rwhod.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1983, 1993 The Regents of the University of California.
 * Copyright (c) 2013 Mariusz Zaborski <[email protected]>
 * 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. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/ioctl.h>
#include <sys/procdesc.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/signal.h>
#include <sys/sysctl.h>
#include <sys/wait.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <protocols/rwhod.h>

#include <ctype.h>
#include <capsicum_helpers.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <netdb.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <timeconv.h>
#include <utmpx.h>
#include <unistd.h>

#define	UNPRIV_USER		"daemon"
#define	UNPRIV_GROUP		"daemon"

#define NO_MULTICAST		0	  /* multicast modes */
#define PER_INTERFACE_MULTICAST	1
#define SCOPED_MULTICAST	2

#define MAX_MULTICAST_SCOPE	32	  /* "site-wide", by convention */

#define INADDR_WHOD_GROUP (u_long)0xe0000103      /* 224.0.1.3 */
						  /* (belongs in protocols/rwhod.h) */

int	insecure_mode;
int	quiet_mode;
int	iff_flag = IFF_POINTOPOINT;
int	multicast_mode = NO_MULTICAST;
int	multicast_scope;
struct	sockaddr_in multicast_addr =
	{ sizeof(multicast_addr), AF_INET, 0, { 0 }, { 0 } };

/*
 * Sleep interval. Don't forget to change the down time check in ruptime
 * if this is changed.
 */
#define SL_INTERVAL (3 * 60)

char	myname[MAXHOSTNAMELEN];

/*
 * We communicate with each neighbor in a list constructed at the time we're
 * started up.  Neighbors are currently directly connected via a hardware
 * interface.
 */
struct	neighbor {
	struct	neighbor *n_next;
	char		 *n_name;		/* interface name */
	struct	sockaddr *n_addr;		/* who to send to */
	int		  n_addrlen;		/* size of address */
	int		  n_flags;		/* should forward?, interface flags */
};

struct	neighbor *neighbors;
struct	whod mywd;
struct	servent	*sp;
int	s;
int	fdp;
pid_t	pid_child_receiver;

#define	WHDRSIZE	(int)(sizeof(mywd) - sizeof(mywd.wd_we))

int	configure(int so);
void	getboottime(int signo __unused);
void	receiver_process(void);
void	rt_xaddrs(caddr_t cp, caddr_t cplim, struct rt_addrinfo *rtinfo);
void	run_as(uid_t *uid, gid_t *gid);
void	quit(const char *msg);
void	sender_process(void);
int	verify(char *name, int maxlen);
static void usage(void) __dead2;

#ifdef DEBUG
char	*interval(int time, char *updown);
void	Sendto(int s, const void *buf, size_t cc, int flags,
	    const struct sockaddr *to, int tolen);
#define	 sendto Sendto
#endif

/*
 * This version of Berkeley's rwhod has been modified to use IP multicast
 * datagrams, under control of a new command-line option:
 *
 *	rwhod -m	causes rwhod to use IP multicast (instead of
 *			broadcast or unicast) on all interfaces that have
 *			the IFF_MULTICAST flag set in their "ifnet" structs
 *			(excluding the loopback interface).  The multicast
 *			reports are sent with a time-to-live of 1, to prevent
 *			forwarding beyond the directly-connected subnet(s).
 *
 *	rwhod -m <ttl>	causes rwhod to send IP multicast datagrams with a
 *			time-to-live of <ttl>, via a SINGLE interface rather
 *			than all interfaces.  <ttl> must be between 0 and
 *			MAX_MULTICAST_SCOPE, defined below.  Note that "-m 1"
 *			is different than "-m", in that "-m 1" specifies
 *			transmission on one interface only.
 *
 * When "-m" is used without a <ttl> argument, the program accepts multicast
 * rwhod reports from all multicast-capable interfaces.  If a <ttl> argument
 * is given, it accepts multicast reports from only one interface, the one
 * on which reports are sent (which may be controlled via the host's routing
 * table).  Regardless of the "-m" option, the program accepts broadcast or
 * unicast reports from all interfaces.  Thus, this program will hear the
 * reports of old, non-multicasting rwhods, but, if multicasting is used,
 * those old rwhods won't hear the reports generated by this program.
 *
 *                  -- Steve Deering, Stanford University, February 1989
 */
int
main(int argc, char *argv[])
{
	int on;
	char *cp;
	struct sockaddr_in soin;
	uid_t unpriv_uid;
	gid_t unpriv_gid;

	on = 1;
	if (getuid())
		errx(1, "not super user");

	run_as(&unpriv_uid, &unpriv_gid);

	argv++;
	argc--;
	while (argc > 0 && *argv[0] == '-') {
		if (strcmp(*argv, "-m") == 0) {
			if (argc > 1 && isdigit(*(argv + 1)[0])) {
				argv++;
				argc--;
				multicast_mode  = SCOPED_MULTICAST;
				multicast_scope = atoi(*argv);
				if (multicast_scope > MAX_MULTICAST_SCOPE) {
					errx(1, "ttl must not exceed %u",
					    MAX_MULTICAST_SCOPE);
				}
			} else {
				multicast_mode = PER_INTERFACE_MULTICAST;
			}
		} else if (strcmp(*argv, "-i") == 0) {
			insecure_mode = 1;
		} else if (strcmp(*argv, "-l") == 0) {
			quiet_mode = 1;
		} else if (strcmp(*argv, "-p") == 0) {
			iff_flag = 0;
		} else {
			usage();
		}
		argv++;
		argc--;
	}
	if (argc > 0)
		usage();
#ifndef DEBUG
	daemon(1, 0);
#endif
	(void) signal(SIGHUP, getboottime);
	openlog("rwhod", LOG_PID | LOG_NDELAY, LOG_DAEMON);
	sp = getservbyname("who", "udp");
	if (sp == NULL) {
		syslog(LOG_ERR, "who/udp: unknown service");
		exit(1);
	}
	if (chdir(_PATH_RWHODIR) < 0) {
		syslog(LOG_ERR, "%s: %m", _PATH_RWHODIR);
		exit(1);
	}
	/*
	 * Establish host name as returned by system.
	 */
	if (gethostname(myname, sizeof(myname) - 1) < 0) {
		syslog(LOG_ERR, "gethostname: %m");
		exit(1);
	}
	if ((cp = strchr(myname, '.')) != NULL)
		*cp = '\0';
	strlcpy(mywd.wd_hostname, myname, sizeof(mywd.wd_hostname));
	getboottime(0);
	if ((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
		syslog(LOG_ERR, "socket: %m");
		exit(1);
	}
	if (setsockopt(s, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on)) < 0) {
		syslog(LOG_ERR, "setsockopt SO_BROADCAST: %m");
		exit(1);
	}
	memset(&soin, 0, sizeof(soin));
	soin.sin_len = sizeof(soin);
	soin.sin_family = AF_INET;
	soin.sin_port = sp->s_port;
	if (bind(s, (struct sockaddr *)&soin, sizeof(soin)) < 0) {
		syslog(LOG_ERR, "bind: %m");
		exit(1);
	}
	if (setgroups(0, NULL) != 0) {
		syslog(LOG_ERR, "setgroups: %m");
		exit(1);
	}
	if (setgid(unpriv_gid) != 0) {
		syslog(LOG_ERR, "setgid: %m");
		exit(1);
	}
	if (setuid(unpriv_uid) != 0) {
		syslog(LOG_ERR, "setuid: %m");
		exit(1);
	}
	if (!configure(s))
		exit(1);
	if (!quiet_mode) {
		pid_child_receiver = pdfork(&fdp, 0);
		if (pid_child_receiver == 0) {
			receiver_process();
		} else if (pid_child_receiver > 0) {
			sender_process();
		} else if (pid_child_receiver == -1) {
			if (errno == ENOSYS) {
				syslog(LOG_ERR,
				    "The pdfork(2) system call is not available - kernel too old.");
			} else {
				syslog(LOG_ERR, "pdfork: %m");
			}
			exit(1);
		}
	} else {
		receiver_process();
	}
}

static void
usage(void)
{

	fprintf(stderr, "usage: rwhod [-i] [-p] [-l] [-m [ttl]]\n");
	exit(1);
}

void
run_as(uid_t *uid, gid_t *gid)
{
	struct passwd *pw;
	struct group *gr;

	pw = getpwnam(UNPRIV_USER);
	if (pw == NULL) {
		syslog(LOG_ERR, "getpwnam(%s): %m", UNPRIV_USER);
		exit(1);
	}
	*uid = pw->pw_uid;

	gr = getgrnam(UNPRIV_GROUP);
	if (gr == NULL) {
		syslog(LOG_ERR, "getgrnam(%s): %m", UNPRIV_GROUP);
		exit(1);
	}
	*gid = gr->gr_gid;
}

/*
 * Check out host name for unprintables
 * and other funnies before allowing a file
 * to be created.  Sorry, but blanks aren't allowed.
 */
int
verify(char *name, int maxlen)
{
	int size;

	size = 0;
	while (*name != '\0' && size < maxlen - 1) {
		if (!isascii((unsigned char)*name) ||
		    !(isalnum((unsigned char)*name) ||
		    ispunct((unsigned char)*name))) {
			return (0);
		}
		name++;
		size++;
	}
	*name = '\0';
	return (size > 0);
}

void
receiver_process(void)
{
	struct sockaddr_in from;
	struct stat st;
	cap_rights_t rights;
	char path[64];
	int dirfd;
	struct whod wd;
	socklen_t len;
	int cc, whod;
	time_t t;

	len = sizeof(from);
	dirfd = open(".", O_RDONLY | O_DIRECTORY);
	if (dirfd < 0) {
		syslog(LOG_WARNING, "%s: %m", _PATH_RWHODIR);
		exit(1);
	}
	cap_rights_init(&rights, CAP_CREATE, CAP_FSTAT, CAP_FTRUNCATE,
	    CAP_LOOKUP, CAP_SEEK, CAP_WRITE);
	if (caph_rights_limit(dirfd, &rights) < 0) {
		syslog(LOG_WARNING, "cap_rights_limit: %m");
		exit(1);
	}
	if (caph_enter() < 0) {
		syslog(LOG_ERR, "cap_enter: %m");
		exit(1);
	}
	for (;;) {
		cc = recvfrom(s, &wd, sizeof(wd), 0, (struct sockaddr *)&from,
		    &len);
		if (cc <= 0) {
			if (cc < 0 && errno != EINTR)
				syslog(LOG_WARNING, "recv: %m");
			continue;
		}
		if (from.sin_port != sp->s_port && !insecure_mode) {
			syslog(LOG_WARNING, "%d: bad source port from %s",
			    ntohs(from.sin_port), inet_ntoa(from.sin_addr));
			continue;
		}
		if (cc < WHDRSIZE) {
			syslog(LOG_WARNING, "short packet from %s",
			    inet_ntoa(from.sin_addr));
			continue;
		}
		if (wd.wd_vers != WHODVERSION)
			continue;
		if (wd.wd_type != WHODTYPE_STATUS)
			continue;
		if (!verify(wd.wd_hostname, sizeof(wd.wd_hostname))) {
			syslog(LOG_WARNING, "malformed host name from %s",
			    inet_ntoa(from.sin_addr));
			continue;
		}
		(void) snprintf(path, sizeof(path), "whod.%s", wd.wd_hostname);
		/*
		 * Rather than truncating and growing the file each time,
		 * use ftruncate if size is less than previous size.
		 */
		whod = openat(dirfd, path, O_WRONLY | O_CREAT, 0644);
		if (whod < 0) {
			syslog(LOG_WARNING, "%s: %m", path);
			continue;
		}
		cap_rights_init(&rights, CAP_FSTAT, CAP_FTRUNCATE, CAP_WRITE);
		if (caph_rights_limit(whod, &rights) < 0) {
			syslog(LOG_WARNING, "cap_rights_limit: %m");
			exit(1);
		}
#if ENDIAN != BIG_ENDIAN
		{
			struct whoent *we;
			int i, n;

			n = (cc - WHDRSIZE) / sizeof(struct whoent);
			/* undo header byte swapping before writing to file */
			wd.wd_sendtime = ntohl(wd.wd_sendtime);
			for (i = 0; i < 3; i++)
				wd.wd_loadav[i] = ntohl(wd.wd_loadav[i]);
			wd.wd_boottime = ntohl(wd.wd_boottime);
			we = wd.wd_we;
			for (i = 0; i < n; i++) {
				we->we_idle = ntohl(we->we_idle);
				we->we_utmp.out_time =
				    ntohl(we->we_utmp.out_time);
				we++;
			}
		}
#endif
		(void) time(&t);
		wd.wd_recvtime = _time_to_int(t);
		(void) write(whod, (char *)&wd, cc);
		if (fstat(whod, &st) < 0 || st.st_size > cc)
			ftruncate(whod, cc);
		(void) close(whod);
	}
	(void) close(dirfd);
}

void
sender_process(void)
{
	int sendcount;
	double avenrun[3];
	time_t now;
	int i, cc, status;
	struct utmpx *ut;
	struct stat stb;
	struct neighbor *np;
	struct whoent *we, *wend;

	sendcount = 0;
	for (;;) {
		we = mywd.wd_we;
		now = time(NULL);
		if (sendcount % 10 == 0)
			getboottime(0);
		sendcount++;
		wend = &mywd.wd_we[1024 / sizeof(struct whoent)];
		setutxent();
		while ((ut = getutxent()) != NULL && we < wend) {
			if (ut->ut_type != USER_PROCESS)
				continue;
			strncpy(we->we_utmp.out_line, ut->ut_line,
			    sizeof(we->we_utmp.out_line));
			strncpy(we->we_utmp.out_name, ut->ut_user,
			    sizeof(we->we_utmp.out_name));
			we->we_utmp.out_time =
			    htonl(_time_to_time32(ut->ut_tv.tv_sec));
			we++;
		}
		endutxent();

		if (chdir(_PATH_DEV) < 0) {
			syslog(LOG_ERR, "chdir(%s): %m", _PATH_DEV);
			exit(1);
		}
		wend = we;
		for (we = mywd.wd_we; we < wend; we++) {
			if (stat(we->we_utmp.out_line, &stb) >= 0)
				we->we_idle = htonl(now - stb.st_atime);
		}
		(void) getloadavg(avenrun,
		    nitems(avenrun));
		for (i = 0; i < 3; i++)
			mywd.wd_loadav[i] = htonl((u_long)(avenrun[i] * 100));
		cc = (char *)wend - (char *)&mywd;
		mywd.wd_sendtime = htonl(_time_to_time32(time(NULL)));
		mywd.wd_vers = WHODVERSION;
		mywd.wd_type = WHODTYPE_STATUS;
		if (multicast_mode == SCOPED_MULTICAST) {
			(void) sendto(s, (char *)&mywd, cc, 0,
			    (struct sockaddr *)&multicast_addr,
			    sizeof(multicast_addr));
		} else {
			for (np = neighbors; np != NULL; np = np->n_next) {
				if (multicast_mode == PER_INTERFACE_MULTICAST &&
				    (np->n_flags & IFF_MULTICAST) != 0) {
					/*
					 * Select the outgoing interface for the
					 * multicast.
					 */
					if (setsockopt(s, IPPROTO_IP,
					    IP_MULTICAST_IF,
					    &(((struct sockaddr_in *)np->n_addr)->sin_addr),
					    sizeof(struct in_addr)) < 0) {
						syslog(LOG_ERR,
						    "setsockopt IP_MULTICAST_IF: %m");
						exit(1);
					}
					(void) sendto(s, (char *)&mywd, cc, 0,
					    (struct sockaddr *)&multicast_addr,
					    sizeof(multicast_addr));
				} else {
					(void) sendto(s, (char *)&mywd, cc, 0,
					    np->n_addr, np->n_addrlen);
				}
			}
		}
		if (chdir(_PATH_RWHODIR) < 0) {
			syslog(LOG_ERR, "chdir(%s): %m", _PATH_RWHODIR);
			exit(1);
		}
		if (waitpid(pid_child_receiver, &status, WNOHANG) ==
		    pid_child_receiver) {
			break;
		}
		sleep(SL_INTERVAL);
	}
}

void
getboottime(int signo __unused)
{
	int mib[2];
	size_t size;
	struct timeval tm;

	mib[0] = CTL_KERN;
	mib[1] = KERN_BOOTTIME;
	size = sizeof(tm);
	if (sysctl(mib, nitems(mib), &tm, &size, NULL, 0) == -1) {
		syslog(LOG_ERR, "cannot get boottime: %m");
		exit(1);
	}
	mywd.wd_boottime = htonl(_time_to_time32(tm.tv_sec));
}

void
quit(const char *msg)
{

	syslog(LOG_ERR, "%s", msg);
	exit(1);
}

void
rt_xaddrs(caddr_t cp, caddr_t cplim, struct rt_addrinfo *rtinfo)
{
	struct sockaddr *sa;
	int i;

	memset(rtinfo->rti_info, 0, sizeof(rtinfo->rti_info));
	for (i = 0; i < RTAX_MAX && cp < cplim; i++) {
		if ((rtinfo->rti_addrs & (1 << i)) == 0)
			continue;
		sa = (struct sockaddr *)cp;
		rtinfo->rti_info[i] = sa;
		cp += SA_SIZE(sa);
	}
}

/*
 * Figure out device configuration and select
 * networks which deserve status information.
 */
int
configure(int so)
{
	struct neighbor *np;
	struct if_msghdr *ifm;
	struct ifa_msghdr *ifam;
	struct sockaddr_dl *sdl;
	size_t needed;
	int mib[6], flags, lflags, len;
	char *buf, *lim, *next;
	struct rt_addrinfo info;

	flags = 0;
	if (multicast_mode != NO_MULTICAST) {
		multicast_addr.sin_addr.s_addr = htonl(INADDR_WHOD_GROUP);
		multicast_addr.sin_port = sp->s_port;
	}

	if (multicast_mode == SCOPED_MULTICAST) {
		struct ip_mreq mreq;
		unsigned char ttl;

		mreq.imr_multiaddr.s_addr = htonl(INADDR_WHOD_GROUP);
		mreq.imr_interface.s_addr = htonl(INADDR_ANY);
		if (setsockopt(so, IPPROTO_IP, IP_ADD_MEMBERSHIP,
		    &mreq, sizeof(mreq)) < 0) {
			syslog(LOG_ERR,
			    "setsockopt IP_ADD_MEMBERSHIP: %m");
			return (0);
		}
		ttl = multicast_scope;
		if (setsockopt(so, IPPROTO_IP, IP_MULTICAST_TTL, &ttl,
		    sizeof(ttl)) < 0) {
			syslog(LOG_ERR,
			    "setsockopt IP_MULTICAST_TTL: %m");
			return (0);
		}
		return (1);
	}

	mib[0] = CTL_NET;
	mib[1] = PF_ROUTE;
	mib[2] = 0;
	mib[3] = AF_INET;
	mib[4] = NET_RT_IFLIST;
	mib[5] = 0;
	if (sysctl(mib, nitems(mib), NULL, &needed, NULL, 0) < 0)
		quit("route-sysctl-estimate");
	if ((buf = malloc(needed)) == NULL)
		quit("malloc");
	if (sysctl(mib, nitems(mib), buf, &needed, NULL, 0) < 0)
		quit("actual retrieval of interface table");
	lim = buf + needed;

	sdl = NULL;		/* XXX just to keep gcc -Wall happy */
	for (next = buf; next < lim; next += ifm->ifm_msglen) {
		ifm = (struct if_msghdr *)next;
		if (ifm->ifm_type == RTM_IFINFO) {
			sdl = (struct sockaddr_dl *)(ifm + 1);
			flags = ifm->ifm_flags;
			continue;
		}
		if ((flags & IFF_UP) == 0)
			continue;
		lflags = IFF_BROADCAST | iff_flag;
		if (multicast_mode == PER_INTERFACE_MULTICAST)
			lflags |= IFF_MULTICAST;
		if ((flags & lflags) == 0)
			continue;
		if (ifm->ifm_type != RTM_NEWADDR)
			quit("out of sync parsing NET_RT_IFLIST");
		ifam = (struct ifa_msghdr *)ifm;
		info.rti_addrs = ifam->ifam_addrs;
		rt_xaddrs((char *)(ifam + 1), ifam->ifam_msglen + (char *)ifam,
		    &info);
		/* gag, wish we could get rid of Internet dependencies */
#define	dstaddr		info.rti_info[RTAX_BRD]
#define	ifaddr		info.rti_info[RTAX_IFA]
#define	IPADDR_SA(x)	((struct sockaddr_in *)(x))->sin_addr.s_addr
#define	PORT_SA(x)	((struct sockaddr_in *)(x))->sin_port
		if (dstaddr == 0 || dstaddr->sa_family != AF_INET)
			continue;
		PORT_SA(dstaddr) = sp->s_port;
		for (np = neighbors; np != NULL; np = np->n_next) {
			if (memcmp(sdl->sdl_data, np->n_name,
			    sdl->sdl_nlen) == 0 &&
			    IPADDR_SA(np->n_addr) == IPADDR_SA(dstaddr)) {
				break;
			}
		}
		if (np != NULL)
			continue;
		len = sizeof(*np) + dstaddr->sa_len + sdl->sdl_nlen + 1;
		np = malloc(len);
		if (np == NULL)
			quit("malloc of neighbor structure");
		memset(np, 0, len);
		np->n_flags = flags;
		np->n_addr = (struct sockaddr *)(np + 1);
		np->n_addrlen = dstaddr->sa_len;
		np->n_name = np->n_addrlen + (char *)np->n_addr;
		memcpy((char *)np->n_addr, (char *)dstaddr, np->n_addrlen);
		memcpy(np->n_name, sdl->sdl_data, sdl->sdl_nlen);
		if (multicast_mode == PER_INTERFACE_MULTICAST &&
		    (flags & IFF_MULTICAST) != 0 &&
		    (flags & IFF_LOOPBACK) == 0) {
			struct ip_mreq mreq;

			memcpy((char *)np->n_addr, (char *)ifaddr,
			    np->n_addrlen);
			mreq.imr_multiaddr.s_addr = htonl(INADDR_WHOD_GROUP);
			mreq.imr_interface.s_addr =
			    ((struct sockaddr_in *)np->n_addr)->sin_addr.s_addr;
			if (setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP,
			    &mreq, sizeof(mreq)) < 0) {
				syslog(LOG_ERR,
				    "setsockopt IP_ADD_MEMBERSHIP: %m");
#if 0
				/* Fall back to broadcast on this if. */
				np->n_flags &= ~IFF_MULTICAST;
#else
				free(np);
				continue;
#endif
			}
		}
		np->n_next = neighbors;
		neighbors = np;
	}
	free(buf);
	return (1);
}

#ifdef DEBUG
void
Sendto(int s, const void *buf, size_t cc, int flags, const struct sockaddr *to,
    int tolen)
{
	struct whod *w;
	struct whoent *we;
	struct sockaddr_in *sin;

	w = (struct whod *)buf;
	sin = (struct sockaddr_in *)to;
	printf("sendto %x.%d\n", ntohl(sin->sin_addr.s_addr),
	    ntohs(sin->sin_port));
	printf("hostname %s %s\n", w->wd_hostname,
	    interval(ntohl(w->wd_sendtime) - ntohl(w->wd_boottime), "  up"));
	printf("load %4.2f, %4.2f, %4.2f\n",
	    ntohl(w->wd_loadav[0]) / 100.0, ntohl(w->wd_loadav[1]) / 100.0,
	    ntohl(w->wd_loadav[2]) / 100.0);
	cc -= WHDRSIZE;
	for (we = w->wd_we, cc /= sizeof(struct whoent); cc > 0; cc--, we++) {
		time_t t = _time32_to_time(ntohl(we->we_utmp.out_time));

		printf("%-8.8s %s:%s %.12s", we->we_utmp.out_name,
		    w->wd_hostname, we->we_utmp.out_line, ctime(&t) + 4);
		we->we_idle = ntohl(we->we_idle) / 60;
		if (we->we_idle != 0) {
			if (we->we_idle >= 100 * 60)
				we->we_idle = 100 * 60 - 1;
			if (we->we_idle >= 60)
				printf(" %2d", we->we_idle / 60);
			else
				printf("   ");
			printf(":%02d", we->we_idle % 60);
		}
		printf("\n");
	}
}

char *
interval(int time, char *updown)
{
	static char resbuf[32];
	int days, hours, minutes;

	if (time < 0 || time > 3 * 30 * 24 * 60 * 60) {
		(void) sprintf(resbuf, "   %s ??:??", updown);
		return (resbuf);
	}
	minutes = (time + 59) / 60;		/* round to minutes */
	hours = minutes / 60;
	minutes %= 60;
	days = hours / 24;
	hours %= 24;
	if (days > 0) {
		(void) sprintf(resbuf, "%s %2d+%02d:%02d",
		    updown, days, hours, minutes);
	} else {
		(void) sprintf(resbuf, "%s    %2d:%02d",
		    updown, hours, minutes);
	}
	return (resbuf);
}
#endif