Re: [PATCH net v2] net: ethtool: netlink: Allow NULL nlattrs when getting a phy_device

[Jakub Kicinski <kuba@kernel.org>]

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@bootlin.com>

Well, this alone doesn't look too bad.. :) Hopefully we can address
adding more suitable handlers for phy ops in net-next.

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.