RE: [net-next 1/2] dummy: add device MTU validation check

-----Original Message-----
From: Sabrina Dubroca [mailto:sd@queasysnail.net]
Sent: 2017年9月22日 20:23
To: Eric Dumazet <redacted>
Cc: Jarod Wilson <redacted>; Zhang Shengju
[off-list ref]; davem@davemloft.net;
willemb@google.com; stephen@networkplumber.org;
netdev@vger.kernel.org
Subject: Re: [net-next 1/2] dummy: add device MTU validation check

2017-09-22, 04:05:09 -0700, Eric Dumazet wrote:

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On Fri, 2017-09-22 at 10:56 +0200, Sabrina Dubroca wrote:

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2017-09-21, 08:02:18 -0700, Eric Dumazet wrote:

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On Thu, 2017-09-21 at 21:32 +0800, Zhang Shengju wrote:

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Currently, any mtu value can be assigned when adding a new dummy

device:

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[~]# ip link add name dummy1 mtu 100000 type dummy [~]# ip link
show dummy1
15: dummy1: <BROADCAST,NOARP> mtu 100000 qdisc noop state

DOWN mode DEFAULT group default qlen 1000

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    link/ether 0a:61:6b:16:14:ce brd ff:ff:ff:ff:ff:ff

This patch adds device MTU validation check.

What is wrong with big MTU on dummy ?

It looks like the "centralize MTU checking" series broke that, but
only for changing the MTU on an existing dummy device. Commit
a52ad514fdf3 defined min_mtu/max_mtu in ether_setup, which dummy
uses, but there was no MTU check in dummy prior to that commit.

It looks like we accept big mtu on loopback, right ?

Yes. I only meant that before commit a52ad514fdf3, there was no range check
on dummy's MTU. Commit 25e3e84b183a ("dummy: expend mtu range for
dummy device") and 8b1efc0f83f1 ("net: remove MTU limits on a few
ether_setup callers") fixed that only partially. It's the same with ifb, btw, it
didn't have any check before a52ad514fdf3, so we should set min_mtu =
max_mtu = 0.

--
Sabrina

I agree, dummy and ifb device should not have any limit on mtu, just like loopback device.
I will send v2 patch, and set min/max_mtu to zero for dummy and ifb device, thanks.

ZSJ