Re: [PATCH v2 2/3] exportfs: allow fs to disable CAP_DAC_READ_SEARCH check

[Erin Shepherd <erin.shepherd@e43.eu>]

On 14/11/2024 05:37, Christoph Hellwig wrote:
> On Wed, Nov 13, 2024 at 05:55:24PM +0000, Erin Shepherd wrote:
>> For pidfs, there is no reason to restrict file handle decoding by
>> CAP_DAC_READ_SEARCH.
> Why is there no reason, i.e. why do you think it is safe.

A process can use both open_by_handle_at to open the exact same set of
pidfds as they can by pidfd_open. i.e. there is no reason to additionally
restrict access to the former API.

>> Introduce an export_ops flag that can indicate
>> this
> Also why is is desirable?
>
> To be this looks more than sketchy with the actual exporting hat on,
> but I guess that's now how the cool kids use open by handle these days.
Right - we have a bunch of API file systems where userspace wants stable
non-reused file references for the same reasons network filesystems do.
The first example of this was cgroupfs, but the same rationale exists for
pidfs and process tracking.