From a8f3a29718f77df3116955d100756f67fafabec0 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Sat, 9 Jan 2016 21:45:11 -0800 Subject: [PATCH] tty: Fix ioctl(FIOASYNC) on hungup file A small race window exists which allows signal-driven async i/o to be enabled for the tty when the file ptr has already been hungup and signal-driven i/o has been disabled: CPU 0 CPU 1 ----- ------ ioctl_fioasync(on) filp->f_op->fasync(on) __tty_hangup() tty_fasync(on) tty_lock() tty_lock() ... . filp->f_op = &hung_up_tty_fops; (waiting) __tty_fasync(off) . tty_unlock() /* gets tty lock */ /* enables FASYNC */ Check the tty has not been hungup while holding tty_lock. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 0140c8669ada..8d26ed79bb4c 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2260,10 +2260,11 @@ out: static int tty_fasync(int fd, struct file *filp, int on) { struct tty_struct *tty = file_tty(filp); - int retval; + int retval = -ENOTTY; tty_lock(tty); - retval = __tty_fasync(fd, filp, on); + if (!tty_hung_up_p(filp)) + retval = __tty_fasync(fd, filp, on); tty_unlock(tty); return retval; -- 2.20.1