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Native methods are defined in Java and written in traditional languages such as C /and C++ [JNI 2006]. The added extensibility comes at the cost of flexibility and portability as because the code no longer conforms to the policies enforced by Java.

Non-Compliant Code Example

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, validating arguments passed to native code, validating return values, defensively copying mutable inputs, and sanitizing untrusted data. 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; consequently, 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.Security manager checks are not conducted in case of native method invocations. Additionally, as demonstrated in the non-compliant code example, it is easy to overlook proper input validation before the call. The doOperation method invokes the nativeOperation native method but fails on multiple validation angles. Also, the access specifier of the native method is public which raises risks associated with untrusted callers. (Note that native methods may even increase susceptibility to non-Java specific vulnerabilities, such as buffer overflows)

public final class NativeMethod {

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

  // wrapperWrapper method that does not perform any lacks security checks orand input validation
  public void doOperation(byte[] data, int offset, int len) {
    nativeOperation(data, offset, len);
  }
  
  static {
    	    System.loadLibrary("NativeMethodLib"); //load Load native library in static initializer of class
    System.loadLibrary("NativeMethodLib"); 
  }
}

Compliant Solution

This compliant solution defines a public wrapper that calls securityManagerCheck() which in turn performs routine permission checks to determine if the succeeding operations can continue. This is followed by input range checking and creation of a declares the native method private. The doOperation() wrapper method checks permissions, creates a defensive copy of the mutable input array , data. Finally the nativeOperation method is called with sanitized inputs. Ensure data, and checks the ranges of the arguments. The nativeOperation() method is consequently called with secure inputs. Note that the validation checks must produce outputs that are coherent with conform to the input requirements of the native implementations/librariesmethods.

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

References

Exceptions

JN100-J-EX0: Native methods that do not require security manager checks, validation of arguments or return values, or defensive copying of mutable inputs (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 exploit inherent vulnerabilities such as buffer overflows in native libraries.

Automated Detection

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

Related Guidelines

Bibliography

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Image Added Image Added Image AddedSecure coding in Java http://java.sun.com/security/seccodeguide.html^{Image Removed}
Java Native Interface: Programmer's Guide and Specification
Java Network Security, 2.2.3 Interfaces and Architectures