Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/net/slcompress.c
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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 * $FreeBSD$ 33 */ 34 35 /* 36 * Routines to compress and uncompess tcp packets (for transmission 37 * over low speed serial lines. 38 * 39 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 40 * - Initial distribution. 41 * 42 */ 43 44 #include <sys/param.h> 45 #include <sys/mbuf.h> 46 #include <sys/systm.h> 47 48 #include <netinet/in.h> 49 #include <netinet/in_systm.h> 50 #include <netinet/ip.h> 51 #include <netinet/tcp.h> 52 53 #include <net/slcompress.h> 54 55 #ifndef SL_NO_STATS 56 #define INCR(counter) ++comp->counter; 57 #else 58 #define INCR(counter) 59 #endif 60 61 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n)) 62 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n)) 63 64 void 65 sl_compress_init(struct slcompress *comp, int max_state) 66 { 67 u_int i; 68 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(struct mbuf *m, struct ip *ip, struct slcompress *comp, 156 int compress_cid) 157 { 158 struct cstate *cs = comp->last_cs->cs_next; 159 u_int hlen = ip->ip_hl; 160 struct tcphdr *oth; 161 struct tcphdr *th; 162 u_int deltaS, deltaA; 163 u_int changes = 0; 164 u_char new_seq[16]; 165 u_char *cp = new_seq; 166 167 /* 168 * Bail if this is an IP fragment or if the TCP packet isn't 169 * `compressible' (i.e., ACK isn't set or some other control bit is 170 * set). (We assume that the caller has already made sure the 171 * packet is IP proto TCP). 172 */ 173 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 174 return (TYPE_IP); 175 176 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 177 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 178 return (TYPE_IP); 179 /* 180 * Packet is compressible -- we're going to send either a 181 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 182 * to locate (or create) the connection state. Special case the 183 * most recently used connection since it's most likely to be used 184 * again & we don't have to do any reordering if it's used. 185 */ 186 INCR(sls_packets) 187 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 188 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 189 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 190 /* 191 * Wasn't the first -- search for it. 192 * 193 * States are kept in a circularly linked list with 194 * last_cs pointing to the end of the list. The 195 * list is kept in lru order by moving a state to the 196 * head of the list whenever it is referenced. Since 197 * the list is short and, empirically, the connection 198 * we want is almost always near the front, we locate 199 * states via linear search. If we don't find a state 200 * for the datagram, the oldest state is (re-)used. 201 */ 202 struct cstate *lcs; 203 struct cstate *lastcs = comp->last_cs; 204 205 do { 206 lcs = cs; cs = cs->cs_next; 207 INCR(sls_searches) 208 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 209 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 210 && *(int32_t *)th == 211 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 212 goto found; 213 } while (cs != lastcs); 214 215 /* 216 * Didn't find it -- re-use oldest cstate. Send an 217 * uncompressed packet that tells the other side what 218 * connection number we're using for this conversation. 219 * Note that since the state list is circular, the oldest 220 * state points to the newest and we only need to set 221 * last_cs to update the lru linkage. 222 */ 223 INCR(sls_misses) 224 comp->last_cs = lcs; 225 hlen += th->th_off; 226 hlen <<= 2; 227 if (hlen > m->m_len) 228 return TYPE_IP; 229 goto uncompressed; 230 231 found: 232 /* 233 * Found it -- move to the front on the connection list. 234 */ 235 if (cs == lastcs) 236 comp->last_cs = lcs; 237 else { 238 lcs->cs_next = cs->cs_next; 239 cs->cs_next = lastcs->cs_next; 240 lastcs->cs_next = cs; 241 } 242 } 243 244 /* 245 * Make sure that only what we expect to change changed. The first 246 * line of the `if' checks the IP protocol version, header length & 247 * type of service. The 2nd line checks the "Don't fragment" bit. 248 * The 3rd line checks the time-to-live and protocol (the protocol 249 * check is unnecessary but costless). The 4th line checks the TCP 250 * header length. The 5th line checks IP options, if any. The 6th 251 * line checks TCP options, if any. If any of these things are 252 * different between the previous & current datagram, we send the 253 * current datagram `uncompressed'. 254 */ 255 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 256 deltaS = hlen; 257 hlen += th->th_off; 258 hlen <<= 2; 259 if (hlen > m->m_len) 260 return TYPE_IP; 261 262 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 263 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 264 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 265 th->th_off != oth->th_off || 266 (deltaS > 5 && 267 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 268 (th->th_off > 5 && 269 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 270 goto uncompressed; 271 272 /* 273 * Figure out which of the changing fields changed. The 274 * receiver expects changes in the order: urgent, window, 275 * ack, seq (the order minimizes the number of temporaries 276 * needed in this section of code). 277 */ 278 if (th->th_flags & TH_URG) { 279 deltaS = ntohs(th->th_urp); 280 ENCODEZ(deltaS); 281 changes |= NEW_U; 282 } else if (th->th_urp != oth->th_urp) 283 /* argh! URG not set but urp changed -- a sensible 284 * implementation should never do this but RFC793 285 * doesn't prohibit the change so we have to deal 286 * with it. */ 287 goto uncompressed; 288 289 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 290 if (deltaS) { 291 ENCODE(deltaS); 292 changes |= NEW_W; 293 } 294 295 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 296 if (deltaA) { 297 if (deltaA > 0xffff) 298 goto uncompressed; 299 ENCODE(deltaA); 300 changes |= NEW_A; 301 } 302 303 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 304 if (deltaS) { 305 if (deltaS > 0xffff) 306 goto uncompressed; 307 ENCODE(deltaS); 308 changes |= NEW_S; 309 } 310 311 switch(changes) { 312 313 case 0: 314 /* 315 * Nothing changed. If this packet contains data and the 316 * last one didn't, this is probably a data packet following 317 * an ack (normal on an interactive connection) and we send 318 * it compressed. Otherwise it's probably a retransmit, 319 * retransmitted ack or window probe. Send it uncompressed 320 * in case the other side missed the compressed version. 321 */ 322 if (ip->ip_len != cs->cs_ip.ip_len && 323 ntohs(cs->cs_ip.ip_len) == hlen) 324 break; 325 326 /* FALLTHROUGH */ 327 328 case SPECIAL_I: 329 case SPECIAL_D: 330 /* 331 * actual changes match one of our special case encodings -- 332 * send packet uncompressed. 333 */ 334 goto uncompressed; 335 336 case NEW_S|NEW_A: 337 if (deltaS == deltaA && 338 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 339 /* special case for echoed terminal traffic */ 340 changes = SPECIAL_I; 341 cp = new_seq; 342 } 343 break; 344 345 case NEW_S: 346 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 347 /* special case for data xfer */ 348 changes = SPECIAL_D; 349 cp = new_seq; 350 } 351 break; 352 } 353 354 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 355 if (deltaS != 1) { 356 ENCODEZ(deltaS); 357 changes |= NEW_I; 358 } 359 if (th->th_flags & TH_PUSH) 360 changes |= TCP_PUSH_BIT; 361 /* 362 * Grab the cksum before we overwrite it below. Then update our 363 * state with this packet's header. 364 */ 365 deltaA = ntohs(th->th_sum); 366 BCOPY(ip, &cs->cs_ip, hlen); 367 368 /* 369 * We want to use the original packet as our compressed packet. 370 * (cp - new_seq) is the number of bytes we need for compressed 371 * sequence numbers. In addition we need one byte for the change 372 * mask, one for the connection id and two for the tcp checksum. 373 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 374 * many bytes of the original packet to toss so subtract the two to 375 * get the new packet size. 376 */ 377 deltaS = cp - new_seq; 378 cp = (u_char *)ip; 379 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 380 comp->last_xmit = cs->cs_id; 381 hlen -= deltaS + 4; 382 cp += hlen; 383 *cp++ = changes | NEW_C; 384 *cp++ = cs->cs_id; 385 } else { 386 hlen -= deltaS + 3; 387 cp += hlen; 388 *cp++ = changes; 389 } 390 m->m_len -= hlen; 391 m->m_data += hlen; 392 *cp++ = deltaA >> 8; 393 *cp++ = deltaA; 394 BCOPY(new_seq, cp, deltaS); 395 INCR(sls_compressed) 396 return (TYPE_COMPRESSED_TCP); 397 398 /* 399 * Update connection state cs & send uncompressed packet ('uncompressed' 400 * means a regular ip/tcp packet but with the 'conversation id' we hope 401 * to use on future compressed packets in the protocol field). 402 */ 403 uncompressed: 404 BCOPY(ip, &cs->cs_ip, hlen); 405 ip->ip_p = cs->cs_id; 406 comp->last_xmit = cs->cs_id; 407 return (TYPE_UNCOMPRESSED_TCP); 408 } 409 410 411 int 412 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 413 { 414 u_char *hdr, *cp; 415 int hlen, vjlen; 416 417 cp = bufp? *bufp: NULL; 418 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 419 if (vjlen < 0) 420 return (0); /* error */ 421 if (vjlen == 0) 422 return (len); /* was uncompressed already */ 423 424 cp += vjlen; 425 len -= vjlen; 426 427 /* 428 * At this point, cp points to the first byte of data in the 429 * packet. If we're not aligned on a 4-byte boundary, copy the 430 * data down so the ip & tcp headers will be aligned. Then back up 431 * cp by the tcp/ip header length to make room for the reconstructed 432 * header (we assume the packet we were handed has enough space to 433 * prepend 128 bytes of header). 434 */ 435 if ((intptr_t)cp & 3) { 436 if (len > 0) 437 BCOPY(cp, ((intptr_t)cp &~ 3), len); 438 cp = (u_char *)((intptr_t)cp &~ 3); 439 } 440 cp -= hlen; 441 len += hlen; 442 BCOPY(hdr, cp, hlen); 443 444 *bufp = cp; 445 return (len); 446 } 447 448 /* 449 * Uncompress a packet of total length total_len. The first buflen 450 * bytes are at buf; this must include the entire (compressed or 451 * uncompressed) TCP/IP header. This procedure returns the length 452 * of the VJ header, with a pointer to the uncompressed IP header 453 * in *hdrp and its length in *hlenp. 454 */ 455 int 456 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 457 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 458 { 459 u_char *cp; 460 u_int hlen, changes; 461 struct tcphdr *th; 462 struct cstate *cs; 463 struct ip *ip; 464 u_int16_t *bp; 465 u_int vjlen; 466 467 switch (type) { 468 469 case TYPE_UNCOMPRESSED_TCP: 470 ip = (struct ip *) buf; 471 if (ip->ip_p >= MAX_STATES) 472 goto bad; 473 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 474 comp->flags &=~ SLF_TOSS; 475 ip->ip_p = IPPROTO_TCP; 476 /* 477 * Calculate the size of the TCP/IP header and make sure that 478 * we don't overflow the space we have available for it. 479 */ 480 hlen = ip->ip_hl << 2; 481 if (hlen + sizeof(struct tcphdr) > buflen) 482 goto bad; 483 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 484 if (hlen > MAX_HDR || hlen > buflen) 485 goto bad; 486 BCOPY(ip, &cs->cs_ip, hlen); 487 cs->cs_hlen = hlen; 488 INCR(sls_uncompressedin) 489 *hdrp = (u_char *) &cs->cs_ip; 490 *hlenp = hlen; 491 return (0); 492 493 default: 494 goto bad; 495 496 case TYPE_COMPRESSED_TCP: 497 break; 498 } 499 /* We've got a compressed packet. */ 500 INCR(sls_compressedin) 501 cp = buf; 502 changes = *cp++; 503 if (changes & NEW_C) { 504 /* Make sure the state index is in range, then grab the state. 505 * If we have a good state index, clear the 'discard' flag. */ 506 if (*cp >= MAX_STATES) 507 goto bad; 508 509 comp->flags &=~ SLF_TOSS; 510 comp->last_recv = *cp++; 511 } else { 512 /* this packet has an implicit state index. If we've 513 * had a line error since the last time we got an 514 * explicit state index, we have to toss the packet. */ 515 if (comp->flags & SLF_TOSS) { 516 INCR(sls_tossed) 517 return (-1); 518 } 519 } 520 cs = &comp->rstate[comp->last_recv]; 521 hlen = cs->cs_ip.ip_hl << 2; 522 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 523 th->th_sum = htons((*cp << 8) | cp[1]); 524 cp += 2; 525 if (changes & TCP_PUSH_BIT) 526 th->th_flags |= TH_PUSH; 527 else 528 th->th_flags &=~ TH_PUSH; 529 530 switch (changes & SPECIALS_MASK) { 531 case SPECIAL_I: 532 { 533 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 534 th->th_ack = htonl(ntohl(th->th_ack) + i); 535 th->th_seq = htonl(ntohl(th->th_seq) + i); 536 } 537 break; 538 539 case SPECIAL_D: 540 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 541 - cs->cs_hlen); 542 break; 543 544 default: 545 if (changes & NEW_U) { 546 th->th_flags |= TH_URG; 547 DECODEU(th->th_urp) 548 } else 549 th->th_flags &=~ TH_URG; 550 if (changes & NEW_W) 551 DECODES(th->th_win) 552 if (changes & NEW_A) 553 DECODEL(th->th_ack) 554 if (changes & NEW_S) 555 DECODEL(th->th_seq) 556 break; 557 } 558 if (changes & NEW_I) { 559 DECODES(cs->cs_ip.ip_id) 560 } else 561 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 562 563 /* 564 * At this point, cp points to the first byte of data in the 565 * packet. Fill in the IP total length and update the IP 566 * header checksum. 567 */ 568 vjlen = cp - buf; 569 buflen -= vjlen; 570 if (buflen < 0) 571 /* we must have dropped some characters (crc should detect 572 * this but the old slip framing won't) */ 573 goto bad; 574 575 total_len += cs->cs_hlen - vjlen; 576 cs->cs_ip.ip_len = htons(total_len); 577 578 /* recompute the ip header checksum */ 579 bp = (u_int16_t *) &cs->cs_ip; 580 cs->cs_ip.ip_sum = 0; 581 for (changes = 0; hlen > 0; hlen -= 2) 582 changes += *bp++; 583 changes = (changes & 0xffff) + (changes >> 16); 584 changes = (changes & 0xffff) + (changes >> 16); 585 cs->cs_ip.ip_sum = ~ changes; 586 587 *hdrp = (u_char *) &cs->cs_ip; 588 *hlenp = cs->cs_hlen; 589 return vjlen; 590 591 bad: 592 comp->flags |= SLF_TOSS; 593 INCR(sls_errorin) 594 return (-1); 595 }
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