linux-kernel - Re: [PATCH] all arches, signal: Move restart_block to struct task

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Message-ID: <20141026171819.GQ7996@ZenIV.linux.org.uk>
Date:	Sun, 26 Oct 2014 17:18:19 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com
Subject: Re: [PATCH] all arches, signal: Move restart_block to struct
 task_struct

On Sun, Oct 26, 2014 at 10:02:16AM -0700, Andy Lutomirski wrote:
> If an attacker can cause a controlled kernel stack overflow,
> overwriting the restart block is a very juicy exploit target.
> Moving the restart block to struct task_struct prevents this type of
> exploit.

The hell it does.  In a _lot_ of cases current is current_thread_info()->task,
which makes your variant just as vulnerable, in addition to being (slightly)
more costly.
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