bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
		      bool *fragstolen, int *delta_truesize)
{
	int i, delta, len = from->len;

	*fragstolen = false;

	if (skb_cloned(to))
		return false;

	if (len <= skb_tailroom(to)) {
		BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
		*delta_truesize = 0;
		return true;
	}

	if (skb_has_frag_list(to) || skb_has_frag_list(from))
		return false;

	if (skb_headlen(from) != 0) {
		struct page *page;
		unsigned int offset;

		if (skb_shinfo(to)->nr_frags +
		    skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
			return false;

		if (skb_head_is_locked(from))
			return false;

		delta = from->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));

		page = virt_to_head_page(from->head);
		offset = from->data - (unsigned char *)page_address(page);

		skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
				   page, offset, skb_headlen(from));
		*fragstolen = true;
	} else {
		if (skb_shinfo(to)->nr_frags +
		    skb_shinfo(from)->nr_frags > MAX_SKB_FRAGS)
			return false;

		delta = from->truesize - SKB_TRUESIZE(skb_end_offset(from));
	}

	WARN_ON_ONCE(delta < len);

	memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
	       skb_shinfo(from)->frags,
	       skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
	skb_shinfo(to)->nr_frags += skb_shinfo(from)->nr_frags;

	if (!skb_cloned(from))
		skb_shinfo(from)->nr_frags = 0;

	/* if the skb is not cloned this does nothing
	 * since we set nr_frags to 0.
	 */
	for (i = 0; i < skb_shinfo(from)->nr_frags; i++)
		skb_frag_ref(from, i);

	to->truesize += delta;
	to->len += len;
	to->data_len += len;

	*delta_truesize = delta;
	return true;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.