tty: fix race in tty_fasync

We need to keep the lock held over the call to __f_setown() to
prevent a PID race.

Thanks to Al Viro for pointing out the problem, and to Travis for
making us look here in the first place.

Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tavis Ormandy <taviso@google.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Julien Tinnes <jln@google.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index f15df40bc318..c6f3b48be9dd 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1951,8 +1951,8 @@ static int tty_fasync(int fd, struct file *filp, int on)
                         pid = task_pid(current);
                         type = PIDTYPE_PID;
                 }
-                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                 retval = __f_setown(filp, pid, type, 0);
+                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                 if (retval)
                         goto out;
         } else {