1 /* $NetBSD: slcompress.c,v 1.42 2024/09/02 18:19:14 andvar 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 uncompress tcp packets (for transmission 37 * over low speed serial lines. 38 * 39 * Van Jacobson (van (at) 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 1.42 2024/09/02 18:19:14 andvar Exp $"); 45 46 #ifdef _KERNEL_OPT 47 #include "opt_inet.h" 48 #endif 49 50 #ifdef INET 51 #include <sys/param.h> 52 #include <sys/mbuf.h> 53 #include <sys/systm.h> 54 #include <sys/module.h> 55 56 #include <netinet/in.h> 57 #include <netinet/in_systm.h> 58 #include <netinet/ip.h> 59 #include <netinet/tcp.h> 60 61 #include <net/slcompress.h> 62 63 #ifndef SL_NO_STATS 64 #define INCR(counter) ++comp->counter; 65 #else 66 #define INCR(counter) 67 #endif 68 69 70 void 71 sl_compress_init(struct slcompress *comp) 72 { 73 u_int i; 74 struct cstate *tstate = comp->tstate; 75 76 memset(comp, 0, sizeof(*comp)); 77 for (i = MAX_STATES - 1; 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_STATES - 1]; 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 90 /* 91 * Like sl_compress_init, but we get to specify the maximum connection 92 * ID to use on transmission. 93 */ 94 void 95 sl_compress_setup(struct slcompress *comp, int max_state) 96 { 97 u_int i; 98 struct cstate *tstate = comp->tstate; 99 100 if (max_state == -1) { 101 max_state = MAX_STATES - 1; 102 memset(comp, 0, sizeof(*comp)); 103 } else { 104 /* Don't reset statistics */ 105 memset(comp->tstate, 0, sizeof(comp->tstate)); 106 memset(comp->rstate, 0, sizeof(comp->rstate)); 107 } 108 for (i = max_state; i > 0; --i) { 109 tstate[i].cs_id = i; 110 tstate[i].cs_next = &tstate[i - 1]; 111 } 112 tstate[0].cs_next = &tstate[max_state]; 113 tstate[0].cs_id = 0; 114 comp->last_cs = &tstate[0]; 115 comp->last_recv = 255; 116 comp->last_xmit = 255; 117 comp->flags = SLF_TOSS; 118 } 119 120 121 /* 122 * ENCODE encodes a number that is known to be non-zero. ENCODEZ checks for 123 * zero (since zero has to be encoded in the long, 3 byte form). 124 */ 125 #define ENCODE(n) { \ 126 if ((uint16_t)(n) >= 256) { \ 127 *cp++ = 0; \ 128 cp[1] = (n); \ 129 cp[0] = (n) >> 8; \ 130 cp += 2; \ 131 } else { \ 132 *cp++ = (n); \ 133 } \ 134 } 135 #define ENCODEZ(n) { \ 136 if ((uint16_t)(n) >= 256 || (uint16_t)(n) == 0) { \ 137 *cp++ = 0; \ 138 cp[1] = (n); \ 139 cp[0] = (n) >> 8; \ 140 cp += 2; \ 141 } else { \ 142 *cp++ = (n); \ 143 } \ 144 } 145 146 #define DECODEL(f) { \ 147 if (*cp == 0) {\ 148 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 149 cp += 3; \ 150 } else { \ 151 (f) = htonl(ntohl(f) + (uint32_t)*cp++); \ 152 } \ 153 } 154 155 #define DECODES(f) { \ 156 if (*cp == 0) {\ 157 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 158 cp += 3; \ 159 } else { \ 160 (f) = htons(ntohs(f) + (uint32_t)*cp++); \ 161 } \ 162 } 163 164 #define DECODEU(f) { \ 165 if (*cp == 0) {\ 166 (f) = htons((cp[1] << 8) | cp[2]); \ 167 cp += 3; \ 168 } else { \ 169 (f) = htons((uint32_t)*cp++); \ 170 } \ 171 } 172 173 u_int 174 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 175 int compress_cid) 176 { 177 struct cstate *cs = comp->last_cs->cs_next; 178 u_int hlen = ip->ip_hl; 179 struct tcphdr *oth; 180 struct tcphdr *th; 181 u_int deltaS, deltaA; 182 u_int changes = 0; 183 u_char new_seq[16]; 184 u_char *cp = new_seq; 185 186 /* 187 * Bail if this is an IP fragment or if the TCP packet isn't 188 * `compressible' (i.e., ACK isn't set or some other control bit is 189 * set). (We assume that the caller has already made sure the 190 * packet is IP proto TCP). 191 */ 192 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 193 return TYPE_IP; 194 195 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 196 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 197 return TYPE_IP; 198 /* 199 * Packet is compressible -- we're going to send either a 200 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 201 * to locate (or create) the connection state. Special case the 202 * most recently used connection since it's most likely to be used 203 * again & we don't have to do any reordering if it's used. 204 */ 205 INCR(sls_packets) 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 != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 209 /* 210 * Wasn't the first -- search for it. 211 * 212 * States are kept in a circularly linked list with last_cs 213 * pointing to the end of the list. The list is kept in lru 214 * order by moving a state to the head of the list whenever it 215 * is referenced. Since the list is short and, empirically, 216 * the connection we want is almost always near the front, we 217 * locate 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 /* Found it -- move to the front on the connection list. */ 251 if (cs == lastcs) 252 comp->last_cs = lcs; 253 else { 254 lcs->cs_next = cs->cs_next; 255 cs->cs_next = lastcs->cs_next; 256 lastcs->cs_next = cs; 257 } 258 } 259 260 /* 261 * Make sure that only what we expect to change changed. The first 262 * line of the `if' checks the IP protocol version, header length & 263 * type of service. The 2nd line checks the "Don't fragment" bit. 264 * The 3rd line checks the time-to-live and protocol (the protocol 265 * check is unnecessary but costless). The 4th line checks the TCP 266 * header length. The 5th line checks IP options, if any. The 6th 267 * line checks TCP options, if any. If any of these things are 268 * different between the previous & current datagram, we send the 269 * current datagram `uncompressed'. 270 */ 271 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 272 deltaS = hlen; 273 hlen += th->th_off; 274 hlen <<= 2; 275 if (hlen > m->m_len) 276 return TYPE_IP; 277 278 if (((uint16_t *)ip)[0] != ((uint16_t *)&cs->cs_ip)[0] || 279 ((uint16_t *)ip)[3] != ((uint16_t *)&cs->cs_ip)[3] || 280 ((uint16_t *)ip)[4] != ((uint16_t *)&cs->cs_ip)[4] || 281 th->th_off != oth->th_off || 282 (deltaS > 5 && 283 memcmp(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 284 (th->th_off > 5 && 285 memcmp(th + 1, oth + 1, (th->th_off - 5) << 2))) 286 goto uncompressed; 287 288 /* 289 * Figure out which of the changing fields changed. The receiver 290 * expects changes in the order: urgent, window, ack, seq (the order 291 * minimizes the number of temporaries needed in this section of code). 292 */ 293 if (th->th_flags & TH_URG) { 294 deltaS = ntohs(th->th_urp); 295 ENCODEZ(deltaS); 296 changes |= NEW_U; 297 } else if (th->th_urp != oth->th_urp) 298 /* 299 * argh! URG not set but urp changed -- a sensible 300 * implementation should never do this but RFC793 doesn't 301 * prohibit the change so we have to deal with it. 302 */ 303 goto uncompressed; 304 305 deltaS = (uint16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 306 if (deltaS) { 307 ENCODE(deltaS); 308 changes |= NEW_W; 309 } 310 311 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 312 if (deltaA) { 313 if (deltaA > 0xffff) 314 goto uncompressed; 315 ENCODE(deltaA); 316 changes |= NEW_A; 317 } 318 319 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 320 if (deltaS) { 321 if (deltaS > 0xffff) 322 goto uncompressed; 323 ENCODE(deltaS); 324 changes |= NEW_S; 325 } 326 327 switch (changes) { 328 case 0: 329 /* 330 * Nothing changed. If this packet contains data and the 331 * last one didn't, this is probably a data packet following 332 * an ack (normal on an interactive connection) and we send 333 * it compressed. Otherwise it's probably a retransmit, 334 * retransmitted ack or window probe. Send it uncompressed 335 * in case the other side missed the compressed version. 336 */ 337 if (ip->ip_len != cs->cs_ip.ip_len && 338 ntohs(cs->cs_ip.ip_len) == hlen) 339 break; 340 341 /* FALLTHROUGH */ 342 343 case SPECIAL_I: 344 case SPECIAL_D: 345 /* 346 * actual changes match one of our special case encodings -- 347 * send packet uncompressed. 348 */ 349 goto uncompressed; 350 351 case NEW_S|NEW_A: 352 if (deltaS == deltaA && 353 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 354 /* special case for echoed terminal traffic */ 355 changes = SPECIAL_I; 356 cp = new_seq; 357 } 358 break; 359 360 case NEW_S: 361 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 362 /* special case for data xfer */ 363 changes = SPECIAL_D; 364 cp = new_seq; 365 } 366 break; 367 } 368 369 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 370 if (deltaS != 1) { 371 ENCODEZ(deltaS); 372 changes |= NEW_I; 373 } 374 if (th->th_flags & TH_PUSH) 375 changes |= TCP_PUSH_BIT; 376 /* 377 * Grab the cksum before we overwrite it below. Then update our 378 * state with this packet's header. 379 */ 380 deltaA = ntohs(th->th_sum); 381 memcpy(&cs->cs_ip, ip, hlen); 382 383 /* 384 * We want to use the original packet as our compressed packet. 385 * (cp - new_seq) is the number of bytes we need for compressed 386 * sequence numbers. In addition we need one byte for the change 387 * mask, one for the connection id and two for the tcp checksum. 388 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 389 * many bytes of the original packet to toss so subtract the two to 390 * get the new packet size. 391 */ 392 deltaS = cp - new_seq; 393 cp = (u_char *)ip; 394 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 395 comp->last_xmit = cs->cs_id; 396 hlen -= deltaS + 4; 397 cp += hlen; 398 *cp++ = changes | NEW_C; 399 *cp++ = cs->cs_id; 400 } else { 401 hlen -= deltaS + 3; 402 cp += hlen; 403 *cp++ = changes; 404 } 405 m->m_len -= hlen; 406 m->m_data += hlen; 407 *cp++ = deltaA >> 8; 408 *cp++ = deltaA; 409 memcpy(cp, new_seq, deltaS); 410 INCR(sls_compressed) 411 return TYPE_COMPRESSED_TCP; 412 413 /* 414 * Update connection state cs & send uncompressed packet 415 * ('uncompressed' means a regular ip/tcp packet but with the 416 * 'conversation id' we hope to use on future compressed packets in the 417 * protocol field). 418 */ 419 uncompressed: 420 memcpy(&cs->cs_ip, ip, hlen); 421 ip->ip_p = cs->cs_id; 422 comp->last_xmit = cs->cs_id; 423 return TYPE_UNCOMPRESSED_TCP; 424 } 425 426 427 int 428 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 429 { 430 u_char *hdr, *cp; 431 int vjlen; 432 u_int hlen; 433 434 cp = bufp ? *bufp : NULL; 435 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 436 if (vjlen < 0) 437 return 0; /* error */ 438 if (vjlen == 0) 439 return len; /* was uncompressed already */ 440 441 cp += vjlen; 442 len -= vjlen; 443 444 /* 445 * At this point, cp points to the first byte of data in the 446 * packet. If we're not aligned on a 4-byte boundary, copy the 447 * data down so the ip & tcp headers will be aligned. Then back up 448 * cp by the tcp/ip header length to make room for the reconstructed 449 * header (we assume the packet we were handed has enough space to 450 * prepend 128 bytes of header). 451 */ 452 if ((long)cp & 3) { 453 if (len > 0) 454 memmove((void *)((long)cp &~ 3), cp, len); 455 cp = (u_char *)((long)cp &~ 3); 456 } 457 cp -= hlen; 458 len += hlen; 459 memcpy(cp, hdr, hlen); 460 461 *bufp = cp; 462 return len; 463 } 464 465 /* 466 * Uncompress a packet of total length total_len. The first buflen bytes are 467 * at buf; this must include the entire (compressed or uncompressed) TCP/IP 468 * header. This procedure returns the length of the VJ header, with a pointer 469 * to the uncompressed IP header in *hdrp and its length in *hlenp. 470 */ 471 int 472 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 473 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 474 { 475 u_char *cp; 476 u_int hlen, changes; 477 struct tcphdr *th; 478 struct cstate *cs; 479 struct ip *ip; 480 uint16_t *bp; 481 u_int vjlen; 482 483 switch (type) { 484 485 case TYPE_UNCOMPRESSED_TCP: 486 if (buf == NULL) 487 goto bad; 488 ip = (struct ip *) buf; 489 if (ip->ip_p >= MAX_STATES) 490 goto bad; 491 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 492 comp->flags &=~ SLF_TOSS; 493 ip->ip_p = IPPROTO_TCP; 494 /* 495 * Calculate the size of the TCP/IP header and make sure that 496 * we don't overflow the space we have available for it. 497 */ 498 hlen = ip->ip_hl << 2; 499 if (hlen + sizeof(struct tcphdr) > buflen) 500 goto bad; 501 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 502 if (hlen > MAX_HDR || hlen > buflen) 503 goto bad; 504 memcpy(&cs->cs_ip, ip, hlen); 505 cs->cs_hlen = hlen; 506 INCR(sls_uncompressedin) 507 *hdrp = (u_char *)&cs->cs_ip; 508 *hlenp = hlen; 509 return 0; 510 511 default: 512 goto bad; 513 514 case TYPE_COMPRESSED_TCP: 515 break; 516 } 517 /* We've got a compressed packet. */ 518 INCR(sls_compressedin) 519 if (buf == NULL) 520 goto bad; 521 cp = buf; 522 changes = *cp++; 523 if (changes & NEW_C) { 524 /* 525 * Make sure the state index is in range, then grab the state. 526 * If we have a good state index, clear the 'discard' flag. 527 */ 528 if (*cp >= MAX_STATES) 529 goto bad; 530 531 comp->flags &=~ SLF_TOSS; 532 comp->last_recv = *cp++; 533 } else { 534 /* 535 * this packet has an implicit state index. If we've had a 536 * line error since the last time we got an explicit state 537 * index, we have to toss the packet. 538 */ 539 if (comp->flags & SLF_TOSS) { 540 INCR(sls_tossed) 541 return -1; 542 } 543 } 544 cs = &comp->rstate[comp->last_recv]; 545 hlen = cs->cs_ip.ip_hl << 2; 546 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 547 th->th_sum = htons((*cp << 8) | cp[1]); 548 cp += 2; 549 if (changes & TCP_PUSH_BIT) 550 th->th_flags |= TH_PUSH; 551 else 552 th->th_flags &=~ TH_PUSH; 553 554 switch (changes & SPECIALS_MASK) { 555 case SPECIAL_I: 556 { 557 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 558 th->th_ack = htonl(ntohl(th->th_ack) + i); 559 th->th_seq = htonl(ntohl(th->th_seq) + i); 560 } 561 break; 562 563 case SPECIAL_D: 564 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 565 - cs->cs_hlen); 566 break; 567 568 default: 569 if (changes & NEW_U) { 570 th->th_flags |= TH_URG; 571 DECODEU(th->th_urp) 572 } else 573 th->th_flags &=~ TH_URG; 574 if (changes & NEW_W) 575 DECODES(th->th_win) 576 if (changes & NEW_A) 577 DECODEL(th->th_ack) 578 if (changes & NEW_S) 579 DECODEL(th->th_seq) 580 break; 581 } 582 if (changes & NEW_I) { 583 DECODES(cs->cs_ip.ip_id) 584 } else 585 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 586 587 /* 588 * At this point, cp points to the first byte of data in the packet. 589 * Fill in the IP total length and update the IP header checksum. 590 */ 591 vjlen = cp - buf; 592 buflen -= vjlen; 593 if (buflen < 0) 594 /* 595 * We must have dropped some characters (crc should detect 596 * this but the old slip framing won't) 597 */ 598 goto bad; 599 600 total_len += cs->cs_hlen - vjlen; 601 cs->cs_ip.ip_len = htons(total_len); 602 603 /* Recompute the ip header checksum */ 604 bp = (uint16_t *)&cs->cs_ip; 605 cs->cs_ip.ip_sum = 0; 606 for (changes = 0; hlen > 0; hlen -= 2) 607 changes += *bp++; 608 changes = (changes & 0xffff) + (changes >> 16); 609 changes = (changes & 0xffff) + (changes >> 16); 610 cs->cs_ip.ip_sum = ~ changes; 611 612 *hdrp = (u_char *)&cs->cs_ip; 613 *hlenp = cs->cs_hlen; 614 return vjlen; 615 616 bad: 617 comp->flags |= SLF_TOSS; 618 INCR(sls_errorin) 619 return -1; 620 } 621 #endif 622 623 MODULE(MODULE_CLASS_MISC, slcompress, NULL); 624 625 static int 626 slcompress_modcmd(modcmd_t cmd, void *arg) 627 { 628 switch (cmd) { 629 case MODULE_CMD_INIT: 630 case MODULE_CMD_FINI: 631 #ifdef INET 632 return 0; 633 #endif 634 case MODULE_CMD_STAT: 635 case MODULE_CMD_AUTOUNLOAD: 636 default: 637 return ENOTTY; 638 } 639 } 640
Indexes created Sun Sep 21 15:09:59 GMT 2025