1/* $NetBSD: slcompress.c,v 1.40 2016/08/05 08:56:36 pgoyette Exp $ */
2/* Id: slcompress.c,v 1.3 1996/05/24 07:04:47 paulus 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/cdefs.h>
44__KERNEL_RCSID(0, "$NetBSD: slcompress.c,v 1.40 2016/08/05 08:56:36 pgoyette Exp $");
45
46#ifdef _KERNEL_OPT
47#include "opt_inet.h"
48#endif
49
50#ifdef INET
51#include <sys/param.h>
52#include <sys/mbuf.h>
53#include <sys/systm.h>
54#include <sys/module.h>
55
56#include <netinet/in.h>
57#include <netinet/in_systm.h>
58#include <netinet/ip.h>
59#include <netinet/tcp.h>
60
61#include <net/slcompress.h>
62
63#ifndef SL_NO_STATS
64#define INCR(counter) ++comp->counter;
65#else
66#define INCR(counter)
67#endif
68
69
70void
71sl_compress_init(struct slcompress *comp)
72{
73 u_int i;
74 struct cstate *tstate = comp->tstate;
75
76 memset(comp, 0, sizeof(*comp));
77 for (i = MAX_STATES - 1; 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_STATES - 1];
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/*
91 * Like sl_compress_init, but we get to specify the maximum connection
92 * ID to use on transmission.
93 */
94void
95sl_compress_setup(struct slcompress *comp, int max_state)
96{
97 u_int i;
98 struct cstate *tstate = comp->tstate;
99
100 if (max_state == -1) {
101 max_state = MAX_STATES - 1;
102 memset(comp, 0, sizeof(*comp));
103 } else {
104 /* Don't reset statistics */
105 memset(comp->tstate, 0, sizeof(comp->tstate));
106 memset(comp->rstate, 0, sizeof(comp->rstate));
107 }
108 for (i = max_state; i > 0; --i) {
109 tstate[i].cs_id = i;
110 tstate[i].cs_next = &tstate[i - 1];
111 }
112 tstate[0].cs_next = &tstate[max_state];
113 tstate[0].cs_id = 0;
114 comp->last_cs = &tstate[0];
115 comp->last_recv = 255;
116 comp->last_xmit = 255;
117 comp->flags = SLF_TOSS;
118}
119
120
121/* ENCODE encodes a number that is known to be non-zero. ENCODEZ
122 * checks for zero (since zero has to be encoded in the long, 3 byte
123 * form).
124 */
125#define ENCODE(n) { \
126 if ((uint16_t)(n) >= 256) { \
127 *cp++ = 0; \
128 cp[1] = (n); \
129 cp[0] = (n) >> 8; \
130 cp += 2; \
131 } else { \
132 *cp++ = (n); \
133 } \
134}
135#define ENCODEZ(n) { \
136 if ((uint16_t)(n) >= 256 || (uint16_t)(n) == 0) { \
137 *cp++ = 0; \
138 cp[1] = (n); \
139 cp[0] = (n) >> 8; \
140 cp += 2; \
141 } else { \
142 *cp++ = (n); \
143 } \
144}
145
146#define DECODEL(f) { \
147 if (*cp == 0) {\
148 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
149 cp += 3; \
150 } else { \
151 (f) = htonl(ntohl(f) + (uint32_t)*cp++); \
152 } \
153}
154
155#define DECODES(f) { \
156 if (*cp == 0) {\
157 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
158 cp += 3; \
159 } else { \
160 (f) = htons(ntohs(f) + (uint32_t)*cp++); \
161 } \
162}
163
164#define DECODEU(f) { \
165 if (*cp == 0) {\
166 (f) = htons((cp[1] << 8) | cp[2]); \
167 cp += 3; \
168 } else { \
169 (f) = htons((uint32_t)*cp++); \
170 } \
171}
172
173u_int
174sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
175 int compress_cid)
176{
177 struct cstate *cs = comp->last_cs->cs_next;
178 u_int hlen = ip->ip_hl;
179 struct tcphdr *oth;
180 struct tcphdr *th;
181 u_int deltaS, deltaA;
182 u_int changes = 0;
183 u_char new_seq[16];
184 u_char *cp = new_seq;
185
186 /*
187 * Bail if this is an IP fragment or if the TCP packet isn't
188 * `compressible' (i.e., ACK isn't set or some other control bit is
189 * set). (We assume that the caller has already made sure the
190 * packet is IP proto TCP).
191 */
192 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
193 return (TYPE_IP);
194
195 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
196 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
197 return (TYPE_IP);
198 /*
199 * Packet is compressible -- we're going to send either a
200 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
201 * to locate (or create) the connection state. Special case the
202 * most recently used connection since it's most likely to be used
203 * again & we don't have to do any reordering if it's used.
204 */
205 INCR(sls_packets)
206 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
207 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
208 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
209 /*
210 * Wasn't the first -- search for it.
211 *
212 * States are kept in a circularly linked list with
213 * last_cs pointing to the end of the list. The
214 * list is kept in lru order by moving a state to the
215 * head of the list whenever it is referenced. Since
216 * the list is short and, empirically, the connection
217 * we want is almost always near the front, we locate
218 * states via linear search. If we don't find a state
219 * for the datagram, the oldest state is (re-)used.
220 */
221 struct cstate *lcs;
222 struct cstate *lastcs = comp->last_cs;
223
224 do {
225 lcs = cs; cs = cs->cs_next;
226 INCR(sls_searches)
227 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
228 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
229 && *(int32_t *)th ==
230 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
231 goto found;
232 } while (cs != lastcs);
233
234 /*
235 * Didn't find it -- re-use oldest cstate. Send an
236 * uncompressed packet that tells the other side what
237 * connection number we're using for this conversation.
238 * Note that since the state list is circular, the oldest
239 * state points to the newest and we only need to set
240 * last_cs to update the lru linkage.
241 */
242 INCR(sls_misses)
243 comp->last_cs = lcs;
244 hlen += th->th_off;
245 hlen <<= 2;
246 if (hlen > m->m_len)
247 return (TYPE_IP);
248 goto uncompressed;
249
250 found:
251 /*
252 * Found it -- move to the front on the connection list.
253 */
254 if (cs == lastcs)
255 comp->last_cs = lcs;
256 else {
257 lcs->cs_next = cs->cs_next;
258 cs->cs_next = lastcs->cs_next;
259 lastcs->cs_next = cs;
260 }
261 }
262
263 /*
264 * Make sure that only what we expect to change changed. The first
265 * line of the `if' checks the IP protocol version, header length &
266 * type of service. The 2nd line checks the "Don't fragment" bit.
267 * The 3rd line checks the time-to-live and protocol (the protocol
268 * check is unnecessary but costless). The 4th line checks the TCP
269 * header length. The 5th line checks IP options, if any. The 6th
270 * line checks TCP options, if any. If any of these things are
271 * different between the previous & current datagram, we send the
272 * current datagram `uncompressed'.
273 */
274 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
275 deltaS = hlen;
276 hlen += th->th_off;
277 hlen <<= 2;
278 if (hlen > m->m_len)
279 return (TYPE_IP);
280
281 if (((uint16_t *)ip)[0] != ((uint16_t *)&cs->cs_ip)[0] ||
282 ((uint16_t *)ip)[3] != ((uint16_t *)&cs->cs_ip)[3] ||
283 ((uint16_t *)ip)[4] != ((uint16_t *)&cs->cs_ip)[4] ||
284 th->th_off != oth->th_off ||
285 (deltaS > 5 &&
286 memcmp(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
287 (th->th_off > 5 &&
288 memcmp(th + 1, oth + 1, (th->th_off - 5) << 2)))
289 goto uncompressed;
290
291 /*
292 * Figure out which of the changing fields changed. The
293 * receiver expects changes in the order: urgent, window,
294 * ack, seq (the order minimizes the number of temporaries
295 * needed in this section of code).
296 */
297 if (th->th_flags & TH_URG) {
298 deltaS = ntohs(th->th_urp);
299 ENCODEZ(deltaS);
300 changes |= NEW_U;
301 } else if (th->th_urp != oth->th_urp)
302 /* argh! URG not set but urp changed -- a sensible
303 * implementation should never do this but RFC793
304 * doesn't prohibit the change so we have to deal
305 * with it. */
306 goto uncompressed;
307
308 deltaS = (uint16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
309 if (deltaS) {
310 ENCODE(deltaS);
311 changes |= NEW_W;
312 }
313
314 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
315 if (deltaA) {
316 if (deltaA > 0xffff)
317 goto uncompressed;
318 ENCODE(deltaA);
319 changes |= NEW_A;
320 }
321
322 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
323 if (deltaS) {
324 if (deltaS > 0xffff)
325 goto uncompressed;
326 ENCODE(deltaS);
327 changes |= NEW_S;
328 }
329
330 switch (changes) {
331
332 case 0:
333 /*
334 * Nothing changed. If this packet contains data and the
335 * last one didn't, this is probably a data packet following
336 * an ack (normal on an interactive connection) and we send
337 * it compressed. Otherwise it's probably a retransmit,
338 * retransmitted ack or window probe. Send it uncompressed
339 * in case the other side missed the compressed version.
340 */
341 if (ip->ip_len != cs->cs_ip.ip_len &&
342 ntohs(cs->cs_ip.ip_len) == hlen)
343 break;
344
345 /* (fall through) */
346
347 case SPECIAL_I:
348 case SPECIAL_D:
349 /*
350 * actual changes match one of our special case encodings --
351 * send packet uncompressed.
352 */
353 goto uncompressed;
354
355 case NEW_S|NEW_A:
356 if (deltaS == deltaA &&
357 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
358 /* special case for echoed terminal traffic */
359 changes = SPECIAL_I;
360 cp = new_seq;
361 }
362 break;
363
364 case NEW_S:
365 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
366 /* special case for data xfer */
367 changes = SPECIAL_D;
368 cp = new_seq;
369 }
370 break;
371 }
372
373 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
374 if (deltaS != 1) {
375 ENCODEZ(deltaS);
376 changes |= NEW_I;
377 }
378 if (th->th_flags & TH_PUSH)
379 changes |= TCP_PUSH_BIT;
380 /*
381 * Grab the cksum before we overwrite it below. Then update our
382 * state with this packet's header.
383 */
384 deltaA = ntohs(th->th_sum);
385 memcpy(&cs->cs_ip, ip, hlen);
386
387 /*
388 * We want to use the original packet as our compressed packet.
389 * (cp - new_seq) is the number of bytes we need for compressed
390 * sequence numbers. In addition we need one byte for the change
391 * mask, one for the connection id and two for the tcp checksum.
392 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
393 * many bytes of the original packet to toss so subtract the two to
394 * get the new packet size.
395 */
396 deltaS = cp - new_seq;
397 cp = (u_char *)ip;
398 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
399 comp->last_xmit = cs->cs_id;
400 hlen -= deltaS + 4;
401 cp += hlen;
402 *cp++ = changes | NEW_C;
403 *cp++ = cs->cs_id;
404 } else {
405 hlen -= deltaS + 3;
406 cp += hlen;
407 *cp++ = changes;
408 }
409 m->m_len -= hlen;
410 m->m_data += hlen;
411 *cp++ = deltaA >> 8;
412 *cp++ = deltaA;
413 memcpy(cp, new_seq, deltaS);
414 INCR(sls_compressed)
415 return (TYPE_COMPRESSED_TCP);
416
417 /*
418 * Update connection state cs & send uncompressed packet ('uncompressed'
419 * means a regular ip/tcp packet but with the 'conversation id' we hope
420 * to use on future compressed packets in the protocol field).
421 */
422uncompressed:
423 memcpy(&cs->cs_ip, ip, hlen);
424 ip->ip_p = cs->cs_id;
425 comp->last_xmit = cs->cs_id;
426 return (TYPE_UNCOMPRESSED_TCP);
427}
428
429
430int
431sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
432{
433 u_char *hdr, *cp;
434 int vjlen;
435 u_int hlen;
436
437 cp = bufp ? *bufp : NULL;
438 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
439 if (vjlen < 0)
440 return (0); /* error */
441 if (vjlen == 0)
442 return (len); /* was uncompressed already */
443
444 cp += vjlen;
445 len -= vjlen;
446
447 /*
448 * At this point, cp points to the first byte of data in the
449 * packet. If we're not aligned on a 4-byte boundary, copy the
450 * data down so the ip & tcp headers will be aligned. Then back up
451 * cp by the tcp/ip header length to make room for the reconstructed
452 * header (we assume the packet we were handed has enough space to
453 * prepend 128 bytes of header).
454 */
455 if ((long)cp & 3) {
456 if (len > 0)
457 memmove((void *)((long)cp &~ 3), cp, len);
458 cp = (u_char *)((long)cp &~ 3);
459 }
460 cp -= hlen;
461 len += hlen;
462 memcpy(cp, hdr, hlen);
463
464 *bufp = cp;
465 return (len);
466}
467
468/*
469 * Uncompress a packet of total length total_len. The first buflen
470 * bytes are at buf; this must include the entire (compressed or
471 * uncompressed) TCP/IP header. This procedure returns the length
472 * of the VJ header, with a pointer to the uncompressed IP header
473 * in *hdrp and its length in *hlenp.
474 */
475int
476sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
477 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
478{
479 u_char *cp;
480 u_int hlen, changes;
481 struct tcphdr *th;
482 struct cstate *cs;
483 struct ip *ip;
484 uint16_t *bp;
485 u_int vjlen;
486
487 switch (type) {
488
489 case TYPE_UNCOMPRESSED_TCP:
490 if (buf == NULL)
491 goto bad;
492 ip = (struct ip *) buf;
493 if (ip->ip_p >= MAX_STATES)
494 goto bad;
495 cs = &comp->rstate[comp->last_recv = ip->ip_p];
496 comp->flags &=~ SLF_TOSS;
497 ip->ip_p = IPPROTO_TCP;
498 /*
499 * Calculate the size of the TCP/IP header and make sure that
500 * we don't overflow the space we have available for it.
501 */
502 hlen = ip->ip_hl << 2;
503 if (hlen + sizeof(struct tcphdr) > buflen)
504 goto bad;
505 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
506 if (hlen > MAX_HDR || hlen > buflen)
507 goto bad;
508 memcpy(&cs->cs_ip, ip, hlen);
509 cs->cs_hlen = hlen;
510 INCR(sls_uncompressedin)
511 *hdrp = (u_char *) &cs->cs_ip;
512 *hlenp = hlen;
513 return (0);
514
515 default:
516 goto bad;
517
518 case TYPE_COMPRESSED_TCP:
519 break;
520 }
521 /* We've got a compressed packet. */
522 INCR(sls_compressedin)
523 if (buf == NULL)
524 goto bad;
525 cp = buf;
526 changes = *cp++;
527 if (changes & NEW_C) {
528 /* Make sure the state index is in range, then grab the state.
529 * If we have a good state index, clear the 'discard' flag. */
530 if (*cp >= MAX_STATES)
531 goto bad;
532
533 comp->flags &=~ SLF_TOSS;
534 comp->last_recv = *cp++;
535 } else {
536 /* this packet has an implicit state index. If we've
537 * had a line error since the last time we got an
538 * explicit state index, we have to toss the packet. */
539 if (comp->flags & SLF_TOSS) {
540 INCR(sls_tossed)
541 return (-1);
542 }
543 }
544 cs = &comp->rstate[comp->last_recv];
545 hlen = cs->cs_ip.ip_hl << 2;
546 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
547 th->th_sum = htons((*cp << 8) | cp[1]);
548 cp += 2;
549 if (changes & TCP_PUSH_BIT)
550 th->th_flags |= TH_PUSH;
551 else
552 th->th_flags &=~ TH_PUSH;
553
554 switch (changes & SPECIALS_MASK) {
555 case SPECIAL_I:
556 {
557 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
558 th->th_ack = htonl(ntohl(th->th_ack) + i);
559 th->th_seq = htonl(ntohl(th->th_seq) + i);
560 }
561 break;
562
563 case SPECIAL_D:
564 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
565 - cs->cs_hlen);
566 break;
567
568 default:
569 if (changes & NEW_U) {
570 th->th_flags |= TH_URG;
571 DECODEU(th->th_urp)
572 } else
573 th->th_flags &=~ TH_URG;
574 if (changes & NEW_W)
575 DECODES(th->th_win)
576 if (changes & NEW_A)
577 DECODEL(th->th_ack)
578 if (changes & NEW_S)
579 DECODEL(th->th_seq)
580 break;
581 }
582 if (changes & NEW_I) {
583 DECODES(cs->cs_ip.ip_id)
584 } else
585 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
586
587 /*
588 * At this point, cp points to the first byte of data in the
589 * packet. Fill in the IP total length and update the IP
590 * header checksum.
591 */
592 vjlen = cp - buf;
593 buflen -= vjlen;
594 if (buflen < 0)
595 /* we must have dropped some characters (crc should detect
596 * this but the old slip framing won't) */
597 goto bad;
598
599 total_len += cs->cs_hlen - vjlen;
600 cs->cs_ip.ip_len = htons(total_len);
601
602 /* recompute the ip header checksum */
603 bp = (uint16_t *) &cs->cs_ip;
604 cs->cs_ip.ip_sum = 0;
605 for (changes = 0; hlen > 0; hlen -= 2)
606 changes += *bp++;
607 changes = (changes & 0xffff) + (changes >> 16);
608 changes = (changes & 0xffff) + (changes >> 16);
609 cs->cs_ip.ip_sum = ~ changes;
610
611 *hdrp = (u_char *) &cs->cs_ip;
612 *hlenp = cs->cs_hlen;
613 return vjlen;
614
615bad:
616 comp->flags |= SLF_TOSS;
617 INCR(sls_errorin)
618 return (-1);
619}
620#endif
621
622MODULE(MODULE_CLASS_MISC, slcompress, NULL);
623
624static int
625slcompress_modcmd(modcmd_t cmd, void *arg)
626{
627 switch (cmd) {
628 case MODULE_CMD_INIT:
629 case MODULE_CMD_FINI:
630#ifdef INET
631 return 0;
632#endif
633 case MODULE_CMD_STAT:
634 case MODULE_CMD_AUTOUNLOAD:
635 default:
636 return ENOTTY;
637 }
638}
639