linux-kernel - Re: [PATCH] net: macsec: fix double free of percpu stats

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Date:   Wed, 14 Jun 2023 23:17:14 +0300
From:   Fedor Pchelkin <pchelkin@...ras.ru>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Sabrina Dubroca <sd@...asysnail.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Raed Salem <raeds@...dia.com>,
        Lior Nahmanson <liorna@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        lvc-project@...uxtesting.org
Subject: Re: [PATCH] net: macsec: fix double free of percpu stats

On Wed, Jun 14, 2023 at 09:01:26AM -0700, Jakub Kicinski wrote:
> On Wed, 14 Jun 2023 14:26:14 +0200 Sabrina Dubroca wrote:
> > > What prevents the device from being opened and used before
> > > macsec_add_dev() has finished? I think we need a fix which 
> > > would move this code before register_netdev(), instead :(  
> > 
> > Can the device be opened in parallel? We're under rtnl here.
> > 
> > If we want to move that code, then we'll also have to move the
> > eth_hw_addr_inherit call that's currently in macsec's ndo_init: in
> > case the user didn't give an SCI, we have to make it up based on the
> > device's mac address (dev_to_sci(dev, ...)), whether it's set by the
> > user or inherited. I can't remember if I had a good reason to put the
> > inherit in ndo_init.
> 
> Ah, you're right, this is a link creation path.

My reply probably won't give any new information now but if the code of
macsec_add_dev() and the parts from ndo_init it depends on which Sabrina
mentioned would be moved before registering netdev then the problem will
go away on its own.

Is it worth moving that code if rtnl_lock is held? Maybe it will be more
persistent to initialize the device for as maximum as possible before
calling register_netdevice()? Overall, it all depends on the reasons why
the code was implemented so initially.