Method with argument of type array of array cannot be instrumented

[histausse]

Hello,
I run into a problem while trying to instrument methods that take an array of array of byte as argument. For exemple:

package com.example.testclassloader;

public class TestA {
    public static int array_of_array(byte[][] arrays) {
        int size = 0;
        for (byte[] arr: arrays) {
            size += arr.length;
        }
        return size;
    }
}

[Android Emulator 5554::TestClassLoader ]-> Java.performNow(() => { })
[Android Emulator 5554::TestClassLoader ]-> TestA =  Java.use("com.example.testclassloader.TestA")
"<class: com.example.testclassloader.TestA>"
[Android Emulator 5554::TestClassLoader ]-> method = TestA.array_of_array
function
[Android Emulator 5554::TestClassLoader ]-> method.argumentTypes
[
    {
        "className": "[[B",
        "defaultValue": "0x0",
        "name": "[[B",
        "size": 1,
        "type": "pointer"
    }
]
[Android Emulator 5554::TestClassLoader ]-> method.overload('[[B').implementation = function(arrays) { s =
 method(arrays); console.log(s); return s; };
function

# after triggering the method in the app:

[Android Emulator 5554::TestClassLoader ]-> Process crashed: java.lang.ClassNotFoundException: Didn't find class "[L[B;" on path: DexPathList[[dex file "/data/data/com.example.testclassloader/code_cache/.overlay/base.apk/classes3.dex", zip file "/data/app/~~NRqmDlxjA4t3ccEvxe4Qlw==/com.example.testclassloader-JhUO40ypsrxE2AIa8f1k4A==/base.apk"],nativeLibraryDirectories=[/data/app/~~NRqmDlxjA4t3ccEvxe4Qlw==/com.example.testclassloader-JhUO40ypsrxE2AIa8f1k4A==/lib/x86_64, /system/lib64, /system_ext/lib64]]

I believe the issue comes from here:

frida-java-bridge/lib/types.js

Line 480 in 1e23abb

const internalTypeName = '[L' + elementTypeName.replace(/\./g, '/') + ';';

I think something like this could be a rough solution, but I did not manage to get frida to use patched version of frida-java-bridge:

diff --git a/lib/types.js b/lib/types.js
index 6a0f977..9b8d91f 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -477,7 +477,13 @@ function getArrayType (typeName, unbox, factory) {
       }

       // The type name we get is not always the correct representation of the type so we make it so here.
-      const internalTypeName = '[L' + elementTypeName.replace(/\./g, '/') + ';';
+      let internalElementTypeName = '';
+      if (elementTypeName.replace[0] === '[') {
+        internalElementTypeName = elementTypeName.replace(/\./g, '/');
+      } else {
+        internalElementTypeName = 'L' + elementTypeName.replace(/\./g, '/') + ';';
+      }
+      const internalTypeName = '[' + internalElementTypeName;
       try {
         result.$w = factory.cast(arr, factory.use(internalTypeName), owned);
       } catch (e) {

PS: Is there some documentation for running a patched java-bridge? I tried https://github.com/frida/frida-tools?tab=readme-ov-file#loading-your-custom-frida-java-bridge and failled

[WanQingGit]

I fixed the problem that the jni type name was wrong for arrays of type primary. Here's my fix

https://zhuanlan.zhihu.com/p/696631835

[WanQingGit]

function makeBaseJniObjectTypeName(typeName) {
if (typeName.length === 1)
return typeName
let convertType = typeName.replace(/./g, '/')
if (convertType[0] !== 'L'){
convertType = 'L' + convertType +';'
}
return convertType
}

function makeJniObjectTypeName(typeName) {
let arrayCount = 0;
while (typeName[arrayCount] === '[') {
arrayCount += 1;
}
if (typeName.length === arrayCount + 1) {
return typeName
}
if (arrayCount > 0) {
const baseType = makeBaseJniObjectTypeName(typeName.slice(arrayCount));
return "[".repeat(arrayCount) + baseType;
}
return makeBaseJniObjectTypeName(typeName);
}

  // const internalTypeName = '[L' + elementTypeName.replace(/\./g, '/') + ';';
  const internalTypeName = '[' + makeJniObjectTypeName(elementTypeName);