linux-kernel - Re: [PATCH v3] fs: introduce pipe-only dump mode suid

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Date:	Fri, 22 Jun 2012 15:26:24 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Alan Cox <alan@...ux.intel.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Rob Landley <rob@...dley.net>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Doug Ledford <dledford@...hat.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Joe Korty <joe.korty@...r.com>,
	David Howells <dhowells@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3] fs: introduce pipe-only dump mode suid_dumpable=3

On Fri, Jun 22, 2012 at 3:20 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Fri, 22 Jun 2012 15:07:45 -0700
> Kees Cook <keescook@...omium.org> wrote:
>
>> mode=2 to disk _should_ break, is my point.
>
> And my point is that we should at least tell people that we broke it.
> I don't believe that returning an EINVAL from the write() is
> sufficient.  Because it introduces a high risk that people will run
> misconfigured systems for lengthy periods and it will cause them to
> have to do a *lot* of work once they discover that their system is
> misbehaving.
>
> So if we really really must instabreak back-compatibility, we should
> shout loudly into syslog about it: tell people that their system is
> broken and tell them what to do about it.
>
> And we should explain and justify this extraordinary action in the
> patch changelog.

Okay, sounds good. Should mode 3 added with mode 2 removed, or just
drop the dangerous behavior from mode 2? I will be loud in either
situation (e.g. with mode 3, setting mode 2 shouts, or when attempt to
write to disk in mode 2, shout).

-Kees

-- 
Kees Cook
Chrome OS Security
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