netdev - Re: [PATCH net-next v4] tcp: Add RFC4898 tcpEStatsPerfDataSegsOut/In

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 10 Mar 2016 09:43:18 -0800
From:	Eric Dumazet <edumazet@...gle.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Chris Rapier <rapier@....edu>,
	Marcelo Ricardo Leitner <mleitner@...hat.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next v4] tcp: Add RFC4898 tcpEStatsPerfDataSegsOut/In

On Thu, Mar 10, 2016 at 9:39 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> On Thu, Mar 10, 2016 at 9:29 AM, Martin KaFai Lau <kafai@...com> wrote:
>> Per RFC4898, they count segments sent/received
>> containing a positive length data segment (that includes
>> retransmission segments carrying data).  Unlike
>> tcpi_segs_out/in, tcpi_data_segs_out/in excludes segments
>> carrying no data (e.g. pure ack).
>>
>> The patch also updates the segs_in in tcp_fastopen_add_skb()
>> so that segs_in >= data_segs_in property is kept.  If
>> tcp_segs_in() helper is used in this fastopen case, tp->segs_in
>> has to be 0 reset first to avoid double counting.  Also, it has
>> to be done before __skb_pull(skb, tcp_hdrlen(skb)) while
>> there is no need to check skb->len since skb has already
>> been confirmed carrying data.  I found it more confusing
>> and chose to directly set segs_in and data_segs_in in
>> this special case.
>
> Note that on my TODO list after commit e11ecddf5128011c936cc5360780190cbc901fdc
> I had the project of pulling TCP headers much earlier in input path
> so that we do not have all these special cases.
>
> Acked-by: Eric Dumazet <edumazet@...gle.com>

Actually, tcp_fastopen_add_skb() can queue a packet with a FIN only,
but no data.

I believe you need to test skb->len before setting tp->data_segs_in