ppp_mppe.c

linux 内核源代码

/*
 * ppp_mppe.c - interface MPPE to the PPP code.
 * This version is for use with Linux kernel 2.6.14+
 *
 * By Frank Cusack <[e-mail]>.
 * 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 <[e-mail]>
 *                 Only need extra skb padding on transmit, not receive.
 *      06/18/04 - Matt Domsch <[e-mail]>, Oleg Makarenko <[e-mail]>
 *                 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 <linux/scatterlist.h>

#include "ppp_mppe.h"

MODULE_AUTHOR("Frank Cusack <[e-mail]>");
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_set_buf(sg, address, 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)
{
	struct hash_desc desc;
	struct scatterlist sg[4];
	unsigned int nbytes;

	sg_init_table(sg, 4);

	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);
}

/*
 * 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)
{
	struct scatterlist sg_in[1], sg_out[1];
	struct blkcipher_desc desc = { .tfm = state->arc4 };

	get_new_key_from_sha(state);
	if (!initial_key) {
		crypto_blkcipher_setkey(state->arc4, state->sha1_digest,
					state->keylen);
		sg_init_table(sg_in, 1);
		sg_init_table(sg_out, 1);
		setup_sg(sg_in, state->sha1_digest, 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, state->sha1_digest, 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 = kzalloc(sizeof(*state), GFP_KERNEL);
	if (state == NULL)
		goto out;


	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 };