netdev - Re: [PATCH net-next 1/1] ethtool/plca: fix potential NULL pointer access

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Date:   Tue, 17 Jan 2023 02:34:26 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Piergiorgio Beruto <piergiorgio.beruto@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Oleksij Rempel <o.rempel@...gutronix.de>,
        mailhol.vincent@...adoo.fr, sudheer.mogilappagari@...el.com,
        sbhatta@...vell.com, linux-doc@...r.kernel.org,
        wangjie125@...wei.com, corbet@....net, lkp@...el.com,
        gal@...dia.com, gustavoars@...nel.org, bagasdotme@...il.com
Subject: Re: [PATCH net-next 1/1] ethtool/plca: fix potential NULL pointer
 access

On Tue, Jan 17, 2023 at 12:57:19AM +0100, Piergiorgio Beruto wrote:
> Fix problem found by syzbot dereferencing a device pointer.
> 
> Signed-off-by: Piergiorgio Beruto <piergiorgio.beruto@...il.com>
> Reported-by: syzbot+8cf35743af243e5f417e@...kaller.appspotmail.com
> Fixes: 8580e16c28f3 ("net/ethtool: add netlink interface for the PLCA RS")
> ---
>  net/ethtool/plca.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/ethtool/plca.c b/net/ethtool/plca.c
> index be7404dc9ef2..bc3d31f99998 100644
> --- a/net/ethtool/plca.c
> +++ b/net/ethtool/plca.c
> @@ -155,6 +155,8 @@ int ethnl_set_plca_cfg(struct sk_buff *skb, struct genl_info *info)
>  		return ret;
>  
>  	dev = req_info.dev;
> +	if(!dev)
> +		return -ENODEV;

Shouldn't be necessary. The fact that you pass "true" to the
"require_dev" argument of ethnl_parse_header_dev_get() takes care
specifically of that.

Looking at that syzbot report, it looks like you solved it with commit
28dbf774bc87 ("plca.c: fix obvious mistake in checking retval"). Or was
that not the only issue?

>  
>  	rtnl_lock();
>  
> -- 
> 2.37.4
>