sudo/script.c

/*
 * Copyright (c) 2009 Todd C. Miller <Todd.Miller@courtesan.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <config.h>

#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif /* HAVE_SYS_SELECT_H */
#include <stdio.h>
#ifdef STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# ifdef HAVE_STDLIB_H
#  include <stdlib.h>
# endif
#endif /* STDC_HEADERS */
#ifdef HAVE_STRING_H
# if defined(HAVE_MEMORY_H) && !defined(STDC_HEADERS)
#  include <memory.h>
# endif
# include <string.h>
#else
# ifdef HAVE_STRINGS_H
#  include <strings.h>
# endif
#endif /* HAVE_STRING_H */
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif /* HAVE_UNISTD_H */
#if TIME_WITH_SYS_TIME
# include <time.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <signal.h>

#ifdef HAVE_UTIL_H
# include <util.h>
#endif
#ifdef HAVE_PTY_H
# include <pty.h>
#endif

#include "sudo.h"

#ifndef lint
__unused static const char rcsid[] = "$Sudo$";
#endif /* lint */

#define SFD_MASTER 0
#define SFD_SLAVE 1
#define SFD_LOG 2
#define SFD_OUTPUT 3
#define SFD_TIMING 4

struct script_buf {
    int len; /* buffer length (how much read in) */
    int off; /* write position (how much already consumed) */
    char buf[16 * 1024];
};

static int script_fds[5];

static sig_atomic_t alive = 1;
static sig_atomic_t suspended = 0;
static sig_atomic_t signo;

static pid_t parent, grandchild;
static int grandchild_status;

#if defined(HAVE_OPENPTY) || defined(HAVE_GRANTPT)
static char slavename[PATH_MAX];
#else
static char slavename[] = "/dev/ptyXX";
#endif

static void script_child __P((char *path, char *argv[]));
static void script_grandchild __P((char *path, char *argv[], int));
static void sync_winsize __P((int src, int dst));
static void handler __P((int s));
static void sigchild __P((int s));
static void sigwinch __P((int s));
static void sigtstp __P((int s));
static void sigrepost __P((int s));
static int get_pty __P((int *master, int *slave));
static void flush_output __P((struct script_buf *output, struct timeval *then,
    struct timeval *now, FILE *ofile, FILE *tfile));

/*
 * TODO: run monitor as root?
 */

static int
fdcompar(v1, v2)
    const void *v1;
    const void *v2;
{
    int i = *(int *)v1;
    int j = *(int *)v2;

    return(script_fds[i] - script_fds[j]);
}

void
script_nextid()
{
    struct stat sb;
    char buf[32], *ep;
    int fd, i, ch;
    unsigned long id = 0;
    int len;
    ssize_t nread;
    char pathbuf[PATH_MAX];

    /*
     * Create _PATH_SUDO_TRANSCRIPT if it doesn't already exist.
     */
    if (stat(_PATH_SUDO_TRANSCRIPT, &sb) != 0) {
	if (mkdir(_PATH_SUDO_TRANSCRIPT, S_IRWXU) != 0)
	    log_error(USE_ERRNO, "Can't mkdir %s", _PATH_SUDO_TRANSCRIPT);
    } else if (!S_ISDIR(sb.st_mode)) {
	log_error(0, "%s exists but is not a directory (0%o)",
	    _PATH_SUDO_TRANSCRIPT, (unsigned int) sb.st_mode);
    }

    /*
     * Open sequence file
     */
    len = snprintf(pathbuf, sizeof(pathbuf), "%s/seq", _PATH_SUDO_TRANSCRIPT);
    if (len <= 0 || len >= sizeof(pathbuf)) {
	errno = ENAMETOOLONG;
	log_error(USE_ERRNO, "%s/seq", pathbuf);
    }
    fd = open(pathbuf, O_RDWR|O_CREAT, S_IRUSR|S_IWUSR);
    if (fd == -1)
	log_error(USE_ERRNO, "cannot open %s", pathbuf);
    lock_file(fd, SUDO_LOCK);

    /* Read seq number (base 36). */
    nread = read(fd, buf, sizeof(buf));
    if (nread != 0) {
	if (nread == -1)
	    log_error(USE_ERRNO, "cannot read %s", pathbuf);
	id = strtoul(buf, &ep, 36);
	if (buf == ep || id >= 2176782336U)
	    log_error(0, "invalid sequence number %s", pathbuf);
    }
    id++;

    /*
     * Convert id to a string and stash in sudo_user.sessid.
     * Note that that least significant digits go at the end of the string.
     */
    for (i = 5; i >= 0; i--) {
	ch = id % 36;
	id /= 36;
	buf[i] = ch < 10 ? ch + '0' : ch - 10 + 'A';
    }
    buf[6] = '\n';

    /* Stash id logging purposes */
    memcpy(sudo_user.sessid, buf, 6);
    sudo_user.sessid[6] = '\0';

    /* Rewind and overwrite old seq file. */
    if (lseek(fd, 0, SEEK_SET) == (off_t)-1 || write(fd, buf, 7) != 7)
	log_error(USE_ERRNO, "Can't write to %s", pathbuf);
    close(fd);
}

static int
build_idpath(pathbuf)
    char *pathbuf;
{
    struct stat sb;
    int i, len;

    if (sudo_user.sessid[0] == '\0')
	log_error(0, "tried to build a session id path without a session id");

    /*
     * Path is of the form /var/log/sudo-session/00/00/01.
     */
    len = snprintf(pathbuf, PATH_MAX, "%s/%c%c/%c%c/%c%c", _PATH_SUDO_TRANSCRIPT,
	sudo_user.sessid[0], sudo_user.sessid[1], sudo_user.sessid[2],
	sudo_user.sessid[3], sudo_user.sessid[4], sudo_user.sessid[5]);
    if (len <= 0 && len >= PATH_MAX) {
	errno = ENAMETOOLONG;
	log_error(USE_ERRNO, "%s/%s", _PATH_SUDO_TRANSCRIPT, sudo_user.sessid);
    }

    /*
     * Create the intermediate subdirs as needed.
     */
    for (i = 6; i > 0; i -= 3) {
	pathbuf[len - i] = '\0';
	if (stat(pathbuf, &sb) != 0) {
	    if (mkdir(pathbuf, S_IRWXU) != 0)
		log_error(USE_ERRNO, "Can't mkdir %s", pathbuf);
	} else if (!S_ISDIR(sb.st_mode)) {
	    log_error(0, "%s: %s", pathbuf, strerror(ENOTDIR));
	}
	pathbuf[len - i] = '/';
    }

    return(len);
}

void
script_setup()
{
    char pathbuf[PATH_MAX];
    int len;

    if (!isatty(STDIN_FILENO))
	log_error(0, "Standard input is not a tty");

    if (!get_pty(&script_fds[SFD_MASTER], &script_fds[SFD_SLAVE]))
	log_error(USE_ERRNO, "Can't get pty");

    /* Copy terminal attrs from stdin -> pty slave. */
    if (!term_copy(STDIN_FILENO, script_fds[SFD_SLAVE], 0))
	log_error(USE_ERRNO, "Can't copy terminal attributes");
    sync_winsize(STDIN_FILENO, script_fds[SFD_SLAVE]);

    if (!term_raw(STDIN_FILENO, 1))
	log_error(USE_ERRNO, "Can't set terminal to raw mode");

    /*
     * Build a path containing the session id split into two-digit subdirs,
     * so ID 000001 becomes /var/log/sudo-session/00/00/01.
     */
    len = build_idpath(pathbuf);

    /*
     * We create 3 files: a log file, one for the raw session data,
     * and one for the timing info.
     */
    script_fds[SFD_LOG] = open(pathbuf, O_CREAT|O_EXCL|O_WRONLY, S_IRUSR|S_IWUSR);
    if (script_fds[SFD_LOG] == -1)
	log_error(USE_ERRNO, "Can't create %s", pathbuf);

    strlcat(pathbuf, ".scr", sizeof(pathbuf));
    script_fds[SFD_OUTPUT] = open(pathbuf, O_CREAT|O_EXCL|O_WRONLY,
	S_IRUSR|S_IWUSR);
    if (script_fds[SFD_OUTPUT] == -1)
	log_error(USE_ERRNO, "Can't create %s", pathbuf);

    pathbuf[len] = '\0';
    strlcat(pathbuf, ".tim", sizeof(pathbuf));
    script_fds[SFD_TIMING] = open(pathbuf, O_CREAT|O_EXCL|O_WRONLY, S_IRUSR|S_IWUSR);
    if (script_fds[SFD_TIMING] == -1)
	log_error(USE_ERRNO, "Can't create %s", pathbuf);
}

int
script_duplow(fd)
    int fd;
{
    int i, j, indices[5];

    /* sort fds so we can dup them safely */
    for (i = 0; i < 5; i++)
	indices[i] = i;
    qsort(indices, 5, sizeof(int), fdcompar);

    /* Move pty master/slave and session fds to low numbered fds. */
    for (i = 0; i < 5; i++) {
	j = indices[i];
	if (script_fds[j] != fd) {
#ifdef HAVE_DUP2
	    dup2(script_fds[j], fd);
#else
	    close(fd);
	    dup(script_fds[j]);
	    close(script_fds[j]);
#endif
	}
	script_fds[j] = fd++;
    }
    return(fd);
}

/* Update output and timing files. */
static void
log_output(buf, n, then, now, ofile, tfile)
    char *buf;
    int n;
    struct timeval *then;
    struct timeval *now;
    FILE *ofile;
    FILE *tfile;
{
    struct timeval tv;

    fwrite(buf, 1, n, ofile);
    timersub(now, then, &tv);
    fprintf(tfile, "%f %d\n",
	tv.tv_sec + ((double)tv.tv_usec / 1000000), n);
    then->tv_sec = now->tv_sec;
    then->tv_usec = now->tv_usec;
}

/*
 * This is a little bit tricky due to how POSIX job control works and
 * we fact that we have two different controlling terminals to deal with.
 * There are three processes:
 *  1) parent, which waits for its child and handles signals send by the child
 *     allow the child to be suspended in the parent session with the
 *     parent controlling tty.  Acts as the "glue" between the two controlling
 *     ttys from a job-control standpoint.
 *  2) child, creates a new session with the pty slave as the controlling tty.
 *     Does all the work passing data to and from the pty and signals parent
 *     when it receives job control-related signals on behalf of grandchild.
 *  3) grandchild, runs the actual command, belongs to child's session and pgrp.
 */
int
script_execv(path, argv)
    char *path;
    char *argv[];
{
    sigaction_t sa, saveint, savehup, saveterm;
    sigaction_t savequit, savetstp, savettin, savettou;
    int status, exitcode = 1;
    pid_t child, pid;

    parent = getpid(); /* so child can pass signals back to us */

    /* Handle window change events in the parent for simplicity. */
    zero_bytes(&sa, sizeof(sa));
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = sigwinch;
    (void) sigaction(SIGWINCH, &sa, NULL);

    /*
     * Catch signals that would otherwise cause the user to end up
     * with the tty in raw mode.  Do this early to avoid a race.
     * NOTE: must not modify sa after this point (it is used later).
     */
    sa.sa_flags = SA_INTERRUPT; /* don't restart system calls */
    sa.sa_handler = handler;
    (void) sigaction(SIGINT, &sa, &saveint);
    (void) sigaction(SIGHUP, &sa, &savehup);
    (void) sigaction(SIGQUIT, &sa, &savequit);
    (void) sigaction(SIGTERM, &sa, &saveterm);
    (void) sigaction(SIGTSTP, &sa, &savetstp);
    (void) sigaction(SIGTTIN, &sa, &savettin);
    (void) sigaction(SIGTTOU, &sa, &savettou);

    /*
     * We have to fork or we cannot create a new session with a new
     * controlling tty.  The parent acts as glue betweem the two sessions.
     */
    child = fork();
    switch (child) {
    case -1:
	log_error(USE_ERRNO, "fork");
    case 0:
	(void) sigaction(SIGINT, &saveint, NULL);
	(void) sigaction(SIGHUP, &savehup, NULL);
	(void) sigaction(SIGQUIT, &savequit, NULL);
	(void) sigaction(SIGTERM, &saveterm, NULL);
	(void) sigaction(SIGTSTP, &savetstp, NULL);
	(void) sigaction(SIGTTIN, &savettin, NULL);
	(void) sigaction(SIGTTOU, &savettou, NULL);
	script_child(path, argv);
	/* NOTREACHED */
	break;
    }

    /* Wait for signal from child or for child to exit. */
    for (;;) {
	pid = waitpid(child, &status, 0);
	if (pid != -1 || errno != EINTR) {
	    /* headed for exit */
	    if (pid == child) {
		if (WIFEXITED(status))
		    exitcode = WEXITSTATUS(status);
		if (WIFSIGNALED(status))
		    exitcode = WTERMSIG(status) | 128;
	    }
	    break;
	}

	/* Restore old tty settings and signal handler. */
	term_restore(STDIN_FILENO);
      check_sig:
	switch (signo) {
	case SIGINT:
	    (void) sigaction(SIGINT, &saveint, NULL);
	    break;
	case SIGHUP:
	    (void) sigaction(SIGHUP, &savehup, NULL);
	    break;
	case SIGQUIT:
	    (void) sigaction(SIGQUIT, &savequit, NULL);
	    break;
	case SIGTERM:
	    (void) sigaction(SIGTERM, &saveterm, NULL);
	    break;
	case SIGTSTP:
	    (void) sigaction(SIGTSTP, &savetstp, NULL);
	    break;
	case SIGTTIN:
	    (void) sigaction(SIGTTIN, &savettin, NULL);
	    break;
	case SIGTTOU:
	    (void) sigaction(SIGTTOU, &savettou, NULL);
	    break;
	default:
	    /* should not happen */
	    break;
	}
	kill(parent, signo); /* re-send signal with handler disabled */
	/* Reinstall signal handler, reset raw mode and continue child */
	(void) sigaction(signo, &sa, NULL);
	if (!term_raw(STDIN_FILENO, 1) && errno == EINTR)
	    goto check_sig;
	kill(child, SIGCONT);
    }

    term_restore(STDIN_FILENO);

    exit(exitcode);
}

void
script_child(path, argv)
    char *path;
    char *argv[];
{
    int n, nready;
    fd_set *fdsr, *fdsw;
    struct script_buf input, output;
    struct timeval now, then;
    sigaction_t sa;
    FILE *idfile, *ofile, *tfile;
    int rbac_enabled = 0;

    /*
     * Start a new session with the parent as the session leader.
     * This allows us to be notified when the child has been suspended.
     */
#ifdef TIOCNOTTY
    n = open(_PATH_TTY, O_RDWR|O_NOCTTY);
    if (n >= 0) {
	/* Disconnect from old controlling tty. */
	if (ioctl(n, TIOCNOTTY, NULL) == -1)
	    warning("cannot disconnect controlling tty");
	close(n);
    }
#endif
    /*
     * Create new session, with the slave as controlling terminal and
     * point std{in,out,err} to it.
     */
#ifdef HAVE_SETSID
    if (setsid() == -1)
	log_error(USE_ERRNO, "setsid");
#else
    setpgrp(0, 0);
#endif
#ifdef TIOCSCTTY
    if (ioctl(script_fds[SFD_SLAVE], TIOCSCTTY, NULL) != 0)
	log_error(USE_ERRNO, "unable to set controlling tty");
#endif

    if ((idfile = fdopen(script_fds[SFD_LOG], "w")) == NULL)
	log_error(USE_ERRNO, "fdopen");
    if ((ofile = fdopen(script_fds[SFD_OUTPUT], "w")) == NULL)
	log_error(USE_ERRNO, "fdopen");
    if ((tfile = fdopen(script_fds[SFD_TIMING], "w")) == NULL)
	log_error(USE_ERRNO, "fdopen");

#ifdef HAVE_SELINUX
    rbac_enabled = is_selinux_enabled() > 0 && user_role != NULL;
    if (rbac_enabled) {
	selinux_prefork(user_role, user_type, script_fds[SFD_SLAVE]);
	/* Re-open slave fd after it has been relabeled */
	close(script_fds[SFD_SLAVE]);
	script_fds[SFD_SLAVE] = open(slavename, O_RDWR|O_NOCTTY, 0);
	if (script_fds[SFD_SLAVE] == -1)
	    log_error(USE_ERRNO, "cannot open %s", slavename);
    }
#endif

    /* Setup signal handlers for child exit, and tty-related signals. */
    zero_bytes(&sa, sizeof(sa));
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;

    /* These tty-related signals get relayed back to the parent. */
    sa.sa_handler = sigtstp;
    sigaction(SIGTSTP, &sa, NULL);
    sigaction(SIGTTIN, &sa, NULL);
    sigaction(SIGTTOU, &sa, NULL);

    /* These signals just get posted to the grandchilds pgrp. */
    sa.sa_handler = sigrepost;
    sigaction(SIGQUIT, &sa, NULL);
    sigaction(SIGINT, &sa, NULL);

    /* Do not want child stop notifications. */
    sa.sa_flags = SA_RESTART | SA_NOCLDSTOP;
    sa.sa_handler = sigchild;
    sigaction(SIGCHLD, &sa, NULL);

    /* Start grandchild and begin reading from pty master. */
    grandchild = fork();
    if (grandchild == -1)
	log_error(USE_ERRNO, "Can't fork");
    if (grandchild == 0) {
	/* setup tty and exec command */
	setpgid(grandchild, grandchild);
	script_grandchild(path, argv, rbac_enabled);
	warning("unable to execute %s", path);
	_exit(127);
    }

    gettimeofday(&then, NULL);

    /* XXX - log more stuff? environment too? */
    fprintf(idfile, "%ld:%s:%s:%s:%s\n", then.tv_sec, user_name,
	runas_pw->pw_name, runas_gr ? runas_gr->gr_name : "", user_tty);
    fprintf(idfile, "%s\n", user_cwd);
    fprintf(idfile, "%s%s%s\n", user_cmnd, user_args ? " " : "",
	user_args ? user_args : "");
    fclose(idfile);

    n = fcntl(script_fds[SFD_MASTER], F_GETFL, 0);
    if (n != -1) {
	n |= O_NONBLOCK;
	(void) fcntl(script_fds[SFD_MASTER], F_SETFL, n);
    }
    n = fcntl(STDIN_FILENO, F_GETFL, 0);
    if (n != -1) {
	n |= O_NONBLOCK;
	(void) fcntl(STDIN_FILENO, F_SETFL, n);
    }
    n = fcntl(STDOUT_FILENO, F_GETFL, 0);
    if (n != -1) {
	n |= O_NONBLOCK;
	(void) fcntl(STDOUT_FILENO, F_SETFL, n);
    }

    /*
     * In the event loop we pass input from stdin to master
     * and pass output from master to stdout and ofile.
     * Note that we've set things up such that master is above
     * stdin and stdout (see sudo.c).
     */
    fdsr = (fd_set *)emalloc2(howmany(script_fds[SFD_MASTER] + 1, NFDBITS),
	sizeof(fd_mask));
    fdsw = (fd_set *)emalloc2(howmany(script_fds[SFD_MASTER] + 1, NFDBITS),
	sizeof(fd_mask));
    zero_bytes(&input, sizeof(input));
    zero_bytes(&output, sizeof(output));
    while (alive) {
	if (input.off == input.len)
	    input.off = input.len = 0;
	if (output.off == output.len)
	    output.off = output.len = 0;

	zero_bytes(fdsw, howmany(script_fds[SFD_MASTER] + 1, NFDBITS) * sizeof(fd_mask));
	zero_bytes(fdsr, howmany(script_fds[SFD_MASTER] + 1, NFDBITS) * sizeof(fd_mask));
	if (input.len != sizeof(input.buf))
	    FD_SET(STDIN_FILENO, fdsr);
	if (output.len != sizeof(output.buf))
	    FD_SET(script_fds[SFD_MASTER], fdsr);
	if (output.len > output.off)
	    FD_SET(STDOUT_FILENO, fdsw);
	if (input.len > input.off)
	    FD_SET(script_fds[SFD_MASTER], fdsw);

	if (suspended) {
	    /* Flush any remaining output to master tty. */
	    flush_output(&output, &then, &now, ofile, tfile);

	    /* Relay signal back to parent for its tty and suspend ourself. */
	    kill(parent, signo);
	    kill(getpid(), SIGSTOP);
	    suspended = 0;
	    killpg(grandchild, SIGCONT);
	}
	nready = select(script_fds[SFD_MASTER] + 1, fdsr, fdsw, NULL, NULL);
	if (nready == -1) {
	    if (errno == EINTR)
		continue;
	    log_error(USE_ERRNO, "select failed");
	}
	if (FD_ISSET(STDIN_FILENO, fdsr)) {
	    n = read(STDIN_FILENO, input.buf + input.len,
		sizeof(input.buf) - input.len);
	    if (n == -1) {
		if (errno == EINTR)
		    continue;
		if (errno != EAGAIN)
		    break;
	    } else {
		if (n == 0)
		    break; /* got EOF */
		input.len += n;
	    }
	}
	if (FD_ISSET(script_fds[SFD_MASTER], fdsw)) {
	    n = write(script_fds[SFD_MASTER], input.buf + input.off,
		input.len - input.off);
	    if (n == -1) {
		if (errno == EINTR)
		    continue;
		if (errno != EAGAIN)
		    break;
	    } else {
		input.off += n;
	    }
	}
	if (FD_ISSET(script_fds[SFD_MASTER], fdsr)) {
	    gettimeofday(&now, NULL);
	    n = read(script_fds[SFD_MASTER], output.buf + output.len,
		sizeof(output.buf) - output.len);
	    if (n == -1) {
		if (errno == EINTR)
		    continue;
		if (errno != EAGAIN)
		    break;
	    } else {
		if (n == 0)
		    break; /* got EOF */

		/* Update output and timing files. */
		log_output(output.buf + output.len, n, &then, &now, ofile, tfile);

		output.len += n;
	    }
	}
	if (FD_ISSET(STDOUT_FILENO, fdsw)) {
	    n = write(STDOUT_FILENO, output.buf + output.off,
		output.len - output.off);
	    if (n == -1) {
		if (errno == EINTR)
		    continue;
		if (errno != EAGAIN)
		    break;
	    } else {
		output.off += n;
	    }
	}
    }

    /* Flush any remaining output to stdout (already updated output file). */
    n = fcntl(STDOUT_FILENO, F_GETFL, 0);
    if (n != -1) {
	n &= ~O_NONBLOCK;
	(void) fcntl(STDOUT_FILENO, F_SETFL, n);
    }
    flush_output(&output, &then, &now, ofile, tfile);

    if (WIFEXITED(grandchild_status))
	exit(WEXITSTATUS(grandchild_status));
    if (WIFSIGNALED(grandchild_status))
	exit(WTERMSIG(grandchild_status) | 128);
    exit(1);
}

static void
flush_output(output, then, now, ofile, tfile)
    struct script_buf *output;
    struct timeval *then;
    struct timeval *now;
    FILE *ofile;
    FILE *tfile;
{
    int n;

    while (output->len > output->off) {
	n = write(STDOUT_FILENO, output->buf + output->off,
	    output->len - output->off);
	if (n <= 0)
	    break;
	output->off += n;
    }

    /* Make sure there is no output remaining on the master pty. */
    for (;;) {
	n = read(script_fds[SFD_MASTER], output->buf, sizeof(output->buf));
	if (n <= 0)
	    break;
	log_output(output->buf, n, &then, &now, ofile, tfile);
	output->off = 0;
	output->len = n;
	do {
	    n = write(STDOUT_FILENO, output->buf + output->off,
		output->len - output->off);
	    if (n <= 0)
		break;
	    output->off += n;
	} while (output->len > output->off);
    }
}

static void
script_grandchild(path, argv, rbac_enabled)
    char *path;
    char *argv[];
    int rbac_enabled;
{
    /* Also set process group here to avoid a race condition. */
    setpgid(0, getpid());

    dup2(script_fds[SFD_SLAVE], STDIN_FILENO);
    dup2(script_fds[SFD_SLAVE], STDOUT_FILENO);
    dup2(script_fds[SFD_SLAVE], STDERR_FILENO);

    /*
     * Close old fds and exec command.
     */
    close(script_fds[SFD_MASTER]);
    close(script_fds[SFD_SLAVE]);
    close(script_fds[SFD_LOG]);
    close(script_fds[SFD_OUTPUT]);
    close(script_fds[SFD_TIMING]);
#ifdef HAVE_SELINUX
    if (rbac_enabled)
      selinux_execv(path, argv);
    else
#endif
    execv(path, argv);
}

static void
sync_winsize(src, dst)
    int src;
    int dst;
{
#ifdef TIOCGWINSZ
    struct winsize win;
    pid_t pgrp;

    if (ioctl(src, TIOCGWINSZ, &win) == 0) {
	    ioctl(dst, TIOCSWINSZ, &win);
#ifdef TIOCGPGRP
	    if (ioctl(dst, TIOCGPGRP, &pgrp) == 0)
		    killpg(pgrp, SIGWINCH);
#endif
    }
#endif
}

/*
 * Generic signal handler for parent, interrupts waitpid() and sets a flag.
 */
static void
handler(s)
    int s;
{
    signo = s;
}

/*
 * Signal handler for grandchild and its descendents.
 */
static void
sigchild(signo)
    int signo;
{
    pid_t pid;
    int serrno = errno;

#ifdef sudo_waitpid
    do {
	pid = sudo_waitpid(grandchild, &grandchild_status, WNOHANG);
	if (pid == grandchild)
	    alive = 0;
	    break;
	}
    } while (pid > 0 || (pid == -1 && errno == EINTR));
#else
    do {
	pid = wait(&grandchild_status);
    } while (pid == -1 && errno == EINTR);
    alive = 0;
#endif

    errno = serrno;
}

static void
sigrepost(s)
    int s;
{
    int serrno = errno;

    /* Re-post signal to child via its process group. */
    killpg(grandchild, s);

    errno = serrno;
}

static void
sigtstp(s)
    int s;
{
    int serrno = errno;

    /* Event loop needs to know which signal to relay to parent. */
    signo = s;

    /* Suspend the command we are running and set state. */
    killpg(grandchild, SIGSTOP);
    suspended = 1;

    errno = serrno;
}

static void
sigwinch(s)
    int s;
{
    int serrno = errno;

    sync_winsize(STDIN_FILENO, script_fds[SFD_SLAVE]);
    errno = serrno;
}

#ifdef HAVE_OPENPTY
static int
get_pty(master, slave)
    int *master;
    int *slave;
{
    struct group *gr;
    gid_t ttygid = -1;

    if ((gr = sudo_getgrnam("tty")) != NULL)
	ttygid = gr->gr_gid;

    if (openpty(master, slave, slavename, NULL, NULL) != 0)
	return(0);
    (void) chown(slavename, runas_pw->pw_uid, ttygid);
    return(1);
}

#else
# ifdef HAVE_GRANTPT
#  ifndef HAVE_POSIX_OPENPT
static int
posix_openpt(oflag)
    int oflag;
{
    int fd;

#   ifdef _AIX
    fd = open("/dev/ptc", oflag);
#   else
    fd = open("/dev/ptmx", oflag);
#   endif
    return(fd);
}
#  endif /* HAVE_POSIX_OPENPT */

static int
get_pty(master, slave)
    int *master;
    int *slave;
{
    char *line;

    *master = posix_openpt(O_RDWR);
    if (*master == -1)
	return(0);

    if (unlockpt(*master) != 0) {
	close(*master);
	return(0);
    }
    (void) grantpt(*master);
    line = ptsname(*master);
    if (line == NULL) {
	close(*master);
	return(0);
    }
    strlcpy(slavename, line, sizeof(slavename));
    *slave = open(slavename, O_RDWR|O_NOCTTY, 0);
    if (*slave == -1) {
	close(*master);
	return(0);
    }
    (void) chown(slavename, runas_pw->pw_uid, -1);
    return(1);
}

# else /* !HAVE_GRANTPT */

static int
get_pty(master, slave)
    int *master;
    int *slave;
{
    char *bank, *cp;
    struct group *gr;
    gid_t ttygid = -1;

    if ((gr = sudo_getgrnam("tty")) != NULL)
	ttygid = gr->gr_gid;

    for (bank = "pqrs"; *bank != '\0'; bank++) {
	slavename[sizeof("/dev/ptyX") - 2] = *bank;
	for (cp = "0123456789abcdef"; *cp != '\0'; cp++) {
	    slavename[sizeof("/dev/ptyXX") - 2] = *cp;
	    *master = open(slavename, O_RDWR, 0);
	    if (*master == -1) {
		if (errno == ENOENT)
		    return(0); /* out of ptys */
		continue; /* already in use */
	    }
	    slavename[sizeof("/dev/p") - 2] = 't';
	    (void) chown(slavename, runas_pw->pw_uid, ttygid);
	    (void) chmod(slavename, S_IRUSR|S_IWUSR|S_IWGRP);
#  ifdef HAVE_REVOKE
	    (void) revoke(slavename);
#  endif
	    *slave = open(slavename, O_RDWR|O_NOCTTY, 0);
	    if (*slave != -1)
		    return(1); /* success */
	    (void) close(*master);
	}
    }
    return(0);
}

# endif /* HAVE_GRANTPT */
#endif /* HAVE_OPENPTY */