linux-kernel - Re: [PATCH v2] kernel: escape non-ASCII and control characters in printk()

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Date:	Sun, 3 Jul 2011 10:42:45 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>,
	Namhyung Kim <namhyung@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kernel: escape non-ASCII and control characters in printk()

On Sun, Jul 3, 2011 at 3:01 AM, Vasiliy Kulikov <segoon@...nwall.com> wrote:
>
> Sigh...  After implementing controls filtering including \n inside of
> %s, I got numerous false positives.  Most of them are startup messages
> with driver/hardware name/version, in drivers/.

Yeah, I was afraid of that. It's going to be a much bigger patch, and
likely somewhat annoying.

That said, if we really want to do this, I think doing it with %s
filtering is the only way, and it would make the default case where
people really don't think about possible user-supplied strings be
safe.

So saying "%s is for pure 7-bit ASCII with no control codes" is
annoying, but would really fix it.

That said, I think it should be unconditional. None of this "safe vs
unsafe" flags, and none of this "printk format strings are different
from other vsprintf format strings". If special characters are a
potential security problem for printk(), then they are a potential
security problem for other things (eg /proc filenames or content etc).

                    Linus
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