Add sun-misc-Unsafe-bad-array-offset.ql

Author: Marcono1234

codeql-custom-queries-java/queries/likely-bugs/sun-misc-Unsafe-bad-array-offset.ql

@@ -0,0 +1,34 @@
+/**
+ * Finds usage of `sun.misc.Unsafe` methods with arrays as argument where the
+ * 'offset' argument is not based on `Unsafe.ARRAY_..._BASE_OFFSET`. This most likely
+ * means that the code is by accident either reading or overwriting the header value
+ * at the start of the array object, which could corrupt it.
+ *
+ * @kind problem
+ * @id todo
+ */
+
+import java
+
+from MethodAccess unsafeCall, Method unsafeMethod, int arrayArgIndex, Expr badOffsetArg
+where
+  unsafeCall.getMethod() = unsafeMethod and
+  unsafeMethod.getDeclaringType().hasQualifiedName("sun.misc", "Unsafe") and
+  unsafeCall.getArgument(arrayArgIndex).getType() instanceof Array and
+  // For all existing `Unsafe` reading and writing methods there is first the `Object` parameter
+  // and then directly afterwards the `long` 'offset' parameter
+  unsafeMethod.getParameterType(arrayArgIndex + 1).hasName("long") and
+  badOffsetArg = unsafeCall.getArgument(arrayArgIndex + 1) and
+  (
+    // If it is a constant, then it is not based on `Unsafe.ARRAY_..._BASE_OFFSET` because those
+    // values are currently not compile time constants in the `Unsafe` implementation
+    badOffsetArg instanceof CompileTimeConstantExpr
+    or
+    // Or variable where all assigned values are constant (and therefore not based on `Unsafe.ARRAY_..._BASE_OFFSET`)
+    // Require that `v.getInitializer()` exists to ignore variables with implicit assigned value, e.g. method parameters
+    // (TODO: This is not completely correct because this excludes local variables which are initalized by a separate assignment)
+    exists(Variable v | v = badOffsetArg.(RValue).getVariable() and exists(v.getInitializer()) |
+      forex(Expr e | e = v.getAnAssignedValue() | e instanceof CompileTimeConstantExpr)
+    )
+  )
+select badOffsetArg, "'offset' argument is missing base offset for array"