cmd-inet/usr.bin/rlogin.c

	rlogin.c revision 740638c8fa5a1c03618a9c75c3161dba57259a17
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*  Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T */
/*    All Rights Reserved   */

/*
 * University Copyright- Copyright (c) 1982, 1986, 1988
 * The Regents of the University of California
 * All Rights Reserved
 *
 * University Acknowledgment- Portions of this document are derived from
 * software developed by the University of California, Berkeley, and its
 * contributors.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 * rlogin - remote login
 */
#include <sys/types.h>
#include <sys/param.h>
#include <sys/errno.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/stropts.h>
#include <sys/ttold.h>
#include <sys/sockio.h>
#include <sys/tty.h>
#include <sys/ptyvar.h>
#include <sys/resource.h>
#include <sys/select.h>
#include <sys/time.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <priv_utils.h>

#include <stdio.h>
#include <errno.h>
#include <pwd.h>
#include <signal.h>
#include <setjmp.h>
#include <netdb.h>
#include <fcntl.h>
#include <locale.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <k5-int.h>
#include <profile/prof_int.h>
#include <com_err.h>
#include <kcmd.h>
#include <krb5.h>

/* signal disposition - signal handler or SIG_IGN, SIG_ERR, etc. */
typedef void (*sigdisp_t)(int);

extern errcode_t    profile_get_options_boolean(profile_t, char **,
    profile_options_boolean *);
extern errcode_t    profile_get_options_string(profile_t, char **,
    profile_option_strings *);

#define RLOGIN_BUFSIZ   (1024 * 50)
static char des_inbuf[2 * RLOGIN_BUFSIZ];
                    /* needs to be > largest read size */
static char des_outbuf[2 * RLOGIN_BUFSIZ];
                    /* needs to be > largest write size */
static krb5_data desinbuf, desoutbuf;
static krb5_encrypt_block eblock;   /* eblock for encrypt/decrypt */
static krb5_keyblock *session_key;
static krb5_creds *cred;
static krb5_context bsd_context;
static krb5_auth_context auth_context;

static char *krb_realm;

static  int krb5auth_flag;  /* Flag set, when KERBEROS is enabled */
static  int fflag, Fflag;   /* Flag set, when option -f / -F used */
static  int encrypt_flag;   /* Flag set, when the "-x" option is used */

/* Flag set, if -PN / -PO is specified */
static boolean_t rcmdoption_done;

/* Flags set, if corres. cmd line options are turned on */
static boolean_t encrypt_done, fwd_done, fwdable_done;

static profile_options_boolean option[] = {
    { "encrypt", &encrypt_flag, 0 },
    { "forward", &fflag, 0 },
    { "forwardable", &Fflag, 0 },
    { NULL, NULL, 0 }
};

static char *rcmdproto;
static profile_option_strings rcmdversion[] = {
    { "rcmd_protocol", &rcmdproto, 0 },
    { NULL, NULL, 0 }
};

static char rlogin[] = "rlogin";

static char *realmdef[] = { "realms", NULL, rlogin, NULL };
static char *appdef[] = { "appdefaults", rlogin, NULL };

#ifndef TIOCPKT_WINDOW
#define TIOCPKT_WINDOW 0x80
#endif /* TIOCPKT_WINDOW */

#ifndef sigmask
#define sigmask(m)  (1 << ((m)-1))
#endif

#define set2mask(setp)  ((setp)->__sigbits[0])
#define mask2set(mask, setp) \
    ((mask) == -1 ? sigfillset(setp) : (((setp)->__sigbits[0]) = (mask)))

#ifdef DEBUG
#define DEBUGOPTSTRING  "D:"
#else
#define DEBUGOPTSTRING  ""
#endif  /* DEBUG */

static  boolean_t ttcompat;
static  struct termios savetty;

static  char *errmsg(int);
static  char *host;
static  int port_number;
static  int rem = -1;
static  char cmdchar = '~';
static  boolean_t nocmdchar;
static  boolean_t eight;
static  boolean_t litout;
static  boolean_t null_local_username;
/*
 * Note that this list of speeds is shorter than the list of speeds
 * supported by termios.  This is because we can't be sure other rlogind's
 * in the world will correctly cope with values other than what 4.2/4.3BSD
 * supported.
 */
static  char *speeds[] =
    { "0", "50", "75", "110", "134", "150", "200", "300",
        "600", "1200", "1800", "2400", "4800", "9600", "19200",
        "38400" };
static  char term[256] = "network";
static  void lostpeer(void);
static  boolean_t dosigwinch;
static  struct winsize winsize;
static  void sigwinch(int);
static  void oob(void);
static  void doit(int);
static  sigdisp_t sigdisp(int);

#define CRLF "\r\n"

static  pid_t child;
static  void catchild(int);
/* LINTED */
static  void copytochild(int);
static  void writeroob(int);
static  void stop(char), echo(char);

static  int defflags, tabflag;
static  int deflflags;
static  char deferase, defkill;
static  struct tchars deftc;
static  struct ltchars defltc;
static  struct tchars notc = { (char)-1, (char)-1, (char)-1,
                (char)-1, (char)-1, (char)-1 };
static  struct ltchars noltc =  { (char)-1, (char)-1, (char)-1,
                (char)-1, (char)-1, (char)-1 };

static  void done(int);
static  void mode(int);
static  int reader(int);
static  void writer(void);
static  void prf(const char *, ...);
static  void sendwindow(void);
static  int compat_ioctl(int, int, void *);

static void
sigsetmask(int mask)
{
    sigset_t oset;
    sigset_t nset;

    (void) sigprocmask(0, NULL, &nset);
    mask2set(mask, &nset);
    (void) sigprocmask(SIG_SETMASK, &nset, &oset);
}

static int
sigblock(int mask)
{
    sigset_t oset;
    sigset_t nset;

    (void) sigprocmask(0, NULL, &nset);
    mask2set(mask, &nset);
    (void) sigprocmask(SIG_BLOCK, &nset, &oset);
    return (set2mask(&oset));
}

static void
pop(int status) {
    if (ttcompat) {
        /*
         * Pop ttcompat module
         */
        (void) ioctl(STDIN_FILENO, I_POP, 0);
    }
    (void) tcsetattr(STDIN_FILENO, TCSANOW, &savetty);
    exit(status);
}

static void
usage(void) {
    (void) fprintf(stderr, "%s\n%s\n",
        gettext("usage: rlogin [-option] [-option...] "
        "[-k realm] [-l username] host"),
        gettext("       where option is e, 8, E, L, A, a, x, "
        "PN / PO, f or F"));
    pop(EXIT_FAILURE);
}

/* PRINTFLIKE(0) */
static void
die(const char *format, ...)
{
    va_list ap;

    va_start(ap, format);
    (void) vfprintf(stderr, format, ap);
    va_end(ap);
    usage();
}

static void
usage_forward(void)
{
    die(gettext("rlogin: Only one of -f and -F allowed.\n"));
}

int
main(int argc, char **argv)
{
    int c;
    char *cp, *cmd, *name = NULL;
    struct passwd *pwd;
    uid_t uid;
    int options = 0, oldmask;
    int on = 1;
    speed_t speed = 0;
    int getattr_ret;
    char *tmp;
    int sock;
    krb5_flags authopts;
    krb5_error_code status;
    enum kcmd_proto kcmd_proto = KCMD_NEW_PROTOCOL;

    (void) setlocale(LC_ALL, "");

#if !defined(TEXT_DOMAIN)
#define TEXT_DOMAIN "SYS_TEST"
#endif
    (void) textdomain(TEXT_DOMAIN);

    if (__init_suid_priv(0, PRIV_NET_PRIVADDR, NULL) == -1) {
        (void) fprintf(stderr,
            gettext("Insufficient privileges, "
            "rlogin must be set-uid root\n"));
        exit(1);
    }

    {
        int it;

        if ((getattr_ret = tcgetattr(STDIN_FILENO, &savetty)) < 0)
            perror("tcgetattr");
        it = ioctl(STDIN_FILENO, I_FIND, "ttcompat");
        if (it < 0) {
            perror("ioctl I_FIND ttcompat");
            return (EXIT_FAILURE);
        }
        if (it == 0) {
            if (ioctl(STDIN_FILENO, I_PUSH, "ttcompat") < 0) {
                perror("ioctl I_PUSH ttcompat");
                exit(EXIT_FAILURE);
            }
            ttcompat = B_TRUE;
        }
    }

    /*
     * Determine command name used to invoke to rlogin(1). Users can
     * create links named by a host pointing to the binary and type
     * "hostname" to log into that host afterwards.
     */
    cmd = strrchr(argv[0], '/');
    cmd = (cmd != NULL) ? (cmd + 1) : argv[0];

    if (strcmp(cmd, rlogin) == 0) {
        if (argc < 2)
            usage();
        if (*argv[1] != '-') {
            host = argv[1];
            argc--;
            argv[1] = argv[0];
            argv++;
        }
    } else {
        host = cmd;
    }

    while ((c = getopt(argc, argv,
        DEBUGOPTSTRING "8AEFLP:ade:fk:l:x")) != -1) {
        switch (c) {
        case '8':
            eight = B_TRUE;
            break;
        case 'A':
            krb5auth_flag = B_TRUE;
            break;
#ifdef DEBUG
        case 'D':
            portnumber = htons(atoi(optarg));
            krb5auth_flag = B_TRUE;
            break;
#endif /* DEBUG */
        case 'E':
            nocmdchar = B_TRUE;
            break;
        case 'F':
            if (fflag)
                usage_forward();
            Fflag = 1;
            krb5auth_flag = B_TRUE;
            fwdable_done = B_TRUE;
            break;
        case 'f':
            if (Fflag)
                usage_forward();
            fflag = 1;
            krb5auth_flag = B_TRUE;
            fwd_done = B_TRUE;
            break;
        case 'L':
            litout = B_TRUE;
            break;
        case 'P':
            if (strcmp(optarg, "N") == 0)
                kcmd_proto = KCMD_NEW_PROTOCOL;
            else if (strcmp(optarg, "O") == 0)
                kcmd_proto = KCMD_OLD_PROTOCOL;
            else
                die(gettext("rlogin: Only -PN or -PO "
                    "allowed.\n"));
            if (rcmdoption_done)
                die(gettext("rlogin: Only one of -PN and -PO "
                    "allowed.\n"));
            rcmdoption_done = B_TRUE;
            krb5auth_flag = B_TRUE;
            break;
        case 'a':
        /*
         * Force the remote host to prompt for a password by sending
         * a NULL username. This option is mutually exclusive with
         * the -A, -x, -f, -F, -k <realm> options.
         */
            null_local_username = B_TRUE;
            break;
        case 'd':
            options |= SO_DEBUG;
            break;
        case 'e': {
            int c;

            cp = optarg;

            if ((c = *cp) != '\\') {
                cmdchar = c;
            } else {
                c = cp[1];
                if (c == '\0' || c == '\\') {
                    cmdchar = '\\';
                } else if (c >= '0' && c <= '7') {
                    long lc;

                    lc = strtol(&cp[1], NULL, 8);
                    if (lc < 0 || lc > 255)
                        die(gettext("rlogin: octal "
                            "escape character %s too "
                            "large.\n"), cp);
                    cmdchar = (char)lc;
                } else {
                    die(gettext("rlogin: unrecognized "
                        "escape character option %s.\n"),
                        cp);
                }
            }
            break;
        }
        case 'k':
            krb_realm = optarg;
            krb5auth_flag = B_TRUE;
            break;
        case 'l':
            name = optarg;
            break;
        case 'x':
            encrypt_flag = 1;
            krb5auth_flag = B_TRUE;
            encrypt_done = B_TRUE;
            break;
        default:
            usage();
        }
    }

    argc -= optind;
    argv += optind;

    if (host == NULL) {
        if (argc == 0)
            usage();
        argc--;
        host = *argv++;
    }

    if (argc > 0)
        usage();

    pwd = getpwuid(uid = getuid());
    if (pwd == NULL) {
        (void) fprintf(stderr, gettext("getpwuid(): can not find "
            "password entry for user id %d."), uid);
        return (EXIT_FAILURE);
    }
    if (name == NULL)
        name = pwd->pw_name;

    /*
     * If the `-a' option is issued on the cmd line, we reset all
     * flags associated with other KRB5 specific options, since
     * the -a option is mutually exclusive with the rest.
     */
    if (null_local_username) {
        krb5auth_flag = B_FALSE;
        fflag = Fflag = encrypt_flag = 0;
        (void) fprintf(stderr, gettext("Note: The -a option nullifies "
                    "all other Kerberos-specific\noptions "
                    "you may have used.\n"));
    }

    if (krb5auth_flag) {
        status = krb5_init_context(&bsd_context);
        if (status) {
            com_err(rlogin, status, gettext("while initializing"
                    " krb5"));
            return (EXIT_FAILURE);
        }
        /*
         * Set up buffers for desread and deswrite.
         */
        desinbuf.data = des_inbuf;
        desoutbuf.data = des_outbuf;
        desinbuf.length = sizeof (des_inbuf);
        desoutbuf.length = sizeof (des_outbuf);

        /*
         * Get our local realm to look up local realm options.
         */
        status = krb5_get_default_realm(bsd_context, &realmdef[1]);
        if (status) {
            com_err(rlogin, status,
                gettext("while getting default realm"));
            return (EXIT_FAILURE);
        }
        /*
         * Check the realms section in krb5.conf for encryption,
         * forward & forwardable info
         */
        profile_get_options_boolean(bsd_context->profile, realmdef,
                        option);
        /*
         * Check the appdefaults section
         */
        profile_get_options_boolean(bsd_context->profile, appdef,
                        option);
        profile_get_options_string(bsd_context->profile, appdef,
                        rcmdversion);

        /*
         * Set the *_flag variables, if the corresponding *_done are
         * set to 1, because we dont want the config file values
         * overriding the command line options.
         */
        if (encrypt_done)
            encrypt_flag = 1;
        if (fwd_done) {
            fflag = 1;
            Fflag = 0;
        } else if (fwdable_done) {
            Fflag = 1;
            fflag = 0;
        }
        if (!rcmdoption_done && (rcmdproto != NULL)) {
            if (strncmp(rcmdproto, "rcmdv2", 6) == 0) {
                kcmd_proto = KCMD_NEW_PROTOCOL;
            } else if (strncmp(rcmdproto, "rcmdv1", 6) == 0) {
                kcmd_proto = KCMD_OLD_PROTOCOL;
            } else {
                (void) fprintf(stderr, gettext("Unrecognized "
                    "KCMD protocol (%s)"), rcmdproto);
                return (EXIT_FAILURE);
            }
        }

        if (encrypt_flag && (!krb5_privacy_allowed())) {
            (void) fprintf(stderr, gettext("rlogin: "
                    "Encryption not supported.\n"));
            return (EXIT_FAILURE);
        }
    }

    if (port_number == 0) {
        if (krb5auth_flag) {
            struct servent *sp;

            /*
             * If the krb5auth_flag is set (via -A, -f, -F, -k) &
             * if there is an entry in /etc/services for Kerberos
             * login, attempt to login with Kerberos. If we fail
             * at any step,  use the standard rlogin
             */
            sp = getservbyname(encrypt_flag ?
                "eklogin" : "klogin", "tcp");
            if (sp == NULL) {
                port_number = encrypt_flag ?
                    htons(2105) : htons(543);
            } else {
                port_number = sp->s_port;
            }
        } else {
            port_number = htons(IPPORT_LOGINSERVER);
        }
    }

    cp = getenv("TERM");
    if (cp) {
        (void) strncpy(term, cp, sizeof (term));
        term[sizeof (term) - 1] = '\0';
    }
    if (getattr_ret == 0) {
        speed = cfgetospeed(&savetty);
        /*
         * "Be conservative in what we send" -- Only send baud rates
         * which at least all 4.x BSD derivatives are known to handle
         * correctly.
         * NOTE:  This code assumes new termios speed values will
         * be "higher" speeds.
         */
        if (speed > B38400)
            speed = B38400;
    }

    /*
     * Only put the terminal speed info in if we have room
     * so we don't overflow the buffer, and only if we have
     * a speed we recognize.
     */
    if (speed > 0 && speed < sizeof (speeds)/sizeof (char *) &&
        strlen(term) + strlen("/") + strlen(speeds[speed]) + 1 <
        sizeof (term)) {
        (void) strcat(term, "/");
        (void) strcat(term, speeds[speed]);
    }
    (void) sigset(SIGPIPE, (sigdisp_t)lostpeer);
    /* will use SIGUSR1 for window size hack, so hold it off */
    oldmask = sigblock(sigmask(SIGURG) | sigmask(SIGUSR1));

    /*
     * Determine if v4 literal address and if so store it to one
     * side. This is to correct the undesired behaviour of rcmd_af
     * which converts a passed in v4 literal address to a v4 mapped
     * v6 literal address. If it was a v4 literal we then re-assign
     * it to host.
     */
    tmp = NULL;
    if (inet_addr(host) != (in_addr_t)-1)
        tmp = host;

    if (krb5auth_flag) {
        authopts = AP_OPTS_MUTUAL_REQUIRED;

        /* Piggy-back forwarding flags on top of authopts; */
        /* they will be reset in kcmd */
        if (fflag || Fflag)
            authopts |= OPTS_FORWARD_CREDS;
        if (Fflag)
            authopts |= OPTS_FORWARDABLE_CREDS;

        status = kcmd(&sock, &host, port_number,
            null_local_username ? "" : pwd->pw_name,
            name, term, NULL,
            "host", krb_realm, bsd_context, &auth_context,
            &cred,
            NULL,       /* No need for sequence number */
            NULL,       /* No need for server seq # */
            authopts,
            0,      /* Not any port # */
            &kcmd_proto);

        if (status != 0) {
            /*
             * If new protocol requested, we dont fallback to
             * less secure ones.
             */
            if (kcmd_proto == KCMD_NEW_PROTOCOL) {
                (void) fprintf(stderr, gettext("rlogin: kcmdv2 "
                    "to host %s failed - %s\n"
                    "Fallback to normal rlogin denied."),
                    host, error_message(status));
                return (EXIT_FAILURE);
            }
            if (status != -1) {
                (void) fprintf(stderr, gettext("rlogin: kcmd "
                        "to host %s failed - %s,\n"
                        "trying normal rlogin...\n\n"),
                        host, error_message(status));
            } else {
                (void) fprintf(stderr,
                    gettext("trying normal rlogin...\n"));
            }
            /*
             * kcmd() failed, so we have to
             * fallback to normal rlogin
             */
            port_number = htons(IPPORT_LOGINSERVER);
            krb5auth_flag = B_FALSE;
            fflag = Fflag = encrypt_flag = 0;
            null_local_username = B_FALSE;
        } else {
            (void) fprintf(stderr,
                gettext("connected with Kerberos V5\n"));

            /*
             * Setup eblock for desread and deswrite.
             */
            session_key = &cred->keyblock;

            if (kcmd_proto == KCMD_NEW_PROTOCOL) {
                status = krb5_auth_con_getlocalsubkey(
                    bsd_context,
                    auth_context,
                    &session_key);
                if (status) {
                    com_err(rlogin, status,
                        "determining subkey for session");
                    return (EXIT_FAILURE);
                }
                if (session_key == NULL) {
                    com_err(rlogin, 0,
                        "no subkey negotiated for "
                        "connection");
                    return (EXIT_FAILURE);
                }
            }

            eblock.crypto_entry = session_key->enctype;
            eblock.key = (krb5_keyblock *)session_key;

            init_encrypt(encrypt_flag, bsd_context, kcmd_proto,
                &desinbuf, &desoutbuf, CLIENT, &eblock);

            rem = sock;
            if (rem < 0)
                pop(EXIT_FAILURE);
        }
    }

    /*
     * Don't merge this with the "if" statement above because
     * "krb5auth_flag" might be set to false inside it.
     */
    if (!krb5auth_flag) {
        rem = rcmd_af(&host, port_number,
            null_local_username ? "" : pwd->pw_name,
            name, term, NULL, AF_INET6);
        if (rem < 0)
            pop(EXIT_FAILURE);
    }

    /* Never need our privilege again */
    __priv_relinquish();

    if (tmp != NULL)
        host = tmp;

    if (options & SO_DEBUG &&
        setsockopt(rem, SOL_SOCKET, SO_DEBUG, (char *)&on,
                sizeof (on)) < 0)
        perror("rlogin: setsockopt (SO_DEBUG)");

    {
        int bufsize = 8192;

        (void) setsockopt(rem, SOL_SOCKET, SO_RCVBUF, (char *)&bufsize,
            sizeof (int));
    }

    doit(oldmask);
    return (0);
}

static void
doit(int oldmask)
{
    struct sgttyb sb;
    int atmark;

    if (ioctl(STDIN_FILENO, TIOCGETP, (char *)&sb) == -1)
        perror("ioctl TIOCGETP");
    defflags = sb.sg_flags;
    tabflag = defflags & O_TBDELAY;
    defflags &= ECHO | O_CRMOD;
    deferase = sb.sg_erase;
    defkill = sb.sg_kill;
    if (ioctl(STDIN_FILENO, TIOCLGET, (char *)&deflflags) == -1)
        perror("ioctl TIOCLGET");
    if (ioctl(STDIN_FILENO, TIOCGETC, (char *)&deftc) == -1)
        perror("ioctl TIOCGETC");
    notc.t_startc = deftc.t_startc;
    notc.t_stopc = deftc.t_stopc;
    if (ioctl(STDIN_FILENO, TIOCGLTC, (char *)&defltc) == -1)
        perror("ioctl TIOCGLTC");
    (void) sigset(SIGINT, SIG_IGN);
    if (sigdisp(SIGHUP) != SIG_IGN)
        (void) sigset(SIGHUP, exit);
    if (sigdisp(SIGQUIT) != SIG_IGN)
        (void) sigset(SIGQUIT, exit);
    child = fork();
    if (child == (pid_t)-1) {
        perror("rlogin: fork");
        done(EXIT_FAILURE);
    }
    if (child == 0) {
        mode(1);
        if (reader(oldmask) == 0) {
            prf(gettext("Connection to %.*s closed."),
                MAXHOSTNAMELEN, host);
            exit(EXIT_SUCCESS);
        }
        (void) sleep(1);
        prf(gettext("\aConnection to %.*s closed."),
            MAXHOSTNAMELEN, host);
        exit(EXIT_FAILURE);
    }

    /*
     * We may still own the socket, and may have a pending SIGURG (or might
     * receive one soon) that we really want to send to the reader.  Set a
     * trap that simply copies such signals to the child.
     */
#ifdef F_SETOWN_BUG_FIXED
    (void) sigset(SIGURG, copytochild);
#else
    (void) sigset(SIGURG, SIG_IGN);
#endif /* F_SETOWN_BUG_FIXED */
    (void) sigset(SIGUSR1, writeroob);
    /*
     * Of course, if the urgent byte already arrived, allowing SIGURG
     * won't get us notification.  So, we check to see if we've got
     * an urgent byte.  If so, force a call to writeroob() to pretend
     * we got SIGURG.
     */
    if (ioctl(rem, SIOCATMARK, &atmark) >= 0) {
        if (atmark)
            writeroob(0);
    }
    sigsetmask(oldmask);
    (void) sigset(SIGCHLD, catchild);
    writer();
    prf(gettext("Closed connection to %.*s."), MAXHOSTNAMELEN, host);
    done(EXIT_SUCCESS);
}

/*
 * Get signal disposition (or signal handler) for a given signal
 */
static sigdisp_t
sigdisp(int sig)
{
    struct sigaction act;

    act.sa_handler = NULL;
    act.sa_flags = 0;
    (void) sigemptyset(&act.sa_mask);
    (void) sigaction(sig, NULL, &act);
    return (act.sa_handler);
}

static void
done(int status)
{
    pid_t w;

    mode(0);
    if (child > 0) {
        /* make sure catchild does not snap it up */
        (void) sigset(SIGCHLD, SIG_DFL);
        if (kill(child, SIGKILL) >= 0)
            while ((w = wait(0)) > (pid_t)0 && w != child)
                /* void */;
    }
    pop(status);
}

/*
 * Copy SIGURGs to the child process.
 */

/* ARGSUSED */
static void
copytochild(int signum)
{

    (void) kill(child, SIGURG);
}

/*
 * This is called when the reader process gets the out-of-band (urgent)
 * request to turn on the window-changing protocol.
 */

/* ARGSUSED */
static void
writeroob(int signum)
{
    int mask;

    if (!dosigwinch) {
        /*
         * Start tracking window size.  It doesn't matter which
         * order the next two are in, because we'll be unconditionally
         * sending a size notification in a moment.
         */
        (void) sigset(SIGWINCH, sigwinch);
        dosigwinch = B_TRUE;

        /*
         * It would be bad if a SIGWINCH came in between the ioctl
         * and sending the data.  It could result in the SIGWINCH
         * handler sending a good message, and then us sending an
         * outdated or inconsistent message.
         *
         * Instead, if the change is made before the
         * ioctl, the sigwinch handler will send a size message
         * and we'll send another, identical, one.  If the change
         * is made after the ioctl, we'll send a message with the
         * old value, and then the sigwinch handler will send
         * a revised, correct one.
         */
        mask = sigblock(sigmask(SIGWINCH));
        if (ioctl(STDIN_FILENO, TIOCGWINSZ, &winsize) == 0)
            sendwindow();
        sigsetmask(mask);
    }
}

/* ARGSUSED */
static void
catchild(int signum)
{
    int options;
    siginfo_t   info;
    int error;

    for (;;) {
        options = WNOHANG | WEXITED;
        error = waitid(P_ALL, 0, &info, options);
        if (error != 0)
            return;
        if (info.si_pid == 0)
            return;
        if (info.si_code == CLD_TRAPPED)
            continue;
        if (info.si_code == CLD_STOPPED)
            continue;
        done(info.si_status);
    }
}

/*
 * writer: write to remote: 0 -> line.
 * ~.   terminate
 * ~^Z  suspend rlogin process.
 * ~^Y  suspend rlogin process, but leave reader alone.
 */
static void
writer(void)
{
    char c;
    int n;
    boolean_t bol = B_TRUE;     /* beginning of line */
    boolean_t local = B_FALSE;

    for (;;) {
        n = read(STDIN_FILENO, &c, 1);
        if (n <= 0) {
            if (n == 0)
                break;
            if (errno == EINTR)
                continue;
            else {
                prf(gettext("Read error from terminal: %s"),
                    errmsg(errno));
                break;
            }
        }
        /*
         * If we're at the beginning of the line
         * and recognize a command character, then
         * we echo locally.  Otherwise, characters
         * are echo'd remotely.  If the command
         * character is doubled, this acts as a
         * force and local echo is suppressed.
         */
        if (bol && !nocmdchar) {
            bol = B_FALSE;
            if (c == cmdchar) {
                local = B_TRUE;
                continue;
            }
        } else if (local) {
            local = B_FALSE;
            if (c == '.' || c == deftc.t_eofc) {
                echo(c);
                break;
            }
            if (c == defltc.t_suspc || c == defltc.t_dsuspc) {
                bol = B_TRUE;
                echo(c);
                stop(c);
                continue;
            }
            if (c != cmdchar) {
                if (deswrite(rem, &cmdchar, 1, 0) < 0) {
                    prf(gettext(
                        "Write error to network: %s"),
                        errmsg(errno));
                    break;
                }
            }
        }
        if ((n = deswrite(rem, &c, 1, 0)) <= 0) {
            if (n == 0)
                prf(gettext("line gone"));
            else
                prf(gettext("Write error to network: %s"),
                    errmsg(errno));
            break;
        }
        bol = c == defkill || c == deftc.t_eofc ||
            c == deftc.t_intrc || c == defltc.t_suspc ||
            c == '\r' || c == '\n';
    }
}

static void
echo(char c)
{
    char buf[8];
    char *p = buf;

    c &= 0177;
    *p++ = cmdchar;
    if (c < ' ') {
        *p++ = '^';
        *p++ = c + '@';
    } else if (c == 0177) {
        *p++ = '^';
        *p++ = '?';
    } else
        *p++ = c;
    *p++ = '\r';
    *p++ = '\n';
    if (write(STDOUT_FILENO, buf, p - buf) < 0)
        prf(gettext("Write error to terminal: %s"), errmsg(errno));
}

static void
stop(char cmdc)
{
    mode(0);
    (void) sigset(SIGCHLD, SIG_IGN);
    (void) kill(cmdc == defltc.t_suspc ? 0 : getpid(), SIGTSTP);
    (void) sigset(SIGCHLD, catchild);
    mode(1);
    sigwinch(0);            /* check for size changes */
}

/* ARGSUSED */
static void
sigwinch(int signum)
{
    struct winsize ws;

    if (dosigwinch && ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) == 0 &&
        memcmp(&winsize, &ws, sizeof (ws)) != 0) {
        winsize = ws;
        sendwindow();
    }
}

/*
 * Send the window size to the server via the magic escape.
 * Note:  SIGWINCH should be blocked when this is called, lest
 * winsize change underneath us and chaos result.
 */
static void
sendwindow(void)
{
    char obuf[4 + sizeof (struct winsize)];
    struct winsize *wp = (struct winsize *)(void *)(obuf+4);

    obuf[0] = -1;
    obuf[1] = -1;
    obuf[2] = 's';
    obuf[3] = 's';
    wp->ws_row = htons(winsize.ws_row);
    wp->ws_col = htons(winsize.ws_col);
    wp->ws_xpixel = htons(winsize.ws_xpixel);
    wp->ws_ypixel = htons(winsize.ws_ypixel);
    if (deswrite(rem, obuf, sizeof (obuf), 0) < 0)
        prf(gettext("Write error to network: %s"), errmsg(errno));
}


/*
 * reader: read from remote: remote -> stdout
 */
#define READING 1
#define WRITING 2

static  char rcvbuf[8 * 1024];
static  int rcvcnt;
static  int rcvstate;
static  pid_t ppid;
static  jmp_buf rcvtop;

static void
oob(void)
{
    int out = FWRITE, atmark, n;
    int rcvd = 0;
    char waste[4*BUFSIZ], mark;
    struct sgttyb sb;
    fd_set exceptfds;
    struct timeval tv;
    int ret;

    FD_ZERO(&exceptfds);
    FD_SET(rem, &exceptfds);
    timerclear(&tv);
    ret = select(rem+1, NULL, NULL, &exceptfds, &tv);
    /*
     * We may get an extra signal at start up time since we are trying
     * to take all precautions not to miss the urgent byte. This
     * means we may get here without any urgent data to process, in which
     * case we do nothing and just return.
     */
    if (ret <= 0)
        return;

    do {
        if (ioctl(rem, SIOCATMARK, &atmark) < 0) {
            break;
        }
        if (!atmark) {
            /*
             * Urgent data not here yet.
             * It may not be possible to send it yet
             * if we are blocked for output
             * and our input buffer is full.
             */
            if (rcvcnt < sizeof (rcvbuf)) {
                n = desread(rem, rcvbuf + rcvcnt,
                    sizeof (rcvbuf) - rcvcnt, 0);
                if (n <= 0)
                    return;
                rcvd += n;
                rcvcnt += n;
            } else {
                /*
                 * We still haven't gotten to the urgent mark
                 * and we're out of buffer space.  Since we
                 * must clear our receive window to allow it
                 * to arrive, we will have to throw away
                 * these bytes.
                 */
                n = desread(rem, waste, sizeof (waste), 0);
                if (n <= 0)
                    return;
            }
        }
    } while (atmark == 0);
    while (recv(rem, &mark, 1, MSG_OOB) < 0) {
        switch (errno) {

        case EWOULDBLOCK:
            /*
             * We've reached the urgent mark, so the next
             * data to arrive will be the urgent, but it must
             * not have arrived yet.
             */
            (void) sleep(1);
            continue;

        default:
            return;
        }
    }
    if (mark & TIOCPKT_WINDOW) {
        /*
         * Let server know about window size changes
         */
        (void) kill(ppid, SIGUSR1);
    }
    if (!eight && (mark & TIOCPKT_NOSTOP)) {
        if (ioctl(STDIN_FILENO, TIOCGETP, (char *)&sb) == -1)
            perror("ioctl TIOCGETP");
        sb.sg_flags &= ~O_CBREAK;
        sb.sg_flags |= O_RAW;
        if (compat_ioctl(STDIN_FILENO, TIOCSETP, &sb) == -1)
            perror("ioctl TIOCSETP 1");
        notc.t_stopc = -1;
        notc.t_startc = -1;
        if (compat_ioctl(STDIN_FILENO, TIOCSETC, &notc) == -1)
            perror("ioctl TIOCSETC");
    }
    if (!eight && (mark & TIOCPKT_DOSTOP)) {
        if (ioctl(STDIN_FILENO, TIOCGETP, (char *)&sb) == -1)
            perror("ioctl TIOCGETP");
        sb.sg_flags &= ~O_RAW;
        sb.sg_flags |= O_CBREAK;
        if (compat_ioctl(STDIN_FILENO, TIOCSETP, &sb) == -1)
            perror("ioctl TIOCSETP 2");
        notc.t_stopc = deftc.t_stopc;
        notc.t_startc = deftc.t_startc;
        if (compat_ioctl(STDIN_FILENO, TIOCSETC, &notc) == -1)
            perror("ioctl TIOCSETC");
    }
    if (mark & TIOCPKT_FLUSHWRITE) {
        if (ioctl(STDOUT_FILENO, TIOCFLUSH, (char *)&out) == -1)
            perror("ioctl TIOCFLUSH");
        for (;;) {
            if (ioctl(rem, SIOCATMARK, &atmark) < 0) {
                perror("ioctl SIOCATMARK");
                break;
            }
            if (atmark)
                break;
            n = desread(rem, waste, sizeof (waste), 0);
            if (n <= 0) {
                if (n < 0)
                    prf(gettext(
                        "Read error from network: %s"),
                        errmsg(errno));
                break;
            }
        }
        /*
         * Don't want any pending data to be output,
         * so clear the recv buffer.
         * If we were hanging on a write when interrupted,
         * don't want it to restart.  If we were reading,
         * restart anyway.
         */
        rcvcnt = 0;
        longjmp(rcvtop, 1);
    }
    /*
     * If we filled the receive buffer while a read was pending,
     * longjmp to the top to restart appropriately.  Don't abort
     * a pending write, however, or we won't know how much was written.
     */
    if (rcvd && rcvstate == READING)
        longjmp(rcvtop, 1);
}

/*
 * reader: read from remote: line -> 1
 */
static int
reader(int oldmask)
{
    /*
     * 4.3bsd or later and SunOS 4.0 or later use the posiitive
     * pid; otherwise use the negative.
     */
    pid_t pid = getpid();
    int n, remaining;
    char *bufp = rcvbuf;

    (void) sigset(SIGTTOU, SIG_IGN);
    (void) sigset(SIGURG, (void (*)())oob);
    ppid = getppid();
    if (fcntl(rem, F_SETOWN, pid) == -1)
        perror("fcntl F_SETOWN");
    /*
     * A SIGURG may have been posted before we were completely forked,
     * which means we may not have received it. To insure we do not miss
     * any urgent data, we force the signal. The signal hander will be
     * able to determine if in fact there is urgent data or not.
     */
    (void) kill(pid, SIGURG);
    (void) setjmp(rcvtop);
    sigsetmask(oldmask);
    for (;;) {
        while ((remaining = rcvcnt - (bufp - rcvbuf)) > 0) {
            rcvstate = WRITING;
            n = write(STDOUT_FILENO, bufp, remaining);
            if (n < 0) {
                if (errno != EINTR) {
                    prf(gettext(
                        "Write error to terminal: %s"),
                        errmsg(errno));
                    return (-1);
                }
                continue;
            }
            bufp += n;
        }
        bufp = rcvbuf;
        rcvcnt = 0;
        rcvstate = READING;
        rcvcnt = desread(rem, rcvbuf, sizeof (rcvbuf), 0);
        if (rcvcnt == 0)
            return (0);
        if (rcvcnt < 0) {
            if (errno == EINTR)
                continue;
            prf(gettext("Read error from network: %s"),
                errmsg(errno));
            return (-1);
        }
    }
}

static void
mode(int f)
{
    struct tchars *tc;
    struct ltchars *ltc;
    struct sgttyb sb;
    int lflags;

    if (ioctl(STDIN_FILENO, TIOCGETP, (char *)&sb) == -1)
        perror("ioctl TIOCGETP");
    if (ioctl(STDIN_FILENO, TIOCLGET, (char *)&lflags) == -1)
        perror("ioctl TIOCLGET");
    switch (f) {

    case 0:
        sb.sg_flags &= ~(O_CBREAK|O_RAW|O_TBDELAY);
        sb.sg_flags |= defflags|tabflag;
        tc = &deftc;
        ltc = &defltc;
        sb.sg_kill = defkill;
        sb.sg_erase = deferase;
        lflags = deflflags;
        break;

    case 1:
        sb.sg_flags |= (eight ? O_RAW : O_CBREAK);
        sb.sg_flags &= ~defflags;
        /* preserve tab delays, but turn off XTABS */
        if ((sb.sg_flags & O_TBDELAY) == O_XTABS)
            sb.sg_flags &= ~O_TBDELAY;
        tc = &notc;
        ltc = &noltc;
        sb.sg_kill = sb.sg_erase = -1;
        if (litout)
            lflags |= LLITOUT;
        break;

    default:
        /*NOTREACHED*/
        return;
    }
    if (compat_ioctl(STDIN_FILENO, TIOCSLTC, ltc) == -1)
        perror("ioctl TIOCSLTC");
    if (compat_ioctl(STDIN_FILENO, TIOCSETC, tc) == -1)
        perror("ioctl TIOCSETC");
    if (compat_ioctl(STDIN_FILENO, TIOCSETP, &sb) == -1)
        perror("ioctl TIOCSETP 3");
    if (compat_ioctl(STDIN_FILENO, TIOCLSET, &lflags) == -1)
        perror("ioctl TIOCLSET");
}

/* PRINTFLIKE(0) */
static void
prf(const char *format, ...)
{
    va_list ap;

    va_start(ap, format);
    (void) vfprintf(stderr, format, ap);
    va_end(ap);
    (void) fputs(CRLF, stderr);
}

static void
lostpeer(void)
{
    (void) sigset(SIGPIPE, SIG_IGN);
    prf(gettext("\aConnection to %.*s closed."), MAXHOSTNAMELEN, host);
    done(EXIT_FAILURE);
}

static char *
errmsg(int errcode)
{
    extern int sys_nerr;

    if (errcode < 0 || errcode > sys_nerr)
        return (gettext("Unknown error"));
    else
        return (strerror(errcode));
}

static int
compat_ioctl(int des, int request, void *arg)
{
    struct termios  tb;
    boolean_t   flag = B_FALSE;

    if (ioctl(des, request, arg) < 0)
        return (-1);

    if (tcgetattr(des, &tb) < 0)
        return (-1);

    if (cfgetispeed(&tb) != cfgetispeed(&savetty)) {
        (void) cfsetispeed(&tb, cfgetispeed(&savetty));
        flag = B_TRUE;
    }
    if (cfgetospeed(&tb) != cfgetospeed(&savetty)) {
        (void) cfsetospeed(&tb, cfgetospeed(&savetty));
        flag = B_TRUE;
    }

    return (flag ? tcsetattr(des, TCSANOW, &tb) : 0);
}