Re: [PATCH v8 net-next 10/12] net: transfer rtnl_lock() requirement from ethtool_set_ethtool_phy_ops() to caller

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Vladimir Oltean <vladimir.oltean@nxp.com>
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>, "Andrew Lunn" <andrew@lunn.ch>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Maxim Georgiev" <glipus@gmail.com>,
	"Horatiu Vultur" <horatiu.vultur@microchip.com>,
	"Köry Maincent" <kory.maincent@bootlin.com>,
	"Maxime Chevallier" <maxime.chevallier@bootlin.com>,
	"Richard Cochran" <richardcochran@gmail.com>,
	"Vadim Fedorenko" <vadim.fedorenko@linux.dev>,
	"Gerhard Engleder" <gerhard@engleder-embedded.com>,
	"Hangbin Liu" <liuhangbin@gmail.com>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Jacob Keller" <jacob.e.keller@intel.com>,
	"Jay Vosburgh" <j.vosburgh@gmail.com>,
	"Andy Gospodarek" <andy@greyhouse.net>,
	"Wei Fang" <wei.fang@nxp.com>,
	"Shenwei Wang" <shenwei.wang@nxp.com>,
	"Clark Wang" <xiaoning.wang@nxp.com>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	UNGLinuxDriver@microchip.com,
	"Lars Povlsen" <lars.povlsen@microchip.com>,
	"Steen Hegelund" <Steen.Hegelund@microchip.com>,
	"Daniel Machon" <daniel.machon@microchip.com>,
	"Simon Horman" <simon.horman@corigine.com>,
	"Casper Andersson" <casper.casan@gmail.com>,
	"Sergey Organov" <sorganov@gmail.com>,
	"Michal Kubecek" <mkubecek@suse.cz>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 net-next 10/12] net: transfer rtnl_lock() requirement from ethtool_set_ethtool_phy_ops() to caller
Date: Tue, 18 Jul 2023 15:31:03 +0100	[thread overview]
Message-ID: <ZLaiJ4G6TaJYGJyU@shell.armlinux.org.uk> (raw)
In-Reply-To: <20230717152709.574773-11-vladimir.oltean@nxp.com>

On Mon, Jul 17, 2023 at 06:27:07PM +0300, Vladimir Oltean wrote:
> phy_init() and phy_exit() will have to do more stuff under rtnl_lock()
> in a future change. Since rtnl_unlock() -> netdev_run_todo() does a lot
> of stuff under the hood, it's a pity to lock and unlock the rtnetlink
> mutex twice in a row.
> 
> Change the calling convention such that the only caller of
> ethtool_set_ethtool_phy_ops(), phy_device.c, provides a context where
> the rtnl_mutex is already acquired.
> 
> Note that phy_exit() wasn't performing the opposite teardown of
> phy_init(). Reverse mdio_bus_init() with ethtool_set_ethtool_phy_ops(),
> so that this is now the case.

To me, this looks buggy.

> @@ -3451,11 +3452,14 @@ static int __init phy_init(void)
>  {
>  	int rc;
>  
> +	rtnl_lock();
> +	ethtool_set_ethtool_phy_ops(&phy_ethtool_phy_ops);
> +	rtnl_unlock();
> +
>  	rc = mdio_bus_init();
>  	if (rc)
>  		return rc;

If mdio_bus_init() fails, and phylib is built as a module, then we
leave ethtool_phy_ops pointing into module space that has potentially
been freed or re-used for another module. This error path needs to
properly clean up.

The same is also true for the other failure paths in phy_init() which
already do not cater for their failures leaving a dangling pointer in
ethtool_phy_ops. This should probably be fixed first in a separate
patch for the net tree.

Thanks.

-- 
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