/*      $OpenBSD: demand.c,v 1.13 2024/08/10 05:32:28 jsg Exp $ */

/*
 * demand.c - Support routines for demand-dialling.
 *
 * Copyright (c) 1989-2002 Paul Mackerras. 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(s) of the authors of this software must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission.
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Paul Mackerras
 *     <paulus@samba.org>".
 *
 * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL THE AUTHORS 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.
 */

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/socket.h>
#ifdef PPP_FILTER
#include <net/if.h>
#include <net/bpf.h>
#include <pcap.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <syslog.h>

#include "pppd.h"
#include "fsm.h"
#include "ipcp.h"
#include "lcp.h"

char *frame;
int framelen;
int framemax;
int escape_flag;
int flush_flag;
int fcs;

struct packet {
    int length;
    struct packet *next;
    unsigned char data[1];
};

struct packet *pend_q;
struct packet *pend_qtail;

static int active_packet(unsigned char *, int);

/*
 * demand_conf - configure the interface for doing dial-on-demand.
 */
void
demand_conf(void)
{
    int i;
    struct protent *protp;

/*    framemax = lcp_allowoptions[0].mru;
    if (framemax < PPP_MRU) */
        framemax = PPP_MRU;
    framemax += PPP_HDRLEN + PPP_FCSLEN;
    frame = malloc(framemax);
    if (frame == NULL)
        novm("demand frame");
    framelen = 0;
    pend_q = NULL;
    escape_flag = 0;
    flush_flag = 0;
    fcs = PPP_INITFCS;

    ppp_send_config(0, PPP_MRU, (u_int32_t) 0, 0, 0);
    ppp_recv_config(0, PPP_MRU, (u_int32_t) 0, 0, 0);

#ifdef PPP_FILTER
    set_filters(&pass_filter, &active_filter);
#endif

    /*
     * Call the demand_conf procedure for each protocol that's got one.
     */
    for (i = 0; (protp = protocols[i]) != NULL; ++i)
        if (protp->enabled_flag && protp->demand_conf != NULL)
            if (!((*protp->demand_conf)(0)))
                die(1);
}

/*
 * demand_drop - set each network protocol to discard packets
 * without an error.
 */
void
demand_drop(void)
{
    struct packet *pkt, *nextpkt;
    int i;
    struct protent *protp;

    for (i = 0; (protp = protocols[i]) != NULL; ++i)
        if (protp->enabled_flag && protp->demand_conf != NULL)
            sifnpmode(0, protp->protocol & ~0x8000, NPMODE_DROP);
    get_loop_output();

    /* discard all saved packets */
    for (pkt = pend_q; pkt != NULL; pkt = nextpkt) {
        nextpkt = pkt->next;
        free(pkt);
    }
    pend_q = NULL;
    framelen = 0;
    flush_flag = 0;
    escape_flag = 0;
    fcs = PPP_INITFCS;
}

/*
 * demand_unblock - set each enabled network protocol to pass packets.
 */
void
demand_unblock(void)
{
    int i;
    struct protent *protp;

    for (i = 0; (protp = protocols[i]) != NULL; ++i)
        if (protp->enabled_flag && protp->demand_conf != NULL)
            sifnpmode(0, protp->protocol & ~0x8000, NPMODE_PASS);
}

/*
 * FCS lookup table as calculated by genfcstab.
 */
static u_short fcstab[256] = {
        0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
        0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
        0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
        0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
        0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
        0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
        0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
        0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
        0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
        0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
        0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
        0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
        0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
        0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
        0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
        0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
        0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
        0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
        0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
        0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
        0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
        0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
        0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
        0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
        0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
        0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
        0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
        0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
        0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
        0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
        0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
        0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

/*
 * loop_chars - process characters received from the loopback.
 * Calls loop_frame when a complete frame has been accumulated.
 * Return value is 1 if we need to bring up the link, 0 otherwise.
 */
int
loop_chars(unsigned char *p, int n)
{
    int c, rv;

    rv = 0;
    for (; n > 0; --n) {
        c = *p++;
        if (c == PPP_FLAG) {
            if (!escape_flag && !flush_flag
                && framelen > 2 && fcs == PPP_GOODFCS) {
                framelen -= 2;
                if (loop_frame(frame, framelen))
                    rv = 1;
            }
            framelen = 0;
            flush_flag = 0;
            escape_flag = 0;
            fcs = PPP_INITFCS;
            continue;
        }
        if (flush_flag)
            continue;
        if (escape_flag) {
            c ^= PPP_TRANS;
            escape_flag = 0;
        } else if (c == PPP_ESCAPE) {
            escape_flag = 1;
            continue;
        }
        if (framelen >= framemax) {
            flush_flag = 1;
            continue;
        }
        frame[framelen++] = c;
        fcs = PPP_FCS(fcs, c);
    }
    return rv;
}

/*
 * loop_frame - given a frame obtained from the loopback,
 * decide whether to bring up the link or not, and, if we want
 * to transmit this frame later, put it on the pending queue.
 * Return value is 1 if we need to bring up the link, 0 otherwise.
 * We assume that the kernel driver has already applied the
 * pass_filter, so we won't get packets it rejected.
 * We apply the active_filter to see if we want this packet to
 * bring up the link.
 */
int
loop_frame(unsigned char *frame, int len)
{
    struct packet *pkt;

    /* log_packet(frame, len, "from loop: ", LOG_DEBUG); */
    if (len < PPP_HDRLEN)
        return 0;
    if ((PPP_PROTOCOL(frame) & 0x8000) != 0)
        return 0;               /* shouldn't get any of these anyway */
    if (!active_packet(frame, len))
        return 0;

    pkt = (struct packet *) malloc(sizeof(struct packet) + len);
    if (pkt != NULL) {
        pkt->length = len;
        pkt->next = NULL;
        memcpy(pkt->data, frame, len);
        if (pend_q == NULL)
            pend_q = pkt;
        else
            pend_qtail->next = pkt;
        pend_qtail = pkt;
    }
    return 1;
}

/*
 * demand_rexmit - Resend all those frames which we got via the
 * loopback, now that the real serial link is up.
 */
void
demand_rexmit(int proto)
{
    struct packet *pkt, *prev, *nextpkt;

    prev = NULL;
    pkt = pend_q;
    pend_q = NULL;
    for (; pkt != NULL; pkt = nextpkt) {
        nextpkt = pkt->next;
        if (PPP_PROTOCOL(pkt->data) == proto) {
            output(0, pkt->data, pkt->length);
            free(pkt);
        } else {
            if (prev == NULL)
                pend_q = pkt;
            else
                prev->next = pkt;
            prev = pkt;
        }
    }
    pend_qtail = prev;
    if (prev != NULL)
        prev->next = NULL;
}

/*
 * Scan a packet to decide whether it is an "active" packet,
 * that is, whether it is worth bringing up the link for.
 */
static int
active_packet(unsigned char *p, int len)
{
    int proto, i;
    struct protent *protp;

    if (len < PPP_HDRLEN)
        return 0;
    proto = PPP_PROTOCOL(p);
#ifdef PPP_FILTER
    if (active_filter.bf_len != 0
        && bpf_filter(active_filter.bf_insns, frame, len, len) == 0)
        return 0;
#endif
    for (i = 0; (protp = protocols[i]) != NULL; ++i) {
        if (protp->protocol < 0xC000 && (protp->protocol & ~0x8000) == proto) {
            if (!protp->enabled_flag)
                return 0;
            if (protp->active_pkt == NULL)
                return 1;
            return (*protp->active_pkt)(p, len);
        }
    }
    return 0;                   /* not a supported protocol !!?? */
}