[PATCH] tty: Fix two reported pid leaks

These leaks were reported by: Catalin Marinas <catalin.marians@gmail.com>
and I have been able to very by inspection they are possible.

When converting tty_io.c to store pids as struct pid pointers instead
of pid_t values it appears I overlooked two places where we stop using
the pid value.  The very obvious one is in do_tty_hangup, and the one
the less obvious one in __proc_set_tty.

When looking into the code __proc_set_tty only has pids that need to
be put because of failures of other parts of the code to properly
perform hangup processing.   Fixing the leak here in __proc_set_tty
is easy and obviously correct so I am doing that first.

Fixing the places that should be performing hangup processing is much
less obviously correct.  So those I'm aiming those patches at -mm.
for now, so the can age a while before they are merged.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_io.c

@@ -1376,6 +1376,8 @@ static void do_tty_hangup(struct work_struct *work)
 	read_unlock(&tasklist_lock);
 
 	tty->flags = 0;
+	put_pid(tty->session);
+	put_pid(tty->pgrp);
 	tty->session = NULL;
 	tty->pgrp = NULL;
 	tty->ctrl_status = 0;
@@ -3841,6 +3843,9 @@ static struct pid *__proc_set_tty(struct task_struct *tsk, struct tty_struct *tt
 {
 	struct pid *old_pgrp;
 	if (tty) {
+		/* We should not have a session or pgrp to here but.... */
+		put_pid(tty->session);
+		put_pid(tty->pgrp);
 		tty->session = get_pid(task_session(tsk));
 		tty->pgrp = get_pid(task_pgrp(tsk));
 	}