[PATCH v2 4/7] tty: Fix ioctl(FIOASYNC) on hungup file

Peter Hurley
2016-01-10T05:46:14Z

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>
---
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 05b0a9c..7113bfa 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;
--
2.7.0