int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
		   int proto)
{
	struct sock *sk;
	struct udphdr *uh = udp_hdr(skb);
	unsigned short ulen;
	struct rtable *rt = (struct rtable*)skb->dst;
	__be32 saddr = ip_hdr(skb)->saddr;
	__be32 daddr = ip_hdr(skb)->daddr;

	/*
	 *  Validate the packet.
	 */
	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
		goto drop;		/* No space for header. */

	ulen = ntohs(uh->len);
	if (ulen > skb->len)
		goto short_packet;

	if (proto == IPPROTO_UDP) {
		/* UDP validates ulen. */
		if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
			goto short_packet;
		uh = udp_hdr(skb);
	}

	if (udp4_csum_init(skb, uh, proto))
		goto csum_error;

	if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
		return __udp4_lib_mcast_deliver(skb, uh, saddr, daddr, udptable);

	sk = __udp4_lib_lookup(saddr, uh->source, daddr, uh->dest,
			       skb->dev->ifindex, udptable        );

	if (sk != NULL) {
		int ret = udp_queue_rcv_skb(sk, skb);
		sock_put(sk);

		/* a return value > 0 means to resubmit the input, but
		 * it wants the return to be -protocol, or 0
		 */
		if (ret > 0)
			return -ret;
		return 0;
	}

	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
		goto drop;
	nf_reset(skb);

	/* No socket. Drop packet silently, if checksum is wrong */
	if (udp_lib_checksum_complete(skb))
		goto csum_error;

	UDP_INC_STATS_BH(UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);

	/*
	 * Hmm.  We got an UDP packet to a port to which we
	 * don't wanna listen.  Ignore it.
	 */
	kfree_skb(skb);
	return 0;

short_packet:
	LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: short packet: From %u.%u.%u.%u:%u %d/%d to %u.%u.%u.%u:%u\n",
		       proto == IPPROTO_UDPLITE ? "-Lite" : "",
		       NIPQUAD(saddr),
		       ntohs(uh->source),
		       ulen,
		       skb->len,
		       NIPQUAD(daddr),
		       ntohs(uh->dest));
	goto drop;

csum_error:
	/*
	 * RFC1122: OK.  Discards the bad packet silently (as far as
	 * the network is concerned, anyway) as per 4.1.3.4 (MUST).
	 */
	LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: bad checksum. From %d.%d.%d.%d:%d to %d.%d.%d.%d:%d ulen %d\n",
		       proto == IPPROTO_UDPLITE ? "-Lite" : "",
		       NIPQUAD(saddr),
		       ntohs(uh->source),
		       NIPQUAD(daddr),
		       ntohs(uh->dest),
		       ulen);
drop:
	UDP_INC_STATS_BH(UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
	kfree_skb(skb);
	return 0;
}
int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
		   int proto)
{
	struct sock *sk;
	struct udphdr *uh = udp_hdr(skb);
	unsigned short ulen;
	struct rtable *rt = (struct rtable*)skb->dst;
	__be32 saddr = ip_hdr(skb)->saddr;
	__be32 daddr = ip_hdr(skb)->daddr;

	 
	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
		goto drop;		 

	ulen = ntohs(uh->len);
	if (ulen > skb->len)
		goto short_packet;

	if (proto == IPPROTO_UDP) {
		 
		if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
			goto short_packet;
		uh = udp_hdr(skb);
	}

	if (udp4_csum_init(skb, uh, proto))
		goto csum_error;

	if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
		return __udp4_lib_mcast_deliver(skb, uh, saddr, daddr, udptable);

	sk = __udp4_lib_lookup(saddr, uh->source, daddr, uh->dest,
			       skb->dev->ifindex, udptable        );

	if (sk != NULL) {
		int ret = udp_queue_rcv_skb(sk, skb);
		sock_put(sk);

		 
		if (ret > 0)
			return -ret;
		return 0;
	}

	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
		goto drop;
	nf_reset(skb);

	 
	if (udp_lib_checksum_complete(skb))
		goto csum_error;

	UDP_INC_STATS_BH(UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);

	 
	kfree_skb(skb);
	return 0;

short_packet:
	LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: short packet: From %u.%u.%u.%u:%u %d/%d to %u.%u.%u.%u:%u\n",
		       proto == IPPROTO_UDPLITE ? "-Lite" : "",
		       NIPQUAD(saddr),
		       ntohs(uh->source),
		       ulen,
		       skb->len,
		       NIPQUAD(daddr),
		       ntohs(uh->dest));
	goto drop;

csum_error:
	 
	LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: bad checksum. From %d.%d.%d.%d:%d to %d.%d.%d.%d:%d ulen %d\n",
		       proto == IPPROTO_UDPLITE ? "-Lite" : "",
		       NIPQUAD(saddr),
		       ntohs(uh->source),
		       NIPQUAD(daddr),
		       ntohs(uh->dest),
		       ulen);
drop:
	UDP_INC_STATS_BH(UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
	kfree_skb(skb);
	return 0;
}