cpp: Add query to detect unsigned integer to signed integer conversions used in pointer arithmetics

cpp/ql/src/experimental/Security/CWE/CWE-787/UnsignedToSignedPointerArith.ql

@@ -0,0 +1,28 @@
+/**
+ * @author Jordy Zomer
+ * @name unsiged to signed used in pointer arithmetic
+ * @description finds unsigned to signed conversions used in pointer arithmetic, potentially causing an out-of-bound access
+ * @id cpp/out-of-bounds
+ * @kind problem
+ * @problem.severity warning
+ * @tags reliability
+ *       security
+ *       external/cwe/cwe-787
+ */
+
+import cpp
+import semmle.code.cpp.dataflow.DataFlow
+import semmle.code.cpp.security.Overflow
+
+from FunctionCall call, Function f, Parameter p, DataFlow::Node sink, PointerArithmeticOperation pao, Operation a, Operation b
+where
+f = call.getTarget() and
+p = f.getAParameter() and
+p.getType().getUnderlyingType().(IntegralType).isSigned() and
+call.getArgument(p.getIndex()).getType().getUnderlyingType().(IntegralType).isUnsigned() and
+pao.getAnOperand() = sink.asExpr() and
+not guardedLesser(a, sink.asExpr()) and
+not guardedGreater(b, call.getArgument(p.getIndex())) and
+not call.getArgument(p.getIndex()).isConstant() and
+DataFlow::localFlow(DataFlow::parameterNode(p), sink)
+select call, "This call: $@  passes an unsigned int to a function that requires a signed int: $@. And then used in pointer arithmetic: $@", call, call.toString(), f, f.toString(), sink, sink.toString()