[ruby-core:70380] [Ruby trunk - Bug #11442] Bug: Symbols should be taintable.

[gwelch925@gmail.com]

Issue #11442 has been updated by Grant Welch.

Subject changed from String#to_sym returns an untainted Symbol. to Bug: Symbols should be taintable.

After some additional testing, I've come to the conclusion that Symbols cannot be tainted (example below). I expect this may be due to the fact that symbols have a dual meaning. 1) They are a String because we want them to be human-readable, and 2) they are a Number so they can be quickly retrieved. It's understandable that Numbers don't carry a taint flag, but since Symbols have practical use cases in place of Strings, they should carry over 'tainted?' when coming from String#to_sym.

~~~
proc {$SAFE=3;(a = :foo).tainted?}.call # => false
~~~

~~~
a = :foo
a.taint
a.tainted? # => false
~~~

Note: I have come to the conclusion that the behavior is as expected, but I am leaving the issue as a Bug (rather than a Feature) because the logic that Symbols should be un-taintable is flawed. 

----------------------------------------
Bug #11442: Bug: Symbols should be taintable.
https://bugs.ruby-lang.org/issues/11442#change-53783

* Author: Grant Welch
* Status: Open
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* ruby -v: ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
Subject: String#to_sym returns an untainted Symbol.

Taint checking can be subverted by a String if a tainted String is converted to a Symbol. After experiencing this issue, I went looking for unit tests in ruby/ruby, ruby/mspec, and ruby/rubyspec, but was unable to come up with any tests that focus on $SAFE. If they exist, could you point out where they are located? If not, I'd be willing to write some.

---------------------------------------------------------------

# Proof of Concept:
~~~
# cat untainted_sym.rb

#!/usr/bin/env ruby -w
print 'Enter a string? '
a = gets
puts "a: #{a.inspect}, tainted? #{a.tainted?}"
b = a.to_sym
puts "b: #{b.inspect}, tainted? #{b.tainted?}"
c = b.to_s
puts "c: #{c.inspect}, tainted? #{c.tainted?}"
puts "a == c: #{a == c}"
~~~

# Output:

~~~
$ ruby -w untainted_sym.rb
Enter a string? foobar
a: "foobar\n", tainted? true
b: :"foobar\n", tainted? false
c: "foobar\n", tainted? false
a == c: true
~~~

# Sample Workaround: (to provide the expected SecurityError)

~~~
# safe_level, 1 or 2
# uncertain_var, some variable that could, potentially, be tainted
untainted_sym = proc { $SAFE=safe_level; eval("'#{uncertain_var}'") && uncertain_var.to_sym}.call   # => Symbol for untainted var, SecurityError for tainted var
~~~

# Versions Tested:
* ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-linux]
* ruby 2.0.0p645 (2015-04-13 revision 50299) [x86_64-linux]
* ruby 2.1.6p336 (2015-04-13 revision 50298) [x86_64-linux]
* ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-linux]




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