Adding upstream version 1.8.27.upstream/1.8.27upstream

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

1 files changed, 1813 insertions, 0 deletions

diff --git a/src/exec_pty.c b/src/exec_pty.c
new file mode 100644
index 0000000..c1ccd4b
--- /dev/null
+++ b/src/exec_pty.c
@@ -0,0 +1,1813 @@
+/*
+ * Copyright (c) 2009-2019 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/stat.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <sys/ioctl.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 <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <termios.h>		/* for struct winsize on HP-UX */
+
+#include "sudo.h"
+#include "sudo_event.h"
+#include "sudo_exec.h"
+#include "sudo_plugin.h"
+#include "sudo_plugin_int.h"
+
+/* Evaluates to true if the event has /dev/tty as its fd. */
+#define USERTTY_EVENT(_ev)	(sudo_ev_get_fd((_ev)) == io_fds[SFD_USERTTY])
+
+#define TERM_COOKED	0
+#define TERM_RAW	1
+
+/* Tail queue of messages to send to the monitor. */
+struct monitor_message {
+    TAILQ_ENTRY(monitor_message) entries;
+    struct command_status cstat;
+};
+TAILQ_HEAD(monitor_message_list, monitor_message);
+
+struct exec_closure_pty {
+    pid_t monitor_pid;
+    pid_t cmnd_pid;
+    pid_t ppgrp;
+    short rows;
+    short cols;
+    struct command_status *cstat;
+    struct command_details *details;
+    struct sudo_event_base *evbase;
+    struct sudo_event *backchannel_event;
+    struct sudo_event *fwdchannel_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 *sigalrm_event;
+    struct sudo_event *sigusr1_event;
+    struct sudo_event *sigusr2_event;
+    struct sudo_event *sigchld_event;
+    struct sudo_event *sigwinch_event;
+    struct monitor_message_list monitor_messages;
+};
+
+/*
+ * I/O buffer with associated read/write events and a logging action.
+ * Used to, e.g. pass data from the pty to the user's terminal
+ * and any I/O logging plugins.
+ */
+struct io_buffer;
+typedef bool (*sudo_io_action_t)(const char *, unsigned int, struct io_buffer *);
+struct io_buffer {
+    SLIST_ENTRY(io_buffer) entries;
+    struct exec_closure_pty *ec;
+    struct sudo_event *revent;
+    struct sudo_event *wevent;
+    sudo_io_action_t action;
+    int len; /* buffer length (how much produced) */
+    int off; /* write position (how much already consumed) */
+    char buf[64 * 1024];
+};
+SLIST_HEAD(io_buffer_list, io_buffer);
+
+static char slavename[PATH_MAX];
+int io_fds[6] = { -1, -1, -1, -1, -1, -1};
+static bool foreground, pipeline;
+static int ttymode = TERM_COOKED;
+static sigset_t ttyblock;
+static struct io_buffer_list iobufs;
+static const char *utmp_user;
+
+static void del_io_events(bool nonblocking);
+static void sync_ttysize(struct exec_closure_pty *ec);
+static int safe_close(int fd);
+static void ev_free_by_fd(struct sudo_event_base *evbase, int fd);
+static void check_foreground(struct exec_closure_pty *ec);
+static void add_io_events(struct sudo_event_base *evbase);
+static void schedule_signal(struct exec_closure_pty *ec, int signo);
+
+/*
+ * Cleanup hook for sudo_fatal()/sudo_fatalx()
+ */
+void
+pty_cleanup(void)
+{
+    debug_decl(cleanup, SUDO_DEBUG_EXEC);
+
+    if (io_fds[SFD_USERTTY] != -1)
+	sudo_term_restore(io_fds[SFD_USERTTY], false);
+    if (utmp_user != NULL)
+	utmp_logout(slavename, 0);
+
+    debug_return;
+}
+
+/*
+ * Allocate a pty if /dev/tty is a tty.
+ * Fills in io_fds[SFD_USERTTY], io_fds[SFD_MASTER], io_fds[SFD_SLAVE]
+ * and slavename globals.
+ */
+static bool
+pty_setup(struct command_details *details, const char *tty)
+{
+    debug_decl(pty_setup, SUDO_DEBUG_EXEC);
+
+    io_fds[SFD_USERTTY] = open(_PATH_TTY, O_RDWR);
+    if (io_fds[SFD_USERTTY] == -1) {
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: no %s, not allocating a pty",
+	    __func__, _PATH_TTY);
+	debug_return_bool(false);
+    }
+
+    if (!get_pty(&io_fds[SFD_MASTER], &io_fds[SFD_SLAVE],
+	slavename, sizeof(slavename), details->euid))
+	sudo_fatal(U_("unable to allocate pty"));
+
+    /* Add entry to utmp/utmpx? */
+    if (ISSET(details->flags, CD_SET_UTMP)) {
+	utmp_user =
+	    details->utmp_user ? details->utmp_user : user_details.username;
+	utmp_login(tty, slavename, io_fds[SFD_SLAVE], utmp_user);
+    }
+
+    sudo_debug_printf(SUDO_DEBUG_INFO,
+	"%s: %s fd %d, pty master fd %d, pty slave fd %d",
+	__func__, _PATH_TTY, io_fds[SFD_USERTTY], io_fds[SFD_MASTER],
+	io_fds[SFD_SLAVE]);
+
+    debug_return_bool(true);
+}
+
+/*
+ * Make the tty slave the controlling tty.
+ * This is only used by the monitor but slavename[] is static.
+ */
+int
+pty_make_controlling(void)
+{
+    if (io_fds[SFD_SLAVE] != -1) {
+#ifdef TIOCSCTTY
+	if (ioctl(io_fds[SFD_SLAVE], TIOCSCTTY, NULL) != 0)
+	    return -1;
+#else
+	/* Set controlling tty by reopening slave. */
+	int fd = open(slavename, O_RDWR);
+	if (fd == -1)
+	    return -1;
+	close(fd);
+#endif
+    }
+    return 0;
+}
+
+/* Call I/O plugin tty input log method. */
+static bool
+log_ttyin(const char *buf, unsigned int n, struct io_buffer *iob)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    bool ret = true;
+    debug_decl(log_ttyin, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_ttyin) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_ttyin(buf, n);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_ttyin = NULL;
+		}
+		ret = false;
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return_bool(ret);
+}
+
+/* Call I/O plugin stdin log method. */
+static bool
+log_stdin(const char *buf, unsigned int n, struct io_buffer *iob)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    bool ret = true;
+    debug_decl(log_stdin, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_stdin) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_stdin(buf, n);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_stdin = NULL;
+		}
+		ret = false;
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return_bool(ret);
+}
+
+/* Call I/O plugin tty output log method. */
+static bool
+log_ttyout(const char *buf, unsigned int n, struct io_buffer *iob)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    bool ret = true;
+    debug_decl(log_ttyout, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_ttyout) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_ttyout(buf, n);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_ttyout = NULL;
+		}
+		ret = false;
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    if (!ret) {
+	/*
+	 * I/O plugin rejected the output, delete the write event
+	 * (user's tty) so we do not display the rejected output.
+	 */
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: deleting and freeing devtty wevent %p", __func__, iob->wevent);
+	sudo_ev_free(iob->wevent);
+	iob->wevent = NULL;
+	iob->off = iob->len = 0;
+    }
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return_bool(ret);
+}
+
+/* Call I/O plugin stdout log method. */
+static bool
+log_stdout(const char *buf, unsigned int n, struct io_buffer *iob)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    bool ret = true;
+    debug_decl(log_stdout, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_stdout) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_stdout(buf, n);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_stdout = NULL;
+		}
+		ret = false;
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    if (!ret) {
+	/*
+	 * I/O plugin rejected the output, delete the write event
+	 * (user's stdout) so we do not display the rejected output.
+	 */
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: deleting and freeing stdout wevent %p", __func__, iob->wevent);
+	sudo_ev_free(iob->wevent);
+	iob->wevent = NULL;
+	iob->off = iob->len = 0;
+    }
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return_bool(ret);
+}
+
+/* Call I/O plugin stderr log method. */
+static bool
+log_stderr(const char *buf, unsigned int n, struct io_buffer *iob)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    bool ret = true;
+    debug_decl(log_stderr, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_stderr) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_stderr(buf, n);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_stderr = NULL;
+		}
+		ret = false;
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    if (!ret) {
+	/*
+	 * I/O plugin rejected the output, delete the write event
+	 * (user's stderr) so we do not display the rejected output.
+	 */
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: deleting and freeing stderr wevent %p", __func__, iob->wevent);
+	sudo_ev_free(iob->wevent);
+	iob->wevent = NULL;
+	iob->off = iob->len = 0;
+    }
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return_bool(ret);
+}
+
+/* Call I/O plugin suspend log method. */
+static void
+log_suspend(int signo)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    debug_decl(log_suspend, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->version < SUDO_API_MKVERSION(1, 13))
+	    continue;
+	if (plugin->u.io->log_suspend) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->log_suspend(signo);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->log_suspend = NULL;
+		}
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return;
+}
+
+/* Call I/O plugin window change log method. */
+static void
+log_winchange(unsigned int rows, unsigned int cols)
+{
+    struct plugin_container *plugin;
+    sigset_t omask;
+    debug_decl(log_winchange, SUDO_DEBUG_EXEC);
+
+    sigprocmask(SIG_BLOCK, &ttyblock, &omask);
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->version < SUDO_API_MKVERSION(1, 12))
+	    continue;
+	if (plugin->u.io->change_winsize) {
+	    int rc;
+
+	    sudo_debug_set_active_instance(plugin->debug_instance);
+	    rc = plugin->u.io->change_winsize(rows, cols);
+	    if (rc <= 0) {
+		if (rc < 0) {
+		    /* Error: disable plugin's I/O function. */
+		    plugin->u.io->change_winsize = NULL;
+		}
+		break;
+	    }
+	}
+    }
+    sudo_debug_set_active_instance(sudo_debug_instance);
+    sigprocmask(SIG_SETMASK, &omask, NULL);
+
+    debug_return;
+}
+
+/*
+ * Check whether we are running in the foregroup.
+ * Updates the foreground global and does lazy init of the
+ * the pty slave as needed.
+ */
+static void
+check_foreground(struct exec_closure_pty *ec)
+{
+    debug_decl(check_foreground, SUDO_DEBUG_EXEC);
+
+    if (io_fds[SFD_USERTTY] != -1) {
+	foreground = tcgetpgrp(io_fds[SFD_USERTTY]) == ec->ppgrp;
+
+	/* Also check for window size changes. */
+	sync_ttysize(ec);
+    }
+
+    debug_return;
+}
+
+/*
+ * Suspend sudo if the underlying command is suspended.
+ * Returns SIGCONT_FG if the command should be resumed in the
+ * foreground or SIGCONT_BG if it is a background process.
+ */
+static int
+suspend_sudo(struct exec_closure_pty *ec, int signo)
+{
+    char signame[SIG2STR_MAX];
+    struct sigaction sa, osa;
+    int ret = 0;
+    debug_decl(suspend_sudo, SUDO_DEBUG_EXEC);
+
+    switch (signo) {
+    case SIGTTOU:
+    case SIGTTIN:
+	/*
+	 * If sudo is already the foreground process, just resume the command
+	 * in the foreground.  If not, we'll suspend sudo and resume later.
+	 */
+	if (!foreground)
+	    check_foreground(ec);
+	if (foreground) {
+	    if (ttymode != TERM_RAW) {
+		if (sudo_term_raw(io_fds[SFD_USERTTY], 0))
+		    ttymode = TERM_RAW;
+	    }
+	    ret = SIGCONT_FG; /* resume command in foreground */
+	    break;
+	}
+	/* FALLTHROUGH */
+    case SIGSTOP:
+    case SIGTSTP:
+	/* Flush any remaining output and deschedule I/O events. */
+	del_io_events(true);
+
+	/* Restore original tty mode before suspending. */
+	if (ttymode != TERM_COOKED)
+	    sudo_term_restore(io_fds[SFD_USERTTY], false);
+
+	/* Log the suspend event. */
+	log_suspend(signo);
+
+	if (sig2str(signo, signame) == -1)
+	    snprintf(signame, sizeof(signame), "%d", signo);
+
+	/* Suspend self and continue command when we resume. */
+	if (signo != SIGSTOP) {
+	    memset(&sa, 0, sizeof(sa));
+	    sigemptyset(&sa.sa_mask);
+	    sa.sa_flags = SA_RESTART;
+	    sa.sa_handler = SIG_DFL;
+	    if (sudo_sigaction(signo, &sa, &osa) != 0)
+		sudo_warn(U_("unable to set handler for signal %d"), signo);
+	}
+	sudo_debug_printf(SUDO_DEBUG_INFO, "kill parent SIG%s", signame);
+	if (killpg(ec->ppgrp, signo) != 0)
+	    sudo_warn("killpg(%d, SIG%s)", (int)ec->ppgrp, signame);
+
+	/* Log the resume event. */
+	log_suspend(SIGCONT);
+
+	/* Check foreground/background status on resume. */
+	check_foreground(ec);
+
+	/*
+	 * We always resume the command in the foreground if sudo itself
+	 * is the foreground process.  This helps work around poorly behaved
+	 * programs that catch SIGTTOU/SIGTTIN but suspend themselves with
+	 * SIGSTOP.  At worst, sudo will go into the background but upon
+	 * resume the command will be runnable.  Otherwise, we can get into
+	 * a situation where the command will immediately suspend itself.
+	 */
+	sudo_debug_printf(SUDO_DEBUG_INFO, "parent is in %s, ttymode %d -> %d",
+	    foreground ? "foreground" : "background", ttymode,
+	    foreground ? TERM_RAW : TERM_COOKED);
+
+	if (foreground) {
+	    /* Foreground process, set tty to raw mode. */
+	    if (sudo_term_raw(io_fds[SFD_USERTTY], 0))
+		ttymode = TERM_RAW;
+	} else {
+	    /* Background process, no access to tty. */
+	    ttymode = TERM_COOKED;
+	}
+
+	if (signo != SIGSTOP) {
+	    if (sudo_sigaction(signo, &osa, NULL) != 0)
+		sudo_warn(U_("unable to restore handler for signal %d"), signo);
+	}
+
+	ret = ttymode == TERM_RAW ? SIGCONT_FG : SIGCONT_BG;
+	break;
+    }
+
+    debug_return_int(ret);
+}
+
+/*
+ * SIGTTIN signal handler for read_callback that just sets a flag.
+ */
+static volatile sig_atomic_t got_sigttin;
+
+static void
+sigttin(int signo)
+{
+    got_sigttin = 1;
+}
+
+/*
+ * Read an iobuf that is ready.
+ */
+static void
+read_callback(int fd, int what, void *v)
+{
+    struct io_buffer *iob = v;
+    struct sudo_event_base *evbase = sudo_ev_get_base(iob->revent);
+    struct sigaction sa, osa;
+    int saved_errno;
+    ssize_t n;
+    debug_decl(read_callback, SUDO_DEBUG_EXEC);
+
+    /*
+     * We ignore SIGTTIN by default but we need to handle it when reading
+     * from the terminal.  A signal event won't work here because the
+     * read() would be restarted, preventing the callback from running.
+     */
+    memset(&sa, 0, sizeof(sa));
+    sigemptyset(&sa.sa_mask);
+    sa.sa_handler = sigttin;
+    got_sigttin = 0;
+    sigaction(SIGTTIN, &sa, &osa);
+    n = read(fd, iob->buf + iob->len, sizeof(iob->buf) - iob->len);
+    saved_errno = errno;
+    sigaction(SIGTTIN, &osa, NULL);
+    errno = saved_errno;
+
+    switch (n) {
+	case -1:
+	    if (got_sigttin) {
+		/* Schedule SIGTTIN to be forwared to the command. */
+		schedule_signal(iob->ec, SIGTTIN);
+	    }
+	    if (errno == EAGAIN || errno == EINTR)
+		break;
+	    /* treat read error as fatal and close the fd */
+	    sudo_debug_printf(SUDO_DEBUG_ERROR,
+		"error reading fd %d: %s", fd, strerror(errno));
+	    /* FALLTHROUGH */
+	case 0:
+	    /* got EOF or pty has gone away */
+	    if (n == 0) {
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "read EOF from fd %d", fd);
+	    }
+	    safe_close(fd);
+	    ev_free_by_fd(evbase, fd);
+	    /* If writer already consumed the buffer, close it too. */
+	    if (iob->wevent != NULL && iob->off == iob->len) {
+		safe_close(sudo_ev_get_fd(iob->wevent));
+		ev_free_by_fd(evbase, sudo_ev_get_fd(iob->wevent));
+		iob->off = iob->len = 0;
+	    }
+	    break;
+	default:
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"read %zd bytes from fd %d", n, fd);
+	    if (!iob->action(iob->buf + iob->len, n, iob)) {
+		terminate_command(iob->ec->cmnd_pid, true);
+		iob->ec->cmnd_pid = -1;
+	    }
+	    iob->len += n;
+	    /* Enable writer now that there is data in the buffer. */
+	    if (iob->wevent != NULL) {
+		if (sudo_ev_add(evbase, iob->wevent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	    /* Re-enable reader if buffer is not full. */
+	    if (iob->len != sizeof(iob->buf)) {
+		if (sudo_ev_add(evbase, iob->revent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	    break;
+    }
+}
+
+/*
+ * SIGTTOU signal handler for write_callback that just sets a flag.
+ */
+static volatile sig_atomic_t got_sigttou;
+
+static void
+sigttou(int signo)
+{
+    got_sigttou = 1;
+}
+
+/*
+ * Write an iobuf that is ready.
+ */
+static void
+write_callback(int fd, int what, void *v)
+{
+    struct io_buffer *iob = v;
+    struct sudo_event_base *evbase = sudo_ev_get_base(iob->wevent);
+    struct sigaction sa, osa;
+    int saved_errno;
+    ssize_t n;
+    debug_decl(write_callback, SUDO_DEBUG_EXEC);
+
+    /*
+     * We ignore SIGTTOU by default but we need to handle it when writing
+     * to the terminal.  A signal event won't work here because the
+     * write() would be restarted, preventing the callback from running.
+     */
+    memset(&sa, 0, sizeof(sa));
+    sigemptyset(&sa.sa_mask);
+    sa.sa_handler = sigttou;
+    got_sigttou = 0;
+    sigaction(SIGTTOU, &sa, &osa);
+    n = write(fd, iob->buf + iob->off, iob->len - iob->off);
+    saved_errno = errno;
+    sigaction(SIGTTOU, &osa, NULL);
+    errno = saved_errno;
+
+    if (n == -1) {
+	switch (errno) {
+	case EPIPE:
+	case ENXIO:
+	case EIO:
+	case EBADF:
+	    /* other end of pipe closed or pty revoked */
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"unable to write %d bytes to fd %d",
+		iob->len - iob->off, fd);
+	    /* Close reader if there is one. */
+	    if (iob->revent != NULL) {
+		safe_close(sudo_ev_get_fd(iob->revent));
+		ev_free_by_fd(evbase, sudo_ev_get_fd(iob->revent));
+	    }
+	    safe_close(fd);
+	    ev_free_by_fd(evbase, fd);
+	    break;
+	case EINTR:
+	    if (got_sigttou) {
+		/* Schedule SIGTTOU to be forwared to the command. */
+		schedule_signal(iob->ec, SIGTTOU);
+	    }
+	    /* FALLTHROUGH */
+	case EAGAIN:
+	    /* not an error */
+	    break;
+	default:
+	    /* XXX - need a way to distinguish non-exec error. */
+	    iob->ec->cstat->type = CMD_ERRNO;
+	    iob->ec->cstat->val = errno;
+	    sudo_debug_printf(SUDO_DEBUG_ERROR,
+		"error writing fd %d: %s", fd, strerror(errno));
+	    sudo_ev_loopbreak(evbase);
+	    break;
+	}
+    } else {
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "wrote %zd bytes to fd %d", n, fd);
+	iob->off += n;
+	/* Reset buffer if fully consumed. */
+	if (iob->off == iob->len) {
+	    iob->off = iob->len = 0;
+	    /* Forward the EOF from reader to writer. */
+	    if (iob->revent == NULL) {
+		safe_close(fd);
+		ev_free_by_fd(evbase, fd);
+	    }
+	}
+	/* Re-enable writer if buffer is not empty. */
+	if (iob->len > iob->off) {
+	    if (sudo_ev_add(evbase, iob->wevent, NULL, false) == -1)
+		sudo_fatal(U_("unable to add event to queue"));
+	}
+	/* Enable reader if buffer is not full. */
+	if (iob->revent != NULL &&
+	    (ttymode == TERM_RAW || !USERTTY_EVENT(iob->revent))) {
+	    if (iob->len != sizeof(iob->buf)) {
+		if (sudo_ev_add(evbase, iob->revent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	}
+    }
+}
+
+static void
+io_buf_new(int rfd, int wfd,
+    bool (*action)(const char *, unsigned int, struct io_buffer *),
+    struct exec_closure_pty *ec, struct io_buffer_list *head)
+{
+    int n;
+    struct io_buffer *iob;
+    debug_decl(io_buf_new, SUDO_DEBUG_EXEC);
+
+    /* Set non-blocking mode. */
+    n = fcntl(rfd, F_GETFL, 0);
+    if (n != -1 && !ISSET(n, O_NONBLOCK))
+	(void) fcntl(rfd, F_SETFL, n | O_NONBLOCK);
+    n = fcntl(wfd, F_GETFL, 0);
+    if (n != -1 && !ISSET(n, O_NONBLOCK))
+	(void) fcntl(wfd, F_SETFL, n | O_NONBLOCK);
+
+    /* Allocate and add to head of list. */
+    if ((iob = malloc(sizeof(*iob))) == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    iob->ec = ec;
+    iob->revent = sudo_ev_alloc(rfd, SUDO_EV_READ, read_callback, iob);
+    iob->wevent = sudo_ev_alloc(wfd, SUDO_EV_WRITE, write_callback, iob);
+    iob->len = 0;
+    iob->off = 0;
+    iob->action = action;
+    iob->buf[0] = '\0';
+    if (iob->revent == NULL || iob->wevent == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    SLIST_INSERT_HEAD(head, iob, entries);
+
+    debug_return;
+}
+
+/*
+ * We already closed the slave pty so reads from the master will not block.
+ */
+static void
+pty_finish(struct command_status *cstat)
+{
+    struct io_buffer *iob;
+    int n;
+    debug_decl(pty_finish, SUDO_DEBUG_EXEC);
+
+    /* Flush any remaining output (the plugin already got it). */
+    if (io_fds[SFD_USERTTY] != -1) {
+	n = fcntl(io_fds[SFD_USERTTY], F_GETFL, 0);
+	if (n != -1 && ISSET(n, O_NONBLOCK)) {
+	    CLR(n, O_NONBLOCK);
+	    (void) fcntl(io_fds[SFD_USERTTY], F_SETFL, n);
+	}
+    }
+    del_io_events(false);
+
+    /* Free I/O buffers. */
+    while ((iob = SLIST_FIRST(&iobufs)) != NULL) {
+	SLIST_REMOVE_HEAD(&iobufs, entries);
+	if (iob->revent != NULL)
+	    sudo_ev_free(iob->revent);
+	if (iob->wevent != NULL)
+	    sudo_ev_free(iob->wevent);
+	free(iob);
+    }
+
+    /* Restore terminal settings. */
+    if (io_fds[SFD_USERTTY] != -1)
+	sudo_term_restore(io_fds[SFD_USERTTY], false);
+
+    /* Update utmp */
+    if (utmp_user != NULL)
+	utmp_logout(slavename, cstat->type == CMD_WSTATUS ? cstat->val : 0);
+
+    debug_return;
+}
+
+/*
+ * Send command status to the monitor (signal or window size change).
+ */
+static void
+send_command_status(struct exec_closure_pty *ec, int type, int val)
+{
+    struct monitor_message *msg;
+    debug_decl(send_command, SUDO_DEBUG_EXEC)
+
+    if ((msg = calloc(1, sizeof(*msg))) == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    msg->cstat.type = type;
+    msg->cstat.val = val;
+    TAILQ_INSERT_TAIL(&ec->monitor_messages, msg, entries);
+
+    if (sudo_ev_add(ec->evbase, ec->fwdchannel_event, NULL, true) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    /* Restart event loop to send the command immediately. */
+    sudo_ev_loopcontinue(ec->evbase);
+
+    debug_return;
+}
+
+/*
+ * Schedule a signal to be forwarded.
+ */
+static void
+schedule_signal(struct exec_closure_pty *ec, int signo)
+{
+    char signame[SIG2STR_MAX];
+    debug_decl(schedule_signal, SUDO_DEBUG_EXEC)
+
+    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);
+    sudo_debug_printf(SUDO_DEBUG_DIAG, "scheduled SIG%s for command", signame);
+
+    send_command_status(ec, CMD_SIGNO, signo);
+
+    debug_return;
+}
+
+static void
+backchannel_cb(int fd, int what, void *v)
+{
+    struct exec_closure_pty *ec = v;
+    struct command_status cstat;
+    ssize_t nread;
+    debug_decl(backchannel_cb, SUDO_DEBUG_EXEC)
+
+    /*
+     * Read command status from the monitor.
+     * Note that the backchannel is a *blocking* socket.
+     */
+    nread = recv(fd, &cstat, sizeof(cstat), MSG_WAITALL);
+    switch (nread) {
+    case -1:
+	switch (errno) {
+	case EINTR:
+	case EAGAIN:
+	    /* Nothing ready. */
+	    break;
+	default:
+	    if (ec->cstat->val == CMD_INVALID) {
+		ec->cstat->type = CMD_ERRNO;
+		ec->cstat->val = errno;
+		sudo_debug_printf(SUDO_DEBUG_ERROR,
+		    "%s: failed to read command status: %s",
+		    __func__, strerror(errno));
+		sudo_ev_loopbreak(ec->evbase);
+	    }
+	    break;
+	}
+	break;
+    case 0:
+	/* EOF, monitor exited or was killed. */
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "EOF on backchannel, monitor dead?");
+	if (ec->cstat->type == CMD_INVALID) {
+	    /* XXX - need new CMD_ type for monitor errors. */
+	    ec->cstat->type = CMD_ERRNO;
+	    ec->cstat->val = ECONNRESET;
+	}
+	sudo_ev_loopexit(ec->evbase);
+	break;
+    case sizeof(cstat):
+	/* Check command status. */
+	switch (cstat.type) {
+	case CMD_PID:
+	    ec->cmnd_pid = cstat.val;
+	    sudo_debug_printf(SUDO_DEBUG_INFO, "executed %s, pid %d",
+		ec->details->command, (int)ec->cmnd_pid);
+	    break;
+	case CMD_WSTATUS:
+	    if (WIFSTOPPED(cstat.val)) {
+		int signo;
+
+		/* Suspend parent and tell monitor how to resume on return. */
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "command stopped, suspending parent");
+		signo = suspend_sudo(ec, WSTOPSIG(cstat.val));
+		schedule_signal(ec, signo);
+		/* Re-enable I/O events */
+		add_io_events(ec->evbase);
+	    } else {
+		/* Command exited or was killed, either way we are done. */
+		sudo_debug_printf(SUDO_DEBUG_INFO, "command exited or was killed");
+		sudo_ev_loopexit(ec->evbase);
+	    }
+	    *ec->cstat = cstat;
+	    break;
+	case CMD_ERRNO:
+	    /* Monitor was unable to execute command or broken pipe. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO, "errno from monitor: %s",
+		strerror(cstat.val));
+	    sudo_ev_loopbreak(ec->evbase);
+	    *ec->cstat = cstat;
+	    break;
+	}
+	/* Keep reading command status messages until EAGAIN or EOF. */
+	break;
+    default:
+	/* Short read, should not happen. */
+	if (ec->cstat->val == CMD_INVALID) {
+	    ec->cstat->type = CMD_ERRNO;
+	    ec->cstat->val = EIO;
+	    sudo_debug_printf(SUDO_DEBUG_ERROR,
+		"%s: failed to read command status: short read", __func__);
+	    sudo_ev_loopbreak(ec->evbase);
+	}
+	break;
+    }
+    debug_return;
+}
+
+/*
+ * Handle changes to the monitors's status (SIGCHLD).
+ */
+static void
+handle_sigchld_pty(struct exec_closure_pty *ec)
+{
+    int n, status;
+    pid_t pid;
+    debug_decl(handle_sigchld_pty, SUDO_DEBUG_EXEC)
+
+    /*
+     * Monitor process was signaled; wait for it as needed.
+     */
+    do {
+	pid = waitpid(ec->monitor_pid, &status, WUNTRACED|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 the monitor dies we get notified via backchannel_cb().
+     * If it was stopped, we should stop too (the command keeps
+     * running in its pty) and continue it when we come back.
+     */
+    if (WIFSTOPPED(status)) {
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "monitor stopped, suspending sudo");
+	n = suspend_sudo(ec, WSTOPSIG(status));
+	kill(pid, SIGCONT);
+	schedule_signal(ec, n);
+	/* Re-enable I/O events */
+	add_io_events(ec->evbase);
+    } else if (WIFSIGNALED(status)) {
+	char signame[SIG2STR_MAX];
+	if (sig2str(WTERMSIG(status), signame) == -1)
+	    snprintf(signame, sizeof(signame), "%d", WTERMSIG(status));
+	sudo_debug_printf(SUDO_DEBUG_INFO, "%s: monitor (%d) killed, SIG%s",
+	    __func__, (int)ec->monitor_pid, signame);
+	ec->monitor_pid = -1;
+    } else {
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: monitor exited, status %d", __func__, WEXITSTATUS(status));
+	ec->monitor_pid = -1;
+    }
+    debug_return;
+}
+
+/* Signal callback */
+static void
+signal_cb_pty(int signo, int what, void *v)
+{
+    struct sudo_ev_siginfo_container *sc = v;
+    struct exec_closure_pty *ec = sc->closure;
+    char signame[SIG2STR_MAX];
+    debug_decl(signal_cb_pty, SUDO_DEBUG_EXEC)
+
+    if (ec->monitor_pid == -1)
+	debug_return;
+
+    if (sig2str(signo, signame) == -1)
+	snprintf(signame, sizeof(signame), "%d", signo);
+    sudo_debug_printf(SUDO_DEBUG_DIAG,
+	"%s: evbase %p, monitor: %d, signo %s(%d), cstat %p", __func__,
+	ec->evbase, (int)ec->monitor_pid, signame, signo, ec->cstat);
+
+    switch (signo) {
+    case SIGCHLD:
+	handle_sigchld_pty(ec);
+	break;
+    case SIGWINCH:
+	sync_ttysize(ec);
+	break;
+    default:
+	/*
+	 * Do not forward signals sent by a process in the command's process
+	 * group, as we don't want the command to indirectly kill itself.
+	 * For example, this can happen with some 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 == ec->ppgrp || si_pgrp == ec->cmnd_pid)
+		    debug_return;
+	    } else if (sc->siginfo->si_pid == ec->cmnd_pid) {
+		debug_return;
+	    }
+	}
+	/* Schedule signal to be forwared to the command. */
+	schedule_signal(ec, signo);
+	break;
+    }
+
+    debug_return;
+}
+
+/*
+ * Forward signals in monitor_messages to the monitor so it can
+ * deliver them to the command.
+ */
+static void
+fwdchannel_cb(int sock, int what, void *v)
+{
+    struct exec_closure_pty *ec = v;
+    char signame[SIG2STR_MAX];
+    struct monitor_message *msg;
+    ssize_t nsent;
+    debug_decl(fwdchannel_cb, SUDO_DEBUG_EXEC)
+
+    while ((msg = TAILQ_FIRST(&ec->monitor_messages)) != NULL) {
+	switch (msg->cstat.type) {
+	case CMD_SIGNO:
+	    if (msg->cstat.val == SIGCONT_FG)
+		strlcpy(signame, "CONT_FG", sizeof(signame));
+	    else if (msg->cstat.val == SIGCONT_BG)
+		strlcpy(signame, "CONT_BG", sizeof(signame));
+	    else if (sig2str(msg->cstat.val, signame) == -1)
+		snprintf(signame, sizeof(signame), "%d", msg->cstat.val);
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"sending SIG%s to monitor over backchannel", signame);
+	    break;
+	case CMD_TTYWINCH:
+	    sudo_debug_printf(SUDO_DEBUG_INFO, "sending window size change "
+		"to monitor over backchannelL %d x %d",
+		msg->cstat.val & 0xffff, (msg->cstat.val >> 16) & 0xffff);
+	    break;
+	default:
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"sending cstat type %d, value %d to monitor over backchannel",
+		msg->cstat.type, msg->cstat.val);
+	    break;
+	}
+	TAILQ_REMOVE(&ec->monitor_messages, msg, entries);
+	nsent = send(sock, &msg->cstat, sizeof(msg->cstat), 0);
+	if (nsent != sizeof(msg->cstat)) {
+	    if (errno == EPIPE) {
+		sudo_debug_printf(SUDO_DEBUG_ERROR,
+		    "broken pipe writing to monitor over backchannel");
+		/* Other end of socket gone, empty out monitor_messages. */
+		free(msg);
+		while ((msg = TAILQ_FIRST(&ec->monitor_messages)) != NULL) {
+		    TAILQ_REMOVE(&ec->monitor_messages, msg, entries);
+		    free(msg);
+		}
+		/* XXX - need new CMD_ type for monitor errors. */
+		ec->cstat->type = CMD_ERRNO;
+		ec->cstat->val = errno;
+		sudo_ev_loopbreak(ec->evbase);
+	    }
+	    break;
+	}
+	free(msg);
+    }
+}
+
+/*
+ * Fill in the exec closure and setup initial exec events.
+ * Allocates events for the signal pipe and backchannel.
+ * Forwarded signals on the backchannel are enabled on demand.
+ */
+static void
+fill_exec_closure_pty(struct exec_closure_pty *ec, struct command_status *cstat,
+    struct command_details *details, pid_t ppgrp, int backchannel)
+{
+    debug_decl(fill_exec_closure_pty, SUDO_DEBUG_EXEC)
+
+    /* Fill in the non-event part of the closure. */
+    ec->cmnd_pid = -1;
+    ec->ppgrp = ppgrp;
+    ec->cstat = cstat;
+    ec->details = details;
+    ec->rows = user_details.ts_rows;
+    ec->cols = user_details.ts_cols;
+    TAILQ_INIT(&ec->monitor_messages);
+
+    /* Setup event base and events. */
+    ec->evbase = sudo_ev_base_alloc();
+    if (ec->evbase == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+
+    /* Event for command status via backchannel. */
+    ec->backchannel_event = sudo_ev_alloc(backchannel,
+	SUDO_EV_READ|SUDO_EV_PERSIST, backchannel_cb, ec);
+    if (ec->backchannel_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->backchannel_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+    sudo_debug_printf(SUDO_DEBUG_INFO, "backchannel fd %d\n", backchannel);
+
+    /* Events for local signals. */
+    ec->sigint_event = sudo_ev_alloc(SIGINT,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigint_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigint_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigquit_event = sudo_ev_alloc(SIGQUIT,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigquit_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigquit_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigtstp_event = sudo_ev_alloc(SIGTSTP,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigtstp_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigtstp_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigterm_event = sudo_ev_alloc(SIGTERM,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigterm_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigterm_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sighup_event = sudo_ev_alloc(SIGHUP,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sighup_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sighup_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigalrm_event = sudo_ev_alloc(SIGALRM,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigalrm_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigalrm_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigusr1_event = sudo_ev_alloc(SIGUSR1,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigusr1_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigusr1_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigusr2_event = sudo_ev_alloc(SIGUSR2,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigusr2_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigusr2_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigchld_event = sudo_ev_alloc(SIGCHLD,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigchld_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigchld_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    ec->sigwinch_event = sudo_ev_alloc(SIGWINCH,
+	SUDO_EV_SIGINFO, signal_cb_pty, ec);
+    if (ec->sigwinch_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+    if (sudo_ev_add(ec->evbase, ec->sigwinch_event, NULL, false) == -1)
+	sudo_fatal(U_("unable to add event to queue"));
+
+    /* The signal forwarding event gets added on demand. */
+    ec->fwdchannel_event = sudo_ev_alloc(backchannel,
+	SUDO_EV_WRITE, fwdchannel_cb, ec);
+    if (ec->fwdchannel_event == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+
+    /* Set the default event base. */
+    sudo_ev_base_setdef(ec->evbase);
+
+    debug_return;
+}
+
+/*
+ * Free the dynamically-allocated contents of the exec closure.
+ */
+static void
+free_exec_closure_pty(struct exec_closure_pty *ec)
+{
+    struct monitor_message *msg;
+    debug_decl(free_exec_closure_pty, SUDO_DEBUG_EXEC)
+
+    sudo_ev_base_free(ec->evbase);
+    sudo_ev_free(ec->backchannel_event);
+    sudo_ev_free(ec->fwdchannel_event);
+    sudo_ev_free(ec->sigint_event);
+    sudo_ev_free(ec->sigquit_event);
+    sudo_ev_free(ec->sigtstp_event);
+    sudo_ev_free(ec->sigterm_event);
+    sudo_ev_free(ec->sighup_event);
+    sudo_ev_free(ec->sigalrm_event);
+    sudo_ev_free(ec->sigusr1_event);
+    sudo_ev_free(ec->sigusr2_event);
+    sudo_ev_free(ec->sigchld_event);
+    sudo_ev_free(ec->sigwinch_event);
+
+    while ((msg = TAILQ_FIRST(&ec->monitor_messages)) != NULL) {
+	TAILQ_REMOVE(&ec->monitor_messages, msg, entries);
+	free(msg);
+    }
+
+    debug_return;
+}
+
+/*
+ * Execute a command in a pty, potentially with I/O loggging, and
+ * wait for it to finish.
+ * 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.
+ */
+bool
+exec_pty(struct command_details *details, struct command_status *cstat)
+{
+    int io_pipe[3][2] = { { -1, -1 }, { -1, -1 }, { -1, -1 } };
+    bool interpose[3] = { false, false, false };
+    struct exec_closure_pty ec = { 0 };
+    struct plugin_container *plugin;
+    sigset_t set, oset;
+    struct sigaction sa;
+    struct stat sb;
+    pid_t ppgrp;
+    int sv[2];
+    debug_decl(exec_pty, SUDO_DEBUG_EXEC)
+
+    /*
+     * Allocate a pty.
+     */
+    if (!pty_setup(details, user_details.tty)) {
+	if (TAILQ_EMPTY(&io_plugins)) {
+	    /* Not logging I/O and didn't allocate a pty. */
+	    debug_return_bool(false);
+	}
+    }
+
+    /*
+     * We communicate with the monitor over a bi-directional pair of sockets.
+     * Parent sends signal info to monitor and monitor sends back wait status.
+     */
+    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1)
+	sudo_fatal(U_("unable to create sockets"));
+
+    /*
+     * We don't want to receive SIGTTIN/SIGTTOU.
+     * XXX - this affects tcsetattr() and tcsetpgrp() too.
+     */
+    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);
+
+    /*
+     * The policy plugin's session init must be run before we fork
+     * or certain pam modules won't be able to track their state.
+     */
+    if (policy_init_session(details) != true)
+	sudo_fatalx(U_("policy plugin failed session initialization"));
+
+    /*
+     * Child will run the command in the pty, parent will pass data
+     * to and from pty.
+     */
+
+    /* So we can block tty-generated signals */
+    sigemptyset(&ttyblock);
+    sigaddset(&ttyblock, SIGINT);
+    sigaddset(&ttyblock, SIGQUIT);
+    sigaddset(&ttyblock, SIGTSTP);
+    sigaddset(&ttyblock, SIGTTIN);
+    sigaddset(&ttyblock, SIGTTOU);
+
+    ppgrp = getpgrp();	/* parent's pgrp, so child can signal us */
+
+    /* Determine whether any of std{in,out,err} should be logged. */
+    TAILQ_FOREACH(plugin, &io_plugins, entries) {
+	if (plugin->u.io->log_stdin)
+	    interpose[STDIN_FILENO] = true;
+	if (plugin->u.io->log_stdout)
+	    interpose[STDOUT_FILENO] = true;
+	if (plugin->u.io->log_stderr)
+	    interpose[STDERR_FILENO] = true;
+    }
+
+    /*
+     * Setup stdin/stdout/stderr for command, to be duped after forking.
+     * In background mode there is no stdin.
+     */
+    if (!ISSET(details->flags, CD_BACKGROUND))
+	io_fds[SFD_STDIN] = io_fds[SFD_SLAVE];
+    io_fds[SFD_STDOUT] = io_fds[SFD_SLAVE];
+    io_fds[SFD_STDERR] = io_fds[SFD_SLAVE];
+
+    if (io_fds[SFD_USERTTY] != -1) {
+	/* Read from /dev/tty, write to pty master */
+	if (!ISSET(details->flags, CD_BACKGROUND)) {
+	    io_buf_new(io_fds[SFD_USERTTY], io_fds[SFD_MASTER],
+		log_ttyin, &ec, &iobufs);
+	}
+
+	/* Read from pty master, write to /dev/tty */
+	io_buf_new(io_fds[SFD_MASTER], io_fds[SFD_USERTTY],
+	    log_ttyout, &ec, &iobufs);
+
+	/* Are we the foreground process? */
+	foreground = tcgetpgrp(io_fds[SFD_USERTTY]) == ppgrp;
+    }
+
+    /*
+     * If stdin, stdout or stderr is not a tty and logging is enabled,
+     * use a pipe to interpose ourselves instead of using the pty fd.
+     */
+    if (io_fds[SFD_STDIN] == -1 || !isatty(STDIN_FILENO)) {
+	if (!interpose[STDIN_FILENO]) {
+	    /* Not logging stdin, do not interpose. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stdin not a tty, not logging");
+	    if (fstat(STDIN_FILENO, &sb) == 0 && S_ISFIFO(sb.st_mode))
+		pipeline = true;
+	    io_fds[SFD_STDIN] = dup(STDIN_FILENO);
+	    if (io_fds[SFD_STDIN] == -1)
+		sudo_fatal("dup");
+	} else {
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stdin not a tty, creating a pipe");
+	    pipeline = true;
+	    if (pipe(io_pipe[STDIN_FILENO]) != 0)
+		sudo_fatal(U_("unable to create pipe"));
+	    io_buf_new(STDIN_FILENO, io_pipe[STDIN_FILENO][1],
+		log_stdin, &ec, &iobufs);
+	    io_fds[SFD_STDIN] = io_pipe[STDIN_FILENO][0];
+	}
+    }
+    if (io_fds[SFD_STDOUT] == -1 || !isatty(STDOUT_FILENO)) {
+	if (!interpose[STDOUT_FILENO]) {
+	    /* Not logging stdout, do not interpose. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stdout not a tty, not logging");
+	    if (fstat(STDOUT_FILENO, &sb) == 0 && S_ISFIFO(sb.st_mode))
+		pipeline = true;
+	    io_fds[SFD_STDOUT] = dup(STDOUT_FILENO);
+	    if (io_fds[SFD_STDOUT] == -1)
+		sudo_fatal("dup");
+	} else {
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stdout not a tty, creating a pipe");
+	    pipeline = true;
+	    if (pipe(io_pipe[STDOUT_FILENO]) != 0)
+		sudo_fatal(U_("unable to create pipe"));
+	    io_buf_new(io_pipe[STDOUT_FILENO][0], STDOUT_FILENO,
+		log_stdout, &ec, &iobufs);
+	    io_fds[SFD_STDOUT] = io_pipe[STDOUT_FILENO][1];
+	}
+    }
+    if (io_fds[SFD_STDERR] == -1 || !isatty(STDERR_FILENO)) {
+	if (!interpose[STDERR_FILENO]) {
+	    /* Not logging stderr, do not interpose. */
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stderr not a tty, not logging");
+	    if (fstat(STDERR_FILENO, &sb) == 0 && S_ISFIFO(sb.st_mode))
+		pipeline = true;
+	    io_fds[SFD_STDERR] = dup(STDERR_FILENO);
+	    if (io_fds[SFD_STDERR] == -1)
+		sudo_fatal("dup");
+	} else {
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"stderr not a tty, creating a pipe");
+	    if (pipe(io_pipe[STDERR_FILENO]) != 0)
+		sudo_fatal(U_("unable to create pipe"));
+	    io_buf_new(io_pipe[STDERR_FILENO][0], STDERR_FILENO,
+		log_stderr, &ec, &iobufs);
+	    io_fds[SFD_STDERR] = io_pipe[STDERR_FILENO][1];
+	}
+    }
+
+    if (foreground) {
+	/* Copy terminal attrs from user tty -> pty slave. */
+	if (!sudo_term_copy(io_fds[SFD_USERTTY], io_fds[SFD_SLAVE])) {
+            sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+                "%s: unable to copy terminal settings to pty", __func__);
+	    foreground = false;
+	} else {
+	    /* Start in raw mode unless part of a pipeline or backgrounded. */
+	    if (!pipeline && !ISSET(details->flags, CD_EXEC_BG)) {
+		if (sudo_term_raw(io_fds[SFD_USERTTY], 0))
+		    ttymode = TERM_RAW;
+	    }
+	}
+    }
+
+    /*
+     * Block signals until we have our handlers setup in the parent so
+     * we don't miss SIGCHLD if the command exits immediately.
+     */
+    sigfillset(&set);
+    sigprocmask(SIG_BLOCK, &set, &oset);
+
+    /* Check for early termination or suspend signals before we fork. */
+    if (sudo_terminated(cstat)) {
+	sigprocmask(SIG_SETMASK, &oset, NULL);
+	debug_return_int(true);
+    }
+
+    ec.monitor_pid = sudo_debug_fork();
+    switch (ec.monitor_pid) {
+    case -1:
+	sudo_fatal(U_("unable to fork"));
+	break;
+    case 0:
+	/* child */
+	close(sv[0]);
+	(void)fcntl(sv[1], F_SETFD, FD_CLOEXEC);
+	/* Close the other end of the stdin/stdout/stderr pipes and exec. */
+	if (io_pipe[STDIN_FILENO][1] != -1)
+	    close(io_pipe[STDIN_FILENO][1]);
+	if (io_pipe[STDOUT_FILENO][0] != -1)
+	    close(io_pipe[STDOUT_FILENO][0]);
+	if (io_pipe[STDERR_FILENO][0] != -1)
+	    close(io_pipe[STDERR_FILENO][0]);
+	/*                      
+	 * If stdin/stdout is not a tty, start command in the background
+	 * since it might be part of a pipeline that reads from /dev/tty.
+	 * In this case, we rely on the command receiving SIGTTOU or SIGTTIN
+	 * when it needs access to the controlling tty.
+	 */                                                              
+	exec_monitor(details, &oset, foreground && !pipeline, sv[1]);
+	cstat->type = CMD_ERRNO;
+	cstat->val = errno;
+	if (send(sv[1], cstat, sizeof(*cstat), 0) == -1) {
+            sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
+                "%s: unable to send status to parent", __func__);
+	}
+	_exit(1);
+    }
+
+    /*
+     * We close the pty slave so only the monitor and command have a
+     * reference to it.  This ensures that we can don't block reading
+     * from the master when the command and monitor have exited.
+     */
+    if (io_fds[SFD_SLAVE] != -1) {
+	close(io_fds[SFD_SLAVE]);
+	io_fds[SFD_SLAVE] = -1;
+    }
+
+    /* Tell the monitor to continue now that the slave is closed. */
+    cstat->type = CMD_SIGNO;
+    cstat->val = 0;
+    while (send(sv[0], cstat, sizeof(*cstat), 0) == -1) {
+	if (errno != EINTR && errno != EAGAIN)
+	    sudo_fatal(U_("unable to send message to monitor process"));
+    }
+
+    /* Close the other end of the stdin/stdout/stderr pipes and socketpair. */
+    if (io_pipe[STDIN_FILENO][0] != -1)
+	close(io_pipe[STDIN_FILENO][0]);
+    if (io_pipe[STDOUT_FILENO][1] != -1)
+	close(io_pipe[STDOUT_FILENO][1]);
+    if (io_pipe[STDERR_FILENO][1] != -1)
+	close(io_pipe[STDERR_FILENO][1]);
+    close(sv[1]);
+
+    /* No longer need execfd. */
+    if (details->execfd != -1) {
+	close(details->execfd);
+	details->execfd = -1;
+    }
+
+    /* Set command timeout if specified. */
+    if (ISSET(details->flags, CD_SET_TIMEOUT))
+	alarm(details->timeout);
+
+    /*
+     * Fill in exec closure, allocate event base, signal events and
+     * the backchannel event.
+     */
+    fill_exec_closure_pty(&ec, cstat, details, ppgrp, sv[0]);
+
+    /* Restore signal mask now that signal handlers are setup. */
+    sigprocmask(SIG_SETMASK, &oset, NULL);
+
+    /*
+     * I/O logging must be in the C locale for floating point numbers
+     * to be logged consistently.
+     */
+    setlocale(LC_ALL, "C");
+
+    /*
+     * In the event loop we pass input from user tty to master
+     * and pass output from master to stdout and IO plugin.
+     */
+    add_io_events(ec.evbase);
+    if (sudo_ev_dispatch(ec.evbase) == -1)
+	sudo_warn(U_("error in event loop"));
+    if (sudo_ev_got_break(ec.evbase)) {
+	/* error from callback or monitor died */
+	sudo_debug_printf(SUDO_DEBUG_ERROR, "event loop exited prematurely");
+	/* XXX - may need to terminate command if cmnd_pid != -1 */
+    }
+
+    /* Flush any remaining output, free I/O bufs and events, do logout. */
+    pty_finish(cstat);
+
+    /* Free things up. */
+    free_exec_closure_pty(&ec);
+
+    debug_return_bool(true);
+}
+
+/*
+ * Schedule I/O events before starting the main event loop or
+ * resuming from suspend.
+ */
+static void
+add_io_events(struct sudo_event_base *evbase)
+{
+    struct io_buffer *iob;
+    debug_decl(add_io_events, SUDO_DEBUG_EXEC);
+
+    /*
+     * Schedule all readers as long as the buffer is not full.
+     * Schedule writers that contain buffered data.
+     * Normally, write buffers are added on demand when data is read.
+     */
+    SLIST_FOREACH(iob, &iobufs, entries) {
+	/* Don't read from /dev/tty if we are not in the foreground. */
+	if (iob->revent != NULL &&
+	    (ttymode == TERM_RAW || !USERTTY_EVENT(iob->revent))) {
+	    if (iob->len != sizeof(iob->buf)) {
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "added I/O revent %p, fd %d, events %d",
+		    iob->revent, iob->revent->fd, iob->revent->events);
+		if (sudo_ev_add(evbase, iob->revent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	}
+	if (iob->wevent != NULL) {
+	    /* Enable writer if buffer is not empty. */
+	    if (iob->len > iob->off) {
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "added I/O wevent %p, fd %d, events %d",
+		    iob->wevent, iob->wevent->fd, iob->wevent->events);
+		if (sudo_ev_add(evbase, iob->wevent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	}
+    }
+    debug_return;
+}
+
+/*
+ * Flush any output buffered in iobufs or readable from fds other
+ * than /dev/tty.  Removes I/O events from the event base when done.
+ */
+static void
+del_io_events(bool nonblocking)
+{
+    struct io_buffer *iob;
+    struct sudo_event_base *evbase;
+    debug_decl(del_io_events, SUDO_DEBUG_EXEC);
+
+    /* Remove iobufs from existing event base. */
+    SLIST_FOREACH(iob, &iobufs, entries) {
+	if (iob->revent != NULL) {
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"deleted I/O revent %p, fd %d, events %d",
+		iob->revent, iob->revent->fd, iob->revent->events);
+	    sudo_ev_del(NULL, iob->revent);
+	}
+	if (iob->wevent != NULL) {
+	    sudo_debug_printf(SUDO_DEBUG_INFO,
+		"deleted I/O wevent %p, fd %d, events %d",
+		iob->wevent, iob->wevent->fd, iob->wevent->events);
+	    sudo_ev_del(NULL, iob->wevent);
+	}
+    }
+
+    /* Create temporary event base for flushing. */
+    evbase = sudo_ev_base_alloc();
+    if (evbase == NULL)
+	sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
+
+    /* Avoid reading from /dev/tty, just flush existing data. */
+    SLIST_FOREACH(iob, &iobufs, entries) {
+	/* Don't read from /dev/tty while flushing. */
+	if (iob->revent != NULL && !USERTTY_EVENT(iob->revent)) {
+	    if (iob->len != sizeof(iob->buf)) {
+		if (sudo_ev_add(evbase, iob->revent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	}
+	/* Flush any write buffers with data in them. */
+	if (iob->wevent != NULL) {
+	    if (iob->len > iob->off) {
+		if (sudo_ev_add(evbase, iob->wevent, NULL, false) == -1)
+		    sudo_fatal(U_("unable to add event to queue"));
+	    }
+	}
+    }
+    sudo_debug_printf(SUDO_DEBUG_INFO,
+	"%s: flushing remaining I/O buffers (nonblocking)", __func__);
+    (void) sudo_ev_loop(evbase, SUDO_EVLOOP_NONBLOCK);
+
+    /*
+     * If not in non-blocking mode, make sure we flush write buffers.
+     * We don't want to read from the pty or stdin since that might block
+     * and the command is no longer running anyway.
+     */
+    if (!nonblocking) {
+	/* Clear out iobufs from event base. */
+	SLIST_FOREACH(iob, &iobufs, entries) {
+	    if (iob->revent != NULL && !USERTTY_EVENT(iob->revent))
+		sudo_ev_del(evbase, iob->revent);
+	    if (iob->wevent != NULL)
+		sudo_ev_del(evbase, iob->wevent);
+	}
+
+	SLIST_FOREACH(iob, &iobufs, entries) {
+	    /* Flush any write buffers with data in them. */
+	    if (iob->wevent != NULL) {
+		if (iob->len > iob->off) {
+		    if (sudo_ev_add(evbase, iob->wevent, NULL, false) == -1)
+			sudo_fatal(U_("unable to add event to queue"));
+		}
+	    }
+	}
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: flushing remaining write buffers (blocking)", __func__);
+	(void) sudo_ev_dispatch(evbase);
+     
+	/* We should now have flushed all write buffers. */
+	SLIST_FOREACH(iob, &iobufs, entries) {
+	    if (iob->wevent != NULL) {
+		if (iob->len > iob->off) {
+		    sudo_debug_printf(SUDO_DEBUG_ERROR,
+			"unflushed data: wevent %p, fd %d, events %d",
+			iob->wevent, iob->wevent->fd, iob->wevent->events);
+		}
+	    }
+	}
+    }
+
+    /* Free temporary event base, removing its events. */
+    sudo_ev_base_free(evbase);
+
+    debug_return;
+}
+
+/*
+ * Check for tty size changes.
+ * Passes the new window size to the I/O plugin and to the monitor.
+ */
+static void
+sync_ttysize(struct exec_closure_pty *ec)
+{
+    struct winsize wsize;
+    debug_decl(sync_ttysize, SUDO_DEBUG_EXEC);
+
+    if (ioctl(io_fds[SFD_USERTTY], TIOCGWINSZ, &wsize) == 0) {
+	if (wsize.ws_row != ec->rows || wsize.ws_col != ec->cols) {
+	    const unsigned int wsize_packed = (wsize.ws_row & 0xffff) |
+		((wsize.ws_col & 0xffff) << 16);
+
+	    /* Log window change event. */
+	    log_winchange(wsize.ws_row, wsize.ws_col);
+
+	    /* Send window change event to monitor process. */
+	    send_command_status(ec, CMD_TTYWINCH, wsize_packed);
+
+	    /* Update rows/cols. */
+	    ec->rows = wsize.ws_row;
+	    ec->cols = wsize.ws_col;
+	}
+    }
+
+    debug_return;
+}
+
+/*
+ * Remove and free any events associated with the specified
+ * file descriptor present in the I/O buffers list.
+ */
+static void
+ev_free_by_fd(struct sudo_event_base *evbase, int fd)
+{
+    struct io_buffer *iob;
+    debug_decl(ev_free_by_fd, SUDO_DEBUG_EXEC);
+
+    /* Deschedule any users of the fd and free up the events. */
+    SLIST_FOREACH(iob, &iobufs, entries) {
+	if (iob->revent != NULL) {
+	    if (sudo_ev_get_fd(iob->revent) == fd) {
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "%s: deleting and freeing revent %p with fd %d",
+		    __func__, iob->revent, fd);
+		sudo_ev_free(iob->revent);
+		iob->revent = NULL;
+	    }
+	}
+	if (iob->wevent != NULL) {
+	    if (sudo_ev_get_fd(iob->wevent) == fd) {
+		sudo_debug_printf(SUDO_DEBUG_INFO,
+		    "%s: deleting and freeing wevent %p with fd %d",
+		    __func__, iob->wevent, fd);
+		sudo_ev_free(iob->wevent);
+		iob->wevent = NULL;
+	    }
+	}
+    }
+    debug_return;
+}
+
+/*
+ * Only close the fd if it is not /dev/tty or std{in,out,err}.
+ * Return value is the same as close(2).
+ */
+static int
+safe_close(int fd)
+{
+    debug_decl(safe_close, SUDO_DEBUG_EXEC);
+
+    /* Avoid closing /dev/tty or std{in,out,err}. */
+    if (fd < 3 || fd == io_fds[SFD_USERTTY]) {
+	sudo_debug_printf(SUDO_DEBUG_INFO,
+	    "%s: not closing fd %d (%s)", __func__, fd, _PATH_TTY);
+	errno = EINVAL;
+	debug_return_int(-1);
+    }
+    sudo_debug_printf(SUDO_DEBUG_INFO, "%s: closing fd %d", __func__, fd);
+    debug_return_int(close(fd));
+}