add library inputs as a source to poly-redos

Author: erik-krogh

ruby/ql/lib/codeql/ruby/security/regexp/PolynomialReDoSCustomizations.qll

@@ -22,7 +22,13 @@ module PolynomialReDoS {
   /**
    * A data flow source node for polynomial regular expression denial-of-service vulnerabilities.
    */
-  abstract class Source extends DataFlow::Node { }
+  abstract class Source extends DataFlow::Node {
+    /**
+     * Gets a string that describes the source.
+     * For use in the alert message.
+     */
+    string describe() { result = "user-provided value" }
+  }
 
   /**
    * A data flow sink node for polynomial regular expression denial-of-service vulnerabilities.
@@ -53,6 +59,15 @@ module PolynomialReDoS {
    */
   class RemoteFlowSourceAsSource extends Source, RemoteFlowSource { }
 
+  import codeql.ruby.frameworks.core.Gem::Gem as Gem
+
+  /** A library input, considered as a flow source. */
+  class LibraryInputAsSource extends Source {
+    LibraryInputAsSource() { this = Gem::getALibraryInput() }
+
+    override string describe() { result = "library input" }
+  }
+
   /**
    * Gets the AST of a regular expression object that can flow to `node`.
    */

ruby/ql/src/change-notes/2022-10-11-poly-redos-lib.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `rb/polynomial-redos` query now considers the entrypoints of the API of a gem as sources.

ruby/ql/src/queries/security/cwe-1333/PolynomialReDoS.ql

@@ -27,4 +27,4 @@ where
 select sinkNode.getHighlight(), source, sink,
   "This $@ that depends on a $@ may run slow on strings " + regexp.getPrefixMessage() +
     "with many repetitions of '" + regexp.getPumpString() + "'.", regexp, "regular expression",
-  source.getNode(), "user-provided value"
+  source.getNode(), source.getNode().(PolynomialReDoS::Source).describe()

ruby/ql/test/query-tests/security/cwe-1333-polynomial-redos/PolynomialReDoS.expected

@@ -23,6 +23,7 @@ edges
 | PolynomialReDoS.rb:29:9:29:18 | ...[...] :  | PolynomialReDoS.rb:30:5:30:5 | b |
 | PolynomialReDoS.rb:31:9:31:14 | call to params :  | PolynomialReDoS.rb:31:9:31:18 | ...[...] :  |
 | PolynomialReDoS.rb:31:9:31:18 | ...[...] :  | PolynomialReDoS.rb:32:5:32:5 | c |
+| lib/index.rb:2:11:2:11 | x :  | lib/index.rb:4:13:4:13 | x |
 nodes
 | PolynomialReDoS.rb:4:12:4:17 | call to params :  | semmle.label | call to params :  |
 | PolynomialReDoS.rb:4:12:4:24 | ...[...] :  | semmle.label | ...[...] :  |
@@ -52,6 +53,8 @@ nodes
 | PolynomialReDoS.rb:32:5:32:5 | c | semmle.label | c |
 | PolynomialReDoS.rb:42:10:42:13 | name | semmle.label | name |
 | PolynomialReDoS.rb:47:10:47:13 | name | semmle.label | name |
+| lib/index.rb:2:11:2:11 | x :  | semmle.label | x :  |
+| lib/index.rb:4:13:4:13 | x | semmle.label | x |
 subpaths
 #select
 | PolynomialReDoS.rb:10:5:10:17 | ... =~ ... | PolynomialReDoS.rb:4:12:4:17 | call to params :  | PolynomialReDoS.rb:10:5:10:8 | name | This $@ that depends on a $@ may run slow on strings with many repetitions of ' '. | PolynomialReDoS.rb:7:19:7:21 | \\s+ | regular expression | PolynomialReDoS.rb:4:12:4:17 | call to params | user-provided value |
@@ -74,3 +77,4 @@ subpaths
 | PolynomialReDoS.rb:32:5:32:20 | call to sub! | PolynomialReDoS.rb:31:9:31:14 | call to params :  | PolynomialReDoS.rb:32:5:32:5 | c | This $@ that depends on a $@ may run slow on strings with many repetitions of ' '. | PolynomialReDoS.rb:7:19:7:21 | \\s+ | regular expression | PolynomialReDoS.rb:31:9:31:14 | call to params | user-provided value |
 | PolynomialReDoS.rb:42:5:45:7 | case ... | PolynomialReDoS.rb:4:12:4:17 | call to params :  | PolynomialReDoS.rb:42:10:42:13 | name | This $@ that depends on a $@ may run slow on strings with many repetitions of ' '. | PolynomialReDoS.rb:7:19:7:21 | \\s+ | regular expression | PolynomialReDoS.rb:4:12:4:17 | call to params | user-provided value |
 | PolynomialReDoS.rb:47:5:50:7 | case ... | PolynomialReDoS.rb:4:12:4:17 | call to params :  | PolynomialReDoS.rb:47:10:47:13 | name | This $@ that depends on a $@ may run slow on strings with many repetitions of ' '. | PolynomialReDoS.rb:48:14:48:16 | \\s+ | regular expression | PolynomialReDoS.rb:4:12:4:17 | call to params | user-provided value |
+| lib/index.rb:4:13:4:26 | call to match | lib/index.rb:2:11:2:11 | x :  | lib/index.rb:4:13:4:13 | x | This $@ that depends on a $@ may run slow on strings with many repetitions of 'a'. | lib/index.rb:4:22:4:23 | a+ | regular expression | lib/index.rb:2:11:2:11 | x | library input |

ruby/ql/test/query-tests/security/cwe-1333-polynomial-redos/lib/index.rb

@@ -0,0 +1,6 @@
+module Foo 
+  def bar(x) 
+    # Run the /a+$/ regex on the input x.
+    match = x.match(/a+$/)
+  end
+end

ruby/ql/test/query-tests/security/cwe-1333-polynomial-redos/poly-redos.gemspec

@@ -0,0 +1,5 @@
+Gem::Specification.new do |s|
+    s.name = 'poly-redos'
+    s.require_path = "lib"
+  end
+