ACK: [SRU][Bionic][PATCH 0/1] Cannot create ipvlans with > 1500 MTU on recent Bionic kernels

[Andrea Righi]

On Thu, May 21, 2020 at 12:14:01PM +0530, Nivedita Singhvi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1879658
> 
> [IMPACT]
> 
> Setting an MTU larger than the default 1500 results in an
> error on the recent (4.15.0-92+) Bionic / Xenial -hwe kernels
> when attempting to create ipvlan interfaces:
> 
> # ip link add test0 mtu 9000 link eno1 type ipvlan mode l2
> RTNETLINK answers: Invalid argument
> 
> This breaks Docker and other applications which use a Jumbo
> MTU (9000) when using ipvlans.
> 
> Breaking commit:
> -------------------
> B: bionic/linux: 4.15.0-92.93
> X-hwe: Ubuntu-hwe-4.15.0-92.93~16.04.1
> 
> * Bionic update: upstream stable patchset 2020-02-21 (LP: #1864261)
>   * net: rtnetlink: validate IFLA_MTU attribute in rtnl_create_link()
> 
> The above patch started enforcing strict range limits for MTU
> and subsequently exposed some latent bugs in previous commits.
> This fixes the breakage in the rtnetlink path, previously fixes
> went into bonding, teaming drivers for the same issue. 
> 
> The mtu checking consolidation had gone into the kernel in the past
> but the max MTU was not actually set so defaulted to 1500.
> 
> 
> Fix commit:
> --------------
> This has been fixed in upstream mainline:
> 
> ipvlan: use ETH_MAX_MTU as max mtu
> commit 548feb33c598dfaf9f8e066b842441ac49b84a8a
> 
> Which went in v4.18-rc2 so is already present in all Cosmic onwards
> kernels. 
> 
> So this is only affects Bionic and Xenial -hwe kernels
> 4.15.0-92 onwards.
> 
> 
> [Test Case]
> 
> On 4.15.0-92+ kernel creating a ipvlan interface of > 1500 results
> in error:
> 
> # ip link add test1 mtu 9000 link eno1 type ipvlan mode l2
> RTNETLINK answers: Invalid argument
> 
> Patched kernels have been tested in our lab and in the process
> of being tested at enterprise users.
> 
> [Regression Potential]
> Small as fix is very small, isolated to ipvlan driver and already
> in Cosmic onwards kernels. 

Small and clean cherry pick, looks good to me.

Acked-by: Andrea Righi <andrea.righi at canonical.com>