Issue #16131 has been updated by Eregon (Benoit Daloze).


I agree it would be best to remove the implicit taint state, and particularly the interaction with $SAFE.

FWIW, TruffleRuby already prevents setting $SAFE to anything else than 0:
https://github.com/oracle/truffleruby/blob/master/doc/user/security.md#unimplemented-security-features

Without $SAFE (which I think most people agree to remove), I think tainting has very few use-cases, which I think doesn't warrant staying a core feature.

Tracking tainting has a performance cost, e.g., String#+ must check if either LHS or RHS is tainted and taint the result in that case.
This can introduce extra polymorphism or branches in code which needs to check for the taint state.

----------------------------------------
Feature #16131: Remove $SAFE, taint and trust
https://bugs.ruby-lang.org/issues/16131#change-81448

* Author: naruse (Yui NARUSE)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Ruby had Taint checking which is originally introduced in Perl.
https://en.wikipedia.org/wiki/Taint_checking

It was intended to provide a useful tool for handle objects which are come from outside.
Input data is set as tainted by default and call untaint if you checked or filtered the value.
Some people used this feature in the age of CGI.

But these days, no one use the mechanism and input libraries usually doesn't support it.
For example rack, as following shows its input is not tainted and the mechanism is unusable.

```
% cat foo.ru
run ->(env) do
  ['200', {'Content-Type' => 'text/plain'}, ["Is QUERY_STRING tainted?: #{env["QUERY_STRING"].tainted?}"]]
end
% rackup foo.ru
[51724] Puma starting in cluster mode...
[51724] * Version 3.12.1 (ruby 2.6.3-p62), codename: Llamas in Pajamas
[51724] * Min threads: 3, max threads: 3
[51724] * Environment: development
[51724] * Process workers: 1
[51724] * Preloading application
[51724] * Listening on tcp://localhost:9292
[51724] Use Ctrl-C to stop
[51737] + Gemfile in context: /Users/naruse/work/td-cdp-api/Gemfile
[51724] - Worker 0 (pid: 51737) booted, phase: 0
```

```
% curl http://localhost:9292/\?foo=1
Is QUERY_STRING tainted?: false
```

Therefore I think Taint checking mechanism is unusable on the current Ruby ecosystem.

On the other hand we experienced multiple vulnerability around $SAFE and taint mechanism.
https://cse.google.com/cse?q=taint&cx=008288045305770251182%3Afvruzsaknew&ie=UTF-8
The cost of maintaining it is expensive.

In conclusion, I think the taint mechanism is too expensive to maintain for the merit of it.
I suggest to remove it.



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