netdev - Re: [PATCH net] vxlan: do not destroy fdb if register

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Date:   Wed, 26 Jun 2019 01:08:47 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] vxlan: do not destroy fdb if register_netdevice() is failed

On Tue, 25 Jun 2019 at 13:12, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:
>

Hi Roopa,

Thank you for the review!

> On Sun, Jun 23, 2019 at 7:18 PM Taehee Yoo <ap420073@...il.com> wrote:
> >
> > On Mon, 24 Jun 2019 at 03:07, David Miller <davem@...emloft.net> wrote:
> > >
> >
> > Hi David,
> >
> > Thank you for the review!
> >
> > > From: Taehee Yoo <ap420073@...il.com>
> > > Date: Thu, 20 Jun 2019 20:51:08 +0900
> > >
> > > > __vxlan_dev_create() destroys FDB using specific pointer which indicates
> > > > a fdb when error occurs.
> > > > But that pointer should not be used when register_netdevice() fails because
> > > > register_netdevice() internally destroys fdb when error occurs.
> > > >
> > > > In order to avoid un-registered dev's notification, fdb destroying routine
> > > > checks dev's register status before notification.
> > >
> > > Simply pass do_notify as false in this failure code path of __vxlan_dev_create(),
> > > thank you.
> >
> > Failure path of __vxlan_dev_create() can't handle do_notify in that case
> > because if register_netdevice() fails it internally calls
> > ->ndo_uninit() which is
> > vxlan_uninit().
> > vxlan_uninit() internally calls vxlan_fdb_delete_default() and it callls
> > vxlan_fdb_destroy().
> > do_notify of vxlan_fdb_destroy() in vxlan_fdb_delete_default() is always true.
> > So, failure path of __vxlan_dev_create() doesn't have any opportunity to
> > handle do_notify.
>
>
> I don't see register_netdevice calling ndo_uninit in case of all
> errors. In the case where it does not,
> does your patch leak the fdb entry ?.
>
> Wondering if we should just use vxlan_fdb_delete_default with a notify
> flag to delete the entry if exists.
> Will that help ?
>
> There is another commit that touched this code path:
> commit 6db9246871394b3a136cd52001a0763676563840
>
> Author: Petr Machata <petrm@...lanox.com>
> Date:   Tue Dec 18 13:16:00 2018 +0000
>     vxlan: Fix error path in __vxlan_dev_create()

I have checked up failure path of register_netdevice().
Yes, this patch leaks fdb entry.
There are 3 failure cases in the register_netdevice().
A. error occurs before calling ->ndo_init().
it doesn't call ->ndo_uninit().
B. error occurs after calling ->ndo_init().
it calls ->ndo_uninit() and dev->reg_state is NETREG_UNINITIALIZED.
C. error occurs after registering netdev. it calls rollback_registered().
rollback_registered() internally calls ->ndo_uninit()
and dev->reg_state is NETREG_UNREGISTERING.

A panic due to these problem could be fixed by using
vxlan_fdb_delete_default() with notify flag.
But notification problem could not be fixed clearly
because of the case C.

I don't have clear solution for the case C.
Please let me know, if you have any good idea for fixing the case C.

Thank you!