[RFC PATCH RESEND] userfaultfd: open userfaultfds with O_RDONLY

[Peter Xu]

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>

-- 
Peter Xu