1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1989, 1993, 1994 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 32 */ 33 34 /* 35 * Routines to compress and uncompess tcp packets (for transmission 36 * over low speed serial lines. 37 * 38 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 39 * - Initial distribution. 40 * 41 */ 42 43 #include <sys/param.h> 44 #include <sys/mbuf.h> 45 #include <sys/systm.h> 46 47 #include <netinet/in.h> 48 #include <netinet/in_systm.h> 49 #include <netinet/ip.h> 50 #include <netinet/tcp.h> 51 52 #include <net/slcompress.h> 53 54 #ifndef SL_NO_STATS 55 #define INCR(counter) ++comp->counter; 56 #else 57 #define INCR(counter) 58 #endif 59 60 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n)) 61 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n)) 62 63 void 64 sl_compress_init(struct slcompress *comp, int max_state) 65 { 66 u_int i; 67 struct cstate *tstate = comp->tstate; 68 69 if (max_state == -1) { 70 max_state = MAX_STATES - 1; 71 bzero((char *)comp, sizeof(*comp)); 72 } else { 73 /* Don't reset statistics */ 74 bzero((char *)comp->tstate, sizeof(comp->tstate)); 75 bzero((char *)comp->rstate, sizeof(comp->rstate)); 76 } 77 for (i = max_state; 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_state]; 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 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 90 * checks for zero (since zero has to be encoded in the long, 3 byte 91 * form). 92 */ 93 #define ENCODE(n) { \ 94 if ((u_int16_t)(n) >= 256) { \ 95 *cp++ = 0; \ 96 cp[1] = (n); \ 97 cp[0] = (n) >> 8; \ 98 cp += 2; \ 99 } else { \ 100 *cp++ = (n); \ 101 } \ 102 } 103 #define ENCODEZ(n) { \ 104 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 105 *cp++ = 0; \ 106 cp[1] = (n); \ 107 cp[0] = (n) >> 8; \ 108 cp += 2; \ 109 } else { \ 110 *cp++ = (n); \ 111 } \ 112 } 113 114 #define DECODEL(f) { \ 115 if (*cp == 0) {\ 116 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 117 cp += 3; \ 118 } else { \ 119 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 120 } \ 121 } 122 123 #define DECODES(f) { \ 124 if (*cp == 0) {\ 125 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 126 cp += 3; \ 127 } else { \ 128 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 129 } \ 130 } 131 132 #define DECODEU(f) { \ 133 if (*cp == 0) {\ 134 (f) = htons((cp[1] << 8) | cp[2]); \ 135 cp += 3; \ 136 } else { \ 137 (f) = htons((u_int32_t)*cp++); \ 138 } \ 139 } 140 141 /* 142 * Attempt to compress an outgoing TCP packet and return the type of 143 * the result. The caller must have already verified that the protocol 144 * is TCP. The first mbuf must contain the complete IP and TCP headers, 145 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 146 * compression state, and "compress_cid" tells us whether it is OK 147 * to leave out the CID field when feasible. 148 * 149 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 150 * if m is an M_PKTHDR mbuf. 151 */ 152 u_int 153 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 154 int compress_cid) 155 { 156 struct cstate *cs = comp->last_cs->cs_next; 157 u_int hlen = ip->ip_hl; 158 struct tcphdr *oth; 159 struct tcphdr *th; 160 u_int deltaS, deltaA; 161 u_int changes = 0; 162 u_char new_seq[16]; 163 u_char *cp = new_seq; 164 165 /* 166 * Bail if this is an IP fragment or if the TCP packet isn't 167 * `compressible' (i.e., ACK isn't set or some other control bit is 168 * set). (We assume that the caller has already made sure the 169 * packet is IP proto TCP). 170 */ 171 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 172 return (TYPE_IP); 173 174 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 175 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 176 return (TYPE_IP); 177 /* 178 * Packet is compressible -- we're going to send either a 179 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 180 * to locate (or create) the connection state. Special case the 181 * most recently used connection since it's most likely to be used 182 * again & we don't have to do any reordering if it's used. 183 */ 184 INCR(sls_packets) 185 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 186 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 187 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 188 /* 189 * Wasn't the first -- search for it. 190 * 191 * States are kept in a circularly linked list with 192 * last_cs pointing to the end of the list. The 193 * list is kept in lru order by moving a state to the 194 * head of the list whenever it is referenced. Since 195 * the list is short and, empirically, the connection 196 * we want is almost always near the front, we locate 197 * states via linear search. If we don't find a state 198 * for the datagram, the oldest state is (re-)used. 199 */ 200 struct cstate *lcs; 201 struct cstate *lastcs = comp->last_cs; 202 203 do { 204 lcs = cs; cs = cs->cs_next; 205 INCR(sls_searches) 206 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 207 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 208 && *(int32_t *)th == 209 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 210 goto found; 211 } while (cs != lastcs); 212 213 /* 214 * Didn't find it -- re-use oldest cstate. Send an 215 * uncompressed packet that tells the other side what 216 * connection number we're using for this conversation. 217 * Note that since the state list is circular, the oldest 218 * state points to the newest and we only need to set 219 * last_cs to update the lru linkage. 220 */ 221 INCR(sls_misses) 222 comp->last_cs = lcs; 223 hlen += th->th_off; 224 hlen <<= 2; 225 if (hlen > m->m_len) 226 return TYPE_IP; 227 goto uncompressed; 228 229 found: 230 /* 231 * Found it -- move to the front on the connection list. 232 */ 233 if (cs == lastcs) 234 comp->last_cs = lcs; 235 else { 236 lcs->cs_next = cs->cs_next; 237 cs->cs_next = lastcs->cs_next; 238 lastcs->cs_next = cs; 239 } 240 } 241 242 /* 243 * Make sure that only what we expect to change changed. The first 244 * line of the `if' checks the IP protocol version, header length & 245 * type of service. The 2nd line checks the "Don't fragment" bit. 246 * The 3rd line checks the time-to-live and protocol (the protocol 247 * check is unnecessary but costless). The 4th line checks the TCP 248 * header length. The 5th line checks IP options, if any. The 6th 249 * line checks TCP options, if any. If any of these things are 250 * different between the previous & current datagram, we send the 251 * current datagram `uncompressed'. 252 */ 253 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 254 deltaS = hlen; 255 hlen += th->th_off; 256 hlen <<= 2; 257 if (hlen > m->m_len) 258 return TYPE_IP; 259 260 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 261 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 262 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 263 th->th_off != oth->th_off || 264 (deltaS > 5 && 265 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 266 (th->th_off > 5 && 267 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 268 goto uncompressed; 269 270 /* 271 * Figure out which of the changing fields changed. The 272 * receiver expects changes in the order: urgent, window, 273 * ack, seq (the order minimizes the number of temporaries 274 * needed in this section of code). 275 */ 276 if (th->th_flags & TH_URG) { 277 deltaS = ntohs(th->th_urp); 278 ENCODEZ(deltaS); 279 changes |= NEW_U; 280 } else if (th->th_urp != oth->th_urp) 281 /* argh! URG not set but urp changed -- a sensible 282 * implementation should never do this but RFC793 283 * doesn't prohibit the change so we have to deal 284 * with it. */ 285 goto uncompressed; 286 287 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 288 if (deltaS) { 289 ENCODE(deltaS); 290 changes |= NEW_W; 291 } 292 293 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 294 if (deltaA) { 295 if (deltaA > 0xffff) 296 goto uncompressed; 297 ENCODE(deltaA); 298 changes |= NEW_A; 299 } 300 301 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 302 if (deltaS) { 303 if (deltaS > 0xffff) 304 goto uncompressed; 305 ENCODE(deltaS); 306 changes |= NEW_S; 307 } 308 309 switch(changes) { 310 case 0: 311 /* 312 * Nothing changed. If this packet contains data and the 313 * last one didn't, this is probably a data packet following 314 * an ack (normal on an interactive connection) and we send 315 * it compressed. Otherwise it's probably a retransmit, 316 * retransmitted ack or window probe. Send it uncompressed 317 * in case the other side missed the compressed version. 318 */ 319 if (ip->ip_len != cs->cs_ip.ip_len && 320 ntohs(cs->cs_ip.ip_len) == hlen) 321 break; 322 323 /* FALLTHROUGH */ 324 325 case SPECIAL_I: 326 case SPECIAL_D: 327 /* 328 * actual changes match one of our special case encodings -- 329 * send packet uncompressed. 330 */ 331 goto uncompressed; 332 333 case NEW_S|NEW_A: 334 if (deltaS == deltaA && 335 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 336 /* special case for echoed terminal traffic */ 337 changes = SPECIAL_I; 338 cp = new_seq; 339 } 340 break; 341 342 case NEW_S: 343 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 344 /* special case for data xfer */ 345 changes = SPECIAL_D; 346 cp = new_seq; 347 } 348 break; 349 } 350 351 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 352 if (deltaS != 1) { 353 ENCODEZ(deltaS); 354 changes |= NEW_I; 355 } 356 if (th->th_flags & TH_PUSH) 357 changes |= TCP_PUSH_BIT; 358 /* 359 * Grab the cksum before we overwrite it below. Then update our 360 * state with this packet's header. 361 */ 362 deltaA = ntohs(th->th_sum); 363 BCOPY(ip, &cs->cs_ip, hlen); 364 365 /* 366 * We want to use the original packet as our compressed packet. 367 * (cp - new_seq) is the number of bytes we need for compressed 368 * sequence numbers. In addition we need one byte for the change 369 * mask, one for the connection id and two for the tcp checksum. 370 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 371 * many bytes of the original packet to toss so subtract the two to 372 * get the new packet size. 373 */ 374 deltaS = cp - new_seq; 375 cp = (u_char *)ip; 376 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 377 comp->last_xmit = cs->cs_id; 378 hlen -= deltaS + 4; 379 cp += hlen; 380 *cp++ = changes | NEW_C; 381 *cp++ = cs->cs_id; 382 } else { 383 hlen -= deltaS + 3; 384 cp += hlen; 385 *cp++ = changes; 386 } 387 m->m_len -= hlen; 388 m->m_data += hlen; 389 *cp++ = deltaA >> 8; 390 *cp++ = deltaA; 391 BCOPY(new_seq, cp, deltaS); 392 INCR(sls_compressed) 393 return (TYPE_COMPRESSED_TCP); 394 395 /* 396 * Update connection state cs & send uncompressed packet ('uncompressed' 397 * means a regular ip/tcp packet but with the 'conversation id' we hope 398 * to use on future compressed packets in the protocol field). 399 */ 400 uncompressed: 401 BCOPY(ip, &cs->cs_ip, hlen); 402 ip->ip_p = cs->cs_id; 403 comp->last_xmit = cs->cs_id; 404 return (TYPE_UNCOMPRESSED_TCP); 405 } 406 407 int 408 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 409 { 410 u_char *hdr, *cp; 411 int hlen, vjlen; 412 413 cp = bufp? *bufp: NULL; 414 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 415 if (vjlen < 0) 416 return (0); /* error */ 417 if (vjlen == 0) 418 return (len); /* was uncompressed already */ 419 420 cp += vjlen; 421 len -= vjlen; 422 423 /* 424 * At this point, cp points to the first byte of data in the 425 * packet. If we're not aligned on a 4-byte boundary, copy the 426 * data down so the ip & tcp headers will be aligned. Then back up 427 * cp by the tcp/ip header length to make room for the reconstructed 428 * header (we assume the packet we were handed has enough space to 429 * prepend 128 bytes of header). 430 */ 431 if ((intptr_t)cp & 3) { 432 if (len > 0) 433 BCOPY(cp, ((intptr_t)cp &~ 3), len); 434 cp = (u_char *)((intptr_t)cp &~ 3); 435 } 436 cp -= hlen; 437 len += hlen; 438 BCOPY(hdr, cp, hlen); 439 440 *bufp = cp; 441 return (len); 442 } 443 444 /* 445 * Uncompress a packet of total length total_len. The first buflen 446 * bytes are at buf; this must include the entire (compressed or 447 * uncompressed) TCP/IP header. This procedure returns the length 448 * of the VJ header, with a pointer to the uncompressed IP header 449 * in *hdrp and its length in *hlenp. 450 */ 451 int 452 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 453 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 454 { 455 u_char *cp; 456 u_int hlen, changes; 457 struct tcphdr *th; 458 struct cstate *cs; 459 struct ip *ip; 460 u_int16_t *bp; 461 u_int vjlen; 462 463 switch (type) { 464 case TYPE_UNCOMPRESSED_TCP: 465 ip = (struct ip *) buf; 466 if (ip->ip_p >= MAX_STATES) 467 goto bad; 468 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 469 comp->flags &=~ SLF_TOSS; 470 ip->ip_p = IPPROTO_TCP; 471 /* 472 * Calculate the size of the TCP/IP header and make sure that 473 * we don't overflow the space we have available for it. 474 */ 475 hlen = ip->ip_hl << 2; 476 if (hlen + sizeof(struct tcphdr) > buflen) 477 goto bad; 478 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 479 if (hlen > MAX_HDR || hlen > buflen) 480 goto bad; 481 BCOPY(ip, &cs->cs_ip, hlen); 482 cs->cs_hlen = hlen; 483 INCR(sls_uncompressedin) 484 *hdrp = (u_char *) &cs->cs_ip; 485 *hlenp = hlen; 486 return (0); 487 488 default: 489 goto bad; 490 491 case TYPE_COMPRESSED_TCP: 492 break; 493 } 494 /* We've got a compressed packet. */ 495 INCR(sls_compressedin) 496 cp = buf; 497 changes = *cp++; 498 if (changes & NEW_C) { 499 /* Make sure the state index is in range, then grab the state. 500 * If we have a good state index, clear the 'discard' flag. */ 501 if (*cp >= MAX_STATES) 502 goto bad; 503 504 comp->flags &=~ SLF_TOSS; 505 comp->last_recv = *cp++; 506 } else { 507 /* this packet has an implicit state index. If we've 508 * had a line error since the last time we got an 509 * explicit state index, we have to toss the packet. */ 510 if (comp->flags & SLF_TOSS) { 511 INCR(sls_tossed) 512 return (-1); 513 } 514 } 515 cs = &comp->rstate[comp->last_recv]; 516 hlen = cs->cs_ip.ip_hl << 2; 517 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 518 th->th_sum = htons((*cp << 8) | cp[1]); 519 cp += 2; 520 if (changes & TCP_PUSH_BIT) 521 th->th_flags |= TH_PUSH; 522 else 523 th->th_flags &=~ TH_PUSH; 524 525 switch (changes & SPECIALS_MASK) { 526 case SPECIAL_I: 527 { 528 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 529 th->th_ack = htonl(ntohl(th->th_ack) + i); 530 th->th_seq = htonl(ntohl(th->th_seq) + i); 531 } 532 break; 533 534 case SPECIAL_D: 535 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 536 - cs->cs_hlen); 537 break; 538 539 default: 540 if (changes & NEW_U) { 541 th->th_flags |= TH_URG; 542 DECODEU(th->th_urp) 543 } else 544 th->th_flags &=~ TH_URG; 545 if (changes & NEW_W) 546 DECODES(th->th_win) 547 if (changes & NEW_A) 548 DECODEL(th->th_ack) 549 if (changes & NEW_S) 550 DECODEL(th->th_seq) 551 break; 552 } 553 if (changes & NEW_I) { 554 DECODES(cs->cs_ip.ip_id) 555 } else 556 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 557 558 /* 559 * At this point, cp points to the first byte of data in the 560 * packet. Fill in the IP total length and update the IP 561 * header checksum. 562 */ 563 vjlen = cp - buf; 564 buflen -= vjlen; 565 if (buflen < 0) 566 /* we must have dropped some characters (crc should detect 567 * this but the old slip framing won't) */ 568 goto bad; 569 570 total_len += cs->cs_hlen - vjlen; 571 cs->cs_ip.ip_len = htons(total_len); 572 573 /* recompute the ip header checksum */ 574 bp = (u_int16_t *) &cs->cs_ip; 575 cs->cs_ip.ip_sum = 0; 576 for (changes = 0; hlen > 0; hlen -= 2) 577 changes += *bp++; 578 changes = (changes & 0xffff) + (changes >> 16); 579 changes = (changes & 0xffff) + (changes >> 16); 580 cs->cs_ip.ip_sum = ~ changes; 581 582 *hdrp = (u_char *) &cs->cs_ip; 583 *hlenp = cs->cs_hlen; 584 return vjlen; 585 586 bad: 587 comp->flags |= SLF_TOSS; 588 INCR(sls_errorin) 589 return (-1); 590 } 591