Ruby: Model Open4 library

Also remove duplicate modeling of Process.spawn.

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

@@ -130,7 +130,6 @@ module Kernel {
    * `Kernel.spawn` takes the same argument forms as `Kernel.system`.
    * See `KernelSystemCall` for details.
    * Ruby documentation: https://docs.ruby-lang.org/en/3.0.0/Kernel.html#method-i-spawn
-   * Methods with the same effect exist in the `Process` and `PTY` classes, so they are also modeled here.
    * TODO: document and handle the env and option arguments.
    * ```
    * spawn([env,] command... [,options]) -> pid
@@ -140,8 +139,6 @@ module Kernel {
     KernelSpawnCall() {
       this.getMethodName() = "spawn" and
       this instanceof KernelMethodCall
-      or
-      this = DataFlow::getConstant(["Process", "PTY"]).getAMethodCall("spawn")
     }
 
     override DataFlow::Node getAnArgument() { result = super.getArgument(_) }

ruby/ql/lib/codeql/ruby/frameworks/stdlib/Open3.qll

@@ -18,10 +18,8 @@ module Open3 {
   class Open3Call extends SystemCommandExecution::Range instanceof DataFlow::CallNode {
     Open3Call() {
       this =
-        API::getTopLevelMember(["Open3", "Open4"])
-            .getAMethodCall([
-                "popen3", "popen2", "popen2e", "capture3", "capture2", "capture2e", "popen4"
-              ])
+        API::getTopLevelMember("Open3")
+            .getAMethodCall(["popen3", "popen2", "popen2e", "capture3", "capture2", "capture2e"])
     }
 
     override DataFlow::Node getAnArgument() { result = super.getArgument(_) }
@@ -33,6 +31,19 @@ module Open3 {
     }
   }
 
+  class Open4Call extends SystemCommandExecution::Range instanceof DataFlow::CallNode {
+    Open4Call() {
+      this = API::getTopLevelMember("Open4").getAMethodCall(["open4", "popen4", "spawn"])
+    }
+
+    override DataFlow::Node getAnArgument() { result = super.getArgument(_) }
+
+    override predicate isShellInterpreted(DataFlow::Node arg) {
+      super.getNumberOfArguments() = 1 and
+      arg = this.getAnArgument()
+    }
+  }
+
   /**
    * A pipeline of system commands constructed via one of the `Open3` methods.
    * These methods accept a variable argument list of commands.

ruby/ql/test/library-tests/frameworks/stdlib/Open3.expected

@@ -11,3 +11,7 @@ open3PipelineCallExecutions
 | Open3.rb:9:1:9:40 | call to pipeline_w |
 | Open3.rb:10:1:10:44 | call to pipeline_start |
 | Open3.rb:11:1:11:38 | call to pipeline |
+open4CallExecutions
+| Open3.rb:13:1:13:24 | call to open4 |
+| Open3.rb:14:1:14:25 | call to popen4 |
+| Open3.rb:15:1:15:23 | call to spawn |

ruby/ql/test/library-tests/frameworks/stdlib/Open3.ql

@@ -4,3 +4,5 @@ import codeql.ruby.DataFlow
 query predicate open3CallExecutions(Open3Call c) { any() }
 
 query predicate open3PipelineCallExecutions(Open3PipelineCall c) { any() }
+
+query predicate open4CallExecutions(Open4Call c) { any() }

ruby/ql/test/library-tests/frameworks/stdlib/Open3.rb

@@ -8,4 +8,8 @@ Open3.pipeline_rw("echo foo", "grep bar")
 Open3.pipeline_r("echo foo", "grep bar")
 Open3.pipeline_w("echo foo", "grep bar")
 Open3.pipeline_start("echo foo", "grep bar")
-Open3.pipeline("echo foo", "grep bar")
+Open3.pipeline("echo foo", "grep bar")
+
+Open4::open4("echo foo")
+Open4::popen4("echo foo")
+Open4.spawn("echo bar")