 499 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 500 if (hlen > MAX_HDR || hlen > buflen) 501 goto bad; 502 BCOPY(ip, &cs->cs_ip, hlen); 503 cs->cs_hlen = hlen; 504 INCR(sls_uncompressedin) 505 *hdrp = (u_char *) &cs->cs_ip; 506 *hlenp = hlen; 507 return (0); 508 509 default: 510 goto bad; 511 512 case TYPE_COMPRESSED_TCP: 513 break; 514 } 515 /* We've got a compressed packet. */ 516 INCR(sls_compressedin) 517 cp = buf; 518 changes = *cp++; 519 if (changes & NEW_C) { 520 /* Make sure the state index is in range, then grab the state. 521 * If we have a good state index, clear the 'discard' flag. */ 522 if (*cp >= MAX_STATES) 523 goto bad; 524 525 comp->flags &=~ SLF_TOSS; 526 comp->last_recv = *cp++; 527 } else { 528 /* this packet has an implicit state index. If we've 529 * had a line error since the last time we got an 530 * explicit state index, we have to toss the packet. */ 531 if (comp->flags & SLF_TOSS) { 532 INCR(sls_tossed) 533 return (-1); 534 } 535 } 536 cs = &comp->rstate[comp->last_recv]; 537 hlen = cs->cs_ip.ip_hl << 2; 538 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 539 th->th_sum = htons((*cp << 8) | cp[1]); 540 cp += 2; 541 if (changes & TCP_PUSH_BIT) 542 th->th_flags |= TH_PUSH; 543 else 544 th->th_flags &=~ TH_PUSH; 545 546 switch (changes & SPECIALS_MASK) { 547 case SPECIAL_I: 548 { 549 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 550 th->th_ack = htonl(ntohl(th->th_ack) + i); 551 th->th_seq = htonl(ntohl(th->th_seq) + i); 552 } 553 break; 554 555 case SPECIAL_D: 556 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 557 - cs->cs_hlen); 558 break; 559 560 default: 561 if (changes & NEW_U) { 562 th->th_flags |= TH_URG; 563 DECODEU(th->th_urp) 564 } else 565 th->th_flags &=~ TH_URG; 566 if (changes & NEW_W) 567 DECODES(th->th_win) 568 if (changes & NEW_A) 569 DECODEL(th->th_ack) 570 if (changes & NEW_S) 571 DECODEL(th->th_seq) 572 break; 573 } 574 if (changes & NEW_I) { 575 DECODES(cs->cs_ip.ip_id) 576 } else 577 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 578 579 /* 580 * At this point, cp points to the first byte of data in the 581 * packet. Fill in the IP total length and update the IP 582 * header checksum. 583 */ 584 vjlen = cp - buf; 585 buflen -= vjlen; 586 if (buflen < 0) 587 /* we must have dropped some characters (crc should detect 588 * this but the old slip framing won't) */ 589 goto bad; 590 591 total_len += cs->cs_hlen - vjlen; 592 cs->cs_ip.ip_len = htons(total_len); 593 594 /* recompute the ip header checksum */ 595 bp = (u_int16_t *) &cs->cs_ip; 596 cs->cs_ip.ip_sum = 0; 597 for (changes = 0; hlen > 0; hlen -= 2) 598 changes += *bp++; 599 changes = (changes & 0xffff) + (changes >> 16); 600 changes = (changes & 0xffff) + (changes >> 16); 601 cs->cs_ip.ip_sum = ~ changes; 602 603 *hdrp = (u_char *) &cs->cs_ip; 604 *hlenp = cs->cs_hlen; 605 return vjlen; 606 607 bad: 608 comp->flags |= SLF_TOSS; 609 INCR(sls_errorin) 610 return (-1); 611 } 612