Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <16e8de51-6b56-3dfe-e9c4-524ab40cdea9@gmail.com>
Date:   Mon, 31 Jan 2022 11:05:58 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.5.1
Subject: Re: [PATCH v3 net-next 3/7] net: ipv4: use kfree_skb_reason() in
 ip_rcv_core()
Content-Language: en-US
To:     menglong8.dong@gmail.com, dsahern@kernel.org, kuba@kernel.org
Cc:     rostedt@goodmis.org, mingo@redhat.com, davem@davemloft.net,
        yoshfuji@linux-ipv6.org, pablo@netfilter.org, kadlec@netfilter.org,
        fw@strlen.de, imagedong@tencent.com, edumazet@google.com,
        alobakin@pm.me, paulb@nvidia.com, keescook@chromium.org,
        talalahmad@google.com, haokexin@gmail.com, memxor@gmail.com,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        cong.wang@bytedance.com, mengensun@tencent.com
References: <20220128073319.1017084-1-imagedong@tencent.com>
 <20220128073319.1017084-4-imagedong@tencent.com>
From:   David Ahern <dsahern@gmail.com>
In-Reply-To: <20220128073319.1017084-4-imagedong@tencent.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 1/28/22 12:33 AM, menglong8.dong@gmail.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;
>  }