aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/net/ppp_mppe.c
blob: f3655fd772f5b765c7f0e33fb693480a255135ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
/*
 * ppp_mppe.c - interface MPPE to the PPP code.
 * This version is for use with Linux kernel 2.6.14+
 *
 * By Frank Cusack <fcusack@fcusack.com>.
 * Copyright (c) 2002,2003,2004 Google, Inc.
 * All rights reserved.
 *
 * License:
 * Permission to use, copy, modify, and distribute this software and its
 * documentation is hereby granted, provided that the above copyright
 * notice appears in all copies.  This software is provided without any
 * warranty, express or implied.
 *
 * ALTERNATIVELY, provided that this notice is retained in full, this product
 * may be distributed under the terms of the GNU General Public License (GPL),
 * in which case the provisions of the GPL apply INSTEAD OF those given above.
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *
 * Changelog:
 *      08/12/05 - Matt Domsch <Matt_Domsch@dell.com>
 *                 Only need extra skb padding on transmit, not receive.
 *      06/18/04 - Matt Domsch <Matt_Domsch@dell.com>, Oleg Makarenko <mole@quadra.ru>
 *                 Use Linux kernel 2.6 arc4 and sha1 routines rather than
 *                 providing our own.
 *      2/15/04 - TS: added #include <version.h> and testing for Kernel
 *                    version before using
 *                    MOD_DEC_USAGE_COUNT/MOD_INC_USAGE_COUNT which are
 *                    deprecated in 2.6
 */

#include <linux/err.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/version.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/mm.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-comp.h>
#include <asm/scatterlist.h>

#include "ppp_mppe.h"

MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
MODULE_DESCRIPTION("Point-to-Point Protocol Microsoft Point-to-Point Encryption support");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("ppp-compress-" __stringify(CI_MPPE));
MODULE_VERSION("1.0.2");

static unsigned int
setup_sg(struct scatterlist *sg, const void *address, unsigned int length)
{
	sg[0].page = virt_to_page(address);
	sg[0].offset = offset_in_page(address);
	sg[0].length = length;
	return length;
}

#define SHA1_PAD_SIZE 40

/*
 * kernel crypto API needs its arguments to be in kmalloc'd memory, not in the module
 * static data area.  That means sha_pad needs to be kmalloc'd.
 */

struct sha_pad {
	unsigned char sha_pad1[SHA1_PAD_SIZE];
	unsigned char sha_pad2[SHA1_PAD_SIZE];
};
static struct sha_pad *sha_pad;

static inline void sha_pad_init(struct sha_pad *shapad)
{
	memset(shapad->sha_pad1, 0x00, sizeof(shapad->sha_pad1));
	memset(shapad->sha_pad2, 0xF2, sizeof(shapad->sha_pad2));
}

/*
 * State for an MPPE (de)compressor.
 */
struct ppp_mppe_state {
	struct crypto_blkcipher *arc4;
	struct crypto_hash *sha1;
	unsigned char *sha1_digest;
	unsigned char master_key[MPPE_MAX_KEY_LEN];
	unsigned char session_key[MPPE_MAX_KEY_LEN];
	unsigned keylen;	/* key length in bytes             */
	/* NB: 128-bit == 16, 40-bit == 8! */
	/* If we want to support 56-bit,   */
	/* the unit has to change to bits  */
	unsigned char bits;	/* MPPE control bits */
	unsigned ccount;	/* 12-bit coherency count (seqno)  */
	unsigned stateful;	/* stateful mode flag */
	int discard;		/* stateful mode packet loss flag */
	int sanity_errors;	/* take down LCP if too many */
	int unit;
	int debug;
	struct compstat stats;
};

/* struct ppp_mppe_state.bits definitions */
#define MPPE_BIT_A	0x80	/* Encryption table were (re)inititalized */
#define MPPE_BIT_B	0x40	/* MPPC only (not implemented) */
#define MPPE_BIT_C	0x20	/* MPPC only (not implemented) */
#define MPPE_BIT_D	0x10	/* This is an encrypted frame */

#define MPPE_BIT_FLUSHED	MPPE_BIT_A
#define MPPE_BIT_ENCRYPTED	MPPE_BIT_D

#define MPPE_BITS(p) ((p)[4] & 0xf0)
#define MPPE_CCOUNT(p) ((((p)[4] & 0x0f) << 8) + (p)[5])
#define MPPE_CCOUNT_SPACE 0x1000	/* The size of the ccount space */

#define MPPE_OVHD	2	/* MPPE overhead/packet */
#define SANITY_MAX	1600	/* Max bogon factor we will tolerate */

/*
 * Key Derivation, from RFC 3078, RFC 3079.
 * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
 */
static void get_new_key_from_sha(struct ppp_mppe_state * state, unsigned char *InterimKey)
{
	struct hash_desc desc;
	struct scatterlist sg[4];
	unsigned int nbytes;

	nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
	nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
			   sizeof(sha_pad->sha_pad1));
	nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
	nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
			   sizeof(sha_pad->sha_pad2));

	desc.tfm = state->sha1;
	desc.flags = 0;

	crypto_hash_digest(&desc, sg, nbytes, state->sha1_digest);

	memcpy(InterimKey, state->sha1_digest, state->keylen);
}

/*
 * Perform the MPPE rekey algorithm, from RFC 3078, sec. 7.3.
 * Well, not what's written there, but rather what they meant.
 */
static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
{
	unsigned char InterimKey[MPPE_MAX_KEY_LEN];
	struct scatterlist sg_in[1], sg_out[1];
	struct blkcipher_desc desc = { .tfm = state->arc4 };

	get_new_key_from_sha(state, InterimKey);
	if (!initial_key) {
		crypto_blkcipher_setkey(state->arc4, InterimKey, state->keylen);
		setup_sg(sg_in, InterimKey, state->keylen);
		setup_sg(sg_out, state->session_key, state->keylen);
		if (crypto_blkcipher_encrypt(&desc, sg_out, sg_in,
					     state->keylen) != 0) {
    		    printk(KERN_WARNING "mppe_rekey: cipher_encrypt failed\n");
		}
	} else {
		memcpy(state->session_key, InterimKey, state->keylen);
	}
	if (state->keylen == 8) {
		/* See RFC 3078 */
		state->session_key[0] = 0xd1;
		state->session_key[1] = 0x26;
		state->session_key[2] = 0x9e;
	}
	crypto_blkcipher_setkey(state->arc4, state->session_key, state->keylen);
}

/*
 * Allocate space for a (de)compressor.
 */
static void *mppe_alloc(unsigned char *options, int optlen)
{
	struct ppp_mppe_state *state;
	unsigned int digestsize;

	if (optlen != CILEN_MPPE + sizeof(state->master_key)
	    || options[0] != CI_MPPE || options[1] != CILEN_MPPE)
		goto out;

	state = (struct ppp_mppe_state *) kmalloc(sizeof(*state), GFP_KERNEL);
	if (state == NULL)
		goto out;

	memset(state, 0, sizeof(*state));

	state->arc4 = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(state->arc4)) {
		state->arc4 = NULL;
		goto out_free;
	}

	state->sha1 = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(state->sha1)) {
		state->sha1 = NULL;
		goto out_free;
	}

	digestsize = crypto_hash_digestsize(state->sha1);
	if (digestsize < MPPE_MAX_KEY_LEN)
		goto out_free;

	state->sha1_digest = kmalloc(digestsize, GFP_KERNEL);
	if (!state->sha1_digest)
		goto out_free;

	/* Save keys. */
	memcpy(state->master_key, &options[CILEN_MPPE],
	       sizeof(state->master_key));
	memcpy(state->session_key, state->master_key,
	       sizeof(state->master_key));

	/*
	 * We defer initial key generation until mppe_init(), as mppe_alloc()
	 * is called frequently during negotiation.
	 */

	return (void *)state;

	out_free:
	    if (state->sha1_digest)
		kfree(state->sha1_digest);
	    if (state->sha1)
		crypto_free_hash(state->sha1);
	    if (state->arc4)
		crypto_free_blkcipher(state->arc4);
	    kfree(state);
	out:
	return NULL;
}

/*
 * Deallocate space for a (de)compressor.
 */
static void mppe_free(void *arg)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
	if (state) {
	    if (state->sha1_digest)
		kfree(state->sha1_digest);
	    if (state->sha1)
		crypto_free_hash(state->sha1);
	    if (state->arc4)
		crypto_free_blkcipher(state->arc4);
	    kfree(state);
	}
}

/*
 * Initialize (de)compressor state.
 */
static int
mppe_init(void *arg, unsigned char *options, int optlen, int unit, int debug,
	  const char *debugstr)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
	unsigned char mppe_opts;

	if (optlen != CILEN_MPPE
	    || options[0] != CI_MPPE || options[1] != CILEN_MPPE)
		return 0;

	MPPE_CI_TO_OPTS(&options[2], mppe_opts);
	if (mppe_opts & MPPE_OPT_128)
		state->keylen = 16;
	else if (mppe_opts & MPPE_OPT_40)
		state->keylen = 8;
	else {
		printk(KERN_WARNING "%s[%d]: unknown key length\n", debugstr,
		       unit);
		return 0;
	}
	if (mppe_opts & MPPE_OPT_STATEFUL)
		state->stateful = 1;

	/* Generate the initial session key. */
	mppe_rekey(state, 1);

	if (debug) {
		int i;
		char mkey[sizeof(state->master_key) * 2 + 1];
		char skey[sizeof(state->session_key) * 2 + 1];

		printk(KERN_DEBUG "%s[%d]: initialized with %d-bit %s mode\n",
		       debugstr, unit, (state->keylen == 16) ? 128 : 40,
		       (state->stateful) ? "stateful" : "stateless");

		for (i = 0; i < sizeof(state->master_key); i++)
			sprintf(mkey + i * 2, "%02x", state->master_key[i]);
		for (i = 0; i < sizeof(state->session_key); i++)
			sprintf(skey + i * 2, "%02x", state->session_key[i]);
		printk(KERN_DEBUG
		       "%s[%d]: keys: master: %s initial session: %s\n",
		       debugstr, unit, mkey, skey);
	}

	/*
	 * Initialize the coherency count.  The initial value is not specified
	 * in RFC 3078, but we can make a reasonable assumption that it will
	 * start at 0.  Setting it to the max here makes the comp/decomp code
	 * do the right thing (determined through experiment).
	 */
	state->ccount = MPPE_CCOUNT_SPACE - 1;

	/*
	 * Note that even though we have initialized the key table, we don't
	 * set the FLUSHED bit.  This is contrary to RFC 3078, sec. 3.1.
	 */
	state->bits = MPPE_BIT_ENCRYPTED;

	state->unit = unit;
	state->debug = debug;

	return 1;
}

static int
mppe_comp_init(void *arg, unsigned char *options, int optlen, int unit,
	       int hdrlen, int debug)
{
	/* ARGSUSED */
	return mppe_init(arg, options, optlen, unit, debug, "mppe_comp_init");
}

/*
 * We received a CCP Reset-Request (actually, we are sending a Reset-Ack),
 * tell the compressor to rekey.  Note that we MUST NOT rekey for
 * every CCP Reset-Request; we only rekey on the next xmit packet.
 * We might get multiple CCP Reset-Requests if our CCP Reset-Ack is lost.
 * So, rekeying for every CCP Reset-Request is broken as the peer will not
 * know how many times we've rekeyed.  (If we rekey and THEN get another
 * CCP Reset-Request, we must rekey again.)
 */
static void mppe_comp_reset(void *arg)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;

	state->bits |= MPPE_BIT_FLUSHED;
}

/*
 * Compress (encrypt) a packet.
 * It's strange to call this a compressor, since the output is always
 * MPPE_OVHD + 2 bytes larger than the input.
 */
static int
mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
	      int isize, int osize)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
	struct blkcipher_desc desc = { .tfm = state->arc4 };
	int proto;
	struct scatterlist sg_in[1], sg_out[1];

	/*
	 * Check that the protocol is in the range we handle.
	 */
	proto = PPP_PROTOCOL(ibuf);
	if (proto < 0x0021 || proto > 0x00fa)
		return 0;

	/* Make sure we have enough room to generate an encrypted packet. */
	if (osize < isize + MPPE_OVHD + 2) {
		/* Drop the packet if we should encrypt it, but can't. */
		printk(KERN_DEBUG "mppe_compress[%d]: osize too small! "
		       "(have: %d need: %d)\n", state->unit,
		       osize, osize + MPPE_OVHD + 2);
		return -1;
	}

	osize = isize + MPPE_OVHD + 2;

	/*
	 * Copy over the PPP header and set control bits.
	 */
	obuf[0] = PPP_ADDRESS(ibuf);
	obuf[1] = PPP_CONTROL(ibuf);
	obuf[2] = PPP_COMP >> 8;	/* isize + MPPE_OVHD + 1 */
	obuf[3] = PPP_COMP;	/* isize + MPPE_OVHD + 2 */
	obuf += PPP_HDRLEN;

	state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
	if (state->debug >= 7)
		printk(KERN_DEBUG "mppe_compress[%d]: ccount %d\n", state->unit,
		       state->ccount);
	obuf[0] = state->ccount >> 8;
	obuf[1] = state->ccount & 0xff;

	if (!state->stateful ||	/* stateless mode     */
	    ((state->ccount & 0xff) == 0xff) ||	/* "flag" packet      */
	    (state->bits & MPPE_BIT_FLUSHED)) {	/* CCP Reset-Request  */
		/* We must rekey */
		if (state->debug && state->stateful)
			printk(KERN_DEBUG "mppe_compress[%d]: rekeying\n",
			       state->unit);
		mppe_rekey(state, 0);
		state->bits |= MPPE_BIT_FLUSHED;
	}
	obuf[0] |= state->bits;
	state->bits &= ~MPPE_BIT_FLUSHED;	/* reset for next xmit */

	obuf += MPPE_OVHD;
	ibuf += 2;		/* skip to proto field */
	isize -= 2;

	/* Encrypt packet */
	setup_sg(sg_in, ibuf, isize);
	setup_sg(sg_out, obuf, osize);
	if (crypto_blkcipher_encrypt(&desc, sg_out, sg_in, isize) != 0) {
		printk(KERN_DEBUG "crypto_cypher_encrypt failed\n");
		return -1;
	}

	state->stats.unc_bytes += isize;
	state->stats.unc_packets++;
	state->stats.comp_bytes += osize;
	state->stats.comp_packets++;

	return osize;
}

/*
 * Since every frame grows by MPPE_OVHD + 2 bytes, this is always going
 * to look bad ... and the longer the link is up the worse it will get.
 */
static void mppe_comp_stats(void *arg, struct compstat *stats)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;

	*stats = state->stats;
}

static int
mppe_decomp_init(void *arg, unsigned char *options, int optlen, int unit,
		 int hdrlen, int mru, int debug)
{
	/* ARGSUSED */
	return mppe_init(arg, options, optlen, unit, debug, "mppe_decomp_init");
}

/*
 * We received a CCP Reset-Ack.  Just ignore it.
 */
static void mppe_decomp_reset(void *arg)
{
	/* ARGSUSED */
	return;
}

/*
 * Decompress (decrypt) an MPPE packet.
 */
static int
mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
		int osize)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
	struct blkcipher_desc desc = { .tfm = state->arc4 };
	unsigned ccount;
	int flushed = MPPE_BITS(ibuf) & MPPE_BIT_FLUSHED;
	int sanity = 0;
	struct scatterlist sg_in[1], sg_out[1];

	if (isize <= PPP_HDRLEN + MPPE_OVHD) {
		if (state->debug)
			printk(KERN_DEBUG
			       "mppe_decompress[%d]: short pkt (%d)\n",
			       state->unit, isize);
		return DECOMP_ERROR;
	}

	/*
	 * Make sure we have enough room to decrypt the packet.
	 * Note that for our test we only subtract 1 byte whereas in
	 * mppe_compress() we added 2 bytes (+MPPE_OVHD);
	 * this is to account for possible PFC.
	 */
	if (osize < isize - MPPE_OVHD - 1) {
		printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
		       "(have: %d need: %d)\n", state->unit,
		       osize, isize - MPPE_OVHD - 1);
		return DECOMP_ERROR;
	}
	osize = isize - MPPE_OVHD - 2;	/* assume no PFC */

	ccount = MPPE_CCOUNT(ibuf);
	if (state->debug >= 7)
		printk(KERN_DEBUG "mppe_decompress[%d]: ccount %d\n",
		       state->unit, ccount);

	/* sanity checks -- terminate with extreme prejudice */
	if (!(MPPE_BITS(ibuf) & MPPE_BIT_ENCRYPTED)) {
		printk(KERN_DEBUG
		       "mppe_decompress[%d]: ENCRYPTED bit not set!\n",
		       state->unit);
		state->sanity_errors += 100;
		sanity = 1;
	}
	if (!state->stateful && !flushed) {
		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set in "
		       "stateless mode!\n", state->unit);
		state->sanity_errors += 100;
		sanity = 1;
	}
	if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set on "
		       "flag packet!\n", state->unit);
		state->sanity_errors += 100;
		sanity = 1;
	}

	if (sanity) {
		if (state->sanity_errors < SANITY_MAX)
			return DECOMP_ERROR;
		else
			/*
			 * Take LCP down if the peer is sending too many bogons.
			 * We don't want to do this for a single or just a few
			 * instances since it could just be due to packet corruption.
			 */
			return DECOMP_FATALERROR;
	}

	/*
	 * Check the coherency count.
	 */

	if (!state->stateful) {
		/* RFC 3078, sec 8.1.  Rekey for every packet. */
		while (state->ccount != ccount) {
			mppe_rekey(state, 0);
			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
		}
	} else {
		/* RFC 3078, sec 8.2. */
		if (!state->discard) {
			/* normal state */
			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
			if (ccount != state->ccount) {
				/*
				 * (ccount > state->ccount)
				 * Packet loss detected, enter the discard state.
				 * Signal the peer to rekey (by sending a CCP Reset-Request).
				 */
				state->discard = 1;
				return DECOMP_ERROR;
			}
		} else {
			/* discard state */
			if (!flushed) {
				/* ccp.c will be silent (no additional CCP Reset-Requests). */
				return DECOMP_ERROR;
			} else {
				/* Rekey for every missed "flag" packet. */
				while ((ccount & ~0xff) !=
				       (state->ccount & ~0xff)) {
					mppe_rekey(state, 0);
					state->ccount =
					    (state->ccount +
					     256) % MPPE_CCOUNT_SPACE;
				}

				/* reset */
				state->discard = 0;
				state->ccount = ccount;
				/*
				 * Another problem with RFC 3078 here.  It implies that the
				 * peer need not send a Reset-Ack packet.  But RFC 1962
				 * requires it.  Hopefully, M$ does send a Reset-Ack; even
				 * though it isn't required for MPPE synchronization, it is
				 * required to reset CCP state.
				 */
			}
		}
		if (flushed)
			mppe_rekey(state, 0);
	}

	/*
	 * Fill in the first part of the PPP header.  The protocol field
	 * comes from the decrypted data.
	 */
	obuf[0] = PPP_ADDRESS(ibuf);	/* +1 */
	obuf[1] = PPP_CONTROL(ibuf);	/* +1 */
	obuf += 2;
	ibuf += PPP_HDRLEN + MPPE_OVHD;
	isize -= PPP_HDRLEN + MPPE_OVHD;	/* -6 */
	/* net osize: isize-4 */

	/*
	 * Decrypt the first byte in order to check if it is
	 * a compressed or uncompressed protocol field.
	 */
	setup_sg(sg_in, ibuf, 1);
	setup_sg(sg_out, obuf, 1);
	if (crypto_blkcipher_decrypt(&desc, sg_out, sg_in, 1) != 0) {
		printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
		return DECOMP_ERROR;
	}

	/*
	 * Do PFC decompression.
	 * This would be nicer if we were given the actual sk_buff
	 * instead of a char *.
	 */
	if ((obuf[0] & 0x01) != 0) {
		obuf[1] = obuf[0];
		obuf[0] = 0;
		obuf++;
		osize++;
	}

	/* And finally, decrypt the rest of the packet. */
	setup_sg(sg_in, ibuf + 1, isize - 1);
	setup_sg(sg_out, obuf + 1, osize - 1);
	if (crypto_blkcipher_decrypt(&desc, sg_out, sg_in, isize - 1)) {
		printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
		return DECOMP_ERROR;
	}

	state->stats.unc_bytes += osize;
	state->stats.unc_packets++;
	state->stats.comp_bytes += isize;
	state->stats.comp_packets++;

	/* good packet credit */
	state->sanity_errors >>= 1;

	return osize;
}

/*
 * Incompressible data has arrived (this should never happen!).
 * We should probably drop the link if the protocol is in the range
 * of what should be encrypted.  At the least, we should drop this
 * packet.  (How to do this?)
 */
static void mppe_incomp(void *arg, unsigned char *ibuf, int icnt)
{
	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;

	if (state->debug &&
	    (PPP_PROTOCOL(ibuf) >= 0x0021 && PPP_PROTOCOL(ibuf) <= 0x00fa))
		printk(KERN_DEBUG
		       "mppe_incomp[%d]: incompressible (unencrypted) data! "
		       "(proto %04x)\n", state->unit, PPP_PROTOCOL(ibuf));

	state->stats.inc_bytes += icnt;
	state->stats.inc_packets++;
	state->stats.unc_bytes += icnt;
	state->stats.unc_packets++;
}

/*************************************************************
 * Module interface table
 *************************************************************/

/*
 * Procedures exported to if_ppp.c.
 */
static struct compressor ppp_mppe = {
	.compress_proto = CI_MPPE,
	.comp_alloc     = mppe_alloc,
	.comp_free      = mppe_free,
	.comp_init      = mppe_comp_init,
	.comp_reset     = mppe_comp_reset,
	.compress       = mppe_compress,
	.comp_stat      = mppe_comp_stats,
	.decomp_alloc   = mppe_alloc,
	.decomp_free    = mppe_free,
	.decomp_init    = mppe_decomp_init,
	.decomp_reset   = mppe_decomp_reset,
	.decompress     = mppe_decompress,
	.incomp         = mppe_incomp,
	.decomp_stat    = mppe_comp_stats,
	.owner          = THIS_MODULE,
	.comp_extra     = MPPE_PAD,
};

/*
 * ppp_mppe_init()
 *
 * Prior to allowing load, try to load the arc4 and sha1 crypto
 * libraries.  The actual use will be allocated later, but
 * this way the module will fail to insmod if they aren't available.
 */

static int __init ppp_mppe_init(void)
{
	int answer;
	if (!(crypto_has_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC) &&
	      crypto_has_hash("sha1", 0, CRYPTO_ALG_ASYNC)))
		return -ENODEV;

	sha_pad = kmalloc(sizeof(struct sha_pad), GFP_KERNEL);
	if (!sha_pad)
		return -ENOMEM;
	sha_pad_init(sha_pad);

	answer = ppp_register_compressor(&ppp_mppe);

	if (answer == 0)
		printk(KERN_INFO "PPP MPPE Compression module registered\n");
	else
		kfree(sha_pad);

	return answer;
}

static void __exit ppp_mppe_cleanup(void)
{
	ppp_unregister_compressor(&ppp_mppe);
	kfree(sha_pad);
}

module_init(ppp_mppe_init);
module_exit(ppp_mppe_cleanup);