Re: [PATCH net-next 8/9] net: ipv6: add skb drop reasons to ip6_rcv_core()

[Eric Dumazet <edumazet@gmail.com>]

On 4/13/22 01:15, menglong8.dong@gmail.com wrote:
> From: Menglong Dong <imagedong@tencent.com>
>
> Replace kfree_skb() used in ip6_rcv_core() with kfree_skb_reason().
> No new drop reasons are added.
>
> Seems now we use 'SKB_DROP_REASON_IP_INHDR' for too many case during
> ipv6 header parse or check, just like what 'IPSTATS_MIB_INHDRERRORS'
> do. Will it be too general and hard to know what happened?
>
> Signed-off-by: Menglong Dong <imagedong@tencent.com>
> Reviewed-by: Jiang Biao <benbjiang@tencent.com>
> Reviewed-by: Hao Peng <flyingpeng@tencent.com>
> ---
>   net/ipv6/ip6_input.c | 24 ++++++++++++++++--------
>   1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
> index b4880c7c84eb..1b925ecb26e9 100644
> --- a/net/ipv6/ip6_input.c
> +++ b/net/ipv6/ip6_input.c
> @@ -145,13 +145,14 @@ static void ip6_list_rcv_finish(struct net *net, struct sock *sk,
>   static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   				    struct net *net)
>   {
> +	enum skb_drop_reason reason;
>   	const struct ipv6hdr *hdr;
>   	u32 pkt_len;
>   	struct inet6_dev *idev;
>   
>   	if (skb->pkt_type == PACKET_OTHERHOST) {
>   		dev_core_stats_rx_otherhost_dropped_inc(skb->dev);
> -		kfree_skb(skb);
> +		kfree_skb_reason(skb, SKB_DROP_REASON_OTHERHOST);
>   		return NULL;
>   	}
>   
> @@ -161,9 +162,12 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   
>   	__IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_IN, skb->len);
>   
> +	SKB_DR_SET(reason, NOT_SPECIFIED);
>   	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL ||
>   	    !idev || unlikely(idev->cnf.disable_ipv6)) {
>   		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
> +		if (unlikely(idev->cnf.disable_ipv6))

idev can be NULL here (according to surrounding code), and we crash :/



> +			SKB_DR_SET(reason, IPV6DISABLED);
>   		goto drop;
>   	}
>   
> @@ -187,8 +191,10 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   
>   	hdr = ipv6_hdr(skb);
>   
> -	if (hdr->version != 6)
> +	if (hdr->version != 6) {
> +		SKB_DR_SET(reason, UNHANDLED_PROTO);
>   		goto err;
> +	}
>   
>   	__IP6_ADD_STATS(net, idev,
>   			IPSTATS_MIB_NOECTPKTS +
> @@ -226,8 +232,10 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   	if (!ipv6_addr_is_multicast(&hdr->daddr) &&
>   	    (skb->pkt_type == PACKET_BROADCAST ||
>   	     skb->pkt_type == PACKET_MULTICAST) &&
> -	    idev->cnf.drop_unicast_in_l2_multicast)
> +	    idev->cnf.drop_unicast_in_l2_multicast) {
> +		SKB_DR_SET(reason, UNICAST_IN_L2_MULTICAST);
>   		goto err;
> +	}
>   
>   	/* RFC4291 2.7
>   	 * Nodes must not originate a packet to a multicast address whose scope
> @@ -256,12 +264,11 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   		if (pkt_len + sizeof(struct ipv6hdr) > skb->len) {
>   			__IP6_INC_STATS(net,
>   					idev, IPSTATS_MIB_INTRUNCATEDPKTS);
> +			SKB_DR_SET(reason, PKT_TOO_SMALL);
>   			goto drop;
>   		}
> -		if (pskb_trim_rcsum(skb, pkt_len + sizeof(struct ipv6hdr))) {
> -			__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
> -			goto drop;
> -		}
> +		if (pskb_trim_rcsum(skb, pkt_len + sizeof(struct ipv6hdr)))
> +			goto err;
>   		hdr = ipv6_hdr(skb);
>   	}
>   
> @@ -282,9 +289,10 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>   	return skb;
>   err:
>   	__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
> +	SKB_DR_OR(reason, IP_INHDR);
>   drop:
>   	rcu_read_unlock();
> -	kfree_skb(skb);
> +	kfree_skb_reason(skb, reason);
>   	return NULL;
>   }
>