static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
			   bool *writable, kvm_pfn_t *pfn)
{
	struct page *page[1];
	int npages = 0;

	might_sleep();

	if (writable)
		*writable = write_fault;

	if (async) {
		down_read(&current->mm->mmap_sem);
		npages = get_user_page_nowait(addr, write_fault, page);
		up_read(&current->mm->mmap_sem);
	} else {
		unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;

		if (write_fault)
			flags |= FOLL_WRITE;

		npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
						   page, flags);
	}
	if (npages != 1)
		return npages;

	/* map read fault as writable if possible */
	if (unlikely(!write_fault) && writable) {
		struct page *wpage[1];

		npages = __get_user_pages_fast(addr, 1, 1, wpage);
		if (npages == 1) {
			*writable = true;
			put_page(page[0]);
			page[0] = wpage[0];
		}

		npages = 1;
	}
	*pfn = page_to_pfn(page[0]);
	return npages;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.