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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Dongseok Yi <dseok.yi@samsung.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Yunsheng Lin <linyunsheng@huawei.com>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4
Date: Mon, 10 May 2021 09:19:43 -0400	[thread overview]
Message-ID: <CA+FuTSepShKoXUJo7ELMMJ4La11J6CsZggJWsQ5MB2_uhAi+OQ@mail.gmail.com> (raw)
In-Reply-To: <00c901d74543$57fa3620$07eea260$@samsung.com>

> > That generates TCP packets with different MSS within the same stream.
> >
> > My suggestion remains to just not change MSS at all. But this has to
> > be a new flag to avoid changing established behavior.
>
> I don't understand why the mss size should be kept in GSO step. Will
> there be any issue with different mss?

This issue has come up before and that has been the feedback from
TCP experts at one point.

> In general, upgrading mss make sense when 6 to 4. The new flag would be
> set by user to not change mss. What happened if user does not set the
> flag? I still think we should fix the issue with a general approach. Or
> can we remove the skb_increase_gso_size line?

Admins that insert such BPF packets should be aware of these issues.
And likely be using clamping. This is a known issue.

We arrived that the flag approach in bpf_skb_net_shrink. Extending
that  to bpf_skb_change_proto would be consistent.

  reply	other threads:[~2021-05-10 13:50 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20210429102143epcas2p4c8747c09a9de28f003c20389c050394a@epcas2p4.samsung.com>
2021-04-29 10:08 ` [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4 Dongseok Yi
2021-05-05 20:55   ` Daniel Borkmann
2021-05-06  0:45     ` Dongseok Yi
2021-05-06  1:45       ` Willem de Bruijn
2021-05-06  2:27         ` Dongseok Yi
2021-05-06 18:21           ` Willem de Bruijn
2021-05-07  0:53             ` Dongseok Yi
2021-05-07  1:25               ` Willem de Bruijn
2021-05-07  1:45                 ` Yunsheng Lin
2021-05-07  1:53                   ` Willem de Bruijn
2021-05-07  8:25                     ` Dongseok Yi
2021-05-07  9:11                       ` Yunsheng Lin
2021-05-07 10:36                         ` Dongseok Yi
2021-05-07 13:50                       ` Willem de Bruijn
2021-05-10  2:22                         ` Dongseok Yi
2021-05-10 13:19                           ` Willem de Bruijn [this message]
2021-05-10 13:46                             ` Willem de Bruijn
2021-05-11  1:11                               ` Dongseok Yi
2021-05-11 17:38                                 ` Willem de Bruijn
2021-05-12  0:45                                   ` Dongseok Yi
     [not found]   ` <CGME20210511065056epcas2p1788505019deb274f5c57650a2f5d7ef0@epcas2p1.samsung.com>
2021-05-11  6:36     ` [PATCH bpf v2] bpf: check BPF_F_ADJ_ROOM_FIXED_GSO when upgrading mss in " Dongseok Yi
2021-05-11 17:42       ` Willem de Bruijn
2021-05-12  6:56         ` Dongseok Yi
     [not found]       ` <CGME20210512074058epcas2p35536c27bdfafaa6431e164c142007f96@epcas2p3.samsung.com>
2021-05-12  7:27         ` [PATCH bpf-next v3] bpf: check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto Dongseok Yi
2021-05-12 14:13           ` Willem de Bruijn
2021-05-18 20:10           ` patchwork-bot+netdevbpf

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