netdev - Re: [PATCH RFC net-next 3/3] Introduce blockcast tc action

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Message-ID: <ZNyRsOB0nfqhZM1m@vergenet.net>
Date: Wed, 16 Aug 2023 11:06:56 +0200
From: Simon Horman <horms@...nel.org>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: jiri@...nulli.us, xiyou.wangcong@...il.com, netdev@...r.kernel.org,
	vladbu@...dia.com, mleitner@...hat.com,
	Victor Nogueira <victor@...atatu.com>,
	Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH RFC net-next 3/3] Introduce blockcast tc action

On Tue, Aug 15, 2023 at 12:25:30PM -0400, Jamal Hadi Salim wrote:
> This action takes advantage of the presence of tc block ports set in the
> datapath and broadcast a packet to all ports on that set with exception of
> the port in which it arrived on..
> 
> Example usage:
>     $ tc qdisc add dev ens7 ingress block 22
>     $ tc qdisc add dev ens8 ingress block 22
> 
> Now we can add a filter using the block index:
> $ tc filter add block 22 protocol ip pref 25 \
>   flower dst_ip 192.168.0.0/16 action blockcast
> 
> Co-developed-by: Victor Nogueira <victor@...atatu.com>
> Signed-off-by: Victor Nogueira <victor@...atatu.com>
> Co-developed-by: Pedro Tammela <pctammela@...atatu.com>
> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>

...

> +//XXX: Refactor mirred code and reuse here before final version
> +static int cast_one(struct sk_buff *skb, const u32 ifindex)
> +{
> +	struct sk_buff *skb2 = skb;
> +	int retval = TC_ACT_PIPE;
> +	struct net_device *dev;
> +	unsigned int rec_level;
> +	bool expects_nh;
> +	int mac_len;
> +	bool at_nh;
> +	int err;
> +
> +	rec_level = __this_cpu_inc_return(redirect_rec_level);
> +	if (unlikely(rec_level > CAST_RECURSION_LIMIT)) {
> +		net_warn_ratelimited("blockcast: exceeded redirect recursion limit on dev %s\n",
> +				     netdev_name(skb->dev));
> +		__this_cpu_dec(redirect_rec_level);
> +		return TC_ACT_SHOT;
> +	}
> +
> +	dev = dev_get_by_index_rcu(dev_net(skb->dev), ifindex);
> +	if (unlikely(!dev)) {
> +		pr_notice_once("blockcast: target device %s is gone\n",
> +			       dev->name);

Hi Jamal,

This code is only executed if dev is NULL, but dev is dereferenced.

> +		__this_cpu_dec(redirect_rec_level);
> +		return TC_ACT_SHOT;
> +	}

...