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. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 34 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $ 35 * $DragonFly: src/sys/net/ppp_layer/slcompress.c,v 1.3 2003/07/26 20:19:34 rob Exp $ 36 */ 37 38 /* 39 * Routines to compress and uncompess tcp packets (for transmission 40 * over low speed serial lines. 41 * 42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 43 * - Initial distribution. 44 * 45 */ 46 47 #include <sys/param.h> 48 #include <sys/mbuf.h> 49 #include <sys/systm.h> 50 51 #include <netinet/in.h> 52 #include <netinet/in_systm.h> 53 #include <netinet/ip.h> 54 #include <netinet/tcp.h> 55 56 #include <net/slcompress.h> 57 58 #ifndef SL_NO_STATS 59 #define INCR(counter) ++comp->counter; 60 #else 61 #define INCR(counter) 62 #endif 63 64 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 65 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 66 #ifndef _KERNEL 67 #define ovbcopy bcopy 68 #endif 69 70 void 71 sl_compress_init(comp, max_state) 72 struct slcompress *comp; 73 int max_state; 74 { 75 u_int i; 76 struct cstate *tstate = comp->tstate; 77 78 if (max_state == -1) { 79 max_state = MAX_STATES - 1; 80 bzero((char *)comp, sizeof(*comp)); 81 } else { 82 /* Don't reset statistics */ 83 bzero((char *)comp->tstate, sizeof(comp->tstate)); 84 bzero((char *)comp->rstate, sizeof(comp->rstate)); 85 } 86 for (i = max_state; i > 0; --i) { 87 tstate[i].cs_id = i; 88 tstate[i].cs_next = &tstate[i - 1]; 89 } 90 tstate[0].cs_next = &tstate[max_state]; 91 tstate[0].cs_id = 0; 92 comp->last_cs = &tstate[0]; 93 comp->last_recv = 255; 94 comp->last_xmit = 255; 95 comp->flags = SLF_TOSS; 96 } 97 98 99 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 100 * checks for zero (since zero has to be encoded in the long, 3 byte 101 * form). 102 */ 103 #define ENCODE(n) { \ 104 if ((u_int16_t)(n) >= 256) { \ 105 *cp++ = 0; \ 106 cp[1] = (n); \ 107 cp[0] = (n) >> 8; \ 108 cp += 2; \ 109 } else { \ 110 *cp++ = (n); \ 111 } \ 112 } 113 #define ENCODEZ(n) { \ 114 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 115 *cp++ = 0; \ 116 cp[1] = (n); \ 117 cp[0] = (n) >> 8; \ 118 cp += 2; \ 119 } else { \ 120 *cp++ = (n); \ 121 } \ 122 } 123 124 #define DECODEL(f) { \ 125 if (*cp == 0) {\ 126 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 127 cp += 3; \ 128 } else { \ 129 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 130 } \ 131 } 132 133 #define DECODES(f) { \ 134 if (*cp == 0) {\ 135 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 136 cp += 3; \ 137 } else { \ 138 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 139 } \ 140 } 141 142 #define DECODEU(f) { \ 143 if (*cp == 0) {\ 144 (f) = htons((cp[1] << 8) | cp[2]); \ 145 cp += 3; \ 146 } else { \ 147 (f) = htons((u_int32_t)*cp++); \ 148 } \ 149 } 150 151 /* 152 * Attempt to compress an outgoing TCP packet and return the type of 153 * the result. The caller must have already verified that the protocol 154 * is TCP. The first mbuf must contain the complete IP and TCP headers, 155 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 156 * compression state, and "compress_cid" tells us whether it is OK 157 * to leave out the CID field when feasible. 158 * 159 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 160 * if m is an M_PKTHDR mbuf. 161 */ 162 u_int 163 sl_compress_tcp(m, ip, comp, compress_cid) 164 struct mbuf *m; 165 struct ip *ip; 166 struct slcompress *comp; 167 int compress_cid; 168 { 169 struct cstate *cs = comp->last_cs->cs_next; 170 u_int hlen = ip->ip_hl; 171 struct tcphdr *oth; 172 struct tcphdr *th; 173 u_int deltaS, deltaA; 174 u_int changes = 0; 175 u_char new_seq[16]; 176 u_char *cp = new_seq; 177 178 /* 179 * Bail if this is an IP fragment or if the TCP packet isn't 180 * `compressible' (i.e., ACK isn't set or some other control bit is 181 * set). (We assume that the caller has already made sure the 182 * packet is IP proto TCP). 183 */ 184 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 185 return (TYPE_IP); 186 187 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 188 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 189 return (TYPE_IP); 190 /* 191 * Packet is compressible -- we're going to send either a 192 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 193 * to locate (or create) the connection state. Special case the 194 * most recently used connection since it's most likely to be used 195 * again & we don't have to do any reordering if it's used. 196 */ 197 INCR(sls_packets) 198 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 199 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 200 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 201 /* 202 * Wasn't the first -- search for it. 203 * 204 * States are kept in a circularly linked list with 205 * last_cs pointing to the end of the list. The 206 * list is kept in lru order by moving a state to the 207 * head of the list whenever it is referenced. Since 208 * the list is short and, empirically, the connection 209 * we want is almost always near the front, we locate 210 * states via linear search. If we don't find a state 211 * for the datagram, the oldest state is (re-)used. 212 */ 213 struct cstate *lcs; 214 struct cstate *lastcs = comp->last_cs; 215 216 do { 217 lcs = cs; cs = cs->cs_next; 218 INCR(sls_searches) 219 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 220 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 221 && *(int32_t *)th == 222 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 223 goto found; 224 } while (cs != lastcs); 225 226 /* 227 * Didn't find it -- re-use oldest cstate. Send an 228 * uncompressed packet that tells the other side what 229 * connection number we're using for this conversation. 230 * Note that since the state list is circular, the oldest 231 * state points to the newest and we only need to set 232 * last_cs to update the lru linkage. 233 */ 234 INCR(sls_misses) 235 comp->last_cs = lcs; 236 hlen += th->th_off; 237 hlen <<= 2; 238 if (hlen > m->m_len) 239 return TYPE_IP; 240 goto uncompressed; 241 242 found: 243 /* 244 * Found it -- move to the front on the connection list. 245 */ 246 if (cs == lastcs) 247 comp->last_cs = lcs; 248 else { 249 lcs->cs_next = cs->cs_next; 250 cs->cs_next = lastcs->cs_next; 251 lastcs->cs_next = cs; 252 } 253 } 254 255 /* 256 * Make sure that only what we expect to change changed. The first 257 * line of the `if' checks the IP protocol version, header length & 258 * type of service. The 2nd line checks the "Don't fragment" bit. 259 * The 3rd line checks the time-to-live and protocol (the protocol 260 * check is unnecessary but costless). The 4th line checks the TCP 261 * header length. The 5th line checks IP options, if any. The 6th 262 * line checks TCP options, if any. If any of these things are 263 * different between the previous & current datagram, we send the 264 * current datagram `uncompressed'. 265 */ 266 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 267 deltaS = hlen; 268 hlen += th->th_off; 269 hlen <<= 2; 270 if (hlen > m->m_len) 271 return TYPE_IP; 272 273 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 274 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 275 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 276 th->th_off != oth->th_off || 277 (deltaS > 5 && 278 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 279 (th->th_off > 5 && 280 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 281 goto uncompressed; 282 283 /* 284 * Figure out which of the changing fields changed. The 285 * receiver expects changes in the order: urgent, window, 286 * ack, seq (the order minimizes the number of temporaries 287 * needed in this section of code). 288 */ 289 if (th->th_flags & TH_URG) { 290 deltaS = ntohs(th->th_urp); 291 ENCODEZ(deltaS); 292 changes |= NEW_U; 293 } else if (th->th_urp != oth->th_urp) 294 /* argh! URG not set but urp changed -- a sensible 295 * implementation should never do this but RFC793 296 * doesn't prohibit the change so we have to deal 297 * with it. */ 298 goto uncompressed; 299 300 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 301 if (deltaS) { 302 ENCODE(deltaS); 303 changes |= NEW_W; 304 } 305 306 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 307 if (deltaA) { 308 if (deltaA > 0xffff) 309 goto uncompressed; 310 ENCODE(deltaA); 311 changes |= NEW_A; 312 } 313 314 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 315 if (deltaS) { 316 if (deltaS > 0xffff) 317 goto uncompressed; 318 ENCODE(deltaS); 319 changes |= NEW_S; 320 } 321 322 switch(changes) { 323 324 case 0: 325 /* 326 * Nothing changed. If this packet contains data and the 327 * last one didn't, this is probably a data packet following 328 * an ack (normal on an interactive connection) and we send 329 * it compressed. Otherwise it's probably a retransmit, 330 * retransmitted ack or window probe. Send it uncompressed 331 * in case the other side missed the compressed version. 332 */ 333 if (ip->ip_len != cs->cs_ip.ip_len && 334 ntohs(cs->cs_ip.ip_len) == hlen) 335 break; 336 337 /* (fall through) */ 338 339 case SPECIAL_I: 340 case SPECIAL_D: 341 /* 342 * actual changes match one of our special case encodings -- 343 * send packet uncompressed. 344 */ 345 goto uncompressed; 346 347 case NEW_S|NEW_A: 348 if (deltaS == deltaA && 349 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 350 /* special case for echoed terminal traffic */ 351 changes = SPECIAL_I; 352 cp = new_seq; 353 } 354 break; 355 356 case NEW_S: 357 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 358 /* special case for data xfer */ 359 changes = SPECIAL_D; 360 cp = new_seq; 361 } 362 break; 363 } 364 365 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 366 if (deltaS != 1) { 367 ENCODEZ(deltaS); 368 changes |= NEW_I; 369 } 370 if (th->th_flags & TH_PUSH) 371 changes |= TCP_PUSH_BIT; 372 /* 373 * Grab the cksum before we overwrite it below. Then update our 374 * state with this packet's header. 375 */ 376 deltaA = ntohs(th->th_sum); 377 BCOPY(ip, &cs->cs_ip, hlen); 378 379 /* 380 * We want to use the original packet as our compressed packet. 381 * (cp - new_seq) is the number of bytes we need for compressed 382 * sequence numbers. In addition we need one byte for the change 383 * mask, one for the connection id and two for the tcp checksum. 384 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 385 * many bytes of the original packet to toss so subtract the two to 386 * get the new packet size. 387 */ 388 deltaS = cp - new_seq; 389 cp = (u_char *)ip; 390 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 391 comp->last_xmit = cs->cs_id; 392 hlen -= deltaS + 4; 393 cp += hlen; 394 *cp++ = changes | NEW_C; 395 *cp++ = cs->cs_id; 396 } else { 397 hlen -= deltaS + 3; 398 cp += hlen; 399 *cp++ = changes; 400 } 401 m->m_len -= hlen; 402 m->m_data += hlen; 403 *cp++ = deltaA >> 8; 404 *cp++ = deltaA; 405 BCOPY(new_seq, cp, deltaS); 406 INCR(sls_compressed) 407 return (TYPE_COMPRESSED_TCP); 408 409 /* 410 * Update connection state cs & send uncompressed packet ('uncompressed' 411 * means a regular ip/tcp packet but with the 'conversation id' we hope 412 * to use on future compressed packets in the protocol field). 413 */ 414 uncompressed: 415 BCOPY(ip, &cs->cs_ip, hlen); 416 ip->ip_p = cs->cs_id; 417 comp->last_xmit = cs->cs_id; 418 return (TYPE_UNCOMPRESSED_TCP); 419 } 420 421 422 int 423 sl_uncompress_tcp(bufp, len, type, comp) 424 u_char **bufp; 425 int len; 426 u_int type; 427 struct slcompress *comp; 428 { 429 u_char *hdr, *cp; 430 int hlen, vjlen; 431 432 cp = bufp? *bufp: NULL; 433 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 434 if (vjlen < 0) 435 return (0); /* error */ 436 if (vjlen == 0) 437 return (len); /* was uncompressed already */ 438 439 cp += vjlen; 440 len -= vjlen; 441 442 /* 443 * At this point, cp points to the first byte of data in the 444 * packet. If we're not aligned on a 4-byte boundary, copy the 445 * data down so the ip & tcp headers will be aligned. Then back up 446 * cp by the tcp/ip header length to make room for the reconstructed 447 * header (we assume the packet we were handed has enough space to 448 * prepend 128 bytes of header). 449 */ 450 if ((intptr_t)cp & 3) { 451 if (len > 0) 452 (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 453 cp = (u_char *)((intptr_t)cp &~ 3); 454 } 455 cp -= hlen; 456 len += hlen; 457 BCOPY(hdr, cp, hlen); 458 459 *bufp = cp; 460 return (len); 461 } 462 463 /* 464 * Uncompress a packet of total length total_len. The first buflen 465 * bytes are at buf; this must include the entire (compressed or 466 * uncompressed) TCP/IP header. This procedure returns the length 467 * of the VJ header, with a pointer to the uncompressed IP header 468 * in *hdrp and its length in *hlenp. 469 */ 470 int 471 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 472 u_char *buf; 473 int buflen, total_len; 474 u_int type; 475 struct slcompress *comp; 476 u_char **hdrp; 477 u_int *hlenp; 478 { 479 u_char *cp; 480 u_int hlen, changes; 481 struct tcphdr *th; 482 struct cstate *cs; 483 struct ip *ip; 484 u_int16_t *bp; 485 u_int vjlen; 486 487 switch (type) { 488 489 case TYPE_UNCOMPRESSED_TCP: 490 ip = (struct ip *) buf; 491 if (ip->ip_p >= MAX_STATES) 492 goto bad; 493 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 494 comp->flags &=~ SLF_TOSS; 495 ip->ip_p = IPPROTO_TCP; 496 /* 497 * Calculate the size of the TCP/IP header and make sure that 498 * we don't overflow the space we have available for it. 499 */ 500 hlen = ip->ip_hl << 2; 501 if (hlen + sizeof(struct tcphdr) > buflen) 502 goto bad; 503 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 504 if (hlen > MAX_HDR || hlen > buflen) 505 goto bad; 506 BCOPY(ip, &cs->cs_ip, hlen); 507 cs->cs_hlen = hlen; 508 INCR(sls_uncompressedin) 509 *hdrp = (u_char *) &cs->cs_ip; 510 *hlenp = hlen; 511 return (0); 512 513 default: 514 goto bad; 515 516 case TYPE_COMPRESSED_TCP: 517 break; 518 } 519 /* We've got a compressed packet. */ 520 INCR(sls_compressedin) 521 cp = buf; 522 changes = *cp++; 523 if (changes & NEW_C) { 524 /* Make sure the state index is in range, then grab the state. 525 * If we have a good state index, clear the 'discard' flag. */ 526 if (*cp >= MAX_STATES) 527 goto bad; 528 529 comp->flags &=~ SLF_TOSS; 530 comp->last_recv = *cp++; 531 } else { 532 /* this packet has an implicit state index. If we've 533 * had a line error since the last time we got an 534 * explicit state index, we have to toss the packet. */ 535 if (comp->flags & SLF_TOSS) { 536 INCR(sls_tossed) 537 return (-1); 538 } 539 } 540 cs = &comp->rstate[comp->last_recv]; 541 hlen = cs->cs_ip.ip_hl << 2; 542 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 543 th->th_sum = htons((*cp << 8) | cp[1]); 544 cp += 2; 545 if (changes & TCP_PUSH_BIT) 546 th->th_flags |= TH_PUSH; 547 else 548 th->th_flags &=~ TH_PUSH; 549 550 switch (changes & SPECIALS_MASK) { 551 case SPECIAL_I: 552 { 553 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 554 th->th_ack = htonl(ntohl(th->th_ack) + i); 555 th->th_seq = htonl(ntohl(th->th_seq) + i); 556 } 557 break; 558 559 case SPECIAL_D: 560 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 561 - cs->cs_hlen); 562 break; 563 564 default: 565 if (changes & NEW_U) { 566 th->th_flags |= TH_URG; 567 DECODEU(th->th_urp) 568 } else 569 th->th_flags &=~ TH_URG; 570 if (changes & NEW_W) 571 DECODES(th->th_win) 572 if (changes & NEW_A) 573 DECODEL(th->th_ack) 574 if (changes & NEW_S) 575 DECODEL(th->th_seq) 576 break; 577 } 578 if (changes & NEW_I) { 579 DECODES(cs->cs_ip.ip_id) 580 } else 581 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 582 583 /* 584 * At this point, cp points to the first byte of data in the 585 * packet. Fill in the IP total length and update the IP 586 * header checksum. 587 */ 588 vjlen = cp - buf; 589 buflen -= vjlen; 590 if (buflen < 0) 591 /* we must have dropped some characters (crc should detect 592 * this but the old slip framing won't) */ 593 goto bad; 594 595 total_len += cs->cs_hlen - vjlen; 596 cs->cs_ip.ip_len = htons(total_len); 597 598 /* recompute the ip header checksum */ 599 bp = (u_int16_t *) &cs->cs_ip; 600 cs->cs_ip.ip_sum = 0; 601 for (changes = 0; hlen > 0; hlen -= 2) 602 changes += *bp++; 603 changes = (changes & 0xffff) + (changes >> 16); 604 changes = (changes & 0xffff) + (changes >> 16); 605 cs->cs_ip.ip_sum = ~ changes; 606 607 *hdrp = (u_char *) &cs->cs_ip; 608 *hlenp = cs->cs_hlen; 609 return vjlen; 610 611 bad: 612 comp->flags |= SLF_TOSS; 613 INCR(sls_errorin) 614 return (-1); 615 } 616