netdev - Re: [PATCH 11/20] ethernet: ucc_geth: fix use-after-free in ucc_geth

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Message-ID: <20201205131928.7d5c8e59@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Sat, 5 Dec 2020 13:19:28 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Li Yang <leoyang.li@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Zhao Qiang <qiang.zhao@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/20] ethernet: ucc_geth: fix use-after-free in
 ucc_geth_remove()

On Sat, 5 Dec 2020 22:04:28 +0100 Rasmus Villemoes wrote:
> On 05/12/2020 21.48, Jakub Kicinski wrote:
> > On Sat,  5 Dec 2020 20:17:34 +0100 Rasmus Villemoes wrote:  
> >> -	unregister_netdev(dev);
> >> -	free_netdev(dev);
> >>  	ucc_geth_memclean(ugeth);
> >>  	if (of_phy_is_fixed_link(np))
> >>  		of_phy_deregister_fixed_link(np);
> >>  	of_node_put(ugeth->ug_info->tbi_node);
> >>  	of_node_put(ugeth->ug_info->phy_node);
> >> +	unregister_netdev(dev);
> >> +	free_netdev(dev);  
> > 
> > Are you sure you want to move the unregister_netdev() as well as the
> > free?
> 
> Hm, dunno, I don't think it's needed per se, but it also shouldn't hurt
> from what I can tell. It seems more natural that they go together, but
> if you prefer a minimal patch that's of course also possible.

I was concerned about the fact that we free things and release
references while the device may still be up (given that it's
unregister_netdev() that will take it down).

> I only noticed because I needed to add a free of the ug_info in a later
> patch.