linux-kernel - Re: [RFC v4 2/2] file, epoll: Implement do_replace() and eventpoll

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Date:   Mon, 27 Mar 2023 07:16:39 -0600
From:   Tycho Andersen <tycho@...ho.pizza>
To:     Christian Brauner <brauner@...nel.org>
Cc:     aloktiagi <aloktiagi@...il.com>, viro@...iv.linux.org.uk,
        willy@...radead.org, David.Laight@...lab.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, hch@...radead.org
Subject: Re: [RFC v4 2/2] file, epoll: Implement do_replace() and
 eventpoll_replace()

On Mon, Mar 27, 2023 at 07:06:46AM -0600, Tycho Andersen wrote:
> On Mon, Mar 27, 2023 at 11:01:06AM +0200, Christian Brauner wrote:
> > On Fri, Mar 24, 2023 at 07:43:13AM -0600, Tycho Andersen wrote:
> > > Perhaps we could add a flag that people could set from SECCOMP_ADDFD
> > > asking for this extra behavior?
> > 
> >         +       if (fd > 0 && addfd->ioctl_flags & SECCOMP_ADDFD_FLAG_EPOLL) {
> >         +               /*
> >         +                * - retrieve old struct file that addfd->fd refered to if any.
> >         +                * - call your epoll seccomp api to update the references in the epoll instance
> >         +                */
> > 			epoll_seccomp_notify()
> >         +       }
> >         +
> >         +       if (fd > 0 && addfd->ioctl_flags & SECCOMP_ADDFD_FLAG_IO_URING) {
> >         +               /*
> >         +                * - call your io_uring seccomp api to update the references in the io_uring instance
> >         +                */
> > 			io_uring_seccomp_notify()
> >         +       }
> 
> Looks reasonable to me, thanks.

One change I might suggest is only using a single flag bit -- we don't
need to consume all of seccomp's remaining flag bits with the various
subsystems. If you want to do this logic for epoll, you almost
certainly want it for io_uring, select, and whatever else is out
there.

Tycho