netdev - Re: [PATCH net] net: devlink: fix UAF in devlink_compat_running

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Date:   Tue, 29 Nov 2022 09:31:40 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Leon Romanovsky <leon@...nel.org>, netdev@...r.kernel.org,
        jiri@...dia.com, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com
Subject: Re: [PATCH net] net: devlink: fix UAF in
 devlink_compat_running_version()

Mon, Nov 28, 2022 at 07:20:43PM CET, kuba@...nel.org wrote:
>On Mon, 28 Nov 2022 10:58:58 +0100 Jiri Pirko wrote:
>> >Long term, we either need to find a way to make the ethtool compat stuff
>> >work correctly or just get rid of it and have affected drivers implement
>> >the relevant ethtool operations instead of relying on devlink.
>> >
>> >[1] https://lore.kernel.org/netdev/20221122121048.776643-1-yangyingliang@huawei.com/  
>> 
>> I just had a call with Ido. We both think that this might be a good
>> solution for -net to avoid the use after free.
>> 
>> For net-next, we eventually should change driver init flows to register
>> devlink instance first and only after that register devlink_port and
>> related netdevice. The ordering is important for the userspace app. For
>> example the init flow:
>> <- RTnetlink new netdev event
>> app sees devlink_port handle in IFLA_DEVLINK_PORT
>> -> query devlink instance using this handle  
>> <- ENODEV
>> 
>> The instance is not registered yet.
>> 
>> So we need to make sure all devlink_port_register() calls are happening
>> after devlink_register(). This is aligned with the original flow before
>> devlink_register() was moved by Leon. Also it is aligned with devlink
>> reload and devlink port split flows.
>
>Cool. Do you also agree with doing proper refcounting for the devlink
>instance struct and the liveness check after locking the instance?

Could you elaborate a bit more? I missed that in the thread and can't
find it. Why do we need it?