Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()?

Jann Horn
2020-01-29T15:00:11Z

On Tue, Jan 28, 2020 at 8:42 PM Jens Axboe <axboe@kernel.dk> wrote:
> On 1/28/20 11:04 AM, Jens Axboe wrote:
> > On 1/28/20 10:19 AM, Jens Axboe wrote:
[...]
> >> #1 adds support for registering the personality of the invoking task,
> >> and #2 adds support for IORING_OP_USE_CREDS. Right now it's limited to
> >> just having one link, it doesn't support a chain of them.
[...]
> I didn't like it becoming a bit too complicated, both in terms of
> implementation and use. And the fact that we'd have to jump through
> hoops to make this work for a full chain.
>
> So I punted and just added sqe->personality and IOSQE_PERSONALITY.
> This makes it way easier to use. Same branch:
>
> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds
>
> I'd feel much better with this variant for 5.6.

Some general feedback from an inspectability/debuggability perspective:

At some point, it might be nice if you could add a .show_fdinfo
handler to the io_uring_fops that makes it possible to get a rough
overview over the state of the uring by reading /proc/$pid/fdinfo/$fd,
just like e.g. eventfd (see eventfd_show_fdinfo()). It might be
helpful for debugging to be able to see information about the fixed
files and buffers that have been registered. Same for the
personalities; that information might also be useful when someone is
trying to figure out what privileges a running process actually has.