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

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Date:   Wed, 26 Oct 2022 23:13:51 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Christian Eggers <ceggers@...i.de>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Arun Ramadoss <arun.ramadoss@...rochip.com>,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, linux@...linux.org.uk, Tristram.Ha@...rochip.com
Subject: Re: [RFC Patch net-next 5/6] net: dsa: microchip: Adding the ptp
 packet reception logic

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.