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tty: Fix ioctl(FIOASYNC) on hungup file

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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>
This commit is contained in:
Peter Hurley 2016-01-09 21:45:11 -08:00 committed by Greg Kroah-Hartman
parent f557474ca3
commit a8f3a29718
1 changed files with 3 additions and 2 deletions
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5
drivers/tty/tty_io.c
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@ -2260,10 +2260,11 @@ static int __tty_fasync(int fd, struct file *filp, int on)
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;