1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1989, 1993, 1994
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32 /*
33 * Routines to compress and uncompess tcp packets (for transmission
34 * over low speed serial lines.
35 *
36 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
37 * - Initial distribution.
38 *
39 */
40
41 #include <sys/param.h>
42 #include <sys/mbuf.h>
43 #include <sys/systm.h>
44
45 #include <netinet/in.h>
46 #include <netinet/in_systm.h>
47 #include <netinet/ip.h>
48 #include <netinet/tcp.h>
49
50 #include <net/slcompress.h>
51
52 #ifndef SL_NO_STATS
53 #define INCR(counter) ++comp->counter;
54 #else
55 #define INCR(counter)
56 #endif
57
58 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n))
59 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
60
61 void
sl_compress_init(struct slcompress * comp,int max_state)62 sl_compress_init(struct slcompress *comp, int max_state)
63 {
64 u_int i;
65 struct cstate *tstate = comp->tstate;
66
67 if (max_state == -1) {
68 max_state = MAX_STATES - 1;
69 bzero((char *)comp, sizeof(*comp));
70 } else {
71 /* Don't reset statistics */
72 bzero((char *)comp->tstate, sizeof(comp->tstate));
73 bzero((char *)comp->rstate, sizeof(comp->rstate));
74 }
75 for (i = max_state; i > 0; --i) {
76 tstate[i].cs_id = i;
77 tstate[i].cs_next = &tstate[i - 1];
78 }
79 tstate[0].cs_next = &tstate[max_state];
80 tstate[0].cs_id = 0;
81 comp->last_cs = &tstate[0];
82 comp->last_recv = 255;
83 comp->last_xmit = 255;
84 comp->flags = SLF_TOSS;
85 }
86
87 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
88 * checks for zero (since zero has to be encoded in the long, 3 byte
89 * form).
90 */
91 #define ENCODE(n) { \
92 if ((u_int16_t)(n) >= 256) { \
93 *cp++ = 0; \
94 cp[1] = (n); \
95 cp[0] = (n) >> 8; \
96 cp += 2; \
97 } else { \
98 *cp++ = (n); \
99 } \
100 }
101 #define ENCODEZ(n) { \
102 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
103 *cp++ = 0; \
104 cp[1] = (n); \
105 cp[0] = (n) >> 8; \
106 cp += 2; \
107 } else { \
108 *cp++ = (n); \
109 } \
110 }
111
112 #define DECODEL(f) { \
113 if (*cp == 0) {\
114 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
115 cp += 3; \
116 } else { \
117 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
118 } \
119 }
120
121 #define DECODES(f) { \
122 if (*cp == 0) {\
123 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
124 cp += 3; \
125 } else { \
126 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
127 } \
128 }
129
130 #define DECODEU(f) { \
131 if (*cp == 0) {\
132 (f) = htons((cp[1] << 8) | cp[2]); \
133 cp += 3; \
134 } else { \
135 (f) = htons((u_int32_t)*cp++); \
136 } \
137 }
138
139 /*
140 * Attempt to compress an outgoing TCP packet and return the type of
141 * the result. The caller must have already verified that the protocol
142 * is TCP. The first mbuf must contain the complete IP and TCP headers,
143 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
144 * compression state, and "compress_cid" tells us whether it is OK
145 * to leave out the CID field when feasible.
146 *
147 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
148 * if m is an M_PKTHDR mbuf.
149 */
150 u_int
sl_compress_tcp(struct mbuf * m,struct ip * ip,struct slcompress * comp,int compress_cid)151 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
152 int compress_cid)
153 {
154 struct cstate *cs = comp->last_cs->cs_next;
155 u_int hlen = ip->ip_hl;
156 struct tcphdr *oth;
157 struct tcphdr *th;
158 u_int deltaS, deltaA;
159 u_int changes = 0;
160 u_char new_seq[16];
161 u_char *cp = new_seq;
162
163 /*
164 * Bail if this is an IP fragment or if the TCP packet isn't
165 * `compressible' (i.e., ACK isn't set or some other control bit is
166 * set). (We assume that the caller has already made sure the
167 * packet is IP proto TCP).
168 */
169 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
170 return (TYPE_IP);
171
172 th = (struct tcphdr *)&((int32_t *)ip)[hlen];
173 if ((tcp_get_flags(th) & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
174 return (TYPE_IP);
175 /*
176 * Packet is compressible -- we're going to send either a
177 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
178 * to locate (or create) the connection state. Special case the
179 * most recently used connection since it's most likely to be used
180 * again & we don't have to do any reordering if it's used.
181 */
182 INCR(sls_packets)
183 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
184 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
185 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
186 /*
187 * Wasn't the first -- search for it.
188 *
189 * States are kept in a circularly linked list with
190 * last_cs pointing to the end of the list. The
191 * list is kept in lru order by moving a state to the
192 * head of the list whenever it is referenced. Since
193 * the list is short and, empirically, the connection
194 * we want is almost always near the front, we locate
195 * states via linear search. If we don't find a state
196 * for the datagram, the oldest state is (re-)used.
197 */
198 struct cstate *lcs;
199 struct cstate *lastcs = comp->last_cs;
200
201 do {
202 lcs = cs; cs = cs->cs_next;
203 INCR(sls_searches)
204 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
205 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
206 && *(int32_t *)th ==
207 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
208 goto found;
209 } while (cs != lastcs);
210
211 /*
212 * Didn't find it -- re-use oldest cstate. Send an
213 * uncompressed packet that tells the other side what
214 * connection number we're using for this conversation.
215 * Note that since the state list is circular, the oldest
216 * state points to the newest and we only need to set
217 * last_cs to update the lru linkage.
218 */
219 INCR(sls_misses)
220 comp->last_cs = lcs;
221 hlen += th->th_off;
222 hlen <<= 2;
223 if (hlen > m->m_len)
224 return TYPE_IP;
225 goto uncompressed;
226
227 found:
228 /*
229 * Found it -- move to the front on the connection list.
230 */
231 if (cs == lastcs)
232 comp->last_cs = lcs;
233 else {
234 lcs->cs_next = cs->cs_next;
235 cs->cs_next = lastcs->cs_next;
236 lastcs->cs_next = cs;
237 }
238 }
239
240 /*
241 * Make sure that only what we expect to change changed. The first
242 * line of the `if' checks the IP protocol version, header length &
243 * type of service. The 2nd line checks the "Don't fragment" bit.
244 * The 3rd line checks the time-to-live and protocol (the protocol
245 * check is unnecessary but costless). The 4th line checks the TCP
246 * header length. The 5th line checks IP options, if any. The 6th
247 * line checks TCP options, if any. If any of these things are
248 * different between the previous & current datagram, we send the
249 * current datagram `uncompressed'.
250 */
251 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
252 deltaS = hlen;
253 hlen += th->th_off;
254 hlen <<= 2;
255 if (hlen > m->m_len)
256 return TYPE_IP;
257
258 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
259 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
260 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
261 th->th_off != oth->th_off ||
262 (deltaS > 5 &&
263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
264 (th->th_off > 5 &&
265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
266 goto uncompressed;
267
268 /*
269 * Figure out which of the changing fields changed. The
270 * receiver expects changes in the order: urgent, window,
271 * ack, seq (the order minimizes the number of temporaries
272 * needed in this section of code).
273 */
274 if (tcp_get_flags(th) & TH_URG) {
275 deltaS = ntohs(th->th_urp);
276 ENCODEZ(deltaS);
277 changes |= NEW_U;
278 } else if (th->th_urp != oth->th_urp)
279 /* argh! URG not set but urp changed -- a sensible
280 * implementation should never do this but RFC793
281 * doesn't prohibit the change so we have to deal
282 * with it. */
283 goto uncompressed;
284
285 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
286 if (deltaS) {
287 ENCODE(deltaS);
288 changes |= NEW_W;
289 }
290
291 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
292 if (deltaA) {
293 if (deltaA > 0xffff)
294 goto uncompressed;
295 ENCODE(deltaA);
296 changes |= NEW_A;
297 }
298
299 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
300 if (deltaS) {
301 if (deltaS > 0xffff)
302 goto uncompressed;
303 ENCODE(deltaS);
304 changes |= NEW_S;
305 }
306
307 switch(changes) {
308 case 0:
309 /*
310 * Nothing changed. If this packet contains data and the
311 * last one didn't, this is probably a data packet following
312 * an ack (normal on an interactive connection) and we send
313 * it compressed. Otherwise it's probably a retransmit,
314 * retransmitted ack or window probe. Send it uncompressed
315 * in case the other side missed the compressed version.
316 */
317 if (ip->ip_len != cs->cs_ip.ip_len &&
318 ntohs(cs->cs_ip.ip_len) == hlen)
319 break;
320
321 /* FALLTHROUGH */
322
323 case SPECIAL_I:
324 case SPECIAL_D:
325 /*
326 * actual changes match one of our special case encodings --
327 * send packet uncompressed.
328 */
329 goto uncompressed;
330
331 case NEW_S|NEW_A:
332 if (deltaS == deltaA &&
333 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
334 /* special case for echoed terminal traffic */
335 changes = SPECIAL_I;
336 cp = new_seq;
337 }
338 break;
339
340 case NEW_S:
341 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
342 /* special case for data xfer */
343 changes = SPECIAL_D;
344 cp = new_seq;
345 }
346 break;
347 }
348
349 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
350 if (deltaS != 1) {
351 ENCODEZ(deltaS);
352 changes |= NEW_I;
353 }
354 if (tcp_get_flags(th) & TH_PUSH)
355 changes |= TCP_PUSH_BIT;
356 /*
357 * Grab the cksum before we overwrite it below. Then update our
358 * state with this packet's header.
359 */
360 deltaA = ntohs(th->th_sum);
361 BCOPY(ip, &cs->cs_ip, hlen);
362
363 /*
364 * We want to use the original packet as our compressed packet.
365 * (cp - new_seq) is the number of bytes we need for compressed
366 * sequence numbers. In addition we need one byte for the change
367 * mask, one for the connection id and two for the tcp checksum.
368 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
369 * many bytes of the original packet to toss so subtract the two to
370 * get the new packet size.
371 */
372 deltaS = cp - new_seq;
373 cp = (u_char *)ip;
374 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
375 comp->last_xmit = cs->cs_id;
376 hlen -= deltaS + 4;
377 cp += hlen;
378 *cp++ = changes | NEW_C;
379 *cp++ = cs->cs_id;
380 } else {
381 hlen -= deltaS + 3;
382 cp += hlen;
383 *cp++ = changes;
384 }
385 m->m_len -= hlen;
386 m->m_data += hlen;
387 *cp++ = deltaA >> 8;
388 *cp++ = deltaA;
389 BCOPY(new_seq, cp, deltaS);
390 INCR(sls_compressed)
391 return (TYPE_COMPRESSED_TCP);
392
393 /*
394 * Update connection state cs & send uncompressed packet ('uncompressed'
395 * means a regular ip/tcp packet but with the 'conversation id' we hope
396 * to use on future compressed packets in the protocol field).
397 */
398 uncompressed:
399 BCOPY(ip, &cs->cs_ip, hlen);
400 ip->ip_p = cs->cs_id;
401 comp->last_xmit = cs->cs_id;
402 return (TYPE_UNCOMPRESSED_TCP);
403 }
404
405 int
sl_uncompress_tcp(u_char ** bufp,int len,u_int type,struct slcompress * comp)406 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
407 {
408 u_char *hdr, *cp;
409 int hlen, vjlen;
410
411 cp = bufp? *bufp: NULL;
412 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
413 if (vjlen < 0)
414 return (0); /* error */
415 if (vjlen == 0)
416 return (len); /* was uncompressed already */
417
418 cp += vjlen;
419 len -= vjlen;
420
421 /*
422 * At this point, cp points to the first byte of data in the
423 * packet. If we're not aligned on a 4-byte boundary, copy the
424 * data down so the ip & tcp headers will be aligned. Then back up
425 * cp by the tcp/ip header length to make room for the reconstructed
426 * header (we assume the packet we were handed has enough space to
427 * prepend 128 bytes of header).
428 */
429 if ((intptr_t)cp & 3) {
430 if (len > 0)
431 BCOPY(cp, ((intptr_t)cp &~ 3), len);
432 cp = (u_char *)((intptr_t)cp &~ 3);
433 }
434 cp -= hlen;
435 len += hlen;
436 BCOPY(hdr, cp, hlen);
437
438 *bufp = cp;
439 return (len);
440 }
441
442 /*
443 * Uncompress a packet of total length total_len. The first buflen
444 * bytes are at buf; this must include the entire (compressed or
445 * uncompressed) TCP/IP header. This procedure returns the length
446 * of the VJ header, with a pointer to the uncompressed IP header
447 * in *hdrp and its length in *hlenp.
448 */
449 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)450 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
451 struct slcompress *comp, u_char **hdrp, u_int *hlenp)
452 {
453 u_char *cp;
454 u_int hlen, changes;
455 struct tcphdr *th;
456 struct cstate *cs;
457 struct ip *ip;
458 u_int16_t *bp;
459 u_int vjlen;
460
461 switch (type) {
462 case TYPE_UNCOMPRESSED_TCP:
463 ip = (struct ip *) buf;
464 if (ip->ip_p >= MAX_STATES)
465 goto bad;
466 cs = &comp->rstate[comp->last_recv = ip->ip_p];
467 comp->flags &=~ SLF_TOSS;
468 ip->ip_p = IPPROTO_TCP;
469 /*
470 * Calculate the size of the TCP/IP header and make sure that
471 * we don't overflow the space we have available for it.
472 */
473 hlen = ip->ip_hl << 2;
474 if (hlen + sizeof(struct tcphdr) > buflen)
475 goto bad;
476 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
477 if (hlen > MAX_HDR || hlen > buflen)
478 goto bad;
479 BCOPY(ip, &cs->cs_ip, hlen);
480 cs->cs_hlen = hlen;
481 INCR(sls_uncompressedin)
482 *hdrp = (u_char *) &cs->cs_ip;
483 *hlenp = hlen;
484 return (0);
485
486 default:
487 goto bad;
488
489 case TYPE_COMPRESSED_TCP:
490 break;
491 }
492 /* We've got a compressed packet. */
493 INCR(sls_compressedin)
494 cp = buf;
495 changes = *cp++;
496 if (changes & NEW_C) {
497 /* Make sure the state index is in range, then grab the state.
498 * If we have a good state index, clear the 'discard' flag. */
499 if (*cp >= MAX_STATES)
500 goto bad;
501
502 comp->flags &=~ SLF_TOSS;
503 comp->last_recv = *cp++;
504 } else {
505 /* this packet has an implicit state index. If we've
506 * had a line error since the last time we got an
507 * explicit state index, we have to toss the packet. */
508 if (comp->flags & SLF_TOSS) {
509 INCR(sls_tossed)
510 return (-1);
511 }
512 }
513 cs = &comp->rstate[comp->last_recv];
514 hlen = cs->cs_ip.ip_hl << 2;
515 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
516 th->th_sum = htons((*cp << 8) | cp[1]);
517 cp += 2;
518 if (changes & TCP_PUSH_BIT)
519 tcp_set_flags(th, tcp_get_flags(th) | TH_PUSH);
520 else
521 tcp_set_flags(th, tcp_get_flags(th) & ~TH_PUSH);
522
523 switch (changes & SPECIALS_MASK) {
524 case SPECIAL_I:
525 {
526 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
527 th->th_ack = htonl(ntohl(th->th_ack) + i);
528 th->th_seq = htonl(ntohl(th->th_seq) + i);
529 }
530 break;
531
532 case SPECIAL_D:
533 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
534 - cs->cs_hlen);
535 break;
536
537 default:
538 if (changes & NEW_U) {
539 tcp_set_flags(th, tcp_get_flags(th) | TH_URG);
540 DECODEU(th->th_urp)
541 } else
542 tcp_set_flags(th, tcp_get_flags(th) & ~TH_URG);
543 if (changes & NEW_W)
544 DECODES(th->th_win)
545 if (changes & NEW_A)
546 DECODEL(th->th_ack)
547 if (changes & NEW_S)
548 DECODEL(th->th_seq)
549 break;
550 }
551 if (changes & NEW_I) {
552 DECODES(cs->cs_ip.ip_id)
553 } else
554 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
555
556 /*
557 * At this point, cp points to the first byte of data in the
558 * packet. Fill in the IP total length and update the IP
559 * header checksum.
560 */
561 vjlen = cp - buf;
562 buflen -= vjlen;
563 if (buflen < 0)
564 /* we must have dropped some characters (crc should detect
565 * this but the old slip framing won't) */
566 goto bad;
567
568 total_len += cs->cs_hlen - vjlen;
569 cs->cs_ip.ip_len = htons(total_len);
570
571 /* recompute the ip header checksum */
572 bp = (u_int16_t *) &cs->cs_ip;
573 cs->cs_ip.ip_sum = 0;
574 for (changes = 0; hlen > 0; hlen -= 2)
575 changes += *bp++;
576 changes = (changes & 0xffff) + (changes >> 16);
577 changes = (changes & 0xffff) + (changes >> 16);
578 cs->cs_ip.ip_sum = ~ changes;
579
580 *hdrp = (u_char *) &cs->cs_ip;
581 *hlenp = cs->cs_hlen;
582 return vjlen;
583
584 bad:
585 comp->flags |= SLF_TOSS;
586 INCR(sls_errorin)
587 return (-1);
588 }
589