Minor fixes for code review

Author: egregius313

java/ql/lib/semmle/code/java/security/TaintedEnvironmentVariableQuery.qll

@@ -2,33 +2,46 @@
 
 private import semmle.code.java.dataflow.ExternalFlow
 private import semmle.code.java.dataflow.FlowSources
-private import semmle.code.java.dataflow.TaintTracking
 private import semmle.code.java.Maps
 private import semmle.code.java.JDK
 
+private class MapPutOrRemove extends MethodCall {
+  MapPutOrRemove() {
+    this.getMethod() instanceof MapMutator and
+    this.getMethod().getName().matches(["put%", "remove"])
+  }
+}
+
 private module ProcessBuilderEnvironmentConfig implements DataFlow::ConfigSig {
   predicate isSource(DataFlow::Node source) {
     exists(MethodCall mc | mc = source.asExpr() |
       mc.getMethod().hasQualifiedName("java.lang", "ProcessBuilder", "environment")
     )
   }
 
-  predicate isSink(DataFlow::Node sink) { sink.asExpr() = any(MapMutation mm).getQualifier() }
+  predicate isSink(DataFlow::Node sink) { sink.asExpr() = any(MapPutOrRemove mm).getQualifier() }
 }
 
 private module ProcessBuilderEnvironmentFlow = DataFlow::Global<ProcessBuilderEnvironmentConfig>;
 
+/**
+ * A node that acts as a sanitizer in configurations related to environment variable injection.
+ */
+abstract class ExecTaintedEnvironmentSanitizer extends DataFlow::Node { }
+
 /**
  * A taint-tracking configuration that tracks flow from unvalidated data to an environment variable for a subprocess.
  */
 module ExecTaintedEnvironmentConfig implements DataFlow::ConfigSig {
   predicate isSource(DataFlow::Node source) { source instanceof ThreatModelFlowSource }
 
+  predicate isBarrier(DataFlow::Node barrier) { barrier instanceof ExecTaintedEnvironmentSanitizer }
+
   predicate isSink(DataFlow::Node sink) {
     sinkNode(sink, "environment-injection")
     or
     // sink is a key or value added to a `ProcessBuilder::environment` map.
-    exists(MapMutation mm | mm.getAnArgument() = sink.asExpr() |
+    exists(MapPutOrRemove mm | mm.getAnArgument() = sink.asExpr() |
       ProcessBuilderEnvironmentFlow::flowToExpr(mm.getQualifier())
     )
   }