Overwrite Function
For example, we have an android application that has this class.
public class my_activity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_activity);
while (true){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
fun(50,30);
}
}
void fun(int x , int y ){
Log.d("Sum" , String.valueOf(x+y));
}
}
We will overwrite fun function that exist in onCreate event handler with this script below.
script.js
console.log("Script loaded successfully ");
Java.perform(function x() { // Silently fails without the sleep from the python code
console.log("Inside java perform function");
// Get a wrapper for our class
var my_class = Java.use("com.example.a11x256.frida_test.my_activity");
// Replace the original implmenetation of the function `fun` with our custom function
my_class.fun.implementation = function(x, y) {
// Print the original arguments
console.log("original call: fun(" + x + ", " + y + ")");
// Call the original implementation of `fun` with args (2,5)
var ret_value = this.fun(2, 5);
return ret_value;
}
});
script.py
import frida
import time
device = frida.get_usb_device(5)
pid = device.spawn(["com.example.a11x256.frida_test"])
print pid
device.resume(pid)
time.sleep(3) # without it Java.perform silently fail
session = device.attach(pid)
script = session.create_script(open('script.js').read())
script.load()
# prevent the python script from terminating
raw_input()
This does not work very well because the function does not return any value.