Re: [kernel-hardening] [RFC 0/4] make call_usermodehelper a bit more "safe"

Greg Kroah-Hartman
2016-12-14T23:16:21Z

On Wed, Dec 14, 2016 at 10:28:18PM +0100, Jason A. Donenfeld wrote:
> Hi Greg,
>
> On Wed, Dec 14, 2016 at 7:50 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > So, anyone have any better ideas? Is this approach worth it? Or should
> > we just go down the "whitelist" path?
>
> I think your approach is generally better than the whitelist path. But
> maybe there's yet a third approach that involves futzing with page
> permissions at runtime. I think grsec does something similar with
> read_mostly function pointer structs. Namely, they make them read-only
> const, and then temporarily twiddle the page permissions if it needs
> to be changed while disabling preemption. There could be a particular
> class of data that needs to be "opened" and "closed" in order to
> modify. Seems like these strings would be a good use of that.

Yes, but that's a much larger issue and if that feature ever lands, we
can switch these strings over to that functionality.

thanks,

greg k-h