Python: Address review comments

- changes `getReceiver` to `getObject`
- fixes `calls` to avoid unwanted cross-talk
- adds some more documentation to highlight the above issue

Author: tausbn

python/ql/src/Security/CWE-327/Ssl.qll

@@ -42,7 +42,7 @@ API::Node sslContextInstance() {
 class WrapSocketCall extends ConnectionCreation, DataFlow::MethodCallNode {
   WrapSocketCall() { this = sslContextInstance().getMember("wrap_socket").getACall() }
 
-  override DataFlow::Node getContext() { result = this.getReceiver() }
+  override DataFlow::Node getContext() { result = this.getObject() }
 }
 
 class OptionsAugOr extends ProtocolRestriction, DataFlow::CfgNode {

python/ql/src/experimental/semmle/python/frameworks/Stdlib.qll

@@ -70,7 +70,7 @@ private module Re {
     CompiledRegex() {
       exists(DataFlow::MethodCallNode patternCall |
         patternCall = API::moduleImport("re").getMember("compile").getACall() and
-        patternCall.flowsTo(this.getReceiver()) and
+        patternCall.flowsTo(this.getObject()) and
         this.getMethodName() instanceof RegexExecutionMethods and
         regexNode = patternCall.getArg(0)
       )

python/ql/src/semmle/python/dataflow/new/internal/DataFlowPublic.qll

@@ -184,23 +184,38 @@ class CallCfgNode extends CfgNode, LocalSourceNode {
  * A data-flow node corresponding to a method call, that is `foo.bar(...)`.
  *
  * Also covers the case where the method lookup is done separately from the call itself, as in
- * `temp = foo.bar; temp(...)`.
+ * `temp = foo.bar; temp(...)`. Note that this is only tracked through local scope.
  */
 class MethodCallNode extends CallCfgNode {
   AttrRead method_lookup;
 
   MethodCallNode() { method_lookup = this.getFunction().getALocalSource() }
 
-  /** Gets the name of the method being invoked (the `bar` in `foo.bar(...)`, if it can be determined. */
+  /**
+   * Gets the name of the method being invoked (the `bar` in `foo.bar(...)`) if it can be determined.
+   *
+   * Note that this method may have multiple results if a single call node represents calls to
+   * multiple different objects and methods. If you want to link up objects and method names
+   * accurately, use the `calls` method instead.
+   */
   string getMethodName() { result = method_lookup.getAttributeName() }
 
-  /** Gets the data-flow node corresponding to the receiver of this call. That is, the `foo` in `foo.bar(...)`. */
-  Node getReceiver() { result = method_lookup.getObject() }
-
-  /** Holds if this data-flow node calls method `methodName` on receiver node `receiver`. */
-  predicate calls(Node receiver, string methodName) {
-    receiver = this.getReceiver() and
-    methodName = this.getMethodName()
+  /**
+   * Gets the data-flow node corresponding to the object receiving this call. That is, the `foo` in
+   * `foo.bar(...)`.
+   *
+   * Note that this method may have multiple results if a single call node represents calls to
+   * multiple different objects and methods. If you want to link up objects and method names
+   * accurately, use the `calls` method instead.
+   */
+  Node getObject() { result = method_lookup.getObject() }
+
+  /** Holds if this data-flow node calls method `methodName` on the object node `object`. */
+  predicate calls(Node object, string methodName) {
+    // As `getObject` and `getMethodName` may both have multiple results, we must look up the object
+    // and method name directly on `method_lookup`.
+    object = method_lookup.getObject() and
+    methodName = method_lookup.getAttributeName()
   }
 }
 

python/ql/src/semmle/python/frameworks/Cryptography.qll

@@ -267,8 +267,11 @@ private module CryptographyModel {
       string algorithmName;
 
       CryptographyGenericCipherOperation() {
-        this.getMethodName() in ["update", "update_into"] and
-        this.getReceiver() in [cipherEncryptor(algorithmName), cipherDecryptor(algorithmName)]
+        exists(DataFlow::Node object, string method |
+          object in [cipherEncryptor(algorithmName), cipherDecryptor(algorithmName)] and
+          method in ["update", "update_into"] and
+          this.calls(object, method)
+        )
       }
 
       override Cryptography::CryptographicAlgorithm getAlgorithm() {

python/ql/test/experimental/dataflow/method-calls/test.expected

@@ -0,0 +1,8 @@
+conjunctive_lookup
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | bar |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | foo |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | bar |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | foo |
+calls_lookup
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | foo |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | bar |

python/ql/test/experimental/dataflow/method-calls/test.py

@@ -0,0 +1,6 @@
+if cond:
+    meth = obj1.foo
+else:
+    meth = obj2.bar
+
+meth()

python/ql/test/experimental/dataflow/method-calls/test.ql

@@ -0,0 +1,18 @@
+import python
+import semmle.python.dataflow.new.DataFlow
+import experimental.dataflow.TestUtil.PrintNode
+
+query predicate conjunctive_lookup(
+  DataFlow::MethodCallNode methCall, string call, string object, string methodName
+) {
+  call = prettyNode(methCall) and
+  object = prettyNode(methCall.getObject()) and
+  methodName = methCall.getMethodName()
+}
+
+query predicate calls_lookup(
+  DataFlow::MethodCallNode methCall, string call, string object, string methodName
+) {
+  call = prettyNode(methCall) and
+  exists(DataFlow::Node o | methCall.calls(o, methodName) and object = prettyNode(o))
+}