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

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Date:	Sun, 26 Jun 2011 21:46:18 +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 Sun, Jun 26, 2011 at 20:26 +0200, Ingo Molnar wrote:
>
> > > > Also, i think it would be better to make this opt-out, i.e. 
> > > > exclude the handful of control characters that are harmful 
> > > > (such as backline and console escape), instead of trying to 
> > > > include the known-useful ones.
> > > 
> > > Do you see any issue with the check above?
> > 
> > There were clear problems with the first version you posted and 
> > that's enough proof to request the exclusion of known-dangerous 
> > characters instead of including known-useful characters.
> 
> It doesn't proof anything.  If I/someone else did a mistake with 
> blacklisting would you say it is enough proof to request the 
> inclusion of well-known allowed characters?

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.

> > A black list is well-defined: it disables the display of certain 
> > characters because they are *known to be dangerous*.
> 
> What do you do with dangerous characters that are *not yet known* 
> to be dangerous?

I'm ready to act on facts only. Also, i really prefer the policy of 
acting on known dangers instead of being afraid of the unknown.

The whole 'trust but verify' thing.

> > A white list on the other hand does it the wrong way around: it 
> > tries to put the 'burden of proof' on the useful, good guys - and 
> > that's counter-productive really.
> 
> Really?  I think strict API definition is productive, unlike using 
> it in cases where it looks like working, but creating tricky and 
> obscure bugs.

You werent really creating a well-defined API here, were you?

> Yes, drawing multicolor logs is funny, but ...egrrr...  printk() is 
> not written for these things.

maybe, but i still think that such a change works better, has fewer 
unintended side effects and is better documented if it excludes known 
dangers instead of trying to include known useful bits imperfectly.

Thanks,

	Ingo
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