linux-kernel - Re: [PATCH v2012.1] fs: symlink restrictions on sticky directories

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Message-ID: <20120106073456.GB14188@elte.hu>
Date:	Fri, 6 Jan 2012 08:34:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rik van Riel <riel@...hat.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Nick Bowler <nbowler@...iptictech.com>,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Federica Teodori <federica.teodori@...glemail.com>,
	Lucian Adrian Grijincu <lucian.grijincu@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dan Rosenberg <drosenberg@...curity.com>,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2012.1] fs: symlink restrictions on sticky directories


* Rik van Riel <riel@...hat.com> wrote:

> On 01/05/2012 03:55 PM, Kees Cook wrote:
> >On Thu, Jan 5, 2012 at 12:08 PM, Nick Bowler<nbowler@...iptictech.com>  wrote:
> 
> >>But this is a brand new feature that changes longstanding behaviour of
> >>various syscalls.  Making it default to enabled is rather mean to users
> >>(since it will tend to get enabled by "oldconfig") and seems almost
> >>guaranteed to cause regressions.
> >
> > I couldn't disagree more. There has been zero evidence of 
> > this change causing anything but regressions in _attacks_. 
> > :P If anything, I think there should be no CONFIG and no 
> > sysctl, and it should be entirely non-optional. But since 
> > this patch needs consensus, I have provided knobs to control 
> > it.
> 
> I agree with you, Kees.
> 
> The behaviour introduced by this patch should produce so few 
> issues, that the new behaviour should probably be on by 
> default.

Up to the point people report regressions.

And yes, I think Kees is perfectly right that the setting of the 
default should be evidence based. (Assuming Al and Linus is fine 
with the whole concept.)

The only specific counter-argument I can see is the spinlock 
performance impact I raised during review. I think we can (and 
should) live with that, and it's probably fixable, BYMMV.

Thanks,

	Ingo
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