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The example below, is inspired by Dowd, assuming that the size of struct buffer is equal to the sizeof(size_t) + (sizeof(char) * 50), which (assuming sizeof(size_t) is 4 bytes) equals is 54 may be incorrect. The size of struct buffer may actually be a larger due to structure padding.

Code Block
struct buffer {
    size_t size;
    char buffer[50];
};

...

void func(struct buffer *buf) {

  struct buffer *buf_cpy = malloc((sizeof(size_t)+(sizeof(char)*50)));
  if (buf_cpy == NULL) {
    /* Handle malloc() error */
  }
  
  ...

  memcpy(buf_cpy,buf, sizeof(struct buffer)); /* May result in a small buffer overflow */
}