 int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 {
	u16 offset = sizeof(struct ipv6hdr);
 	unsigned int packet_len = skb_tail_pointer(skb) -
 		skb_network_header(skb);
 	int found_rhdr = 0;
 	*nexthdr = &ipv6_hdr(skb)->nexthdr;
 
 	while (offset <= packet_len) {
 		struct ipv6_opt_hdr *exthdr;
 
 		switch (**nexthdr) {
 
		case NEXTHDR_HOP:
			break;
		case NEXTHDR_ROUTING:
			found_rhdr = 1;
			break;
		case NEXTHDR_DEST:
#if IS_ENABLED(CONFIG_IPV6_MIP6)
			if (ipv6_find_tlv(skb, offset, IPV6_TLV_HAO) >= 0)
				break;
#endif
			if (found_rhdr)
				return offset;
			break;
		default:
			return offset;
		}

		if (offset + sizeof(struct ipv6_opt_hdr) > packet_len)
			return -EINVAL;
 
 		exthdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) +
 						 offset);
		offset += ipv6_optlen(exthdr);
 		*nexthdr = &exthdr->nexthdr;
 	}
 
	return -EINVAL;
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.