Re: [MAINTAINERS/KERNEL SUMMIT] Trust and maintenance of file systems

Dave Chinner
2023-09-07T02:22:46Z

On Wed, Sep 06, 2023 at 09:53:27PM -0400, Steven Rostedt wrote:
> On Thu, 7 Sep 2023 08:54:38 +1000
> Dave Chinner <david@fromorbit.com> wrote:
>
> > And let's not forget: removing a filesystem from the kernel is not
> > removing end user support for extracting data from old filesystems.
> > We have VMs for that - we can run pretty much any kernel ever built
> > inside a VM, so users that need to extract data from a really old
> > filesystem we no longer support in a modern kernel can simply boot
> > up an old distro that did support it and extract the data that way.
>
> Of course there's the case of trying to recreate a OS that can run on a
> very old kernel. Just building an old kernel is difficult today because
> today's compilers will refuse to build them (I've hit issues in bisections
> because of that!)
>
> You could argue that you could just install an old OS into the VM, but that
> too requires access to that old OS.

Well, yes - why would anyone even bother trying to build an ancient
kernel when all they need to do is download an iso and point the VM
at it?

> Anyway, what about just having read-only be the minimum for supporting a
> file system? We can say "sorry, due to no one maintaining this file system,
> we will no longer allow write access." But I'm guessing that just
> supporting reading an old file system is much easier than modifying one
> (wasn't that what we did with NTFS for the longest time?)

"Read only" doesn't mean the filesytsem implementation is in any way
secure, robust or trustworthy - the kernel is still parsing
untrusted data in ring 0 using unmaintained, bit-rotted, untested
code....

-Dave.
--
Dave Chinner
david@fromorbit.com