Re: "Local variables" denial-of-service attack

[Stefan Monnier]

>    Local Variab*les:
>    byte-compile-warnings: #1=("circular" "object" . #1#)
>    End:

> Visiting such a file will result in Emacs hanging and consuming all
> CPU time. (Normally, aborting with C-g is possible. However, if the
> file is opened with emacsclient there seems to be no way to recover.)

Hmm... that's not good.  It's not the end of the world since it's "only"
a DoS, but we should try and fix it.  I see two ways:
1 - don't allow (in file-local vars and .dir-local.el) the # escapes
    that permit creation of those circular objects.
2 - be more careful about circularities in the
    safe-local-variable predicates.

Nb 1 is easier and will solve it "for all cases", so it's probably
a better choice.  Of course, it also "denies service" to those rare
individuals who used circular data in file-local variables for
non-DoS purposes.  I don't know if there are any on this planet, tho.


        Stefan