CPP: Add DataFlow to strdup.

Author: geoffw0

cpp/ql/src/semmle/code/cpp/models/implementations/Strdup.qll

@@ -1,9 +1,12 @@
 import semmle.code.cpp.models.interfaces.Allocation
+import semmle.code.cpp.models.interfaces.ArrayFunction
+import semmle.code.cpp.models.interfaces.DataFlow
+import semmle.code.cpp.models.interfaces.Taint
 
 /**
  * A `strdup` style allocation function.
  */
-class StrdupFunction extends AllocationFunction {
+class StrdupFunction extends AllocationFunction, ArrayFunction, DataFlowFunction {
   StrdupFunction() {
     exists(string name |
       hasGlobalOrStdName(name) and
@@ -28,4 +31,15 @@ class StrdupFunction extends AllocationFunction {
       )
     )
   }
+
+  override predicate hasArrayInput(int bufParam) { bufParam = 0 }
+
+  override predicate hasArrayWithNullTerminator(int bufParam) { bufParam = 0 }
+
+  override predicate hasDataFlow(FunctionInput input, FunctionOutput output) {
+    // These always copy the full value of the input buffer to the result
+    // buffer
+    input.isParameterDeref(0) and
+    output.isReturnValueDeref()
+  }
 }