bug#37656: 27.0.50; Arbitrary code execution with special `mode:'

[Eli Zaretskii]

> From: Adam Plaice <plaiceadam@gmail.com>
> Date: Wed, 16 Oct 2019 02:35:58 +0200
> Cc: 37656@debbugs.gnu.org, Emacs developers <emacs-devel@gnu.org>
> 
> Unfortunately, I've realised that a similar problem can be introduced
> with directory variables.

Indeed, and I expect the same problem to pop up in other places.

Which is why I think the problem should be solved in those modes which
allow execution of arbitrary code via file-local variables without any
security precautions or other limitations, at least under user
control.

> (Should I file separate bug for this as it's closely related but not
> quite the same?)

No, it's the same problem, and I don't like the proposed solution for
the reasons explained above.  I think we need a different solution.