Re: [RFC Patch net-next 5/6] net: dsa: microchip: Adding the ptp packet reception logic

From: Vladimir Oltean <olteanv@gmail.com>
To: Christian Eggers <ceggers@arri.de>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	Arun Ramadoss <arun.ramadoss@microchip.com>,
	woojung.huh@microchip.com, UNGLinuxDriver@microchip.com,
	andrew@lunn.ch, vivien.didelot@gmail.com, f.fainelli@gmail.com,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, linux@armlinux.org.uk,
	Tristram.Ha@microchip.com
Subject: Re: [RFC Patch net-next 5/6] net: dsa: microchip: Adding the ptp packet reception logic
Date: Wed, 26 Oct 2022 23:13:51 +0300	[thread overview]
Message-ID: <20221026201351.iqh5776hqnyoj56v@skbuf> (raw)
In-Reply-To: <4458429.LvFx2qVVIh@n95hx1g2>

On Tue, Oct 25, 2022 at 08:17:37AM +0200, Christian Eggers wrote:
> > +static int ksz_connect_tag_protocol(struct dsa_switch *ds,
> > +				    enum dsa_tag_protocol proto)
> > +{
> > +	struct ksz_tagger_data *tagger_data;
> > +
> > +	tagger_data = ksz_tagger_data(ds);
> 
> NULL pointer dereference is here:
> 
> ksz_connect() is only called for "lan937x", not for the other KSZ switches.
> If ksz_connect() shall only be called for PTP switches, the result of
> ksz_tagger_data() may be NULL.
> 
> > +	tagger_data->meta_tstamp_handler = ksz_tstamp_reconstruct;
> > +
> > +	return 0;
> > +}
> > +

The observation is correct. All other drivers which use this API check
the protocol given as argument, and for good reason. Only "lan937x"
allocates tagger-owned storage in Arun's implementation, but the common
ksz library supports more tagging protocols.