linux-kernel - Re: [PATCH] tty: fix leakage of -ERESTARTSYS to userland

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Date:	Wed, 30 May 2007 11:05:13 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: fix leakage of -ERESTARTSYS to userland

On Tue, 29 May 2007 22:44:35 +0400
Oleg Nesterov <oleg@...sign.ru> wrote:

> Spotted by Satoru Takeuchi.
> 
> kill_pgrp(task_pgrp(current)) sends the signal to the current's thread group,
> but can choose any sub-thread as a target for signal_wake_up(). This means
> that job_control() and tty_check_change() may return -ERESTARTSYS without
> signal_pending().
> 
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
> 
> --- t/drivers/char/n_tty.c~	2007-04-05 12:18:26.000000000 +0400
> +++ t/drivers/char/n_tty.c	2007-05-28 10:57:58.000000000 +0400
> @@ -1191,6 +1191,7 @@ static int job_control(struct tty_struct
>  			    is_current_pgrp_orphaned())
>  				return -EIO;
>  			kill_pgrp(task_pgrp(current), SIGTTIN, 1);
> +			set_thread_flag(TIF_SIGPENDING);
>  			return -ERESTARTSYS;
>  		}
>  	}
> --- t/drivers/char/tty_io.c~	2007-04-05 12:18:26.000000000 +0400
> +++ t/drivers/char/tty_io.c	2007-05-29 22:15:52.000000000 +0400
> @@ -1121,7 +1121,8 @@ int tty_check_change(struct tty_struct *
>  		return 0;
>  	if (is_current_pgrp_orphaned())
>  		return -EIO;
> -	(void) kill_pgrp(task_pgrp(current), SIGTTOU, 1);
> +	kill_pgrp(task_pgrp(current), SIGTTOU, 1);
> +	set_thread_flag(TIF_SIGPENDING);
>  	return -ERESTARTSYS;
>  }
>  

Are there other callers of kill_pgrp() which have the same problem?

Perhaps we should have a kill_pgrp_self() which takes care of doing
this, rather than open-coding it.  Something with a comment which
explains what's going on ;)
-
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