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 * $Id: slcompress.c,v 1.5 1995/05/30 08:08:33 rgrimes Exp $ 35 */ 36 37 /* 38 * Routines to compress and uncompess tcp packets (for transmission 39 * over low speed serial lines. 40 * 41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 42 * - Initial distribution. 43 * 44 */ 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/mbuf.h> 49 50 #include <netinet/in.h> 51 #include <netinet/in_systm.h> 52 #include <netinet/ip.h> 53 #include <netinet/tcp.h> 54 55 #include <net/slcompress.h> 56 57 #ifndef SL_NO_STATS 58 #define INCR(counter) ++comp->counter; 59 #else 60 #define INCR(counter) 61 #endif 62 63 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 64 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 65 #ifndef KERNEL 66 #define ovbcopy bcopy 67 #endif 68 69 void 70 sl_compress_init(comp, max_state) 71 struct slcompress *comp; 72 int max_state; 73 { 74 register u_int i; 75 register struct cstate *tstate = comp->tstate; 76 77 if (max_state == -1) 78 max_state = MAX_STATES - 1; 79 bzero((char *)comp, sizeof(*comp)); 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_short)(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_short)(n) >= 256 || (u_short)(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_long)*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_long)*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_long)*cp++); \ 142 } \ 143 } 144 145 u_int 146 sl_compress_tcp(m, ip, comp, compress_cid) 147 struct mbuf *m; 148 register struct ip *ip; 149 struct slcompress *comp; 150 int compress_cid; 151 { 152 register struct cstate *cs = comp->last_cs->cs_next; 153 register u_int hlen = ip->ip_hl; 154 register struct tcphdr *oth; 155 register struct tcphdr *th; 156 register u_int deltaS, deltaA; 157 register u_int changes = 0; 158 u_char new_seq[16]; 159 register u_char *cp = new_seq; 160 161 /* 162 * Bail if this is an IP fragment or if the TCP packet isn't 163 * `compressible' (i.e., ACK isn't set or some other control bit is 164 * set). (We assume that the caller has already made sure the 165 * packet is IP proto TCP). 166 */ 167 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 168 return (TYPE_IP); 169 170 th = (struct tcphdr *)&((int *)ip)[hlen]; 171 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 172 return (TYPE_IP); 173 /* 174 * Packet is compressible -- we're going to send either a 175 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 176 * to locate (or create) the connection state. Special case the 177 * most recently used connection since it's most likely to be used 178 * again & we don't have to do any reordering if it's used. 179 */ 180 INCR(sls_packets) 181 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 182 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 183 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 184 /* 185 * Wasn't the first -- search for it. 186 * 187 * States are kept in a circularly linked list with 188 * last_cs pointing to the end of the list. The 189 * list is kept in lru order by moving a state to the 190 * head of the list whenever it is referenced. Since 191 * the list is short and, empirically, the connection 192 * we want is almost always near the front, we locate 193 * states via linear search. If we don't find a state 194 * for the datagram, the oldest state is (re-)used. 195 */ 196 register struct cstate *lcs; 197 register struct cstate *lastcs = comp->last_cs; 198 199 do { 200 lcs = cs; cs = cs->cs_next; 201 INCR(sls_searches) 202 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 203 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 204 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 205 goto found; 206 } while (cs != lastcs); 207 208 /* 209 * Didn't find it -- re-use oldest cstate. Send an 210 * uncompressed packet that tells the other side what 211 * connection number we're using for this conversation. 212 * Note that since the state list is circular, the oldest 213 * state points to the newest and we only need to set 214 * last_cs to update the lru linkage. 215 */ 216 INCR(sls_misses) 217 comp->last_cs = lcs; 218 hlen += th->th_off; 219 hlen <<= 2; 220 goto uncompressed; 221 222 found: 223 /* 224 * Found it -- move to the front on the connection list. 225 */ 226 if (cs == lastcs) 227 comp->last_cs = lcs; 228 else { 229 lcs->cs_next = cs->cs_next; 230 cs->cs_next = lastcs->cs_next; 231 lastcs->cs_next = cs; 232 } 233 } 234 235 /* 236 * Make sure that only what we expect to change changed. The first 237 * line of the `if' checks the IP protocol version, header length & 238 * type of service. The 2nd line checks the "Don't fragment" bit. 239 * The 3rd line checks the time-to-live and protocol (the protocol 240 * check is unnecessary but costless). The 4th line checks the TCP 241 * header length. The 5th line checks IP options, if any. The 6th 242 * line checks TCP options, if any. If any of these things are 243 * different between the previous & current datagram, we send the 244 * current datagram `uncompressed'. 245 */ 246 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 247 deltaS = hlen; 248 hlen += th->th_off; 249 hlen <<= 2; 250 251 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 252 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 253 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 254 th->th_off != oth->th_off || 255 (deltaS > 5 && 256 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 257 (th->th_off > 5 && 258 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 259 goto uncompressed; 260 261 /* 262 * Figure out which of the changing fields changed. The 263 * receiver expects changes in the order: urgent, window, 264 * ack, seq (the order minimizes the number of temporaries 265 * needed in this section of code). 266 */ 267 if (th->th_flags & TH_URG) { 268 deltaS = ntohs(th->th_urp); 269 ENCODEZ(deltaS); 270 changes |= NEW_U; 271 } else if (th->th_urp != oth->th_urp) 272 /* argh! URG not set but urp changed -- a sensible 273 * implementation should never do this but RFC793 274 * doesn't prohibit the change so we have to deal 275 * with it. */ 276 goto uncompressed; 277 278 deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win)); 279 if (deltaS) { 280 ENCODE(deltaS); 281 changes |= NEW_W; 282 } 283 284 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 285 if (deltaA) { 286 if (deltaA > 0xffff) 287 goto uncompressed; 288 ENCODE(deltaA); 289 changes |= NEW_A; 290 } 291 292 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 293 if (deltaS) { 294 if (deltaS > 0xffff) 295 goto uncompressed; 296 ENCODE(deltaS); 297 changes |= NEW_S; 298 } 299 300 switch(changes) { 301 302 case 0: 303 /* 304 * Nothing changed. If this packet contains data and the 305 * last one didn't, this is probably a data packet following 306 * an ack (normal on an interactive connection) and we send 307 * it compressed. Otherwise it's probably a retransmit, 308 * retransmitted ack or window probe. Send it uncompressed 309 * in case the other side missed the compressed version. 310 */ 311 if (ip->ip_len != cs->cs_ip.ip_len && 312 ntohs(cs->cs_ip.ip_len) == hlen) 313 break; 314 315 /* (fall through) */ 316 317 case SPECIAL_I: 318 case SPECIAL_D: 319 /* 320 * actual changes match one of our special case encodings -- 321 * send packet uncompressed. 322 */ 323 goto uncompressed; 324 325 case NEW_S|NEW_A: 326 if (deltaS == deltaA && 327 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 328 /* special case for echoed terminal traffic */ 329 changes = SPECIAL_I; 330 cp = new_seq; 331 } 332 break; 333 334 case NEW_S: 335 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 336 /* special case for data xfer */ 337 changes = SPECIAL_D; 338 cp = new_seq; 339 } 340 break; 341 } 342 343 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 344 if (deltaS != 1) { 345 ENCODEZ(deltaS); 346 changes |= NEW_I; 347 } 348 if (th->th_flags & TH_PUSH) 349 changes |= TCP_PUSH_BIT; 350 /* 351 * Grab the cksum before we overwrite it below. Then update our 352 * state with this packet's header. 353 */ 354 deltaA = ntohs(th->th_sum); 355 BCOPY(ip, &cs->cs_ip, hlen); 356 357 /* 358 * We want to use the original packet as our compressed packet. 359 * (cp - new_seq) is the number of bytes we need for compressed 360 * sequence numbers. In addition we need one byte for the change 361 * mask, one for the connection id and two for the tcp checksum. 362 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 363 * many bytes of the original packet to toss so subtract the two to 364 * get the new packet size. 365 */ 366 deltaS = cp - new_seq; 367 cp = (u_char *)ip; 368 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 369 comp->last_xmit = cs->cs_id; 370 hlen -= deltaS + 4; 371 cp += hlen; 372 *cp++ = changes | NEW_C; 373 *cp++ = cs->cs_id; 374 } else { 375 hlen -= deltaS + 3; 376 cp += hlen; 377 *cp++ = changes; 378 } 379 m->m_len -= hlen; 380 m->m_data += hlen; 381 *cp++ = deltaA >> 8; 382 *cp++ = deltaA; 383 BCOPY(new_seq, cp, deltaS); 384 INCR(sls_compressed) 385 return (TYPE_COMPRESSED_TCP); 386 387 /* 388 * Update connection state cs & send uncompressed packet ('uncompressed' 389 * means a regular ip/tcp packet but with the 'conversation id' we hope 390 * to use on future compressed packets in the protocol field). 391 */ 392 uncompressed: 393 BCOPY(ip, &cs->cs_ip, hlen); 394 ip->ip_p = cs->cs_id; 395 comp->last_xmit = cs->cs_id; 396 return (TYPE_UNCOMPRESSED_TCP); 397 } 398 399 400 int 401 sl_uncompress_tcp(bufp, len, type, comp) 402 u_char **bufp; 403 int len; 404 u_int type; 405 struct slcompress *comp; 406 { 407 u_char *hdr, *cp; 408 int hlen, vjlen; 409 410 cp = bufp? *bufp: NULL; 411 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 412 if (vjlen < 0) 413 return (0); /* error */ 414 if (vjlen == 0) 415 return (len); /* was uncompressed already */ 416 417 cp += vjlen; 418 len -= vjlen; 419 420 /* 421 * At this point, cp points to the first byte of data in the 422 * packet. If we're not aligned on a 4-byte boundary, copy the 423 * data down so the ip & tcp headers will be aligned. Then back up 424 * cp by the tcp/ip header length to make room for the reconstructed 425 * header (we assume the packet we were handed has enough space to 426 * prepend 128 bytes of header). 427 */ 428 if ((int)cp & 3) { 429 if (len > 0) 430 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 431 cp = (u_char *)((int)cp &~ 3); 432 } 433 cp -= hlen; 434 len += hlen; 435 BCOPY(hdr, cp, hlen); 436 437 *bufp = cp; 438 return (len); 439 } 440 441 /* 442 * Uncompress a packet of total length total_len. The first buflen 443 * bytes are at buf; this must include the entire (compressed or 444 * uncompressed) TCP/IP header. This procedure returns the length 445 * of the VJ header, with a pointer to the uncompressed IP header 446 * in *hdrp and its length in *hlenp. 447 */ 448 int 449 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 450 u_char *buf; 451 int buflen, total_len; 452 u_int type; 453 struct slcompress *comp; 454 u_char **hdrp; 455 u_int *hlenp; 456 { 457 register u_char *cp; 458 register u_int hlen, changes; 459 register struct tcphdr *th; 460 register struct cstate *cs; 461 register struct ip *ip; 462 register u_short *bp; 463 register u_int vjlen; 464 465 switch (type) { 466 467 case TYPE_UNCOMPRESSED_TCP: 468 ip = (struct ip *) buf; 469 if (ip->ip_p >= MAX_STATES) 470 goto bad; 471 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 472 comp->flags &=~ SLF_TOSS; 473 ip->ip_p = IPPROTO_TCP; 474 hlen = ip->ip_hl; 475 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 476 hlen <<= 2; 477 BCOPY(ip, &cs->cs_ip, hlen); 478 cs->cs_hlen = hlen; 479 INCR(sls_uncompressedin) 480 *hdrp = (u_char *) &cs->cs_ip; 481 *hlenp = hlen; 482 return (0); 483 484 default: 485 goto bad; 486 487 case TYPE_COMPRESSED_TCP: 488 break; 489 } 490 /* We've got a compressed packet. */ 491 INCR(sls_compressedin) 492 cp = buf; 493 changes = *cp++; 494 if (changes & NEW_C) { 495 /* Make sure the state index is in range, then grab the state. 496 * If we have a good state index, clear the 'discard' flag. */ 497 if (*cp >= MAX_STATES) 498 goto bad; 499 500 comp->flags &=~ SLF_TOSS; 501 comp->last_recv = *cp++; 502 } else { 503 /* this packet has an implicit state index. If we've 504 * had a line error since the last time we got an 505 * explicit state index, we have to toss the packet. */ 506 if (comp->flags & SLF_TOSS) { 507 INCR(sls_tossed) 508 return (-1); 509 } 510 } 511 cs = &comp->rstate[comp->last_recv]; 512 hlen = cs->cs_ip.ip_hl << 2; 513 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 514 th->th_sum = htons((*cp << 8) | cp[1]); 515 cp += 2; 516 if (changes & TCP_PUSH_BIT) 517 th->th_flags |= TH_PUSH; 518 else 519 th->th_flags &=~ TH_PUSH; 520 521 switch (changes & SPECIALS_MASK) { 522 case SPECIAL_I: 523 { 524 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 525 th->th_ack = htonl(ntohl(th->th_ack) + i); 526 th->th_seq = htonl(ntohl(th->th_seq) + i); 527 } 528 break; 529 530 case SPECIAL_D: 531 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 532 - cs->cs_hlen); 533 break; 534 535 default: 536 if (changes & NEW_U) { 537 th->th_flags |= TH_URG; 538 DECODEU(th->th_urp) 539 } else 540 th->th_flags &=~ TH_URG; 541 if (changes & NEW_W) 542 DECODES(th->th_win) 543 if (changes & NEW_A) 544 DECODEL(th->th_ack) 545 if (changes & NEW_S) 546 DECODEL(th->th_seq) 547 break; 548 } 549 if (changes & NEW_I) { 550 DECODES(cs->cs_ip.ip_id) 551 } else 552 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 553 554 /* 555 * At this point, cp points to the first byte of data in the 556 * packet. Fill in the IP total length and update the IP 557 * header checksum. 558 */ 559 vjlen = cp - buf; 560 buflen -= vjlen; 561 if (buflen < 0) 562 /* we must have dropped some characters (crc should detect 563 * this but the old slip framing won't) */ 564 goto bad; 565 566 total_len += cs->cs_hlen - vjlen; 567 cs->cs_ip.ip_len = htons(total_len); 568 569 /* recompute the ip header checksum */ 570 bp = (u_short *) &cs->cs_ip; 571 cs->cs_ip.ip_sum = 0; 572 for (changes = 0; hlen > 0; hlen -= 2) 573 changes += *bp++; 574 changes = (changes & 0xffff) + (changes >> 16); 575 changes = (changes & 0xffff) + (changes >> 16); 576 cs->cs_ip.ip_sum = ~ changes; 577 578 *hdrp = (u_char *) &cs->cs_ip; 579 *hlenp = cs->cs_hlen; 580 return vjlen; 581 582 bad: 583 comp->flags |= SLF_TOSS; 584 INCR(sls_errorin) 585 return (-1); 586 } 587