linux-kernel - Re: [PATCH] staging: dgnc: fix potential format string flaw

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Message-ID: <CAGXu5jLm1RNp4mB2KfeRumTqeWgcAsZ4CpQQQGA67WukERefXQ@mail.gmail.com>
Date:	Tue, 10 Sep 2013 22:19:17 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Joe Perches <joe@...ches.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lidza Louina <lidza.louina@...il.com>,
	Tushar Behera <tushar.behera@...aro.org>,
	devel@...verdev.osuosl.org
Subject: Re: [PATCH] staging: dgnc: fix potential format string flaw

On Tue, Sep 10, 2013 at 10:00 PM, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2013-09-10 at 21:41 -0700, Kees Cook wrote:
>> Make sure that format strings cannot leak into printk() calls from the
>> msgbuf string.
>
>         printf(string);
> vs
>         printf("%s", string);
>
> How does this help?

In the former case, format characters will get processed by the
sprintf logic. In the latter, they are printed as-is. In this specific
case, if there was a way to inject strings like "ohai %n" into the
msgbuf string, the former would actually attempt to resolve the %n. In
the simple case, this could lead to Oopses, and in the unlucky case,
it could allow arbitrary memory writing and execution control.

http://en.wikipedia.org/wiki/Uncontrolled_format_string

-Kees

-- 
Kees Cook
Chrome OS Security
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