netdev - Bug in computing data_len in tcp

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Date:	Wed, 30 Nov 2011 17:48:04 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Linux Netdev List <netdev@...r.kernel.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
Subject: Bug in computing data_len in tcp_sendmsg?

I believe that skb->data_len might no be computed correctly in
tcp_sendmsg.  Specifically, when skb_add_data_nocache (or
skb_add_data) is called skb->data_len is not updated (skb_put only
updates skb->len).  This results in the datalen in the head skbuf
being zero so any subsequent uses of the value lead to incorrect
results.  For instance, skb_headlen returns the length of the head
skbu data and not just that of the headers.  If I'm reading this
correctly, it's a pretty fundamental bug.

I don't have a fix for this yet.

Tom
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