[Rd] [External] R hang/bug with circular references and promises

[iuke-tier@ey m@iii@g oii uiow@@edu]

On Mon, 13 May 2024, Ivan Krylov wrote:

> [You don't often get email from ikrylov using disroot.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> On Mon, 13 May 2024 09:54:27 -0500 (CDT)
> luke-tierney--- via R-devel <r-devel using r-project.org> wrote:
>
>> Looks like I added that warning 22 years ago, so that should be enough
>> notice :-). I'll look into removing it now.
>

For now I have just changed the internal code to throw an error
if the change would produce a cycle (r86545). This gives

     > e <- new.env()
     > parent.env(e) <- e
     Error in `parent.env<-`(`*tmp*`, value = <environment>) :
       cycles in parent chains are not allowed

> Dear Luke,
>
> I've got a somewhat niche use case: as a way of protecting myself
> against rogue *.rds files and vulnerabilities in the C code, I've been
> manually unserializing "plain" data objects (without anything
> executable), including environments, in R [1].

I would try using two passes: create the environments in the first pass
and in a second pass, either over the file or a new object with place holders, fill them in.

> I see that SET_ENCLOS() is already commented as "not API and probably
> should not be <...> used". Do you think there is a way to recreate an
> environment, taking the REFSXP entries into account, without
> `parent.env<-`?  Would you recommend to abandon the folly of
> unserializing environments manually?

SET_ENCLOS is one of a number of SET... functions that are not in the
API and should not be since they are potentially unsafe to use. (One
that is in the API and needs to be removed is SET_TYPEOF). So we would
like to move them out of installed headers and not export them as
entry points. For this particular case most uses I see are something
like

     env = allocSExp(ENVSXP);
     SET_FRAME(env, R_NilValue);
     SET_ENCLOS(env, parent);
     SET_HASHTAB(env, R_NilValue);
     SET_ATTRIB(env, R_NilValue);

which could just use

      env = R_NewEnv(parent, FALSE, 0);

Best,

luke

>
> --
> Best regards,
> Ivan
>
> [1]
> https://codeberg.org/aitap/unserializeData/src/commit/33d72705c1ee265349b3e369874ce4b47f9cd358/R/unserialize.R#L289-L313
>

-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu/