[RFC 0/4] Landlock: ioctl support

[Mickaël Salaün]

On 24/05/2023 23:43, Jeff Xu wrote:
> Sorry for the late reply.
>>
>> (Looking in the direction of Jeff Xu, who has inquired about Landlock
>> for Chromium in the past -- do you happen to know in which ways you'd
>> want to restrict ioctls, if you have that need? :))
>>
> 
> Regarding this patch, here is some feedback from ChromeOS:
>   - In the short term: we are looking to integrate Landlock into our
> sandboxer, so the ability to restrict to a specific device is huge.
> - Fundamentally though, in the effort of bringing process expected
> behaviour closest to allowed behaviour, the ability to speak of
> ioctl() path access in Landlock would be huge -- at least we can
> continue to enumerate in policy what processes are allowed to do, even
> if we still lack the ability to restrict individual ioctl commands for
> a specific device node.

Thanks for the feedback!

> 
> Regarding medium term:
> My thoughts are, from software architecture point of view, it would be
> nice to think in planes: i.e. Data plane / Control plane/ Signaling
> Plane/Normal User Plane/Privileged User Plane. Let the application
> define its planes, and assign operations to them. Landlock provides
> data structure and syscall to construct the planes.

I'm not sure to follow this plane thing. Could you give examples for 
these planes applied to Landlock?


> 
> However, one thing I'm not sure is the third arg from ioctl:
> int ioctl(int fd, unsigned long request, ...);
> Is it possible for the driver to use the same request id, then put
> whatever into the third arg ? how to deal with that effectively ?

I'm not sure about the value of all the arguments (except the command 
one) vs. the complexity to filter them, but we could discuss that when 
we'll reach this step.

> 
> For real world user cases, Dmitry Torokhov (added to list) can help.

Yes please!

> 
> PS: There is also lwn article about SELinux implementation of ioctl: [1]
> [1] https://lwn.net/Articles/428140/

Thanks for the pointer, this shows how complex this IOCTL access control 
is. For Landlock, I'd like to provide the minimal required features to 
enable user space to define their own rules, which means to let user 
space (and especially libraries) to identify useful or potentially 
harmful IOCTLs.

> 
> Thanks!
> -Jeff Xu