linux-kernel - Re: [PATCHv3 xfstests 2/3] generic: test openat and new O

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Date:	Wed, 18 Mar 2015 10:17:55 +0000
From:	David Drysdale <drysdale@...gle.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Meredydd Luff <meredydd@...atehouse.org>,
	Will Drewry <wad@...omium.org>,
	Jorge Lucangeli Obes <jorgelo@...gle.com>,
	Ricky Zhou <rickyz@...gle.com>,
	Lee Campbell <leecam@...gle.com>,
	Julien Tinnes <jln@...gle.com>,
	Mike Depinet <mdepinet@...gle.com>,
	James Morris <james.l.morris@...cle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	Christoph Hellwig <hch@...radead.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	fstests@...r.kernel.org
Subject: Re: [PATCHv3 xfstests 2/3] generic: test openat and new O_BENEATH flag

[resend, remembering to tick the Plaintext button this time -- sorry]

On Wed, Mar 18, 2015 at 2:52 AM, Dave Chinner <david@...morbit.com> wrote:
> On Tue, Mar 17, 2015 at 08:33:27AM -0700, Kees Cook wrote:
>> On Mon, Mar 16, 2015 at 4:24 PM, Dave Chinner
>> <david@...morbit.com> wrote:
>> > On Mon, Mar 09, 2015 at 02:00:11PM +0000, David Drysdale wrote:
>> >> Test basic openat(2) behaviour.
>> >>
>> >> Test that if O_BENEATH flag is set, openat() will only open
>> >> paths that have no .. component and do not start with /.
>> >> Symlinks are also checked for the same restrictions.
>> >>
>> >> Signed-off-by: David Drysdale <drysdale@...gle.com> ---
>> >> .gitignore            |   1 + common/openat         |  61
>> >> ++++++++++++++++++++++++++++++ src/Makefile          |   3 +-
>> >> src/openat.c          | 100
>> >> +++++++++++++++++++++++++++++++++++++++++++++++++
>> >
>> > This strikes me as something that shoul dbe added to xfs_io for
>> > testing, as it already supports a heap of other open flags and
>> > xfstests is already dependent on it.
>>
>> While I don't see a problem adding this to xfs_io, I'd still like
>> to see this test live in the kernel tree too.
>
> You can do whatever you want with the kernel tree - it doesn't
> concern me at all.
>
>> Having it in the
>> same source means more testing, IMO.
>
> That's complete bunk, though.  This helper binary is a limited use,
> one shot test that can't be combined with anything else.  "sharing"
> the source code across multiple different test suites doesn't change
> that. However, putting support into xfs_io means it will get more
> testing because we can *easily* use the functionality in many, many
> different ways.

It's useful to have a simple self-test in the kernel tree, so
that kernel developers (and their buildbots) can catch any
obvious regressions that might arise when working in related
areas, without requiring any other dependencies.

(Personally, I also think it's good that new kernel APIs
come with demonstrations of their use in userspace in a
nearby commit.)

OTOH, testing openat() behaviour should clearly be a part of
the xfstests suite (as a general/comprehensive filesystem
test repository), and Dave makes a good point that putting
the openat() functionality into xfs_io allows for more flexible
test combinations.

So I guess ideally we should end up with:
 a) Reinstate the kernel-tree selftests from the earlier iteration.
 b) Add openat test functionality into xfs_io
 c) Migrate the new xfstests cases to use xfs_io rather than
   a local openat utility program

However, given that I've already moved the test code once,
and that a)-c) involve three different source trees, I'd like
to de-couple things:
- Concentrate on kernel changes and a) on the LKML.
 - If & when the kernel changes make progress, return to
   b) and c).

Sound sensible?

Thanks,
David.

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@...morbit.com
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