static bool ieee80211_validate_radiotap_len(struct sk_buff *skb)
{
	struct ieee80211_radiotap_header *rthdr =
		(struct ieee80211_radiotap_header *)skb->data;

	/* check for not even having the fixed radiotap header part */
	if (unlikely(skb->len < sizeof(struct ieee80211_radiotap_header)))
		return false; /* too short to be possibly valid */

	/* is it a header version we can trust to find length from? */
	if (unlikely(rthdr->it_version))
		return false; /* only version 0 is supported */

	/* does the skb contain enough to deliver on the alleged length? */
	if (unlikely(skb->len < ieee80211_get_radiotap_len(skb->data)))
		return false; /* skb too short for claimed rt header extent */

	return true;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.