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Catch SIGCONT and restore terminal settings on resume from SIGSTOP.

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While we cannot catch SIGSTOP, we _can_ catch SIGCONT and set
/dev/tty to raw mode when running in the foreground.  Ignore SIGCONT
in suspend_sudo_pty() so we don't call resume_terminal() twice.
This commit is contained in:
Todd C. Miller
2023-03-21 19:11:31 -06:00
parent 1772fc7b66
commit 0fcbcaede0
1 changed files with 75 additions and 35 deletions
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110
src/exec_pty.c
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@@ -172,6 +172,43 @@ check_foreground(struct exec_closure *ec)
debug_return_int(ret);
}
/*
* Restore the terminal when sudo is resumed in response to SIGCONT.
*/
static bool
resume_terminal(struct exec_closure *ec)
{
debug_decl(resume_terminal, SUDO_DEBUG_EXEC);
if (check_foreground(ec) == -1) {
/* User's tty was revoked. */
debug_return_bool(false);
}
/*
* 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;
}
debug_return_bool(true);
}
/*
* Suspend sudo if the underlying command is suspended.
* Returns SIGCONT_FG if the command should be resumed in the
@@ -181,10 +218,21 @@ static int
suspend_sudo_pty(struct exec_closure *ec, int signo)
{
char signame[SIG2STR_MAX];
struct sigaction sa, osa;
struct sigaction sa, osa, saved_sigcont;
int ret = 0;
debug_decl(suspend_sudo_pty, SUDO_DEBUG_EXEC);
/*
* Ignore SIGCONT when we suspend to avoid calling resume_terminal()
* multiple times.
*/
memset(&sa, 0, sizeof(sa));
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
sa.sa_handler = SIG_IGN;
if (sudo_sigaction(signo, &sa, &saved_sigcont) != 0)
sudo_warn(U_("unable to set handler for SIGCONT"));
switch (signo) {
case SIGTTOU:
case SIGTTIN:
@@ -209,6 +257,7 @@ suspend_sudo_pty(struct exec_closure *ec, int signo)
FALLTHROUGH;
case SIGSTOP:
case SIGTSTP:
default:
/* Flush any remaining output and deschedule I/O events. */
del_io_events(true);
@@ -226,13 +275,11 @@ suspend_sudo_pty(struct exec_closure *ec, int 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 SIG%s"), signame);
}
/*
* We stop sudo's process group, even if sudo is not the process
* group leader. If we only send the signal to sudo itself,
@@ -250,37 +297,6 @@ suspend_sudo_pty(struct exec_closure *ec, int signo)
"no parent to suspend, terminating command.");
terminate_command(ec->cmnd_pid, true);
ec->cmnd_pid = -1;
break;
}
/* Log the resume event. */
log_suspend(ec, SIGCONT);
/* Check foreground/background status on resume. */
if (check_foreground(ec) == -1) {
/* User's tty was revoked. */
break;
}
/*
* 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) {
@@ -288,10 +304,24 @@ suspend_sudo_pty(struct exec_closure *ec, int signo)
sudo_warn(U_("unable to restore handler for SIG%s"), signame);
}
/* If we failed to suspend, the command is no longer running. */
if (ec->cmnd_pid == -1)
break;
/* Log the resume event. */
log_suspend(ec, SIGCONT);
/* Restore the user's terminal settings. */
if (!resume_terminal(ec))
break;
ret = ttymode == TERM_RAW ? SIGCONT_FG : SIGCONT_BG;
break;
}
if (sudo_sigaction(signo, &saved_sigcont, NULL) != 0)
sudo_warn(U_("unable to restore handler for SIGCONT"));
debug_return_int(ret);
}
@@ -799,6 +829,9 @@ signal_cb_pty(int signo, int what, void *v)
case SIGCHLD:
handle_sigchld_pty(ec);
break;
case SIGCONT:
resume_terminal(ec);
break;
case SIGWINCH:
sync_ttysize(ec);
break;
@@ -986,6 +1019,13 @@ fill_exec_closure(struct exec_closure *ec, struct command_status *cstat,
if (sudo_ev_add(ec->evbase, ec->sigchld_event, NULL, false) == -1)
sudo_fatal("%s", U_("unable to add event to queue"));
ec->sigcont_event = sudo_ev_alloc(SIGCONT,
SUDO_EV_SIGINFO, signal_cb_pty, ec);
if (ec->sigcont_event == NULL)
sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
if (sudo_ev_add(ec->evbase, ec->sigcont_event, NULL, false) == -1)
sudo_fatal("%s", 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)