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