sandboxing Guile extensions

sandboxing Guile extensions

[Noneayour Business]

   I have a GUI app
     http://www.lightandmatter.com/ogr/ogr.html
   in which I've just implemented a very rudimentary extension mechanism
   using Guile. I'm not an experienced lisp programmer at all. This has
   been
   my first use of lisp beyond "hello, world."

   The purpose of my extension is to let users run their own arbitrary
   code
   in certain situations. However, this means that someone could in
   principle
   create a Trojan horse attack in which they embed some malicious Guile
   code in a document and send it to someone else and try to get them to
   open the document.

   I see that Guile 2.2.1 has a sandboxing mechanism:

   https://www.gnu.org/software/guile/manual/html_node/Sandboxed-Evaluatio
   n.html
   However, this seems entirely focused on preventing excessive use of
   resources. Is there any way to have Guile run in a sandbox similar to
   the javascript or java applet sandbox, where it doesn't have access to
   the file system and so on? E.g., could I delete certain parts of the
   libraries
   before handing control over to the user-supplied code, or can the
   interpreter
   be started up without some of the standard libraries?

   I'm currently running Guile by starting up an interpreter through a
   shell
   for each evaluation of the user's function:
     https://github.com/bcrowell/opengrade/blob/master/Extension.pm

   Thanks in advance for any suggestions!

     Ben Crowell

Re: sandboxing Guile extensions

[tantalum]

i think it is possible to restrict the bindings available for code that 
is evaluated with eval-in-sandbox. eval-in-sandbox accepts a keyword 
argument named #:module for supplying a module object which gives all 
bindings that will be available to the evaluated code. a module with the 
allowed bindings can be created with make-sandbox-module.

here is an example:

```
(import (ice-9 sandbox))

(define env (make-sandbox-module (list (quote ((guile) display 
string-append)))))

(define result
   (eval-in-sandbox (quote (display string-append)) #:time-limit 2 
#:module env))
```

when i remove string-append from the list, the code evaluation fails 
with an unbound variable exception. the argument to make-sandbox-module 
is a list of lists, where for each the first element is a module name 
and the rest are binding names to include from that module. there are a 
few default sets, for example the variables string-bindings, 
list-bindings, number-bindings, etc.

the preset sets are also just lists and can be appended
```
(make-sandbox-module
   (append
     core-bindings string-bindings symbol-bindings list-bindings 
number-bindings
     (quote (
       ((my example module) link-files include-files)))))
```

if eval-in-sandbox would not exist, one would perhaps use eval from 
(rnrs eval), which can also take a module that restricts available 
features.

Re: sandboxing Guile extensions

[Noneayour Business]

   Thanks for the help with this! I hadn't understood the docs well enough
   to understand that the
   sandbox module did allow restrictions on what library functions were
   available.

   Unfortunately the sandbox module is only available with guile 2.2+,
   which makes it impractical
   for my application, since I can't expect users to compile the latest
   version from source.