static int skb_checksum_setup_ip(struct sk_buff *skb, bool recalculate)
{
	unsigned int off;
	bool fragment;
	int err;

	fragment = false;

	err = skb_maybe_pull_tail(skb,
				  sizeof(struct iphdr),
				  MAX_IP_HDR_LEN);
	if (err < 0)
		goto out;

	if (ip_hdr(skb)->frag_off & htons(IP_OFFSET | IP_MF))
		fragment = true;

	off = ip_hdrlen(skb);

	err = -EPROTO;

	if (fragment)
		goto out;

	switch (ip_hdr(skb)->protocol) {
	case IPPROTO_TCP:
		err = skb_maybe_pull_tail(skb,
					  off + sizeof(struct tcphdr),
					  MAX_IP_HDR_LEN);
		if (err < 0)
			goto out;

		if (!skb_partial_csum_set(skb, off,
					  offsetof(struct tcphdr, check))) {
			err = -EPROTO;
			goto out;
		}

		if (recalculate)
			tcp_hdr(skb)->check =
				~csum_tcpudp_magic(ip_hdr(skb)->saddr,
						   ip_hdr(skb)->daddr,
						   skb->len - off,
						   IPPROTO_TCP, 0);
		break;
	case IPPROTO_UDP:
		err = skb_maybe_pull_tail(skb,
					  off + sizeof(struct udphdr),
					  MAX_IP_HDR_LEN);
		if (err < 0)
			goto out;

		if (!skb_partial_csum_set(skb, off,
					  offsetof(struct udphdr, check))) {
			err = -EPROTO;
			goto out;
		}

		if (recalculate)
			udp_hdr(skb)->check =
				~csum_tcpudp_magic(ip_hdr(skb)->saddr,
						   ip_hdr(skb)->daddr,
						   skb->len - off,
						   IPPROTO_UDP, 0);
		break;
	default:
		goto out;
	}

	err = 0;

out:
	return err;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.