netdev - Re: [PATCH net v4 00/12] Fix possbile memleaks when fail to register

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Message-Id: <20170502.153029.1605231216574026914.davem@davemloft.net>
Date:   Tue, 02 May 2017 15:30:29 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     gfree.wind@...mail.com
Cc:     jiri@...nulli.us, mareklindner@...mailbox.ch,
        sw@...onwunderlich.de, a@...table.cc, kuznet@....inr.ac.ru,
        jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
        steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        netdev@...r.kernel.org
Subject: Re: [PATCH net v4 00/12] Fix possbile memleaks when fail to
 register_netdevice

From: gfree.wind@...mail.com
Date: Tue,  2 May 2017 13:58:42 +0800

> These following drivers allocate kinds of resources in its ndo_init
> func, free some of them or all in the destructor func. Then there is
> one memleak that some errors happen after register_netdevice invokes
> the ndo_init callback. Because only the ndo_uninit callback is invoked
> in the error handler of register_netdevice, but destructor not.
> 
> In my original approach, I tried to free the resources in the newlink
> func when fail to register_netdevice, like destructor did except not
> free the net_dev. This method is not good when destructor is changed,
> and the memleak could be not fixed when there is no newlink callback.
> 
> Now create one new func used to free the resources in the destructor,
> and the ndo_uninit func also could invokes it when fail to register
> the net_device by comparing the dev->reg_state with NETREG_UNINITIALIZED.
> If there is no existing ndo_uninit, just add one.
> 
> This solution doesn't only make sure free all resources in any case,
> but also follows the original desgin that some resources could be kept
> until the destructor executes normally after register the device
> successfully.

I want to think about this some more.

It is really unfortunate that resources are allocated strictly from
the ndo_init() yet released in two different callbacks which are
invoked only in certain (different) situations.

Just the fact that we have to make an internal netdev state test
in the ndo_uninit callback to get this right is a big red flag
to me.