linux-kernel - Re: Possible "struct pid" leak from tty

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Message-ID: <m1veh5q6s7.fsf@ebiederm.dsl.xmission.com>
Date:	Tue, 13 Mar 2007 13:31:52 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Catalin Marinas" <catalin.marinas@...il.com>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: Possible "struct pid" leak from tty_io.c

"Catalin Marinas" <catalin.marinas@...il.com> writes:

> On 09/03/07, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>> If I can manage to focus on this, it looks like the information I need to
>> start fixing this.
>
> I had a look at the second leak reported it seems to be caused by the
> same proc_set_tty() call but, in this case, there is no
> disassociate_tty() call for the task (and the patch I posted is not
> enough). Maybe something like below (no thourough testing):
>
> diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
> index db91398..ea6ca7d 100644
> --- a/drivers/char/tty_io.c
> +++ b/drivers/char/tty_io.c
> @@ -3854,7 +3854,14 @@ EXPORT_SYMBOL(tty_devnum);
>
> void proc_clear_tty(struct task_struct *p)
> {
> +	struct tty_struct *tty;
> +
> 	spin_lock_irq(&p->sighand->siglock);
> +	tty = p->signal->tty;
> +	if (tty) {
> +		put_pid(tty->session);
> +		put_pid(tty->pgrp);
> +	}
> 	p->signal->tty = NULL;
> 	spin_unlock_irq(&p->sighand->siglock);
> }

This patch can't be right.  Not the way proc_clear_tty is called
once for each process in the session, plus we aren't clearing
tty->session and tty->pgrp here. 

If the above patch works it's a fluke.

Still it is the right general area of the code.  I've just started
looking at this it is going to take me a bit to come up to speed on
this code again and see what silly thing is missing.

Eric
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