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/*
* SPDX-License-Identifier: ISC
*
* Copyright (c) 2009-2023 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 <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <pathnames.h>
#include <sudo_debug.h>
#include <sudo_fatal.h>
#include <sudo_gettext.h>
#include <sudo_exec.h>
static volatile sig_atomic_t got_sigttou;
/*
* SIGTTOU signal handler for tcsetpgrp_nobg() that just sets a flag.
*/
static void
sigttou(int signo)
{
got_sigttou = 1;
}
/*
* Like tcsetpgrp() but restarts on EINTR _except_ for SIGTTOU.
* Returns 0 on success or -1 on failure, setting errno.
* Sets got_sigttou on failure if interrupted by SIGTTOU.
*/
static int
tcsetpgrp_nobg(int fd, pid_t pgrp_id)
{
struct sigaction sa, osa;
int rc;
debug_decl(tcsetpgrp_nobg, SUDO_DEBUG_UTIL);
/*
* If we receive SIGTTOU from tcsetpgrp() it means we are
* not in the foreground process group.
* This avoid a TOCTOU race compared to using tcgetpgrp().
*/
memset(&sa, 0, sizeof(sa));
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0; /* do not restart syscalls */
sa.sa_handler = sigttou;
got_sigttou = 0;
(void)sigaction(SIGTTOU, &sa, &osa);
do {
rc = tcsetpgrp(fd, pgrp_id);
} while (rc != 0 && errno == EINTR && !got_sigttou);
(void)sigaction(SIGTTOU, &osa, NULL);
debug_return_int(rc);
}
/*
* Suspend the main process in response to an interactive child process
* being suspended.
*/
void
sudo_suspend_parent(int signo, pid_t my_pid, pid_t my_pgrp, pid_t cmnd_pid,
void *closure, void (*callback)(void *, int))
{
struct sigaction sa, osa;
pid_t saved_pgrp = -1;
int fd;
debug_decl(sudo_suspend_parent, SUDO_DEBUG_EXEC);
/*
* Save the controlling terminal's process group so we can restore
* it after we resume, if needed. Most well-behaved shells change
* the pgrp back to its original value before suspending so we must
* not try to restore in that case, lest we race with the command
* upon resume, potentially stopping sudo with SIGTTOU while the
* command continues to run.
*/
fd = open(_PATH_TTY, O_RDWR);
if (fd != -1) {
saved_pgrp = tcgetpgrp(fd);
if (saved_pgrp == -1) {
close(fd);
fd = -1;
}
}
if (saved_pgrp != -1) {
/*
* Command was stopped trying to access the controlling
* terminal. If the command has a different pgrp and we
* own the controlling terminal, give it to the command's
* pgrp and let it continue.
*/
if (signo == SIGTTOU || signo == SIGTTIN) {
if (saved_pgrp == my_pgrp) {
pid_t cmnd_pgrp = getpgid(cmnd_pid);
if (cmnd_pgrp != my_pgrp) {
if (tcsetpgrp_nobg(fd, cmnd_pgrp) == 0) {
if (killpg(cmnd_pgrp, SIGCONT) != 0)
sudo_warn("kill(%d, SIGCONT)", (int)cmnd_pgrp);
close(fd);
debug_return;
}
}
}
}
}
/* Run callback before we suspend. */
if (callback != NULL)
callback(closure, signo);
if (signo == SIGTSTP) {
memset(&sa, 0, sizeof(sa));
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
sa.sa_handler = SIG_DFL;
if (sigaction(SIGTSTP, &sa, &osa) != 0)
sudo_warn(U_("unable to set handler for signal %d"), SIGTSTP);
}
if (kill(my_pid, signo) != 0)
sudo_warn("kill(%d, %d)", (int)my_pid, signo);
if (signo == SIGTSTP) {
if (sigaction(SIGTSTP, &osa, NULL) != 0)
sudo_warn(U_("unable to restore handler for signal %d"), SIGTSTP);
}
/* Run callback on resume. */
if (callback != NULL)
callback(closure, SIGCONT);
if (saved_pgrp != -1) {
/*
* On resume, restore foreground process group, if different.
* Otherwise, we cannot resume some shells (pdksh).
*
* It is possible that we are no longer the foreground process,
* use tcsetpgrp_nobg() to prevent sudo from receiving SIGTTOU.
*/
if (saved_pgrp != my_pgrp)
tcsetpgrp_nobg(fd, saved_pgrp);
close(fd);
}
debug_return;
}
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