linux-kernel - Re: [PATCH v2 2/2] tty: check tcsetpgrp p is a process group

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Date:	Sun, 28 Jun 2015 12:07:14 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Patrick Donnelly <batrick@...bytes.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] tty: check tcsetpgrp p is a process group

On 06/27/2015 08:51 PM, Patrick Donnelly wrote:
> This fixes a bug where a process can set the foreground process group to its
> pid even if its pid is not a valid pgrp.
> 
> Signed-off-by: Patrick Donnelly <batrick@...bytes.com>
> ---
>  drivers/tty/tty_io.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index fbb55db..01b4769 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -2579,6 +2579,9 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
>  	retval = -ESRCH;
>  	if (!pgrp)
>  		goto out_unlock;
> +	retval = -EINVAL;
> +	if (!pid_task(pgrp, PIDTYPE_PGID))
> +		goto out_unlock;

This change implies that the sequence in session_of_pgrp() that specifically
checks for pid_task(pgrp, PIDTYPE_PGID) == NULL is not doing anything
useful. However, that hypothesis is directly contradicted by the
comment above session_of_pgrp()

"* This checks not only the pgrp, but falls back on the pid if no
 * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
 * without this..."

Regards,
Peter Hurley

>  	retval = -EPERM;
>  	if (session_of_pgrp(pgrp) != task_session(current))
>  		goto out_unlock;
> 

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