HardenedBSD/usr.sbin/pppd/sys-bsd.c

/*
 * sys-bsd.c - System-dependent procedures for setting up
 * PPP interfaces on bsd-4.4-ish systems (including 386BSD, NetBSD, etc.)
 *
 * Copyright (c) 1989 Carnegie Mellon University.
 * 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 Carnegie Mellon University.  The name of the
 * University 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.
 */

#ifndef lint
static char rcsid[] = "$Id: sys-bsd.c,v 1.7 1994/05/30 06:10:07 paulus Exp $";
#endif

/*
 * TODO:
 */

#include <syslog.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/errno.h>

#include <net/if.h>
#include <net/if_ppp.h>
#include <net/route.h>
#include <net/if_dl.h>
#include <netinet/in.h>

#if RTM_VERSION >= 3
#include <netinet/if_ether.h>
#endif

#include "pppd.h"
#include "ppp.h"

static int initdisc = -1;		/* Initial TTY discipline */
extern int kdebugflag;
static int rtm_seq;

/*
 * establish_ppp - Turn the serial port into a ppp interface.
 */
void
establish_ppp()
{
    int pppdisc = PPPDISC;
    int x;

    if (ioctl(fd, TIOCGETD, &initdisc) < 0) {
	syslog(LOG_ERR, "ioctl(TIOCGETD): %m");
	die(1);
    }
    if (ioctl(fd, TIOCSETD, &pppdisc) < 0) {
	syslog(LOG_ERR, "ioctl(TIOCSETD): %m");
	die(1);
    }

    /*
     * Find out which interface we were given.
     */
    if (ioctl(fd, PPPIOCGUNIT, &ifunit) < 0) {	
	syslog(LOG_ERR, "ioctl(PPPIOCGUNIT): %m");
	die(1);
    }

    /*
     * Enable debug in the driver if requested.
     */
    if (kdebugflag) {
	if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	    syslog(LOG_WARNING, "ioctl (PPPIOCGFLAGS): %m");
	} else {
	    x |= (kdebugflag & 0xFF) * SC_DEBUG;
	    if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0)
		syslog(LOG_WARNING, "ioctl(PPPIOCSFLAGS): %m");
	}
    }
}


/*
 * disestablish_ppp - Restore the serial port to normal operation.
 * This shouldn't call die() because it's called from die().
 */
void
disestablish_ppp()
{
    int x;
    char *s;

    if (initdisc >= 0) {
	/*
	 * Check whether the link seems not to be 8-bit clean.
	 */
	if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) == 0) {
	    s = NULL;
	    switch (~x & (SC_RCV_B7_0|SC_RCV_B7_1|SC_RCV_EVNP|SC_RCV_ODDP)) {
	    case SC_RCV_B7_0:
		s = "bit 7 set to 1";
		break;
	    case SC_RCV_B7_1:
		s = "bit 7 set to 0";
		break;
	    case SC_RCV_EVNP:
		s = "odd parity";
		break;
	    case SC_RCV_ODDP:
		s = "even parity";
		break;
	    }
	    if (s != NULL) {
		syslog(LOG_WARNING, "Serial link is not 8-bit clean:");
		syslog(LOG_WARNING, "All received characters had %s", s);
	    }
	}
	if (ioctl(fd, TIOCSETD, &initdisc) < 0)
	    syslog(LOG_ERR, "ioctl(TIOCSETD): %m");
    }
}


/*
 * output - Output PPP packet.
 */
void
output(unit, p, len)
    int unit;
    u_char *p;
    int len;
{
    if (unit != 0)
	MAINDEBUG((LOG_WARNING, "output: unit != 0!"));
    if (debug)
	log_packet(p, len, "sent ");

    if (write(fd, p, len) < 0) {
	syslog(LOG_ERR, "write: %m");
	die(1);
    }
}


/*
 * read_packet - get a PPP packet from the serial device.
 */
int
read_packet(buf)
    u_char *buf;
{
    int len;

    if ((len = read(fd, buf, MTU + DLLHEADERLEN)) < 0) {
	if (errno == EWOULDBLOCK) {
	    MAINDEBUG((LOG_DEBUG, "read(fd): EWOULDBLOCK"));
	    return -1;
	}
	syslog(LOG_ERR, "read(fd): %m");
	die(1);
    }
    return len;
}


/*
 * ppp_send_config - configure the transmit characteristics of
 * the ppp interface.
 */
void
ppp_send_config(unit, mtu, asyncmap, pcomp, accomp)
    int unit, mtu;
    u_long asyncmap;
    int pcomp, accomp;
{
    u_int x;
    struct ifreq ifr;

    strncpy(ifr.ifr_name, ifname, sizeof (ifr.ifr_name));
    ifr.ifr_mtu = mtu;
    if (ioctl(s, SIOCSIFMTU, (caddr_t) &ifr) < 0) {
	syslog(LOG_ERR, "ioctl(SIOCSIFMTU): %m");
	quit();
    }

    if (ioctl(fd, PPPIOCSASYNCMAP, (caddr_t) &asyncmap) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSASYNCMAP): %m");
	quit();
    }

    if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl (PPPIOCGFLAGS): %m");
	quit();
    }
    x = pcomp? x | SC_COMP_PROT: x &~ SC_COMP_PROT;
    x = accomp? x | SC_COMP_AC: x &~ SC_COMP_AC;
    if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	quit();
    }
}


/*
 * ppp_set_xaccm - set the extended transmit ACCM for the interface.
 */
void
ppp_set_xaccm(unit, accm)
    int unit;
    ext_accm accm;
{
    if (ioctl(fd, PPPIOCSXASYNCMAP, accm) < 0 && errno != ENOTTY)
	syslog(LOG_WARNING, "ioctl(set extended ACCM): %m");
}


/*
 * ppp_recv_config - configure the receive-side characteristics of
 * the ppp interface.
 */
void
ppp_recv_config(unit, mru, asyncmap, pcomp, accomp)
    int unit, mru;
    u_long asyncmap;
    int pcomp, accomp;
{
    int x;

    if (ioctl(fd, PPPIOCSMRU, (caddr_t) &mru) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSMRU): %m");
	quit();
    }
    if (ioctl(fd, PPPIOCSRASYNCMAP, (caddr_t) &asyncmap) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSRASYNCMAP): %m");
	quit();
    }
    if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl (PPPIOCGFLAGS): %m");
	quit();
    }
    x = !accomp? x | SC_REJ_COMP_AC: x &~ SC_REJ_COMP_AC;
    if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	quit();
    }
}

/*
 * sifvjcomp - config tcp header compression
 */
int
sifvjcomp(u, vjcomp, cidcomp, maxcid)
    int u, vjcomp, cidcomp, maxcid;
{
    u_int x;

    if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl (PPPIOCGFLAGS): %m");
	return 0;
    }
    x = vjcomp ? x | SC_COMP_TCP: x &~ SC_COMP_TCP;
    x = cidcomp? x & ~SC_NO_TCP_CCID: x | SC_NO_TCP_CCID;
    if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	return 0;
    }
    if (ioctl(fd, PPPIOCSMAXCID, (caddr_t) &maxcid) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	return 0;
    }
    return 1;
}

/*
 * sifup - Config the interface up and enable IP packets to pass.
 */
int
sifup(u)
    int u;
{
    struct ifreq ifr;
    u_int x;

    strncpy(ifr.ifr_name, ifname, sizeof (ifr.ifr_name));
    if (ioctl(s, SIOCGIFFLAGS, (caddr_t) &ifr) < 0) {
	syslog(LOG_ERR, "ioctl (SIOCGIFFLAGS): %m");
	return 0;
    }
    ifr.ifr_flags |= IFF_UP;
    if (ioctl(s, SIOCSIFFLAGS, (caddr_t) &ifr) < 0) {
	syslog(LOG_ERR, "ioctl(SIOCSIFFLAGS): %m");
	return 0;
    }
    if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl (PPPIOCGFLAGS): %m");
	return 0;
    }
    x |= SC_ENABLE_IP;
    if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	return 0;
    }
    return 1;
}

/*
 * sifdown - Config the interface down and disable IP.
 */
int
sifdown(u)
    int u;
{
    struct ifreq ifr;
    u_int x;
    int rv;

    rv = 1;
    if (ioctl(fd, PPPIOCGFLAGS, (caddr_t) &x) < 0) {
	syslog(LOG_ERR, "ioctl (PPPIOCGFLAGS): %m");
	rv = 0;
    } else {
	x &= ~SC_ENABLE_IP;
	if (ioctl(fd, PPPIOCSFLAGS, (caddr_t) &x) < 0) {
	    syslog(LOG_ERR, "ioctl(PPPIOCSFLAGS): %m");
	    rv = 0;
	}
    }
    strncpy(ifr.ifr_name, ifname, sizeof (ifr.ifr_name));
    if (ioctl(s, SIOCGIFFLAGS, (caddr_t) &ifr) < 0) {
	syslog(LOG_ERR, "ioctl (SIOCGIFFLAGS): %m");
	rv = 0;
    } else {
	ifr.ifr_flags &= ~IFF_UP;
	if (ioctl(s, SIOCSIFFLAGS, (caddr_t) &ifr) < 0) {
	    syslog(LOG_ERR, "ioctl(SIOCSIFFLAGS): %m");
	    rv = 0;
	}
    }
    return rv;
}

/*
 * SET_SA_FAMILY - set the sa_family field of a struct sockaddr,
 * if it exists.
 */
#define SET_SA_FAMILY(addr, family)		\
    BZERO((char *) &(addr), sizeof(addr));	\
    addr.sa_family = (family); 			\
    addr.sa_len = sizeof(addr);

/*
 * sifaddr - Config the interface IP addresses and netmask.
 */
int
sifaddr(u, o, h, m)
    int u;
    u_long o, h, m;
{
    struct ifaliasreq ifra;

    strncpy(ifra.ifra_name, ifname, sizeof(ifra.ifra_name));
    SET_SA_FAMILY(ifra.ifra_addr, AF_INET);
    ((struct sockaddr_in *) &ifra.ifra_addr)->sin_addr.s_addr = o;
    SET_SA_FAMILY(ifra.ifra_broadaddr, AF_INET);
    ((struct sockaddr_in *) &ifra.ifra_broadaddr)->sin_addr.s_addr = h;
    if (m != 0) {
	SET_SA_FAMILY(ifra.ifra_mask, AF_INET);
	((struct sockaddr_in *) &ifra.ifra_mask)->sin_addr.s_addr = m;
    } else
	BZERO(&ifra.ifra_mask, sizeof(ifra.ifra_mask));
    if (ioctl(s, SIOCAIFADDR, (caddr_t) &ifra) < 0) {
	if (errno != EEXIST) {
	    syslog(LOG_ERR, "ioctl(SIOCAIFADDR): %m");
	    return 0;
	}
	syslog(LOG_WARNING, "ioctl(SIOCAIFADDR): Address already exists");
    }
    return 1;
}

/*
 * cifaddr - Clear the interface IP addresses, and delete routes
 * through the interface if possible.
 */
int
cifaddr(u, o, h)
    int u;
    u_long o, h;
{
    struct ifaliasreq ifra;

    strncpy(ifra.ifra_name, ifname, sizeof(ifra.ifra_name));
    SET_SA_FAMILY(ifra.ifra_addr, AF_INET);
    ((struct sockaddr_in *) &ifra.ifra_addr)->sin_addr.s_addr = o;
    SET_SA_FAMILY(ifra.ifra_broadaddr, AF_INET);
    ((struct sockaddr_in *) &ifra.ifra_broadaddr)->sin_addr.s_addr = h;
    BZERO(&ifra.ifra_mask, sizeof(ifra.ifra_mask));
    if (ioctl(s, SIOCDIFADDR, (caddr_t) &ifra) < 0) {
	syslog(LOG_WARNING, "ioctl(SIOCDIFADDR): %m");
	return 0;
    }
    return 1;
}


/*
 * sifdefaultroute - assign a default route through the address given.
 */
int
sifdefaultroute(u, g)
    int u;
    u_long g;
{
    return dodefaultroute(g, 's');
}

/*
 * cifdefaultroute - delete a default route through the address given.
 */
int
cifdefaultroute(u, g)
    int u;
    u_long g;
{
    return dodefaultroute(g, 'c');
}

/*
 * dodefaultroute - talk to a routing socket to add/delete a default route.
 */
int
dodefaultroute(g, cmd)
    u_long g;
    int cmd;
{
    int routes;
    struct {
	struct rt_msghdr	hdr;
	struct sockaddr_in	dst;
	struct sockaddr_in	gway;
	struct sockaddr_in	mask;
    } rtmsg;

    if ((routes = socket(PF_ROUTE, SOCK_RAW, AF_INET)) < 0) {
	syslog(LOG_ERR, "%cifdefaultroute: opening routing socket: %m", cmd);
	return 0;
    }

    memset(&rtmsg, 0, sizeof(rtmsg));
    rtmsg.hdr.rtm_type = cmd == 's'? RTM_ADD: RTM_DELETE;
    rtmsg.hdr.rtm_flags = RTF_UP | RTF_GATEWAY;
    rtmsg.hdr.rtm_version = RTM_VERSION;
    rtmsg.hdr.rtm_seq = ++rtm_seq;
    rtmsg.hdr.rtm_addrs = RTA_DST | RTA_GATEWAY | RTA_NETMASK;
    rtmsg.dst.sin_len = sizeof(rtmsg.dst);
    rtmsg.dst.sin_family = AF_INET;
    rtmsg.gway.sin_len = sizeof(rtmsg.gway);
    rtmsg.gway.sin_family = AF_INET;
    rtmsg.gway.sin_addr.s_addr = g;
    rtmsg.mask.sin_len = sizeof(rtmsg.dst);
    rtmsg.mask.sin_family = AF_INET;

    rtmsg.hdr.rtm_msglen = sizeof(rtmsg);
    if (write(routes, &rtmsg, sizeof(rtmsg)) < 0) {
	syslog(LOG_ERR, "%s default route: %m", cmd=='s'? "add": "delete");
	close(routes);
	return 0;
    }

    close(routes);
    return 1;
}

#if RTM_VERSION >= 3

/*
 * sifproxyarp - Make a proxy ARP entry for the peer.
 */
static struct {
    struct rt_msghdr		hdr;
    struct sockaddr_inarp	dst;
    struct sockaddr_dl		hwa;
    char			extra[128];
} arpmsg;

static int arpmsg_valid;

int
sifproxyarp(unit, hisaddr)
    int unit;
    u_long hisaddr;
{
    int routes;
    int l;

    /*
     * Get the hardware address of an interface on the same subnet
     * as our local address.
     */
    memset(&arpmsg, 0, sizeof(arpmsg));
    if (!get_ether_addr(hisaddr, &arpmsg.hwa)) {
	syslog(LOG_ERR, "Cannot determine ethernet address for proxy ARP");
	return 0;
    }

    if ((routes = socket(PF_ROUTE, SOCK_RAW, AF_INET)) < 0) {
	syslog(LOG_ERR, "sifproxyarp: opening routing socket: %m");
	return 0;
    }

    arpmsg.hdr.rtm_type = RTM_ADD;
    arpmsg.hdr.rtm_flags = RTF_ANNOUNCE | RTF_HOST | RTF_STATIC;
    arpmsg.hdr.rtm_version = RTM_VERSION;
    arpmsg.hdr.rtm_seq = ++rtm_seq;
    arpmsg.hdr.rtm_addrs = RTA_DST | RTA_GATEWAY;
    arpmsg.hdr.rtm_inits = RTV_EXPIRE;
    arpmsg.dst.sin_len = sizeof(struct sockaddr_inarp);
    arpmsg.dst.sin_family = AF_INET;
    arpmsg.dst.sin_addr.s_addr = hisaddr;
    arpmsg.dst.sin_other = SIN_PROXY;

    arpmsg.hdr.rtm_msglen = (char *) &arpmsg.hwa - (char *) &arpmsg
	+ arpmsg.hwa.sdl_len;
    if (write(routes, &arpmsg, arpmsg.hdr.rtm_msglen) < 0) {
	syslog(LOG_ERR, "add proxy arp entry: %m");
	close(routes);
	return 0;
    }

    close(routes);
    arpmsg_valid = 1;
    return 1;
}

/*
 * cifproxyarp - Delete the proxy ARP entry for the peer.
 */
int
cifproxyarp(unit, hisaddr)
    int unit;
    u_long hisaddr;
{
    int routes;

    if (!arpmsg_valid)
	return 0;
    arpmsg_valid = 0;

    arpmsg.hdr.rtm_type = RTM_DELETE;
    arpmsg.hdr.rtm_seq = ++rtm_seq;

    if ((routes = socket(PF_ROUTE, SOCK_RAW, AF_INET)) < 0) {
	syslog(LOG_ERR, "sifproxyarp: opening routing socket: %m");
	return 0;
    }

    if (write(routes, &arpmsg, arpmsg.hdr.rtm_msglen) < 0) {
	syslog(LOG_ERR, "delete proxy arp entry: %m");
	close(routes);
	return 0;
    }

    close(routes);
    return 1;
}

#else	/* RTM_VERSION */

/*
 * sifproxyarp - Make a proxy ARP entry for the peer.
 */
int
sifproxyarp(unit, hisaddr)
    int unit;
    u_long hisaddr;
{
    struct arpreq arpreq;
    struct {
	struct sockaddr_dl	sdl;
	char			space[128];
    } dls;

    BZERO(&arpreq, sizeof(arpreq));

    /*
     * Get the hardware address of an interface on the same subnet
     * as our local address.
     */
    if (!get_ether_addr(hisaddr, &dls.sdl)) {
	syslog(LOG_ERR, "Cannot determine ethernet address for proxy ARP");
	return 0;
    }

    arpreq.arp_ha.sa_len = sizeof(struct sockaddr);
    arpreq.arp_ha.sa_family = AF_UNSPEC;
    BCOPY(LLADDR(&dls.sdl), arpreq.arp_ha.sa_data, dls.sdl.sdl_alen);
    SET_SA_FAMILY(arpreq.arp_pa, AF_INET);
    ((struct sockaddr_in *) &arpreq.arp_pa)->sin_addr.s_addr = hisaddr;
    arpreq.arp_flags = ATF_PERM | ATF_PUBL;
    if (ioctl(s, SIOCSARP, (caddr_t)&arpreq) < 0) {
	syslog(LOG_ERR, "ioctl(SIOCSARP): %m");
	return 0;
    }

    return 1;
}

/*
 * cifproxyarp - Delete the proxy ARP entry for the peer.
 */
int
cifproxyarp(unit, hisaddr)
    int unit;
    u_long hisaddr;
{
    struct arpreq arpreq;

    BZERO(&arpreq, sizeof(arpreq));
    SET_SA_FAMILY(arpreq.arp_pa, AF_INET);
    ((struct sockaddr_in *) &arpreq.arp_pa)->sin_addr.s_addr = hisaddr;
    if (ioctl(s, SIOCDARP, (caddr_t)&arpreq) < 0) {
	syslog(LOG_WARNING, "ioctl(SIOCDARP): %m");
	return 0;
    }
    return 1;
}
#endif	/* RTM_VERSION */


/*
 * get_ether_addr - get the hardware address of an interface on the
 * the same subnet as ipaddr.
 */
#define MAX_IFS		32

int
get_ether_addr(ipaddr, hwaddr)
    u_long ipaddr;
    struct sockaddr_dl *hwaddr;
{
    struct ifreq *ifr, *ifend, *ifp;
    u_long ina, mask;
    struct sockaddr_dl *dla;
    struct ifreq ifreq;
    struct ifconf ifc;
    struct ifreq ifs[MAX_IFS];

    ifc.ifc_len = sizeof(ifs);
    ifc.ifc_req = ifs;
    if (ioctl(s, SIOCGIFCONF, &ifc) < 0) {
	syslog(LOG_ERR, "ioctl(SIOCGIFCONF): %m");
	return 0;
    }

    /*
     * Scan through looking for an interface with an Internet
     * address on the same subnet as `ipaddr'.
     */
    ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
    for (ifr = ifc.ifc_req; ifr < ifend; ) {
	if (ifr->ifr_addr.sa_family == AF_INET) {
	    ina = ((struct sockaddr_in *) &ifr->ifr_addr)->sin_addr.s_addr;
	    strncpy(ifreq.ifr_name, ifr->ifr_name, sizeof(ifreq.ifr_name));
	    /*
	     * Check that the interface is up, and not point-to-point
	     * or loopback.
	     */
	    if (ioctl(s, SIOCGIFFLAGS, &ifreq) < 0)
		continue;
	    if ((ifreq.ifr_flags &
		 (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|IFF_LOOPBACK|IFF_NOARP))
		 != (IFF_UP|IFF_BROADCAST))
		continue;
	    /*
	     * Get its netmask and check that it's on the right subnet.
	     */
	    if (ioctl(s, SIOCGIFNETMASK, &ifreq) < 0)
		continue;
	    mask = ((struct sockaddr_in *) &ifr->ifr_addr)->sin_addr.s_addr;
	    if ((ipaddr & mask) != (ina & mask))
		continue;

	    break;
	}
	ifr = (struct ifreq *) ((char *)&ifr->ifr_addr + ifr->ifr_addr.sa_len);
    }

    if (ifr >= ifend)
	return 0;
    syslog(LOG_INFO, "found interface %s for proxy arp", ifr->ifr_name);

    /*
     * Now scan through again looking for a link-level address
     * for this interface.
     */
    ifp = ifr;
    for (ifr = ifc.ifc_req; ifr < ifend; ) {
	if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
	    && ifr->ifr_addr.sa_family == AF_LINK) {
	    /*
	     * Found the link-level address - copy it out
	     */
	    dla = (struct sockaddr_dl *) &ifr->ifr_addr;
	    BCOPY(dla, hwaddr, dla->sdl_len);
	    return 1;
	}
	ifr = (struct ifreq *) ((char *)&ifr->ifr_addr + ifr->ifr_addr.sa_len);
    }

    return 0;
}


/*
 * ppp_available - check whether the system has any ppp interfaces
 * (in fact we check whether we can do an ioctl on ppp0).
 */
int
ppp_available()
{
    int s, ok;
    struct ifreq ifr;

    if ((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
	return 1;		/* can't tell - maybe we're not root */

    strncpy(ifr.ifr_name, "ppp0", sizeof (ifr.ifr_name));
    ok = ioctl(s, SIOCGIFFLAGS, (caddr_t) &ifr) >= 0;
    close(s);

    return ok;
}