linux-kernel - Re: Enabling hardlink restrictions to the Linux VFS in 3.6 by default

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Date:	Fri, 26 Oct 2012 11:57:32 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Holger Kiehl <Holger.Kiehl@....de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Nick Bowler <nbowler@...iptictech.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Theodore Ts'o" <tytso@....edu>
Subject: Re: Enabling hardlink restrictions to the Linux VFS in 3.6 by default

On Fri, Oct 26, 2012 at 10:22 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Thu, Oct 25, 2012 at 5:13 AM, Holger Kiehl <Holger.Kiehl@....de> wrote:
>>
>> as of linux 3.6 hardlink restrictions to the Linux VFS have been enabled
>> by default. This breaks the application AFD [1] of which I am the author.
>
> Ok, we had a previous report of breakage, but that was just local
> scripting. Since that was just a single user (Nick Bowler), and he was
> ok with just fixing his setup, I let it go, waiting to see if anybody
> else reacted.
>
> There may well have been other users that had odd breakage, but didn't
> realize what the cause was.
>
> Regardless, clearly this does break things, and as such needs to be
> undone. We do not cause regressions that people notice in the kernel.
>
> So I've defaulted these things to off, and marked it for stable. See
> commit 561ec64ae67e ("VFS: don't do protected {sym,hard}links by
> default"). Either distributions can enable it with some security
> setting (along with the other security things they do, like the whole
> selinux thing), or we might at some future date make some config
> option for "boot up in hard-*ss mode that may break things", but for
> now we clearly cannot enable it by default.
>
> I've added people from the original commit and the previous discussion
> to the cc, and marked the commit for stable too.

Ok, seems fair. I've sent a patch to add the config options.

-Kees

-- 
Kees Cook
Chrome OS Security
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