Subject: Re: [RFC v2 net-next 7/7] af_packet: use sk_skb_reason_drop to free rx packets

From: Simon Horman <[email-masked]>
Date: Tue, 4 Jun 2024 16:18:55 +0100

On Fri, May 31, 2024 at 06:43:00PM -0700, Yan Zhai wrote:
> Replace kfree_skb_reason with sk_skb_reason_drop and pass the receiving
> socket to the tracepoint.
> 
> Signed-off-by: Yan Zhai <[email-masked]>
> ---
>  net/packet/af_packet.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index fce390887591..3133d4eb4a1b 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c

Hi Yan Zhai,

Near the top of packet_rcv,
immediately after local variable declarations, and
before sk is initialised is the following:

	if (skb->pkt_type == PACKET_LOOPBACK)
		goto drop;

> @@ -2226,7 +2226,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
>  		skb->len = skb_len;
>  	}
>  drop:
> -	kfree_skb_reason(skb, drop_reason);
> +	sk_skb_reason_drop(sk, skb, drop_reason);

So sk may be used uninitialised here.

Similarly in tpacket_rcv()

Flagged by clang-18 W=1 allmodconfig builds on x86_64.

>  	return 0;
>  }
>  
> @@ -2494,7 +2494,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  		skb->len = skb_len;
>  	}
>  drop:
> -	kfree_skb_reason(skb, drop_reason);
> +	sk_skb_reason_drop(sk, skb, drop_reason);
>  	return 0;
>  
>  drop_n_account:
> @@ -2503,7 +2503,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  	drop_reason = SKB_DROP_REASON_PACKET_SOCK_ERROR;
>  
>  	sk->sk_data_ready(sk);
> -	kfree_skb_reason(copy_skb, drop_reason);
> +	sk_skb_reason_drop(sk, copy_skb, drop_reason);
>  	goto drop_n_restore;
>  }
>  
> -- 
> 2.30.2
> 
>