UnsafeReflectiveConstructionCast
Prefer `asSubclass` instead of casting the result of `newInstance`, to detect classes of incorrect type before invoking their constructors.This way, if the class is of the incorrect type,it will throw an exception before invoking its constructor.

Severity
WARNING
Tags
FragileCode
Has Fix?
REQUIRES_HUMAN_ATTENTION

The problem

Prefer asSubclass instead of casting the result of newInstance to detect classes of incorrect type before invoking their constructors. This way, if the class is of the incorrect type, it will throw an exception before invoking its constructor.

(Foo) Class.forName(someString).getDeclaredConstructor(...).newInstance(args);

Should be written as

Class.forName(someString).asSubclass(Foo.class).getDeclaredConstructor(...).newInstance();

This has caused issues in the past:

CVE-2014-7911 - http://seclists.org/fulldisclosure/2014/Nov/51

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("UnsafeReflectiveConstructionCast") to the enclosing element.


Negative examples

UnsafeReflectiveConstructionCastNegativeCases.java

/*
 * Copyright 2018 The Error Prone Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.errorprone.bugpatterns.testdata;

/**
 * Negative cases for {@link UnsafeReflectiveConstructionCast}.
 *
 * @author bhagwani@google.com (Sumit Bhagwani)
 */
public class UnsafeReflectiveConstructionCastNegativeCases {

  public String newInstanceDirectCall() throws Exception {
    return (String) Class.forName("java.lang.String").newInstance();
  }

  public String newInstanceDirectlyOnClassAndGetDeclaredConstructor() throws Exception {
    return (String) String.class.getDeclaredConstructor().newInstance();
  }

  public String newInstanceDirectlyOnClassAndNewInstance() throws Exception {
    return (String) String.class.newInstance();
  }

  public String invocationWithAsSubclass() throws Exception {
    return Class.forName("java.lang.String").asSubclass(String.class).newInstance();
  }

  public class Supplier<T> {
    public T get(String className) {
      try {
        return (T) Class.forName(className).getDeclaredConstructor().newInstance();
      } catch (ReflectiveOperationException e) {
        throw new IllegalStateException(e);
      }
    }
  }
}