1/*	$NetBSD: bsd-comp.c,v 1.19 2008/11/25 02:40:36 cube Exp $	*/
2/*	Id: bsd-comp.c,v 1.6 1996/08/28 06:31:58 paulus Exp 	*/
3
4/* Because this code is derived from the 4.3BSD compress source:
5 *
6 *
7 * Copyright (c) 1985, 1986 The Regents of the University of California.
8 * All rights reserved.
9 *
10 * This code is derived from software contributed to Berkeley by
11 * James A. Woods, derived from original work by Spencer Thomas
12 * and Joseph Orost.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 * 1. Redistributions of source code must retain the above copyright
18 *    notice, this list of conditions and the following disclaimer.
19 * 2. Redistributions in binary form must reproduce the above copyright
20 *    notice, this list of conditions and the following disclaimer in the
21 *    documentation and/or other materials provided with the distribution.
22 * 3. Neither the name of the University nor the names of its contributors
23 *    may be used to endorse or promote products derived from this software
24 *    without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * SUCH DAMAGE.
37 */
38
39/*
40 * This version is for use with mbufs on BSD-derived systems.
41 */
42
43#include <sys/cdefs.h>
44__KERNEL_RCSID(0, "$NetBSD: bsd-comp.c,v 1.19 2008/11/25 02:40:36 cube Exp $");
45
46#include <sys/param.h>
47#include <sys/systm.h>
48#include <sys/mbuf.h>
49#include <sys/socket.h>
50#include <sys/module.h>
51#include <net/if.h>
52#include <net/if_types.h>
53#include <net/ppp_defs.h>
54#include <net/if_ppp.h>
55
56#define PACKETPTR	struct mbuf *
57#include <net/ppp-comp.h>
58
59#if DO_BSD_COMPRESS
60/*
61 * PPP "BSD compress" compression
62 *  The differences between this compression and the classic BSD LZW
63 *  source are obvious from the requirement that the classic code worked
64 *  with files while this handles arbitrarily long streams that
65 *  are broken into packets.  They are:
66 *
67 *	When the code size expands, a block of junk is not emitted by
68 *	    the compressor and not expected by the decompressor.
69 *
70 *	New codes are not necessarily assigned every time an old
71 *	    code is output by the compressor.  This is because a packet
72 *	    end forces a code to be emitted, but does not imply that a
73 *	    new sequence has been seen.
74 *
75 *	The compression ratio is checked at the first end of a packet
76 *	    after the appropriate gap.	Besides simplifying and speeding
77 *	    things up, this makes it more likely that the transmitter
78 *	    and receiver will agree when the dictionary is cleared when
79 *	    compression is not going well.
80 */
81
82/*
83 * A dictionary for doing BSD compress.
84 */
85struct bsd_db {
86    int	    totlen;			/* length of this structure */
87    u_int   hsize;			/* size of the hash table */
88    u_char  hshift;			/* used in hash function */
89    u_char  n_bits;			/* current bits/code */
90    u_char  maxbits;
91    u_char  debug;
92    u_char  unit;
93    uint16_t seqno;			/* sequence # of next packet */
94    u_int   hdrlen;			/* header length to preallocate */
95    u_int   mru;
96    u_int   maxmaxcode;			/* largest valid code */
97    u_int   max_ent;			/* largest code in use */
98    u_int   in_count;			/* uncompressed bytes, aged */
99    u_int   bytes_out;			/* compressed bytes, aged */
100    u_int   ratio;			/* recent compression ratio */
101    u_int   checkpoint;			/* when to next check the ratio */
102    u_int   clear_count;		/* times dictionary cleared */
103    u_int   incomp_count;		/* incompressible packets */
104    u_int   incomp_bytes;		/* incompressible bytes */
105    u_int   uncomp_count;		/* uncompressed packets */
106    u_int   uncomp_bytes;		/* uncompressed bytes */
107    u_int   comp_count;			/* compressed packets */
108    u_int   comp_bytes;			/* compressed bytes */
109    uint16_t *lens;			/* array of lengths of codes */
110    struct bsd_dict {
111	union {				/* hash value */
112	    uint32_t	fcode;
113	    struct {
114#if BYTE_ORDER == LITTLE_ENDIAN
115		uint16_t prefix;	/* preceding code */
116		u_char	suffix;		/* last character of new code */
117		u_char	pad;
118#else
119		u_char	pad;
120		u_char	suffix;		/* last character of new code */
121		uint16_t prefix;	/* preceding code */
122#endif
123	    } hs;
124	} f;
125	uint16_t codem1;		/* output of hash table -1 */
126	uint16_t cptr;			/* map code to hash table entry */
127    } dict[1];
128};
129
130#define BSD_OVHD	2		/* BSD compress overhead/packet */
131#define BSD_INIT_BITS	BSD_MIN_BITS
132
133static void	*bsd_comp_alloc(u_char *options, int opt_len);
134static void	*bsd_decomp_alloc(u_char *options, int opt_len);
135static void	bsd_free(void *state);
136static int	bsd_comp_init(void *state, u_char *options, int opt_len,
137			      int unit, int hdrlen, int debug);
138static int	bsd_decomp_init(void *state, u_char *options, int opt_len,
139				int unit, int hdrlen, int mru, int debug);
140static int	bsd_compress(void *state, struct mbuf **mret,
141			     struct mbuf *mp, int slen, int maxolen);
142static void	bsd_incomp(void *state, struct mbuf *dmsg);
143static int	bsd_decompress(void *state, struct mbuf *cmp,
144			       struct mbuf **dmpp);
145static void	bsd_reset(void *state);
146static void	bsd_comp_stats(void *state, struct compstat *stats);
147
148/*
149 * Procedures exported to if_ppp.c.
150 */
151static struct compressor ppp_bsd_compress = {
152    .compress_proto =	CI_BSD_COMPRESS,
153    .comp_alloc =	bsd_comp_alloc,
154    .comp_free =	bsd_free,
155    .comp_init =	bsd_comp_init,
156    .comp_reset =	bsd_reset,
157    .compress =		bsd_compress,
158    .comp_stat =	bsd_comp_stats,
159    .decomp_alloc =	bsd_decomp_alloc,
160    .decomp_free =	bsd_free,
161    .decomp_init =	bsd_decomp_init,
162    .decomp_reset =	bsd_reset,
163    .decompress =	bsd_decompress,
164    .incomp =		bsd_incomp,
165    .decomp_stat =	bsd_comp_stats,
166};
167
168/*
169 * the next two codes should not be changed lightly, as they must not
170 * lie within the contiguous general code space.
171 */
172#define CLEAR	256			/* table clear output code */
173#define FIRST	257			/* first free entry */
174#define LAST	255
175
176#define MAXCODE(b)	((1 << (b)) - 1)
177#define BADCODEM1	MAXCODE(BSD_MAX_BITS)
178
179#define BSD_HASH(prefix,suffix,hshift)	((((uint32_t)(suffix)) << (hshift)) \
180					 ^ (uint32_t)(prefix))
181#define BSD_KEY(prefix,suffix)		((((uint32_t)(suffix)) << 16) \
182					 + (uint32_t)(prefix))
183
184#define CHECK_GAP	10000		/* Ratio check interval */
185
186#define RATIO_SCALE_LOG	8
187#define RATIO_SCALE	(1<<RATIO_SCALE_LOG)
188#define RATIO_MAX	(0x7fffffff>>RATIO_SCALE_LOG)
189
190static void	bsd_clear(struct bsd_db *);
191static int	bsd_check(struct bsd_db *);
192static void	*bsd_alloc(u_char *, int, int);
193static int	bsd_init(struct bsd_db *, u_char *, int, int, int, int,
194			 int, int);
195
196/*
197 * clear the dictionary
198 */
199static void
200bsd_clear(struct bsd_db *db)
201{
202    db->clear_count++;
203    db->max_ent = FIRST-1;
204    db->n_bits = BSD_INIT_BITS;
205    db->ratio = 0;
206    db->bytes_out = 0;
207    db->in_count = 0;
208    db->checkpoint = CHECK_GAP;
209}
210
211/*
212 * If the dictionary is full, then see if it is time to reset it.
213 *
214 * Compute the compression ratio using fixed-point arithmetic
215 * with 8 fractional bits.
216 *
217 * Since we have an infinite stream instead of a single file,
218 * watch only the local compression ratio.
219 *
220 * Since both peers must reset the dictionary at the same time even in
221 * the absence of CLEAR codes (while packets are incompressible), they
222 * must compute the same ratio.
223 */
224static int				/* 1=output CLEAR */
225bsd_check(struct bsd_db *db)
226{
227    u_int new_ratio;
228
229    if (db->in_count >= db->checkpoint) {
230	/* age the ratio by limiting the size of the counts */
231	if (db->in_count >= RATIO_MAX
232	    || db->bytes_out >= RATIO_MAX) {
233	    db->in_count -= db->in_count/4;
234	    db->bytes_out -= db->bytes_out/4;
235	}
236
237	db->checkpoint = db->in_count + CHECK_GAP;
238
239	if (db->max_ent >= db->maxmaxcode) {
240	    /* Reset the dictionary only if the ratio is worse,
241	     * or if it looks as if it has been poisoned
242	     * by incompressible data.
243	     *
244	     * This does not overflow, because
245	     *	db->in_count <= RATIO_MAX.
246	     */
247	    new_ratio = db->in_count << RATIO_SCALE_LOG;
248	    if (db->bytes_out != 0)
249		new_ratio /= db->bytes_out;
250
251	    if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE) {
252		bsd_clear(db);
253		return 1;
254	    }
255	    db->ratio = new_ratio;
256	}
257    }
258    return 0;
259}
260
261/*
262 * Return statistics.
263 */
264static void
265bsd_comp_stats(void *state, struct compstat *stats)
266{
267    struct bsd_db *db = (struct bsd_db *) state;
268    u_int out;
269
270    stats->unc_bytes = db->uncomp_bytes;
271    stats->unc_packets = db->uncomp_count;
272    stats->comp_bytes = db->comp_bytes;
273    stats->comp_packets = db->comp_count;
274    stats->inc_bytes = db->incomp_bytes;
275    stats->inc_packets = db->incomp_count;
276    stats->ratio = db->in_count;
277    out = db->bytes_out;
278    if (stats->ratio <= 0x7fffff)
279	stats->ratio <<= 8;
280    else
281	out >>= 8;
282    if (out != 0)
283	stats->ratio /= out;
284}
285
286/*
287 * Reset state, as on a CCP ResetReq.
288 */
289static void
290bsd_reset(void *state)
291{
292    struct bsd_db *db = (struct bsd_db *) state;
293
294    db->seqno = 0;
295    bsd_clear(db);
296    db->clear_count = 0;
297}
298
299/*
300 * Allocate space for a (de) compressor.
301 */
302static void *
303bsd_alloc(u_char *options, int opt_len, int decomp)
304{
305    int bits;
306    u_int newlen, hsize, hshift, maxmaxcode;
307    struct bsd_db *db;
308
309    if (opt_len < CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
310	|| options[1] != CILEN_BSD_COMPRESS
311	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
312	return NULL;
313    bits = BSD_NBITS(options[2]);
314    switch (bits) {
315    case 9:			/* needs 82152 for both directions */
316    case 10:			/* needs 84144 */
317    case 11:			/* needs 88240 */
318    case 12:			/* needs 96432 */
319	hsize = 5003;
320	hshift = 4;
321	break;
322    case 13:			/* needs 176784 */
323	hsize = 9001;
324	hshift = 5;
325	break;
326    case 14:			/* needs 353744 */
327	hsize = 18013;
328	hshift = 6;
329	break;
330    case 15:			/* needs 691440 */
331	hsize = 35023;
332	hshift = 7;
333	break;
334    case 16:			/* needs 1366160--far too much, */
335	/* hsize = 69001; */	/* and 69001 is too big for cptr */
336	/* hshift = 8; */	/* in struct bsd_db */
337	/* break; */
338    default:
339	return NULL;
340    }
341
342    maxmaxcode = MAXCODE(bits);
343    newlen = sizeof(*db) + (hsize-1) * (sizeof(db->dict[0]));
344    db = malloc(newlen, M_DEVBUF, M_NOWAIT|M_ZERO);
345    if (!db)
346	return NULL;
347
348    if (!decomp) {
349	db->lens = NULL;
350    } else {
351	db->lens = malloc((maxmaxcode+1) * sizeof(db->lens[0]),
352	    M_DEVBUF, M_NOWAIT);
353	if (!db->lens) {
354	    free(db, M_DEVBUF);
355	    return NULL;
356	}
357    }
358
359    db->totlen = newlen;
360    db->hsize = hsize;
361    db->hshift = hshift;
362    db->maxmaxcode = maxmaxcode;
363    db->maxbits = bits;
364
365    return (void *) db;
366}
367
368static void
369bsd_free(void *state)
370{
371    struct bsd_db *db = (struct bsd_db *) state;
372
373    if (db->lens)
374	free(db->lens, M_DEVBUF);
375    free(db, M_DEVBUF);
376}
377
378static void *
379bsd_comp_alloc(u_char *options, int opt_len)
380{
381    return bsd_alloc(options, opt_len, 0);
382}
383
384static void *
385bsd_decomp_alloc(u_char *options, int opt_len)
386{
387    return bsd_alloc(options, opt_len, 1);
388}
389
390/*
391 * Initialize the database.
392 */
393static int
394bsd_init(struct bsd_db *db, u_char *options, int opt_len, int unit, int hdrlen,
395    int mru, int debug, int decomp)
396{
397    int i;
398
399    if (opt_len < CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
400	|| options[1] != CILEN_BSD_COMPRESS
401	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
402	|| BSD_NBITS(options[2]) != db->maxbits
403	|| (decomp && db->lens == NULL))
404	return 0;
405
406    if (decomp) {
407	i = LAST+1;
408	while (i != 0)
409	    db->lens[--i] = 1;
410    }
411    i = db->hsize;
412    while (i != 0) {
413	db->dict[--i].codem1 = BADCODEM1;
414	db->dict[i].cptr = 0;
415    }
416
417    db->unit = unit;
418    db->hdrlen = hdrlen;
419    db->mru = mru;
420#ifndef DEBUG
421    if (debug)
422#endif
423	db->debug = 1;
424
425    bsd_reset(db);
426
427    return 1;
428}
429
430static int
431bsd_comp_init(void *state, u_char *options, int opt_len, int unit, int hdrlen,
432              int debug)
433{
434    return bsd_init((struct bsd_db *) state, options, opt_len,
435		    unit, hdrlen, 0, debug, 0);
436}
437
438static int
439bsd_decomp_init(void *state, u_char *options, int opt_len, int unit, int hdrlen,
440                int mru, int debug)
441{
442    return bsd_init((struct bsd_db *) state, options, opt_len,
443		    unit, hdrlen, mru, debug, 1);
444}
445
446
447/*
448 * compress a packet
449 *	One change from the BSD compress command is that when the
450 *	code size expands, we do not output a bunch of padding.
451 */
452int					/* new slen */
453bsd_compress(void *state,
454             struct mbuf **mret /* return compressed mbuf chain here */,
455	     struct mbuf *mp /* from here */,
456	     int slen, int maxolen)
457{
458    struct bsd_db *db = (struct bsd_db *) state;
459    int hshift = db->hshift;
460    u_int max_ent = db->max_ent;
461    u_int n_bits = db->n_bits;
462    u_int bitno = 32;
463    uint32_t accm = 0, fcode;
464    struct bsd_dict *dictp;
465    u_char c;
466    int hval, disp, ent, ilen;
467    u_char *rptr, *wptr;
468    u_char *cp_end;
469    int olen;
470    struct mbuf *m;
471
472#define PUTBYTE(v) {					\
473    ++olen;						\
474    if (wptr) {						\
475	*wptr++ = (v);					\
476	if (wptr >= cp_end) {				\
477	    m->m_len = wptr - mtod(m, u_char *);	\
478	    MGET(m->m_next, M_DONTWAIT, MT_DATA);	\
479	    m = m->m_next;				\
480	    if (m) {					\
481		m->m_len = 0;				\
482		if (maxolen - olen > MLEN)		\
483		    MCLGET(m, M_DONTWAIT);		\
484		wptr = mtod(m, u_char *);		\
485		cp_end = wptr + M_TRAILINGSPACE(m);	\
486	    } else					\
487		wptr = NULL;				\
488	}						\
489    }							\
490}
491
492#define OUTPUT(ent) {					\
493    bitno -= n_bits;					\
494    accm |= ((ent) << bitno);				\
495    do {						\
496	PUTBYTE(accm >> 24);				\
497	accm <<= 8;					\
498	bitno += 8;					\
499    } while (bitno <= 24);				\
500}
501
502    /*
503     * If the protocol is not in the range we're interested in,
504     * just return without compressing the packet.  If it is,
505     * the protocol becomes the first byte to compress.
506     */
507    rptr = mtod(mp, u_char *);
508    ent = PPP_PROTOCOL(rptr);
509    if (ent < 0x21 || ent > 0xf9) {
510	*mret = NULL;
511	return slen;
512    }
513
514    /* Don't generate compressed packets which are larger than
515       the uncompressed packet. */
516    if (maxolen > slen)
517	maxolen = slen;
518
519    /* Allocate one mbuf to start with. */
520    MGET(m, M_DONTWAIT, MT_DATA);
521    *mret = m;
522    if (m != NULL) {
523	m->m_len = 0;
524	if (maxolen + db->hdrlen > MLEN)
525	    MCLGET(m, M_DONTWAIT);
526	m->m_data += db->hdrlen;
527	wptr = mtod(m, u_char *);
528	cp_end = wptr + M_TRAILINGSPACE(m);
529    } else
530	wptr = cp_end = NULL;
531
532    /*
533     * Copy the PPP header over, changing the protocol,
534     * and install the 2-byte packet sequence number.
535     */
536    if (wptr) {
537	*wptr++ = PPP_ADDRESS(rptr);	/* assumes the ppp header is */
538	*wptr++ = PPP_CONTROL(rptr);	/* all in one mbuf */
539	*wptr++ = 0;			/* change the protocol */
540	*wptr++ = PPP_COMP;
541	*wptr++ = db->seqno >> 8;
542	*wptr++ = db->seqno;
543    }
544    ++db->seqno;
545
546    olen = 0;
547    rptr += PPP_HDRLEN;
548    slen = mp->m_len - PPP_HDRLEN;
549    ilen = slen + 1;
550    for (;;) {
551	if (slen <= 0) {
552	    mp = mp->m_next;
553	    if (!mp)
554		break;
555	    rptr = mtod(mp, u_char *);
556	    slen = mp->m_len;
557	    if (!slen)
558		continue;   /* handle 0-length buffers */
559	    ilen += slen;
560	}
561
562	slen--;
563	c = *rptr++;
564	fcode = BSD_KEY(ent, c);
565	hval = BSD_HASH(ent, c, hshift);
566	dictp = &db->dict[hval];
567
568	/* Validate and then check the entry. */
569	if (dictp->codem1 >= max_ent)
570	    goto nomatch;
571	if (dictp->f.fcode == fcode) {
572	    ent = dictp->codem1+1;
573	    continue;	/* found (prefix,suffix) */
574	}
575
576	/* continue probing until a match or invalid entry */
577	disp = (hval == 0) ? 1 : hval;
578	do {
579	    hval += disp;
580	    if (hval >= db->hsize)
581		hval -= db->hsize;
582	    dictp = &db->dict[hval];
583	    if (dictp->codem1 >= max_ent)
584		goto nomatch;
585	} while (dictp->f.fcode != fcode);
586	ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
587	continue;
588
589    nomatch:
590	OUTPUT(ent);		/* output the prefix */
591
592	/* code -> hashtable */
593	if (max_ent < db->maxmaxcode) {
594	    struct bsd_dict *dictp2;
595	    /* expand code size if needed */
596	    if (max_ent >= MAXCODE(n_bits))
597		db->n_bits = ++n_bits;
598
599	    /* Invalidate old hash table entry using
600	     * this code, and then take it over.
601	     */
602	    dictp2 = &db->dict[max_ent+1];
603	    if (db->dict[dictp2->cptr].codem1 == max_ent)
604		db->dict[dictp2->cptr].codem1 = BADCODEM1;
605	    dictp2->cptr = hval;
606	    dictp->codem1 = max_ent;
607	    dictp->f.fcode = fcode;
608
609	    db->max_ent = ++max_ent;
610	}
611	ent = c;
612    }
613
614    OUTPUT(ent);		/* output the last code */
615    db->bytes_out += olen;
616    db->in_count += ilen;
617    if (bitno < 32)
618	++db->bytes_out;	/* count complete bytes */
619
620    if (bsd_check(db))
621	OUTPUT(CLEAR);		/* do not count the CLEAR */
622
623    /*
624     * Pad dribble bits of last code with ones.
625     * Do not emit a completely useless byte of ones.
626     */
627    if (bitno != 32)
628	PUTBYTE((accm | (0xff << (bitno-8))) >> 24);
629
630    if (m != NULL) {
631	m->m_len = wptr - mtod(m, u_char *);
632	m->m_next = NULL;
633    }
634
635    /*
636     * Increase code size if we would have without the packet
637     * boundary and as the decompressor will.
638     */
639    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
640	db->n_bits++;
641
642    db->uncomp_bytes += ilen;
643    ++db->uncomp_count;
644    if (olen + PPP_HDRLEN + BSD_OVHD > maxolen) {
645	/* throw away the compressed stuff if it is longer than uncompressed */
646	if (*mret != NULL) {
647	    m_freem(*mret);
648	    *mret = NULL;
649	}
650	++db->incomp_count;
651	db->incomp_bytes += ilen;
652    } else {
653	++db->comp_count;
654	db->comp_bytes += olen + BSD_OVHD;
655    }
656
657    return olen + PPP_HDRLEN + BSD_OVHD;
658#undef OUTPUT
659#undef PUTBYTE
660}
661
662
663/*
664 * Update the "BSD Compress" dictionary on the receiver for
665 * incompressible data by pretending to compress the incoming data.
666 */
667static void
668bsd_incomp(void *state, struct mbuf *dmsg)
669{
670    struct bsd_db *db = (struct bsd_db *) state;
671    u_int hshift = db->hshift;
672    u_int max_ent = db->max_ent;
673    u_int n_bits = db->n_bits;
674    struct bsd_dict *dictp;
675    uint32_t fcode;
676    u_char c;
677    uint32_t hval, disp;
678    int slen, ilen;
679    u_int bitno = 7;
680    u_char *rptr;
681    u_int ent;
682
683    /*
684     * If the protocol is not in the range we're interested in,
685     * just return without looking at the packet.  If it is,
686     * the protocol becomes the first byte to "compress".
687     */
688    rptr = mtod(dmsg, u_char *);
689    ent = PPP_PROTOCOL(rptr);
690    if (ent < 0x21 || ent > 0xf9)
691	return;
692
693    db->seqno++;
694    ilen = 1;		/* count the protocol as 1 byte */
695    rptr += PPP_HDRLEN;
696    slen = dmsg->m_len - PPP_HDRLEN;
697    for (;;) {
698	if (slen <= 0) {
699	    dmsg = dmsg->m_next;
700	    if (!dmsg)
701		break;
702	    rptr = mtod(dmsg, u_char *);
703	    slen = dmsg->m_len;
704	    continue;
705	}
706	ilen += slen;
707
708	do {
709	    c = *rptr++;
710	    fcode = BSD_KEY(ent, c);
711	    hval = BSD_HASH(ent, c, hshift);
712	    dictp = &db->dict[hval];
713
714	    /* validate and then check the entry */
715	    if (dictp->codem1 >= max_ent)
716		goto nomatch;
717	    if (dictp->f.fcode == fcode) {
718		ent = dictp->codem1+1;
719		continue;   /* found (prefix,suffix) */
720	    }
721
722	    /* continue probing until a match or invalid entry */
723	    disp = (hval == 0) ? 1 : hval;
724	    do {
725		hval += disp;
726		if (hval >= db->hsize)
727		    hval -= db->hsize;
728		dictp = &db->dict[hval];
729		if (dictp->codem1 >= max_ent)
730		    goto nomatch;
731	    } while (dictp->f.fcode != fcode);
732	    ent = dictp->codem1+1;
733	    continue;	/* finally found (prefix,suffix) */
734
735	nomatch:		/* output (count) the prefix */
736	    bitno += n_bits;
737
738	    /* code -> hashtable */
739	    if (max_ent < db->maxmaxcode) {
740		struct bsd_dict *dictp2;
741		/* expand code size if needed */
742		if (max_ent >= MAXCODE(n_bits))
743		    db->n_bits = ++n_bits;
744
745		/* Invalidate previous hash table entry
746		 * assigned this code, and then take it over.
747		 */
748		dictp2 = &db->dict[max_ent+1];
749		if (db->dict[dictp2->cptr].codem1 == max_ent)
750		    db->dict[dictp2->cptr].codem1 = BADCODEM1;
751		dictp2->cptr = hval;
752		dictp->codem1 = max_ent;
753		dictp->f.fcode = fcode;
754
755		db->max_ent = ++max_ent;
756		db->lens[max_ent] = db->lens[ent]+1;
757	    }
758	    ent = c;
759	} while (--slen != 0);
760    }
761    bitno += n_bits;		/* output (count) the last code */
762    db->bytes_out += bitno/8;
763    db->in_count += ilen;
764    (void)bsd_check(db);
765
766    ++db->incomp_count;
767    db->incomp_bytes += ilen;
768    ++db->uncomp_count;
769    db->uncomp_bytes += ilen;
770
771    /* Increase code size if we would have without the packet
772     * boundary and as the decompressor will.
773     */
774    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
775	db->n_bits++;
776}
777
778
779/*
780 * Decompress "BSD Compress".
781 *
782 * Because of patent problems, we return DECOMP_ERROR for errors
783 * found by inspecting the input data and for system problems, but
784 * DECOMP_FATALERROR for any errors which could possibly be said to
785 * be being detected "after" decompression.  For DECOMP_ERROR,
786 * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
787 * infringing a patent of Motorola's if we do, so we take CCP down
788 * instead.
789 *
790 * Given that the frame has the correct sequence number and a good FCS,
791 * errors such as invalid codes in the input most likely indicate a
792 * bug, so we return DECOMP_FATALERROR for them in order to turn off
793 * compression, even though they are detected by inspecting the input.
794 */
795int
796bsd_decompress(void *state, struct mbuf *cmp, struct mbuf **dmpp)
797{
798    struct bsd_db *db = (struct bsd_db *) state;
799    u_int max_ent = db->max_ent;
800    uint32_t accm = 0;
801    u_int bitno = 32;		/* 1st valid bit in accm */
802    u_int n_bits = db->n_bits;
803    u_int tgtbitno = 32-n_bits;	/* bitno when we have a code */
804    struct bsd_dict *dictp;
805    int explen, i, seq, len;
806    u_int incode, oldcode, finchar;
807    u_char *p, *rptr, *wptr;
808    struct mbuf *m, *dmp, *mret;
809    int adrs, ctrl, ilen;
810    int space, codelen, extra;
811
812    /*
813     * Save the address/control from the PPP header
814     * and then get the sequence number.
815     */
816    *dmpp = NULL;
817    rptr = mtod(cmp, u_char *);
818    adrs = PPP_ADDRESS(rptr);
819    ctrl = PPP_CONTROL(rptr);
820    rptr += PPP_HDRLEN;
821    len = cmp->m_len - PPP_HDRLEN;
822    seq = 0;
823    for (i = 0; i < 2; ++i) {
824	while (len <= 0) {
825	    cmp = cmp->m_next;
826	    if (cmp == NULL)
827		return DECOMP_ERROR;
828	    rptr = mtod(cmp, u_char *);
829	    len = cmp->m_len;
830	}
831	seq = (seq << 8) + *rptr++;
832	--len;
833    }
834
835    /*
836     * Check the sequence number and give up if it differs from
837     * the value we're expecting.
838     */
839    if (seq != db->seqno) {
840	if (db->debug)
841	    printf("bsd_decomp%d: bad sequence # %d, expected %d\n",
842		   db->unit, seq, db->seqno - 1);
843	return DECOMP_ERROR;
844    }
845    ++db->seqno;
846
847    /*
848     * Allocate one mbuf to start with.
849     */
850    MGETHDR(dmp, M_DONTWAIT, MT_DATA);
851    if (dmp == NULL)
852	return DECOMP_ERROR;
853    mret = dmp;
854    dmp->m_len = 0;
855    dmp->m_next = NULL;
856    MCLGET(dmp, M_DONTWAIT);
857    dmp->m_data += db->hdrlen;
858    wptr = mtod(dmp, u_char *);
859    space = M_TRAILINGSPACE(dmp) - PPP_HDRLEN + 1;
860
861    /*
862     * Fill in the ppp header, but not the last byte of the protocol
863     * (that comes from the decompressed data).
864     */
865    wptr[0] = adrs;
866    wptr[1] = ctrl;
867    wptr[2] = 0;
868    wptr += PPP_HDRLEN - 1;
869
870    ilen = len;
871    oldcode = CLEAR;
872    explen = 0;
873    for (;;) {
874	if (len == 0) {
875	    cmp = cmp->m_next;
876	    if (!cmp)		/* quit at end of message */
877		break;
878	    rptr = mtod(cmp, u_char *);
879	    len = cmp->m_len;
880	    ilen += len;
881	    continue;		/* handle 0-length buffers */
882	}
883
884	/*
885	 * Accumulate bytes until we have a complete code.
886	 * Then get the next code, relying on the 32-bit,
887	 * unsigned accm to mask the result.
888	 */
889	bitno -= 8;
890	accm |= *rptr++ << bitno;
891	--len;
892	if (tgtbitno < bitno)
893	    continue;
894	incode = accm >> tgtbitno;
895	accm <<= n_bits;
896	bitno += n_bits;
897
898	if (incode == CLEAR) {
899	    /*
900	     * The dictionary must only be cleared at
901	     * the end of a packet.  But there could be an
902	     * empty mbuf at the end.
903	     */
904	    if (len > 0 || cmp->m_next != NULL) {
905		while ((cmp = cmp->m_next) != NULL)
906		    len += cmp->m_len;
907		if (len > 0) {
908		    m_freem(mret);
909		    if (db->debug)
910			printf("bsd_decomp%d: bad CLEAR\n", db->unit);
911		    return DECOMP_FATALERROR;	/* probably a bug */
912		}
913	    }
914	    bsd_clear(db);
915	    explen = ilen = 0;
916	    break;
917	}
918
919	if (incode > max_ent + 2 || incode > db->maxmaxcode
920	    || (incode > max_ent && oldcode == CLEAR)) {
921	    m_freem(mret);
922	    if (db->debug) {
923		printf("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
924		       db->unit, incode, oldcode);
925		printf("max_ent=0x%x explen=%d seqno=%d\n",
926		       max_ent, explen, db->seqno);
927	    }
928	    return DECOMP_FATALERROR;	/* probably a bug */
929	}
930
931	/* Special case for KwKwK string. */
932	if (incode > max_ent) {
933	    finchar = oldcode;
934	    extra = 1;
935	} else {
936	    finchar = incode;
937	    extra = 0;
938	}
939
940	codelen = db->lens[finchar];
941	explen += codelen + extra;
942	if (explen > db->mru + 1) {
943	    m_freem(mret);
944	    if (db->debug) {
945		printf("bsd_decomp%d: ran out of mru\n", db->unit);
946#ifdef DEBUG
947		while ((cmp = cmp->m_next) != NULL)
948		    len += cmp->m_len;
949		printf("  len=%d, finchar=0x%x, codelen=%d, explen=%d\n",
950		       len, finchar, codelen, explen);
951#endif
952	    }
953	    return DECOMP_FATALERROR;
954	}
955
956	/*
957	 * For simplicity, the decoded characters go in a single mbuf,
958	 * so we allocate a single extra cluster mbuf if necessary.
959	 */
960	if ((space -= codelen + extra) < 0) {
961	    dmp->m_len = wptr - mtod(dmp, u_char *);
962	    MGET(m, M_DONTWAIT, MT_DATA);
963	    if (m == NULL) {
964		m_freem(mret);
965		return DECOMP_ERROR;
966	    }
967	    m->m_len = 0;
968	    m->m_next = NULL;
969	    dmp->m_next = m;
970	    MCLGET(m, M_DONTWAIT);
971	    space = M_TRAILINGSPACE(m) - (codelen + extra);
972	    if (space < 0) {
973		/* now that's what I call *compression*. */
974		m_freem(mret);
975		return DECOMP_ERROR;
976	    }
977	    dmp = m;
978	    wptr = mtod(dmp, u_char *);
979	}
980
981	/*
982	 * Decode this code and install it in the decompressed buffer.
983	 */
984	p = (wptr += codelen);
985	while (finchar > LAST) {
986	    dictp = &db->dict[db->dict[finchar].cptr];
987#ifdef DEBUG
988	    if (--codelen <= 0 || dictp->codem1 != finchar-1)
989		goto bad;
990#endif
991	    *--p = dictp->f.hs.suffix;
992	    finchar = dictp->f.hs.prefix;
993	}
994	*--p = finchar;
995
996#ifdef DEBUG
997	if (--codelen != 0)
998	    printf("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
999		   db->unit, codelen, incode, max_ent);
1000#endif
1001
1002	if (extra)		/* the KwKwK case again */
1003	    *wptr++ = finchar;
1004
1005	/*
1006	 * If not first code in a packet, and
1007	 * if not out of code space, then allocate a new code.
1008	 *
1009	 * Keep the hash table correct so it can be used
1010	 * with uncompressed packets.
1011	 */
1012	if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
1013	    struct bsd_dict *dictp2;
1014	    uint32_t fcode;
1015	    uint32_t hval, disp;
1016
1017	    fcode = BSD_KEY(oldcode,finchar);
1018	    hval = BSD_HASH(oldcode,finchar,db->hshift);
1019	    dictp = &db->dict[hval];
1020
1021	    /* look for a free hash table entry */
1022	    if (dictp->codem1 < max_ent) {
1023		disp = (hval == 0) ? 1 : hval;
1024		do {
1025		    hval += disp;
1026		    if (hval >= db->hsize)
1027			hval -= db->hsize;
1028		    dictp = &db->dict[hval];
1029		} while (dictp->codem1 < max_ent);
1030	    }
1031
1032	    /*
1033	     * Invalidate previous hash table entry
1034	     * assigned this code, and then take it over
1035	     */
1036	    dictp2 = &db->dict[max_ent+1];
1037	    if (db->dict[dictp2->cptr].codem1 == max_ent) {
1038		db->dict[dictp2->cptr].codem1 = BADCODEM1;
1039	    }
1040	    dictp2->cptr = hval;
1041	    dictp->codem1 = max_ent;
1042	    dictp->f.fcode = fcode;
1043
1044	    db->max_ent = ++max_ent;
1045	    db->lens[max_ent] = db->lens[oldcode]+1;
1046
1047	    /* Expand code size if needed. */
1048	    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
1049		db->n_bits = ++n_bits;
1050		tgtbitno = 32-n_bits;
1051	    }
1052	}
1053	oldcode = incode;
1054    }
1055    dmp->m_len = wptr - mtod(dmp, u_char *);
1056
1057    /*
1058     * Keep the checkpoint right so that incompressible packets
1059     * clear the dictionary at the right times.
1060     */
1061    db->bytes_out += ilen;
1062    db->in_count += explen;
1063    if (bsd_check(db) && db->debug) {
1064	printf("bsd_decomp%d: peer should have cleared dictionary\n",
1065	       db->unit);
1066    }
1067
1068    ++db->comp_count;
1069    db->comp_bytes += ilen + BSD_OVHD;
1070    ++db->uncomp_count;
1071    db->uncomp_bytes += explen;
1072
1073    *dmpp = mret;
1074    return DECOMP_OK;
1075
1076#ifdef DEBUG
1077 bad:
1078    if (codelen <= 0) {
1079	printf("bsd_decomp%d: fell off end of chain ", db->unit);
1080	printf("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
1081	       incode, finchar, db->dict[finchar].cptr, max_ent);
1082    } else if (dictp->codem1 != finchar-1) {
1083	printf("bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",
1084	       db->unit, incode, finchar);
1085	printf("oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode,
1086	       db->dict[finchar].cptr, dictp->codem1);
1087    }
1088    m_freem(mret);
1089    return DECOMP_FATALERROR;
1090#endif /* DEBUG */
1091}
1092
1093MODULE(MODULE_CLASS_MISC, ppp_bsdcomp, NULL);
1094
1095static int
1096ppp_bsdcomp_modcmd(modcmd_t cmd, void *arg)
1097{
1098
1099	switch (cmd) {
1100	case MODULE_CMD_INIT:
1101		return ppp_register_compressor(&ppp_bsd_compress, 1);
1102	case MODULE_CMD_FINI:
1103		return ppp_unregister_compressor(&ppp_bsd_compress, 1);
1104	case MODULE_CMD_STAT:
1105		return 0;
1106	default:
1107		return ENOTTY;
1108	}
1109
1110	return ENOTTY;
1111}
1112#endif /* DO_BSD_COMPRESS */
1113