Page History

struct buffer {
  size_t size;
  char bufferC[50];
} buff;

/* ... */

void func(const struct buffer *buf) {

  /* Assumes
   * Incorrectly assumes sizeof( struct buffer) =
   * sizeof( size_t) + 50 * sizeof( char) = 54buff.bufferC) 
   */
  struct buffer *buf_cpy = (struct buffer *)malloc(54(
    sizeof(size_t) + sizeof(buff.bufferC)
  );

  if (buf_cpy == NULL) {
    /* Handle malloc() error */
  }

  /*
   * With padding, sizeof(struct buffer) may be greater than
   * 54 sizeof(size_t) + sizeof(buff.bufferC), causing some data  
   * to be written outside the bounds 
   * of the memory allocated.
   */
  memcpy(buf_cpy, buf, sizeof(struct buffer));

  /* ... */

  free(buf_cpy);
}

enum {buffer_size = 50};

struct buffer {
  size_t size;
  char bufferC[buffer_size];
} buff;

/* ... */

void func(const struct buffer *buf) {

  struct buffer *buf_cpy = 
    (struct buffer *)malloc(sizeof(struct buffer));

  if (buf_cpy == NULL) {
    /* Handle malloc() error */
  }

  /* ... */

  memcpy(buf_cpy, buf, sizeof(struct buffer));

  /* ... */

  free(buf_cpy);
}