int (*side_one[MATRIX][MATRIX])[MATRIX] = { { white_l1, white_l2, white_l3 }, { white_m1, white_m2, white_m3 }, { white_r1, white_r2, white_r3 } };

fillit((*side_one[MATRIX][MATRIX])[MATRIX]);

gcc -O4 test.c -o test -s
test.c: In function ‘fillit':
test.c:63:16: warning: assignment to ‘int *' from ‘int' makes pointer from integer without a cast [-Wint-conversion]
    *side[s][t] = randval;
                ^
test.c: In function ‘main':
test.c:457:40: warning: passing argument 1 of ‘fillit' makes pointer from integer without a cast [-Wint-conversion]
      fillit((*side_one[MATRIX][MATRIX])[MATRIX]);
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
test.c:53:19: note: expected ‘int * (*)[1000][1000]' but argument is of type ‘int'
 void fillit(int *(side[MATRIX][MATRIX])[MATRIX]){
             ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

void fillit(int *(side[MATRIX][MATRIX])[MATRIX]){
  int r, s, t, randval;

  for (r = 0; side[r] != 0; r++){     
     for (s = 0; s < MATRIX; s++){
    FILE *f;
    for (t = 0; t < MATRIX; t++) {
        f = fopen("/dev/urandom", "r");
        fread(&side, sizeof(randval), 1, f);
        if (side[s][t] != NULL){
            *side[s][t] = randval;
        }
        fclose(f);
    }
     }
   }
}