ppp_mppe.c

  1/*
  2 * ppp_mppe.c - interface MPPE to the PPP code.
  3 * This version is for use with Linux kernel 2.6.14+
  4 *
  5 * By Frank Cusack <fcusack@fcusack.com>.
  6 * Copyright (c) 2002,2003,2004 Google, Inc.
  7 * All rights reserved.
  8 *
  9 * License:
 10 * Permission to use, copy, modify, and distribute this software and its
 11 * documentation is hereby granted, provided that the above copyright
 12 * notice appears in all copies.  This software is provided without any
 13 * warranty, express or implied.
 14 *
 15 * ALTERNATIVELY, provided that this notice is retained in full, this product
 16 * may be distributed under the terms of the GNU General Public License (GPL),
 17 * in which case the provisions of the GPL apply INSTEAD OF those given above.
 18 *
 19 *   This program is free software; you can redistribute it and/or modify
 20 *   it under the terms of the GNU General Public License as published by
 21 *   the Free Software Foundation; either version 2 of the License, or
 22 *   (at your option) any later version.
 23 *
 24 *   This program is distributed in the hope that it will be useful,
 25 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 26 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 27 *   GNU General Public License for more details.
 28 *
 29 *   You should have received a copy of the GNU General Public License
 30 *   along with this program; if not, see <http://www.gnu.org/licenses/>.
 31 *
 32 *
 33 * Changelog:
 34 *      08/12/05 - Matt Domsch <Matt_Domsch@dell.com>
 35 *                 Only need extra skb padding on transmit, not receive.
 36 *      06/18/04 - Matt Domsch <Matt_Domsch@dell.com>, Oleg Makarenko <mole@quadra.ru>
 37 *                 Use Linux kernel 2.6 arc4 and sha1 routines rather than
 38 *                 providing our own.
 39 *      2/15/04 - TS: added #include <version.h> and testing for Kernel
 40 *                    version before using
 41 *                    MOD_DEC_USAGE_COUNT/MOD_INC_USAGE_COUNT which are
 42 *                    deprecated in 2.6
 43 */
 44
 45#include <crypto/arc4.h>
 46#include <crypto/sha1.h>
 47#include <linux/err.h>
 48#include <linux/fips.h>
 49#include <linux/module.h>
 50#include <linux/kernel.h>
 51#include <linux/init.h>
 52#include <linux/types.h>
 53#include <linux/slab.h>
 54#include <linux/string.h>
 55#include <linux/mm.h>
 56#include <linux/ppp_defs.h>
 57#include <linux/ppp-comp.h>
 58#include <linux/unaligned.h>
 59
 60#include "ppp_mppe.h"
 61
 62MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
 63MODULE_DESCRIPTION("Point-to-Point Protocol Microsoft Point-to-Point Encryption support");
 64MODULE_LICENSE("Dual BSD/GPL");
 65MODULE_ALIAS("ppp-compress-" __stringify(CI_MPPE));
 66MODULE_VERSION("1.0.2");
 67
 68#define SHA1_PAD_SIZE 40
 69static const u8 sha_pad1[SHA1_PAD_SIZE] = { 0 };
 70static const u8 sha_pad2[SHA1_PAD_SIZE] = { [0 ... SHA1_PAD_SIZE - 1] = 0xF2 };
 71
 72/*
 73 * State for an MPPE (de)compressor.
 74 */
 75struct ppp_mppe_state {
 76	struct arc4_ctx arc4;
 77	unsigned char sha1_digest[SHA1_DIGEST_SIZE];
 78	unsigned char master_key[MPPE_MAX_KEY_LEN];
 79	unsigned char session_key[MPPE_MAX_KEY_LEN];
 80	unsigned keylen;	/* key length in bytes             */
 81	/* NB: 128-bit == 16, 40-bit == 8! */
 82	/* If we want to support 56-bit,   */
 83	/* the unit has to change to bits  */
 84	unsigned char bits;	/* MPPE control bits */
 85	unsigned ccount;	/* 12-bit coherency count (seqno)  */
 86	unsigned stateful;	/* stateful mode flag */
 87	int discard;		/* stateful mode packet loss flag */
 88	int sanity_errors;	/* take down LCP if too many */
 89	int unit;
 90	int debug;
 91	struct compstat stats;
 92};
 93
 94/* struct ppp_mppe_state.bits definitions */
 95#define MPPE_BIT_A	0x80	/* Encryption table were (re)inititalized */
 96#define MPPE_BIT_B	0x40	/* MPPC only (not implemented) */
 97#define MPPE_BIT_C	0x20	/* MPPC only (not implemented) */
 98#define MPPE_BIT_D	0x10	/* This is an encrypted frame */
 99
100#define MPPE_BIT_FLUSHED	MPPE_BIT_A
101#define MPPE_BIT_ENCRYPTED	MPPE_BIT_D
102
103#define MPPE_BITS(p) ((p)[4] & 0xf0)
104#define MPPE_CCOUNT(p) ((((p)[4] & 0x0f) << 8) + (p)[5])
105#define MPPE_CCOUNT_SPACE 0x1000	/* The size of the ccount space */
106
107#define MPPE_OVHD	2	/* MPPE overhead/packet */
108#define SANITY_MAX	1600	/* Max bogon factor we will tolerate */
109
110/*
111 * Key Derivation, from RFC 3078, RFC 3079.
112 * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
113 */
114static void get_new_key_from_sha(struct ppp_mppe_state * state)
115{
116	struct sha1_ctx ctx;
117
118	sha1_init(&ctx);
119	sha1_update(&ctx, state->master_key, state->keylen);
120	sha1_update(&ctx, sha_pad1, sizeof(sha_pad1));
121	sha1_update(&ctx, state->session_key, state->keylen);
122	sha1_update(&ctx, sha_pad2, sizeof(sha_pad2));
123	sha1_final(&ctx, state->sha1_digest);
124}
125
126/*
127 * Perform the MPPE rekey algorithm, from RFC 3078, sec. 7.3.
128 * Well, not what's written there, but rather what they meant.
129 */
130static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
131{
132	get_new_key_from_sha(state);
133	if (!initial_key) {
134		arc4_setkey(&state->arc4, state->sha1_digest, state->keylen);
135		arc4_crypt(&state->arc4, state->session_key, state->sha1_digest,
136			   state->keylen);
137	} else {
138		memcpy(state->session_key, state->sha1_digest, state->keylen);
139	}
140	if (state->keylen == 8) {
141		/* See RFC 3078 */
142		state->session_key[0] = 0xd1;
143		state->session_key[1] = 0x26;
144		state->session_key[2] = 0x9e;
145	}
146	arc4_setkey(&state->arc4, state->session_key, state->keylen);
147}
148
149/*
150 * Allocate space for a (de)compressor.
151 */
152static void *mppe_alloc(unsigned char *options, int optlen)
153{
154	struct ppp_mppe_state *state;
155
156	if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
157	    options[0] != CI_MPPE || options[1] != CILEN_MPPE ||
158	    fips_enabled)
159		return NULL;
160
161	state = kzalloc(sizeof(*state), GFP_KERNEL);
162	if (state == NULL)
163		return NULL;
164
165	/* Save keys. */
166	memcpy(state->master_key, &options[CILEN_MPPE],
167	       sizeof(state->master_key));
168	memcpy(state->session_key, state->master_key,
169	       sizeof(state->master_key));
170
171	/*
172	 * We defer initial key generation until mppe_init(), as mppe_alloc()
173	 * is called frequently during negotiation.
174	 */
175
176	return (void *)state;
177}
178
179/*
180 * Deallocate space for a (de)compressor.
181 */
182static void mppe_free(void *arg)
183{
184	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
185
186	kfree_sensitive(state);
187}
188
189/*
190 * Initialize (de)compressor state.
191 */
192static int
193mppe_init(void *arg, unsigned char *options, int optlen, int unit, int debug,
194	  const char *debugstr)
195{
196	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
197	unsigned char mppe_opts;
198
199	if (optlen != CILEN_MPPE ||
200	    options[0] != CI_MPPE || options[1] != CILEN_MPPE)
201		return 0;
202
203	MPPE_CI_TO_OPTS(&options[2], mppe_opts);
204	if (mppe_opts & MPPE_OPT_128)
205		state->keylen = 16;
206	else if (mppe_opts & MPPE_OPT_40)
207		state->keylen = 8;
208	else {
209		printk(KERN_WARNING "%s[%d]: unknown key length\n", debugstr,
210		       unit);
211		return 0;
212	}
213	if (mppe_opts & MPPE_OPT_STATEFUL)
214		state->stateful = 1;
215
216	/* Generate the initial session key. */
217	mppe_rekey(state, 1);
218
219	if (debug) {
220		printk(KERN_DEBUG "%s[%d]: initialized with %d-bit %s mode\n",
221		       debugstr, unit, (state->keylen == 16) ? 128 : 40,
222		       (state->stateful) ? "stateful" : "stateless");
223		printk(KERN_DEBUG
224		       "%s[%d]: keys: master: %*phN initial session: %*phN\n",
225		       debugstr, unit,
226		       (int)sizeof(state->master_key), state->master_key,
227		       (int)sizeof(state->session_key), state->session_key);
228	}
229
230	/*
231	 * Initialize the coherency count.  The initial value is not specified
232	 * in RFC 3078, but we can make a reasonable assumption that it will
233	 * start at 0.  Setting it to the max here makes the comp/decomp code
234	 * do the right thing (determined through experiment).
235	 */
236	state->ccount = MPPE_CCOUNT_SPACE - 1;
237
238	/*
239	 * Note that even though we have initialized the key table, we don't
240	 * set the FLUSHED bit.  This is contrary to RFC 3078, sec. 3.1.
241	 */
242	state->bits = MPPE_BIT_ENCRYPTED;
243
244	state->unit = unit;
245	state->debug = debug;
246
247	return 1;
248}
249
250static int
251mppe_comp_init(void *arg, unsigned char *options, int optlen, int unit,
252	       int hdrlen, int debug)
253{
254	/* ARGSUSED */
255	return mppe_init(arg, options, optlen, unit, debug, "mppe_comp_init");
256}
257
258/*
259 * We received a CCP Reset-Request (actually, we are sending a Reset-Ack),
260 * tell the compressor to rekey.  Note that we MUST NOT rekey for
261 * every CCP Reset-Request; we only rekey on the next xmit packet.
262 * We might get multiple CCP Reset-Requests if our CCP Reset-Ack is lost.
263 * So, rekeying for every CCP Reset-Request is broken as the peer will not
264 * know how many times we've rekeyed.  (If we rekey and THEN get another
265 * CCP Reset-Request, we must rekey again.)
266 */
267static void mppe_comp_reset(void *arg)
268{
269	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
270
271	state->bits |= MPPE_BIT_FLUSHED;
272}
273
274/*
275 * Compress (encrypt) a packet.
276 * It's strange to call this a compressor, since the output is always
277 * MPPE_OVHD + 2 bytes larger than the input.
278 */
279static int
280mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
281	      int isize, int osize)
282{
283	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
284	int proto;
285
286	/*
287	 * Check that the protocol is in the range we handle.
288	 */
289	proto = PPP_PROTOCOL(ibuf);
290	if (proto < 0x0021 || proto > 0x00fa)
291		return 0;
292
293	/* Make sure we have enough room to generate an encrypted packet. */
294	if (osize < isize + MPPE_OVHD + 2) {
295		/* Drop the packet if we should encrypt it, but can't. */
296		printk(KERN_DEBUG "mppe_compress[%d]: osize too small! "
297		       "(have: %d need: %d)\n", state->unit,
298		       osize, osize + MPPE_OVHD + 2);
299		return -1;
300	}
301
302	osize = isize + MPPE_OVHD + 2;
303
304	/*
305	 * Copy over the PPP header and set control bits.
306	 */
307	obuf[0] = PPP_ADDRESS(ibuf);
308	obuf[1] = PPP_CONTROL(ibuf);
309	put_unaligned_be16(PPP_COMP, obuf + 2);
310	obuf += PPP_HDRLEN;
311
312	state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
313	if (state->debug >= 7)
314		printk(KERN_DEBUG "mppe_compress[%d]: ccount %d\n", state->unit,
315		       state->ccount);
316	put_unaligned_be16(state->ccount, obuf);
317
318	if (!state->stateful ||	/* stateless mode     */
319	    ((state->ccount & 0xff) == 0xff) ||	/* "flag" packet      */
320	    (state->bits & MPPE_BIT_FLUSHED)) {	/* CCP Reset-Request  */
321		/* We must rekey */
322		if (state->debug && state->stateful)
323			printk(KERN_DEBUG "mppe_compress[%d]: rekeying\n",
324			       state->unit);
325		mppe_rekey(state, 0);
326		state->bits |= MPPE_BIT_FLUSHED;
327	}
328	obuf[0] |= state->bits;
329	state->bits &= ~MPPE_BIT_FLUSHED;	/* reset for next xmit */
330
331	obuf += MPPE_OVHD;
332	ibuf += 2;		/* skip to proto field */
333	isize -= 2;
334
335	arc4_crypt(&state->arc4, obuf, ibuf, isize);
336
337	state->stats.unc_bytes += isize;
338	state->stats.unc_packets++;
339	state->stats.comp_bytes += osize;
340	state->stats.comp_packets++;
341
342	return osize;
343}
344
345/*
346 * Since every frame grows by MPPE_OVHD + 2 bytes, this is always going
347 * to look bad ... and the longer the link is up the worse it will get.
348 */
349static void mppe_comp_stats(void *arg, struct compstat *stats)
350{
351	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
352
353	*stats = state->stats;
354}
355
356static int
357mppe_decomp_init(void *arg, unsigned char *options, int optlen, int unit,
358		 int hdrlen, int mru, int debug)
359{
360	/* ARGSUSED */
361	return mppe_init(arg, options, optlen, unit, debug, "mppe_decomp_init");
362}
363
364/*
365 * We received a CCP Reset-Ack.  Just ignore it.
366 */
367static void mppe_decomp_reset(void *arg)
368{
369	/* ARGSUSED */
370	return;
371}
372
373/*
374 * Decompress (decrypt) an MPPE packet.
375 */
376static int
377mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
378		int osize)
379{
380	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
381	unsigned ccount;
382	int flushed = MPPE_BITS(ibuf) & MPPE_BIT_FLUSHED;
383
384	if (isize <= PPP_HDRLEN + MPPE_OVHD) {
385		if (state->debug)
386			printk(KERN_DEBUG
387			       "mppe_decompress[%d]: short pkt (%d)\n",
388			       state->unit, isize);
389		return DECOMP_ERROR;
390	}
391
392	/*
393	 * Make sure we have enough room to decrypt the packet.
394	 * Note that for our test we only subtract 1 byte whereas in
395	 * mppe_compress() we added 2 bytes (+MPPE_OVHD);
396	 * this is to account for possible PFC.
397	 */
398	if (osize < isize - MPPE_OVHD - 1) {
399		printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
400		       "(have: %d need: %d)\n", state->unit,
401		       osize, isize - MPPE_OVHD - 1);
402		return DECOMP_ERROR;
403	}
404	osize = isize - MPPE_OVHD - 2;	/* assume no PFC */
405
406	ccount = MPPE_CCOUNT(ibuf);
407	if (state->debug >= 7)
408		printk(KERN_DEBUG "mppe_decompress[%d]: ccount %d\n",
409		       state->unit, ccount);
410
411	/* sanity checks -- terminate with extreme prejudice */
412	if (!(MPPE_BITS(ibuf) & MPPE_BIT_ENCRYPTED)) {
413		printk(KERN_DEBUG
414		       "mppe_decompress[%d]: ENCRYPTED bit not set!\n",
415		       state->unit);
416		state->sanity_errors += 100;
417		goto sanity_error;
418	}
419	if (!state->stateful && !flushed) {
420		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set in "
421		       "stateless mode!\n", state->unit);
422		state->sanity_errors += 100;
423		goto sanity_error;
424	}
425	if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
426		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set on "
427		       "flag packet!\n", state->unit);
428		state->sanity_errors += 100;
429		goto sanity_error;
430	}
431
432	/*
433	 * Check the coherency count.
434	 */
435
436	if (!state->stateful) {
437		/* Discard late packet */
438		if ((ccount - state->ccount) % MPPE_CCOUNT_SPACE
439						> MPPE_CCOUNT_SPACE / 2) {
440			state->sanity_errors++;
441			goto sanity_error;
442		}
443
444		/* RFC 3078, sec 8.1.  Rekey for every packet. */
445		while (state->ccount != ccount) {
446			mppe_rekey(state, 0);
447			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
448		}
449	} else {
450		/* RFC 3078, sec 8.2. */
451		if (!state->discard) {
452			/* normal state */
453			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
454			if (ccount != state->ccount) {
455				/*
456				 * (ccount > state->ccount)
457				 * Packet loss detected, enter the discard state.
458				 * Signal the peer to rekey (by sending a CCP Reset-Request).
459				 */
460				state->discard = 1;
461				return DECOMP_ERROR;
462			}
463		} else {
464			/* discard state */
465			if (!flushed) {
466				/* ccp.c will be silent (no additional CCP Reset-Requests). */
467				return DECOMP_ERROR;
468			} else {
469				/* Rekey for every missed "flag" packet. */
470				while ((ccount & ~0xff) !=
471				       (state->ccount & ~0xff)) {
472					mppe_rekey(state, 0);
473					state->ccount =
474					    (state->ccount +
475					     256) % MPPE_CCOUNT_SPACE;
476				}
477
478				/* reset */
479				state->discard = 0;
480				state->ccount = ccount;
481				/*
482				 * Another problem with RFC 3078 here.  It implies that the
483				 * peer need not send a Reset-Ack packet.  But RFC 1962
484				 * requires it.  Hopefully, M$ does send a Reset-Ack; even
485				 * though it isn't required for MPPE synchronization, it is
486				 * required to reset CCP state.
487				 */
488			}
489		}
490		if (flushed)
491			mppe_rekey(state, 0);
492	}
493
494	/*
495	 * Fill in the first part of the PPP header.  The protocol field
496	 * comes from the decrypted data.
497	 */
498	obuf[0] = PPP_ADDRESS(ibuf);	/* +1 */
499	obuf[1] = PPP_CONTROL(ibuf);	/* +1 */
500	obuf += 2;
501	ibuf += PPP_HDRLEN + MPPE_OVHD;
502	isize -= PPP_HDRLEN + MPPE_OVHD;	/* -6 */
503	/* net osize: isize-4 */
504
505	/*
506	 * Decrypt the first byte in order to check if it is
507	 * a compressed or uncompressed protocol field.
508	 */
509	arc4_crypt(&state->arc4, obuf, ibuf, 1);
510
511	/*
512	 * Do PFC decompression.
513	 * This would be nicer if we were given the actual sk_buff
514	 * instead of a char *.
515	 */
516	if ((obuf[0] & 0x01) != 0) {
517		obuf[1] = obuf[0];
518		obuf[0] = 0;
519		obuf++;
520		osize++;
521	}
522
523	/* And finally, decrypt the rest of the packet. */
524	arc4_crypt(&state->arc4, obuf + 1, ibuf + 1, isize - 1);
525
526	state->stats.unc_bytes += osize;
527	state->stats.unc_packets++;
528	state->stats.comp_bytes += isize;
529	state->stats.comp_packets++;
530
531	/* good packet credit */
532	state->sanity_errors >>= 1;
533
534	return osize;
535
536sanity_error:
537	if (state->sanity_errors < SANITY_MAX)
538		return DECOMP_ERROR;
539	else
540		/* Take LCP down if the peer is sending too many bogons.
541		 * We don't want to do this for a single or just a few
542		 * instances since it could just be due to packet corruption.
543		 */
544		return DECOMP_FATALERROR;
545}
546
547/*
548 * Incompressible data has arrived (this should never happen!).
549 * We should probably drop the link if the protocol is in the range
550 * of what should be encrypted.  At the least, we should drop this
551 * packet.  (How to do this?)
552 */
553static void mppe_incomp(void *arg, unsigned char *ibuf, int icnt)
554{
555	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
556
557	if (state->debug &&
558	    (PPP_PROTOCOL(ibuf) >= 0x0021 && PPP_PROTOCOL(ibuf) <= 0x00fa))
559		printk(KERN_DEBUG
560		       "mppe_incomp[%d]: incompressible (unencrypted) data! "
561		       "(proto %04x)\n", state->unit, PPP_PROTOCOL(ibuf));
562
563	state->stats.inc_bytes += icnt;
564	state->stats.inc_packets++;
565	state->stats.unc_bytes += icnt;
566	state->stats.unc_packets++;
567}
568
569/*************************************************************
570 * Module interface table
571 *************************************************************/
572
573/*
574 * Procedures exported to if_ppp.c.
575 */
576static struct compressor ppp_mppe = {
577	.compress_proto = CI_MPPE,
578	.comp_alloc     = mppe_alloc,
579	.comp_free      = mppe_free,
580	.comp_init      = mppe_comp_init,
581	.comp_reset     = mppe_comp_reset,
582	.compress       = mppe_compress,
583	.comp_stat      = mppe_comp_stats,
584	.decomp_alloc   = mppe_alloc,
585	.decomp_free    = mppe_free,
586	.decomp_init    = mppe_decomp_init,
587	.decomp_reset   = mppe_decomp_reset,
588	.decompress     = mppe_decompress,
589	.incomp         = mppe_incomp,
590	.decomp_stat    = mppe_comp_stats,
591	.owner          = THIS_MODULE,
592	.comp_extra     = MPPE_PAD,
593};
594
595static int __init ppp_mppe_init(void)
596{
597	int answer;
598
599	if (fips_enabled)
600		return -ENODEV;
601
602	answer = ppp_register_compressor(&ppp_mppe);
603
604	if (answer == 0)
605		printk(KERN_INFO "PPP MPPE Compression module registered\n");
606
607	return answer;
608}
609
610static void __exit ppp_mppe_cleanup(void)
611{
612	ppp_unregister_compressor(&ppp_mppe);
613}
614
615module_init(ppp_mppe_init);
616module_exit(ppp_mppe_cleanup);