Re: [PATCH 03/11] net: devres: relax devm_register_netdev()

From: Bartosz Golaszewski <brgl@bgdev.pl>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	"David S . Miller" <davem@davemloft.net>,
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	Mark Lee <Mark-MC.Lee@mediatek.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Rob Herring <robh+dt@kernel.org>,
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	Fabien Parent <fparent@baylibre.com>,
	Stephane Le Provost <stephane.leprovost@mediatek.com>,
	Pedro Tsai <pedro.tsai@mediatek.com>,
	Andrew Perepech <andrew.perepech@mediatek.com>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>
Subject: Re: [PATCH 03/11] net: devres: relax devm_register_netdev()
Date: Tue, 23 Jun 2020 11:12:24 +0200	[thread overview]
Message-ID: <CAMRc=MfF1RbQCJ62QhscFLu1HKYRc9M-2SMep1_vTJ2xhKjLAA@mail.gmail.com> (raw)
In-Reply-To: <20200622154943.02782b5a@kicinski-fedora-PC1C0HJN>

wt., 23 cze 2020 o 00:49 Jakub Kicinski <kuba@kernel.org> napisał(a):
>
> On Mon, 22 Jun 2020 12:00:48 +0200 Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > This devres helper registers a release callback that only unregisters
> > the net_device. It works perfectly fine with netdev structs that are
> > not managed on their own. There's no reason to check this - drop the
> > warning.
> >
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>
> I think the reasoning for this suggestion was to catch possible UAF
> errors. The netdev doesn't necessarily has to be from devm_alloc_*
> but it has to be part of devm-ed memory or memory which is freed
> after driver's remove callback.
>

Yes I understand that UAF was the concern here, but this limitation is
unnecessary. In its current form devm_register_netdev() only works for
struct net_device allocated with devm_alloc_etherdev(). Meanwhile
calling alloc_netdev() (which doesn't have its devm counterpart yet -
I may look into it shortly), then registering a devm action with
devm_add_action_or_reset() which would free this memory is a perfectly
fine use case. This patch would make it possible.

> Are there cases in practice where you've seen the netdev not being
> devm allocated?

As I said above - alloc_netdev() used by wireless, can, usb etc.
drivers doesn't have a devres variant.

Bartosz