Sysmalloc: Assertion

Question

main: malloc.c:2405: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || ((unsigned long) (old_size) >= MINSIZE && prev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed.

When trying to produce a doubly linked list where the user can only add to the head or tail, I end up getting the lovely abortion message at the top.

I have used gdb to narrow it down to what function it is that is causing this, but I really don't know what I'm doing wrong. It allocates the first node, then after that, it throws me the error.
The function is as follows:

data* initD(){
    data *D = NULL;

    D = malloc(sizeof(data*));
    if (!D){
        printf("Error in allocation of data\n");
        exit(0);
    }

    D->head = NULL;
    D->tail = NULL;
    D->next = NULL;
    D->prev = NULL;
    D->val = -1;

    return D; 
}

Answer 1

You're writing outside of your allocated buffer.

That's because your malloc call passes the wrong size:

D = malloc(sizeof(data*));  // allocate memory for a single pointer

should be:

D = malloc(sizeof(data));  // allocate memory for a whole struct

But really,

D = malloc(sizeof *D);  // allocate memory for whatever D points to

is best because then you don't need to see the declaration of D to check that this line is correct.