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

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

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

quoted

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

quoted

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

quoted

Currently, any mtu value can be assigned when adding a new dummy device:
[~]# 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
    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