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JNI dll crashing app after injection

jacapiwsko (72)
Hello, why my app crash after injecting this dll? I got this code from Visual Studio Debugger:
 
 
Unhandled exception at 0x00000000352B10CB in javaw.exe: 0xC0000005: Access violation reading location 0x0000000000000000.


This is my DLL code:
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// dllmain.cpp : Defines the entry point for the DLL application.
#include "pch.h"
#include "jni.h"
#include <iostream>

JavaVM* jvm;
JNIEnv* env;
HANDLE jvmHandle;
FARPROC func_JNI_GetCreatedJavaVMs;
JavaVMInitArgs vm_args;

void init() {
    AllocConsole();
    freopen_s((FILE**)stdout, "CONOUT$", "w", stdout);
    std::cout << "This works" << std::endl;
 
    typedef jint(JNICALL* GetCreatedJavaVMs)(JavaVM**, jsize, jsize*);
    GetCreatedJavaVMs jni_GetCreatedJavaVMs;
    jni_GetCreatedJavaVMs = (GetCreatedJavaVMs)GetProcAddress(GetModuleHandle(
        TEXT("jvm.dll")), "JNI_GetCreatedJavaVMs");

    std::cout << "CreatedJavaVMs: "<<jni_GetCreatedJavaVMs << std::endl;

    std::cout << "JVM load succeeded: Version ";
    jint ver = env->GetVersion();
    std::cout << ((ver >> 16) & 0x0f) << "." << (ver & 0x0f) << std::endl;




    //if (getEnvStat == JNI_EDETACHED)
    //{
    //     vm->AttachCurrentThread((void**)&env, NULL);
    // }

    /*if (env != nullptr)
    {
        //start
    }


    if (env->ExceptionCheck())
    {
        env->ExceptionDescribe();
    }

    vm->DetachCurrentThread();*/

}

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    init();
    return TRUE;
}
salem c (3685)
> freopen_s((FILE**)stdout, "CONOUT$", "w", stdout);
What's that cast?

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/freopen-s-wfreopen-s?view=vs-2019

Why isn't it
freopen_s(&stdout, "CONOUT$", "w", stdout);
jacapiwsko (72)
Thanks, will test It later.

Got this error:

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E0158	expression must be an lvalue or a function designator

Error	C2102	'&' requires l-value


Last edited on
salem c (3685)
jacapiwsko (72)
nope, are You sure crashes is caused by this cast?
 
 
freopen_s((FILE**)stdout, "CONOUT$", "w", stdout);
salem c (3685)
Are you?

> errno_t freopen( FILE** pFile, const char *path, const char *mode, FILE *stream );
The parameters have different levels of indirection.

Just papering over that fact with a cast doesn't create magic.
jacapiwsko (72)
Without console it crashing too. This error probably is caused by sth else (still dont know what is this).

Calling JNI functions crashing my app ;/

Fixed, "vm->AttachCurrentThread((void**)&env, NULL);" should be before calling any env functions
Last edited on
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