ppp_mppe.c

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/*
 * ppp_mppe.c - interface MPPE to the PPP code.
 * This version is for use with Linux kernel 2.6.14+
 *
 * By Frank Cusack <[email protected]>.
 * 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 <[email protected]>
 *                 Only need extra skb padding on transmit, not receive.
 *      06/18/04 - Matt Domsch <[email protected]>, Oleg Makarenko <[email protected]>
 *                 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 <[email protected]>");
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 };
    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)\n", 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\n", 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\n",
                   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\n");
        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;
    int sanity = 0;
    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)\n",
                   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)\n", 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\n",
               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!\n",
               state->unit);
        state->sanity_errors += 100;
        sanity = 1;
    }
    if (!state->stateful && !flushed) {
        printk(KERN_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) {
        printk(KERN_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 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;
    }

    /*
     * 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 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\n");
        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\n");
        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;
}

/*
 * 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)\n", 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\n");
    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);