netdev - Re: [PATCH] tun: avoid double free in tun_free

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Date:   Thu, 9 Dec 2021 15:26:45 -0500
From:   George Kennedy <george.kennedy@...cle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tun: avoid double free in tun_free_netdev



On 12/8/2021 6:58 PM, Jakub Kicinski wrote:
> On Wed, 8 Dec 2021 11:44:02 -0500 George Kennedy wrote:
>>> It looks like a lot of the problem is duplicate unwind.
>>> Why does err_free_flow, err_free_stat etc unwinds need to exist if
>>> the free_netdev is going to do same thing.
>> Maybe instead do not call security_tun_dev_free_security(tun->security)
>> in err_free_flow if it's going to be done anyway in tun_free_netdev().
> That won't be good either. register_netdevice() has multiple failure
> modes, it may or may not call the destructor depending on where it
> fails. Either the stuff that destructor undoes needs to be moved to
> ndo_init (which is what destructor always pairs with), or you can check
> dev->reg_state. If dev->reg_state is NETREG_UNREGISTERING that means
> the destructor will be caller later.
>
> The ndo_init way is preferable, just cut and past the appropriate lines
> preceding registration into a ndo_init callback.
Thank you Jakub,

Looking at other ndo_init's to try and figure out how much before 
register_netdevice() should go in it.

George