1 /* $OpenBSD: slcompress.c,v 1.12 2015/12/03 14:34:48 blambert Exp $ */
2 /* $NetBSD: slcompress.c,v 1.17 1997/05/17 21:12:10 christos Exp $ */
3
4 /*
5 * Copyright (c) 1989, 1993, 1994
6 * The Regents of the University of California. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
32 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
33 */
34
35 /*
36 * Routines to compress and uncompess tcp packets (for transmission
37 * over low speed serial lines.
38 *
39 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
40 * - Initial distribution.
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/ip.h>
49 #include <netinet/tcp.h>
50
51 #include <net/slcompress.h>
52
53 #ifndef SL_NO_STATS
54 #define INCR(counter) ++comp->counter;
55 #else
56 #define INCR(counter)
57 #endif
58
59 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
60 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
61
62 void
sl_compress_init(struct slcompress * comp)63 sl_compress_init(struct slcompress *comp)
64 {
65 u_int i;
66 struct cstate *tstate = comp->tstate;
67
68 bzero((char *)comp, sizeof(*comp));
69 for (i = MAX_STATES - 1; i > 0; --i) {
70 tstate[i].cs_id = i;
71 tstate[i].cs_next = &tstate[i - 1];
72 }
73 tstate[0].cs_next = &tstate[MAX_STATES - 1];
74 tstate[0].cs_id = 0;
75 comp->last_cs = &tstate[0];
76 comp->last_recv = 255;
77 comp->last_xmit = 255;
78 comp->flags = SLF_TOSS;
79 }
80
81
82 /*
83 * Like sl_compress_init, but we get to specify the maximum connection
84 * ID to use on transmission.
85 */
86 void
sl_compress_setup(struct slcompress * comp,int max_state)87 sl_compress_setup(struct slcompress *comp, int max_state)
88 {
89 u_int i;
90 struct cstate *tstate = comp->tstate;
91
92 if (max_state == -1) {
93 max_state = MAX_STATES - 1;
94 bzero((char *)comp, sizeof(*comp));
95 } else {
96 /* Don't reset statistics */
97 bzero((char *)comp->tstate, sizeof(comp->tstate));
98 bzero((char *)comp->rstate, sizeof(comp->rstate));
99 }
100 for (i = max_state; i > 0; --i) {
101 tstate[i].cs_id = i;
102 tstate[i].cs_next = &tstate[i - 1];
103 }
104 tstate[0].cs_next = &tstate[max_state];
105 tstate[0].cs_id = 0;
106 comp->last_cs = &tstate[0];
107 comp->last_recv = 255;
108 comp->last_xmit = 255;
109 comp->flags = SLF_TOSS;
110 }
111
112
113 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
114 * checks for zero (since zero has to be encoded in the long, 3 byte
115 * form).
116 */
117 #define ENCODE(n) { \
118 if ((u_int16_t)(n) >= 256) { \
119 *cp++ = 0; \
120 cp[1] = (n); \
121 cp[0] = (n) >> 8; \
122 cp += 2; \
123 } else { \
124 *cp++ = (n); \
125 } \
126 }
127 #define ENCODEZ(n) { \
128 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
129 *cp++ = 0; \
130 cp[1] = (n); \
131 cp[0] = (n) >> 8; \
132 cp += 2; \
133 } else { \
134 *cp++ = (n); \
135 } \
136 }
137
138 #define DECODEL(f) { \
139 if (*cp == 0) {\
140 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
141 cp += 3; \
142 } else { \
143 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
144 } \
145 }
146
147 #define DECODES(f) { \
148 if (*cp == 0) {\
149 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
150 cp += 3; \
151 } else { \
152 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
153 } \
154 }
155
156 #define DECODEU(f) { \
157 if (*cp == 0) {\
158 (f) = htons((cp[1] << 8) | cp[2]); \
159 cp += 3; \
160 } else { \
161 (f) = htons((u_int32_t)*cp++); \
162 } \
163 }
164
165 u_int
sl_compress_tcp(struct mbuf * m,struct ip * ip,struct slcompress * comp,int compress_cid)166 sl_compress_tcp(struct mbuf *m, struct ip *ip, 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 goto uncompressed;
239
240 found:
241 /*
242 * Found it -- move to the front on the connection list.
243 */
244 if (cs == lastcs)
245 comp->last_cs = lcs;
246 else {
247 lcs->cs_next = cs->cs_next;
248 cs->cs_next = lastcs->cs_next;
249 lastcs->cs_next = cs;
250 }
251 }
252
253 /*
254 * Make sure that only what we expect to change changed. The first
255 * line of the `if' checks the IP protocol version, header length &
256 * type of service. The 2nd line checks the "Don't fragment" bit.
257 * The 3rd line checks the time-to-live and protocol (the protocol
258 * check is unnecessary but costless). The 4th line checks the TCP
259 * header length. The 5th line checks IP options, if any. The 6th
260 * line checks TCP options, if any. If any of these things are
261 * different between the previous & current datagram, we send the
262 * current datagram `uncompressed'.
263 */
264 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
265 deltaS = hlen;
266 hlen += th->th_off;
267 hlen <<= 2;
268
269 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
270 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
271 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
272 th->th_off != oth->th_off ||
273 (deltaS > 5 &&
274 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
275 (th->th_off > 5 &&
276 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
277 goto uncompressed;
278
279 /*
280 * Figure out which of the changing fields changed. The
281 * receiver expects changes in the order: urgent, window,
282 * ack, seq (the order minimizes the number of temporaries
283 * needed in this section of code).
284 */
285 if (th->th_flags & TH_URG) {
286 deltaS = ntohs(th->th_urp);
287 ENCODEZ(deltaS);
288 changes |= NEW_U;
289 } else if (th->th_urp != oth->th_urp)
290 /* argh! URG not set but urp changed -- a sensible
291 * implementation should never do this but RFC793
292 * doesn't prohibit the change so we have to deal
293 * with it. */
294 goto uncompressed;
295
296 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
297 if (deltaS) {
298 ENCODE(deltaS);
299 changes |= NEW_W;
300 }
301
302 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
303 if (deltaA) {
304 if (deltaA > 0xffff)
305 goto uncompressed;
306 ENCODE(deltaA);
307 changes |= NEW_A;
308 }
309
310 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
311 if (deltaS) {
312 if (deltaS > 0xffff)
313 goto uncompressed;
314 ENCODE(deltaS);
315 changes |= NEW_S;
316 }
317
318 switch(changes) {
319
320 case 0:
321 /*
322 * Nothing changed. If this packet contains data and the
323 * last one didn't, this is probably a data packet following
324 * an ack (normal on an interactive connection) and we send
325 * it compressed. Otherwise it's probably a retransmit,
326 * retransmitted ack or window probe. Send it uncompressed
327 * in case the other side missed the compressed version.
328 */
329 if (ip->ip_len != cs->cs_ip.ip_len &&
330 ntohs(cs->cs_ip.ip_len) == hlen)
331 break;
332
333 /* FALLTHROUGH */
334
335 case SPECIAL_I:
336 case SPECIAL_D:
337 /*
338 * actual changes match one of our special case encodings --
339 * send packet uncompressed.
340 */
341 goto uncompressed;
342
343 case NEW_S|NEW_A:
344 if (deltaS == deltaA &&
345 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
346 /* special case for echoed terminal traffic */
347 changes = SPECIAL_I;
348 cp = new_seq;
349 }
350 break;
351
352 case NEW_S:
353 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
354 /* special case for data xfer */
355 changes = SPECIAL_D;
356 cp = new_seq;
357 }
358 break;
359 }
360
361 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
362 if (deltaS != 1) {
363 ENCODEZ(deltaS);
364 changes |= NEW_I;
365 }
366 if (th->th_flags & TH_PUSH)
367 changes |= TCP_PUSH_BIT;
368 /*
369 * Grab the cksum before we overwrite it below. Then update our
370 * state with this packet's header.
371 */
372 deltaA = ntohs(th->th_sum);
373 BCOPY(ip, &cs->cs_ip, hlen);
374
375 /*
376 * We want to use the original packet as our compressed packet.
377 * (cp - new_seq) is the number of bytes we need for compressed
378 * sequence numbers. In addition we need one byte for the change
379 * mask, one for the connection id and two for the tcp checksum.
380 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
381 * many bytes of the original packet to toss so subtract the two to
382 * get the new packet size.
383 */
384 deltaS = cp - new_seq;
385 cp = (u_char *)ip;
386 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
387 comp->last_xmit = cs->cs_id;
388 hlen -= deltaS + 4;
389 cp += hlen;
390 *cp++ = changes | NEW_C;
391 *cp++ = cs->cs_id;
392 } else {
393 hlen -= deltaS + 3;
394 cp += hlen;
395 *cp++ = changes;
396 }
397 m->m_len -= hlen;
398 m->m_data += hlen;
399 *cp++ = deltaA >> 8;
400 *cp++ = deltaA;
401 BCOPY(new_seq, cp, deltaS);
402 INCR(sls_compressed)
403 return (TYPE_COMPRESSED_TCP);
404
405 /*
406 * Update connection state cs & send uncompressed packet ('uncompressed'
407 * means a regular ip/tcp packet but with the 'conversation id' we hope
408 * to use on future compressed packets in the protocol field).
409 */
410 uncompressed:
411 BCOPY(ip, &cs->cs_ip, hlen);
412 ip->ip_p = cs->cs_id;
413 comp->last_xmit = cs->cs_id;
414 return (TYPE_UNCOMPRESSED_TCP);
415 }
416
417
418 int
sl_uncompress_tcp(u_char ** bufp,int len,u_int type,struct slcompress * comp)419 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
420 {
421 u_char *hdr, *cp;
422 int hlen, vjlen;
423
424 cp = bufp? *bufp: NULL;
425 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
426 if (vjlen < 0)
427 return (0); /* error */
428 if (vjlen == 0)
429 return (len); /* was uncompressed already */
430
431 cp += vjlen;
432 len -= vjlen;
433
434 /*
435 * At this point, cp points to the first byte of data in the
436 * packet. If we're not aligned on a 4-byte boundary, copy the
437 * data down so the ip & tcp headers will be aligned. Then back up
438 * cp by the tcp/ip header length to make room for the reconstructed
439 * header (we assume the packet we were handed has enough space to
440 * prepend 128 bytes of header).
441 */
442 if ((long)cp & 3) {
443 if (len > 0)
444 (void) memmove((caddr_t)((long)cp &~ 3), cp, len);
445 cp = (u_char *)((long)cp &~ 3);
446 }
447 cp -= hlen;
448 len += hlen;
449 BCOPY(hdr, cp, hlen);
450
451 *bufp = cp;
452 return (len);
453 }
454
455 /*
456 * Uncompress a packet of total length total_len. The first buflen
457 * bytes are at buf; this must include the entire (compressed or
458 * uncompressed) TCP/IP header. This procedure returns the length
459 * of the VJ header, with a pointer to the uncompressed IP header
460 * in *hdrp and its length in *hlenp.
461 */
462 int
sl_uncompress_tcp_core(u_char * buf,int buflen,int total_len,u_int type,struct slcompress * comp,u_char ** hdrp,u_int * hlenp)463 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
464 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
465 {
466 u_char *cp;
467 u_int hlen, changes;
468 struct tcphdr *th;
469 struct cstate *cs;
470 struct ip *ip;
471 u_int16_t *bp;
472 u_int vjlen;
473
474 switch (type) {
475
476 case TYPE_UNCOMPRESSED_TCP:
477 ip = (struct ip *) buf;
478 if (ip->ip_p >= MAX_STATES)
479 goto bad;
480 cs = &comp->rstate[comp->last_recv = ip->ip_p];
481 comp->flags &=~ SLF_TOSS;
482 ip->ip_p = IPPROTO_TCP;
483 /*
484 * Calculate the size of the TCP/IP header and make sure that
485 * we don't overflow the space we have available for it.
486 */
487 hlen = ip->ip_hl << 2;
488 if (hlen + sizeof(struct tcphdr) > buflen)
489 goto bad;
490 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
491 if (hlen > MAX_HDR || hlen > buflen)
492 goto bad;
493 BCOPY(ip, &cs->cs_ip, hlen);
494 cs->cs_hlen = hlen;
495 INCR(sls_uncompressedin)
496 *hdrp = (u_char *) &cs->cs_ip;
497 *hlenp = hlen;
498 return (0);
499
500 default:
501 goto bad;
502
503 case TYPE_COMPRESSED_TCP:
504 break;
505 }
506 /* We've got a compressed packet. */
507 INCR(sls_compressedin)
508 cp = buf;
509 changes = *cp++;
510 if (changes & NEW_C) {
511 /* Make sure the state index is in range, then grab the state.
512 * If we have a good state index, clear the 'discard' flag. */
513 if (*cp >= MAX_STATES)
514 goto bad;
515
516 comp->flags &=~ SLF_TOSS;
517 comp->last_recv = *cp++;
518 } else {
519 /* this packet has an implicit state index. If we've
520 * had a line error since the last time we got an
521 * explicit state index, we have to toss the packet. */
522 if (comp->flags & SLF_TOSS) {
523 INCR(sls_tossed)
524 return (-1);
525 }
526 }
527 cs = &comp->rstate[comp->last_recv];
528 hlen = cs->cs_ip.ip_hl << 2;
529 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
530 th->th_sum = htons((*cp << 8) | cp[1]);
531 cp += 2;
532 if (changes & TCP_PUSH_BIT)
533 th->th_flags |= TH_PUSH;
534 else
535 th->th_flags &=~ TH_PUSH;
536
537 switch (changes & SPECIALS_MASK) {
538 case SPECIAL_I:
539 {
540 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
541 th->th_ack = htonl(ntohl(th->th_ack) + i);
542 th->th_seq = htonl(ntohl(th->th_seq) + i);
543 }
544 break;
545
546 case SPECIAL_D:
547 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
548 - cs->cs_hlen);
549 break;
550
551 default:
552 if (changes & NEW_U) {
553 th->th_flags |= TH_URG;
554 DECODEU(th->th_urp)
555 } else
556 th->th_flags &=~ TH_URG;
557 if (changes & NEW_W)
558 DECODES(th->th_win)
559 if (changes & NEW_A)
560 DECODEL(th->th_ack)
561 if (changes & NEW_S)
562 DECODEL(th->th_seq)
563 break;
564 }
565 if (changes & NEW_I) {
566 DECODES(cs->cs_ip.ip_id)
567 } else
568 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
569
570 /*
571 * At this point, cp points to the first byte of data in the
572 * packet. Fill in the IP total length and update the IP
573 * header checksum.
574 */
575 vjlen = cp - buf;
576 buflen -= vjlen;
577 if (buflen < 0)
578 /* we must have dropped some characters (crc should detect
579 * this but the old slip framing won't) */
580 goto bad;
581
582 total_len += cs->cs_hlen - vjlen;
583 cs->cs_ip.ip_len = htons(total_len);
584
585 /* recompute the ip header checksum */
586 bp = (u_int16_t *) &cs->cs_ip;
587 cs->cs_ip.ip_sum = 0;
588 for (changes = 0; hlen > 0; hlen -= 2)
589 changes += *bp++;
590 changes = (changes & 0xffff) + (changes >> 16);
591 changes = (changes & 0xffff) + (changes >> 16);
592 cs->cs_ip.ip_sum = ~ changes;
593
594 *hdrp = (u_char *) &cs->cs_ip;
595 *hlenp = cs->cs_hlen;
596 return vjlen;
597
598 bad:
599 comp->flags |= SLF_TOSS;
600 INCR(sls_errorin)
601 return (-1);
602 }
603