/*      $NetBSD: rarpd.c,v 1.62 2026/04/08 16:51:28 htodd Exp $ */

/*
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution.  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 ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#include <sys/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1990\
 The Regents of the University of California.  All rights reserved.");
#endif /* not lint */

#ifndef lint
__RCSID("$NetBSD: rarpd.c,v 1.62 2026/04/08 16:51:28 htodd Exp $");
#endif


/*
 * rarpd - Reverse ARP Daemon
 *
 * Usage:       rarpd -a [-d|-f] [-l]
 *              rarpd [-d|-f] [-l] interface [...]
 */

#include <sys/param.h>
#include <sys/file.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/ioctl.h>

#include <net/bpf.h>
#include <net/if.h>
#include <net/if_dl.h>
#ifdef __NetBSD__
#include <net/if_ether.h>
#endif
#include <net/if_types.h>
#include <netinet/in.h>
#ifdef __NetBSD__
#include <netinet/if_inarp.h>
#else
#include <netinet/if_ether.h>
#endif

#include <arpa/inet.h>

#include <errno.h>
#include <dirent.h>
#include <paths.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <util.h>
#include <ifaddrs.h>

#define FATAL           1       /* fatal error occurred */
#define NONFATAL        0       /* non fatal error occurred */

/*
 * The structure for each interface.
 */
struct if_info {
        int     ii_fd;          /* BPF file descriptor */
        u_char  ii_eaddr[6];    /* Ethernet address of this interface */
        u_int32_t  ii_ipaddr;   /* IP address of this interface */
        u_int32_t  ii_netmask;  /* subnet or net mask */
        char    *ii_name;       /* interface name */
        struct if_info *ii_alias;
        struct if_info *ii_next;
};
/*
 * The list of all interfaces that are being listened to.  rarp_loop()
 * "selects" on the descriptors in this list.
 */
static struct if_info *iflist;

static u_int32_t choose_ipaddr(u_int32_t **, u_int32_t, u_int32_t);
static void     debug(const char *,...) __printflike(1, 2);
static void     init_some(char *name);
static void     init_one(char *, u_int32_t);
static u_int32_t        ipaddrtonetmask(u_int32_t);
static void     lookup_eaddr(char *, u_char *);
static void     lookup_ipaddr(char *, u_int32_t *, u_int32_t *);
static void     rarp_loop(void) __dead;
static int      rarp_open(char *);
static void     rarp_process(struct if_info *, u_char *);
static void     rarp_reply(struct if_info *, struct ether_header *, u_int32_t,
                           struct hostent *);
static void     rarperr(int, const char *,...) __printflike(2, 3);

#if defined(__NetBSD__)
#include "mkarp.h"
#else
static void     update_arptab(u_char *, u_int32_t);
#endif

__dead static void      usage(void);

static int      bpf_open(void);
static int      rarp_check(u_char *, int);

#ifdef REQUIRE_TFTPBOOT
static int      rarp_bootable(u_int32_t);
#endif

static int aflag = 0;           /* listen on "all" interfaces  */
static int dflag = 0;           /* print debugging messages */
static int fflag = 0;           /* don't fork */
static int lflag = 0;           /* log all replies */

int
main(int argc, char **argv)
{
        int     op;

        setprogname(*argv);
        /* All error reporting is done through syslogs. */
        openlog(getprogname(), LOG_PID, LOG_DAEMON);

        opterr = 0;
        while ((op = getopt(argc, argv, "adfl")) != -1) {
                switch (op) {
                case 'a':
                        ++aflag;
                        break;

                case 'd':
                        ++dflag;
                        break;

                case 'f':
                        ++fflag;
                        break;

                case 'l':
                        ++lflag;
                        break;

                default:
                        usage();
                        /* NOTREACHED */
                }
        }
        argc -= optind;
        argv += optind;

        if ((aflag && argc != 0) || (!aflag && argc == 0))
                usage();

        if ((!fflag) && (!dflag)) {
                if (daemon(0, 0))
                        rarperr(FATAL, "daemon");
                pidfile(NULL);
        }

        if (aflag)
                init_some(NULL);
        else {
                while (argc--)
                        init_some(*argv++);
        }

        rarp_loop();
        /* NOTREACHED */
        return (0);
}

/*
 * Add 'ifname' to the interface list.  Lookup its IP address and network
 * mask and Ethernet address, and open a BPF file for it.
 */
static void
init_one(char *ifname, u_int32_t ipaddr)
{
        struct if_info *h;
        struct if_info *p;
        int fd;

        for (h = iflist; h != NULL; h = h->ii_next) {
                if (!strcmp(h->ii_name, ifname))
                        break;
        }
        if (h == NULL) {
                fd = rarp_open(ifname);
                if (fd < 0)
                        return;
        } else {
                fd = h->ii_fd;
        }

        p = (struct if_info *)malloc(sizeof(*p));
        if (p == 0) {
                rarperr(FATAL, "malloc: %s", strerror(errno));
                /* NOTREACHED */
        }
        p->ii_name = strdup(ifname);
        if (p->ii_name == 0) {
                rarperr(FATAL, "malloc: %s", strerror(errno));
                /* NOTREACHED */
        }
        if (h != NULL) {
                p->ii_alias = h->ii_alias;
                h->ii_alias = p;
        } else {
                p->ii_next = iflist;
                iflist = p;
        }

        p->ii_fd = fd;
        p->ii_ipaddr = ipaddr;
        lookup_eaddr(ifname, p->ii_eaddr);
        lookup_ipaddr(ifname, &p->ii_ipaddr, &p->ii_netmask);
}

/*
 * Initialize all "candidate" interfaces that are in the system
 * configuration list.  A "candidate" is up, not loopback and not
 * point to point.
 */
static void
init_some(char *name)
{
        struct ifaddrs *ifap, *ifa, *p;

        if (getifaddrs(&ifap) != 0) {
                rarperr(FATAL, "getifaddrs: %s", strerror(errno));
                /* NOTREACHED */
        }

        p = NULL;
        for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
#define SIN(s)  ((struct sockaddr_in *) (s))
                if (ifa->ifa_addr->sa_family != AF_INET)
                        continue;
                if (name && strcmp(name, ifa->ifa_name))
                        continue;
                if (p && !strcmp(p->ifa_name, ifa->ifa_name) &&
                    SIN(p->ifa_addr)->sin_addr.s_addr == SIN(ifa->ifa_addr)->sin_addr.s_addr)
                        continue;
                p = ifa;
                if ((ifa->ifa_flags &
                     (IFF_UP | IFF_LOOPBACK | IFF_POINTOPOINT)) != IFF_UP)
                        continue;
                init_one(ifa->ifa_name, SIN(ifa->ifa_addr)->sin_addr.s_addr);
#undef  SIN
        }
        freeifaddrs(ifap);
}

static void
usage(void)
{
        (void) fprintf(stderr, "Usage: %s -a [-d|-f] [-l]\n", getprogname());
        (void) fprintf(stderr, "\t%s [-d|-f] [-l] interface [...]\n",
            getprogname());
        exit(1);
}

static int
bpf_open(void)
{
        int     fd;
        const char *device = _PATH_BPF;
        fd = open(device, O_RDWR);

        if (fd < 0) {
                rarperr(FATAL, "%s: %s", device, strerror(errno));
                /* NOTREACHED */
        }
        return fd;
}
/*
 * Open a BPF file and attach it to the interface named 'device'.
 * Set immediate mode, and set a filter that accepts only RARP requests.
 */
static int
rarp_open(char *device)
{
        int     fd;
        struct ifreq ifr;
        u_int   dlt;
        int     immediate;
        u_int   bufsize;

        static struct bpf_insn insns[] = {
                BPF_STMT(BPF_LD | BPF_H | BPF_ABS, 12),
                BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ETHERTYPE_REVARP, 0, 3),
                BPF_STMT(BPF_LD | BPF_H | BPF_ABS, 20),
                BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ARPOP_REVREQUEST, 0, 1),
                BPF_STMT(BPF_RET | BPF_K, 
                    sizeof(struct arphdr) + 
                    2 * ETHER_ADDR_LEN + 2 * sizeof(struct in_addr) +
                    sizeof(struct ether_header)),
                BPF_STMT(BPF_RET | BPF_K, 0),
        };
        static struct bpf_program filter = {
                sizeof insns / sizeof(insns[0]),
                insns
        };

        fd = bpf_open();

        /* Set immediate mode so packets are processed as they arrive. */
        immediate = 1;
        if (ioctl(fd, BIOCIMMEDIATE, &immediate) < 0) {
                rarperr(FATAL, "BIOCIMMEDIATE: %s", strerror(errno));
                /* NOTREACHED */
        }
        /* Set a 32k buffer size for kernel use */
        bufsize = 32768;
        if (ioctl(fd, BIOCSBLEN, &bufsize) < 0) {
                rarperr(NONFATAL, "BIOCSBLEN:%d: %s", bufsize, strerror(errno));
        }
        (void)strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
        if (ioctl(fd, BIOCSETIF, (caddr_t) & ifr) < 0) {
                if (aflag) {    /* for -a skip non-Ethernet interfaces */
                        close(fd);
                        return(-1);
                }
                rarperr(FATAL, "BIOCSETIF: %s", strerror(errno));
                /* NOTREACHED */
        }
        /* Check that the data link layer is an Ethernet; this code won't work
         * with anything else. */
        if (ioctl(fd, BIOCGDLT, (caddr_t) & dlt) < 0) {
                rarperr(FATAL, "BIOCGDLT: %s", strerror(errno));
                /* NOTREACHED */
        }
        if (dlt != DLT_EN10MB) {
                if (aflag) {    /* for -a skip non-Ethernet interfaces */
                        close(fd);
                        return(-1);
                }
                rarperr(FATAL, "%s is not an Ethernet", device);
                /* NOTREACHED */
        }
        /* Set filter program. */
        if (ioctl(fd, BIOCSETF, (caddr_t) & filter) < 0) {
                rarperr(FATAL, "BIOCSETF: %s", strerror(errno));
                /* NOTREACHED */
        }
        return fd;
}
/*
 * Perform various sanity checks on the RARP request packet.  Return
 * false on failure and log the reason.
 */
static int
rarp_check(u_char *p, int len)
{
        struct ether_header *ep = (struct ether_header *) p;
#ifdef __NetBSD__
        struct arphdr *ap = (struct arphdr *) (p + sizeof(*ep));
#else
        struct ether_arp *ap = (struct ether_arp *) (p + sizeof(*ep));
#endif

        if (len < (int)(sizeof(*ep) + sizeof(*ap))) {
                rarperr(NONFATAL, "truncated request");
                return 0;
        }
#ifdef __NetBSD__
        /* now that we know the fixed part of the ARP hdr is there: */
        if (len < (int)(sizeof(*ap) + 2 * ap->ar_hln + 2 * ap->ar_pln)) {
                rarperr(NONFATAL, "truncated request");
                return 0;
        }
#endif
        /* XXX This test might be better off broken out... */
#ifdef __FreeBSD__
        /* BPF (incorrectly) returns this in host order. */
        if (ep->ether_type != ETHERTYPE_REVARP ||
#else
        if (ntohs (ep->ether_type) != ETHERTYPE_REVARP ||
#endif
#ifdef __NetBSD__
            ntohs (ap->ar_hrd) != ARPHRD_ETHER ||
            ntohs (ap->ar_op) != ARPOP_REVREQUEST ||
            ntohs (ap->ar_pro) != ETHERTYPE_IP ||
            ap->ar_hln != 6 || ap->ar_pln != 4) {
#else
            ntohs (ap->arp_hrd) != ARPHRD_ETHER ||
            ntohs (ap->arp_op) != ARPOP_REVREQUEST ||
            ntohs (ap->arp_pro) != ETHERTYPE_IP ||
            ap->arp_hln != 6 || ap->arp_pln != 4) {
#endif
                rarperr(NONFATAL, "request fails sanity check");
                return 0;
        }
#ifdef __NetBSD__
        if (memcmp((char *) &ep->ether_shost, ar_sha(ap), 6) != 0) {
#else
        if (memcmp((char *) &ep->ether_shost, ap->arp_sha, 6) != 0) {
#endif
                rarperr(NONFATAL, "ether/arp sender address mismatch");
                return 0;
        }
        {
#ifdef __NetBSD__
                uint8_t *tha = ar_tha(ap);

                if (!tha || memcmp(ar_sha(ap), tha, 6) != 0) {
#else
                if (memcmp((char *) &ap->arp_sha, (char *) &ap->arp_tha, 6) != 0) {
#endif
                        rarperr(NONFATAL, "ether/arp target address mismatch");
                        return 0;
                }
        }
        return 1;
}

/*
 * Loop indefinitely listening for RARP requests on the
 * interfaces in 'iflist'.
 */
static void
rarp_loop(void)
{
        u_char *buf, *bp, *ep;
        int     cc, fd;
        fd_set  fds, listeners;
        int     bufsize, maxfd = 0;
        struct if_info *ii;

        if (iflist == 0) {
                rarperr(FATAL, "no interfaces");
                /* NOTREACHED */
        }
        if (ioctl(iflist->ii_fd, BIOCGBLEN, (caddr_t) & bufsize) < 0) {
                rarperr(FATAL, "BIOCGBLEN: %s", strerror(errno));
                /* NOTREACHED */
        }
        buf = (u_char *) malloc((unsigned) bufsize);
        if (buf == 0) {
                rarperr(FATAL, "malloc: %s", strerror(errno));
                /* NOTREACHED */
        }
        /*
         * Find the highest numbered file descriptor for select().
         * Initialize the set of descriptors to listen to.
         */
        FD_ZERO(&fds);
        for (ii = iflist; ii; ii = ii->ii_next) {
                FD_SET(ii->ii_fd, &fds);
                if (ii->ii_fd > maxfd)
                        maxfd = ii->ii_fd;
        }
        while (1) {
                listeners = fds;
                if (select(maxfd + 1, &listeners, (struct fd_set *) 0,
                        (struct fd_set *) 0, (struct timeval *) 0) < 0) {
                        rarperr(FATAL, "select: %s", strerror(errno));
                        /* NOTREACHED */
                }
                for (ii = iflist; ii; ii = ii->ii_next) {
                        fd = ii->ii_fd;
                        if (!FD_ISSET(fd, &listeners))
                                continue;
                again:
                        cc = read(fd, (char *) buf, bufsize);
                        /* Don't choke when we get ptraced */
                        if (cc < 0 && errno == EINTR)
                                goto again;
                        /* Due to a SunOS bug, after 2^31 bytes, the file
                         * offset overflows and read fails with EINVAL.  The
                         * lseek() to 0 will fix things. */
                        if (cc < 0) {
                                if (errno == EINVAL &&
                                    (lseek(fd, 0, SEEK_CUR) + bufsize) < 0) {
                                        (void)lseek(fd, 0, 0);
                                        goto again;
                                }
                                rarperr(FATAL, "read: %s", strerror(errno));
                                /* NOTREACHED */
                        }
                        /* Loop through the packet(s) */
#define bhp ((struct bpf_hdr *)bp)
                        bp = buf;
                        ep = bp + cc;
                        while (bp < ep) {
                                int caplen, hdrlen;

                                caplen = bhp->bh_caplen;
                                hdrlen = bhp->bh_hdrlen;
                                debug("received packet on %s", ii->ii_name);

                                if (rarp_check(bp + hdrlen, caplen))
                                        rarp_process(ii, bp + hdrlen);
                                bp += BPF_WORDALIGN(hdrlen + caplen);
                        }
                }
        }
}

#ifdef REQUIRE_TFTPBOOT

#ifndef TFTP_DIR
#define TFTP_DIR "/tftpboot"
#endif

/*
 * True if this server can boot the host whose IP address is 'addr'.
 * This check is made by looking in the tftp directory for the
 * configuration file.
 */
static int
rarp_bootable(u_int32_t addr)
{
        struct dirent *dent;
        DIR *d;
        char    ipname[9];
        static DIR *dd = 0;

        (void)snprintf(ipname, sizeof(ipname), "%08X", addr);
        /* If directory is already open, rewind it.  Otherwise, open it. */
        if (d = dd)
                rewinddir(d);
        else {
                if (chdir(TFTP_DIR) == -1) {
                        rarperr(FATAL, "chdir: %s", strerror(errno));
                        /* NOTREACHED */
                }
                d = opendir(".");
                if (d == 0) {
                        rarperr(FATAL, "opendir: %s", strerror(errno));
                        /* NOTREACHED */
                }
                dd = d;
        }
        while (dent = readdir(d))
                if (strncmp(dent->d_name, ipname, 8) == 0)
                        return 1;
        return 0;
}
#endif /* REQUIRE_TFTPBOOT */

/*
 * Given a list of IP addresses, 'alist', return the first address that
 * is on network 'net'; 'netmask' is a mask indicating the network portion
 * of the address.
 */
static u_int32_t
choose_ipaddr(u_int32_t **alist, u_int32_t net, u_int32_t netmask)
{

        for (; *alist; ++alist) {
                if ((**alist & netmask) == net)
                        return **alist;
        }
        return 0;
}
/*
 * Answer the RARP request in 'pkt', on the interface 'ii'.  'pkt' has
 * already been checked for validity.  The reply is overlaid on the request.
 */
static void
rarp_process(struct if_info *ii, u_char *pkt)
{
        struct ether_header *ep;
        struct hostent *hp;
        u_int32_t  target_ipaddr = 0;
        char    ename[MAXHOSTNAMELEN + 1];
        struct  in_addr in;

        ep = (struct ether_header *) pkt;

        if (ether_ntohost(ename, (struct ether_addr *)&ep->ether_shost) != 0) {
                debug("no IP address for %s",
                    ether_ntoa((struct ether_addr *)&ep->ether_shost));
                return;
        }
        ename[sizeof(ename)-1] = '\0';

        if ((hp = gethostbyname(ename)) == 0) {
                debug("gethostbyname(%s) failed: %s", ename,
                    hstrerror(h_errno));
                return;
        }

        /* Choose correct address from list. */
        if (hp->h_addrtype != AF_INET) {
                rarperr(FATAL, "cannot handle non IP addresses");
                /* NOTREACHED */
        }
        for (;; ii = ii->ii_alias) {
                target_ipaddr = choose_ipaddr((u_int32_t **) hp->h_addr_list,
                    ii->ii_ipaddr & ii->ii_netmask, ii->ii_netmask);
                if (target_ipaddr != 0)
                        break;
                if (ii->ii_alias == NULL)
                        break;
        }

        if (target_ipaddr == 0) {
                in.s_addr = ii->ii_ipaddr & ii->ii_netmask;
                rarperr(NONFATAL, "cannot find %s on net %s",
                    ename, inet_ntoa(in));
                return;
        }
#ifdef REQUIRE_TFTPBOOT
        if (rarp_bootable(htonl(target_ipaddr)))
#endif
                rarp_reply(ii, ep, target_ipaddr, hp);
#ifdef REQUIRE_TFTPBOOT
        else
                debug("%08X not bootable", htonl(target_ipaddr));
#endif
}
/*
 * Lookup the Ethernet address of the interface attached to the BPF
 * file descriptor 'fd'; return it in 'eaddr'.
 */
static void
lookup_eaddr(char *ifname, u_char *eaddr)
{
        struct ifaddrs *ifap, *ifa;
        struct sockaddr_dl *sdl;

        if (getifaddrs(&ifap) != 0) {
                rarperr(FATAL, "getifaddrs: %s", strerror(errno));
                /* NOTREACHED */
        }

        for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
                sdl = (struct sockaddr_dl *)ifa->ifa_addr;
                if (sdl->sdl_family != AF_LINK || sdl->sdl_type != IFT_ETHER ||
                    sdl->sdl_alen != 6)
                        continue;
                if (!strcmp(ifa->ifa_name, ifname)) {
                        memmove((caddr_t)eaddr, (caddr_t)LLADDR(sdl), 6);
                        debug("%s: %x:%x:%x:%x:%x:%x",
                            ifa->ifa_name, eaddr[0], eaddr[1],
                            eaddr[2], eaddr[3], eaddr[4], eaddr[5]);
                        freeifaddrs(ifap);
                        return;
                }
        }
        rarperr(FATAL, "lookup_eaddr: Never saw interface `%s'!", ifname);
        freeifaddrs(ifap);
}
/*
 * Lookup the IP address and network mask of the interface named 'ifname'.
 */
static void
lookup_ipaddr(char *ifname, u_int32_t *addrp, u_int32_t *netmaskp)
{
        int     fd;

        /* Use datagram socket to get IP address. */
        if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
                rarperr(FATAL, "socket: %s", strerror(errno));
                /* NOTREACHED */
        }
        if (*addrp == INADDR_ANY) {
                struct ifreq ifr;
                memset(&ifr, 0, sizeof(ifr));
                (void)strncpy(ifr.ifr_name, ifname, sizeof ifr.ifr_name);
                if (ioctl(fd, SIOCGIFADDR, (char *) &ifr) < 0) {
                        rarperr(FATAL, "SIOCGIFADDR: %s", strerror(errno));
                        /* NOTREACHED */
                }
                *addrp = ((struct sockaddr_in *) & ifr.ifr_addr)->sin_addr.s_addr;
                if (ioctl(fd, SIOCGIFNETMASK, (char *) &ifr) < 0) {
                        perror("SIOCGIFNETMASK");
                        exit(1);
                }
                *netmaskp = ((struct sockaddr_in *) & ifr.ifr_addr)->sin_addr.s_addr;
        } else {
                struct ifaliasreq ifra;
                memset(&ifra, 0, sizeof(ifra));
                (void)strncpy(ifra.ifra_name, ifname, sizeof ifra.ifra_name);
                ((struct sockaddr_in *) & ifra.ifra_addr)->sin_family = AF_INET;
                ((struct sockaddr_in *) & ifra.ifra_addr)->sin_addr.s_addr = *addrp;
                if (ioctl(fd, SIOCGIFALIAS, (char *) &ifra) < 0) {
                        rarperr(FATAL, "SIOCGIFALIAS: %s", strerror(errno));
                        /* NOTREACHED */
                }
                *addrp = ((struct sockaddr_in *) & ifra.ifra_addr)->sin_addr.s_addr;
                *netmaskp = ((struct sockaddr_in *) & ifra.ifra_mask)->sin_addr.s_addr;
        }
        /* If SIOCGIFNETMASK didn't work, figure out a mask from the IP
         * address class. */
        if (*netmaskp == 0)
                *netmaskp = ipaddrtonetmask(*addrp);

        (void)close(fd);
}
/*
 * Poke the kernel arp tables with the Ethernet/ip address combination
 * given.  When processing a reply, we must do this so that the booting
 * host (i.e. the guy running rarpd), won't try to ARP for the hardware
 * address of the guy being booted (he cannot answer the ARP).
 */
#ifndef __NetBSD__
static void
update_arptab(u_char *ep, u_int32_t ipaddr)
{
        struct arpreq request;
        struct sockaddr_in *sin;

        request.arp_flags = 0;
        sin = (struct sockaddr_in *) & request.arp_pa;
        sin->sin_family = AF_INET;
        sin->sin_addr.s_addr = ipaddr;
        request.arp_ha.sa_family = AF_UNSPEC;
        /* This is needed #if defined(COMPAT_43) && BYTE_ORDER != BIG_ENDIAN,
           because AF_UNSPEC is zero and the kernel assumes that a zero
           sa_family means that the real sa_family value is in sa_len.  */
        request.arp_ha.sa_len = 16; /* XXX */
        memmove((char *) request.arp_ha.sa_data, (char *)ep, 6);

#if 0
        s = socket(AF_INET, SOCK_DGRAM, 0);
        if (ioctl(s, SIOCSARP, (caddr_t) & request) < 0) {
                rarperr(NONFATAL, "SIOCSARP: %s", strerror(errno));
        }
        (void)close(s);
#endif
}
#endif

/*
 * Build a reverse ARP packet and sent it out on the interface.
 * 'ep' points to a valid ARPOP_REVREQUEST.  The ARPOP_REVREPLY is built
 * on top of the request, then written to the network.
 *
 * RFC 903 defines the ether_arp fields as follows.  The following comments
 * are taken (more or less) straight from this document.
 *
 * ARPOP_REVREQUEST
 *
 * arp_sha is the hardware address of the sender of the packet.
 * arp_spa is undefined.
 * arp_tha is the 'target' hardware address.
 *   In the case where the sender wishes to determine his own
 *   protocol address, this, like arp_sha, will be the hardware
 *   address of the sender.
 * arp_tpa is undefined.
 *
 * ARPOP_REVREPLY
 *
 * arp_sha is the hardware address of the responder (the sender of the
 *   reply packet).
 * arp_spa is the protocol address of the responder (see the note below).
 * arp_tha is the hardware address of the target, and should be the same as
 *   that which was given in the request.
 * arp_tpa is the protocol address of the target, that is, the desired address.
 *
 * Note that the requirement that arp_spa be filled in with the responder's
 * protocol is purely for convenience.  For instance, if a system were to use
 * both ARP and RARP, then the inclusion of the valid protocol-hardware
 * address pair (arp_spa, arp_sha) may eliminate the need for a subsequent
 * ARP request.
 */
static void
rarp_reply(struct if_info *ii, struct ether_header *ep, u_int32_t ipaddr,
           struct hostent *hp)
{
        int     n;
#ifdef __NetBSD__
        struct arphdr *ap = (struct arphdr *) (ep + 1);
#else
        struct ether_arp *ap = (struct ether_arp *) (ep + 1);
#endif

        int     len;

#ifdef __NetBSD__
        (void)mkarp((u_int8_t *)ar_sha(ap), ipaddr);
#else
        update_arptab((u_char *) & ap->arp_sha, ipaddr);
#endif

        /* Build the rarp reply by modifying the rarp request in place. */
#ifdef __FreeBSD__
        /* BPF (incorrectly) wants this in host order. */
        ep->ether_type = ETHERTYPE_REVARP;
#else
        ep->ether_type = htons(ETHERTYPE_REVARP);
#endif
#ifdef __NetBSD__
        ap->ar_hrd = htons(ARPHRD_ETHER);
        ap->ar_pro = htons(ETHERTYPE_IP);
        ap->ar_op = htons(ARPOP_REVREPLY);

        memmove((char *) &ep->ether_dhost, ar_sha(ap), 6);
        memmove((char *) &ep->ether_shost, (char *) ii->ii_eaddr, 6);
        memmove(ar_sha(ap), (char *) ii->ii_eaddr, 6);

        memmove(ar_tpa(ap), (char *) &ipaddr, 4);
        /* Target hardware is unchanged. */
        memmove(ar_spa(ap), (char *) &ii->ii_ipaddr, 4);

        len = sizeof(*ep) + sizeof(*ap) + 
            2 * ap->ar_pln + 2 * ap->ar_hln;
#else
        ap->ea_hdr.ar_hrd = htons(ARPHRD_ETHER);
        ap->ea_hdr.ar_pro = htons(ETHERTYPE_IP);
        ap->arp_op = htons(ARPOP_REVREPLY);

        memmove((char *) &ep->ether_dhost, (char *) &ap->arp_sha, 6);
        memmove((char *) &ep->ether_shost, (char *) ii->ii_eaddr, 6);
        memmove((char *) &ap->arp_sha, (char *) ii->ii_eaddr, 6);

        memmove((char *) ap->arp_tpa, (char *) &ipaddr, 4);
        /* Target hardware is unchanged. */
        memmove((char *) ap->arp_spa, (char *) &ii->ii_ipaddr, 4);

        len = sizeof(*ep) + sizeof(*ap);
#endif

        debug("%s asked; %s replied",
            ether_ntoa((struct ether_addr *)ar_tha(ap)), hp->h_name);
        if (lflag)
                syslog(LOG_INFO, "%s asked; %s replied",
                    ether_ntoa((struct ether_addr *)ar_tha(ap)), hp->h_name);
        n = write(ii->ii_fd, (char *) ep, len);
        if (n != len) {
                rarperr(NONFATAL, "write: only %d of %d bytes written", n, len);
        }
}
/*
 * Get the netmask of an IP address.  This routine is used if
 * SIOCGIFNETMASK doesn't work.
 */
static u_int32_t
ipaddrtonetmask(u_int32_t addr)
{

        if (IN_CLASSA(addr))
                return IN_CLASSA_NET;
        if (IN_CLASSB(addr))
                return IN_CLASSB_NET;
        if (IN_CLASSC(addr))
                return IN_CLASSC_NET;
        rarperr(FATAL, "unknown IP address class: %08X", addr);
        /* NOTREACHED */
        return(-1);
}

#include <stdarg.h>

static void
rarperr(int fatal, const char *fmt,...)
{
        va_list ap;

        va_start(ap, fmt);
        if (dflag) {
                if (fatal)
                        (void)fprintf(stderr, "%s: error: ", getprogname());
                else
                        (void)fprintf(stderr, "%s: warning: ", getprogname());
                (void)vfprintf(stderr, fmt, ap);
                va_end(ap);
                va_start(ap, fmt);
                (void)fprintf(stderr, "\n");
        }
        vsyslog(LOG_ERR, fmt, ap);
        va_end(ap);
        if (fatal)
                exit(1);
        /* NOTREACHED */
}

static void
debug(const char *fmt,...)
{
        va_list ap;

        va_start(ap, fmt);
        if (dflag) {
                (void)fprintf(stderr, "%s: ", getprogname());
                (void)vfprintf(stderr, fmt, ap);
                va_end(ap);
                va_start(ap, fmt);
                (void)fprintf(stderr, "\n");
        }
        vsyslog(LOG_WARNING, fmt, ap);
        va_end(ap);
}