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