Re: [RFC] Keyrings: How to make them more useful

[David 'equinox' Lamparter <equinox@diac24.net>]

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Hi all,

On Thu, Jun 12, 2025 at 01:36:50PM +0100, David Howells wrote:
> I think work needs to be done on the keyrings subsystem to make them more
> useful for network filesystems and other kernel services such as TLS and
> crypto.

As someone who has recently tried to use keyrings from userspace (in
order to bind key material to a TPM, and have it never enter user
memory), I would note two things here:

* the request_key() syscall seems to be blocking.  Of course you can
  work around that by creating a thread, but is it not possible to
  create a better API?

* the trusted key / TPM bits are incredibly poorly documented.  It's
  basically "cobble together things from old patch descriptions", e.g.
  https://marc.info/?l=linux-keyrings&m=160074197025246
  (I still have not figured out how to do this correctly.  Some of that
  is to blame on the TPM bits, but not all.)

I guess the kernel itself doesn't care about the blocking API, but for
trusted keys...  you'll have to tie things together from user space, and
I don't see how anyone can do that, especially with any level of
confidence that they didn't accidentally leave some wide-open hole (as
in - you might well get something to work, but without docs you can't
check you actually did it *right*.)  This is really improving keyctl
itself (i.e. how its commands are invoked) and also its documentation.


Hope this isn't too negative as feedback,

equi


P.S.: I wish I could submit patches for this.  I can't, because I don't
understand it.