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Wiki Markup Native methods are defined in Java and written in traditional languages such as C and C++ \[ [JNI 2006|AA. Bibliography#JNI 06]\]. The added extensibility comes at the cost of flexibility and portability as because the code no longer conforms to the policies enforced by Java. In the past, native methods were used for performing platform specific operations, interfacing with legacy library code and improving program performance \[[Bloch 2008|AA. Bibliography#Bloch 08]\]. Although this is no longer completely true --- because of poor portability, security, and (ironically) performance issues --- native code is still used to interface with legacy code.Native methods have been used for performing platform-specific operations, interfacing with legacy library code, and improving program performance [Bloch 2008].

Defining a wrapper method facilitates installing appropriate security manager checks, performing input validation before passing the arguments to the native code or when obtaining validating arguments passed to native code, validating return values, defensively copying mutable inputs, and sanitizing untrusted data. As a result Consequently, every native method must be private , and must be invoked only by a wrapper method.

Noncompliant Code Example

In this noncompliant code example, the nativeOperation() method is both native and public; for that reasonconsequently, untrusted callers may invoke it. Native method invocations bypass security manager checks.

This example includes the doOperation() wrapper method, which invokes the nativeOperation() native method but fails to provide input validation or security checks.

public final class NativeMethod {

  // publicPublic native method
  public native void nativeOperation(byte[] data, int offset, int len);

  // wrapperWrapper method that lacks security checks and input validation
  public void doOperation(byte[] data, int offset, int len) {
    nativeOperation(data, offset, len);
  }
  
  static {
    // loadLoad native library in static initializer of class
    System.loadLibrary("NativeMethodLib"); 
  }
}

Compliant Solution

This compliant solution declares the native method private. The doOperation() wrapper method performs routine permission checking to determine whether the succeeding operations are permitted to continue. The method also checks permissions, creates a defensive copy of the mutable input array data as well as performs range checking , and checks the ranges of the arguments. The nativeOperation() method is consequently called with safe secure inputs. Note that the validation checks must produce outputs that conform to the input requirements of the native methods.

public final class NativeMethodWrapper {

  // privatePrivate native method
  private native void nativeOperation(byte[] data, int offset, int len);

  // wrapperWrapper method performs SecurityManager and input validation checks
  public void doOperation(byte[] data, int offset, int len) {
    // permissionPermission needed to invoke native method
    securityManagerCheck();

    if (data == null) {
      throw new NullPointerException();
    }

    // copyCopy mutable input
    data = data.clone();

    // validateValidate input
    if ((offset < 0) || (len < 0) || (offset > (data.length - len))) {
      throw new IllegalArgumentException();
    }

    nativeOperation(data, offset, len);
  }

  static {
    // loadLoad native library in static initializer of class
    System.loadLibrary("NativeMethodLib"); 
  }
}

Exceptions

SEC08JN100-J-EX00EX0: Native methods that do not require security manager checks, validation of arguments or return values, defensively or defensive copying of mutable inputs do not need to be wrapped — (for example, the standard C function int rand(void)) do not need to be wrapped.

Risk Assessment

Failure to define wrappers around native methods can allow unprivileged callers to invoke them and consequently exploit inherent vulnerabilities such as those resulting from invalid inputsbuffer overflows in native libraries.

Automated Detection

...

Automated detection is not feasible in the fully general case. However, an approach similar to Design Fragments \ [[Fairbanks 07|AA. Bibliography#Fairbanks 07]\] could assist both programmers and static analysis tools.Fairbanks 2007] could assist both programmers and static analysis tools.

Tool	Version	Checker	Description
Parasoft Jtest	Include Page Parasoft_V Parasoft_V	CERT.JNI00.NATIW	Use wrapper methods to secure native methods

Related Guidelines

Bibliography

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Image Added Image Added Image AddedSEC07-J. Call the superclass's getPermissions method when writing a custom class loader      14. Platform Security (SEC)      15. Runtime Environment (ENV)