static bool packet_extra_vlan_len_allowed(const struct net_device *dev,
					  struct sk_buff *skb)
{
	/* Earlier code assumed this would be a VLAN pkt, double-check
	 * this now that we have the actual packet in hand. We can only
	 * do this check on Ethernet devices.
	 */
	if (unlikely(dev->type != ARPHRD_ETHER))
		return false;

	skb_reset_mac_header(skb);
	return likely(eth_hdr(skb)->h_proto == htons(ETH_P_8021Q));
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.