linux-kernel - Re: [PATCH] Yama: turn process ancestry check into function

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Date:	Wed, 14 Jul 2010 09:19:09 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	kees.cook@...onical.com
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] Yama: turn process ancestry check into function

Kees Cook wrote:
> +static int task_is_descendant(struct task_struct *parent,
> +			      struct task_struct *child)
> +{
> +	int rc = 0;
> +	struct task_struct *walker = child;
> +
> +	if (!parent || !child)
> +		return 0;

parent (== current) is !NULL and
child (in original code) is !NULL.
You can remove this check unless you are planning to call
this function from other places.

> +	if (mode == PTRACE_MODE_ATTACH &&
> +	    ptrace_scope &&
> +	    !task_is_descendant(current, child) &&
> +	    !capable(CAP_SYS_PTRACE))
> +		rc = -EPERM;

I don't know how heavy capable(CAP_SYS_PTRACE) is.
But checking !capable(CAP_SYS_PTRACE) before
!task_is_descendant(current, child) might be lighter.
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