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 * from: @(#)slcompress.c 8.2 (Berkeley) 4/16/94 34 * $Id: slcompress.c,v 1.8 1994/05/13 06:03:25 mycroft 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 #include <sys/param.h> 46 #include <sys/mbuf.h> 47 48 #include <netinet/in.h> 49 #include <netinet/in_systm.h> 50 #include <netinet/ip.h> 51 #include <netinet/tcp.h> 52 53 #include <net/slcompress.h> 54 55 #ifndef SL_NO_STATS 56 #define INCR(counter) ++comp->counter; 57 #else 58 #define INCR(counter) 59 #endif 60 61 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 62 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 63 #ifndef KERNEL 64 #define ovbcopy bcopy 65 #endif 66 67 void 68 sl_compress_init(comp, max_state) 69 struct slcompress *comp; 70 int max_state; 71 { 72 register u_int i; 73 register struct cstate *tstate = comp->tstate; 74 75 if (max_state == -1) 76 max_state = MAX_STATES - 1; 77 bzero((char *)comp, sizeof(*comp)); 78 for (i = max_state; i > 0; --i) { 79 tstate[i].cs_id = i; 80 tstate[i].cs_next = &tstate[i - 1]; 81 } 82 tstate[0].cs_next = &tstate[max_state]; 83 tstate[0].cs_id = 0; 84 comp->last_cs = &tstate[0]; 85 comp->last_recv = 255; 86 comp->last_xmit = 255; 87 comp->flags = SLF_TOSS; 88 } 89 90 91 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 92 * checks for zero (since zero has to be encoded in the long, 3 byte 93 * form). 94 */ 95 #define ENCODE(n) { \ 96 if ((u_short)(n) >= 256) { \ 97 *cp++ = 0; \ 98 cp[1] = (n); \ 99 cp[0] = (n) >> 8; \ 100 cp += 2; \ 101 } else { \ 102 *cp++ = (n); \ 103 } \ 104 } 105 #define ENCODEZ(n) { \ 106 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 107 *cp++ = 0; \ 108 cp[1] = (n); \ 109 cp[0] = (n) >> 8; \ 110 cp += 2; \ 111 } else { \ 112 *cp++ = (n); \ 113 } \ 114 } 115 116 #define DECODEL(f) { \ 117 if (*cp == 0) {\ 118 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 119 cp += 3; \ 120 } else { \ 121 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 122 } \ 123 } 124 125 #define DECODES(f) { \ 126 if (*cp == 0) {\ 127 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 128 cp += 3; \ 129 } else { \ 130 (f) = htons(ntohs(f) + (u_long)*cp++); \ 131 } \ 132 } 133 134 #define DECODEU(f) { \ 135 if (*cp == 0) {\ 136 (f) = htons((cp[1] << 8) | cp[2]); \ 137 cp += 3; \ 138 } else { \ 139 (f) = htons((u_long)*cp++); \ 140 } \ 141 } 142 143 u_int 144 sl_compress_tcp(m, ip, comp, compress_cid) 145 struct mbuf *m; 146 register struct ip *ip; 147 struct slcompress *comp; 148 int compress_cid; 149 { 150 register struct cstate *cs = comp->last_cs->cs_next; 151 register u_int hlen = ip->ip_hl; 152 register struct tcphdr *oth; 153 register struct tcphdr *th; 154 register u_int deltaS, deltaA; 155 register u_int changes = 0; 156 u_char new_seq[16]; 157 register u_char *cp = new_seq; 158 159 /* 160 * Bail if this is an IP fragment or if the TCP packet isn't 161 * `compressible' (i.e., ACK isn't set or some other control bit is 162 * set). (We assume that the caller has already made sure the 163 * packet is IP proto TCP). 164 */ 165 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 166 return (TYPE_IP); 167 168 th = (struct tcphdr *)&((int *)ip)[hlen]; 169 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 170 return (TYPE_IP); 171 /* 172 * Packet is compressible -- we're going to send either a 173 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 174 * to locate (or create) the connection state. Special case the 175 * most recently used connection since it's most likely to be used 176 * again & we don't have to do any reordering if it's used. 177 */ 178 INCR(sls_packets) 179 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 180 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 181 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 182 /* 183 * Wasn't the first -- search for it. 184 * 185 * States are kept in a circularly linked list with 186 * last_cs pointing to the end of the list. The 187 * list is kept in lru order by moving a state to the 188 * head of the list whenever it is referenced. Since 189 * the list is short and, empirically, the connection 190 * we want is almost always near the front, we locate 191 * states via linear search. If we don't find a state 192 * for the datagram, the oldest state is (re-)used. 193 */ 194 register struct cstate *lcs; 195 register struct cstate *lastcs = comp->last_cs; 196 197 do { 198 lcs = cs; cs = cs->cs_next; 199 INCR(sls_searches) 200 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 201 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 202 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 203 goto found; 204 } while (cs != lastcs); 205 206 /* 207 * Didn't find it -- re-use oldest cstate. Send an 208 * uncompressed packet that tells the other side what 209 * connection number we're using for this conversation. 210 * Note that since the state list is circular, the oldest 211 * state points to the newest and we only need to set 212 * last_cs to update the lru linkage. 213 */ 214 INCR(sls_misses) 215 comp->last_cs = lcs; 216 hlen += th->th_off; 217 hlen <<= 2; 218 goto uncompressed; 219 220 found: 221 /* 222 * Found it -- move to the front on the connection list. 223 */ 224 if (cs == lastcs) 225 comp->last_cs = lcs; 226 else { 227 lcs->cs_next = cs->cs_next; 228 cs->cs_next = lastcs->cs_next; 229 lastcs->cs_next = cs; 230 } 231 } 232 233 /* 234 * Make sure that only what we expect to change changed. The first 235 * line of the `if' checks the IP protocol version, header length & 236 * type of service. The 2nd line checks the "Don't fragment" bit. 237 * The 3rd line checks the time-to-live and protocol (the protocol 238 * check is unnecessary but costless). The 4th line checks the TCP 239 * header length. The 5th line checks IP options, if any. The 6th 240 * line checks TCP options, if any. If any of these things are 241 * different between the previous & current datagram, we send the 242 * current datagram `uncompressed'. 243 */ 244 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 245 deltaS = hlen; 246 hlen += th->th_off; 247 hlen <<= 2; 248 249 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 250 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 251 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 252 th->th_off != oth->th_off || 253 (deltaS > 5 && 254 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 255 (th->th_off > 5 && 256 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 257 goto uncompressed; 258 259 /* 260 * Figure out which of the changing fields changed. The 261 * receiver expects changes in the order: urgent, window, 262 * ack, seq (the order minimizes the number of temporaries 263 * needed in this section of code). 264 */ 265 if (th->th_flags & TH_URG) { 266 deltaS = ntohs(th->th_urp); 267 ENCODEZ(deltaS); 268 changes |= NEW_U; 269 } else if (th->th_urp != oth->th_urp) 270 /* argh! URG not set but urp changed -- a sensible 271 * implementation should never do this but RFC793 272 * doesn't prohibit the change so we have to deal 273 * with it. */ 274 goto uncompressed; 275 276 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { 277 ENCODE(deltaS); 278 changes |= NEW_W; 279 } 280 281 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 282 if (deltaA > 0xffff) 283 goto uncompressed; 284 ENCODE(deltaA); 285 changes |= NEW_A; 286 } 287 288 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 289 if (deltaS > 0xffff) 290 goto uncompressed; 291 ENCODE(deltaS); 292 changes |= NEW_S; 293 } 294 295 switch(changes) { 296 297 case 0: 298 /* 299 * Nothing changed. If this packet contains data and the 300 * last one didn't, this is probably a data packet following 301 * an ack (normal on an interactive connection) and we send 302 * it compressed. Otherwise it's probably a retransmit, 303 * retransmitted ack or window probe. Send it uncompressed 304 * in case the other side missed the compressed version. 305 */ 306 if (ip->ip_len != cs->cs_ip.ip_len && 307 ntohs(cs->cs_ip.ip_len) == hlen) 308 break; 309 310 /* (fall through) */ 311 312 case SPECIAL_I: 313 case SPECIAL_D: 314 /* 315 * actual changes match one of our special case encodings -- 316 * send packet uncompressed. 317 */ 318 goto uncompressed; 319 320 case NEW_S|NEW_A: 321 if (deltaS == deltaA && 322 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 323 /* special case for echoed terminal traffic */ 324 changes = SPECIAL_I; 325 cp = new_seq; 326 } 327 break; 328 329 case NEW_S: 330 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 331 /* special case for data xfer */ 332 changes = SPECIAL_D; 333 cp = new_seq; 334 } 335 break; 336 } 337 338 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 339 if (deltaS != 1) { 340 ENCODEZ(deltaS); 341 changes |= NEW_I; 342 } 343 if (th->th_flags & TH_PUSH) 344 changes |= TCP_PUSH_BIT; 345 /* 346 * Grab the cksum before we overwrite it below. Then update our 347 * state with this packet's header. 348 */ 349 deltaA = ntohs(th->th_sum); 350 BCOPY(ip, &cs->cs_ip, hlen); 351 352 /* 353 * We want to use the original packet as our compressed packet. 354 * (cp - new_seq) is the number of bytes we need for compressed 355 * sequence numbers. In addition we need one byte for the change 356 * mask, one for the connection id and two for the tcp checksum. 357 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 358 * many bytes of the original packet to toss so subtract the two to 359 * get the new packet size. 360 */ 361 deltaS = cp - new_seq; 362 cp = (u_char *)ip; 363 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 364 comp->last_xmit = cs->cs_id; 365 hlen -= deltaS + 4; 366 cp += hlen; 367 *cp++ = changes | NEW_C; 368 *cp++ = cs->cs_id; 369 } else { 370 hlen -= deltaS + 3; 371 cp += hlen; 372 *cp++ = changes; 373 } 374 m->m_len -= hlen; 375 m->m_data += hlen; 376 *cp++ = deltaA >> 8; 377 *cp++ = deltaA; 378 BCOPY(new_seq, cp, deltaS); 379 INCR(sls_compressed) 380 return (TYPE_COMPRESSED_TCP); 381 382 /* 383 * Update connection state cs & send uncompressed packet ('uncompressed' 384 * means a regular ip/tcp packet but with the 'conversation id' we hope 385 * to use on future compressed packets in the protocol field). 386 */ 387 uncompressed: 388 BCOPY(ip, &cs->cs_ip, hlen); 389 ip->ip_p = cs->cs_id; 390 comp->last_xmit = cs->cs_id; 391 return (TYPE_UNCOMPRESSED_TCP); 392 } 393 394 395 int 396 sl_uncompress_tcp(bufp, len, type, comp) 397 u_char **bufp; 398 int len; 399 u_int type; 400 struct slcompress *comp; 401 { 402 403 return sl_uncompress_tcp_part(bufp, len, len, type, comp); 404 } 405 406 /* 407 * Uncompress a packet of total length total_len. The first buflen 408 * bytes are at *bufp; this must include the entire (compressed or 409 * uncompressed) TCP/IP header. In addition, there must be enough 410 * clear space before *bufp to build a full-length TCP/IP header. 411 */ 412 int 413 sl_uncompress_tcp_part(bufp, buflen, total_len, type, comp) 414 u_char **bufp; 415 int buflen, total_len; 416 u_int type; 417 struct slcompress *comp; 418 { 419 register u_char *cp; 420 register u_int hlen, changes; 421 register struct tcphdr *th; 422 register struct cstate *cs; 423 register struct ip *ip; 424 425 switch (type) { 426 427 case TYPE_UNCOMPRESSED_TCP: 428 ip = (struct ip *) *bufp; 429 if (ip->ip_p >= MAX_STATES) 430 goto bad; 431 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 432 comp->flags &=~ SLF_TOSS; 433 ip->ip_p = IPPROTO_TCP; 434 hlen = ip->ip_hl; 435 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 436 hlen <<= 2; 437 BCOPY(ip, &cs->cs_ip, hlen); 438 cs->cs_ip.ip_sum = 0; 439 cs->cs_hlen = hlen; 440 INCR(sls_uncompressedin) 441 return (total_len); 442 443 default: 444 goto bad; 445 446 case TYPE_COMPRESSED_TCP: 447 break; 448 } 449 /* We've got a compressed packet. */ 450 INCR(sls_compressedin) 451 cp = *bufp; 452 changes = *cp++; 453 if (changes & NEW_C) { 454 /* Make sure the state index is in range, then grab the state. 455 * If we have a good state index, clear the 'discard' flag. */ 456 if (*cp >= MAX_STATES) 457 goto bad; 458 459 comp->flags &=~ SLF_TOSS; 460 comp->last_recv = *cp++; 461 } else { 462 /* this packet has an implicit state index. If we've 463 * had a line error since the last time we got an 464 * explicit state index, we have to toss the packet. */ 465 if (comp->flags & SLF_TOSS) { 466 INCR(sls_tossed) 467 return (0); 468 } 469 } 470 cs = &comp->rstate[comp->last_recv]; 471 hlen = cs->cs_ip.ip_hl << 2; 472 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 473 th->th_sum = htons((*cp << 8) | cp[1]); 474 cp += 2; 475 if (changes & TCP_PUSH_BIT) 476 th->th_flags |= TH_PUSH; 477 else 478 th->th_flags &=~ TH_PUSH; 479 480 switch (changes & SPECIALS_MASK) { 481 case SPECIAL_I: 482 { 483 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 484 th->th_ack = htonl(ntohl(th->th_ack) + i); 485 th->th_seq = htonl(ntohl(th->th_seq) + i); 486 } 487 break; 488 489 case SPECIAL_D: 490 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 491 - cs->cs_hlen); 492 break; 493 494 default: 495 if (changes & NEW_U) { 496 th->th_flags |= TH_URG; 497 DECODEU(th->th_urp) 498 } else 499 th->th_flags &=~ TH_URG; 500 if (changes & NEW_W) 501 DECODES(th->th_win) 502 if (changes & NEW_A) 503 DECODEL(th->th_ack) 504 if (changes & NEW_S) 505 DECODEL(th->th_seq) 506 break; 507 } 508 if (changes & NEW_I) { 509 DECODES(cs->cs_ip.ip_id) 510 } else 511 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 512 513 /* 514 * At this point, cp points to the first byte of data in the 515 * packet. If we're not aligned on a 4-byte boundary, copy the 516 * data down so the ip & tcp headers will be aligned. Then back up 517 * cp by the tcp/ip header length to make room for the reconstructed 518 * header (we assume the packet we were handed has enough space to 519 * prepend 128 bytes of header). Adjust the length to account for 520 * the new header & fill in the IP total length. 521 */ 522 buflen -= (cp - *bufp); 523 total_len -= (cp - *bufp); 524 if (buflen < 0) 525 /* we must have dropped some characters (crc should detect 526 * this but the old slip framing won't) */ 527 goto bad; 528 529 if ((int)cp & 3) { 530 if (buflen > 0) 531 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), buflen); 532 cp = (u_char *)((int)cp &~ 3); 533 } 534 cp -= cs->cs_hlen; 535 total_len += cs->cs_hlen; 536 cs->cs_ip.ip_len = htons(total_len); 537 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 538 *bufp = cp; 539 540 /* recompute the ip header checksum */ 541 { 542 register u_short *bp = (u_short *)cp; 543 for (changes = 0; hlen > 0; hlen -= 2) 544 changes += *bp++; 545 changes = (changes & 0xffff) + (changes >> 16); 546 changes = (changes & 0xffff) + (changes >> 16); 547 ((struct ip *)cp)->ip_sum = ~ changes; 548 } 549 return (total_len); 550 bad: 551 comp->flags |= SLF_TOSS; 552 INCR(sls_errorin) 553 return (0); 554 } 555