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");