netdev - Re: [PATCH v3 net-next 3/7] net: ipv4: use kfree_skb_reason() in ip_rcv

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Date:   Mon, 31 Jan 2022 11:05:58 -0700
From:   David Ahern <dsahern@...il.com>
To:     menglong8.dong@...il.com, dsahern@...nel.org, kuba@...nel.org
Cc:     rostedt@...dmis.org, mingo@...hat.com, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, pablo@...filter.org, kadlec@...filter.org,
        fw@...len.de, imagedong@...cent.com, edumazet@...gle.com,
        alobakin@...me, paulb@...dia.com, keescook@...omium.org,
        talalahmad@...gle.com, haokexin@...il.com, memxor@...il.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        cong.wang@...edance.com, mengensun@...cent.com
Subject: Re: [PATCH v3 net-next 3/7] net: ipv4: use kfree_skb_reason() in
 ip_rcv_core()

On 1/28/22 12:33 AM, menglong8.dong@...il.com wrote:
\> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index 3a025c011971..627fad437593 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -436,13 +436,18 @@ static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
>  static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
>  {
>  	const struct iphdr *iph;
> +	int drop_reason;
>  	u32 len;
>  
> +	drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;

move this line down, right before:

	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
		goto inhdr_error;

> +
>  	/* When the interface is in promisc. mode, drop all the crap
>  	 * that it receives, do not try to analyse it.
>  	 */
> -	if (skb->pkt_type == PACKET_OTHERHOST)
> +	if (skb->pkt_type == PACKET_OTHERHOST) {
> +		drop_reason = SKB_DROP_REASON_OTHERHOST;
>  		goto drop;
> +	}
>  
>  	__IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
>  
> @@ -488,6 +493,7 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
>  
>  	len = ntohs(iph->tot_len);
>  	if (skb->len < len) {
> +		drop_reason = SKB_DROP_REASON_PKT_TOO_SMALL;
>  		__IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
>  		goto drop;
>  	} else if (len < (iph->ihl*4))
> @@ -516,11 +522,13 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
>  	return skb;
>  
>  csum_error:
> +	drop_reason = SKB_DROP_REASON_IP_CSUM;
>  	__IP_INC_STATS(net, IPSTATS_MIB_CSUMERRORS);
>  inhdr_error:
> +	drop_reason = drop_reason ?: SKB_DROP_REASON_IP_INHDR;

That makes assumptions about the value of SKB_DROP_REASON_NOT_SPECIFIED.
Make that line:
	if (drop_reason != SKB_DROP_REASON_NOT_SPECIFIED)
		drop_reason = SKB_DROP_REASON_IP_INHDR;

>  	__IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
>  drop:
> -	kfree_skb(skb);
> +	kfree_skb_reason(skb, drop_reason);
>  out:
>  	return NULL;
>  }