[R-pkg-devel] Sanitize Input Code for a Shiny App

[Simon Urbanek]

Bill,

the short answer is you can't limit anything at R level. Any attempts to create a list of "bad" commands are trivial to circumvent since you can compute on the language in R, so you can construct and call functions with trivial operations. Similarly, since R allows the loading of binary code the same applies for arbitrary code. So if you give users access to R, you should assume that is equivalent to allowing arbitrary code execution. Therefore all you can do is limit the resources and reach - as you pointed out using a container is a good idea so each session is only limited to a single container that goes away when the session ends. Similarly you can restrict main parts of R and the system to be read-only in the container.

In practice, that's why real analytic systems are about provenance rather than prevention. For example, in RCloud all code is first committed to a git repository outside of the container before it can be executed, so malicious users can do whatever they want, but they cannot hide the malicious code they used as the container cannot manipulate the history.

As for package installation - again, it's impossible to prevent it in general unless you make everything read-only which also prevents the users from doing meaningful work. So the real question what do you want to allow the user to do - why would you need to allow literal R code evaluation? The other alternative is to simply limit the interaction not allowing the user to submit arbitrary code, only tweak parameters or use GUI to select particular choices. Obviously, that is a lot easier to secure.

Cheers,
Simon


> On 27/02/2023, at 8:36 AM, bill using denney.ws wrote:
> 
> Hello,
> 
> 
> 
> I'm working to develop a Shiny app where I'd like to have an advanced
> capability to accept user input and run the code.  For the code received,
> I'd like to be able to prevent R from doing things other than working within
> the R session.  For example, I want to prevent `system("rm -rf /*")`.
> 
> 
> 
> One method to achieve this is to run the R session within a Docker container
> and perform the security around the container.  The user could do some
> things within the container, but they would be limited.
> 
> 
> 
> What I'd like to be able to do is to sanitize the inputs to ensure that it
> won't to things including installing packages, running system commands,
> reading and writing to the filesystem, and accessing the network.  I'd like
> to allow the user to do almost anything they want within R, so making a list
> of acceptable commands is not accomplishing the goal.  I could try to do
> something like:
> 
> 
> 
> *	have acceptable packages loaded, only,
> *	don't allow loading additional packages,
> *	deny a set of known-bad commands (e.g. system, system2, etc.)
> *	deny any attempt to run from additional packages (exclude calls with
> a double-colon or triple-colon)
> 
> 
> 
> The method I just described seems like it would not work well because it
> assumes that the known-bad commands is comprehensive and that I'm being
> creative enough in ways that users could try to break things.
> 
> 
> 
> Is there a good way to sanitize arbitrary code from users to prevent
> malicious behavior?
> 
> 
> Thanks,
> 
> 
> 
> Bill
> 
> 
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> 
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