chap.c

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/*
 * chap.c - Crytographic Handshake Authentication Protocol.
 *
 * Copyright (c) 1991 Gregory M. Christy.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by Gregory M. Christy.  The name of the author may not be used to
 * endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */


/*
 * TODO:
 */

#include <stdio.h>
#include <string.h>

#include "syslog.h"
#include "ppp.h"
#include "chap.h"
#include "md5.h"

#define BCOPY(p0, p1, n) memmove (p1, p0, n)

chap_state chap[NUM_PPP];		/* CHAP state; one for each unit */

static void ChapChallengeTimeout __P((caddr_t));
static void ChapResponseTimeout __P((caddr_t));
static void ChapReceiveChallenge __P((chap_state *, u_char *, u_char, int));
static void ChapReceiveResponse __P((chap_state *, u_char *, u_char, int));
static void ChapReceiveSuccess __P((chap_state *, u_char *, u_char, int));
static void ChapReceiveFailure __P((chap_state *, u_char *, u_char, int));
static void ChapSendStatus __P((chap_state *, int));
static void ChapSendChallenge __P((chap_state *));
static void ChapSendResponse __P((chap_state *));
static void ChapGenChallenge __P((chap_state *));
static void ChapRechallenge __P((caddr_t));

extern double drand48 __P((void));
extern void srand48 __P((long));

/*
 * ChapInit - Initialize a CHAP unit.
 */
void
ChapInit(unit)
    int unit;
{
    chap_state *cstate = &chap[unit];

    bzero(cstate, sizeof(*cstate));
    cstate->unit = unit;
    cstate->clientstate = CHAPCS_INITIAL;
    cstate->serverstate = CHAPSS_INITIAL;
    cstate->timeouttime = CHAP_DEFTIMEOUT;
    cstate->max_transmits = CHAP_DEFTRANSMITS;
    /* random number generator is initialized in magic_init */
}


/*
 * ChapAuthWithPeer - Authenticate us with our peer (start client).
 *
 */
void
ChapAuthWithPeer(unit, our_name, digest)
    int unit;
    char *our_name;
    int digest;
{
    chap_state *cstate = &chap[unit];

    cstate->resp_name = our_name;
    cstate->resp_type = digest;

    if (cstate->clientstate == CHAPCS_INITIAL ||
	cstate->clientstate == CHAPCS_PENDING) {
	/* lower layer isn't up - wait until later */
	cstate->clientstate = CHAPCS_PENDING;
	return;
    }

    /*
     * We get here as a result of LCP coming up.
     * So even if CHAP was open before, we will 
     * have to re-authenticate ourselves.
     */
    cstate->clientstate = CHAPCS_LISTEN;
}


/*
 * ChapAuthPeer - Authenticate our peer (start server).
 */
void
ChapAuthPeer(unit, our_name, digest)
    int unit;
    char *our_name;
    int digest;
{
    chap_state *cstate = &chap[unit];
  
    cstate->chal_name = our_name;
    cstate->chal_type = digest;

    if (cstate->serverstate == CHAPSS_INITIAL ||
	cstate->serverstate == CHAPSS_PENDING) {
	/* lower layer isn't up - wait until later */
	cstate->serverstate = CHAPSS_PENDING;
	return;
    }

    ChapGenChallenge(cstate);
    ChapSendChallenge(cstate);		/* crank it up dude! */
    cstate->serverstate = CHAPSS_INITIAL_CHAL;
}


/*
 * ChapChallengeTimeout - Timeout expired on sending challenge.
 */
static void
ChapChallengeTimeout(arg)
    caddr_t arg;
{
    chap_state *cstate = (chap_state *) arg;
  
    /* if we aren't sending challenges, don't worry.  then again we */
    /* probably shouldn't be here either */
    if (cstate->serverstate != CHAPSS_INITIAL_CHAL &&
	cstate->serverstate != CHAPSS_RECHALLENGE)
	return;

    if (cstate->chal_transmits >= cstate->max_transmits) {
	/* give up on peer */
	syslog(LOG_ERR, "Peer failed to respond to CHAP challenge");
	cstate->serverstate = CHAPSS_BADAUTH;
	auth_peer_fail(cstate->unit, PPP_CHAP);
	return;
    }

    ChapSendChallenge(cstate);		/* Re-send challenge */
}


/*
 * ChapResponseTimeout - Timeout expired on sending response.
 */
static void
ChapResponseTimeout(arg)
    caddr_t arg;
{
    chap_state *cstate = (chap_state *) arg;

    /* if we aren't sending a response, don't worry. */
    if (cstate->clientstate != CHAPCS_RESPONSE)
	return;

    ChapSendResponse(cstate);		/* re-send response */
}


/*
 * ChapRechallenge - Time to challenge the peer again.
 */
static void
ChapRechallenge(arg)
    caddr_t arg;
{
    chap_state *cstate = (chap_state *) arg;

    /* if we aren't sending a response, don't worry. */
    if (cstate->serverstate != CHAPSS_OPEN)
	return;

    ChapGenChallenge(cstate);
    ChapSendChallenge(cstate);
    cstate->serverstate = CHAPSS_RECHALLENGE;
}


/*
 * ChapLowerUp - The lower layer is up.
 *
 * Start up if we have pending requests.
 */
void
ChapLowerUp(unit)
    int unit;
{
    chap_state *cstate = &chap[unit];
  
    if (cstate->clientstate == CHAPCS_INITIAL)
	cstate->clientstate = CHAPCS_CLOSED;
    else if (cstate->clientstate == CHAPCS_PENDING)
	cstate->clientstate = CHAPCS_LISTEN;

    if (cstate->serverstate == CHAPSS_INITIAL)
	cstate->serverstate = CHAPSS_CLOSED;
    else if (cstate->serverstate == CHAPSS_PENDING) {
	ChapGenChallenge(cstate);
	ChapSendChallenge(cstate);
	cstate->serverstate = CHAPSS_INITIAL_CHAL;
    }
}


/*
 * ChapLowerDown - The lower layer is down.
 *
 * Cancel all timeouts.
 */
void
ChapLowerDown(unit)
    int unit;
{
    chap_state *cstate = &chap[unit];
  
    /* Timeout(s) pending?  Cancel if so. */
    if (cstate->serverstate == CHAPSS_INITIAL_CHAL ||
	cstate->serverstate == CHAPSS_RECHALLENGE)
	UNTIMEOUT(ChapChallengeTimeout, (caddr_t) cstate);
    else if (cstate->serverstate == CHAPSS_OPEN
	     && cstate->chal_interval != 0)
	UNTIMEOUT(ChapRechallenge, (caddr_t) cstate);
    if (cstate->clientstate == CHAPCS_RESPONSE)
	UNTIMEOUT(ChapResponseTimeout, (caddr_t) cstate);

    cstate->clientstate = CHAPCS_INITIAL;
    cstate->serverstate = CHAPSS_INITIAL;
}


/*
 * ChapProtocolReject - Peer doesn't grok CHAP.
 */
void
ChapProtocolReject(unit)
    int unit;
{
    chap_state *cstate = &chap[unit];

    if (cstate->serverstate != CHAPSS_INITIAL &&
	cstate->serverstate != CHAPSS_CLOSED)
	auth_peer_fail(unit, PPP_CHAP);
    if (cstate->clientstate != CHAPCS_INITIAL &&
	cstate->clientstate != CHAPCS_CLOSED)
	auth_withpeer_fail(unit, PPP_CHAP);
    ChapLowerDown(unit);		/* shutdown chap */
}


/*
 * ChapInput - Input CHAP packet.
 */
void
ChapInput(unit, inpacket, packet_len)
    int unit;
    u_char *inpacket;
    int packet_len;
{
    chap_state *cstate = &chap[unit];
    u_char *inp;
    u_char code, id;
    int len;
  
    /*
     * Parse header (code, id and length).
     * If packet too short, drop it.
     */
    inp = inpacket;
    if (packet_len < CHAP_HEADERLEN) {
	CHAPDEBUG((LOG_INFO, "ChapInput: rcvd short header."));
	return;
    }
    GETCHAR(code, inp);
    GETCHAR(id, inp);
    GETSHORT(len, inp);
    if (len < CHAP_HEADERLEN) {
	CHAPDEBUG((LOG_INFO, "ChapInput: rcvd illegal length."));
	return;
    }
    if (len > packet_len) {
	CHAPDEBUG((LOG_INFO, "ChapInput: rcvd short packet."));
	return;
    }
    len -= CHAP_HEADERLEN;
  
    /*
     * Action depends on code (as in fact it usually does :-).
     */
    switch (code) {
    case CHAP_CHALLENGE:
	ChapReceiveChallenge(cstate, inp, id, len);
	break;
    
    case CHAP_RESPONSE:
	ChapReceiveResponse(cstate, inp, id, len);
	break;
    
    case CHAP_FAILURE:
	ChapReceiveFailure(cstate, inp, id, len);
	break;

    case CHAP_SUCCESS:
	ChapReceiveSuccess(cstate, inp, id, len);
	break;

    default:				/* Need code reject? */
	syslog(LOG_WARNING, "Unknown CHAP code (%d) received.", code);
	break;
    }
}


/*
 * ChapReceiveChallenge - Receive Challenge and send Response.
 */
static void
ChapReceiveChallenge( chap_state *cstate, u_char *inp, u_char id, int len)
{
    int rchallenge_len;
    u_char *rchallenge;
    int secret_len;
    char secret[MAXSECRETLEN];
    char rhostname[256];
    MD5_CTX mdContext;
 
    CHAPDEBUG((LOG_INFO, "ChapReceiveChallenge: Rcvd id %d.", id));
    if (cstate->clientstate == CHAPCS_CLOSED ||
	cstate->clientstate == CHAPCS_PENDING) {
	CHAPDEBUG((LOG_INFO, "ChapReceiveChallenge: in state %d",
		   cstate->clientstate));
	return;
    }

    if (len < 2) {
	CHAPDEBUG((LOG_INFO, "ChapReceiveChallenge: rcvd short packet."));
	return;
    }

    GETCHAR(rchallenge_len, inp);
    len -= sizeof (u_char) + rchallenge_len;	/* now name field length */
    if (len < 0) {
	CHAPDEBUG((LOG_INFO, "ChapReceiveChallenge: rcvd short packet."));
	return;
    }
    rchallenge = inp;
    INCPTR(rchallenge_len, inp);

    if (len >= sizeof(rhostname))
	len = sizeof(rhostname) - 1;
    BCOPY(inp, rhostname, (size_t)len);
    rhostname[len] = '\000';

    CHAPDEBUG((LOG_INFO, "ChapReceiveChallenge: received name field: %s",
	       rhostname));

    /* get secret for authenticating ourselves with the specified host */
    if (!get_secret(cstate->unit,  rhostname, cstate->resp_name,
		    secret, (long *) &secret_len, 0)) {
	secret_len = 0;		/* assume null secret if can't find one */
	syslog(LOG_WARNING, "No CHAP secret found for authenticating us to %s",
	       rhostname);
    }

    /* cancel response send timeout if necessary */
    if (cstate->clientstate == CHAPCS_RESPONSE)
	UNTIMEOUT(ChapResponseTimeout, (caddr_t) cstate);

    cstate->resp_id = id;
    cstate->resp_transmits = 0;

    /*  generate MD based on negotiated type */
    switch (cstate->resp_type) { 

    case CHAP_DIGEST_MD5:		/* only MD5 is defined for now */
	MD5Init(&mdContext);
	MD5Update(&mdContext, &cstate->resp_id, (unsigned int) 1);
	MD5Update(&mdContext, (u_char *)secret, (unsigned int) secret_len);
	MD5Update(&mdContext, rchallenge, (unsigned int) rchallenge_len);
	MD5Final(&mdContext);
	BCOPY(mdContext.digest, cstate->response, MD5_SIGNATURE_SIZE);
	cstate->resp_length = MD5_SIGNATURE_SIZE;