From 6aae6d0231921093f596f1113432c157d2b343f5 Mon Sep 17 00:00:00 2001 From: Thomas Jarosch Date: Thu, 2 Feb 2017 12:48:35 +0100 Subject: [PATCH] lxc_setup_tios(): Ignore SIGTTOU and SIGTTIN signals Prevent an endless loop while executing lxc-attach in the background: The kernel might fire SIGTTOU while an ioctl() in tcsetattr() is executed. When the ioctl() is resumed and retries, the signal handler interrupts it again. We can't configure the TTY to stop sending the signals in the first place since that is a modification/write to the TTY already. Still we clear the TOSTOP flag to prevent further signals. Command to reproduce the hang: ---------------------------- cat > lxc_hang.sh << EOF /usr/bin/timeout 5s /usr/bin/lxc-attach -n SOMECONTAINER -- /bin/true EOF sh lxc_hang.sh # hangs ---------------------------- Signed-off-by: Thomas Jarosch --- src/lxc/console.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/src/lxc/console.c b/src/lxc/console.c index 908ead0af..0cfc9ab84 100644 --- a/src/lxc/console.c +++ b/src/lxc/console.c @@ -257,6 +257,14 @@ int lxc_setup_tios(int fd, struct termios *oldtios) return -1; } + /* ensure we don't end up in an endless loop: + * The kernel might fire SIGTTOU while an + * ioctl() in tcsetattr() is executed. When the ioctl() + * is resumed and retries, the signal handler interrupts it again. + */ + signal (SIGTTIN, SIG_IGN); + signal (SIGTTOU, SIG_IGN); + newtios = *oldtios; /* We use the same settings that ssh does. */ @@ -265,7 +273,7 @@ int lxc_setup_tios(int fd, struct termios *oldtios) #ifdef IUCLC newtios.c_iflag &= ~IUCLC; #endif - newtios.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL); + newtios.c_lflag &= ~(TOSTOP | ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL); #ifdef IEXTEN newtios.c_lflag &= ~IEXTEN; #endif -- 2.47.2