linux-kernel - Re: [PATCH] vsprintf: ignore arguments to %n

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Message-ID: <52E7FCF1.10705@gmail.com>
Date:	Wed, 29 Jan 2014 07:54:41 +1300
From:	Ryan Mallon <rmallon@...il.com>
To:	Kees Cook <keescook@...omium.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Joe Perches <joe@...ches.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Olof Johansson <olof@...om.net>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	Daniel Borkmann <dborkman@...hat.com>
Subject: Re: [PATCH] vsprintf: ignore arguments to %n

On 29/01/14 09:51, Kees Cook wrote:

> On Mon, Jan 27, 2014 at 5:02 PM, Ryan Mallon <rmallon@...il.com> wrote:
>> On 28/01/14 11:39, Kees Cook wrote:
>>> If arguments are consumed without output when encountering %n, it
>>> could be used to benefit or improve information leak attacks that were
>>> exposed via a limited size buffer. Since %n is not used by the kernel,
>>> there is no reason to make an info leak attack any easier.
>>
>> I was thinking more like the following. Print the warning if %n is
>> detected in format_decode(), but otherwise just remove the handling of
>> %n outright and treat it like any other invalid format specifier.
>> Something like this completely untested patch. Thoughts?
> 
> I'd be totally fine with it. Minor typo in the comment before the
> WARN_ONCE (should be "its" instead of "it"), but otherwise looks good.
> Consider it:
> 
> Acked-by: Kees Cook <keescook@...omium.org>
> 
> It builds and boots fine for me, FWIW.
> 
> -Kees
> 


It looks like your second version already got added to Andrew's mm tree.
I'm happy to repost mine with a fixed typo and proper signed-off by if
you'd rather use that version.

~Ryan
 
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