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

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Message-ID: <20110701121202.GB28008@elte.hu>
Date:	Fri, 1 Jul 2011 14:12:02 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	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,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] kernel: escape non-ASCII and control characters in
 printk()


* Vasiliy Kulikov <segoon@...nwall.com> wrote:

> On Mon, Jun 27, 2011 at 00:01 +0200, Ingo Molnar wrote:
> > * Vasiliy Kulikov <segoon@...nwall.com> wrote:
> > > On Sun, Jun 26, 2011 at 21:46 +0200, Ingo Molnar wrote:
> > > > No, because the problems such a mistake causes are not equivalent: it 
> > > > would have been far more harmful to not print out the *very real* 
> > > > product names written in some non-US language than to accidentally 
> > > > include some control character you did not think of.
> > > 
> > > ???
> > > 
> > > Not "not print", but print in "crypted" form.  The information 
> > > is still not lost, you can obviously restore it to the original 
> > > form, with some effort, but possible.  Compare it with the harm 
> > > of log spoofing - it is not "restorable".
> > 
> > The harm of 'potential' log spoofing affecting exactly zero known 
> > users right now,
> 
> ???
> 
> A potential thing affects all users that *can be* affected by 
> actual log spoofing.  This is what the word "potential" means.

Yes, but there's a world of a difference between alleged harm and 
actual demonstrated harm.

That is a not so fine distinction that is often missed in security 
circles! :-)

So what i asked for before and what i ask for here is to protect 
against real, specific harm. If we just 'protect' against things that 
look dangerous it's easy to over-protect and cause colletaral damage. 
(like the UTF-8 details the v1 patch missed)

> Analogy: if some privilege escalation bug is found in some very 
> core code then all users iteracting with an untrusted security 
> domains (local users, network, etc.) being able to exploit it would 
> be affected. It is silly to say that nobody is affected because you 
> just don't know any such cases of this bug exploitation in the 
> past.

That analogy does not hold. If a security hole is obvious at first 
sight then we'll indeed fix it without waiting for someone to be 
exploited.

But here the actual 'harm' is a lot less clear and what i'm trying to 
steer you towards is to be more fact-based and less belief-based. The 
only 'harm' that got demonstrated so far was collateral damage caused 
by the v1 patch ...

Thanks,

	Ingo
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