GNU buffer overflow using malloc

问题

I am running in a loop the following function:

int* rpermute(int n)
{
    int* a = malloc(n * sizeof(int));
    int  k;

    for (k = 0; k < n; k++)
    {
       a[k] = k;
    }

    for (k = n - 1; k > 0; k--)
    {
       int j    = rand() % (k + 1);
       int temp = a[j];
       a[j]     = a[k];
       a[k]     = temp;
   }

   return a;
}

If I set a new int variable in my code every variable is changing, I assume it is a buffer overflow problem.

Running the valgrind i get the following:

==4459== 73,036 bytes in 19 blocks are definitely lost in loss record 1 of 1

==4459==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)

==4459==    by 0x402CFB: rpermute (in /home/giwrgos/Desktop/crowdv22/crowd_evacuation)

==4459==    by 0x403378: main (in /home/giwrgos/Desktop/crowdv22/crowd_evacuation)

I use linux through the virtualbox but I have set enough storage and ram, what should I do?

回答1:

EDIT: See poster's comment below, the problem is not in this code after all.

You should simply free() the memory allocated in and returned by rpermute(). This must be done in the code from where you call rpermute(), once you're done with this array.

I understand that you regenerate this array for differing int values (the n parameter of rpermute()). Perhaps you simply assign a new output to the array you keep:

int* array;
...
array = rpermute(100);

// Some time later.
array = rpermute(200);  // Previous array memory is leaking.

You should do instead:

free(array);
array = rpermute(200);

Note that this is not a 'buffer over flow', but a memory leak instead. I checked you code for buffer overflow: index of a points outside it, but this seemed to be ok in both loops.

来源：https://stackoverflow.com/questions/20922765/gnu-buffer-overflow-using-malloc

标签

malloc

overflow

buffer

gnu