Adding upstream version 1.8.27.upstream/1.8.27upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 719 insertions, 0 deletions

diff --git a/src/exec_monitor.c b/src/exec_monitor.c
new file mode 100644
index 0000000..4a81b5d
--- /dev/null
+++ b/src/exec_monitor.c
@@ -0,0 +1,719 @@
+/*
+ * Copyright (c) 2009-2018 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * 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.
+ */
+
+/*
+ * This is an open source non-commercial project. Dear PVS-Studio, please check it.
+ * PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef HAVE_STRING_H
+# include <string.h>
+#endif /* HAVE_STRING_H */
+#ifdef HAVE_STRINGS_H
+# include <strings.h>
+#endif /* HAVE_STRINGS_H */
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <termios.h>
+
+#include "sudo.h"
+#include "sudo_event.h"
+#include "sudo_exec.h"
+#include "sudo_plugin.h"
+#include "sudo_plugin_int.h"
+
+struct monitor_closure {
+    pid_t cmnd_pid;
+    pid_t cmnd_pgrp;
+    pid_t mon_pgrp;
+    int backchannel;
+    struct command_status *cstat;
+    struct sudo_event_base *evbase;
+    struct sudo_event *errpipe_event;
+    struct sudo_event *backchannel_event;
+    struct sudo_event *sigint_event;
+    struct sudo_event *sigquit_event;
+    struct sudo_event *sigtstp_event;
+    struct sudo_event *sigterm_event;
+    struct sudo_event *sighup_event;
+    struct sudo_event *sigusr1_event;
+    struct sudo_event *sigusr2_event;
+    struct sudo_event *sigchld_event;
+};
+
+static bool tty_initialized;
+
+/*
+ * Deliver a signal to the running command.
+ * The signal was either forwarded to us by the parent sudo process
+ * or was received by the monitor itself.
+ *
+ * There are two "special" signals, SIGCONT_FG and SIGCONT_BG that
+ * also specify whether the command should have the controlling tty.
+ */
+static void
+deliver_signal(struct monitor_closure *mc, int signo, bool from_parent)
+{
+    char signame[SIG2STR_MAX];
+    debug_decl(deliver_signal, SUDO_DEBUG_EXEC);
+
+    /* Avoid killing more than a single process or process group. */
+    if (mc->cmnd_pid <= 0)
+	debug_return;
+
+    if (signo == SIGCONT_FG)
+	strlcpy(signame, "CONT_FG", sizeof(signame));
+    else if (signo == SIGCONT_BG)
+	strlcpy(signame, "CONT_BG", sizeof(signame));
+    else if (sig2str(signo, signame) == -1)
+	snprintf(signame, sizeof(signame), "%d", signo);
+
+    /* Handle signal from parent or monitor. */
+    sudo_debug_printf(SUDO_DEBUG_INFO, "received SIG%s%s",
+	signame, from_parent ? " from parent" : "");
+    switch (signo) {
+    case SIGALRM:
+	terminate_command(mc->cmnd_pid, true);
+	break;
+    case SIGCONT_FG:
+	/* Continue in foreground, grant it controlling tty. */
+	if (tcsetpgrp(io_fds[SFD_SLAVE], mc->cmnd_pgrp) == -1) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+		"%s: unable to set foreground pgrp to %d (command)",
+		__func__, (int)mc->cmnd_pgrp);
+	}
+	/* Lazily initialize the pty if needed. */
+	if (!tty_initialized) {
+	    if (sudo_term_copy(io_fds[SFD_USERTTY], io_fds[SFD_SLAVE]))
+		    tty_initialized = true;
+	}
+	killpg(mc->cmnd_pid, SIGCONT);
+	break;
+    case SIGCONT_BG:
+	/* Continue in background, I take controlling tty. */
+	if (tcsetpgrp(io_fds[SFD_SLAVE], mc->mon_pgrp) == -1) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+		"%s: unable to set foreground pgrp to %d (monitor)",
+		__func__, (int)mc->mon_pgrp);
+	}
+	killpg(mc->cmnd_pid, SIGCONT);
+	break;
+    case SIGKILL:
+	_exit(1); /* XXX */
+	/* NOTREACHED */
+    default:
+	/* Relay signal to command. */
+	killpg(mc->cmnd_pid, signo);
+	break;
+    }
+    debug_return;
+}
+
+/*
+ * Unpack rows and cols from a CMD_TTYWINCH value, set the new window
+ * size on the pty slave and inform the command of the change.
+ */
+static void
+handle_winch(struct monitor_closure *mc, unsigned int wsize_packed)
+{
+    struct winsize wsize, owsize;
+    debug_decl(handle_winch, SUDO_DEBUG_EXEC);
+
+    /* Rows and colums are stored as two shorts packed into a single int. */
+    wsize.ws_row = wsize_packed & 0xffff;
+    wsize.ws_col = (wsize_packed >> 16) & 0xffff;
+
+    if (ioctl(io_fds[SFD_SLAVE], TIOCGWINSZ, &owsize) == 0 &&
+	(wsize.ws_row != owsize.ws_row || wsize.ws_col != owsize.ws_col)) {
+
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "window size change %dx%d -> %dx%d",
+	    owsize.ws_col, owsize.ws_row, wsize.ws_col, wsize.ws_row);
+
+	(void)ioctl(io_fds[SFD_SLAVE], TIOCSWINSZ, &wsize);
+	deliver_signal(mc, SIGWINCH, true);
+    }
+
+    debug_return;
+}
+
+/*
+ * Send status to parent over socketpair.
+ * Return value is the same as send(2).
+ */
+static int
+send_status(int fd, struct command_status *cstat)
+{
+    int n = -1;
+    debug_decl(send_status, SUDO_DEBUG_EXEC);
+
+    if (cstat->type != CMD_INVALID) {
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "sending status message to parent: [%d, %d]",
+	    cstat->type, cstat->val);
+	n = send(fd, cstat, sizeof(*cstat), 0);
+	if (n != sizeof(*cstat)) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+		"%s: unable to send status to parent", __func__);
+	}
+	cstat->type = CMD_INVALID; /* prevent re-sending */
+    }
+    debug_return_int(n);
+}
+
+/*
+ * Wait for command status after receiving SIGCHLD.
+ * If the command was stopped, the status is send back to the parent.
+ * Otherwise, cstat is filled in but not sent.
+ */
+static void
+mon_handle_sigchld(struct monitor_closure *mc)
+{
+    char signame[SIG2STR_MAX];
+    int status;
+    pid_t pid;
+    debug_decl(mon_handle_sigchld, SUDO_DEBUG_EXEC);
+
+    /* Read command status. */
+    do {
+	pid = waitpid(mc->cmnd_pid, &status, WUNTRACED|WCONTINUED|WNOHANG);
+    } while (pid == -1 && errno == EINTR);
+    switch (pid) {
+    case 0:
+	errno = ECHILD;
+	/* FALLTHROUGH */
+    case -1:
+	sudo_warn(U_("%s: %s"), __func__, "waitpid");
+	debug_return;
+    }
+
+    if (WIFCONTINUED(status)) {
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: command (%d) resumed",
+	    __func__, (int)mc->cmnd_pid);
+    } else if (WIFSTOPPED(status)) {
+	if (sig2str(WSTOPSIG(status), signame) == -1)
+	    snprintf(signame, sizeof(signame), "%d", WSTOPSIG(status));
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: command (%d) stopped, SIG%s",
+	    __func__, (int)mc->cmnd_pid, signame);
+    } else if (WIFSIGNALED(status)) {
+	if (sig2str(WTERMSIG(status), signame) == -1)
+	    snprintf(signame, sizeof(signame), "%d", WTERMSIG(status));
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: command (%d) killed, SIG%s",
+	    __func__, (int)mc->cmnd_pid, signame);
+	mc->cmnd_pid = -1;
+    } else if (WIFEXITED(status)) {
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: command (%d) exited: %d",
+	    __func__, (int)mc->cmnd_pid, WEXITSTATUS(status));
+	mc->cmnd_pid = -1;
+    } else {
+	sudo_debug_printf(SUDO_DEBUG_WARN,
+	    "%s: unexpected wait status %d for command (%d)",
+	    __func__, status, (int)mc->cmnd_pid);
+    }
+
+    /* Don't overwrite execve() failure with child exit status. */
+    if (mc->cstat->type == CMD_INVALID) {
+	/*
+	 * Store wait status in cstat and forward to parent if stopped.
+	 * Parent does not expect SIGCONT so don't bother sending it.
+	 */
+	if (!WIFCONTINUED(status)) {
+	    mc->cstat->type = CMD_WSTATUS;
+	    mc->cstat->val = status;
+	    if (WIFSTOPPED(status)) {
+		/* Save the foreground pgid so we can restore it later. */
+		pid = tcgetpgrp(io_fds[SFD_SLAVE]);
+		if (pid != mc->mon_pgrp)
+		    mc->cmnd_pgrp = pid;
+		send_status(mc->backchannel, mc->cstat);
+	    }
+	}
+    } else {
+	sudo_debug_printf(SUDO_DEBUG_WARN,
+	    "%s: not overwriting command status %d,%d with %d,%d",
+	    __func__, mc->cstat->type, mc->cstat->val, CMD_WSTATUS, status);
+    }
+
+    debug_return;
+}
+
+static void
+mon_signal_cb(int signo, int what, void *v)
+{
+    struct sudo_ev_siginfo_container *sc = v;
+    struct monitor_closure *mc = sc->closure;
+    debug_decl(mon_signal_cb, SUDO_DEBUG_EXEC);
+
+    /*
+     * Handle SIGCHLD specially and deliver other signals
+     * directly to the command.
+     */
+    if (signo == SIGCHLD) {
+	mon_handle_sigchld(mc);
+	if (mc->cmnd_pid == -1) {
+	    /* Command exited or was killed, exit event loop. */
+	    sudo_ev_loopexit(mc->evbase);
+	}
+    } else {
+	/*
+	 * If the signal came from the process group of the command we ran,
+	 * do not forward it as we don't want the child to indirectly kill
+	 * itself.  This can happen with, e.g., BSD-derived versions of
+	 * reboot that call kill(-1, SIGTERM) to kill all other processes.
+	 */
+	if (USER_SIGNALED(sc->siginfo) && sc->siginfo->si_pid != 0) {
+	    pid_t si_pgrp = getpgid(sc->siginfo->si_pid);
+	    if (si_pgrp != -1) {
+		if (si_pgrp == mc->cmnd_pgrp)
+		    debug_return;
+	    } else if (sc->siginfo->si_pid == mc->cmnd_pid) {
+		    debug_return;
+	    }
+	}
+	deliver_signal(mc, signo, false);
+    }
+    debug_return;
+}
+
+/* Note: this is basically the same as errpipe_cb() in exec_nopty.c */
+static void
+mon_errpipe_cb(int fd, int what, void *v)
+{
+    struct monitor_closure *mc = v;
+    ssize_t nread;
+    int errval;
+    debug_decl(mon_errpipe_cb, SUDO_DEBUG_EXEC);
+
+    /*
+     * Read errno from child or EOF when command is executed.
+     * Note that the error pipe is *blocking*.
+     */
+    nread = read(fd, &errval, sizeof(errval));
+    switch (nread) {
+    case -1:
+	if (errno != EAGAIN && errno != EINTR) {
+	    if (mc->cstat->val == CMD_INVALID) {
+		/* XXX - need a way to distinguish non-exec error. */
+		mc->cstat->type = CMD_ERRNO;
+		mc->cstat->val = errno;
+	    }
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+		"%s: failed to read error pipe", __func__);
+	    sudo_ev_loopbreak(mc->evbase);
+	}
+	break;
+    default:
+	if (nread == 0) {
+	    /* The error pipe closes when the command is executed. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO, "EOF on error pipe");
+	} else {
+	    /* Errno value when child is unable to execute command. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO, "errno from child: %s",
+		strerror(errval));
+	    mc->cstat->type = CMD_ERRNO;
+	    mc->cstat->val = errval;
+	}
+	sudo_ev_del(mc->evbase, mc->errpipe_event);
+	close(fd);
+	break;
+    }
+    debug_return;
+}
+
+static void
+mon_backchannel_cb(int fd, int what, void *v)
+{
+    struct monitor_closure *mc = v;
+    struct command_status cstmp;
+    ssize_t n;
+    debug_decl(mon_backchannel_cb, SUDO_DEBUG_EXEC);
+
+    /*
+     * Read command from backchannel, should be a signal.
+     * Note that the backchannel is a *blocking* socket.
+     */
+    n = recv(fd, &cstmp, sizeof(cstmp), MSG_WAITALL);
+    if (n != sizeof(cstmp)) {
+	if (n == -1) {
+	    if (errno == EINTR || errno == EAGAIN)
+		debug_return;
+	    sudo_warn(U_("error reading from socketpair"));
+	} else {
+	    /* short read or EOF, parent process died? */
+	}
+	/* XXX - need a way to distinguish non-exec error. */
+	mc->cstat->type = CMD_ERRNO;
+	mc->cstat->val = n ? EIO : ECONNRESET;
+	sudo_ev_loopbreak(mc->evbase);
+    } else {
+	switch (cstmp.type) {
+	case CMD_TTYWINCH:
+	    handle_winch(mc, cstmp.val);
+	    break;
+	case CMD_SIGNO:
+	    deliver_signal(mc, cstmp.val, true);
+	    break;
+	default:
+	    sudo_warnx(U_("unexpected reply type on backchannel: %d"), cstmp.type);
+	    break;
+	}
+    }
+    debug_return;
+}
+
+/*
+ * Sets up std{in,out,err} and executes the actual command.
+ * Returns only if execve() fails.
+ */
+static void
+exec_cmnd_pty(struct command_details *details, bool foreground, int errfd)
+{
+    volatile pid_t self = getpid();
+    debug_decl(exec_cmnd_pty, SUDO_DEBUG_EXEC);
+
+    /* Register cleanup function */
+    sudo_fatal_callback_register(pty_cleanup);
+
+    /* Set command process group here too to avoid a race. */
+    setpgid(0, self);
+
+    /* Wire up standard fds, note that stdout/stderr may be pipes. */
+    if (io_fds[SFD_STDIN] != STDIN_FILENO) {
+	if (dup2(io_fds[SFD_STDIN], STDIN_FILENO) == -1)
+	    sudo_fatal("dup2");
+	if (io_fds[SFD_STDIN] != io_fds[SFD_SLAVE])
+	    close(io_fds[SFD_STDIN]);
+    }
+    if (io_fds[SFD_STDOUT] != STDOUT_FILENO) {
+	if (dup2(io_fds[SFD_STDOUT], STDOUT_FILENO) == -1)
+	    sudo_fatal("dup2");
+	if (io_fds[SFD_STDOUT] != io_fds[SFD_SLAVE])
+	    close(io_fds[SFD_STDOUT]);
+    }
+    if (io_fds[SFD_STDERR] != STDERR_FILENO) {
+	if (dup2(io_fds[SFD_STDERR], STDERR_FILENO) == -1)
+	    sudo_fatal("dup2");
+	if (io_fds[SFD_STDERR] != io_fds[SFD_SLAVE])
+	    close(io_fds[SFD_STDERR]);
+    }
+
+    /* Wait for parent to grant us the tty if we are foreground. */
+    if (foreground && !ISSET(details->flags, CD_EXEC_BG)) {
+	struct timespec ts = { 0, 1000 };  /* 1us */
+	sudo_debug_printf(SUDO_DEBUG_DEBUG, "%s: waiting for controlling tty",
+	    __func__);
+	while (tcgetpgrp(io_fds[SFD_SLAVE]) != self)
+	    nanosleep(&ts, NULL);
+	sudo_debug_printf(SUDO_DEBUG_DEBUG, "%s: got controlling tty",
+	    __func__);
+    }
+
+    /* Done with the pty slave, don't leak it. */
+    if (io_fds[SFD_SLAVE] != -1)
+	close(io_fds[SFD_SLAVE]);
+
+    /* Execute command; only returns on error. */
+    sudo_debug_printf(SUDO_DEBUG_INFO, "executing %s in the %s",
+	details->command, foreground ? "foreground" : "background");
+    exec_cmnd(details, errfd);
+
+    debug_return;
+}
+
+/*
+ * Fill in the monitor closure and setup initial events.
+ * Allocates read events for the signal pipe, error pipe and backchannel.
+ */
+static void
+fill_exec_closure_monitor(struct monitor_closure *mc,
+    struct command_status *cstat, int errfd, int backchannel)
+{
+    debug_decl(fill_exec_closure_monitor, SUDO_DEBUG_EXEC);
+    
+    /* Fill in the non-event part of the closure. */
+    mc->cstat = cstat;
+    mc->backchannel = backchannel;
+    mc->mon_pgrp = getpgrp();
+
+    /* Setup event base and events. */
+    mc->evbase = sudo_ev_base_alloc();
+    if (mc->evbase == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+
+    /* Event for command status via errfd. */
+    mc->errpipe_event = sudo_ev_alloc(errfd,
+	SUDO_EV_READ|SUDO_EV_PERSIST, mon_errpipe_cb, mc);
+    if (mc->errpipe_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->errpipe_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    /* Event for forwarded signals via backchannel. */
+    mc->backchannel_event = sudo_ev_alloc(backchannel,
+	SUDO_EV_READ|SUDO_EV_PERSIST, mon_backchannel_cb, mc);
+    if (mc->backchannel_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->backchannel_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    /* Events for local signals. */
+    mc->sigint_event = sudo_ev_alloc(SIGINT,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigint_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigint_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigquit_event = sudo_ev_alloc(SIGQUIT,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigquit_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigquit_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigtstp_event = sudo_ev_alloc(SIGTSTP,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigtstp_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigtstp_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigterm_event = sudo_ev_alloc(SIGTERM,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigterm_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigterm_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sighup_event = sudo_ev_alloc(SIGHUP,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sighup_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sighup_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigusr1_event = sudo_ev_alloc(SIGUSR1,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigusr1_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigusr1_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigusr2_event = sudo_ev_alloc(SIGUSR2,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigusr2_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigusr2_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    mc->sigchld_event = sudo_ev_alloc(SIGCHLD,
+	SUDO_EV_SIGINFO, mon_signal_cb, mc);
+    if (mc->sigchld_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(mc->evbase, mc->sigchld_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    /* Clear the default event base. */
+    sudo_ev_base_setdef(NULL);
+
+    debug_return;
+}
+
+/*
+ * Monitor process that creates a new session with the controlling tty,
+ * resets signal handlers and forks a child to call exec_cmnd_pty().
+ * Waits for status changes from the command and relays them to the
+ * parent and relays signals from the parent to the command.
+ * Must be called with signals blocked and the old signal mask in oset.
+ * Returns an error if fork(2) fails, else calls _exit(2).
+ */
+int
+exec_monitor(struct command_details *details, sigset_t *oset,
+    bool foreground, int backchannel)
+{
+    struct monitor_closure mc = { 0 };
+    struct command_status cstat;
+    struct sigaction sa;
+    int errpipe[2];
+    debug_decl(exec_monitor, SUDO_DEBUG_EXEC);
+
+    /* The pty master is not used by the monitor. */
+    if (io_fds[SFD_MASTER] != -1)
+	close(io_fds[SFD_MASTER]);
+
+    /* Ignore any SIGTTIN or SIGTTOU we receive (shouldn't be possible). */
+    memset(&sa, 0, sizeof(sa));
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART;
+    sa.sa_handler = SIG_IGN;
+    if (sudo_sigaction(SIGTTIN, &sa, NULL) != 0)
+	sudo_warn(U_("unable to set handler for signal %d"), SIGTTIN);
+    if (sudo_sigaction(SIGTTOU, &sa, NULL) != 0)
+	sudo_warn(U_("unable to set handler for signal %d"), SIGTTOU);
+
+    /* If we are starting in the foreground, the pty was already initialized. */
+    if (foreground)
+	tty_initialized = true;
+
+    /*
+     * Start a new session with the parent as the session leader
+     * and the slave pty as the controlling terminal.
+     * This allows us to be notified when the command has been suspended.
+     */
+    if (setsid() == -1) {
+	sudo_warn("setsid");
+	goto bad;
+    }
+    if (pty_make_controlling() == -1) {
+	sudo_warn(U_("unable to set controlling tty"));
+	goto bad;
+    }
+
+    /*
+     * We use a pipe to get errno if execve(2) fails in the child.
+     */
+    if (pipe2(errpipe, O_CLOEXEC) != 0)
+	sudo_fatal(U_("unable to create pipe"));
+
+    /*
+     * Before forking, wait for the main sudo process to tell us to go.
+     * Avoids race conditions when the command exits quickly.
+     */
+    while (recv(backchannel, &cstat, sizeof(cstat), MSG_WAITALL) == -1) {
+	if (errno != EINTR && errno != EAGAIN)
+	    sudo_fatal(U_("unable to receive message from parent"));
+    }
+
+    mc.cmnd_pid = sudo_debug_fork();
+    switch (mc.cmnd_pid) {
+    case -1:
+	sudo_warn(U_("unable to fork"));
+	goto bad;
+    case 0:
+	/* child */
+	sigprocmask(SIG_SETMASK, oset, NULL);
+	close(backchannel);
+	close(errpipe[0]);
+	if (io_fds[SFD_USERTTY] != -1)
+	    close(io_fds[SFD_USERTTY]);
+	restore_signals();
+
+	/* setup tty and exec command */
+	exec_cmnd_pty(details, foreground, errpipe[1]);
+	if (write(errpipe[1], &errno, sizeof(int)) == -1)
+	    sudo_warn(U_("unable to execute %s"), details->command);
+	_exit(1);
+    }
+    close(errpipe[1]);
+
+    /* No longer need execfd. */
+    if (details->execfd != -1) {
+	close(details->execfd);
+	details->execfd = -1;
+    }
+
+    /* Send the command's pid to main sudo process. */
+    cstat.type = CMD_PID;
+    cstat.val = mc.cmnd_pid;
+    send_status(backchannel, &cstat);
+
+    /*
+     * Create new event base and register read events for the
+     * signal pipe, error pipe, and backchannel.
+     */
+    fill_exec_closure_monitor(&mc, &cstat, errpipe[0], backchannel);
+
+    /* Restore signal mask now that signal handlers are setup. */
+    sigprocmask(SIG_SETMASK, oset, NULL);
+
+    /* If any of stdin/stdout/stderr are pipes, close them in parent. */
+    if (io_fds[SFD_STDIN] != io_fds[SFD_SLAVE])
+	close(io_fds[SFD_STDIN]);
+    if (io_fds[SFD_STDOUT] != io_fds[SFD_SLAVE])
+	close(io_fds[SFD_STDOUT]);
+    if (io_fds[SFD_STDERR] != io_fds[SFD_SLAVE])
+	close(io_fds[SFD_STDERR]);
+
+    /* Put command in its own process group. */
+    mc.cmnd_pgrp = mc.cmnd_pid;
+    setpgid(mc.cmnd_pid, mc.cmnd_pgrp);
+
+    /* Make the command the foreground process for the pty slave. */
+    if (foreground && !ISSET(details->flags, CD_EXEC_BG)) {
+	if (tcsetpgrp(io_fds[SFD_SLAVE], mc.cmnd_pgrp) == -1) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+		"%s: unable to set foreground pgrp to %d (command)",
+		__func__, (int)mc.cmnd_pgrp);
+	}
+    }
+
+    /*
+     * Wait for errno on pipe, signal on backchannel or for SIGCHLD.
+     * The event loop ends when the child is no longer running and
+     * the error pipe is closed.
+     */
+    cstat.type = CMD_INVALID;
+    cstat.val = 0;
+    (void) sudo_ev_dispatch(mc.evbase);
+    if (mc.cmnd_pid != -1) {
+	pid_t pid;
+
+	/* Command still running, did the parent die? */
+	sudo_debug_printf(SUDO_DEBUG_ERROR,
+	    "Command still running after event loop exit, terminating");
+	terminate_command(mc.cmnd_pid, true);
+	do {
+	    pid = waitpid(mc.cmnd_pid, NULL, 0);
+	} while (pid == -1 && errno == EINTR);
+	/* XXX - update cstat with wait status? */
+    }
+
+    /*
+     * Take the controlling tty.  This prevents processes spawned by the
+     * command from receiving SIGHUP when the session leader (us) exits.
+     */
+    if (tcsetpgrp(io_fds[SFD_SLAVE], mc.mon_pgrp) == -1) {
+	sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+	    "%s: unable to set foreground pgrp to %d (monitor)",
+	    __func__, (int)mc.mon_pgrp);
+    }
+
+    /* Send parent status. */
+    send_status(backchannel, &cstat);
+
+#ifdef HAVE_SELINUX
+    if (ISSET(details->flags, CD_RBAC_ENABLED)) {
+	if (selinux_restore_tty() != 0)
+	    sudo_warnx(U_("unable to restore tty label"));
+    }
+#endif
+    sudo_debug_exit_int(__func__, __FILE__, __LINE__, sudo_debug_subsys, 1);
+    _exit(1);
+
+bad:
+    debug_return_int(-1);
+}