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. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 30 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $ 31 * $DragonFly: src/sys/net/ppp_layer/slcompress.c,v 1.5 2006/01/14 11:05:18 swildner Exp $ 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((char *)(p1), (char *)(p2), (int)(n)) 61 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(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 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) { 311 312 case 0: 313 /* 314 * Nothing changed. If this packet contains data and the 315 * last one didn't, this is probably a data packet following 316 * an ack (normal on an interactive connection) and we send 317 * it compressed. Otherwise it's probably a retransmit, 318 * retransmitted ack or window probe. Send it uncompressed 319 * in case the other side missed the compressed version. 320 */ 321 if (ip->ip_len != cs->cs_ip.ip_len && 322 ntohs(cs->cs_ip.ip_len) == hlen) 323 { 324 break; 325 } 326 327 /* (fall through) */ 328 329 case SPECIAL_I: 330 case SPECIAL_D: 331 /* 332 * actual changes match one of our special case encodings -- 333 * send packet uncompressed. 334 */ 335 goto uncompressed; 336 337 case NEW_S|NEW_A: 338 if (deltaS == deltaA && 339 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 340 /* special case for echoed terminal traffic */ 341 changes = SPECIAL_I; 342 cp = new_seq; 343 } 344 break; 345 346 case NEW_S: 347 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 348 /* special case for data xfer */ 349 changes = SPECIAL_D; 350 cp = new_seq; 351 } 352 break; 353 } 354 355 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 356 if (deltaS != 1) { 357 ENCODEZ(deltaS); 358 changes |= NEW_I; 359 } 360 if (th->th_flags & TH_PUSH) 361 changes |= TCP_PUSH_BIT; 362 /* 363 * Grab the cksum before we overwrite it below. Then update our 364 * state with this packet's header. 365 */ 366 deltaA = ntohs(th->th_sum); 367 BCOPY(ip, &cs->cs_ip, hlen); 368 369 /* 370 * We want to use the original packet as our compressed packet. 371 * (cp - new_seq) is the number of bytes we need for compressed 372 * sequence numbers. In addition we need one byte for the change 373 * mask, one for the connection id and two for the tcp checksum. 374 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 375 * many bytes of the original packet to toss so subtract the two to 376 * get the new packet size. 377 */ 378 deltaS = cp - new_seq; 379 cp = (u_char *)ip; 380 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 381 comp->last_xmit = cs->cs_id; 382 hlen -= deltaS + 4; 383 cp += hlen; 384 *cp++ = changes | NEW_C; 385 *cp++ = cs->cs_id; 386 } else { 387 hlen -= deltaS + 3; 388 cp += hlen; 389 *cp++ = changes; 390 } 391 m->m_len -= hlen; 392 m->m_data += hlen; 393 *cp++ = deltaA >> 8; 394 *cp++ = deltaA; 395 BCOPY(new_seq, cp, deltaS); 396 INCR(sls_compressed) 397 return (TYPE_COMPRESSED_TCP); 398 399 /* 400 * Update connection state cs & send uncompressed packet ('uncompressed' 401 * means a regular ip/tcp packet but with the 'conversation id' we hope 402 * to use on future compressed packets in the protocol field). 403 */ 404 uncompressed: 405 BCOPY(ip, &cs->cs_ip, hlen); 406 ip->ip_p = cs->cs_id; 407 comp->last_xmit = cs->cs_id; 408 return (TYPE_UNCOMPRESSED_TCP); 409 } 410 411 412 int 413 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 414 { 415 u_char *hdr, *cp; 416 int hlen, vjlen; 417 418 cp = bufp? *bufp: NULL; 419 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 420 if (vjlen < 0) 421 return (0); /* error */ 422 if (vjlen == 0) 423 return (len); /* was uncompressed already */ 424 425 cp += vjlen; 426 len -= vjlen; 427 428 /* 429 * At this point, cp points to the first byte of data in the 430 * packet. If we're not aligned on a 4-byte boundary, copy the 431 * data down so the ip & tcp headers will be aligned. Then back up 432 * cp by the tcp/ip header length to make room for the reconstructed 433 * header (we assume the packet we were handed has enough space to 434 * prepend 128 bytes of header). 435 */ 436 if ((intptr_t)cp & 3) { 437 if (len > 0) 438 bcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 439 cp = (u_char *)((intptr_t)cp &~ 3); 440 } 441 cp -= hlen; 442 len += hlen; 443 BCOPY(hdr, cp, hlen); 444 445 *bufp = cp; 446 return (len); 447 } 448 449 /* 450 * Uncompress a packet of total length total_len. The first buflen 451 * bytes are at buf; this must include the entire (compressed or 452 * uncompressed) TCP/IP header. This procedure returns the length 453 * of the VJ header, with a pointer to the uncompressed IP header 454 * in *hdrp and its length in *hlenp. 455 */ 456 int 457 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 458 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 459 { 460 u_char *cp; 461 u_int hlen, changes; 462 struct tcphdr *th; 463 struct cstate *cs; 464 struct ip *ip; 465 u_int16_t *bp; 466 u_int vjlen; 467 468 switch (type) { 469 470 case TYPE_UNCOMPRESSED_TCP: 471 ip = (struct ip *) buf; 472 if (ip->ip_p >= MAX_STATES) 473 goto bad; 474 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 475 comp->flags &=~ SLF_TOSS; 476 ip->ip_p = IPPROTO_TCP; 477 /* 478 * Calculate the size of the TCP/IP header and make sure that 479 * we don't overflow the space we have available for it. 480 */ 481 hlen = ip->ip_hl << 2; 482 if (hlen + sizeof(struct tcphdr) > buflen) 483 goto bad; 484 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 485 if (hlen > MAX_HDR || hlen > buflen) 486 goto bad; 487 BCOPY(ip, &cs->cs_ip, hlen); 488 cs->cs_hlen = hlen; 489 INCR(sls_uncompressedin) 490 *hdrp = (u_char *) &cs->cs_ip; 491 *hlenp = hlen; 492 return (0); 493 494 default: 495 goto bad; 496 497 case TYPE_COMPRESSED_TCP: 498 break; 499 } 500 /* We've got a compressed packet. */ 501 INCR(sls_compressedin) 502 cp = buf; 503 changes = *cp++; 504 if (changes & NEW_C) { 505 /* Make sure the state index is in range, then grab the state. 506 * If we have a good state index, clear the 'discard' flag. */ 507 if (*cp >= MAX_STATES) 508 goto bad; 509 510 comp->flags &=~ SLF_TOSS; 511 comp->last_recv = *cp++; 512 } else { 513 /* this packet has an implicit state index. If we've 514 * had a line error since the last time we got an 515 * explicit state index, we have to toss the packet. */ 516 if (comp->flags & SLF_TOSS) { 517 INCR(sls_tossed) 518 return (-1); 519 } 520 } 521 cs = &comp->rstate[comp->last_recv]; 522 hlen = cs->cs_ip.ip_hl << 2; 523 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 524 th->th_sum = htons((*cp << 8) | cp[1]); 525 cp += 2; 526 if (changes & TCP_PUSH_BIT) 527 th->th_flags |= TH_PUSH; 528 else 529 th->th_flags &=~ TH_PUSH; 530 531 switch (changes & SPECIALS_MASK) { 532 case SPECIAL_I: 533 { 534 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 535 th->th_ack = htonl(ntohl(th->th_ack) + i); 536 th->th_seq = htonl(ntohl(th->th_seq) + i); 537 } 538 break; 539 540 case SPECIAL_D: 541 th->th_seq = htonl(ntohl(th->th_seq) + 542 ntohs(cs->cs_ip.ip_len) - 543 cs->cs_hlen); 544 break; 545 546 default: 547 if (changes & NEW_U) { 548 th->th_flags |= TH_URG; 549 DECODEU(th->th_urp) 550 } else 551 th->th_flags &=~ TH_URG; 552 if (changes & NEW_W) 553 DECODES(th->th_win) 554 if (changes & NEW_A) 555 DECODEL(th->th_ack) 556 if (changes & NEW_S) 557 DECODEL(th->th_seq) 558 break; 559 } 560 if (changes & NEW_I) { 561 DECODES(cs->cs_ip.ip_id) 562 } else 563 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 564 565 /* 566 * At this point, cp points to the first byte of data in the 567 * packet. Fill in the IP total length and update the IP 568 * header checksum. 569 */ 570 vjlen = cp - buf; 571 buflen -= vjlen; 572 if (buflen < 0) 573 /* we must have dropped some characters (crc should detect 574 * this but the old slip framing won't) */ 575 goto bad; 576 577 total_len += cs->cs_hlen - vjlen; 578 cs->cs_ip.ip_len = htons(total_len); 579 580 /* recompute the ip header checksum */ 581 bp = (u_int16_t *) &cs->cs_ip; 582 cs->cs_ip.ip_sum = 0; 583 for (changes = 0; hlen > 0; hlen -= 2) 584 changes += *bp++; 585 changes = (changes & 0xffff) + (changes >> 16); 586 changes = (changes & 0xffff) + (changes >> 16); 587 cs->cs_ip.ip_sum = ~ changes; 588 589 *hdrp = (u_char *) &cs->cs_ip; 590 *hlenp = cs->cs_hlen; 591 return vjlen; 592 593 bad: 594 comp->flags |= SLF_TOSS; 595 INCR(sls_errorin) 596 return (-1); 597 } 598