static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
{
	int err;
	u8 nexthdr;
	unsigned int off;
	unsigned int len;
	bool fragment;
	bool done;

	fragment = false;
	done = false;

	off = sizeof(struct ipv6hdr);

	err = skb_maybe_pull_tail(skb, off, MAX_IPV6_HDR_LEN);
	if (err < 0)
		goto out;

	nexthdr = ipv6_hdr(skb)->nexthdr;

	len = sizeof(struct ipv6hdr) + ntohs(ipv6_hdr(skb)->payload_len);
	while (off <= len && !done) {
		switch (nexthdr) {
		case IPPROTO_DSTOPTS:
		case IPPROTO_HOPOPTS:
		case IPPROTO_ROUTING: {
			struct ipv6_opt_hdr *hp;

			err = skb_maybe_pull_tail(skb,
						  off +
						  sizeof(struct ipv6_opt_hdr),
						  MAX_IPV6_HDR_LEN);
			if (err < 0)
				goto out;

			hp = OPT_HDR(struct ipv6_opt_hdr, skb, off);
			nexthdr = hp->nexthdr;
			off += ipv6_optlen(hp);
			break;
		}
		case IPPROTO_AH: {
			struct ip_auth_hdr *hp;

			err = skb_maybe_pull_tail(skb,
						  off +
						  sizeof(struct ip_auth_hdr),
						  MAX_IPV6_HDR_LEN);
			if (err < 0)
				goto out;

			hp = OPT_HDR(struct ip_auth_hdr, skb, off);
			nexthdr = hp->nexthdr;
			off += ipv6_authlen(hp);
			break;
		}
		case IPPROTO_FRAGMENT: {
			struct frag_hdr *hp;

			err = skb_maybe_pull_tail(skb,
						  off +
						  sizeof(struct frag_hdr),
						  MAX_IPV6_HDR_LEN);
			if (err < 0)
				goto out;

			hp = OPT_HDR(struct frag_hdr, skb, off);

			if (hp->frag_off & htons(IP6_OFFSET | IP6_MF))
				fragment = true;

			nexthdr = hp->nexthdr;
			off += sizeof(struct frag_hdr);
			break;
		}
		default:
			done = true;
			break;
		}
	}

	err = -EPROTO;

	if (!done || fragment)
		goto out;

	switch (nexthdr) {
	case IPPROTO_TCP:
		err = skb_maybe_pull_tail(skb,
					  off + sizeof(struct tcphdr),
					  MAX_IPV6_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_ipv6_magic(&ipv6_hdr(skb)->saddr,
						 &ipv6_hdr(skb)->daddr,
						 skb->len - off,
						 IPPROTO_TCP, 0);
		break;
	case IPPROTO_UDP:
		err = skb_maybe_pull_tail(skb,
					  off + sizeof(struct udphdr),
					  MAX_IPV6_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_ipv6_magic(&ipv6_hdr(skb)->saddr,
						 &ipv6_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.