2 * Routines to compress and uncompress tcp packets (for transmission
3 * over low speed serial lines).
5 * Copyright (c) 1989 Regents of the University of California.
8 * Redistribution and use in source and binary forms are permitted
9 * provided that the above copyright notice and this paragraph are
10 * duplicated in all such forms and that any documentation,
11 * advertising materials, and other materials related to such
12 * distribution and use acknowledge that the software was developed
13 * by the University of California, Berkeley. The name of the
14 * University may not be used to endorse or promote products derived
15 * from this software without specific prior written permission.
16 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
21 * - Initial distribution.
24 * modified for KA9Q Internet Software Package by
25 * Katie Stevens (dkstevens@ucdavis.edu)
26 * University of California, Davis
28 * - 01-31-90 initial adaptation (from 1.19)
29 * PPP.05 02-15-90 [ks]
30 * PPP.08 05-02-90 [ks] use PPP protocol field to signal compression
31 * PPP.15 09-90 [ks] improve mbuf handling
32 * PPP.16 11-02 [karn] substantially rewritten to use NOS facilities
34 * - Feb 1991 Bill_Simpson@um.cc.umich.edu
35 * variable number of conversation slots
36 * allow zero or one slots
39 * - Jul 1994 Dmitry Gorodchanin
40 * Fixes for memory leaks.
41 * - Oct 1994 Dmitry Gorodchanin
43 * - Jan 1995 Bjorn Ekwall
44 * Use ip_fast_csum from ip.h
45 * - July 1995 Christos A. Polyzols
46 * Spotted bug in tcp option checking
49 * This module is a difficult issue. It's clearly inet code but it's also clearly
50 * driver code belonging close to PPP and SLIP
53 #include <linux/module.h>
54 #include <linux/slab.h>
55 #include <linux/types.h>
56 #include <linux/string.h>
57 #include <linux/errno.h>
58 #include <linux/kernel.h>
59 #include <net/slhc_vj.h>
62 /* Entire module is for IP only */
64 #include <linux/socket.h>
65 #include <linux/sockios.h>
66 #include <linux/termios.h>
68 #include <linux/fcntl.h>
69 #include <linux/inet.h>
70 #include <linux/netdevice.h>
72 #include <net/protocol.h>
75 #include <linux/skbuff.h>
77 #include <linux/timer.h>
78 #include <asm/system.h>
79 #include <asm/uaccess.h>
80 #include <net/checksum.h>
81 #include <asm/unaligned.h>
83 static unsigned char *encode(unsigned char *cp, unsigned short n);
84 static long decode(unsigned char **cpp);
85 static unsigned char * put16(unsigned char *cp, unsigned short x);
86 static unsigned short pull16(unsigned char **cpp);
88 /* Initialize compression data structure
89 * slots must be in range 0 to 255 (zero meaning no compression)
92 slhc_init(int rslots, int tslots)
95 register struct cstate *ts;
96 struct slcompress *comp;
98 comp = kzalloc(sizeof(struct slcompress), GFP_KERNEL);
102 if ( rslots > 0 && rslots < 256 ) {
103 size_t rsize = rslots * sizeof(struct cstate);
104 comp->rstate = kzalloc(rsize, GFP_KERNEL);
107 comp->rslot_limit = rslots - 1;
110 if ( tslots > 0 && tslots < 256 ) {
111 size_t tsize = tslots * sizeof(struct cstate);
112 comp->tstate = kzalloc(tsize, GFP_KERNEL);
115 comp->tslot_limit = tslots - 1;
118 comp->xmit_oldest = 0;
119 comp->xmit_current = 255;
120 comp->recv_current = 255;
122 * don't accept any packets with implicit index until we get
123 * one with an explicit index. Otherwise the uncompress code
124 * will try to use connection 255, which is almost certainly
127 comp->flags |= SLF_TOSS;
131 for(i = comp->tslot_limit; i > 0; --i){
133 ts[i].next = &(ts[i - 1]);
135 ts[0].next = &(ts[comp->tslot_limit]);
149 /* Free a compression data structure */
151 slhc_free(struct slcompress *comp)
153 if ( comp == NULLSLCOMPR )
156 if ( comp->tstate != NULLSLSTATE )
157 kfree( comp->tstate );
159 if ( comp->rstate != NULLSLSTATE )
160 kfree( comp->rstate );
166 /* Put a short in host order into a char array in network order */
167 static inline unsigned char *
168 put16(unsigned char *cp, unsigned short x)
177 /* Encode a number */
178 static unsigned char *
179 encode(unsigned char *cp, unsigned short n)
181 if(n >= 256 || n == 0){
190 /* Pull a 16-bit integer in host order from buffer in network byte order */
191 static unsigned short
192 pull16(unsigned char **cpp)
202 /* Decode a number */
204 decode(unsigned char **cpp)
210 return pull16(cpp) & 0xffff; /* pull16 returns -1 on error */
212 return x & 0xff; /* -1 if PULLCHAR returned error */
217 * icp and isize are the original packet.
218 * ocp is a place to put a copy if necessary.
219 * cpp is initially a pointer to icp. If the copy is used,
224 slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
225 unsigned char *ocp, unsigned char **cpp, int compress_cid)
227 register struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
228 register struct cstate *lcs = ocs;
229 register struct cstate *cs = lcs->next;
230 register unsigned long deltaS, deltaA;
231 register short changes = 0;
233 unsigned char new_seq[16];
234 register unsigned char *cp = new_seq;
236 struct tcphdr *th, *oth;
241 * Don't play with runt packets.
244 if(isize<sizeof(struct iphdr))
247 ip = (struct iphdr *) icp;
249 /* Bail if this packet isn't TCP, or is an IP fragment */
250 if (ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x3fff)) {
251 /* Send as regular IP */
252 if(ip->protocol != IPPROTO_TCP)
253 comp->sls_o_nontcp++;
258 /* Extract TCP header */
260 th = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
261 hlen = ip->ihl*4 + th->doff*4;
263 /* Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
264 * some other control bit is set). Also uncompressible if
267 if(hlen > isize || th->syn || th->fin || th->rst ||
269 /* TCP connection stuff; send as regular IP */
274 * Packet is compressible -- we're going to send either a
275 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way,
276 * we need to locate (or create) the connection state.
278 * States are kept in a circularly linked list with
279 * xmit_oldest pointing to the end of the list. The
280 * list is kept in lru order by moving a state to the
281 * head of the list whenever it is referenced. Since
282 * the list is short and, empirically, the connection
283 * we want is almost always near the front, we locate
284 * states via linear search. If we don't find a state
285 * for the datagram, the oldest state is (re-)used.
288 if( ip->saddr == cs->cs_ip.saddr
289 && ip->daddr == cs->cs_ip.daddr
290 && th->source == cs->cs_tcp.source
291 && th->dest == cs->cs_tcp.dest)
294 /* if current equal oldest, at end of list */
299 comp->sls_o_searches++;
302 * Didn't find it -- re-use oldest cstate. Send an
303 * uncompressed packet that tells the other side what
304 * connection number we're using for this conversation.
306 * Note that since the state list is circular, the oldest
307 * state points to the newest and we only need to set
308 * xmit_oldest to update the lru linkage.
310 comp->sls_o_misses++;
311 comp->xmit_oldest = lcs->cs_this;
316 * Found it -- move to the front on the connection list.
319 /* found at most recently used */
320 } else if (cs == ocs) {
321 /* found at least recently used */
322 comp->xmit_oldest = lcs->cs_this;
324 /* more than 2 elements */
325 lcs->next = cs->next;
326 cs->next = ocs->next;
331 * Make sure that only what we expect to change changed.
332 * Check the following:
333 * IP protocol version, header length & type of service.
334 * The "Don't fragment" bit.
335 * The time-to-live field.
336 * The TCP header length.
337 * IP options, if any.
338 * TCP options, if any.
339 * If any of these things are different between the previous &
340 * current datagram, we send the current datagram `uncompressed'.
344 if(ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl
345 || ip->tos != cs->cs_ip.tos
346 || (ip->frag_off & htons(0x4000)) != (cs->cs_ip.frag_off & htons(0x4000))
347 || ip->ttl != cs->cs_ip.ttl
348 || th->doff != cs->cs_tcp.doff
349 || (ip->ihl > 5 && memcmp(ip+1,cs->cs_ipopt,((ip->ihl)-5)*4) != 0)
350 || (th->doff > 5 && memcmp(th+1,cs->cs_tcpopt,((th->doff)-5)*4) != 0)){
355 * Figure out which of the changing fields changed. The
356 * receiver expects changes in the order: urgent, window,
357 * ack, seq (the order minimizes the number of temporaries
358 * needed in this section of code).
361 deltaS = ntohs(th->urg_ptr);
362 cp = encode(cp,deltaS);
364 } else if(th->urg_ptr != oth->urg_ptr){
365 /* argh! URG not set but urp changed -- a sensible
366 * implementation should never do this but RFC793
367 * doesn't prohibit the change so we have to deal
371 if((deltaS = ntohs(th->window) - ntohs(oth->window)) != 0){
372 cp = encode(cp,deltaS);
375 if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
376 if(deltaA > 0x0000ffff)
378 cp = encode(cp,deltaA);
381 if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
382 if(deltaS > 0x0000ffff)
384 cp = encode(cp,deltaS);
389 case 0: /* Nothing changed. If this packet contains data and the
390 * last one didn't, this is probably a data packet following
391 * an ack (normal on an interactive connection) and we send
392 * it compressed. Otherwise it's probably a retransmit,
393 * retransmitted ack or window probe. Send it uncompressed
394 * in case the other side missed the compressed version.
396 if(ip->tot_len != cs->cs_ip.tot_len &&
397 ntohs(cs->cs_ip.tot_len) == hlen)
403 /* actual changes match one of our special case encodings --
404 * send packet uncompressed.
408 if(deltaS == deltaA &&
409 deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
410 /* special case for echoed terminal traffic */
416 if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
417 /* special case for data xfer */
423 deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);
425 cp = encode(cp,deltaS);
429 changes |= TCP_PUSH_BIT;
430 /* Grab the cksum before we overwrite it below. Then update our
431 * state with this packet's header.
434 memcpy(&cs->cs_ip,ip,20);
435 memcpy(&cs->cs_tcp,th,20);
436 /* We want to use the original packet as our compressed packet.
437 * (cp - new_seq) is the number of bytes we need for compressed
438 * sequence numbers. In addition we need one byte for the change
439 * mask, one for the connection id and two for the tcp checksum.
440 * So, (cp - new_seq) + 4 bytes of header are needed.
442 deltaS = cp - new_seq;
443 if(compress_cid == 0 || comp->xmit_current != cs->cs_this){
446 *cp++ = changes | NEW_C;
448 comp->xmit_current = cs->cs_this;
454 *(__sum16 *)cp = csum;
456 /* deltaS is now the size of the change section of the compressed header */
457 memcpy(cp,new_seq,deltaS); /* Write list of deltas */
458 memcpy(cp+deltaS,icp+hlen,isize-hlen);
459 comp->sls_o_compressed++;
460 ocp[0] |= SL_TYPE_COMPRESSED_TCP;
461 return isize - hlen + deltaS + (cp - ocp);
463 /* Update connection state cs & send uncompressed packet (i.e.,
464 * a regular ip/tcp packet but with the 'conversation id' we hope
465 * to use on future compressed packets in the protocol field).
468 memcpy(&cs->cs_ip,ip,20);
469 memcpy(&cs->cs_tcp,th,20);
471 memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
473 memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);
474 comp->xmit_current = cs->cs_this;
475 comp->sls_o_uncompressed++;
476 memcpy(ocp, icp, isize);
478 ocp[9] = cs->cs_this;
479 ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;
485 slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
487 register int changes;
489 register struct tcphdr *thp;
490 register struct iphdr *ip;
491 register struct cstate *cs;
493 unsigned char *cp = icp;
495 /* We've got a compressed packet; read the change byte */
496 comp->sls_i_compressed++;
503 /* Make sure the state index is in range, then grab the state.
504 * If we have a good state index, clear the 'discard' flag.
506 x = *cp++; /* Read conn index */
507 if(x < 0 || x > comp->rslot_limit)
510 comp->flags &=~ SLF_TOSS;
511 comp->recv_current = x;
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 comp->sls_i_tossed++;
521 cs = &comp->rstate[comp->recv_current];
525 thp->check = *(__sum16 *)cp;
528 thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
530 * we can use the same number for the length of the saved header and
531 * the current one, because the packet wouldn't have been sent
532 * as compressed unless the options were the same as the previous one
535 hdrlen = ip->ihl * 4 + thp->doff * 4;
537 switch(changes & SPECIALS_MASK){
538 case SPECIAL_I: /* Echoed terminal traffic */
541 i = ntohs(ip->tot_len) - hdrlen;
542 thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);
543 thp->seq = htonl( ntohl(thp->seq) + i);
547 case SPECIAL_D: /* Unidirectional data */
548 thp->seq = htonl( ntohl(thp->seq) +
549 ntohs(ip->tot_len) - hdrlen);
555 if((x = decode(&cp)) == -1) {
558 thp->urg_ptr = htons(x);
562 if((x = decode(&cp)) == -1) {
565 thp->window = htons( ntohs(thp->window) + x);
568 if((x = decode(&cp)) == -1) {
571 thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
574 if((x = decode(&cp)) == -1) {
577 thp->seq = htonl( ntohl(thp->seq) + x);
582 if((x = decode(&cp)) == -1) {
585 ip->id = htons (ntohs (ip->id) + x);
587 ip->id = htons (ntohs (ip->id) + 1);
590 * At this point, cp points to the first byte of data in the
591 * packet. Put the reconstructed TCP and IP headers back on the
592 * packet. Recalculate IP checksum (but not TCP checksum).
595 len = isize - (cp - icp);
599 ip->tot_len = htons(len);
602 memmove(icp + hdrlen, cp, len - hdrlen);
609 memcpy(cp, cs->cs_ipopt, (ip->ihl - 5) * 4);
610 cp += (ip->ihl - 5) * 4;
613 put_unaligned(ip_fast_csum(icp, ip->ihl),
614 &((struct iphdr *)icp)->check);
620 memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);
621 cp += ((thp->doff) - 5) * 4;
627 return slhc_toss( comp );
632 slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
634 register struct cstate *cs;
640 /* The packet is shorter than a legal IP header */
642 return slhc_toss( comp );
644 /* Peek at the IP header's IHL field to find its length */
647 /* The IP header length field is too small */
649 return slhc_toss( comp );
652 icp[9] = IPPROTO_TCP;
654 if (ip_fast_csum(icp, ihl)) {
655 /* Bad IP header checksum; discard */
656 comp->sls_i_badcheck++;
657 return slhc_toss( comp );
659 if(index > comp->rslot_limit) {
661 return slhc_toss(comp);
664 /* Update local state */
665 cs = &comp->rstate[comp->recv_current = index];
666 comp->flags &=~ SLF_TOSS;
667 memcpy(&cs->cs_ip,icp,20);
668 memcpy(&cs->cs_tcp,icp + ihl*4,20);
670 memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
671 if (cs->cs_tcp.doff > 5)
672 memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
673 cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
674 /* Put headers back on packet
675 * Neither header checksum is recalculated
677 comp->sls_i_uncompressed++;
682 slhc_toss(struct slcompress *comp)
684 if ( comp == NULLSLCOMPR )
687 comp->flags |= SLF_TOSS;
691 #else /* CONFIG_INET */
694 slhc_toss(struct slcompress *comp)
696 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_toss");
700 slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
702 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_uncompress");
706 slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
707 unsigned char *ocp, unsigned char **cpp, int compress_cid)
709 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_compress");
714 slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
716 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_remember");
721 slhc_free(struct slcompress *comp)
723 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_free");
726 slhc_init(int rslots, int tslots)
728 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_init");
732 #endif /* CONFIG_INET */
734 /* VJ header compression */
735 EXPORT_SYMBOL(slhc_init);
736 EXPORT_SYMBOL(slhc_free);
737 EXPORT_SYMBOL(slhc_remember);
738 EXPORT_SYMBOL(slhc_compress);
739 EXPORT_SYMBOL(slhc_uncompress);
740 EXPORT_SYMBOL(slhc_toss);
742 MODULE_LICENSE("Dual BSD/GPL");