Re: [PATCH 2/4] mm: introduce external memory hinting API

[Daniel Colascione]

On Mon, Jan 13, 2020 at 11:10 AM Christian Brauner
<christian.brauner@xxxxxxxxxx> wrote:
> This does not
> affect the permission checking you're performing here.

Pidfds-as-capabilities sounds like a good change. Can you clarify what
you mean here though? Do you mean that in order to perform some
process-directed operation X on process Y, the pidfd passed to X must
have been opened with PIDFD_CAP_X *and* the process *using* the pidfds
must be able to perform operation X on process Y? Or do pidfds in this
model "carry" permissions in the same way that an ordinary file
descriptor "carries" the ability to write to a file if it was opened
with O_WRONLY even if the FD is passed to a process that couldn't
otherwise write to that file? Right now, pidfds are identity-only and
always rely on the caller's permissions. I like the capability bit
model because it makes pidfds more consistent with other file
descriptors and enabled delegation of capabilities across the system.