xref: /linux/drivers/net/ppp/bsd_comp.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
1 /*
2  * Update: The Berkeley copyright was changed, and the change
3  * is retroactive to all "true" BSD software (ie everything
4  * from UCB as opposed to other peoples code that just carried
5  * the same license). The new copyright doesn't clash with the
6  * GPL, so the module-only restriction has been removed..
7  */
8 
9 /* Because this code is derived from the 4.3BSD compress source:
10  *
11  * Copyright (c) 1985, 1986 The Regents of the University of California.
12  * All rights reserved.
13  *
14  * This code is derived from software contributed to Berkeley by
15  * James A. Woods, derived from original work by Spencer Thomas
16  * and Joseph Orost.
17  *
18  * Redistribution and use in source and binary forms, with or without
19  * modification, are permitted provided that the following conditions
20  * are met:
21  * 1. Redistributions of source code must retain the above copyright
22  *    notice, this list of conditions and the following disclaimer.
23  * 2. Redistributions in binary form must reproduce the above copyright
24  *    notice, this list of conditions and the following disclaimer in the
25  *    documentation and/or other materials provided with the distribution.
26  * 3. All advertising materials mentioning features or use of this software
27  *    must display the following acknowledgement:
28  *	This product includes software developed by the University of
29  *	California, Berkeley and its contributors.
30  * 4. Neither the name of the University nor the names of its contributors
31  *    may be used to endorse or promote products derived from this software
32  *    without specific prior written permission.
33  *
34  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
35  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
36  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
37  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
38  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
39  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
40  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
41  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
42  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
43  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
44  * SUCH DAMAGE.
45  */
46 
47 /*
48  * This version is for use with contiguous buffers on Linux-derived systems.
49  *
50  *  ==FILEVERSION 20000226==
51  *
52  *  NOTE TO MAINTAINERS:
53  *     If you modify this file at all, please set the number above to the
54  *     date of the modification as YYMMDD (year month day).
55  *     bsd_comp.c is shipped with a PPP distribution as well as with
56  *     the kernel; if everyone increases the FILEVERSION number above,
57  *     then scripts can do the right thing when deciding whether to
58  *     install a new bsd_comp.c file. Don't change the format of that
59  *     line otherwise, so the installation script can recognize it.
60  *
61  * From: bsd_comp.c,v 1.3 1994/12/08 01:59:58 paulus Exp
62  */
63 
64 #include <linux/module.h>
65 #include <linux/init.h>
66 #include <linux/slab.h>
67 #include <linux/vmalloc.h>
68 #include <linux/string.h>
69 
70 #include <linux/ppp_defs.h>
71 
72 #undef   PACKETPTR
73 #define  PACKETPTR 1
74 #include <linux/ppp-comp.h>
75 #undef   PACKETPTR
76 
77 #include <asm/byteorder.h>
78 
79 /*
80  * PPP "BSD compress" compression
81  *  The differences between this compression and the classic BSD LZW
82  *  source are obvious from the requirement that the classic code worked
83  *  with files while this handles arbitrarily long streams that
84  *  are broken into packets.  They are:
85  *
86  *	When the code size expands, a block of junk is not emitted by
87  *	    the compressor and not expected by the decompressor.
88  *
89  *	New codes are not necessarily assigned every time an old
90  *	    code is output by the compressor.  This is because a packet
91  *	    end forces a code to be emitted, but does not imply that a
92  *	    new sequence has been seen.
93  *
94  *	The compression ratio is checked at the first end of a packet
95  *	    after the appropriate gap.	Besides simplifying and speeding
96  *	    things up, this makes it more likely that the transmitter
97  *	    and receiver will agree when the dictionary is cleared when
98  *	    compression is not going well.
99  */
100 
101 /*
102  * Macros to extract protocol version and number of bits
103  * from the third byte of the BSD Compress CCP configuration option.
104  */
105 
106 #define BSD_VERSION(x)	((x) >> 5)
107 #define BSD_NBITS(x)	((x) & 0x1F)
108 
109 #define BSD_CURRENT_VERSION	1
110 
111 /*
112  * A dictionary for doing BSD compress.
113  */
114 
115 struct bsd_dict {
116     union {				/* hash value */
117 	unsigned long	fcode;
118 	struct {
119 #if defined(__LITTLE_ENDIAN)		/* Little endian order */
120 	    unsigned short	prefix;	/* preceding code */
121 	    unsigned char	suffix; /* last character of new code */
122 	    unsigned char	pad;
123 #elif defined(__BIG_ENDIAN)		/* Big endian order */
124 	    unsigned char	pad;
125 	    unsigned char	suffix; /* last character of new code */
126 	    unsigned short	prefix; /* preceding code */
127 #else
128 #error Endianness not defined...
129 #endif
130 	} hs;
131     } f;
132     unsigned short codem1;		/* output of hash table -1 */
133     unsigned short cptr;		/* map code to hash table entry */
134 };
135 
136 struct bsd_db {
137     int	    totlen;			/* length of this structure */
138     unsigned int   hsize;		/* size of the hash table */
139     unsigned char  hshift;		/* used in hash function */
140     unsigned char  n_bits;		/* current bits/code */
141     unsigned char  maxbits;		/* maximum bits/code */
142     unsigned char  debug;		/* non-zero if debug desired */
143     unsigned char  unit;		/* ppp unit number */
144     unsigned short seqno;		/* sequence # of next packet */
145     unsigned int   mru;			/* size of receive (decompress) bufr */
146     unsigned int   maxmaxcode;		/* largest valid code */
147     unsigned int   max_ent;		/* largest code in use */
148     unsigned int   in_count;		/* uncompressed bytes, aged */
149     unsigned int   bytes_out;		/* compressed bytes, aged */
150     unsigned int   ratio;		/* recent compression ratio */
151     unsigned int   checkpoint;		/* when to next check the ratio */
152     unsigned int   clear_count;		/* times dictionary cleared */
153     unsigned int   incomp_count;	/* incompressible packets */
154     unsigned int   incomp_bytes;	/* incompressible bytes */
155     unsigned int   uncomp_count;	/* uncompressed packets */
156     unsigned int   uncomp_bytes;	/* uncompressed bytes */
157     unsigned int   comp_count;		/* compressed packets */
158     unsigned int   comp_bytes;		/* compressed bytes */
159     unsigned short  *lens;		/* array of lengths of codes */
160     struct bsd_dict *dict;		/* dictionary */
161 };
162 
163 #define BSD_OVHD	2		/* BSD compress overhead/packet */
164 #define MIN_BSD_BITS	9
165 #define BSD_INIT_BITS	MIN_BSD_BITS
166 #define MAX_BSD_BITS	15
167 
168 static void	bsd_free (void *state);
169 static void	*bsd_alloc(unsigned char *options, int opt_len, int decomp);
170 static void	*bsd_comp_alloc (unsigned char *options, int opt_len);
171 static void	*bsd_decomp_alloc (unsigned char *options, int opt_len);
172 
173 static int	bsd_init        (void *db, unsigned char *options,
174 			         int opt_len, int unit, int debug, int decomp);
175 static int	bsd_comp_init   (void *state, unsigned char *options,
176 			         int opt_len, int unit, int opthdr, int debug);
177 static int	bsd_decomp_init (void *state, unsigned char *options,
178 				 int opt_len, int unit, int opthdr, int mru,
179 				 int debug);
180 
181 static void	bsd_reset (void *state);
182 static void	bsd_comp_stats (void *state, struct compstat *stats);
183 
184 static int	bsd_compress (void *state, unsigned char *rptr,
185 			      unsigned char *obuf, int isize, int osize);
186 static void	bsd_incomp (void *state, unsigned char *ibuf, int icnt);
187 
188 static int	bsd_decompress (void *state, unsigned char *ibuf, int isize,
189 				unsigned char *obuf, int osize);
190 
191 /* These are in ppp_generic.c */
192 extern int  ppp_register_compressor   (struct compressor *cp);
193 extern void ppp_unregister_compressor (struct compressor *cp);
194 
195 /*
196  * the next two codes should not be changed lightly, as they must not
197  * lie within the contiguous general code space.
198  */
199 #define CLEAR	256			/* table clear output code */
200 #define FIRST	257			/* first free entry */
201 #define LAST	255
202 
203 #define MAXCODE(b)	((1 << (b)) - 1)
204 #define BADCODEM1	MAXCODE(MAX_BSD_BITS)
205 
206 #define BSD_HASH(prefix,suffix,hshift) ((((unsigned long)(suffix))<<(hshift)) \
207 					 ^ (unsigned long)(prefix))
208 #define BSD_KEY(prefix,suffix)		((((unsigned long)(suffix)) << 16) \
209 					 + (unsigned long)(prefix))
210 
211 #define CHECK_GAP	10000		/* Ratio check interval */
212 
213 #define RATIO_SCALE_LOG	8
214 #define RATIO_SCALE	(1<<RATIO_SCALE_LOG)
215 #define RATIO_MAX	(0x7fffffff>>RATIO_SCALE_LOG)
216 
217 /*
218  * clear the dictionary
219  */
220 
221 static void
bsd_clear(struct bsd_db * db)222 bsd_clear(struct bsd_db *db)
223 {
224     db->clear_count++;
225     db->max_ent      = FIRST-1;
226     db->n_bits       = BSD_INIT_BITS;
227     db->bytes_out    = 0;
228     db->in_count     = 0;
229     db->ratio	     = 0;
230     db->checkpoint   = CHECK_GAP;
231 }
232 
233 /*
234  * If the dictionary is full, then see if it is time to reset it.
235  *
236  * Compute the compression ratio using fixed-point arithmetic
237  * with 8 fractional bits.
238  *
239  * Since we have an infinite stream instead of a single file,
240  * watch only the local compression ratio.
241  *
242  * Since both peers must reset the dictionary at the same time even in
243  * the absence of CLEAR codes (while packets are incompressible), they
244  * must compute the same ratio.
245  */
246 
bsd_check(struct bsd_db * db)247 static int bsd_check (struct bsd_db *db)	/* 1=output CLEAR */
248   {
249     unsigned int new_ratio;
250 
251     if (db->in_count >= db->checkpoint)
252       {
253 	/* age the ratio by limiting the size of the counts */
254 	if (db->in_count >= RATIO_MAX || db->bytes_out >= RATIO_MAX)
255 	  {
256 	    db->in_count  -= (db->in_count  >> 2);
257 	    db->bytes_out -= (db->bytes_out >> 2);
258 	  }
259 
260 	db->checkpoint = db->in_count + CHECK_GAP;
261 
262 	if (db->max_ent >= db->maxmaxcode)
263 	  {
264 	    /* Reset the dictionary only if the ratio is worse,
265 	     * or if it looks as if it has been poisoned
266 	     * by incompressible data.
267 	     *
268 	     * This does not overflow, because
269 	     *	db->in_count <= RATIO_MAX.
270 	     */
271 
272 	    new_ratio = db->in_count << RATIO_SCALE_LOG;
273 	    if (db->bytes_out != 0)
274 	      {
275 		new_ratio /= db->bytes_out;
276 	      }
277 
278 	    if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE)
279 	      {
280 		bsd_clear (db);
281 		return 1;
282 	      }
283 	    db->ratio = new_ratio;
284 	  }
285       }
286     return 0;
287   }
288 
289 /*
290  * Return statistics.
291  */
292 
bsd_comp_stats(void * state,struct compstat * stats)293 static void bsd_comp_stats (void *state, struct compstat *stats)
294   {
295     struct bsd_db *db = (struct bsd_db *) state;
296 
297     stats->unc_bytes    = db->uncomp_bytes;
298     stats->unc_packets  = db->uncomp_count;
299     stats->comp_bytes   = db->comp_bytes;
300     stats->comp_packets = db->comp_count;
301     stats->inc_bytes    = db->incomp_bytes;
302     stats->inc_packets  = db->incomp_count;
303     stats->in_count     = db->in_count;
304     stats->bytes_out    = db->bytes_out;
305   }
306 
307 /*
308  * Reset state, as on a CCP ResetReq.
309  */
310 
bsd_reset(void * state)311 static void bsd_reset (void *state)
312   {
313     struct bsd_db *db = (struct bsd_db *) state;
314 
315     bsd_clear(db);
316 
317     db->seqno       = 0;
318     db->clear_count = 0;
319   }
320 
321 /*
322  * Release the compression structure
323  */
324 
bsd_free(void * state)325 static void bsd_free (void *state)
326 {
327 	struct bsd_db *db = state;
328 
329 	if (!db)
330 		return;
331 
332 /*
333  * Release the dictionary
334  */
335 	vfree(db->dict);
336 	db->dict = NULL;
337 /*
338  * Release the string buffer
339  */
340 	vfree(db->lens);
341 	db->lens = NULL;
342 /*
343  * Finally release the structure itself.
344  */
345 	kfree(db);
346 }
347 
348 /*
349  * Allocate space for a (de) compressor.
350  */
351 
bsd_alloc(unsigned char * options,int opt_len,int decomp)352 static void *bsd_alloc (unsigned char *options, int opt_len, int decomp)
353   {
354     int bits;
355     unsigned int hsize, hshift, maxmaxcode;
356     struct bsd_db *db;
357 
358     if (opt_len != 3 || options[0] != CI_BSD_COMPRESS || options[1] != 3
359 	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
360       {
361 	return NULL;
362       }
363 
364     bits = BSD_NBITS(options[2]);
365 
366     switch (bits)
367       {
368     case 9:			/* needs 82152 for both directions */
369     case 10:			/* needs 84144 */
370     case 11:			/* needs 88240 */
371     case 12:			/* needs 96432 */
372 	hsize = 5003;
373 	hshift = 4;
374 	break;
375     case 13:			/* needs 176784 */
376 	hsize = 9001;
377 	hshift = 5;
378 	break;
379     case 14:			/* needs 353744 */
380 	hsize = 18013;
381 	hshift = 6;
382 	break;
383     case 15:			/* needs 691440 */
384 	hsize = 35023;
385 	hshift = 7;
386 	break;
387     case 16:			/* needs 1366160--far too much, */
388 	/* hsize = 69001; */	/* and 69001 is too big for cptr */
389 	/* hshift = 8; */	/* in struct bsd_db */
390 	/* break; */
391     default:
392 	return NULL;
393       }
394 /*
395  * Allocate the main control structure for this instance.
396  */
397     maxmaxcode = MAXCODE(bits);
398     db         = kzalloc(sizeof (struct bsd_db),
399 					    GFP_KERNEL);
400     if (!db)
401       {
402 	return NULL;
403       }
404 
405 /*
406  * Allocate space for the dictionary. This may be more than one page in
407  * length.
408  */
409     db->dict = vmalloc(array_size(hsize, sizeof(struct bsd_dict)));
410     if (!db->dict)
411       {
412 	bsd_free (db);
413 	return NULL;
414       }
415 
416 /*
417  * If this is the compression buffer then there is no length data.
418  */
419     if (!decomp)
420       {
421 	db->lens = NULL;
422       }
423 /*
424  * For decompression, the length information is needed as well.
425  */
426     else
427       {
428         db->lens = vmalloc(array_size(sizeof(db->lens[0]), (maxmaxcode + 1)));
429 	if (!db->lens)
430 	  {
431 	    bsd_free (db);
432 	    return NULL;
433 	  }
434       }
435 /*
436  * Initialize the data information for the compression code
437  */
438     db->totlen     = sizeof (struct bsd_db)   +
439 		    (sizeof (struct bsd_dict) * hsize);
440 
441     db->hsize      = hsize;
442     db->hshift     = hshift;
443     db->maxmaxcode = maxmaxcode;
444     db->maxbits    = bits;
445 
446     return (void *) db;
447   }
448 
bsd_comp_alloc(unsigned char * options,int opt_len)449 static void *bsd_comp_alloc (unsigned char *options, int opt_len)
450   {
451     return bsd_alloc (options, opt_len, 0);
452   }
453 
bsd_decomp_alloc(unsigned char * options,int opt_len)454 static void *bsd_decomp_alloc (unsigned char *options, int opt_len)
455   {
456     return bsd_alloc (options, opt_len, 1);
457   }
458 
459 /*
460  * Initialize the database.
461  */
462 
bsd_init(void * state,unsigned char * options,int opt_len,int unit,int debug,int decomp)463 static int bsd_init (void *state, unsigned char *options,
464 		     int opt_len, int unit, int debug, int decomp)
465   {
466     struct bsd_db *db = state;
467     int indx;
468 
469     if ((opt_len != 3) || (options[0] != CI_BSD_COMPRESS) || (options[1] != 3)
470 	|| (BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
471 	|| (BSD_NBITS(options[2]) != db->maxbits)
472 	|| (decomp && db->lens == NULL))
473       {
474 	return 0;
475       }
476 
477     if (decomp)
478       {
479 	indx = LAST;
480 	do
481 	  {
482 	    db->lens[indx] = 1;
483 	  }
484 	while (indx-- > 0);
485       }
486 
487     indx = db->hsize;
488     while (indx-- != 0)
489       {
490 	db->dict[indx].codem1 = BADCODEM1;
491 	db->dict[indx].cptr   = 0;
492       }
493 
494     db->unit = unit;
495     db->mru  = 0;
496 #ifndef DEBUG
497     if (debug)
498 #endif
499       db->debug = 1;
500 
501     bsd_reset(db);
502 
503     return 1;
504   }
505 
bsd_comp_init(void * state,unsigned char * options,int opt_len,int unit,int opthdr,int debug)506 static int bsd_comp_init (void *state, unsigned char *options,
507 			  int opt_len, int unit, int opthdr, int debug)
508   {
509     return bsd_init (state, options, opt_len, unit, debug, 0);
510   }
511 
bsd_decomp_init(void * state,unsigned char * options,int opt_len,int unit,int opthdr,int mru,int debug)512 static int bsd_decomp_init (void *state, unsigned char *options,
513 			    int opt_len, int unit, int opthdr, int mru,
514 			    int debug)
515   {
516     return bsd_init (state, options, opt_len, unit, debug, 1);
517   }
518 
519 /*
520  * Obtain pointers to the various structures in the compression tables
521  */
522 
523 #define dict_ptrx(p,idx) &(p->dict[idx])
524 #define lens_ptrx(p,idx) &(p->lens[idx])
525 
526 #ifdef DEBUG
lens_ptr(struct bsd_db * db,int idx)527 static unsigned short *lens_ptr(struct bsd_db *db, int idx)
528   {
529     if ((unsigned int) idx > (unsigned int) db->maxmaxcode)
530       {
531 	printk ("<9>ppp: lens_ptr(%d) > max\n", idx);
532 	idx = 0;
533       }
534     return lens_ptrx (db, idx);
535   }
536 
dict_ptr(struct bsd_db * db,int idx)537 static struct bsd_dict *dict_ptr(struct bsd_db *db, int idx)
538   {
539     if ((unsigned int) idx >= (unsigned int) db->hsize)
540       {
541 	printk ("<9>ppp: dict_ptr(%d) > max\n", idx);
542 	idx = 0;
543       }
544     return dict_ptrx (db, idx);
545   }
546 
547 #else
548 #define lens_ptr(db,idx) lens_ptrx(db,idx)
549 #define dict_ptr(db,idx) dict_ptrx(db,idx)
550 #endif
551 
552 /*
553  * compress a packet
554  *
555  *	The result of this function is the size of the compressed
556  *	packet. A zero is returned if the packet was not compressed
557  *	for some reason, such as the size being larger than uncompressed.
558  *
559  *	One change from the BSD compress command is that when the
560  *	code size expands, we do not output a bunch of padding.
561  */
562 
bsd_compress(void * state,unsigned char * rptr,unsigned char * obuf,int isize,int osize)563 static int bsd_compress (void *state, unsigned char *rptr, unsigned char *obuf,
564 			 int isize, int osize)
565   {
566     struct bsd_db *db;
567     int hshift;
568     unsigned int max_ent;
569     unsigned int n_bits;
570     unsigned int bitno;
571     unsigned long accm;
572     int ent;
573     unsigned long fcode;
574     struct bsd_dict *dictp;
575     unsigned char c;
576     int hval;
577     int disp;
578     int ilen;
579     int mxcode;
580     unsigned char *wptr;
581     int olen;
582 
583 #define PUTBYTE(v)			\
584   {					\
585     ++olen;				\
586     if (wptr)				\
587       {					\
588 	*wptr++ = (unsigned char) (v);	\
589 	if (olen >= osize)		\
590 	  {				\
591 	    wptr = NULL;		\
592 	  }				\
593       }					\
594   }
595 
596 #define OUTPUT(ent)			\
597   {					\
598     bitno -= n_bits;			\
599     accm |= ((ent) << bitno);		\
600     do					\
601       {					\
602 	PUTBYTE(accm >> 24);		\
603 	accm <<= 8;			\
604 	bitno += 8;			\
605       }					\
606     while (bitno <= 24);		\
607   }
608 
609   /*
610    * If the protocol is not in the range we're interested in,
611    * just return without compressing the packet.  If it is,
612    * the protocol becomes the first byte to compress.
613    */
614 
615     ent = PPP_PROTOCOL(rptr);
616     if (ent < 0x21 || ent > 0xf9)
617       {
618 	return 0;
619       }
620 
621     db      = (struct bsd_db *) state;
622     hshift  = db->hshift;
623     max_ent = db->max_ent;
624     n_bits  = db->n_bits;
625     bitno   = 32;
626     accm    = 0;
627     mxcode  = MAXCODE (n_bits);
628 
629     /* Initialize the output pointers */
630     wptr  = obuf;
631     olen  = PPP_HDRLEN + BSD_OVHD;
632 
633     if (osize > isize)
634       {
635 	osize = isize;
636       }
637 
638     /* This is the PPP header information */
639     if (wptr)
640       {
641 	*wptr++ = PPP_ADDRESS(rptr);
642 	*wptr++ = PPP_CONTROL(rptr);
643 	*wptr++ = 0;
644 	*wptr++ = PPP_COMP;
645 	*wptr++ = db->seqno >> 8;
646 	*wptr++ = db->seqno;
647       }
648 
649     /* Skip the input header */
650     rptr  += PPP_HDRLEN;
651     isize -= PPP_HDRLEN;
652     ilen   = ++isize;	/* Low byte of protocol is counted as input */
653 
654     while (--ilen > 0)
655       {
656 	c     = *rptr++;
657 	fcode = BSD_KEY  (ent, c);
658 	hval  = BSD_HASH (ent, c, hshift);
659 	dictp = dict_ptr (db, hval);
660 
661 	/* Validate and then check the entry. */
662 	if (dictp->codem1 >= max_ent)
663 	  {
664 	    goto nomatch;
665 	  }
666 
667 	if (dictp->f.fcode == fcode)
668 	  {
669 	    ent = dictp->codem1 + 1;
670 	    continue;	/* found (prefix,suffix) */
671 	  }
672 
673 	/* continue probing until a match or invalid entry */
674 	disp = (hval == 0) ? 1 : hval;
675 
676 	do
677 	  {
678 	    hval += disp;
679 	    if (hval >= db->hsize)
680 	      {
681 		hval -= db->hsize;
682 	      }
683 	    dictp = dict_ptr (db, hval);
684 	    if (dictp->codem1 >= max_ent)
685 	      {
686 		goto nomatch;
687 	      }
688 	  }
689 	while (dictp->f.fcode != fcode);
690 
691 	ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
692 	continue;
693 
694 nomatch:
695 	OUTPUT(ent);		/* output the prefix */
696 
697 	/* code -> hashtable */
698 	if (max_ent < db->maxmaxcode)
699 	  {
700 	    struct bsd_dict *dictp2;
701 	    struct bsd_dict *dictp3;
702 	    int    indx;
703 
704 	    /* expand code size if needed */
705 	    if (max_ent >= mxcode)
706 	      {
707 		db->n_bits = ++n_bits;
708 		mxcode     = MAXCODE (n_bits);
709 	      }
710 
711 	    /* Invalidate old hash table entry using
712 	     * this code, and then take it over.
713 	     */
714 
715 	    dictp2 = dict_ptr (db, max_ent + 1);
716 	    indx   = dictp2->cptr;
717 	    dictp3 = dict_ptr (db, indx);
718 
719 	    if (dictp3->codem1 == max_ent)
720 	      {
721 		dictp3->codem1 = BADCODEM1;
722 	      }
723 
724 	    dictp2->cptr   = hval;
725 	    dictp->codem1  = max_ent;
726 	    dictp->f.fcode = fcode;
727 	    db->max_ent    = ++max_ent;
728 
729 	    if (db->lens)
730 	      {
731 		unsigned short *len1 = lens_ptr (db, max_ent);
732 		unsigned short *len2 = lens_ptr (db, ent);
733 		*len1 = *len2 + 1;
734 	      }
735 	  }
736 	ent = c;
737       }
738 
739     OUTPUT(ent);		/* output the last code */
740 
741     db->bytes_out    += olen - PPP_HDRLEN - BSD_OVHD;
742     db->uncomp_bytes += isize;
743     db->in_count     += isize;
744     ++db->uncomp_count;
745     ++db->seqno;
746 
747     if (bitno < 32)
748       {
749 	++db->bytes_out; /* must be set before calling bsd_check */
750       }
751 
752     /*
753      * Generate the clear command if needed
754      */
755 
756     if (bsd_check(db))
757       {
758 	OUTPUT (CLEAR);
759       }
760 
761     /*
762      * Pad dribble bits of last code with ones.
763      * Do not emit a completely useless byte of ones.
764      */
765 
766     if (bitno != 32)
767       {
768 	PUTBYTE((accm | (0xff << (bitno-8))) >> 24);
769       }
770 
771     /*
772      * Increase code size if we would have without the packet
773      * boundary because the decompressor will do so.
774      */
775 
776     if (max_ent >= mxcode && max_ent < db->maxmaxcode)
777       {
778 	db->n_bits++;
779       }
780 
781     /* If output length is too large then this is an incomplete frame. */
782     if (wptr == NULL)
783       {
784 	++db->incomp_count;
785 	db->incomp_bytes += isize;
786 	olen              = 0;
787       }
788     else /* Count the number of compressed frames */
789       {
790 	++db->comp_count;
791 	db->comp_bytes += olen;
792       }
793 
794     /* Return the resulting output length */
795     return olen;
796 #undef OUTPUT
797 #undef PUTBYTE
798   }
799 
800 /*
801  * Update the "BSD Compress" dictionary on the receiver for
802  * incompressible data by pretending to compress the incoming data.
803  */
804 
bsd_incomp(void * state,unsigned char * ibuf,int icnt)805 static void bsd_incomp (void *state, unsigned char *ibuf, int icnt)
806   {
807     (void) bsd_compress (state, ibuf, (char *) 0, icnt, 0);
808   }
809 
810 /*
811  * Decompress "BSD Compress".
812  *
813  * Because of patent problems, we return DECOMP_ERROR for errors
814  * found by inspecting the input data and for system problems, but
815  * DECOMP_FATALERROR for any errors which could possibly be said to
816  * be being detected "after" decompression.  For DECOMP_ERROR,
817  * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
818  * infringing a patent of Motorola's if we do, so we take CCP down
819  * instead.
820  *
821  * Given that the frame has the correct sequence number and a good FCS,
822  * errors such as invalid codes in the input most likely indicate a
823  * bug, so we return DECOMP_FATALERROR for them in order to turn off
824  * compression, even though they are detected by inspecting the input.
825  */
826 
bsd_decompress(void * state,unsigned char * ibuf,int isize,unsigned char * obuf,int osize)827 static int bsd_decompress (void *state, unsigned char *ibuf, int isize,
828 			   unsigned char *obuf, int osize)
829   {
830     struct bsd_db *db;
831     unsigned int max_ent;
832     unsigned long accm;
833     unsigned int bitno;		/* 1st valid bit in accm */
834     unsigned int n_bits;
835     unsigned int tgtbitno;	/* bitno when we have a code */
836     struct bsd_dict *dictp;
837     int explen;
838     int seq;
839     unsigned int incode;
840     unsigned int oldcode;
841     unsigned int finchar;
842     unsigned char *p;
843     unsigned char *wptr;
844     int adrs;
845     int ctrl;
846     int ilen;
847     int codelen;
848     int extra;
849 
850     db       = (struct bsd_db *) state;
851     max_ent  = db->max_ent;
852     accm     = 0;
853     bitno    = 32;		/* 1st valid bit in accm */
854     n_bits   = db->n_bits;
855     tgtbitno = 32 - n_bits;	/* bitno when we have a code */
856 
857     /*
858      * Save the address/control from the PPP header
859      * and then get the sequence number.
860      */
861 
862     adrs  = PPP_ADDRESS (ibuf);
863     ctrl  = PPP_CONTROL (ibuf);
864 
865     seq   = (ibuf[4] << 8) + ibuf[5];
866 
867     ibuf += (PPP_HDRLEN + 2);
868     ilen  = isize - (PPP_HDRLEN + 2);
869 
870     /*
871      * Check the sequence number and give up if it differs from
872      * the value we're expecting.
873      */
874 
875     if (seq != db->seqno)
876       {
877 	if (db->debug)
878 	  {
879 	    printk("bsd_decomp%d: bad sequence # %d, expected %d\n",
880 		   db->unit, seq, db->seqno - 1);
881 	  }
882 	return DECOMP_ERROR;
883       }
884 
885     ++db->seqno;
886     db->bytes_out += ilen;
887 
888     /*
889      * Fill in the ppp header, but not the last byte of the protocol
890      * (that comes from the decompressed data).
891      */
892 
893     wptr    = obuf;
894     *wptr++ = adrs;
895     *wptr++ = ctrl;
896     *wptr++ = 0;
897 
898     oldcode = CLEAR;
899     explen  = 3;
900 
901     /*
902      * Keep the checkpoint correctly so that incompressible packets
903      * clear the dictionary at the proper times.
904      */
905 
906     for (;;)
907       {
908 	if (ilen-- <= 0)
909 	  {
910 	    db->in_count += (explen - 3); /* don't count the header */
911 	    break;
912 	  }
913 
914 	/*
915 	 * Accumulate bytes until we have a complete code.
916 	 * Then get the next code, relying on the 32-bit,
917 	 * unsigned accm to mask the result.
918 	 */
919 
920 	bitno -= 8;
921 	accm  |= *ibuf++ << bitno;
922 	if (tgtbitno < bitno)
923 	  {
924 	    continue;
925 	  }
926 
927 	incode = accm >> tgtbitno;
928 	accm <<= n_bits;
929 	bitno += n_bits;
930 
931 	/*
932 	 * The dictionary must only be cleared at the end of a packet.
933 	 */
934 
935 	if (incode == CLEAR)
936 	  {
937 	    if (ilen > 0)
938 	      {
939 		if (db->debug)
940 		  {
941 		    printk("bsd_decomp%d: bad CLEAR\n", db->unit);
942 		  }
943 		return DECOMP_FATALERROR;	/* probably a bug */
944 	      }
945 
946 	    bsd_clear(db);
947 	    break;
948 	  }
949 
950 	if ((incode > max_ent + 2) || (incode > db->maxmaxcode)
951 	    || (incode > max_ent && oldcode == CLEAR))
952 	  {
953 	    if (db->debug)
954 	      {
955 		printk("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
956 		       db->unit, incode, oldcode);
957 		printk("max_ent=0x%x explen=%d seqno=%d\n",
958 		       max_ent, explen, db->seqno);
959 	      }
960 	    return DECOMP_FATALERROR;	/* probably a bug */
961 	  }
962 
963 	/* Special case for KwKwK string. */
964 	if (incode > max_ent)
965 	  {
966 	    finchar = oldcode;
967 	    extra   = 1;
968 	  }
969 	else
970 	  {
971 	    finchar = incode;
972 	    extra   = 0;
973 	  }
974 
975 	codelen = *(lens_ptr (db, finchar));
976 	explen += codelen + extra;
977 	if (explen > osize)
978 	  {
979 	    if (db->debug)
980 	      {
981 		printk("bsd_decomp%d: ran out of mru\n", db->unit);
982 #ifdef DEBUG
983 		printk("  len=%d, finchar=0x%x, codelen=%d, explen=%d\n",
984 		       ilen, finchar, codelen, explen);
985 #endif
986 	      }
987 	    return DECOMP_FATALERROR;
988 	  }
989 
990 	/*
991 	 * Decode this code and install it in the decompressed buffer.
992 	 */
993 
994 	wptr += codelen;
995 	p     = wptr;
996 	while (finchar > LAST)
997 	  {
998 	    struct bsd_dict *dictp2 = dict_ptr (db, finchar);
999 
1000 	    dictp = dict_ptr (db, dictp2->cptr);
1001 #ifdef DEBUG
1002 	    if (--codelen <= 0 || dictp->codem1 != finchar-1)
1003 	      {
1004 		if (codelen <= 0)
1005 		  {
1006 		    printk("bsd_decomp%d: fell off end of chain ", db->unit);
1007 		    printk("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
1008 			   incode, finchar, dictp2->cptr, max_ent);
1009 		  }
1010 		else
1011 		  {
1012 		    if (dictp->codem1 != finchar-1)
1013 		      {
1014 			printk("bsd_decomp%d: bad code chain 0x%x "
1015 			       "finchar=0x%x ",
1016 			       db->unit, incode, finchar);
1017 
1018 			printk("oldcode=0x%x cptr=0x%x codem1=0x%x\n",
1019 			       oldcode, dictp2->cptr, dictp->codem1);
1020 		      }
1021 		  }
1022 		return DECOMP_FATALERROR;
1023 	      }
1024 #endif
1025 	    *--p    = dictp->f.hs.suffix;
1026 	    finchar = dictp->f.hs.prefix;
1027 	  }
1028 	*--p = finchar;
1029 
1030 #ifdef DEBUG
1031 	if (--codelen != 0)
1032 	  {
1033 	    printk("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
1034 		   db->unit, codelen, incode, max_ent);
1035 	  }
1036 #endif
1037 
1038 	if (extra)		/* the KwKwK case again */
1039 	  {
1040 	    *wptr++ = finchar;
1041 	  }
1042 
1043 	/*
1044 	 * If not first code in a packet, and
1045 	 * if not out of code space, then allocate a new code.
1046 	 *
1047 	 * Keep the hash table correct so it can be used
1048 	 * with uncompressed packets.
1049 	 */
1050 
1051 	if (oldcode != CLEAR && max_ent < db->maxmaxcode)
1052 	  {
1053 	    struct bsd_dict *dictp2, *dictp3;
1054 	    unsigned short  *lens1,  *lens2;
1055 	    unsigned long fcode;
1056 	    int hval, disp, indx;
1057 
1058 	    fcode = BSD_KEY(oldcode,finchar);
1059 	    hval  = BSD_HASH(oldcode,finchar,db->hshift);
1060 	    dictp = dict_ptr (db, hval);
1061 
1062 	    /* look for a free hash table entry */
1063 	    if (dictp->codem1 < max_ent)
1064 	      {
1065 		disp = (hval == 0) ? 1 : hval;
1066 		do
1067 		  {
1068 		    hval += disp;
1069 		    if (hval >= db->hsize)
1070 		      {
1071 			hval -= db->hsize;
1072 		      }
1073 		    dictp = dict_ptr (db, hval);
1074 		  }
1075 		while (dictp->codem1 < max_ent);
1076 	      }
1077 
1078 	    /*
1079 	     * Invalidate previous hash table entry
1080 	     * assigned this code, and then take it over
1081 	     */
1082 
1083 	    dictp2 = dict_ptr (db, max_ent + 1);
1084 	    indx   = dictp2->cptr;
1085 	    dictp3 = dict_ptr (db, indx);
1086 
1087 	    if (dictp3->codem1 == max_ent)
1088 	      {
1089 		dictp3->codem1 = BADCODEM1;
1090 	      }
1091 
1092 	    dictp2->cptr   = hval;
1093 	    dictp->codem1  = max_ent;
1094 	    dictp->f.fcode = fcode;
1095 	    db->max_ent    = ++max_ent;
1096 
1097 	    /* Update the length of this string. */
1098 	    lens1  = lens_ptr (db, max_ent);
1099 	    lens2  = lens_ptr (db, oldcode);
1100 	    *lens1 = *lens2 + 1;
1101 
1102 	    /* Expand code size if needed. */
1103 	    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
1104 	      {
1105 		db->n_bits = ++n_bits;
1106 		tgtbitno   = 32-n_bits;
1107 	      }
1108 	  }
1109 	oldcode = incode;
1110       }
1111 
1112     ++db->comp_count;
1113     ++db->uncomp_count;
1114     db->comp_bytes   += isize - BSD_OVHD - PPP_HDRLEN;
1115     db->uncomp_bytes += explen;
1116 
1117     if (bsd_check(db))
1118       {
1119 	if (db->debug)
1120 	  {
1121 	    printk("bsd_decomp%d: peer should have cleared dictionary on %d\n",
1122 		   db->unit, db->seqno - 1);
1123 	  }
1124       }
1125     return explen;
1126   }
1127 
1128 /*************************************************************
1129  * Table of addresses for the BSD compression module
1130  *************************************************************/
1131 
1132 static struct compressor ppp_bsd_compress = {
1133 	.compress_proto =	CI_BSD_COMPRESS,
1134 	.comp_alloc =		bsd_comp_alloc,
1135 	.comp_free =		bsd_free,
1136 	.comp_init =		bsd_comp_init,
1137 	.comp_reset =		bsd_reset,
1138 	.compress =		bsd_compress,
1139 	.comp_stat =		bsd_comp_stats,
1140 	.decomp_alloc =		bsd_decomp_alloc,
1141 	.decomp_free =		bsd_free,
1142 	.decomp_init =		bsd_decomp_init,
1143 	.decomp_reset =		bsd_reset,
1144 	.decompress =		bsd_decompress,
1145 	.incomp =		bsd_incomp,
1146 	.decomp_stat =		bsd_comp_stats,
1147 	.owner =		THIS_MODULE
1148 };
1149 
1150 /*************************************************************
1151  * Module support routines
1152  *************************************************************/
1153 
bsdcomp_init(void)1154 static int __init bsdcomp_init(void)
1155 {
1156 	int answer = ppp_register_compressor(&ppp_bsd_compress);
1157 	if (answer == 0)
1158 		printk(KERN_INFO "PPP BSD Compression module registered\n");
1159 	return answer;
1160 }
1161 
bsdcomp_cleanup(void)1162 static void __exit bsdcomp_cleanup(void)
1163 {
1164 	ppp_unregister_compressor(&ppp_bsd_compress);
1165 }
1166 
1167 module_init(bsdcomp_init);
1168 module_exit(bsdcomp_cleanup);
1169 MODULE_DESCRIPTION("PPP BSD-Compress compression module");
1170 MODULE_LICENSE("Dual BSD/GPL");
1171 MODULE_ALIAS("ppp-compress-" __stringify(CI_BSD_COMPRESS));
1172