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/types.h>
55 #include <linux/string.h>
56 #include <linux/errno.h>
57 #include <linux/kernel.h>
58 #include <net/slhc_vj.h>
61 /* Entire module is for IP only */
63 #include <linux/socket.h>
64 #include <linux/sockios.h>
65 #include <linux/termios.h>
67 #include <linux/fcntl.h>
68 #include <linux/inet.h>
69 #include <linux/netdevice.h>
71 #include <net/protocol.h>
74 #include <linux/skbuff.h>
76 #include <linux/timer.h>
77 #include <asm/system.h>
78 #include <asm/uaccess.h>
79 #include <net/checksum.h>
80 #include <asm/unaligned.h>
82 static unsigned char *encode(unsigned char *cp, unsigned short n);
83 static long decode(unsigned char **cpp);
84 static unsigned char * put16(unsigned char *cp, unsigned short x);
85 static unsigned short pull16(unsigned char **cpp);
87 /* Initialize compression data structure
88 * slots must be in range 0 to 255 (zero meaning no compression)
91 slhc_init(int rslots, int tslots)
94 register struct cstate *ts;
95 struct slcompress *comp;
97 comp = (struct slcompress *)kmalloc(sizeof(struct slcompress),
101 memset(comp, 0, sizeof(struct slcompress));
103 if ( rslots > 0 && rslots < 256 ) {
104 size_t rsize = rslots * sizeof(struct cstate);
105 comp->rstate = (struct cstate *) kmalloc(rsize, GFP_KERNEL);
108 memset(comp->rstate, 0, rsize);
109 comp->rslot_limit = rslots - 1;
112 if ( tslots > 0 && tslots < 256 ) {
113 size_t tsize = tslots * sizeof(struct cstate);
114 comp->tstate = (struct cstate *) kmalloc(tsize, GFP_KERNEL);
117 memset(comp->tstate, 0, tsize);
118 comp->tslot_limit = tslots - 1;
121 comp->xmit_oldest = 0;
122 comp->xmit_current = 255;
123 comp->recv_current = 255;
125 * don't accept any packets with implicit index until we get
126 * one with an explicit index. Otherwise the uncompress code
127 * will try to use connection 255, which is almost certainly
130 comp->flags |= SLF_TOSS;
134 for(i = comp->tslot_limit; i > 0; --i){
136 ts[i].next = &(ts[i - 1]);
138 ts[0].next = &(ts[comp->tslot_limit]);
144 kfree((unsigned char *)comp->rstate);
146 kfree((unsigned char *)comp);
152 /* Free a compression data structure */
154 slhc_free(struct slcompress *comp)
156 if ( comp == NULLSLCOMPR )
159 if ( comp->tstate != NULLSLSTATE )
160 kfree( comp->tstate );
162 if ( comp->rstate != NULLSLSTATE )
163 kfree( comp->rstate );
169 /* Put a short in host order into a char array in network order */
170 static inline unsigned char *
171 put16(unsigned char *cp, unsigned short x)
180 /* Encode a number */
182 encode(unsigned char *cp, unsigned short n)
184 if(n >= 256 || n == 0){
193 /* Pull a 16-bit integer in host order from buffer in network byte order */
194 static unsigned short
195 pull16(unsigned char **cpp)
205 /* Decode a number */
207 decode(unsigned char **cpp)
213 return pull16(cpp) & 0xffff; /* pull16 returns -1 on error */
215 return x & 0xff; /* -1 if PULLCHAR returned error */
220 * icp and isize are the original packet.
221 * ocp is a place to put a copy if necessary.
222 * cpp is initially a pointer to icp. If the copy is used,
227 slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
228 unsigned char *ocp, unsigned char **cpp, int compress_cid)
230 register struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
231 register struct cstate *lcs = ocs;
232 register struct cstate *cs = lcs->next;
233 register unsigned long deltaS, deltaA;
234 register short changes = 0;
236 unsigned char new_seq[16];
237 register unsigned char *cp = new_seq;
239 struct tcphdr *th, *oth;
243 * Don't play with runt packets.
246 if(isize<sizeof(struct iphdr))
249 ip = (struct iphdr *) icp;
251 /* Bail if this packet isn't TCP, or is an IP fragment */
252 if (ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x3fff)) {
253 /* Send as regular IP */
254 if(ip->protocol != IPPROTO_TCP)
255 comp->sls_o_nontcp++;
260 /* Extract TCP header */
262 th = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
263 hlen = ip->ihl*4 + th->doff*4;
265 /* Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
266 * some other control bit is set). Also uncompressible if
269 if(hlen > isize || th->syn || th->fin || th->rst ||
271 /* TCP connection stuff; send as regular IP */
276 * Packet is compressible -- we're going to send either a
277 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way,
278 * we need to locate (or create) the connection state.
280 * States are kept in a circularly linked list with
281 * xmit_oldest pointing to the end of the list. The
282 * list is kept in lru order by moving a state to the
283 * head of the list whenever it is referenced. Since
284 * the list is short and, empirically, the connection
285 * we want is almost always near the front, we locate
286 * states via linear search. If we don't find a state
287 * for the datagram, the oldest state is (re-)used.
290 if( ip->saddr == cs->cs_ip.saddr
291 && ip->daddr == cs->cs_ip.daddr
292 && th->source == cs->cs_tcp.source
293 && th->dest == cs->cs_tcp.dest)
296 /* if current equal oldest, at end of list */
301 comp->sls_o_searches++;
304 * Didn't find it -- re-use oldest cstate. Send an
305 * uncompressed packet that tells the other side what
306 * connection number we're using for this conversation.
308 * Note that since the state list is circular, the oldest
309 * state points to the newest and we only need to set
310 * xmit_oldest to update the lru linkage.
312 comp->sls_o_misses++;
313 comp->xmit_oldest = lcs->cs_this;
318 * Found it -- move to the front on the connection list.
321 /* found at most recently used */
322 } else if (cs == ocs) {
323 /* found at least recently used */
324 comp->xmit_oldest = lcs->cs_this;
326 /* more than 2 elements */
327 lcs->next = cs->next;
328 cs->next = ocs->next;
333 * Make sure that only what we expect to change changed.
334 * Check the following:
335 * IP protocol version, header length & type of service.
336 * The "Don't fragment" bit.
337 * The time-to-live field.
338 * The TCP header length.
339 * IP options, if any.
340 * TCP options, if any.
341 * If any of these things are different between the previous &
342 * current datagram, we send the current datagram `uncompressed'.
346 if(ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl
347 || ip->tos != cs->cs_ip.tos
348 || (ip->frag_off & htons(0x4000)) != (cs->cs_ip.frag_off & htons(0x4000))
349 || ip->ttl != cs->cs_ip.ttl
350 || th->doff != cs->cs_tcp.doff
351 || (ip->ihl > 5 && memcmp(ip+1,cs->cs_ipopt,((ip->ihl)-5)*4) != 0)
352 || (th->doff > 5 && memcmp(th+1,cs->cs_tcpopt,((th->doff)-5)*4) != 0)){
357 * Figure out which of the changing fields changed. The
358 * receiver expects changes in the order: urgent, window,
359 * ack, seq (the order minimizes the number of temporaries
360 * needed in this section of code).
363 deltaS = ntohs(th->urg_ptr);
364 cp = encode(cp,deltaS);
366 } else if(th->urg_ptr != oth->urg_ptr){
367 /* argh! URG not set but urp changed -- a sensible
368 * implementation should never do this but RFC793
369 * doesn't prohibit the change so we have to deal
373 if((deltaS = ntohs(th->window) - ntohs(oth->window)) != 0){
374 cp = encode(cp,deltaS);
377 if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
378 if(deltaA > 0x0000ffff)
380 cp = encode(cp,deltaA);
383 if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
384 if(deltaS > 0x0000ffff)
386 cp = encode(cp,deltaS);
391 case 0: /* Nothing changed. If this packet contains data and the
392 * last one didn't, this is probably a data packet following
393 * an ack (normal on an interactive connection) and we send
394 * it compressed. Otherwise it's probably a retransmit,
395 * retransmitted ack or window probe. Send it uncompressed
396 * in case the other side missed the compressed version.
398 if(ip->tot_len != cs->cs_ip.tot_len &&
399 ntohs(cs->cs_ip.tot_len) == hlen)
405 /* actual changes match one of our special case encodings --
406 * send packet uncompressed.
410 if(deltaS == deltaA &&
411 deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
412 /* special case for echoed terminal traffic */
418 if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
419 /* special case for data xfer */
425 deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);
427 cp = encode(cp,deltaS);
431 changes |= TCP_PUSH_BIT;
432 /* Grab the cksum before we overwrite it below. Then update our
433 * state with this packet's header.
435 deltaA = ntohs(th->check);
436 memcpy(&cs->cs_ip,ip,20);
437 memcpy(&cs->cs_tcp,th,20);
438 /* We want to use the original packet as our compressed packet.
439 * (cp - new_seq) is the number of bytes we need for compressed
440 * sequence numbers. In addition we need one byte for the change
441 * mask, one for the connection id and two for the tcp checksum.
442 * So, (cp - new_seq) + 4 bytes of header are needed.
444 deltaS = cp - new_seq;
445 if(compress_cid == 0 || comp->xmit_current != cs->cs_this){
448 *cp++ = changes | NEW_C;
450 comp->xmit_current = cs->cs_this;
456 cp = put16(cp,(short)deltaA); /* Write TCP checksum */
457 /* deltaS is now the size of the change section of the compressed header */
458 memcpy(cp,new_seq,deltaS); /* Write list of deltas */
459 memcpy(cp+deltaS,icp+hlen,isize-hlen);
460 comp->sls_o_compressed++;
461 ocp[0] |= SL_TYPE_COMPRESSED_TCP;
462 return isize - hlen + deltaS + (cp - ocp);
464 /* Update connection state cs & send uncompressed packet (i.e.,
465 * a regular ip/tcp packet but with the 'conversation id' we hope
466 * to use on future compressed packets in the protocol field).
469 memcpy(&cs->cs_ip,ip,20);
470 memcpy(&cs->cs_tcp,th,20);
472 memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
474 memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);
475 comp->xmit_current = cs->cs_this;
476 comp->sls_o_uncompressed++;
477 memcpy(ocp, icp, isize);
479 ocp[9] = cs->cs_this;
480 ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;
486 slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
488 register int changes;
490 register struct tcphdr *thp;
491 register struct iphdr *ip;
492 register struct cstate *cs;
494 unsigned char *cp = icp;
496 /* We've got a compressed packet; read the change byte */
497 comp->sls_i_compressed++;
504 /* Make sure the state index is in range, then grab the state.
505 * If we have a good state index, clear the 'discard' flag.
507 x = *cp++; /* Read conn index */
508 if(x < 0 || x > comp->rslot_limit)
511 comp->flags &=~ SLF_TOSS;
512 comp->recv_current = x;
514 /* this packet has an implicit state index. If we've
515 * had a line error since the last time we got an
516 * explicit state index, we have to toss the packet. */
517 if(comp->flags & SLF_TOSS){
518 comp->sls_i_tossed++;
522 cs = &comp->rstate[comp->recv_current];
526 if((x = pull16(&cp)) == -1) { /* Read the TCP checksum */
529 thp->check = htons(x);
531 thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
533 * we can use the same number for the length of the saved header and
534 * the current one, because the packet wouldn't have been sent
535 * as compressed unless the options were the same as the previous one
538 hdrlen = ip->ihl * 4 + thp->doff * 4;
540 switch(changes & SPECIALS_MASK){
541 case SPECIAL_I: /* Echoed terminal traffic */
544 i = ntohs(ip->tot_len) - hdrlen;
545 thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);
546 thp->seq = htonl( ntohl(thp->seq) + i);
550 case SPECIAL_D: /* Unidirectional data */
551 thp->seq = htonl( ntohl(thp->seq) +
552 ntohs(ip->tot_len) - hdrlen);
558 if((x = decode(&cp)) == -1) {
561 thp->urg_ptr = htons(x);
565 if((x = decode(&cp)) == -1) {
568 thp->window = htons( ntohs(thp->window) + x);
571 if((x = decode(&cp)) == -1) {
574 thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
577 if((x = decode(&cp)) == -1) {
580 thp->seq = htonl( ntohl(thp->seq) + x);
585 if((x = decode(&cp)) == -1) {
588 ip->id = htons (ntohs (ip->id) + x);
590 ip->id = htons (ntohs (ip->id) + 1);
593 * At this point, cp points to the first byte of data in the
594 * packet. Put the reconstructed TCP and IP headers back on the
595 * packet. Recalculate IP checksum (but not TCP checksum).
598 len = isize - (cp - icp);
602 ip->tot_len = htons(len);
605 memmove(icp + hdrlen, cp, len - hdrlen);
612 memcpy(cp, cs->cs_ipopt, (ip->ihl - 5) * 4);
613 cp += (ip->ihl - 5) * 4;
616 put_unaligned(ip_fast_csum(icp, ip->ihl),
617 &((struct iphdr *)icp)->check);
623 memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);
624 cp += ((thp->doff) - 5) * 4;
630 return slhc_toss( comp );
635 slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
637 register struct cstate *cs;
643 /* The packet is shorter than a legal IP header */
645 return slhc_toss( comp );
647 /* Peek at the IP header's IHL field to find its length */
650 /* The IP header length field is too small */
652 return slhc_toss( comp );
655 icp[9] = IPPROTO_TCP;
657 if (ip_fast_csum(icp, ihl)) {
658 /* Bad IP header checksum; discard */
659 comp->sls_i_badcheck++;
660 return slhc_toss( comp );
662 if(index > comp->rslot_limit) {
664 return slhc_toss(comp);
667 /* Update local state */
668 cs = &comp->rstate[comp->recv_current = index];
669 comp->flags &=~ SLF_TOSS;
670 memcpy(&cs->cs_ip,icp,20);
671 memcpy(&cs->cs_tcp,icp + ihl*4,20);
673 memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
674 if (cs->cs_tcp.doff > 5)
675 memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
676 cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
677 /* Put headers back on packet
678 * Neither header checksum is recalculated
680 comp->sls_i_uncompressed++;
685 slhc_toss(struct slcompress *comp)
687 if ( comp == NULLSLCOMPR )
690 comp->flags |= SLF_TOSS;
695 /* VJ header compression */
696 EXPORT_SYMBOL(slhc_init);
697 EXPORT_SYMBOL(slhc_free);
698 EXPORT_SYMBOL(slhc_remember);
699 EXPORT_SYMBOL(slhc_compress);
700 EXPORT_SYMBOL(slhc_uncompress);
701 EXPORT_SYMBOL(slhc_toss);
705 int init_module(void)
707 printk(KERN_INFO "CSLIP: code copyright 1989 Regents of the University of California\n");
711 void cleanup_module(void)
717 #else /* CONFIG_INET */
721 slhc_toss(struct slcompress *comp)
723 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_toss");
727 slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
729 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_uncompress");
733 slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
734 unsigned char *ocp, unsigned char **cpp, int compress_cid)
736 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_compress");
741 slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
743 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_remember");
748 slhc_free(struct slcompress *comp)
750 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_free");
754 slhc_init(int rslots, int tslots)
756 printk(KERN_DEBUG "Called IP function on non IP-system: slhc_init");
759 EXPORT_SYMBOL(slhc_init);
760 EXPORT_SYMBOL(slhc_free);
761 EXPORT_SYMBOL(slhc_remember);
762 EXPORT_SYMBOL(slhc_compress);
763 EXPORT_SYMBOL(slhc_uncompress);
764 EXPORT_SYMBOL(slhc_toss);
766 #endif /* CONFIG_INET */
767 MODULE_LICENSE("Dual BSD/GPL");