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Wiki MarkupNative methods are defined in Java and written in traditional languages such as C and C++ \ [[JNI 06|AA. Java References#JNI 06]\]). The added extensibility comes at the cost of flexibility and portability as the code no longer conforms to the policies enforced by Java. In the past, native method were used for performing platform specific operations, interfacing with legacy library code and improving program performance \[[Bloch 08|AA. Java References#Bloch 08]\]. Although this is not completely true in present times (due to poor portability, safety and quite ironically, performance issues), they are still used to interface with legacy codeJNI 2006]. The added extensibility comes at the cost of flexibility and portability because the code no longer conforms to the policies enforced by Java. 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 codevalidating arguments passed to native code, validating return values, defensively copying mutable inputs and sanitizing user supplied input, 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 Security manager checks are not conducted automatically in case of native method invocations. Additionally, as demonstrated in the noncompliant code example, it is easy to overlook proper input validation before the call. The doOperation() method invokes the nativeOperation() native method but fails to provide adequate input validation . Also, the access specifier of the native method is public which raises risks associated with untrusted callers. or security checks.

public final class NativeMethod {

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

  // wrapperWrapper method that does not perform anylacks security checks orand 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 makes declares the actual native method private and 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 the creation of a . The doOperation() wrapper method checks permissions, creates a defensive copy of the mutable input array data, data and input range checking and checks the ranges of the parametersarguments. Finally the The nativeOperation() method is consequently called with sanitized secure inputs. Ensure 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 {
    // loadLoad native library in static initializer of class
    System.loadLibrary("NativeMethodLib"); 
  }
}

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 those resulting from invalid input validationbuffer overflows in native libraries.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

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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 AddedDirect Use of Unsafe JNI"SEC10-J. Call the superclass's getPermissions method when writing a custom class loader      02. Platform Security (SEC)      SEC31-J. Guard doPrivileged blocks against untrusted invocations