source: S-port/trunk/Middlewares/Third_Party/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 "netif/ppp/ppp_opts.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"
#include "netif/ppp/pppcrypt.h"

#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)
{
        lwip_sha1_context sha1_ctx;
        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.
         */
        lwip_sha1_init(&sha1_ctx);
        lwip_sha1_starts(&sha1_ctx);
        lwip_sha1_update(&sha1_ctx, state->master_key, state->keylen);
        lwip_sha1_update(&sha1_ctx, mppe_sha1_pad1, SHA1_PAD_SIZE);
        lwip_sha1_update(&sha1_ctx, state->session_key, state->keylen);
        lwip_sha1_update(&sha1_ctx, mppe_sha1_pad2, SHA1_PAD_SIZE);
        lwip_sha1_finish(&sha1_ctx, sha1_digest);
        lwip_sha1_free(&sha1_ctx);
        MEMCPY(state->session_key, sha1_digest, state->keylen);

        if (!initial_key) {
                lwip_arc4_init(&state->arc4);
                lwip_arc4_setup(&state->arc4, sha1_digest, state->keylen);
                lwip_arc4_crypt(&state->arc4, state->session_key, state->keylen);
                lwip_arc4_free(&state->arc4);
        }
        if (state->keylen == 8) {
                /* See RFC 3078 */
                state->session_key[0] = 0xd1;
                state->session_key[1] = 0x26;
                state->session_key[2] = 0x9e;
        }
        lwip_arc4_init(&state->arc4);
        lwip_arc4_setup(&state->arc4, state->session_key, state->keylen);
}

/*
 * Set key, used by MSCHAP before mppe_init() is actually called by CCP so we
 * don't have to keep multiple copies of keys.
 */
void mppe_set_key(ppp_pcb *pcb, ppp_mppe_state *state, u8_t *key) {
        LWIP_UNUSED_ARG(pcb);
        MEMCPY(state->master_key, key, MPPE_MAX_KEY_LEN);
}

/*
 * Initialize (de)compressor state.
 */
void
mppe_init(ppp_pcb *pcb, ppp_mppe_state *state, u8_t options)
{
#if PPP_DEBUG
        const u8_t *debugstr = (const u8_t*)"mppe_comp_init";
        if (&pcb->mppe_decomp == state) {
            debugstr = (const u8_t*)"mppe_decomp_init";
        }
#endif /* PPP_DEBUG */

        /* Save keys. */
        MEMCPY(state->session_key, state->master_key, sizeof(state->master_key));

        if (options & MPPE_OPT_128)
                state->keylen = 16;
        else if (options & MPPE_OPT_40)
                state->keylen = 8;
        else {
                PPPDEBUG(LOG_DEBUG, ("%s[%d]: unknown key length\n", debugstr,
                        pcb->netif->num));
                lcp_close(pcb, "MPPE required but peer negotiation failed");
                return;
        }
        if (options & MPPE_OPT_STATEFUL)
                state->stateful = 1;

        /* Generate the initial session key. */
        mppe_rekey(state, 1);

#if PPP_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, pcb->netif->num, (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, pcb->netif->num, mkey, skey));
        }
#endif /* PPP_DEBUG */

        /*
         * 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;
}

/*
 * 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_pcb *pcb, ppp_mppe_state *state)
{
        LWIP_UNUSED_ARG(pcb);
        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_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb, u16_t protocol)
{
        struct pbuf *n, *np;
        u8_t *pl;
        err_t err;

        LWIP_UNUSED_ARG(pcb);

        /* TCP stack requires that we don't change the packet payload, therefore we copy
         * the whole packet before encryption.
         */
        np = pbuf_alloc(PBUF_RAW, MPPE_OVHD + sizeof(protocol) + (*pb)->tot_len, PBUF_RAM);
        if (!np) {
                return ERR_MEM;
        }

        /* Hide MPPE header + protocol */
        pbuf_remove_header(np, MPPE_OVHD + sizeof(protocol));

        if ((err = pbuf_copy(np, *pb)) != ERR_OK) {
                pbuf_free(np);
                return err;
        }

        /* Reveal MPPE header + protocol */
        pbuf_add_header(np, MPPE_OVHD + sizeof(protocol));

        *pb = np;
        pl = (u8_t*)np->payload;

        state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
        PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: ccount %d\n", pcb->netif->num, 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->stateful) {
                        PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: rekeying\n", pcb->netif->num));
                }
                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 protocol */
        /* FIXME: add PFC support */
        pl[0] = protocol >> 8;
        pl[1] = protocol;

        /* Hide MPPE header */
        pbuf_remove_header(np, MPPE_OVHD);

        /* Encrypt packet */
        for (n = np; n != NULL; n = n->next) {
                lwip_arc4_crypt(&state->arc4, (u8_t*)n->payload, n->len);
                if (n->tot_len == n->len) {
                        break;
                }
        }

        /* Reveal MPPE header */
        pbuf_add_header(np, MPPE_OVHD);

        return ERR_OK;
}

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

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

        /* MPPE Header */
        if (n0->len < MPPE_OVHD) {
                PPPDEBUG(LOG_DEBUG,
                       ("mppe_decompress[%d]: short pkt (%d)\n",
                       pcb->netif->num, n0->len));
                state->sanity_errors += 100;
                goto sanity_error;
        }

        pl = (u8_t*)n0->payload;
        flushed = MPPE_BITS(pl) & MPPE_BIT_FLUSHED;
        ccount = MPPE_CCOUNT(pl);
        PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: ccount %d\n",
               pcb->netif->num, 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",
                       pcb->netif->num));
                state->sanity_errors += 100;
                goto sanity_error;
        }
        if (!state->stateful && !flushed) {
                PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set in "
                       "stateless mode!\n", pcb->netif->num));
                state->sanity_errors += 100;
                goto sanity_error;
        }
        if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
                PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set on "
                       "flag packet!\n", pcb->netif->num));
                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;
                                ccp_resetrequest(pcb);
                                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_remove_header(n0, MPPE_OVHD);

        /* Decrypt the packet. */
        for (n = n0; n != NULL; n = n->next) {
                lwip_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;

sanity_error:
        if (state->sanity_errors >= SANITY_MAX) {
                /*
                 * 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.
                 */
                lcp_close(pcb, "Too many MPPE errors");
        }
        return ERR_BUF;
}

#endif /* PPP_SUPPORT && MPPE_SUPPORT */