netdev - Re: [PATCH 1/2] [IPV4] UDP: Always checksum even if without socket filter

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Date:	Thu, 15 Nov 2007 20:04:31 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	wangchen@...fujitsu.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] [IPV4] UDP: Always checksum even if without socket
 filter

From: Wang Chen <wangchen@...fujitsu.com>
Date: Fri, 16 Nov 2007 11:18:16 +0800

> Actually, I tested and found this issue.
> I sent 50 udp packets, which have wrong checksum, to my
> machine.
> Before the patch being applied, /proc/net/snmp's udp
> InDatagrams increased, and InErrors didn't increase.
> After the patch being applied, InErrors increased correctly
> and InDatagrams stayed unchanging.

That's right, InDataGrams will increase even if we haven't
verified the checksum yet.

When the user does a recvmsg() or a poll() on the socket,
we will notice the bad checksum then and increment InErrors.
We could in this case correct the InDatagrams counter by
decrementing it in this case.
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