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/config.h>
54 #include <linux/module.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 */
63 #include <linux/sched.h>
65 #include <linux/socket.h>
66 #include <linux/sockios.h>
67 #include <linux/termios.h>
69 #include <linux/fcntl.h>
70 #include <linux/inet.h>
71 #include <linux/netdevice.h>
73 #include <net/protocol.h>
76 #include <linux/skbuff.h>
78 #include <linux/timer.h>
79 #include <asm/system.h>
80 #include <asm/uaccess.h>
81 #include <net/checksum.h>
82 #include <asm/unaligned.h>
86 static unsigned char *encode(unsigned char *cp
, unsigned short n
);
87 static long decode(unsigned char **cpp
);
88 static unsigned char * put16(unsigned char *cp
, unsigned short x
);
89 static unsigned short pull16(unsigned char **cpp
);
91 /* Initialize compression data structure
92 * slots must be in range 0 to 255 (zero meaning no compression)
95 slhc_init(int rslots
, int tslots
)
98 register struct cstate
*ts
;
99 struct slcompress
*comp
;
102 comp
= (struct slcompress
*)kmalloc(sizeof(struct slcompress
),
106 memset(comp
, 0, sizeof(struct slcompress
));
108 if ( rslots
> 0 && rslots
< 256 ) {
109 size_t rsize
= rslots
* sizeof(struct cstate
);
110 comp
->rstate
= (struct cstate
*) kmalloc(rsize
, GFP_KERNEL
);
113 memset(comp
->rstate
, 0, rsize
);
114 comp
->rslot_limit
= rslots
- 1;
117 if ( tslots
> 0 && tslots
< 256 ) {
118 size_t tsize
= tslots
* sizeof(struct cstate
);
119 comp
->tstate
= (struct cstate
*) kmalloc(tsize
, GFP_KERNEL
);
122 memset(comp
->tstate
, 0, tsize
);
123 comp
->tslot_limit
= tslots
- 1;
126 comp
->xmit_oldest
= 0;
127 comp
->xmit_current
= 255;
128 comp
->recv_current
= 255;
130 * don't accept any packets with implicit index until we get
131 * one with an explicit index. Otherwise the uncompress code
132 * will try to use connection 255, which is almost certainly
135 comp
->flags
|= SLF_TOSS
;
139 for(i
= comp
->tslot_limit
; i
> 0; --i
){
141 ts
[i
].next
= &(ts
[i
- 1]);
143 ts
[0].next
= &(ts
[comp
->tslot_limit
]);
149 kfree((unsigned char *)comp
->rstate
);
151 kfree((unsigned char *)comp
);
158 /* Free a compression data structure */
160 slhc_free(struct slcompress
*comp
)
162 if ( comp
== NULLSLCOMPR
)
165 if ( comp
->tstate
!= NULLSLSTATE
)
166 kfree( comp
->tstate
);
168 if ( comp
->rstate
!= NULLSLSTATE
)
169 kfree( comp
->rstate
);
176 /* Put a short in host order into a char array in network order */
177 static inline unsigned char *
178 put16(unsigned char *cp
, unsigned short x
)
187 /* Encode a number */
189 encode(unsigned char *cp
, unsigned short n
)
191 if(n
>= 256 || n
== 0){
200 /* Pull a 16-bit integer in host order from buffer in network byte order */
201 static unsigned short
202 pull16(unsigned char **cpp
)
212 /* Decode a number */
214 decode(unsigned char **cpp
)
220 return pull16(cpp
) & 0xffff; /* pull16 returns -1 on error */
222 return x
& 0xff; /* -1 if PULLCHAR returned error */
227 * icp and isize are the original packet.
228 * ocp is a place to put a copy if necessary.
229 * cpp is initially a pointer to icp. If the copy is used,
234 slhc_compress(struct slcompress
*comp
, unsigned char *icp
, int isize
,
235 unsigned char *ocp
, unsigned char **cpp
, int compress_cid
)
237 register struct cstate
*ocs
= &(comp
->tstate
[comp
->xmit_oldest
]);
238 register struct cstate
*lcs
= ocs
;
239 register struct cstate
*cs
= lcs
->next
;
240 register unsigned long deltaS
, deltaA
;
241 register short changes
= 0;
243 unsigned char new_seq
[16];
244 register unsigned char *cp
= new_seq
;
246 struct tcphdr
*th
, *oth
;
250 * Don't play with runt packets.
253 if(isize
<sizeof(struct iphdr
))
256 ip
= (struct iphdr
*) icp
;
258 /* Bail if this packet isn't TCP, or is an IP fragment */
259 if(ip
->protocol
!= IPPROTO_TCP
|| (ntohs(ip
->frag_off
) & 0x1fff) ||
260 (ip
->frag_off
& 32)){
261 /* Send as regular IP */
262 if(ip
->protocol
!= IPPROTO_TCP
)
263 comp
->sls_o_nontcp
++;
268 /* Extract TCP header */
270 th
= (struct tcphdr
*)(((unsigned char *)ip
) + ip
->ihl
*4);
271 hlen
= ip
->ihl
*4 + th
->doff
*4;
273 /* Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
274 * some other control bit is set). Also uncompressible if
277 if(hlen
> isize
|| th
->syn
|| th
->fin
|| th
->rst
||
279 /* TCP connection stuff; send as regular IP */
284 * Packet is compressible -- we're going to send either a
285 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way,
286 * we need to locate (or create) the connection state.
288 * States are kept in a circularly linked list with
289 * xmit_oldest pointing to the end of the list. The
290 * list is kept in lru order by moving a state to the
291 * head of the list whenever it is referenced. Since
292 * the list is short and, empirically, the connection
293 * we want is almost always near the front, we locate
294 * states via linear search. If we don't find a state
295 * for the datagram, the oldest state is (re-)used.
298 if( ip
->saddr
== cs
->cs_ip
.saddr
299 && ip
->daddr
== cs
->cs_ip
.daddr
300 && th
->source
== cs
->cs_tcp
.source
301 && th
->dest
== cs
->cs_tcp
.dest
)
304 /* if current equal oldest, at end of list */
309 comp
->sls_o_searches
++;
312 * Didn't find it -- re-use oldest cstate. Send an
313 * uncompressed packet that tells the other side what
314 * connection number we're using for this conversation.
316 * Note that since the state list is circular, the oldest
317 * state points to the newest and we only need to set
318 * xmit_oldest to update the lru linkage.
320 comp
->sls_o_misses
++;
321 comp
->xmit_oldest
= lcs
->cs_this
;
326 * Found it -- move to the front on the connection list.
329 /* found at most recently used */
330 } else if (cs
== ocs
) {
331 /* found at least recently used */
332 comp
->xmit_oldest
= lcs
->cs_this
;
334 /* more than 2 elements */
335 lcs
->next
= cs
->next
;
336 cs
->next
= ocs
->next
;
341 * Make sure that only what we expect to change changed.
342 * Check the following:
343 * IP protocol version, header length & type of service.
344 * The "Don't fragment" bit.
345 * The time-to-live field.
346 * The TCP header length.
347 * IP options, if any.
348 * TCP options, if any.
349 * If any of these things are different between the previous &
350 * current datagram, we send the current datagram `uncompressed'.
355 || ip
->version
!= cs
->cs_ip
.version
|| ip
->ihl
!= cs
->cs_ip
.ihl
356 || ip
->tos
!= cs
->cs_ip
.tos
357 || (ip
->frag_off
& 64) != (cs
->cs_ip
.frag_off
& 64)
358 || ip
->ttl
!= cs
->cs_ip
.ttl
359 || th
->doff
!= cs
->cs_tcp
.doff
360 || (ip
->ihl
> 5 && memcmp(ip
+1,cs
->cs_ipopt
,((ip
->ihl
)-5)*4) != 0)
361 || (th
->doff
> 5 && memcmp(th
+1,cs
->cs_tcpopt
,((th
->doff
)-5)*4) != 0)){
366 * Figure out which of the changing fields changed. The
367 * receiver expects changes in the order: urgent, window,
368 * ack, seq (the order minimizes the number of temporaries
369 * needed in this section of code).
372 deltaS
= ntohs(th
->urg_ptr
);
373 cp
= encode(cp
,deltaS
);
375 } else if(th
->urg_ptr
!= oth
->urg_ptr
){
376 /* argh! URG not set but urp changed -- a sensible
377 * implementation should never do this but RFC793
378 * doesn't prohibit the change so we have to deal
382 if((deltaS
= ntohs(th
->window
) - ntohs(oth
->window
)) != 0){
383 cp
= encode(cp
,deltaS
);
386 if((deltaA
= ntohl(th
->ack_seq
) - ntohl(oth
->ack_seq
)) != 0L){
387 if(deltaA
> 0x0000ffff)
389 cp
= encode(cp
,deltaA
);
392 if((deltaS
= ntohl(th
->seq
) - ntohl(oth
->seq
)) != 0L){
393 if(deltaS
> 0x0000ffff)
395 cp
= encode(cp
,deltaS
);
400 case 0: /* Nothing changed. If this packet contains data and the
401 * last one didn't, this is probably a data packet following
402 * an ack (normal on an interactive connection) and we send
403 * it compressed. Otherwise it's probably a retransmit,
404 * retransmitted ack or window probe. Send it uncompressed
405 * in case the other side missed the compressed version.
407 if(ip
->tot_len
!= cs
->cs_ip
.tot_len
&&
408 ntohs(cs
->cs_ip
.tot_len
) == hlen
)
414 /* actual changes match one of our special case encodings --
415 * send packet uncompressed.
419 if(deltaS
== deltaA
&&
420 deltaS
== ntohs(cs
->cs_ip
.tot_len
) - hlen
){
421 /* special case for echoed terminal traffic */
427 if(deltaS
== ntohs(cs
->cs_ip
.tot_len
) - hlen
){
428 /* special case for data xfer */
434 deltaS
= ntohs(ip
->id
) - ntohs(cs
->cs_ip
.id
);
436 cp
= encode(cp
,deltaS
);
440 changes
|= TCP_PUSH_BIT
;
441 /* Grab the cksum before we overwrite it below. Then update our
442 * state with this packet's header.
444 deltaA
= ntohs(th
->check
);
445 memcpy(&cs
->cs_ip
,ip
,20);
446 memcpy(&cs
->cs_tcp
,th
,20);
447 /* We want to use the original packet as our compressed packet.
448 * (cp - new_seq) is the number of bytes we need for compressed
449 * sequence numbers. In addition we need one byte for the change
450 * mask, one for the connection id and two for the tcp checksum.
451 * So, (cp - new_seq) + 4 bytes of header are needed.
453 deltaS
= cp
- new_seq
;
454 if(compress_cid
== 0 || comp
->xmit_current
!= cs
->cs_this
){
457 *cp
++ = changes
| NEW_C
;
459 comp
->xmit_current
= cs
->cs_this
;
465 cp
= put16(cp
,(short)deltaA
); /* Write TCP checksum */
466 /* deltaS is now the size of the change section of the compressed header */
467 memcpy(cp
,new_seq
,deltaS
); /* Write list of deltas */
468 memcpy(cp
+deltaS
,icp
+hlen
,isize
-hlen
);
469 comp
->sls_o_compressed
++;
470 ocp
[0] |= SL_TYPE_COMPRESSED_TCP
;
471 return isize
- hlen
+ deltaS
+ (cp
- ocp
);
473 /* Update connection state cs & send uncompressed packet (i.e.,
474 * a regular ip/tcp packet but with the 'conversation id' we hope
475 * to use on future compressed packets in the protocol field).
478 memcpy(&cs
->cs_ip
,ip
,20);
479 memcpy(&cs
->cs_tcp
,th
,20);
481 memcpy(cs
->cs_ipopt
, ip
+1, ((ip
->ihl
) - 5) * 4);
483 memcpy(cs
->cs_tcpopt
, th
+1, ((th
->doff
) - 5) * 4);
484 comp
->xmit_current
= cs
->cs_this
;
485 comp
->sls_o_uncompressed
++;
486 memcpy(ocp
, icp
, isize
);
488 ocp
[9] = cs
->cs_this
;
489 ocp
[0] |= SL_TYPE_UNCOMPRESSED_TCP
;
495 slhc_uncompress(struct slcompress
*comp
, unsigned char *icp
, int isize
)
497 register int changes
;
499 register struct tcphdr
*thp
;
500 register struct iphdr
*ip
;
501 register struct cstate
*cs
;
503 unsigned char *cp
= icp
;
505 /* We've got a compressed packet; read the change byte */
506 comp
->sls_i_compressed
++;
513 /* Make sure the state index is in range, then grab the state.
514 * If we have a good state index, clear the 'discard' flag.
516 x
= *cp
++; /* Read conn index */
517 if(x
< 0 || x
> comp
->rslot_limit
)
520 comp
->flags
&=~ SLF_TOSS
;
521 comp
->recv_current
= x
;
523 /* this packet has an implicit state index. If we've
524 * had a line error since the last time we got an
525 * explicit state index, we have to toss the packet. */
526 if(comp
->flags
& SLF_TOSS
){
527 comp
->sls_i_tossed
++;
531 cs
= &comp
->rstate
[comp
->recv_current
];
535 if((x
= pull16(&cp
)) == -1) { /* Read the TCP checksum */
538 thp
->check
= htons(x
);
540 thp
->psh
= (changes
& TCP_PUSH_BIT
) ? 1 : 0;
542 * we can use the same number for the length of the saved header and
543 * the current one, because the packet wouldn't have been sent
544 * as compressed unless the options were the same as the previous one
547 hdrlen
= ip
->ihl
* 4 + thp
->doff
* 4;
549 switch(changes
& SPECIALS_MASK
){
550 case SPECIAL_I
: /* Echoed terminal traffic */
553 i
= ntohs(ip
->tot_len
) - hdrlen
;
554 thp
->ack_seq
= htonl( ntohl(thp
->ack_seq
) + i
);
555 thp
->seq
= htonl( ntohl(thp
->seq
) + i
);
559 case SPECIAL_D
: /* Unidirectional data */
560 thp
->seq
= htonl( ntohl(thp
->seq
) +
561 ntohs(ip
->tot_len
) - hdrlen
);
567 if((x
= decode(&cp
)) == -1) {
570 thp
->urg_ptr
= htons(x
);
574 if((x
= decode(&cp
)) == -1) {
577 thp
->window
= htons( ntohs(thp
->window
) + x
);
580 if((x
= decode(&cp
)) == -1) {
583 thp
->ack_seq
= htonl( ntohl(thp
->ack_seq
) + x
);
586 if((x
= decode(&cp
)) == -1) {
589 thp
->seq
= htonl( ntohl(thp
->seq
) + x
);
594 if((x
= decode(&cp
)) == -1) {
597 ip
->id
= htons (ntohs (ip
->id
) + x
);
599 ip
->id
= htons (ntohs (ip
->id
) + 1);
602 * At this point, cp points to the first byte of data in the
603 * packet. Put the reconstructed TCP and IP headers back on the
604 * packet. Recalculate IP checksum (but not TCP checksum).
607 len
= isize
- (cp
- icp
);
611 ip
->tot_len
= htons(len
);
614 memmove(icp
+ hdrlen
, cp
, len
- hdrlen
);
621 memcpy(cp
, cs
->cs_ipopt
, (ip
->ihl
- 5) * 4);
622 cp
+= (ip
->ihl
- 5) * 4;
625 put_unaligned(ip_fast_csum(icp
, ip
->ihl
),
626 &((struct iphdr
*)icp
)->check
);
632 memcpy(cp
, cs
->cs_tcpopt
, ((thp
->doff
) - 5) * 4);
633 cp
+= ((thp
->doff
) - 5) * 4;
639 return slhc_toss( comp
);
644 slhc_remember(struct slcompress
*comp
, unsigned char *icp
, int isize
)
646 register struct cstate
*cs
;
652 /* The packet is shorter than a legal IP header */
654 return slhc_toss( comp
);
656 /* Peek at the IP header's IHL field to find its length */
659 /* The IP header length field is too small */
661 return slhc_toss( comp
);
664 icp
[9] = IPPROTO_TCP
;
666 if (ip_fast_csum(icp
, ihl
)) {
667 /* Bad IP header checksum; discard */
668 comp
->sls_i_badcheck
++;
669 return slhc_toss( comp
);
671 if(index
> comp
->rslot_limit
) {
673 return slhc_toss(comp
);
676 /* Update local state */
677 cs
= &comp
->rstate
[comp
->recv_current
= index
];
678 comp
->flags
&=~ SLF_TOSS
;
679 memcpy(&cs
->cs_ip
,icp
,20);
680 memcpy(&cs
->cs_tcp
,icp
+ ihl
*4,20);
682 memcpy(cs
->cs_ipopt
, icp
+ sizeof(struct iphdr
), (ihl
- 5) * 4);
683 if (cs
->cs_tcp
.doff
> 5)
684 memcpy(cs
->cs_tcpopt
, icp
+ ihl
*4 + sizeof(struct tcphdr
), (cs
->cs_tcp
.doff
- 5) * 4);
685 cs
->cs_hsize
= ihl
*2 + cs
->cs_tcp
.doff
*2;
686 /* Put headers back on packet
687 * Neither header checksum is recalculated
689 comp
->sls_i_uncompressed
++;
695 slhc_toss(struct slcompress
*comp
)
697 if ( comp
== NULLSLCOMPR
)
700 comp
->flags
|= SLF_TOSS
;
705 void slhc_i_status(struct slcompress
*comp
)
707 if (comp
!= NULLSLCOMPR
) {
708 printk("\t%d Cmp, %d Uncmp, %d Bad, %d Tossed\n",
709 comp
->sls_i_compressed
,
710 comp
->sls_i_uncompressed
,
717 void slhc_o_status(struct slcompress
*comp
)
719 if (comp
!= NULLSLCOMPR
) {
720 printk("\t%d Cmp, %d Uncmp, %d AsIs, %d NotTCP\n",
721 comp
->sls_o_compressed
,
722 comp
->sls_o_uncompressed
,
725 printk("\t%10d Searches, %10d Misses\n",
726 comp
->sls_o_searches
,
731 /* Should this be surrounded with "#ifdef CONFIG_MODULES" ? */
732 /* VJ header compression */
733 EXPORT_SYMBOL(slhc_init
);
734 EXPORT_SYMBOL(slhc_free
);
735 EXPORT_SYMBOL(slhc_remember
);
736 EXPORT_SYMBOL(slhc_compress
);
737 EXPORT_SYMBOL(slhc_uncompress
);
738 EXPORT_SYMBOL(slhc_toss
);
742 int init_module(void)
744 printk(KERN_INFO
"CSLIP: code copyright 1989 Regents of the University of California\n");
748 void cleanup_module(void)
754 #else /* CONFIG_INET */
758 slhc_toss(struct slcompress
*comp
)
760 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_toss");
764 slhc_uncompress(struct slcompress
*comp
, unsigned char *icp
, int isize
)
766 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_uncompress");
770 slhc_compress(struct slcompress
*comp
, unsigned char *icp
, int isize
,
771 unsigned char *ocp
, unsigned char **cpp
, int compress_cid
)
773 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_compress");
778 slhc_remember(struct slcompress
*comp
, unsigned char *icp
, int isize
)
780 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_remember");
785 slhc_free(struct slcompress
*comp
)
787 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_free");
791 slhc_init(int rslots
, int tslots
)
793 printk(KERN_DEBUG
"Called IP function on non IP-system: slhc_init");
796 EXPORT_SYMBOL(slhc_init
);
797 EXPORT_SYMBOL(slhc_free
);
798 EXPORT_SYMBOL(slhc_remember
);
799 EXPORT_SYMBOL(slhc_compress
);
800 EXPORT_SYMBOL(slhc_uncompress
);
801 EXPORT_SYMBOL(slhc_toss
);
803 #endif /* CONFIG_INET */