[RFC PATCH RESEND] userfaultfd: open userfaultfds with O_RDONLY

[Paul Moore]

On Tue, Jul 12, 2022 at 10:22 AM Peter Xu <peterx at redhat.com> wrote:
> On Fri, Jul 08, 2022 at 11:34:51AM +0200, Ondrej Mosnacek wrote:
> > Since userfaultfd doesn't implement a write operation, it is more
> > appropriate to open it read-only.
> >
> > When userfaultfds are opened read-write like it is now, and such fd is
> > passed from one process to another, SELinux will check both read and
> > write permissions for the target process, even though it can't actually
> > do any write operation on the fd later.
> >
> > Inspired by the following bug report, which has hit the SELinux scenario
> > described above:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1974559
> >
> > Reported-by: Robert O'Callahan <roc at ocallahan.org>
> > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization")
> > Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
>
> Acked-by: Peter Xu <peterx at redhat.com>

Thanks Peter.

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