4.2 UDP

[RWS at MIT-XX.ARPA]

From:  Robert W. Scheifler <RWS at MIT-XX.ARPA>

My earlier UDP bug fixes were not completely wonderful.  Here is my final
rewrite.  In /sys/netinet/udp_usrreq.c in udp_output(), the code
	ui->ui_ulen = htons((u_short)ui->ui_len);
should be changed to
	ui->ui_len = htons((u_short)ui->ui_len);
	ui->ui_ulen = ui->ui_len;
and the code
	ui->ui_sum = in_cksum(m, sizeof (struct udpiphdr) + len)
should be changed to
	if (udpcksum) {
		if (!(ui->ui_sum = in_cksum(m, sizeof (struct udpiphdr) + len)))
			ui->ui_sum = -1;
	}
In udp_input(), the code
	if (udpcksum) {
		ui->ui_next = ui->ui_prev = 0;
		ui->ui_x1 = 0;
		ui->ui_len = htons((u_short)len);
		if (ui->ui_sum = in_cksum(m, len + sizeof (struct ip))) {
			udpstat.udps_badsum++;
			m_freem(m);
			return;
		}
	}
should be changed to
	if (udpcksum && ui->ui_sum) {
		ui->ui_next = ui->ui_prev = 0;
		ui->ui_x1 = 0;
		ui->ui_len = htons((u_short)len);
		if (in_cksum(m, len + sizeof (struct ip))) {
			udpstat.udps_badsum++;
			m_freem(m);
			return;
		}
	}
Then
	int	udpcksum;
can be changed to
	int	udpcksum = 1;
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