Re: [PATCH 1/1 V2] mqueue: Implment generic xattr support

[David Graziano <david.graziano@rockwellcollins.com>]

On Mon, Dec 5, 2016 at 9:37 AM, Paul Moore <paul@paul-moore.com> wrote:
> On Mon, Nov 28, 2016 at 3:04 PM, David Graziano
> <david.graziano@rockwellcollins.com> wrote:
>> On Wed, Nov 9, 2016 at 4:25 PM, Paul Moore <paul@paul-moore.com> wrote:
>>> On Wed, Nov 9, 2016 at 11:25 AM, David Graziano
>>> <david.graziano@rockwellcollins.com> wrote:
>>>> On Mon, Nov 7, 2016 at 4:23 PM, Paul Moore <paul@paul-moore.com> wrote:
>>>>> On Mon, Nov 7, 2016 at 3:46 PM, David Graziano
>>>>> <david.graziano@rockwellcollins.com> wrote:
>>>>>> This patch adds support for generic extended attributes within the
>>>>>> POSIX message queues filesystem and setting them by consulting the LSM.
>>>>>> This is needed so that the security.selinux extended attribute can be
>>>>>> set via a SELinux named type transition on file inodes created within
>>>>>> the filesystem. The implementation and LSM call back function are based
>>>>>> off tmpfs/shmem.
>>>>>>
>>>>>> Signed-off-by: David Graziano <david.graziano@rockwellcollins.com>
>>>>>> ---
>>>>>>  ipc/mqueue.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>  1 file changed, 46 insertions(+)
>>>>>
>>>>> Hi David,
>>>>>
>>>>> At first glance this looks reasonable to me, I just have a two
>>>>> questions/comments:
>>>>>
>>>>> * Can you explain your current need for this functionality?  For
>>>>> example, what are you trying to do that is made easier by allowing
>>>>> greater message queue labeling flexibility?  This helps put things in
>>>>> context and helps people review and comment on your patch.
>>>>>
>>>>> * How have you tested this?  While this patch is not SELinux specific,
>>>>> I think adding a test to the selinux-testsuite[1] would be worthwhile.
>>>>> The other LSM maintainers may suggest something similar if they have
>>>>> an established public testsuite.
>>>>>
>>>>> [1] https://github.com/SELinuxProject/selinux-testsuite
>>>>
>>>> Hi Paul,
>>>>
>>>> I needed to write a selinux policy for a set of custom applications that use
>>>> POSIX message queues for their IPC. The queues are created by one
>>>> application and we needed a way for selinux to enforce which of the other
>>>> apps are able to read/write to each individual queue. Uniquely labeling them
>>>> based on the app that created them and the file name seemed to be our best
>>>> solution since it’s an embedded system and we don’t have restorecond to
>>>> handle any relabeling.
>>>
>>> In the future putting things like the above in the patch description
>>> can be helpful.  In other words, instead of simply saying this allows
>>> you to better control the labels assigned to message queues, you could
>>> expand upon it by saying that this patch allows you to better control
>>> which applications have access to a given queue.  Yes, I realize that
>>> is implied by better control over the labels, but being explicit is
>>> rarely a bad thing when it comes to patch descriptions.
>>>
>>> I've never rejected a patch for a description that was too lengthy,
>>> but I have rejected patches that need better descriptions ;)
>>>
>>>> To test this patch I used both a selinux enabled, buildroot based qemu target
>>>> with a customized selinux policy and test C app to create the mqueues. I also
>>>> tested with our real apps and selinux policy on our target hardware. I can
>>>> certainly look at adding a test to the selinux-testsuite if that would
>>>> be helpful.
>>>
>>> Please do.  I've been requiring tests for all new SELinux
>>> functionality lately; this isn't strictly a SELinux patch but I think
>>> it is a good practice regardless.
>>
>> Sorry for the delay. I have created a pull request within the
>> selinux-testsuite github
>> project with a set of mqueue tests.
>
> For anyone who is curious:
>
> * https://github.com/SELinuxProject/selinux-testsuite/pull/10
>
> Aside from a naming nit, the tests look good to me and I have no
> problem with the kernel patch; it doesn't appear any of the other LSM
> maintainers do either.  I'm happy to pull this into the SELinux tree
> (for v4.11, it's a little late for v4.10 I think), but I think
> Christoph made a good point about consolidation, have you had a chance
> to look at that?
>

I've made the update for the naming nit in the pull request.
I agree with Christoph's point but doing so is a bit outside my expertise at
this point. I would be open to suggestions as to where the function should be
consolidated and work on a second patchset with the update. Maybe in
fs/xattr.c as a simple_xattr_initxattrs function?
-David


> --
> paul moore
> www.paul-moore.com