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Full Discussion: Linux read and write external memory.
Top Forums Programming Linux read and write external memory. Post 302506626 by lilezek on Monday 21st of March 2011 05:55:46 PM
Old 03-21-2011
I'm getting in trouble trying to do this. Firstly, a c++ problem:

This is on memory.cpp (it got compiled):
Code:
template<class T>
bool peekValue(T * value, char * offset, pid_t pid)
{
    // Get /proc/$pid/mem
    char mem_file_name[255];
    sprintf(mem_file_name, "/proc/%d/mem", pid);
    // Opening /proc/$pid/mem
    FILE * mem_fd = fopen(mem_file_name, "r");
    // Tracing the app.
    if (ptrace(PTRACE_ATTACH, pid, NULL, NULL) == -1)
        return false;
    // Force it to wait
    if (waitpid(pid, NULL, 0) == -1)
    {
        ptrace(PTRACE_DETACH, pid, NULL, NULL);
        return false;
    }
    // Move pointer to offset.
    fseek(mem_fd, (long int)offset, SEEK_SET);
    // Read from memory.
    fread(value, 1, sizeof(T), mem_fd);
    // End petrace.
    ptrace(PTRACE_DETACH, pid, NULL, NULL);
    return true;
}

and in main.cpp:

Code:
many includes after:

int main(int argc, char ** argv)
{
    programinfo pnfo;
    int m;
    long int offset = 0;

    ...
    cout << "Enter the PID of the program you want to hack" << endl;
    cin >> pnfo.pid;
    cout << "Enter the pointer to int you want to read" << endl;
    cin >> offset;
    pnfo.mem_blocks = getMemoryMemblocks(pnfo.pid);
    peekValue<int>(&m, (char*)offset, pnfo.pid);
    cout << m << endl;
    return 0;
}

Got error (from linker):
Code:
/home/***/proyectos/xeat_engine/main.cpp|22|undefined reference to `bool peekValue<int>(int*, char*, int)'|

So I changed it to:
Code:
/*template<class T>*/
bool peekValue(int * value, char * offset, pid_t pid)
{
    // Get /proc/$pid/mem
    char mem_file_name[255];
    sprintf(mem_file_name, "/proc/%d/mem", pid);
    // Opening /proc/$pid/mem
    FILE * mem_fd = fopen(mem_file_name, "r");
    // Tracing the app. This fails:
    if (ptrace(PTRACE_ATTACH, pid, NULL, NULL) == -1)
        return false;
    // Force it to wait
    if (waitpid(pid, NULL, 0) == -1)
    {
        ptrace(PTRACE_DETACH, pid, NULL, NULL);
        return false;
    }
    // Move pointer to offset.
    fseek(mem_fd, (long int)offset, SEEK_SET);
    // Read from memory.
    fread(value, 1, sizeof(int), mem_fd);
    // End petrace.
    ptrace(PTRACE_DETACH, pid, NULL, NULL);
    return true;
}

And:

Code:
many includes after:

int main(int argc, char ** argv)
{
    programinfo pnfo;
    int m;
    long int offset = 0;

    ...
    cout << "Enter the PID of the program you want to hack" << endl;
    cin >> pnfo.pid;
    cout << "Enter the pointer to int you want to read" << endl;
    cin >> offset;
    pnfo.mem_blocks = getMemoryMemblocks(pnfo.pid);
    peekValue/*<int>*/(&m, (char*)offset, pnfo.pid);
    cout << m << endl;
    return 0;
}

It "works". Any idea about this?

The second question is that it "works". It means the function got executed but it doesn't do its job. It fails on ptrace attachment. I'm trying to ptrace pid 6000, which is the pid of neverball (a videogame of a ball), but it returns -1.

What are the conditions to do a ptrace? Any idea?

Thank you for read.

---------- Post updated at 04:55 PM ---------- Previous update was at 11:09 AM ----------

I've solved the above problem (super user privileges).

Now I'm wonder a thing. Is to write in /proc/pid/mem possible?
Last edited by lilezek; 03-21-2011 at 01:35 PM..
 

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