/*
   * ppp_mppe.c - interface MPPE to the PPP code.
   * This version is for use with Linux kernel 2.6.14+
   *
   * 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.
   *
   * 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, see <http://www.gnu.org/licenses/>.
   *
   *
   * 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 <linux/err.h>
  #include <linux/module.h>
  #include <linux/kernel.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 <asm/unaligned.h>
  
  #include "ppp_mppe.h"
  
  MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
  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
  ");
  		}
  	} 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
  ", 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
  ",
  		       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
  ",
  		       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 };
  	int proto;
  	struct scatterlist sg_in[1], sg_out[1];
  
  	/*
  	 * Check that the protocol is in the range we handle.
  	 */
  	proto = PPP_PROTOCOL(ibuf);
  	if (proto < 0x0021 || proto > 0x00fa)
  		return 0;
  
  	/* Make sure we have enough room to generate an encrypted packet. */
  	if (osize < isize + MPPE_OVHD + 2) {
  		/* Drop the packet if we should encrypt it, but can't. */
  		printk(KERN_DEBUG "mppe_compress[%d]: osize too small! "
  		       "(have: %d need: %d)
  ", state->unit,
  		       osize, osize + MPPE_OVHD + 2);
  		return -1;
  	}
  
  	osize = isize + MPPE_OVHD + 2;
  
  	/*
  	 * Copy over the PPP header and set control bits.
  	 */
  	obuf[0] = PPP_ADDRESS(ibuf);
  	obuf[1] = PPP_CONTROL(ibuf);
  	put_unaligned_be16(PPP_COMP, obuf + 2);
  	obuf += PPP_HDRLEN;
  
  	state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
  	if (state->debug >= 7)
  		printk(KERN_DEBUG "mppe_compress[%d]: ccount %d
  ", state->unit,
  		       state->ccount);
  	put_unaligned_be16(state->ccount, obuf);
  
  	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)
  			printk(KERN_DEBUG "mppe_compress[%d]: rekeying
  ",
  			       state->unit);
  		mppe_rekey(state, 0);
  		state->bits |= MPPE_BIT_FLUSHED;
  	}
  	obuf[0] |= state->bits;
  	state->bits &= ~MPPE_BIT_FLUSHED;	/* reset for next xmit */
  
  	obuf += MPPE_OVHD;
  	ibuf += 2;		/* skip to proto field */
  	isize -= 2;
  
  	/* Encrypt packet */
  	sg_init_table(sg_in, 1);
  	sg_init_table(sg_out, 1);
  	setup_sg(sg_in, ibuf, isize);
  	setup_sg(sg_out, obuf, osize);
  	if (crypto_blkcipher_encrypt(&desc, sg_out, sg_in, isize) != 0) {
  		printk(KERN_DEBUG "crypto_cypher_encrypt failed
  ");
  		return -1;
  	}
  
  	state->stats.unc_bytes += isize;
  	state->stats.unc_packets++;
  	state->stats.comp_bytes += osize;
  	state->stats.comp_packets++;
  
  	return osize;
  }
  
  /*
   * Since every frame grows by MPPE_OVHD + 2 bytes, this is always going
   * to look bad ... and the longer the link is up the worse it will get.
   */
  static void mppe_comp_stats(void *arg, struct compstat *stats)
  {
  	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
  
  	*stats = state->stats;
  }
  
  static int
  mppe_decomp_init(void *arg, unsigned char *options, int optlen, int unit,
  		 int hdrlen, int mru, int debug)
  {
  	/* ARGSUSED */
  	return mppe_init(arg, options, optlen, unit, debug, "mppe_decomp_init");
  }
  
  /*
   * We received a CCP Reset-Ack.  Just ignore it.
   */
  static void mppe_decomp_reset(void *arg)
  {
  	/* ARGSUSED */
  	return;
  }
  
  /*
   * Decompress (decrypt) an MPPE packet.
   */
  static int
  mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
  		int osize)
  {
  	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
  	struct blkcipher_desc desc = { .tfm = state->arc4 };
  	unsigned ccount;
  	int flushed = MPPE_BITS(ibuf) & MPPE_BIT_FLUSHED;
  	struct scatterlist sg_in[1], sg_out[1];
  
  	if (isize <= PPP_HDRLEN + MPPE_OVHD) {
  		if (state->debug)
  			printk(KERN_DEBUG
  			       "mppe_decompress[%d]: short pkt (%d)
  ",
  			       state->unit, isize);
  		return DECOMP_ERROR;
  	}
  
  	/*
  	 * Make sure we have enough room to decrypt the packet.
  	 * Note that for our test we only subtract 1 byte whereas in
  	 * mppe_compress() we added 2 bytes (+MPPE_OVHD);
  	 * this is to account for possible PFC.
  	 */
  	if (osize < isize - MPPE_OVHD - 1) {
  		printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
  		       "(have: %d need: %d)
  ", state->unit,
  		       osize, isize - MPPE_OVHD - 1);
  		return DECOMP_ERROR;
  	}
  	osize = isize - MPPE_OVHD - 2;	/* assume no PFC */
  
  	ccount = MPPE_CCOUNT(ibuf);
  	if (state->debug >= 7)
  		printk(KERN_DEBUG "mppe_decompress[%d]: ccount %d
  ",
  		       state->unit, ccount);
  
  	/* sanity checks -- terminate with extreme prejudice */
  	if (!(MPPE_BITS(ibuf) & MPPE_BIT_ENCRYPTED)) {
  		printk(KERN_DEBUG
  		       "mppe_decompress[%d]: ENCRYPTED bit not set!
  ",
  		       state->unit);
  		state->sanity_errors += 100;
  		goto sanity_error;
  	}
  	if (!state->stateful && !flushed) {
  		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set in "
  		       "stateless mode!
  ", state->unit);
  		state->sanity_errors += 100;
  		goto sanity_error;
  	}
  	if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
  		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set on "
  		       "flag packet!
  ", state->unit);
  		state->sanity_errors += 100;
  		goto sanity_error;
  	}
  
  	/*
  	 * Check the coherency count.
  	 */
  
  	if (!state->stateful) {
  		/* Discard late packet */
  		if ((ccount - state->ccount) % MPPE_CCOUNT_SPACE
  						> MPPE_CCOUNT_SPACE / 2) {
  			state->sanity_errors++;
  			goto sanity_error;
  		}
  
  		/* 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 DECOMP_ERROR;
  			}
  		} else {
  			/* discard state */
  			if (!flushed) {
  				/* ccp.c will be silent (no additional CCP Reset-Requests). */
  				return DECOMP_ERROR;
  			} 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);
  	}
  
  	/*
  	 * Fill in the first part of the PPP header.  The protocol field
  	 * comes from the decrypted data.
  	 */
  	obuf[0] = PPP_ADDRESS(ibuf);	/* +1 */
  	obuf[1] = PPP_CONTROL(ibuf);	/* +1 */
  	obuf += 2;
  	ibuf += PPP_HDRLEN + MPPE_OVHD;
  	isize -= PPP_HDRLEN + MPPE_OVHD;	/* -6 */
  	/* net osize: isize-4 */
  
  	/*
  	 * Decrypt the first byte in order to check if it is
  	 * a compressed or uncompressed protocol field.
  	 */
  	sg_init_table(sg_in, 1);
  	sg_init_table(sg_out, 1);
  	setup_sg(sg_in, ibuf, 1);
  	setup_sg(sg_out, obuf, 1);
  	if (crypto_blkcipher_decrypt(&desc, sg_out, sg_in, 1) != 0) {
  		printk(KERN_DEBUG "crypto_cypher_decrypt failed
  ");
  		return DECOMP_ERROR;
  	}
  
  	/*
  	 * Do PFC decompression.
  	 * This would be nicer if we were given the actual sk_buff
  	 * instead of a char *.
  	 */
  	if ((obuf[0] & 0x01) != 0) {
  		obuf[1] = obuf[0];
  		obuf[0] = 0;
  		obuf++;
  		osize++;
  	}
  
  	/* And finally, decrypt the rest of the packet. */
  	setup_sg(sg_in, ibuf + 1, isize - 1);
  	setup_sg(sg_out, obuf + 1, osize - 1);
  	if (crypto_blkcipher_decrypt(&desc, sg_out, sg_in, isize - 1)) {
  		printk(KERN_DEBUG "crypto_cypher_decrypt failed
  ");
  		return DECOMP_ERROR;
  	}
  
  	state->stats.unc_bytes += osize;
  	state->stats.unc_packets++;
  	state->stats.comp_bytes += isize;
  	state->stats.comp_packets++;
  
  	/* good packet credit */
  	state->sanity_errors >>= 1;
  
  	return osize;
  
  sanity_error:
  	if (state->sanity_errors < SANITY_MAX)
  		return DECOMP_ERROR;
  	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.
  		 */
  		return DECOMP_FATALERROR;
  }
  
  /*
   * 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?)
   */
  static void mppe_incomp(void *arg, unsigned char *ibuf, int icnt)
  {
  	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
  
  	if (state->debug &&
  	    (PPP_PROTOCOL(ibuf) >= 0x0021 && PPP_PROTOCOL(ibuf) <= 0x00fa))
  		printk(KERN_DEBUG
  		       "mppe_incomp[%d]: incompressible (unencrypted) data! "
  		       "(proto %04x)
  ", state->unit, PPP_PROTOCOL(ibuf));
  
  	state->stats.inc_bytes += icnt;
  	state->stats.inc_packets++;
  	state->stats.unc_bytes += icnt;
  	state->stats.unc_packets++;
  }
  
  /*************************************************************
   * Module interface table
   *************************************************************/
  
  /*
   * Procedures exported to if_ppp.c.
   */
  static struct compressor ppp_mppe = {
  	.compress_proto = CI_MPPE,
  	.comp_alloc     = mppe_alloc,
  	.comp_free      = mppe_free,
  	.comp_init      = mppe_comp_init,
  	.comp_reset     = mppe_comp_reset,
  	.compress       = mppe_compress,
  	.comp_stat      = mppe_comp_stats,
  	.decomp_alloc   = mppe_alloc,
  	.decomp_free    = mppe_free,
  	.decomp_init    = mppe_decomp_init,
  	.decomp_reset   = mppe_decomp_reset,
  	.decompress     = mppe_decompress,
  	.incomp         = mppe_incomp,
  	.decomp_stat    = mppe_comp_stats,
  	.owner          = THIS_MODULE,
  	.comp_extra     = MPPE_PAD,
  };
  
  /*
   * ppp_mppe_init()
   *
   * Prior to allowing load, try to load the arc4 and sha1 crypto
   * libraries.  The actual use will be allocated later, but
   * this way the module will fail to insmod if they aren't available.
   */
  
  static int __init ppp_mppe_init(void)
  {
  	int answer;
  	if (!(crypto_has_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC) &&
  	      crypto_has_hash("sha1", 0, CRYPTO_ALG_ASYNC)))
  		return -ENODEV;
  
  	sha_pad = kmalloc(sizeof(struct sha_pad), GFP_KERNEL);
  	if (!sha_pad)
  		return -ENOMEM;
  	sha_pad_init(sha_pad);
  
  	answer = ppp_register_compressor(&ppp_mppe);
  
  	if (answer == 0)
  		printk(KERN_INFO "PPP MPPE Compression module registered
  ");
  	else
  		kfree(sha_pad);
  
  	return answer;
  }
  
  static void __exit ppp_mppe_cleanup(void)
  {
  	ppp_unregister_compressor(&ppp_mppe);
  	kfree(sha_pad);
  }
  
  module_init(ppp_mppe_init);
  module_exit(ppp_mppe_cleanup);