linux-kernel - Re: [PATCH net v2] net: ethtool: netlink: Allow NULL nlattrs when getting a phy

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Message-ID: <fc925b52-edcd-425a-aee4-da5df007892c@microchip.com>
Date: Tue, 4 Mar 2025 12:35:42 +0000
From: <Parthiban.Veerasooran@...rochip.com>
To: <maxime.chevallier@...tlin.com>, <kuba@...nel.org>
CC: <davem@...emloft.net>, <andrew@...n.ch>, <edumazet@...gle.com>,
	<pabeni@...hat.com>, <hkallweit1@...il.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <thomas.petazzoni@...tlin.com>,
	<linux-arm-kernel@...ts.infradead.org>, <christophe.leroy@...roup.eu>,
	<herve.codina@...tlin.com>, <f.fainelli@...il.com>,
	<vladimir.oltean@....com>, <kory.maincent@...tlin.com>,
	<o.rempel@...gutronix.de>, <horms@...nel.org>, <romain.gantois@...tlin.com>,
	<piergiorgio.beruto@...il.com>
Subject: Re: [PATCH net v2] net: ethtool: netlink: Allow NULL nlattrs when
 getting a phy_device

Hi All,

On 04/03/25 3:22 pm, Maxime Chevallier wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Mon, 3 Mar 2025 16:10:24 -0800
> Jakub Kicinski <kuba@...nel.org> wrote:
> 
>> On Sat,  1 Mar 2025 15:11:13 +0100 Maxime Chevallier wrote:
>>> ethnl_req_get_phydev() is used to lookup a phy_device, in the case an
>>> ethtool netlink command targets a specific phydev within a netdev's
>>> topology.
>>>
>>> It takes as a parameter a const struct nlattr *header that's used for
>>> error handling :
>>>
>>>         if (!phydev) {
>>>                 NL_SET_ERR_MSG_ATTR(extack, header,
>>>                                     "no phy matching phyindex");
>>>                 return ERR_PTR(-ENODEV);
>>>         }
>>>
>>> In the notify path after a ->set operation however, there's no request
>>> attributes available.
>>>
>>> The typical callsite for the above function looks like:
>>>
>>>      phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_XXX_HEADER],
>>>                                    info->extack);
>>>
>>> So, when tb is NULL (such as in the ethnl notify path), we have a nice
>>> crash.
>>>
>>> It turns out that there's only the PLCA command that is in that case, as
>>> the other phydev-specific commands don't have a notification.
>>>
>>> This commit fixes the crash by passing the cmd index and the nlattr
>>> array separately, allowing NULL-checking it directly inside the helper.
>>>
>>> Fixes: c15e065b46dc ("net: ethtool: Allow passing a phy index for some commands")
>>> Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
>>
>> Well, this alone doesn't look too bad.. :) Hopefully we can address
>> adding more suitable handlers for phy ops in net-next.
> 
> Yeah I'm cooking something to improve on that, and I have also dusted
> off a netdevsim patch I had written back when working on the
> phy_link_topology that adds very very basic PHY support so that we can
> start covering all these commands with proper tests. I'll hopefully send
> something in the coming week or so.
> 
>> Didn't someone report this, tho? I vaguely remember seeing an email,
>> unless they said they don't want to be credited maybe we should add
>> a Reported-by tag? You can post it in reply, no need to repost
>> the patch.
> 
> Parthiban reported this without CC: netdev, but I think it's fair to
> add :
> 
> Reported-by: Parthiban Veerasooran <parthiban.veerasooran@...rochip.com>
Thank you for fixing the issue.

Best regards,
Parthiban V
> 
> I didn't include it in the first place because checkpatch complained
> about a reported-by tag without a "Closes:", which we don't have
> because of the private reporting :)
> 
> Thanks Jakub,
> 
> Maxime