Re: RFA/RFC: Add stack recursion limit to libiberty's demangler

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Nov 30, 2018 at 05:55:52AM -0800, Ian Lance Taylor wrote:
> Nick Clifton <nickc@redhat.com> writes:
> 
> > I did consider just having a fixed limit, that the user cannot change, but
> > I thought that this might be rejected by reviewers.  (On the grounds that
> > different limits are appropriate to different execution environments).
> > Note - enabling or disabling the recursion limit is controlled by a separate
> > feature of the proposed patch, ie the new DMGL_RECURSE_LIMIT flag in the 
> > options field of the cplus_demangleXXX() functions.  But there is not enough
> > room in the options field to also include a recursion limit value.
> 
> I think it would be fine to have a large fixed limit plus a flag to
> disable the limit.  I can't think of any reason why a program would want
> to change the limit unless it has complete trust in the symbols it is
> demangling, and in that case it may as well simply disable the limit.

Well, disabling the limit is what the people fuzzing it will use then
and report it still crashes.
We'd need to document that if somebody asks for no limit, then we don't
consider any cases of running as out of stack etc. as bugs, and simply
people shouldn't set that on when running on untrusted symbols.

	Jakub