netdev - Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to gre

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Date:   Tue, 15 Mar 2022 20:08:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     menglong8.dong@...il.com
Cc:     dsahern@...nel.org, rostedt@...dmis.org, mingo@...hat.com,
        xeb@...l.ru, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        imagedong@...cent.com, edumazet@...gle.com, kafai@...com,
        talalahmad@...gle.com, keescook@...omium.org, alobakin@...me,
        flyingpeng@...cent.com, mengensun@...cent.com,
        dongli.zhang@...cle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Biao Jiang <benbjiang@...cent.com>
Subject: Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to
 gre_rcv()

On Mon, 14 Mar 2022 21:33:10 +0800 menglong8.dong@...il.com wrote:
> +	reason = SKB_DROP_REASON_NOT_SPECIFIED;
>  	if (!pskb_may_pull(skb, 12))
>  		goto drop;

REASON_HDR_TRUNC ?

>  	ver = skb->data[1]&0x7f;
> -	if (ver >= GREPROTO_MAX)
> +	if (ver >= GREPROTO_MAX) {
> +		reason = SKB_DROP_REASON_GRE_VERSION;

TBH I'm still not sure what level of granularity we should be shooting
for with the reasons. I'd throw all unexpected header values into one 
bucket, not go for a reason per field, per protocol. But as I'm said
I'm not sure myself, so we can keep what you have..

>  		goto drop;
> +	}
>  
>  	rcu_read_lock();
>  	proto = rcu_dereference(gre_proto[ver]);
> -	if (!proto || !proto->handler)
> +	if (!proto || !proto->handler) {
> +		reason = SKB_DROP_REASON_GRE_NOHANDLER;

I think the ->handler check is defensive programming, there's no
protocol upstream which would leave handler NULL.

This is akin to SKB_DROP_REASON_PTYPE_ABSENT, we can reuse that or add
a new reason, but I'd think the phrasing should be kept similar.

>  		goto drop_unlock;
> +	}
>  	ret = proto->handler(skb);