1 /*
2 * mppe.c - interface MPPE to the PPP code.
3 *
4 * By Frank Cusack <fcusack@fcusack.com>.
5 * Copyright (c) 2002,2003,2004 Google, Inc.
6 * All rights reserved.
7 *
8 * License:
9 * Permission to use, copy, modify, and distribute this software and its
10 * documentation is hereby granted, provided that the above copyright
11 * notice appears in all copies. This software is provided without any
12 * warranty, express or implied.
13 *
14 * Changelog:
15 * 08/12/05 - Matt Domsch <Matt_Domsch@dell.com>
16 * Only need extra skb padding on transmit, not receive.
17 * 06/18/04 - Matt Domsch <Matt_Domsch@dell.com>, Oleg Makarenko <mole@quadra.ru>
18 * Use Linux kernel 2.6 arc4 and sha1 routines rather than
19 * providing our own.
20 * 2/15/04 - TS: added #include <version.h> and testing for Kernel
21 * version before using
22 * MOD_DEC_USAGE_COUNT/MOD_INC_USAGE_COUNT which are
23 * deprecated in 2.6
24 */
25
26 #include "netif/ppp/ppp_opts.h"
27 #if PPP_SUPPORT && MPPE_SUPPORT /* don't build if not configured for use in lwipopts.h */
28
29 #include <string.h>
30
31 #include "lwip/err.h"
32
33 #include "netif/ppp/ppp_impl.h"
34 #include "netif/ppp/ccp.h"
35 #include "netif/ppp/mppe.h"
36 #include "netif/ppp/pppdebug.h"
37 #include "netif/ppp/pppcrypt.h"
38
39 #define SHA1_SIGNATURE_SIZE 20
40
41 /* ppp_mppe_state.bits definitions */
42 #define MPPE_BIT_A 0x80 /* Encryption table were (re)inititalized */
43 #define MPPE_BIT_B 0x40 /* MPPC only (not implemented) */
44 #define MPPE_BIT_C 0x20 /* MPPC only (not implemented) */
45 #define MPPE_BIT_D 0x10 /* This is an encrypted frame */
46
47 #define MPPE_BIT_FLUSHED MPPE_BIT_A
48 #define MPPE_BIT_ENCRYPTED MPPE_BIT_D
49
50 #define MPPE_BITS(p) ((p)[0] & 0xf0)
51 #define MPPE_CCOUNT(p) ((((p)[0] & 0x0f) << 8) + (p)[1])
52 #define MPPE_CCOUNT_SPACE 0x1000 /* The size of the ccount space */
53
54 #define MPPE_OVHD 2 /* MPPE overhead/packet */
55 #define SANITY_MAX 1600 /* Max bogon factor we will tolerate */
56
57 /*
58 * Perform the MPPE rekey algorithm, from RFC 3078, sec. 7.3.
59 * Well, not what's written there, but rather what they meant.
60 */
mppe_rekey(ppp_mppe_state * state,int initial_key)61 static void mppe_rekey(ppp_mppe_state * state, int initial_key)
62 {
63 lwip_sha1_context sha1_ctx;
64 u8_t sha1_digest[SHA1_SIGNATURE_SIZE];
65
66 /*
67 * Key Derivation, from RFC 3078, RFC 3079.
68 * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
69 */
70 lwip_sha1_init(&sha1_ctx);
71 lwip_sha1_starts(&sha1_ctx);
72 lwip_sha1_update(&sha1_ctx, state->master_key, state->keylen);
73 lwip_sha1_update(&sha1_ctx, mppe_sha1_pad1, SHA1_PAD_SIZE);
74 lwip_sha1_update(&sha1_ctx, state->session_key, state->keylen);
75 lwip_sha1_update(&sha1_ctx, mppe_sha1_pad2, SHA1_PAD_SIZE);
76 lwip_sha1_finish(&sha1_ctx, sha1_digest);
77 lwip_sha1_free(&sha1_ctx);
78 MEMCPY(state->session_key, sha1_digest, state->keylen);
79
80 if (!initial_key) {
81 lwip_arc4_init(&state->arc4);
82 lwip_arc4_setup(&state->arc4, sha1_digest, state->keylen);
83 lwip_arc4_crypt(&state->arc4, state->session_key, state->keylen);
84 lwip_arc4_free(&state->arc4);
85 }
86 if (state->keylen == 8) {
87 /* See RFC 3078 */
88 state->session_key[0] = 0xd1;
89 state->session_key[1] = 0x26;
90 state->session_key[2] = 0x9e;
91 }
92 lwip_arc4_init(&state->arc4);
93 lwip_arc4_setup(&state->arc4, state->session_key, state->keylen);
94 }
95
96 /*
97 * Set key, used by MSCHAP before mppe_init() is actually called by CCP so we
98 * don't have to keep multiple copies of keys.
99 */
mppe_set_key(ppp_pcb * pcb,ppp_mppe_state * state,u8_t * key)100 void mppe_set_key(ppp_pcb *pcb, ppp_mppe_state *state, u8_t *key) {
101 LWIP_UNUSED_ARG(pcb);
102 MEMCPY(state->master_key, key, MPPE_MAX_KEY_LEN);
103 }
104
105 /*
106 * Initialize (de)compressor state.
107 */
108 void
mppe_init(ppp_pcb * pcb,ppp_mppe_state * state,u8_t options)109 mppe_init(ppp_pcb *pcb, ppp_mppe_state *state, u8_t options)
110 {
111 #if PPP_DEBUG
112 const u8_t *debugstr = (const u8_t*)"mppe_comp_init";
113 if (&pcb->mppe_decomp == state) {
114 debugstr = (const u8_t*)"mppe_decomp_init";
115 }
116 #endif /* PPP_DEBUG */
117
118 /* Save keys. */
119 MEMCPY(state->session_key, state->master_key, sizeof(state->master_key));
120
121 if (options & MPPE_OPT_128)
122 state->keylen = 16;
123 else if (options & MPPE_OPT_40)
124 state->keylen = 8;
125 else {
126 PPPDEBUG(LOG_DEBUG, ("%s[%d]: unknown key length\n", debugstr,
127 pcb->netif->num));
128 lcp_close(pcb, "MPPE required but peer negotiation failed");
129 return;
130 }
131 if (options & MPPE_OPT_STATEFUL)
132 state->stateful = 1;
133
134 /* Generate the initial session key. */
135 mppe_rekey(state, 1);
136
137 #if PPP_DEBUG
138 {
139 int i;
140 char mkey[sizeof(state->master_key) * 2 + 1];
141 char skey[sizeof(state->session_key) * 2 + 1];
142
143 PPPDEBUG(LOG_DEBUG, ("%s[%d]: initialized with %d-bit %s mode\n",
144 debugstr, pcb->netif->num, (state->keylen == 16) ? 128 : 40,
145 (state->stateful) ? "stateful" : "stateless"));
146
147 for (i = 0; i < (int)sizeof(state->master_key); i++)
148 sprintf(mkey + i * 2, "%02x", state->master_key[i]);
149 for (i = 0; i < (int)sizeof(state->session_key); i++)
150 sprintf(skey + i * 2, "%02x", state->session_key[i]);
151 PPPDEBUG(LOG_DEBUG,
152 ("%s[%d]: keys: master: %s initial session: %s\n",
153 debugstr, pcb->netif->num, mkey, skey));
154 }
155 #endif /* PPP_DEBUG */
156
157 /*
158 * Initialize the coherency count. The initial value is not specified
159 * in RFC 3078, but we can make a reasonable assumption that it will
160 * start at 0. Setting it to the max here makes the comp/decomp code
161 * do the right thing (determined through experiment).
162 */
163 state->ccount = MPPE_CCOUNT_SPACE - 1;
164
165 /*
166 * Note that even though we have initialized the key table, we don't
167 * set the FLUSHED bit. This is contrary to RFC 3078, sec. 3.1.
168 */
169 state->bits = MPPE_BIT_ENCRYPTED;
170 }
171
172 /*
173 * We received a CCP Reset-Request (actually, we are sending a Reset-Ack),
174 * tell the compressor to rekey. Note that we MUST NOT rekey for
175 * every CCP Reset-Request; we only rekey on the next xmit packet.
176 * We might get multiple CCP Reset-Requests if our CCP Reset-Ack is lost.
177 * So, rekeying for every CCP Reset-Request is broken as the peer will not
178 * know how many times we've rekeyed. (If we rekey and THEN get another
179 * CCP Reset-Request, we must rekey again.)
180 */
mppe_comp_reset(ppp_pcb * pcb,ppp_mppe_state * state)181 void mppe_comp_reset(ppp_pcb *pcb, ppp_mppe_state *state)
182 {
183 LWIP_UNUSED_ARG(pcb);
184 state->bits |= MPPE_BIT_FLUSHED;
185 }
186
187 /*
188 * Compress (encrypt) a packet.
189 * It's strange to call this a compressor, since the output is always
190 * MPPE_OVHD + 2 bytes larger than the input.
191 */
192 err_t
mppe_compress(ppp_pcb * pcb,ppp_mppe_state * state,struct pbuf ** pb,u16_t protocol)193 mppe_compress(ppp_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb, u16_t protocol)
194 {
195 struct pbuf *n, *np;
196 u8_t *pl;
197 err_t err;
198
199 LWIP_UNUSED_ARG(pcb);
200
201 /* TCP stack requires that we don't change the packet payload, therefore we copy
202 * the whole packet before encryption.
203 */
204 np = pbuf_alloc(PBUF_RAW, MPPE_OVHD + sizeof(protocol) + (*pb)->tot_len, PBUF_RAM);
205 if (!np) {
206 return ERR_MEM;
207 }
208
209 /* Hide MPPE header + protocol */
210 pbuf_remove_header(np, MPPE_OVHD + sizeof(protocol));
211
212 if ((err = pbuf_copy(np, *pb)) != ERR_OK) {
213 pbuf_free(np);
214 return err;
215 }
216
217 /* Reveal MPPE header + protocol */
218 pbuf_add_header(np, MPPE_OVHD + sizeof(protocol));
219
220 *pb = np;
221 pl = (u8_t*)np->payload;
222
223 state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
224 PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: ccount %d\n", pcb->netif->num, state->ccount));
225 /* FIXME: use PUT* macros */
226 pl[0] = state->ccount>>8;
227 pl[1] = state->ccount;
228
229 if (!state->stateful || /* stateless mode */
230 ((state->ccount & 0xff) == 0xff) || /* "flag" packet */
231 (state->bits & MPPE_BIT_FLUSHED)) { /* CCP Reset-Request */
232 /* We must rekey */
233 if (state->stateful) {
234 PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: rekeying\n", pcb->netif->num));
235 }
236 mppe_rekey(state, 0);
237 state->bits |= MPPE_BIT_FLUSHED;
238 }
239 pl[0] |= state->bits;
240 state->bits &= ~MPPE_BIT_FLUSHED; /* reset for next xmit */
241 pl += MPPE_OVHD;
242
243 /* Add protocol */
244 /* FIXME: add PFC support */
245 pl[0] = protocol >> 8;
246 pl[1] = protocol;
247
248 /* Hide MPPE header */
249 pbuf_remove_header(np, MPPE_OVHD);
250
251 /* Encrypt packet */
252 for (n = np; n != NULL; n = n->next) {
253 lwip_arc4_crypt(&state->arc4, (u8_t*)n->payload, n->len);
254 if (n->tot_len == n->len) {
255 break;
256 }
257 }
258
259 /* Reveal MPPE header */
260 pbuf_add_header(np, MPPE_OVHD);
261
262 return ERR_OK;
263 }
264
265 /*
266 * We received a CCP Reset-Ack. Just ignore it.
267 */
mppe_decomp_reset(ppp_pcb * pcb,ppp_mppe_state * state)268 void mppe_decomp_reset(ppp_pcb *pcb, ppp_mppe_state *state)
269 {
270 LWIP_UNUSED_ARG(pcb);
271 LWIP_UNUSED_ARG(state);
272 return;
273 }
274
275 /*
276 * Decompress (decrypt) an MPPE packet.
277 */
278 err_t
mppe_decompress(ppp_pcb * pcb,ppp_mppe_state * state,struct pbuf ** pb)279 mppe_decompress(ppp_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb)
280 {
281 struct pbuf *n0 = *pb, *n;
282 u8_t *pl;
283 u16_t ccount;
284 u8_t flushed;
285
286 /* MPPE Header */
287 if (n0->len < MPPE_OVHD) {
288 PPPDEBUG(LOG_DEBUG,
289 ("mppe_decompress[%d]: short pkt (%d)\n",
290 pcb->netif->num, n0->len));
291 state->sanity_errors += 100;
292 goto sanity_error;
293 }
294
295 pl = (u8_t*)n0->payload;
296 flushed = MPPE_BITS(pl) & MPPE_BIT_FLUSHED;
297 ccount = MPPE_CCOUNT(pl);
298 PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: ccount %d\n",
299 pcb->netif->num, ccount));
300
301 /* sanity checks -- terminate with extreme prejudice */
302 if (!(MPPE_BITS(pl) & MPPE_BIT_ENCRYPTED)) {
303 PPPDEBUG(LOG_DEBUG,
304 ("mppe_decompress[%d]: ENCRYPTED bit not set!\n",
305 pcb->netif->num));
306 state->sanity_errors += 100;
307 goto sanity_error;
308 }
309 if (!state->stateful && !flushed) {
310 PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set in "
311 "stateless mode!\n", pcb->netif->num));
312 state->sanity_errors += 100;
313 goto sanity_error;
314 }
315 if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
316 PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set on "
317 "flag packet!\n", pcb->netif->num));
318 state->sanity_errors += 100;
319 goto sanity_error;
320 }
321
322 /*
323 * Check the coherency count.
324 */
325
326 if (!state->stateful) {
327 /* Discard late packet */
328 if ((ccount - state->ccount) % MPPE_CCOUNT_SPACE > MPPE_CCOUNT_SPACE / 2) {
329 state->sanity_errors++;
330 goto sanity_error;
331 }
332
333 /* RFC 3078, sec 8.1. Rekey for every packet. */
334 while (state->ccount != ccount) {
335 mppe_rekey(state, 0);
336 state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
337 }
338 } else {
339 /* RFC 3078, sec 8.2. */
340 if (!state->discard) {
341 /* normal state */
342 state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
343 if (ccount != state->ccount) {
344 /*
345 * (ccount > state->ccount)
346 * Packet loss detected, enter the discard state.
347 * Signal the peer to rekey (by sending a CCP Reset-Request).
348 */
349 state->discard = 1;
350 ccp_resetrequest(pcb);
351 return ERR_BUF;
352 }
353 } else {
354 /* discard state */
355 if (!flushed) {
356 /* ccp.c will be silent (no additional CCP Reset-Requests). */
357 return ERR_BUF;
358 } else {
359 /* Rekey for every missed "flag" packet. */
360 while ((ccount & ~0xff) !=
361 (state->ccount & ~0xff)) {
362 mppe_rekey(state, 0);
363 state->ccount =
364 (state->ccount +
365 256) % MPPE_CCOUNT_SPACE;
366 }
367
368 /* reset */
369 state->discard = 0;
370 state->ccount = ccount;
371 /*
372 * Another problem with RFC 3078 here. It implies that the
373 * peer need not send a Reset-Ack packet. But RFC 1962
374 * requires it. Hopefully, M$ does send a Reset-Ack; even
375 * though it isn't required for MPPE synchronization, it is
376 * required to reset CCP state.
377 */
378 }
379 }
380 if (flushed)
381 mppe_rekey(state, 0);
382 }
383
384 /* Hide MPPE header */
385 pbuf_remove_header(n0, MPPE_OVHD);
386
387 /* Decrypt the packet. */
388 for (n = n0; n != NULL; n = n->next) {
389 lwip_arc4_crypt(&state->arc4, (u8_t*)n->payload, n->len);
390 if (n->tot_len == n->len) {
391 break;
392 }
393 }
394
395 /* good packet credit */
396 state->sanity_errors >>= 1;
397
398 return ERR_OK;
399
400 sanity_error:
401 if (state->sanity_errors >= SANITY_MAX) {
402 /*
403 * Take LCP down if the peer is sending too many bogons.
404 * We don't want to do this for a single or just a few
405 * instances since it could just be due to packet corruption.
406 */
407 lcp_close(pcb, "Too many MPPE errors");
408 }
409 return ERR_BUF;
410 }
411
412 #endif /* PPP_SUPPORT && MPPE_SUPPORT */
413