lwip/src/netif/ppp/mppe.c

/*
 * mppe.c - interface MPPE to the PPP code.
 *
 * 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.
 *
 * 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 "lwip/opt.h"
#if PPP_SUPPORT && MPPE_SUPPORT  /* don't build if not configured for use in lwipopts.h */

#include <string.h>

#include "lwip/err.h"

#include "netif/ppp/ppp_impl.h"
#include "netif/ppp/ccp.h"
#include "netif/ppp/mppe.h"
#include "netif/ppp/pppdebug.h"

#if LWIP_INCLUDED_POLARSSL_SHA1
#include "netif/ppp/polarssl/sha1.h"
#else
#include "polarssl/sha1.h"
#endif

#if LWIP_INCLUDED_POLARSSL_ARC4
#include "netif/ppp/polarssl/arc4.h"
#else
#include "polarssl/arc4.h"
#endif

#define SHA1_SIGNATURE_SIZE 20

/* 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)[0] & 0xf0)
#define MPPE_CCOUNT(p) ((((p)[0] & 0x0f) << 8) + (p)[1])
#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 */

/*
 * 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(ppp_mppe_state * state, int initial_key)
{
	sha1_context sha1;
	u8_t sha1_digest[SHA1_SIGNATURE_SIZE];

	/*
	 * Key Derivation, from RFC 3078, RFC 3079.
	 * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
	 */
	sha1_starts(&sha1);
	sha1_update(&sha1, state->master_key, state->keylen);
	sha1_update(&sha1, (unsigned char *)mppe_sha1_pad1, SHA1_PAD_SIZE);
	sha1_update(&sha1, state->session_key, state->keylen);
	sha1_update(&sha1, (unsigned char *)mppe_sha1_pad2, SHA1_PAD_SIZE);
	sha1_finish(&sha1, sha1_digest);
	MEMCPY(state->session_key, sha1_digest, state->keylen);

	if (!initial_key) {
		arc4_setup(&state->arc4, sha1_digest, state->keylen);
		arc4_crypt(&state->arc4, state->session_key, state->keylen);
	}
	if (state->keylen == 8) {
		/* See RFC 3078 */
		state->session_key[0] = 0xd1;
		state->session_key[1] = 0x26;
		state->session_key[2] = 0x9e;
	}
	arc4_setup(&state->arc4, state->session_key, state->keylen);
}

/*
 * Initialize (de)compressor state.
 */
int
mppe_init(ppp_mppe_state *state, unsigned char *options, int optlen, u8_t unit, u8_t debug,
	  const char *debugstr)
{
	unsigned char mppe_opts;

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

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

	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 {
		PPPDEBUG(LOG_DEBUG, ("%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];

		PPPDEBUG(LOG_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 < (int)sizeof(state->master_key); i++)
			sprintf(mkey + i * 2, "%02x", state->master_key[i]);
		for (i = 0; i < (int)sizeof(state->session_key); i++)
			sprintf(skey + i * 2, "%02x", state->session_key[i]);
		PPPDEBUG(LOG_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;
}

/*
 * 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.)
 */
void mppe_comp_reset(ppp_mppe_state *state)
{
	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.
 */
err_t
mppe_compress(ppp_mppe_state *state, struct pbuf **pb, u16_t protocol)
{
	struct pbuf *np, *n;
	u8_t *pl;

	/* FIXME: try to use pbuf_header() here! */
	np = pbuf_alloc(PBUF_RAW, MPPE_OVHD + sizeof(protocol), PBUF_RAM);
	if (!np) {
	  return ERR_MEM;
	}
	pbuf_chain(np, *pb);
	pl = (u8_t*)np->payload;

	state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
	if (state->debug)
		PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: ccount %d\n", state->unit,
		       state->ccount));
	/* FIXME: use PUT* macros */
	pl[0] = state->ccount>>8;
	pl[1] = state->ccount;

	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)
			PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: rekeying\n",
			       state->unit));
		mppe_rekey(state, 0);
		state->bits |= MPPE_BIT_FLUSHED;
	}
	pl[0] |= state->bits;
	state->bits &= ~MPPE_BIT_FLUSHED;	/* reset for next xmit */
	pl += MPPE_OVHD;

	/* Add and encrypt protocol */
	/* FIXME: add PFC support */
	pl[0] = protocol >> 8;
	pl[1] = protocol;
	arc4_crypt(&state->arc4, pl, sizeof(protocol));

	/* Encrypt packet */
	for (n = *pb; n != NULL; n = n->next) {
		arc4_crypt(&state->arc4, (u8_t*)n->payload, n->len);
		if (n->tot_len == n->len) {
			break;
		}
	}

	*pb = np;
	return ERR_OK;
}

/*
 * We received a CCP Reset-Ack.  Just ignore it.
 */
void mppe_decomp_reset(ppp_mppe_state *state)
{
	LWIP_UNUSED_ARG(state);
	return;
}

/*
 * Decompress (decrypt) an MPPE packet.
 */
err_t
mppe_decompress(ppp_mppe_state *state, struct pbuf **pb)
{
	struct pbuf *n0 = *pb, *n;
	u8_t *pl;
	u16_t ccount;
	u8_t flushed;
	u8_t sanity = 0;

	/* MPPE Header */
	if (n0->len < MPPE_OVHD) {
		if (state->debug)
			PPPDEBUG(LOG_DEBUG,
			       ("mppe_decompress[%d]: short pkt (%d)\n",
			       state->unit, n0->len));
		return ERR_BUF;
	}

	pl = (u8_t*)n0->payload;
	flushed = MPPE_BITS(pl) & MPPE_BIT_FLUSHED;
	ccount = MPPE_CCOUNT(pl);
	if (state->debug)
		PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: ccount %d\n",
		       state->unit, ccount));

	/* sanity checks -- terminate with extreme prejudice */
	if (!(MPPE_BITS(pl) & MPPE_BIT_ENCRYPTED)) {
		PPPDEBUG(LOG_DEBUG,
		       ("mppe_decompress[%d]: ENCRYPTED bit not set!\n",
		       state->unit));
		state->sanity_errors += 100;
		sanity = 1;
	}
	if (!state->stateful && !flushed) {
		PPPDEBUG(LOG_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) {
		PPPDEBUG(LOG_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 ERR_BUF;
		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.
			 */
			/* FIXME: call lcp_close() here */
			return ERR_BUF;
	}

	/*
	 * 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 ERR_BUF;
			}
		} else {
			/* discard state */
			if (!flushed) {
				/* ccp.c will be silent (no additional CCP Reset-Requests). */
				return ERR_BUF;
			} 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);
	}

	/* Hide MPPE header */
	pbuf_header(n0, -(s16_t)(MPPE_OVHD));

	/* Decrypt the packet. */
	for (n = n0; n != NULL; n = n->next) {
		arc4_crypt(&state->arc4, (u8_t*)n->payload, n->len);
		if (n->tot_len == n->len) {
			break;
		}
	}

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

	return ERR_OK;
}

/*
 * 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?)
 */
void mppe_incomp(ppp_mppe_state *state, unsigned char *ibuf, int icnt)
{
	LWIP_UNUSED_ARG(icnt);

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

#endif /* PPP_SUPPORT && MPPE_SUPPORT */