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 #ifndef _KERNEL 63 #define ovbcopy bcopy 64 #endif 65 66 void 67 sl_compress_init(struct slcompress *comp, int max_state) 68 { 69 u_int i; 70 struct cstate *tstate = comp->tstate; 71 72 if (max_state == -1) { 73 max_state = MAX_STATES - 1; 74 bzero((char *)comp, sizeof(*comp)); 75 } else { 76 /* Don't reset statistics */ 77 bzero((char *)comp->tstate, sizeof(comp->tstate)); 78 bzero((char *)comp->rstate, sizeof(comp->rstate)); 79 } 80 for (i = max_state; i > 0; --i) { 81 tstate[i].cs_id = i; 82 tstate[i].cs_next = &tstate[i - 1]; 83 } 84 tstate[0].cs_next = &tstate[max_state]; 85 tstate[0].cs_id = 0; 86 comp->last_cs = &tstate[0]; 87 comp->last_recv = 255; 88 comp->last_xmit = 255; 89 comp->flags = SLF_TOSS; 90 } 91 92 93 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 94 * checks for zero (since zero has to be encoded in the long, 3 byte 95 * form). 96 */ 97 #define ENCODE(n) { \ 98 if ((u_int16_t)(n) >= 256) { \ 99 *cp++ = 0; \ 100 cp[1] = (n); \ 101 cp[0] = (n) >> 8; \ 102 cp += 2; \ 103 } else { \ 104 *cp++ = (n); \ 105 } \ 106 } 107 #define ENCODEZ(n) { \ 108 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 109 *cp++ = 0; \ 110 cp[1] = (n); \ 111 cp[0] = (n) >> 8; \ 112 cp += 2; \ 113 } else { \ 114 *cp++ = (n); \ 115 } \ 116 } 117 118 #define DECODEL(f) { \ 119 if (*cp == 0) {\ 120 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 121 cp += 3; \ 122 } else { \ 123 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 124 } \ 125 } 126 127 #define DECODES(f) { \ 128 if (*cp == 0) {\ 129 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 130 cp += 3; \ 131 } else { \ 132 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 133 } \ 134 } 135 136 #define DECODEU(f) { \ 137 if (*cp == 0) {\ 138 (f) = htons((cp[1] << 8) | cp[2]); \ 139 cp += 3; \ 140 } else { \ 141 (f) = htons((u_int32_t)*cp++); \ 142 } \ 143 } 144 145 /* 146 * Attempt to compress an outgoing TCP packet and return the type of 147 * the result. The caller must have already verified that the protocol 148 * is TCP. The first mbuf must contain the complete IP and TCP headers, 149 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 150 * compression state, and "compress_cid" tells us whether it is OK 151 * to leave out the CID field when feasible. 152 * 153 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 154 * if m is an M_PKTHDR mbuf. 155 */ 156 u_int 157 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 158 int compress_cid) 159 { 160 struct cstate *cs = comp->last_cs->cs_next; 161 u_int hlen = ip->ip_hl; 162 struct tcphdr *oth; 163 struct tcphdr *th; 164 u_int deltaS, deltaA; 165 u_int changes = 0; 166 u_char new_seq[16]; 167 u_char *cp = new_seq; 168 169 /* 170 * Bail if this is an IP fragment or if the TCP packet isn't 171 * `compressible' (i.e., ACK isn't set or some other control bit is 172 * set). (We assume that the caller has already made sure the 173 * packet is IP proto TCP). 174 */ 175 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 176 return (TYPE_IP); 177 178 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 179 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 180 return (TYPE_IP); 181 /* 182 * Packet is compressible -- we're going to send either a 183 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 184 * to locate (or create) the connection state. Special case the 185 * most recently used connection since it's most likely to be used 186 * again & we don't have to do any reordering if it's used. 187 */ 188 INCR(sls_packets) 189 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 190 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 191 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 192 /* 193 * Wasn't the first -- search for it. 194 * 195 * States are kept in a circularly linked list with 196 * last_cs pointing to the end of the list. The 197 * list is kept in lru order by moving a state to the 198 * head of the list whenever it is referenced. Since 199 * the list is short and, empirically, the connection 200 * we want is almost always near the front, we locate 201 * states via linear search. If we don't find a state 202 * for the datagram, the oldest state is (re-)used. 203 */ 204 struct cstate *lcs; 205 struct cstate *lastcs = comp->last_cs; 206 207 do { 208 lcs = cs; cs = cs->cs_next; 209 INCR(sls_searches) 210 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 211 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 212 && *(int32_t *)th == 213 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 214 goto found; 215 } while (cs != lastcs); 216 217 /* 218 * Didn't find it -- re-use oldest cstate. Send an 219 * uncompressed packet that tells the other side what 220 * connection number we're using for this conversation. 221 * Note that since the state list is circular, the oldest 222 * state points to the newest and we only need to set 223 * last_cs to update the lru linkage. 224 */ 225 INCR(sls_misses) 226 comp->last_cs = lcs; 227 hlen += th->th_off; 228 hlen <<= 2; 229 if (hlen > m->m_len) 230 return TYPE_IP; 231 goto uncompressed; 232 233 found: 234 /* 235 * Found it -- move to the front on the connection list. 236 */ 237 if (cs == lastcs) 238 comp->last_cs = lcs; 239 else { 240 lcs->cs_next = cs->cs_next; 241 cs->cs_next = lastcs->cs_next; 242 lastcs->cs_next = cs; 243 } 244 } 245 246 /* 247 * Make sure that only what we expect to change changed. The first 248 * line of the `if' checks the IP protocol version, header length & 249 * type of service. The 2nd line checks the "Don't fragment" bit. 250 * The 3rd line checks the time-to-live and protocol (the protocol 251 * check is unnecessary but costless). The 4th line checks the TCP 252 * header length. The 5th line checks IP options, if any. The 6th 253 * line checks TCP options, if any. If any of these things are 254 * different between the previous & current datagram, we send the 255 * current datagram `uncompressed'. 256 */ 257 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 258 deltaS = hlen; 259 hlen += th->th_off; 260 hlen <<= 2; 261 if (hlen > m->m_len) 262 return TYPE_IP; 263 264 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 265 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 266 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 267 th->th_off != oth->th_off || 268 (deltaS > 5 && 269 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 270 (th->th_off > 5 && 271 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 272 goto uncompressed; 273 274 /* 275 * Figure out which of the changing fields changed. The 276 * receiver expects changes in the order: urgent, window, 277 * ack, seq (the order minimizes the number of temporaries 278 * needed in this section of code). 279 */ 280 if (th->th_flags & TH_URG) { 281 deltaS = ntohs(th->th_urp); 282 ENCODEZ(deltaS); 283 changes |= NEW_U; 284 } else if (th->th_urp != oth->th_urp) 285 /* argh! URG not set but urp changed -- a sensible 286 * implementation should never do this but RFC793 287 * doesn't prohibit the change so we have to deal 288 * with it. */ 289 goto uncompressed; 290 291 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 292 if (deltaS) { 293 ENCODE(deltaS); 294 changes |= NEW_W; 295 } 296 297 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 298 if (deltaA) { 299 if (deltaA > 0xffff) 300 goto uncompressed; 301 ENCODE(deltaA); 302 changes |= NEW_A; 303 } 304 305 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 306 if (deltaS) { 307 if (deltaS > 0xffff) 308 goto uncompressed; 309 ENCODE(deltaS); 310 changes |= NEW_S; 311 } 312 313 switch(changes) { 314 315 case 0: 316 /* 317 * Nothing changed. If this packet contains data and the 318 * last one didn't, this is probably a data packet following 319 * an ack (normal on an interactive connection) and we send 320 * it compressed. Otherwise it's probably a retransmit, 321 * retransmitted ack or window probe. Send it uncompressed 322 * in case the other side missed the compressed version. 323 */ 324 if (ip->ip_len != cs->cs_ip.ip_len && 325 ntohs(cs->cs_ip.ip_len) == hlen) 326 break; 327 328 /* (fall through) */ 329 330 case SPECIAL_I: 331 case SPECIAL_D: 332 /* 333 * actual changes match one of our special case encodings -- 334 * send packet uncompressed. 335 */ 336 goto uncompressed; 337 338 case NEW_S|NEW_A: 339 if (deltaS == deltaA && 340 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 341 /* special case for echoed terminal traffic */ 342 changes = SPECIAL_I; 343 cp = new_seq; 344 } 345 break; 346 347 case NEW_S: 348 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 349 /* special case for data xfer */ 350 changes = SPECIAL_D; 351 cp = new_seq; 352 } 353 break; 354 } 355 356 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 357 if (deltaS != 1) { 358 ENCODEZ(deltaS); 359 changes |= NEW_I; 360 } 361 if (th->th_flags & TH_PUSH) 362 changes |= TCP_PUSH_BIT; 363 /* 364 * Grab the cksum before we overwrite it below. Then update our 365 * state with this packet's header. 366 */ 367 deltaA = ntohs(th->th_sum); 368 BCOPY(ip, &cs->cs_ip, hlen); 369 370 /* 371 * We want to use the original packet as our compressed packet. 372 * (cp - new_seq) is the number of bytes we need for compressed 373 * sequence numbers. In addition we need one byte for the change 374 * mask, one for the connection id and two for the tcp checksum. 375 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 376 * many bytes of the original packet to toss so subtract the two to 377 * get the new packet size. 378 */ 379 deltaS = cp - new_seq; 380 cp = (u_char *)ip; 381 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 382 comp->last_xmit = cs->cs_id; 383 hlen -= deltaS + 4; 384 cp += hlen; 385 *cp++ = changes | NEW_C; 386 *cp++ = cs->cs_id; 387 } else { 388 hlen -= deltaS + 3; 389 cp += hlen; 390 *cp++ = changes; 391 } 392 m->m_len -= hlen; 393 m->m_data += hlen; 394 *cp++ = deltaA >> 8; 395 *cp++ = deltaA; 396 BCOPY(new_seq, cp, deltaS); 397 INCR(sls_compressed) 398 return (TYPE_COMPRESSED_TCP); 399 400 /* 401 * Update connection state cs & send uncompressed packet ('uncompressed' 402 * means a regular ip/tcp packet but with the 'conversation id' we hope 403 * to use on future compressed packets in the protocol field). 404 */ 405 uncompressed: 406 BCOPY(ip, &cs->cs_ip, hlen); 407 ip->ip_p = cs->cs_id; 408 comp->last_xmit = cs->cs_id; 409 return (TYPE_UNCOMPRESSED_TCP); 410 } 411 412 413 int 414 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 415 { 416 u_char *hdr, *cp; 417 int hlen, vjlen; 418 419 cp = bufp? *bufp: NULL; 420 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 421 if (vjlen < 0) 422 return (0); /* error */ 423 if (vjlen == 0) 424 return (len); /* was uncompressed already */ 425 426 cp += vjlen; 427 len -= vjlen; 428 429 /* 430 * At this point, cp points to the first byte of data in the 431 * packet. If we're not aligned on a 4-byte boundary, copy the 432 * data down so the ip & tcp headers will be aligned. Then back up 433 * cp by the tcp/ip header length to make room for the reconstructed 434 * header (we assume the packet we were handed has enough space to 435 * prepend 128 bytes of header). 436 */ 437 if ((intptr_t)cp & 3) { 438 if (len > 0) 439 ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 440 cp = (u_char *)((intptr_t)cp &~ 3); 441 } 442 cp -= hlen; 443 len += hlen; 444 BCOPY(hdr, cp, hlen); 445 446 *bufp = cp; 447 return (len); 448 } 449 450 /* 451 * Uncompress a packet of total length total_len. The first buflen 452 * bytes are at buf; this must include the entire (compressed or 453 * uncompressed) TCP/IP header. This procedure returns the length 454 * of the VJ header, with a pointer to the uncompressed IP header 455 * in *hdrp and its length in *hlenp. 456 */ 457 int 458 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 459 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 460 { 461 u_char *cp; 462 u_int hlen, changes; 463 struct tcphdr *th; 464 struct cstate *cs; 465 struct ip *ip; 466 u_int16_t *bp; 467 u_int vjlen; 468 469 switch (type) { 470 471 case TYPE_UNCOMPRESSED_TCP: 472 ip = (struct ip *) buf; 473 if (ip->ip_p >= MAX_STATES) 474 goto bad; 475 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 476 comp->flags &=~ SLF_TOSS; 477 ip->ip_p = IPPROTO_TCP; 478 /* 479 * Calculate the size of the TCP/IP header and make sure that 480 * we don't overflow the space we have available for it. 481 */ 482 hlen = ip->ip_hl << 2; 483 if (hlen + sizeof(struct tcphdr) > buflen) 484 goto bad; 485 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 486 if (hlen > MAX_HDR || hlen > buflen) 487 goto bad; 488 BCOPY(ip, &cs->cs_ip, hlen); 489 cs->cs_hlen = hlen; 490 INCR(sls_uncompressedin) 491 *hdrp = (u_char *) &cs->cs_ip; 492 *hlenp = hlen; 493 return (0); 494 495 default: 496 goto bad; 497 498 case TYPE_COMPRESSED_TCP: 499 break; 500 } 501 /* We've got a compressed packet. */ 502 INCR(sls_compressedin) 503 cp = buf; 504 changes = *cp++; 505 if (changes & NEW_C) { 506 /* Make sure the state index is in range, then grab the state. 507 * If we have a good state index, clear the 'discard' flag. */ 508 if (*cp >= MAX_STATES) 509 goto bad; 510 511 comp->flags &=~ SLF_TOSS; 512 comp->last_recv = *cp++; 513 } else { 514 /* this packet has an implicit state index. If we've 515 * had a line error since the last time we got an 516 * explicit state index, we have to toss the packet. */ 517 if (comp->flags & SLF_TOSS) { 518 INCR(sls_tossed) 519 return (-1); 520 } 521 } 522 cs = &comp->rstate[comp->last_recv]; 523 hlen = cs->cs_ip.ip_hl << 2; 524 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 525 th->th_sum = htons((*cp << 8) | cp[1]); 526 cp += 2; 527 if (changes & TCP_PUSH_BIT) 528 th->th_flags |= TH_PUSH; 529 else 530 th->th_flags &=~ TH_PUSH; 531 532 switch (changes & SPECIALS_MASK) { 533 case SPECIAL_I: 534 { 535 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 536 th->th_ack = htonl(ntohl(th->th_ack) + i); 537 th->th_seq = htonl(ntohl(th->th_seq) + i); 538 } 539 break; 540 541 case SPECIAL_D: 542 th->th_seq = htonl(ntohl(th->th_seq) + 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