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 1.5 2006/01/14 11:05:18 swildner 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(struct slcompress *comp, int max_state) 72 { 73 u_int i; 74 struct cstate *tstate = comp->tstate; 75 76 if (max_state == -1) { 77 max_state = MAX_STATES - 1; 78 bzero((char *)comp, sizeof(*comp)); 79 } else { 80 /* Don't reset statistics */ 81 bzero((char *)comp->tstate, sizeof(comp->tstate)); 82 bzero((char *)comp->rstate, sizeof(comp->rstate)); 83 } 84 for (i = max_state; i > 0; --i) { 85 tstate[i].cs_id = i; 86 tstate[i].cs_next = &tstate[i - 1]; 87 } 88 tstate[0].cs_next = &tstate[max_state]; 89 tstate[0].cs_id = 0; 90 comp->last_cs = &tstate[0]; 91 comp->last_recv = 255; 92 comp->last_xmit = 255; 93 comp->flags = SLF_TOSS; 94 } 95 96 97 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 98 * checks for zero (since zero has to be encoded in the long, 3 byte 99 * form). 100 */ 101 #define ENCODE(n) { \ 102 if ((u_int16_t)(n) >= 256) { \ 103 *cp++ = 0; \ 104 cp[1] = (n); \ 105 cp[0] = (n) >> 8; \ 106 cp += 2; \ 107 } else { \ 108 *cp++ = (n); \ 109 } \ 110 } 111 #define ENCODEZ(n) { \ 112 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 113 *cp++ = 0; \ 114 cp[1] = (n); \ 115 cp[0] = (n) >> 8; \ 116 cp += 2; \ 117 } else { \ 118 *cp++ = (n); \ 119 } \ 120 } 121 122 #define DECODEL(f) { \ 123 if (*cp == 0) {\ 124 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 125 cp += 3; \ 126 } else { \ 127 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 128 } \ 129 } 130 131 #define DECODES(f) { \ 132 if (*cp == 0) {\ 133 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 134 cp += 3; \ 135 } else { \ 136 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 137 } \ 138 } 139 140 #define DECODEU(f) { \ 141 if (*cp == 0) {\ 142 (f) = htons((cp[1] << 8) | cp[2]); \ 143 cp += 3; \ 144 } else { \ 145 (f) = htons((u_int32_t)*cp++); \ 146 } \ 147 } 148 149 /* 150 * Attempt to compress an outgoing TCP packet and return the type of 151 * the result. The caller must have already verified that the protocol 152 * is TCP. The first mbuf must contain the complete IP and TCP headers, 153 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 154 * compression state, and "compress_cid" tells us whether it is OK 155 * to leave out the CID field when feasible. 156 * 157 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 158 * if m is an M_PKTHDR mbuf. 159 */ 160 u_int 161 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 162 int compress_cid) 163 { 164 struct cstate *cs = comp->last_cs->cs_next; 165 u_int hlen = ip->ip_hl; 166 struct tcphdr *oth; 167 struct tcphdr *th; 168 u_int deltaS, deltaA; 169 u_int changes = 0; 170 u_char new_seq[16]; 171 u_char *cp = new_seq; 172 173 /* 174 * Bail if this is an IP fragment or if the TCP packet isn't 175 * `compressible' (i.e., ACK isn't set or some other control bit is 176 * set). (We assume that the caller has already made sure the 177 * packet is IP proto TCP). 178 */ 179 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 180 return (TYPE_IP); 181 182 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 183 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 184 return (TYPE_IP); 185 /* 186 * Packet is compressible -- we're going to send either a 187 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 188 * to locate (or create) the connection state. Special case the 189 * most recently used connection since it's most likely to be used 190 * again & we don't have to do any reordering if it's used. 191 */ 192 INCR(sls_packets) 193 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 194 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 195 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 196 /* 197 * Wasn't the first -- search for it. 198 * 199 * States are kept in a circularly linked list with 200 * last_cs pointing to the end of the list. The 201 * list is kept in lru order by moving a state to the 202 * head of the list whenever it is referenced. Since 203 * the list is short and, empirically, the connection 204 * we want is almost always near the front, we locate 205 * states via linear search. If we don't find a state 206 * for the datagram, the oldest state is (re-)used. 207 */ 208 struct cstate *lcs; 209 struct cstate *lastcs = comp->last_cs; 210 211 do { 212 lcs = cs; cs = cs->cs_next; 213 INCR(sls_searches) 214 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 215 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 216 && *(int32_t *)th == 217 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 218 goto found; 219 } while (cs != lastcs); 220 221 /* 222 * Didn't find it -- re-use oldest cstate. Send an 223 * uncompressed packet that tells the other side what 224 * connection number we're using for this conversation. 225 * Note that since the state list is circular, the oldest 226 * state points to the newest and we only need to set 227 * last_cs to update the lru linkage. 228 */ 229 INCR(sls_misses) 230 comp->last_cs = lcs; 231 hlen += th->th_off; 232 hlen <<= 2; 233 if (hlen > m->m_len) 234 return TYPE_IP; 235 goto uncompressed; 236 237 found: 238 /* 239 * Found it -- move to the front on the connection list. 240 */ 241 if (cs == lastcs) 242 comp->last_cs = lcs; 243 else { 244 lcs->cs_next = cs->cs_next; 245 cs->cs_next = lastcs->cs_next; 246 lastcs->cs_next = cs; 247 } 248 } 249 250 /* 251 * Make sure that only what we expect to change changed. The first 252 * line of the `if' checks the IP protocol version, header length & 253 * type of service. The 2nd line checks the "Don't fragment" bit. 254 * The 3rd line checks the time-to-live and protocol (the protocol 255 * check is unnecessary but costless). The 4th line checks the TCP 256 * header length. The 5th line checks IP options, if any. The 6th 257 * line checks TCP options, if any. If any of these things are 258 * different between the previous & current datagram, we send the 259 * current datagram `uncompressed'. 260 */ 261 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 262 deltaS = hlen; 263 hlen += th->th_off; 264 hlen <<= 2; 265 if (hlen > m->m_len) 266 return TYPE_IP; 267 268 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 269 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 270 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 271 th->th_off != oth->th_off || 272 (deltaS > 5 && 273 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 274 (th->th_off > 5 && 275 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 276 goto uncompressed; 277 278 /* 279 * Figure out which of the changing fields changed. The 280 * receiver expects changes in the order: urgent, window, 281 * ack, seq (the order minimizes the number of temporaries 282 * needed in this section of code). 283 */ 284 if (th->th_flags & TH_URG) { 285 deltaS = ntohs(th->th_urp); 286 ENCODEZ(deltaS); 287 changes |= NEW_U; 288 } else if (th->th_urp != oth->th_urp) 289 /* argh! URG not set but urp changed -- a sensible 290 * implementation should never do this but RFC793 291 * doesn't prohibit the change so we have to deal 292 * with it. */ 293 goto uncompressed; 294 295 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 296 if (deltaS) { 297 ENCODE(deltaS); 298 changes |= NEW_W; 299 } 300 301 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 302 if (deltaA) { 303 if (deltaA > 0xffff) 304 goto uncompressed; 305 ENCODE(deltaA); 306 changes |= NEW_A; 307 } 308 309 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 310 if (deltaS) { 311 if (deltaS > 0xffff) 312 goto uncompressed; 313 ENCODE(deltaS); 314 changes |= NEW_S; 315 } 316 317 switch(changes) { 318 319 case 0: 320 /* 321 * Nothing changed. If this packet contains data and the 322 * last one didn't, this is probably a data packet following 323 * an ack (normal on an interactive connection) and we send 324 * it compressed. Otherwise it's probably a retransmit, 325 * retransmitted ack or window probe. Send it uncompressed 326 * in case the other side missed the compressed version. 327 */ 328 if (ip->ip_len != cs->cs_ip.ip_len && 329 ntohs(cs->cs_ip.ip_len) == hlen) 330 break; 331 332 /* (fall through) */ 333 334 case SPECIAL_I: 335 case SPECIAL_D: 336 /* 337 * actual changes match one of our special case encodings -- 338 * send packet uncompressed. 339 */ 340 goto uncompressed; 341 342 case NEW_S|NEW_A: 343 if (deltaS == deltaA && 344 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 345 /* special case for echoed terminal traffic */ 346 changes = SPECIAL_I; 347 cp = new_seq; 348 } 349 break; 350 351 case NEW_S: 352 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 353 /* special case for data xfer */ 354 changes = SPECIAL_D; 355 cp = new_seq; 356 } 357 break; 358 } 359 360 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 361 if (deltaS != 1) { 362 ENCODEZ(deltaS); 363 changes |= NEW_I; 364 } 365 if (th->th_flags & TH_PUSH) 366 changes |= TCP_PUSH_BIT; 367 /* 368 * Grab the cksum before we overwrite it below. Then update our 369 * state with this packet's header. 370 */ 371 deltaA = ntohs(th->th_sum); 372 BCOPY(ip, &cs->cs_ip, hlen); 373 374 /* 375 * We want to use the original packet as our compressed packet. 376 * (cp - new_seq) is the number of bytes we need for compressed 377 * sequence numbers. In addition we need one byte for the change 378 * mask, one for the connection id and two for the tcp checksum. 379 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 380 * many bytes of the original packet to toss so subtract the two to 381 * get the new packet size. 382 */ 383 deltaS = cp - new_seq; 384 cp = (u_char *)ip; 385 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 386 comp->last_xmit = cs->cs_id; 387 hlen -= deltaS + 4; 388 cp += hlen; 389 *cp++ = changes | NEW_C; 390 *cp++ = cs->cs_id; 391 } else { 392 hlen -= deltaS + 3; 393 cp += hlen; 394 *cp++ = changes; 395 } 396 m->m_len -= hlen; 397 m->m_data += hlen; 398 *cp++ = deltaA >> 8; 399 *cp++ = deltaA; 400 BCOPY(new_seq, cp, deltaS); 401 INCR(sls_compressed) 402 return (TYPE_COMPRESSED_TCP); 403 404 /* 405 * Update connection state cs & send uncompressed packet ('uncompressed' 406 * means a regular ip/tcp packet but with the 'conversation id' we hope 407 * to use on future compressed packets in the protocol field). 408 */ 409 uncompressed: 410 BCOPY(ip, &cs->cs_ip, hlen); 411 ip->ip_p = cs->cs_id; 412 comp->last_xmit = cs->cs_id; 413 return (TYPE_UNCOMPRESSED_TCP); 414 } 415 416 417 int 418 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 419 { 420 u_char *hdr, *cp; 421 int hlen, vjlen; 422 423 cp = bufp? *bufp: NULL; 424 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 425 if (vjlen < 0) 426 return (0); /* error */ 427 if (vjlen == 0) 428 return (len); /* was uncompressed already */ 429 430 cp += vjlen; 431 len -= vjlen; 432 433 /* 434 * At this point, cp points to the first byte of data in the 435 * packet. If we're not aligned on a 4-byte boundary, copy the 436 * data down so the ip & tcp headers will be aligned. Then back up 437 * cp by the tcp/ip header length to make room for the reconstructed 438 * header (we assume the packet we were handed has enough space to 439 * prepend 128 bytes of header). 440 */ 441 if ((intptr_t)cp & 3) { 442 if (len > 0) 443 ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len); 444 cp = (u_char *)((intptr_t)cp &~ 3); 445 } 446 cp -= hlen; 447 len += hlen; 448 BCOPY(hdr, cp, hlen); 449 450 *bufp = cp; 451 return (len); 452 } 453 454 /* 455 * Uncompress a packet of total length total_len. The first buflen 456 * bytes are at buf; this must include the entire (compressed or 457 * uncompressed) TCP/IP header. This procedure returns the length 458 * of the VJ header, with a pointer to the uncompressed IP header 459 * in *hdrp and its length in *hlenp. 460 */ 461 int 462 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 463 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 464 { 465 u_char *cp; 466 u_int hlen, changes; 467 struct tcphdr *th; 468 struct cstate *cs; 469 struct ip *ip; 470 u_int16_t *bp; 471 u_int vjlen; 472 473 switch (type) { 474 475 case TYPE_UNCOMPRESSED_TCP: 476 ip = (struct ip *) buf; 477 if (ip->ip_p >= MAX_STATES) 478 goto bad; 479 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 480 comp->flags &=~ SLF_TOSS; 481 ip->ip_p = IPPROTO_TCP; 482 /* 483 * Calculate the size of the TCP/IP header and make sure that 484 * we don't overflow the space we have available for it. 485 */ 486 hlen = ip->ip_hl << 2; 487 if (hlen + sizeof(struct tcphdr) > buflen) 488 goto bad; 489 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 490 if (hlen > MAX_HDR || hlen > buflen) 491 goto bad; 492 BCOPY(ip, &cs->cs_ip, hlen); 493 cs->cs_hlen = hlen; 494 INCR(sls_uncompressedin) 495 *hdrp = (u_char *) &cs->cs_ip; 496 *hlenp = hlen; 497 return (0); 498 499 default: 500 goto bad; 501 502 case TYPE_COMPRESSED_TCP: 503 break; 504 } 505 /* We've got a compressed packet. */ 506 INCR(sls_compressedin) 507 cp = buf; 508 changes = *cp++; 509 if (changes & NEW_C) { 510 /* Make sure the state index is in range, then grab the state. 511 * If we have a good state index, clear the 'discard' flag. */ 512 if (*cp >= MAX_STATES) 513 goto bad; 514 515 comp->flags &=~ SLF_TOSS; 516 comp->last_recv = *cp++; 517 } else { 518 /* this packet has an implicit state index. If we've 519 * had a line error since the last time we got an 520 * explicit state index, we have to toss the packet. */ 521 if (comp->flags & SLF_TOSS) { 522 INCR(sls_tossed) 523 return (-1); 524 } 525 } 526 cs = &comp->rstate[comp->last_recv]; 527 hlen = cs->cs_ip.ip_hl << 2; 528 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 529 th->th_sum = htons((*cp << 8) | cp[1]); 530 cp += 2; 531 if (changes & TCP_PUSH_BIT) 532 th->th_flags |= TH_PUSH; 533 else 534 th->th_flags &=~ TH_PUSH; 535 536 switch (changes & SPECIALS_MASK) { 537 case SPECIAL_I: 538 { 539 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 540 th->th_ack = htonl(ntohl(th->th_ack) + i); 541 th->th_seq = htonl(ntohl(th->th_seq) + i); 542 } 543 break; 544 545 case SPECIAL_D: 546 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 547 - cs->cs_hlen); 548 break; 549 550 default: 551 if (changes & NEW_U) { 552 th->th_flags |= TH_URG; 553 DECODEU(th->th_urp) 554 } else 555 th->th_flags &=~ TH_URG; 556 if (changes & NEW_W) 557 DECODES(th->th_win) 558 if (changes & NEW_A) 559 DECODEL(th->th_ack) 560 if (changes & NEW_S) 561 DECODEL(th->th_seq) 562 break; 563 } 564 if (changes & NEW_I) { 565 DECODES(cs->cs_ip.ip_id) 566 } else 567 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 568 569 /* 570 * At this point, cp points to the first byte of data in the 571 * packet. Fill in the IP total length and update the IP 572 * header checksum. 573 */ 574 vjlen = cp - buf; 575 buflen -= vjlen; 576 if (buflen < 0) 577 /* we must have dropped some characters (crc should detect 578 * this but the old slip framing won't) */ 579 goto bad; 580 581 total_len += cs->cs_hlen - vjlen; 582 cs->cs_ip.ip_len = htons(total_len); 583 584 /* recompute the ip header checksum */ 585 bp = (u_int16_t *) &cs->cs_ip; 586 cs->cs_ip.ip_sum = 0; 587 for (changes = 0; hlen > 0; hlen -= 2) 588 changes += *bp++; 589 changes = (changes & 0xffff) + (changes >> 16); 590 changes = (changes & 0xffff) + (changes >> 16); 591 cs->cs_ip.ip_sum = ~ changes; 592 593 *hdrp = (u_char *) &cs->cs_ip; 594 *hlenp = cs->cs_hlen; 595 return vjlen; 596 597 bad: 598 comp->flags |= SLF_TOSS; 599 INCR(sls_errorin) 600 return (-1); 601 } 602