static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
			  int flags)
{
	struct sock *sk = sock->sk;
	struct sk_buff *skb;
	int copied, err;
	int vnet_hdr_len = 0;
	unsigned int origlen = 0;

	err = -EINVAL;
	if (flags & ~(MSG_PEEK|MSG_DONTWAIT|MSG_TRUNC|MSG_CMSG_COMPAT|MSG_ERRQUEUE))
		goto out;

#if 0
	/* What error should we return now? EUNATTACH? */
	if (pkt_sk(sk)->ifindex < 0)
		return -ENODEV;
#endif

	if (flags & MSG_ERRQUEUE) {
		err = sock_recv_errqueue(sk, msg, len,
					 SOL_PACKET, PACKET_TX_TIMESTAMP);
		goto out;
	}

	/*
	 *	Call the generic datagram receiver. This handles all sorts
	 *	of horrible races and re-entrancy so we can forget about it
	 *	in the protocol layers.
	 *
	 *	Now it will return ENETDOWN, if device have just gone down,
	 *	but then it will block.
	 */

	skb = skb_recv_datagram(sk, flags, flags & MSG_DONTWAIT, &err);

	/*
	 *	An error occurred so return it. Because skb_recv_datagram()
	 *	handles the blocking we don't see and worry about blocking
	 *	retries.
	 */

	if (skb == NULL)
		goto out;

	if (pkt_sk(sk)->pressure)
		packet_rcv_has_room(pkt_sk(sk), NULL);

	if (pkt_sk(sk)->has_vnet_hdr) {
		err = packet_rcv_vnet(msg, skb, &len);
		if (err)
			goto out_free;
		vnet_hdr_len = sizeof(struct virtio_net_hdr);
	}

	/* You lose any data beyond the buffer you gave. If it worries
	 * a user program they can ask the device for its MTU
	 * anyway.
	 */
	copied = skb->len;
	if (copied > len) {
		copied = len;
		msg->msg_flags |= MSG_TRUNC;
	}

	err = skb_copy_datagram_msg(skb, 0, msg, copied);
	if (err)
		goto out_free;

	if (sock->type != SOCK_PACKET) {
		struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;

		/* Original length was stored in sockaddr_ll fields */
		origlen = PACKET_SKB_CB(skb)->sa.origlen;
		sll->sll_family = AF_PACKET;
		sll->sll_protocol = skb->protocol;
	}

	sock_recv_ts_and_drops(msg, sk, skb);

	if (msg->msg_name) {
		/* If the address length field is there to be filled
		 * in, we fill it in now.
		 */
		if (sock->type == SOCK_PACKET) {
			__sockaddr_check_size(sizeof(struct sockaddr_pkt));
			msg->msg_namelen = sizeof(struct sockaddr_pkt);
		} else {
			struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;

			msg->msg_namelen = sll->sll_halen +
				offsetof(struct sockaddr_ll, sll_addr);
		}
		memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa,
		       msg->msg_namelen);
	}

	if (pkt_sk(sk)->auxdata) {
		struct tpacket_auxdata aux;

		aux.tp_status = TP_STATUS_USER;
		if (skb->ip_summed == CHECKSUM_PARTIAL)
			aux.tp_status |= TP_STATUS_CSUMNOTREADY;
		else if (skb->pkt_type != PACKET_OUTGOING &&
			 (skb->ip_summed == CHECKSUM_COMPLETE ||
			  skb_csum_unnecessary(skb)))
			aux.tp_status |= TP_STATUS_CSUM_VALID;

		aux.tp_len = origlen;
		aux.tp_snaplen = skb->len;
		aux.tp_mac = 0;
		aux.tp_net = skb_network_offset(skb);
		if (skb_vlan_tag_present(skb)) {
			aux.tp_vlan_tci = skb_vlan_tag_get(skb);
			aux.tp_vlan_tpid = ntohs(skb->vlan_proto);
			aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
		} else {
			aux.tp_vlan_tci = 0;
			aux.tp_vlan_tpid = 0;
		}
		put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
	}

	/*
	 *	Free or return the buffer as appropriate. Again this
	 *	hides all the races and re-entrancy issues from us.
	 */
	err = vnet_hdr_len + ((flags&MSG_TRUNC) ? skb->len : copied);

out_free:
	skb_free_datagram(sk, skb);
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.