From: Wei Yongjun <[EMAIL PROTECTED]>
Date: Thu, 23 Feb 2006 16:03:18 -0500
> IPv4 UDP does not discard the datagram with invalid checksum. UDP can
> validate UDP checksums correctly only when socket filtering instructions
> is set. If socket filtering instructions is not set, datagram with
> invalid checksum will be passed to the application.
We check the checksum later, in parallel with the copy of
the packet data into userspace.
See udp_recvmsg(), where we do this:
if (skb->ip_summed==CHECKSUM_UNNECESSARY) {
err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
msg->msg_iov,
copied);
} else if (msg->msg_flags&MSG_TRUNC) {
if (__udp_checksum_complete(skb))
goto csum_copy_err;
err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
msg->msg_iov,
copied);
} else {
err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct
udphdr), msg->msg_iov);
if (err == -EINVAL)
goto csum_copy_err;
}
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