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
62 MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
63 MODULE_DESCRIPTION("Point-to-Point Protocol Microsoft Point-to-Point Encryption support");
64 MODULE_LICENSE("Dual BSD/GPL");
65 MODULE_ALIAS("ppp-compress-" __stringify(CI_MPPE));
66 MODULE_VERSION("1.0.2");
67
68 #define SHA1_PAD_SIZE 40
69 static const u8 sha_pad1[SHA1_PAD_SIZE] = { 0 };
70 static const u8 sha_pad2[SHA1_PAD_SIZE] = { [0 ... SHA1_PAD_SIZE - 1] = 0xF2 };
71
72 /*
73 * State for an MPPE (de)compressor.
74 */
75 struct 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 */
get_new_key_from_sha(struct ppp_mppe_state * state)114 static 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 */
mppe_rekey(struct ppp_mppe_state * state,int initial_key)130 static 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 */
mppe_alloc(unsigned char * options,int optlen)152 static 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_obj(*state);
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 */
mppe_free(void * arg)182 static 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 */
192 static int
mppe_init(void * arg,unsigned char * options,int optlen,int unit,int debug,const char * debugstr)193 mppe_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
250 static int
mppe_comp_init(void * arg,unsigned char * options,int optlen,int unit,int hdrlen,int debug)251 mppe_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 */
mppe_comp_reset(void * arg)267 static 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 */
279 static int
mppe_compress(void * arg,unsigned char * ibuf,unsigned char * obuf,int isize,int osize)280 mppe_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 */
mppe_comp_stats(void * arg,struct compstat * stats)349 static 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
356 static int
mppe_decomp_init(void * arg,unsigned char * options,int optlen,int unit,int hdrlen,int mru,int debug)357 mppe_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 */
mppe_decomp_reset(void * arg)367 static void mppe_decomp_reset(void *arg)
368 {
369 /* ARGSUSED */
370 return;
371 }
372
373 /*
374 * Decompress (decrypt) an MPPE packet.
375 */
376 static int
mppe_decompress(void * arg,unsigned char * ibuf,int isize,unsigned char * obuf,int osize)377 mppe_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
536 sanity_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 */
mppe_incomp(void * arg,unsigned char * ibuf,int icnt)553 static 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 */
576 static 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
ppp_mppe_init(void)595 static 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
ppp_mppe_cleanup(void)610 static void __exit ppp_mppe_cleanup(void)
611 {
612 ppp_unregister_compressor(&ppp_mppe);
613 }
614
615 module_init(ppp_mppe_init);
616 module_exit(ppp_mppe_cleanup);
617