add library for reasoning about gems and .gemspec files

ruby/ql/lib/codeql/ruby/frameworks/Core.qll

@@ -7,6 +7,7 @@ private import codeql.ruby.DataFlow
 private import codeql.ruby.dataflow.FlowSummary
 import core.BasicObject::BasicObject
 import core.Object::Object
+import core.Gem::Gem
 import core.Kernel::Kernel
 import core.Module
 import core.Array

ruby/ql/lib/codeql/ruby/frameworks/core/Gem.qll

@@ -0,0 +1,92 @@
+/**
+ * Provides modeling for the `Gem` module and `.gemspec` files.
+ */
+
+private import ruby
+private import Ast
+private import codeql.ruby.ApiGraphs
+
+/** Provides modeling for the `Gem` module and `.gemspec` files. */
+module Gem {
+  /** A .gemspec file that lists properties of a Ruby gem. */
+  class GemSpec instanceof File {
+    API::Node specCall;
+
+    GemSpec() {
+      this.getExtension() = "gemspec" and
+      specCall = API::root().getMember("Gem").getMember("Specification").getMethod("new") and
+      specCall.getLocation().getFile() = this
+    }
+
+    /** Gets the name of this .gemspec file. */
+    string toString() { result = File.super.getBaseName() }
+
+    /**
+     * Gets a value of the `name` property of this .gemspec file.
+     * These properties are set using the `Gem::Specification.new` method.
+     */
+    private Expr getSpecProperty(string key) {
+      exists(Expr rhs |
+        rhs =
+          specCall
+              .getBlock()
+              .getParameter(0)
+              .getMethod(key + "=")
+              .getParameter(0)
+              .asSink()
+              .asExpr()
+              .getExpr()
+              .(Ast::AssignExpr)
+              .getRightOperand()
+      |
+        result = rhs
+        or
+        // some properties are arrays, we just unfold them
+        result = rhs.(ArrayLiteral).getAnElement()
+      )
+    }
+
+    /** Gets the name of the gem */
+    string getName() { result = getSpecProperty("name").getConstantValue().getString() }
+
+    /** Gets a path that is loaded when the gem is required */
+    private string getARequirePath() {
+      result = getSpecProperty(["require_paths", "require_path"]).getConstantValue().getString()
+      or
+      not exists(getSpecProperty(["require_paths", "require_path"]).getConstantValue().getString()) and
+      result = "lib" // the default is "lib"
+    }
+
+    /** Gets a file that is loaded when the gem is required. */
+    private File getAnRequiredFile() {
+      result = File.super.getParentContainer().getFolder(getARequirePath()).getAChildContainer*()
+    }
+
+    /** Gets a class/module that is exported by this gem. */
+    private ModuleBase getAPublicModule() {
+      result.(Toplevel).getLocation().getFile() = getAnRequiredFile()
+      or
+      result = getAPublicModule().getAModule()
+      or
+      result = getAPublicModule().getAClass()
+      or
+      result = getAPublicModule().getStmt(_).(SingletonClass)
+    }
+
+    /** Gets a parameter from an exported method, which is an input to this gem. */
+    DataFlow::ParameterNode getAnInputParameter() {
+      exists(MethodBase method | method = getAPublicModule().getAMethod() |
+        result.getParameter() = method.getAParameter() and
+        method.isPublic()
+      )
+    }
+  }
+
+  /** Gets a parameter that is an input to a named gem. */
+  DataFlow::ParameterNode getALibraryInput() {
+    exists(GemSpec spec |
+      exists(spec.getName()) and // we only consider `.gemspec` files that have a name
+      result = spec.getAnInputParameter()
+    )
+  }
+}