[PATCH] lsm, io_uring: add LSM hooks to for the new uring_cmd file op

[Jens Axboe]

On 7/15/22 1:50 PM, Paul Moore wrote:
> On Fri, Jul 15, 2022 at 3:07 PM Jens Axboe <axboe at kernel.dk> wrote:
>> On 7/15/22 12:46 PM, Paul Moore wrote:
>>> On Thu, Jul 14, 2022 at 9:00 PM Luis Chamberlain <mcgrof at kernel.org> wrote:
>>>> On Wed, Jul 13, 2022 at 11:00:42PM -0400, Paul Moore wrote:
>>>>> On Wed, Jul 13, 2022 at 8:05 PM Luis Chamberlain <mcgrof at kernel.org> wrote:
>>>>>>
>>>>>> io-uring cmd support was added through ee692a21e9bf ("fs,io_uring:
>>>>>> add infrastructure for uring-cmd"), this extended the struct
>>>>>> file_operations to allow a new command which each subsystem can use
>>>>>> to enable command passthrough. Add an LSM specific for the command
>>>>>> passthrough which enables LSMs to inspect the command details.
>>>>>>
>>>>>> This was discussed long ago without no clear pointer for something
>>>>>> conclusive, so this enables LSMs to at least reject this new file
>>>>>> operation.
>>>>>>
>>>>>> [0] https://lkml.kernel.org/r/8adf55db-7bab-f59d-d612-ed906b948d19@schaufler-ca.com
>>>>>
>>>>> [NOTE: I now see that the IORING_OP_URING_CMD has made it into the
>>>>> v5.19-rcX releases, I'm going to be honest and say that I'm
>>>>> disappointed you didn't post the related LSM additions
>>>>
>>>> It does not mean I didn't ask for them too.
>>>>
>>>>> until
>>>>> v5.19-rc6, especially given our earlier discussions.]
>>>>
>>>> And hence since I don't see it either, it's on us now.
>>>
>>> It looks like I owe you an apology, Luis.  While my frustration over
>>> io_uring remains, along with my disappointment that the io_uring
>>> developers continue to avoid discussing access controls with the LSM
>>> community, you are not the author of the IORING_OP_URING_CMD.   You
>>> are simply trying to do the right thing by adding the necessary LSM
>>> controls and in my confusion I likely caused you a bit of frustration;
>>> I'm sorry for that.
>>
>> Maybe, just maybe, outbursts like this are why there's not a lot of
>> incentive to collaborate on this? I get why it can seem frustrating and
>> that you are being ignored, but I think it's more likely that people
>> just don't think of adding these hooks. I don't use any of the access
>> controls, nor do I really have a good idea which one exists and what
>> they do. None of the external developers or internal use cases we have
>> use any of this, and nobody outside of the developers of these kernel
>> features have ever brought it up...
> 
> While my response may have been misdirected (once again, sorry Luis),
> I feel that expressing frustration about the LSMs being routinely left
> out of the discussion when new functionality is added to the kernel is
> a reasonable response; especially when one considers the history of
> this particular situation.  I was willing to attribute the initial
> LSM/audit omission in io_uring to an honest oversight, and the fact
> that we were able to work together to get something in place was a
> good thing which gave me some hope.  However, the issue around
> IORING_OP_URING_CMD was brought up earlier this year and many of us on
> the LSM side expressed concern, only to see the code present in
> v5.19-rcX with little heads-up given outside of Luis' patch a few days
> ago.  You can call my comments an outburst if you like, but it seems
> like an appropriate reaction in this case.

I agree that it should've been part of the initial series. As mentioned
above, I wasn't much apart of that earlier discussion in the series, and
hence missed that it was missing. And as also mentioned, LSM isn't much
on my radar as nobody I know uses it. This will cause oversights, even
if they are unfortunate. My point is just that no ill intent should be
assumed here.

>> I don't mind getting these added, but since I wasn't really part of
>> driving this particular feature, it wasn't on my radar.
> 
> I generally don't care who authors a commit, it's that code itself
> that matters, not who wrote it.  However, since you mentioned it I
> went back to check, and it looks like you authored the basic
> IORING_OP_URING_CMD infrastructure according to ee692a21e9bf
> ("fs,io_uring: add infrastructure for uring-cmd"); that seems like a
> decent level of awareness to me.

I did author the basic framework of it, but Kanchan took over driving it
to completion and was the one doing the posting of it at that point.
It's not like I merge code I'm not aware of, we even discussed it at
LSFMM this year and nobody brought up the LSM oversight. Luis was there
too I believe.

The lack of awareness refers to the LSM side, not io_uring obviously.
I'm very much aware of what code I merge and have co-authored, goes
without saying.

>>>> Given a clear solution is not easily tangible at this point
>>>> I was hoping perhaps at least the abilility to enable LSMs to
>>>> reject uring-cmd would be better than nothing at this point.
>>>
>>> Without any cooperation from the io_uring developers, that is likely
>>> what we will have to do.  I know there was a lot of talk about this
>>> functionality not being like another ioctl(), but from a LSM
>>> perspective I think that is how we will need to treat it.
>>
>> Again this perceived ill intent. What are you looking for here?
> 
> We expressed concern earlier this year and were largely ignored, and
> when the functionality was merged into mainline the LSM community was
> not notified despite our previous comments.  Perhaps there is no ill
> intent on the side of io_uring, but from my perspective it sure seems
> like there was an effort to avoid the LSM community.
> 
> As far as what I'm looking for, I think basic consideration for
> comments coming from the LSM community would be a good start.  We
> obviously have had some success in the past with this, which is why
> I'm a bit shocked that our IORING_OP_URING_CMD comments from earlier
> this year appeared to fall on deaf ears.

I guess it's just somewhat lack of interest, since most of us don't have
to deal with anything that uses LSM. And then it mostly just gets in the
way and adds overhead, both from a runtime and maintainability point of
view, which further reduces the motivation.

I don't think it's an effort to avoid the LSM community.

For this particular case, I do agree that it should've been picked up
and been apart of the initial merge. I'll keep a closer eye on that in
the future.

>>>>>> Signed-off-by: Luis Chamberlain <mcgrof at kernel.org>
>>
>>> Well, we're at -rc6 right now which means IORING_OP_URING_CMD is
>>> happening and it's unlikely the LSM folks are going to be able to
>>> influence the design/implementation much at this point so we have to
>>> do the best we can.  Given the existing constraints, I think your
>>> patch is reasonable (although please do shift the hook call site down
>>> a bit as discussed above), we just need to develop the LSM
>>> implementations to go along with it.
>>>
>>> Luis, can you respin and resend the patch with the requested changes?
>>>
>>> Casey, it looks like Smack and SELinux are the only LSMs to implement
>>> io_uring access controls.  Given the hook that Luis developed in this
>>> patch, could you draft a patch for Smack to add the necessary checks?
>>> I'll do the same for SELinux.  My initial thinking is that all we can
>>> really do is check the access between the creds on the current task
>>> (any overrides will have already taken place by the time the LSM hook
>>> is called) with the io_uring_cmd:file label/creds; we won't be able to
>>> provide much permission granularity for all the reasons previously
>>> discussed, but I suspect that will be more of a SELinux problem than a
>>> Smack problem (although I suspect Smack will need to treat this as
>>> both a read and a write, which is likely less than ideal).
>>>
>>> I think it's doubtful we will have all of this ready and tested in
>>> time for v5.19, but I think we can have it ready shortly after that
>>> and I'll mark all of the patches for -stable when I send them to
>>> Linus.
>>>
>>> I also think we should mark the patches with a 'Fixes:' line that
>>> points at the IORING_OP_URING_CMD commit, ee692a21e9bf ("fs,io_uring:
>>> add infrastructure for uring-cmd").
>>>
>>> How does that sound to everyone?
>>
>> Let's do it the right way for 5.20, and then get it marked for a
>> backport. That will be trivial enough and will hit 5.19-stable shortly
>> as well. Rushing it now with 1 week before release will most likely
>> yield a worse long term result.
> 
> That is what I suggested above; it looks like we are on the same page
> at least with the resolution.  I'll plan on bundling Luis' hook patch,
> Casey's Smack patch, the SELinux patch and send them up to Linus once
> they are ready.  If you, and/or other io_uring developers, could
> review Luis' LSM hook patch from an io_uring perspective and add your
> Ack/Review-by tag I would appreciate it.

Right, we agree on that, and I already did send an ack on the v2 of the
patch. Just be aware that it, as of now. depends on the io_uring tree
and won't apply cleanly to 5.19-rc, as mentioned in that reply too.

-- 
Jens Axboe