Re: [RFC] Add netdev all_adj_list refcnt propagation to fix panic

[David Miller <davem@davemloft.net>]

From: Andrew Collins <acollins@cradlepoint.com>
Date: Tue, 29 Mar 2016 11:25:03 -0600

> This is an RFC patch to fix a relatively easily reproducible kernel
> panic related to the all_adj_list handling for netdevs in recent kernels.
> 
> This is more to generate discussion than anything else.  I don't
> particularly like this approach, I'm hoping someone has a better idea.
> 
> The following sequence of commands will reproduce the issue:
> 
> ip link add link eth0 name eth0.100 type vlan id 100
> ip link add link eth0 name eth0.200 type vlan id 200
> ip link add name testbr type bridge
> ip link set eth0.100 master testbr
> ip link set eth0.200 master testbr
> ip link add link testbr mac0 type macvlan
> ip link delete dev testbr
> 
> This creates an upper/lower tree of (excuse the poor ASCII art):
> 
>             /---eth0.100-eth0
> mac0-testbr-
>             \---eth0.200-eth0
> 
> When testbr is deleted, the all_adj_lists are walked, and eth0 is deleted twice from
> the mac0 list. Unfortunately, during setup in __netdev_upper_dev_link, only one
> reference to eth0 is added, so this results in a panic.
> 
> This change adds reference count propagation so things are handled properly.
> 
> Matthias Schiffer reported a similar crash in batman-adv:
> 
> https://github.com/freifunk-gluon/gluon/issues/680
> https://www.open-mesh.org/issues/247
> 
> which this patch also seems to resolve.

Veaceslav, please look into this.

Thanks.