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 <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 0140c86..8d26ed7 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2260,10 +2260,11 @@
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;