/*      $OpenBSD: fsm.c,v 1.9 2024/08/09 05:16:13 deraadt Exp $ */

/*
 * fsm.c - {Link, IP} Control Protocol Finite State Machine.
 *
 * Copyright (c) 1984-2000 Carnegie Mellon University. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Office of Technology Transfer
 *      Carnegie Mellon University
 *      5000 Forbes Avenue
 *      Pittsburgh, PA  15213-3890
 *      (412) 268-4387, fax: (412) 268-7395
 *      tech-transfer@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * TODO:
 * Randomize fsm id on link/init.
 * Deal with variable outgoing MTU.
 */

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <syslog.h>

#include "pppd.h"
#include "fsm.h"

static void fsm_timeout(void *);
static void fsm_rconfreq(fsm *, int, u_char *, int);
static void fsm_rconfack(fsm *, int, u_char *, int);
static void fsm_rconfnakrej(fsm *, int, int, u_char *, int);
static void fsm_rtermreq(fsm *, int, u_char *, int);
static void fsm_rtermack(fsm *);
static void fsm_rcoderej(fsm *, u_char *, int);
static void fsm_sconfreq(fsm *, int);

#define PROTO_NAME(f)   ((f)->callbacks->proto_name)

int peer_mru[NUM_PPP];


/*
 * fsm_init - Initialize fsm.
 *
 * Initialize fsm state.
 */
void
fsm_init(fsm *f)
{
    f->state = INITIAL;
    f->flags = 0;
    f->id = 0;                          /* XXX Start with random id? */
    f->timeouttime = DEFTIMEOUT;
    f->maxconfreqtransmits = DEFMAXCONFREQS;
    f->maxtermtransmits = DEFMAXTERMREQS;
    f->maxnakloops = DEFMAXNAKLOOPS;
    f->term_reason_len = 0;
}


/*
 * fsm_lowerup - The lower layer is up.
 */
void
fsm_lowerup(fsm *f)
{
    switch( f->state ){
    case INITIAL:
        f->state = CLOSED;
        break;

    case STARTING:
        if( f->flags & OPT_SILENT )
            f->state = STOPPED;
        else {
            /* Send an initial configure-request */
            fsm_sconfreq(f, 0);
            f->state = REQSENT;
        }
        break;

    default:
        FSMDEBUG((LOG_INFO, "%s: Up event in state %d!",
                  PROTO_NAME(f), f->state));
    }
}


/*
 * fsm_lowerdown - The lower layer is down.
 *
 * Cancel all timeouts and inform upper layers.
 */
void
fsm_lowerdown(fsm *f)
{
    switch( f->state ){
    case CLOSED:
        f->state = INITIAL;
        break;

    case STOPPED:
        f->state = STARTING;
        if( f->callbacks->starting )
            (*f->callbacks->starting)(f);
        break;

    case CLOSING:
        f->state = INITIAL;
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        break;

    case STOPPING:
    case REQSENT:
    case ACKRCVD:
    case ACKSENT:
        f->state = STARTING;
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        break;

    case OPENED:
        if( f->callbacks->down )
            (*f->callbacks->down)(f);
        f->state = STARTING;
        break;

    default:
        FSMDEBUG((LOG_INFO, "%s: Down event in state %d!",
                  PROTO_NAME(f), f->state));
    }
}


/*
 * fsm_open - Link is allowed to come up.
 */
void
fsm_open(fsm *f)
{
    switch( f->state ){
    case INITIAL:
        f->state = STARTING;
        if( f->callbacks->starting )
            (*f->callbacks->starting)(f);
        break;

    case CLOSED:
        if( f->flags & OPT_SILENT )
            f->state = STOPPED;
        else {
            /* Send an initial configure-request */
            fsm_sconfreq(f, 0);
            f->state = REQSENT;
        }
        break;

    case CLOSING:
        f->state = STOPPING;
        /* fall through */
    case STOPPED:
    case OPENED:
        if( f->flags & OPT_RESTART ){
            fsm_lowerdown(f);
            fsm_lowerup(f);
        }
        break;
    }
}


/*
 * fsm_close - Start closing connection.
 *
 * Cancel timeouts and either initiate close or possibly go directly to
 * the CLOSED state.
 */
void
fsm_close(fsm *f, char *reason)
{
    f->term_reason = reason;
    f->term_reason_len = (reason == NULL? 0: strlen(reason));
    switch( f->state ){
    case STARTING:
        f->state = INITIAL;
        break;
    case STOPPED:
        f->state = CLOSED;
        break;
    case STOPPING:
        f->state = CLOSING;
        break;

    case REQSENT:
    case ACKRCVD:
    case ACKSENT:
    case OPENED:
        if( f->state != OPENED )
            UNTIMEOUT(fsm_timeout, f);  /* Cancel timeout */
        else if( f->callbacks->down )
            (*f->callbacks->down)(f);   /* Inform upper layers we're down */

        /* Init restart counter, send Terminate-Request */
        f->retransmits = f->maxtermtransmits;
        fsm_sdata(f, TERMREQ, f->reqid = ++f->id,
                  (u_char *) f->term_reason, f->term_reason_len);
        TIMEOUT(fsm_timeout, f, f->timeouttime);
        --f->retransmits;

        f->state = CLOSING;
        break;
    }
}


/*
 * fsm_timeout - Timeout expired.
 */
static void
fsm_timeout(void *arg)
{
    fsm *f = (fsm *) arg;

    switch (f->state) {
    case CLOSING:
    case STOPPING:
        if( f->retransmits <= 0 ){
            /*
             * We've waited for an ack long enough.  Peer probably heard us.
             */
            f->state = (f->state == CLOSING)? CLOSED: STOPPED;
            if( f->callbacks->finished )
                (*f->callbacks->finished)(f);
        } else {
            /* Send Terminate-Request */
            fsm_sdata(f, TERMREQ, f->reqid = ++f->id,
                      (u_char *) f->term_reason, f->term_reason_len);
            TIMEOUT(fsm_timeout, f, f->timeouttime);
            --f->retransmits;
        }
        break;

    case REQSENT:
    case ACKRCVD:
    case ACKSENT:
        if (f->retransmits <= 0) {
            syslog(LOG_WARNING, "%s: timeout sending Config-Requests",
                   PROTO_NAME(f));
            f->state = STOPPED;
            if( (f->flags & OPT_PASSIVE) == 0 && f->callbacks->finished )
                (*f->callbacks->finished)(f);

        } else {
            /* Retransmit the configure-request */
            if (f->callbacks->retransmit)
                (*f->callbacks->retransmit)(f);
            fsm_sconfreq(f, 1);         /* Re-send Configure-Request */
            if( f->state == ACKRCVD )
                f->state = REQSENT;
        }
        break;

    default:
        FSMDEBUG((LOG_INFO, "%s: Timeout event in state %d!",
                  PROTO_NAME(f), f->state));
    }
}


/*
 * fsm_input - Input packet.
 */
void
fsm_input(fsm *f, u_char *inpacket, int l)
{
    u_char *inp;
    u_char code, id;
    int len;

    /*
     * Parse header (code, id and length).
     * If packet too short, drop it.
     */
    inp = inpacket;
    if (l < HEADERLEN) {
        FSMDEBUG((LOG_WARNING, "fsm_input(%x): Rcvd short header.",
                  f->protocol));
        return;
    }
    GETCHAR(code, inp);
    GETCHAR(id, inp);
    GETSHORT(len, inp);
    if (len < HEADERLEN) {
        FSMDEBUG((LOG_INFO, "fsm_input(%x): Rcvd illegal length.",
                  f->protocol));
        return;
    }
    if (len > l) {
        FSMDEBUG((LOG_INFO, "fsm_input(%x): Rcvd short packet.",
                  f->protocol));
        return;
    }
    len -= HEADERLEN;           /* subtract header length */

    if( f->state == INITIAL || f->state == STARTING ){
        FSMDEBUG((LOG_INFO, "fsm_input(%x): Rcvd packet in state %d.",
                  f->protocol, f->state));
        return;
    }

    /*
     * Action depends on code.
     */
    switch (code) {
    case CONFREQ:
        fsm_rconfreq(f, id, inp, len);
        break;
    
    case CONFACK:
        fsm_rconfack(f, id, inp, len);
        break;
    
    case CONFNAK:
    case CONFREJ:
        fsm_rconfnakrej(f, code, id, inp, len);
        break;
    
    case TERMREQ:
        fsm_rtermreq(f, id, inp, len);
        break;
    
    case TERMACK:
        fsm_rtermack(f);
        break;
    
    case CODEREJ:
        fsm_rcoderej(f, inp, len);
        break;
    
    default:
        if( !f->callbacks->extcode
           || !(*f->callbacks->extcode)(f, code, id, inp, len) )
            fsm_sdata(f, CODEREJ, ++f->id, inpacket, len + HEADERLEN);
        break;
    }
}


/*
 * fsm_rconfreq - Receive Configure-Request.
 */
static void
fsm_rconfreq(fsm *f, int id, u_char *inp, int len)
{
    int code, reject_if_disagree;

    FSMDEBUG((LOG_INFO, "fsm_rconfreq(%s): Rcvd id %d.", PROTO_NAME(f), id));
    switch( f->state ){
    case CLOSED:
        /* Go away, we're closed */
        fsm_sdata(f, TERMACK, id, NULL, 0);
        return;
    case CLOSING:
    case STOPPING:
        return;

    case OPENED:
        /* Go down and restart negotiation */
        if( f->callbacks->down )
            (*f->callbacks->down)(f);   /* Inform upper layers */
        fsm_sconfreq(f, 0);             /* Send initial Configure-Request */
        break;

    case STOPPED:
        /* Negotiation started by our peer */
        fsm_sconfreq(f, 0);             /* Send initial Configure-Request */
        f->state = REQSENT;
        break;
    }

    /*
     * Pass the requested configuration options
     * to protocol-specific code for checking.
     */
    if (f->callbacks->reqci){           /* Check CI */
        reject_if_disagree = (f->nakloops >= f->maxnakloops);
        code = (*f->callbacks->reqci)(f, inp, &len, reject_if_disagree);
    } else if (len)
        code = CONFREJ;                 /* Reject all CI */
    else
        code = CONFACK;

    /* send the Ack, Nak or Rej to the peer */
    fsm_sdata(f, code, id, inp, len);

    if (code == CONFACK) {
        if (f->state == ACKRCVD) {
            UNTIMEOUT(fsm_timeout, f);  /* Cancel timeout */
            f->state = OPENED;
            if (f->callbacks->up)
                (*f->callbacks->up)(f); /* Inform upper layers */
        } else
            f->state = ACKSENT;
        f->nakloops = 0;

    } else {
        /* we sent CONFACK or CONFREJ */
        if (f->state != ACKRCVD)
            f->state = REQSENT;
        if( code == CONFNAK )
            ++f->nakloops;
    }
}


/*
 * fsm_rconfack - Receive Configure-Ack.
 */
static void
fsm_rconfack(fsm *f, int id, u_char *inp, int len)
{
    FSMDEBUG((LOG_INFO, "fsm_rconfack(%s): Rcvd id %d.",
              PROTO_NAME(f), id));

    if (id != f->reqid || f->seen_ack)          /* Expected id? */
        return;                                 /* Nope, toss... */
    if( !(f->callbacks->ackci? (*f->callbacks->ackci)(f, inp, len):
          (len == 0)) ){
        /* Ack is bad - ignore it */
        log_packet(inp, len, "Received bad configure-ack: ", LOG_ERR);
        FSMDEBUG((LOG_INFO, "%s: received bad Ack (length %d)",
                  PROTO_NAME(f), len));
        return;
    }
    f->seen_ack = 1;

    switch (f->state) {
    case CLOSED:
    case STOPPED:
        fsm_sdata(f, TERMACK, id, NULL, 0);
        break;

    case REQSENT:
        f->state = ACKRCVD;
        f->retransmits = f->maxconfreqtransmits;
        break;

    case ACKRCVD:
        /* Huh? an extra valid Ack? oh well... */
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        fsm_sconfreq(f, 0);
        f->state = REQSENT;
        break;

    case ACKSENT:
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        f->state = OPENED;
        f->retransmits = f->maxconfreqtransmits;
        if (f->callbacks->up)
            (*f->callbacks->up)(f);     /* Inform upper layers */
        break;

    case OPENED:
        /* Go down and restart negotiation */
        if (f->callbacks->down)
            (*f->callbacks->down)(f);   /* Inform upper layers */
        fsm_sconfreq(f, 0);             /* Send initial Configure-Request */
        f->state = REQSENT;
        break;
    }
}


/*
 * fsm_rconfnakrej - Receive Configure-Nak or Configure-Reject.
 */
static void
fsm_rconfnakrej(fsm *f, int code, int id, u_char *inp, int len)
{
    int (*proc)(fsm *, u_char *, int);
    int ret;

    FSMDEBUG((LOG_INFO, "fsm_rconfnakrej(%s): Rcvd id %d.",
              PROTO_NAME(f), id));

    if (id != f->reqid || f->seen_ack)  /* Expected id? */
        return;                         /* Nope, toss... */
    proc = (code == CONFNAK)? f->callbacks->nakci: f->callbacks->rejci;
    if (!proc || !(ret = proc(f, inp, len))) {
        /* Nak/reject is bad - ignore it */
        log_packet(inp, len, "Received bad configure-nak/rej: ", LOG_ERR);
        FSMDEBUG((LOG_INFO, "%s: received bad %s (length %d)",
                  PROTO_NAME(f), (code==CONFNAK? "Nak": "reject"), len));
        return;
    }
    f->seen_ack = 1;

    switch (f->state) {
    case CLOSED:
    case STOPPED:
        fsm_sdata(f, TERMACK, id, NULL, 0);
        break;

    case REQSENT:
    case ACKSENT:
        /* They didn't agree to what we wanted - try another request */
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        if (ret < 0)
            f->state = STOPPED;         /* kludge for stopping CCP */
        else
            fsm_sconfreq(f, 0);         /* Send Configure-Request */
        break;

    case ACKRCVD:
        /* Got a Nak/reject when we had already had an Ack?? oh well... */
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        fsm_sconfreq(f, 0);
        f->state = REQSENT;
        break;

    case OPENED:
        /* Go down and restart negotiation */
        if (f->callbacks->down)
            (*f->callbacks->down)(f);   /* Inform upper layers */
        fsm_sconfreq(f, 0);             /* Send initial Configure-Request */
        f->state = REQSENT;
        break;
    }
}


/*
 * fsm_rtermreq - Receive Terminate-Req.
 */
static void
fsm_rtermreq(fsm *f, int id, u_char *p, int len)
{
    char str[80];

    FSMDEBUG((LOG_INFO, "fsm_rtermreq(%s): Rcvd id %d.",
              PROTO_NAME(f), id));

    switch (f->state) {
    case ACKRCVD:
    case ACKSENT:
        f->state = REQSENT;             /* Start over but keep trying */
        break;

    case OPENED:
        if (len > 0) {
            fmtmsg(str, sizeof(str), "%0.*v", len, p);
            syslog(LOG_INFO, "%s terminated by peer (%s)", PROTO_NAME(f), str);
        } else
            syslog(LOG_INFO, "%s terminated by peer", PROTO_NAME(f));
        if (f->callbacks->down)
            (*f->callbacks->down)(f);   /* Inform upper layers */
        f->retransmits = 0;
        f->state = STOPPING;
        TIMEOUT(fsm_timeout, f, f->timeouttime);
        break;
    }

    fsm_sdata(f, TERMACK, id, NULL, 0);
}


/*
 * fsm_rtermack - Receive Terminate-Ack.
 */
static void
fsm_rtermack(fsm *f)
{
    FSMDEBUG((LOG_INFO, "fsm_rtermack(%s).", PROTO_NAME(f)));

    switch (f->state) {
    case CLOSING:
        UNTIMEOUT(fsm_timeout, f);
        f->state = CLOSED;
        if( f->callbacks->finished )
            (*f->callbacks->finished)(f);
        break;
    case STOPPING:
        UNTIMEOUT(fsm_timeout, f);
        f->state = STOPPED;
        if( f->callbacks->finished )
            (*f->callbacks->finished)(f);
        break;

    case ACKRCVD:
        f->state = REQSENT;
        break;

    case OPENED:
        if (f->callbacks->down)
            (*f->callbacks->down)(f);   /* Inform upper layers */
        fsm_sconfreq(f, 0);
        break;
    }
}


/*
 * fsm_rcoderej - Receive an Code-Reject.
 */
static void
fsm_rcoderej(fsm *f, u_char *inp, int len)
{
    u_char code, id;

    FSMDEBUG((LOG_INFO, "fsm_rcoderej(%s).", PROTO_NAME(f)));

    if (len < HEADERLEN) {
        FSMDEBUG((LOG_INFO, "fsm_rcoderej: Rcvd short Code-Reject packet!"));
        return;
    }
    GETCHAR(code, inp);
    GETCHAR(id, inp);
    syslog(LOG_WARNING, "%s: Rcvd Code-Reject for code %d, id %d",
           PROTO_NAME(f), code, id);

    if( f->state == ACKRCVD )
        f->state = REQSENT;
}


/*
 * fsm_protreject - Peer doesn't speak this protocol.
 *
 * Treat this as a catastrophic error (RXJ-).
 */
void
fsm_protreject(fsm *f)
{
    switch( f->state ){
    case CLOSING:
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        /* fall through */
    case CLOSED:
        f->state = CLOSED;
        if( f->callbacks->finished )
            (*f->callbacks->finished)(f);
        break;

    case STOPPING:
    case REQSENT:
    case ACKRCVD:
    case ACKSENT:
        UNTIMEOUT(fsm_timeout, f);      /* Cancel timeout */
        /* fall through */
    case STOPPED:
        f->state = STOPPED;
        if( f->callbacks->finished )
            (*f->callbacks->finished)(f);
        break;

    case OPENED:
        if( f->callbacks->down )
            (*f->callbacks->down)(f);

        /* Init restart counter, send Terminate-Request */
        f->retransmits = f->maxtermtransmits;
        fsm_sdata(f, TERMREQ, f->reqid = ++f->id,
                  (u_char *) f->term_reason, f->term_reason_len);
        TIMEOUT(fsm_timeout, f, f->timeouttime);
        --f->retransmits;

        f->state = STOPPING;
        break;

    default:
        FSMDEBUG((LOG_INFO, "%s: Protocol-reject event in state %d!",
                  PROTO_NAME(f), f->state));
    }
}


/*
 * fsm_sconfreq - Send a Configure-Request.
 */
static void
fsm_sconfreq(fsm *f, int retransmit)
{
    u_char *outp;
    int cilen;

    if( f->state != REQSENT && f->state != ACKRCVD && f->state != ACKSENT ){
        /* Not currently negotiating - reset options */
        if( f->callbacks->resetci )
            (*f->callbacks->resetci)(f);
        f->nakloops = 0;
    }

    if( !retransmit ){
        /* New request - reset retransmission counter, use new ID */
        f->retransmits = f->maxconfreqtransmits;
        f->reqid = ++f->id;
    }

    f->seen_ack = 0;

    /*
     * Make up the request packet
     */
    outp = outpacket_buf + PPP_HDRLEN + HEADERLEN;
    if( f->callbacks->cilen && f->callbacks->addci ){
        cilen = (*f->callbacks->cilen)(f);
        if( cilen > peer_mru[f->unit] - HEADERLEN )
            cilen = peer_mru[f->unit] - HEADERLEN;
        if (f->callbacks->addci)
            (*f->callbacks->addci)(f, outp, &cilen);
    } else
        cilen = 0;

    /* send the request to our peer */
    fsm_sdata(f, CONFREQ, f->reqid, outp, cilen);

    /* start the retransmit timer */
    --f->retransmits;
    TIMEOUT(fsm_timeout, f, f->timeouttime);

    FSMDEBUG((LOG_INFO, "%s: sending Configure-Request, id %d",
              PROTO_NAME(f), f->reqid));
}


/*
 * fsm_sdata - Send some data.
 *
 * Used for all packets sent to our peer by this module.
 */
void
fsm_sdata(fsm *f, int code, int id, u_char *data, int datalen)
{
    u_char *outp;
    int outlen;

    /* Adjust length to be smaller than MTU */
    outp = outpacket_buf;
    if (datalen > peer_mru[f->unit] - HEADERLEN)
        datalen = peer_mru[f->unit] - HEADERLEN;
    if (datalen && data != outp + PPP_HDRLEN + HEADERLEN)
        BCOPY(data, outp + PPP_HDRLEN + HEADERLEN, datalen);
    outlen = datalen + HEADERLEN;
    MAKEHEADER(outp, f->protocol);
    PUTCHAR(code, outp);
    PUTCHAR(id, outp);
    PUTSHORT(outlen, outp);
    output(f->unit, outpacket_buf, outlen + PPP_HDRLEN);

    FSMDEBUG((LOG_INFO, "fsm_sdata(%s): Sent code %d, id %d.",
              PROTO_NAME(f), code, id));
}