netdev - Re: [PATCH net-next v4 3/6] net: dsa: Introduce dsa tagger data operation.

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Message-ID: <YxdGR/TPuNf7E0w1@lunn.ch>
Date:   Tue, 6 Sep 2022 15:08:23 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Mattias Forsblad <mattias.forsblad@...il.com>
Cc:     netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v4 3/6] net: dsa: Introduce dsa tagger data
 operation.

>  		switch (code) {
>  		case DSA_CODE_FRAME2REG:
> -			/* Remote management is not implemented yet,
> -			 * drop.
> -			 */
> +			tagger_data = ds->tagger_data;
> +			if (likely(tagger_data->decode_frame2reg))
> +				tagger_data->decode_frame2reg(dev, skb);
>  			return NULL;
>  		case DSA_CODE_ARP_MIRROR:
>  		case DSA_CODE_POLICY_MIRROR:
> @@ -323,6 +326,25 @@ static struct sk_buff *dsa_rcv_ll(struct sk_buff *skb, struct net_device *dev,
>  	return skb;
>  }
  
> +static void dsa_tag_disconnect(struct dsa_switch *ds)
> +{
> +	kfree(ds->tagger_data);
> +	ds->tagger_data = NULL;
> +}


Probably a question for Vladimir.

Is there a potential use after free here? Is it guaranteed that the
masters dev->dsa_ptr will be cleared before the disconnect function is
called?

Also, the receive function checks for tagger_data->decode_frame2reg,
but does not check for tagger_data != NULL.

This is just a straight copy of tag_qca, so if there are issues here,
they are probably not new issues.

     Andrew