Function udp_input

freebsd/netinet/udp_usrreq.c:392–754

}

int
udp_input(struct mbuf **mp, int *offp, int proto)
{
	struct ip *ip;
	struct udphdr *uh;
	struct ifnet *ifp;
	struct inpcb *inp;
	uint16_t len, ip_len;
	struct inpcbinfo *pcbinfo;
	struct ip save_ip;
	struct sockaddr_in udp_in[2];
	struct mbuf *m;
	struct m_tag *fwd_tag;
	int cscov_partial, iphlen;

	m = *mp;
	iphlen = *offp;
	ifp = m->m_pkthdr.rcvif;
	*mp = NULL;
	UDPSTAT_INC(udps_ipackets);

	/*
	 * Strip IP options, if any; should skip this, make available to
	 * user, and use on returned packets, but we don't yet have a way to
	 * check the checksum with options still present.
	 */
	if (iphlen > sizeof (struct ip)) {
		ip_stripoptions(m);
		iphlen = sizeof(struct ip);
	}

	/*
	 * Get IP and UDP header together in first mbuf.
	 */
	if (m->m_len < iphlen + sizeof(struct udphdr)) {
		if ((m = m_pullup(m, iphlen + sizeof(struct udphdr))) == NULL) {
			UDPSTAT_INC(udps_hdrops);
			return (IPPROTO_DONE);
		}
	}
	ip = mtod(m, struct ip *);
	uh = (struct udphdr *)((caddr_t)ip + iphlen);
	cscov_partial = (proto == IPPROTO_UDPLITE) ? 1 : 0;

	/*
	 * Destination port of 0 is illegal, based on RFC768.
	 */
	if (uh->uh_dport == 0)
		goto badunlocked;

	/*
	 * Construct sockaddr format source address.  Stuff source address
	 * and datagram in user buffer.
	 */
	bzero(&udp_in[0], sizeof(struct sockaddr_in) * 2);
	udp_in[0].sin_len = sizeof(struct sockaddr_in);
	udp_in[0].sin_family = AF_INET;
	udp_in[0].sin_port = uh->uh_sport;