netdev - Re: [PATCH] net: Adding parameter detection in __ethtool_get_link

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Date:   Thu, 29 Aug 2019 08:01:38 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "liudongxu3@...wei.com" <liudongxu3@...wei.com>,
        "eric.dumazet@...il.com" <eric.dumazet@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: Adding parameter detection in
 __ethtool_get_link_ksettings.

On Tue, Aug 27, 2019 at 07:01:41PM +0000, Saeed Mahameed wrote:
> On Mon, 2019-08-26 at 17:47 +0800, Dongxu Liu wrote:
> 
> > Maybe "if (!dev->ethtool_ops)" is more accurate for this bug.
> > 
> 
> Also i am not sure about this, could be a bug in the device driver your
> enslaving.
> 
> alloc_netdev_mqs will assign &default_ethtool_ops to dev->ethtool_ops ,
> if user provided setup callback didn't assign the driver specific
> ethtool_ops.

Dongxu said he encountered the null pointer dereference in a 3.10
kernel, not current mainline. But commit 2c60db037034 ("net: provide a
default dev->ethtool_ops") which introduced default_ethtool_ops came in
3.7-rc1 so 3.10 should have it already. There is indeed something wrong.

I don't think we should add either check unless we positively know that
dev->ethtool_ops can be null with current mainline kernel. And even
then, it would probably be more appropriate to fix the code which caused
it.

Michal