linux-kernel - Re: [RFC v2 net-next 7/7] af_packet: use sk_skb_reason

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Date: Tue, 4 Jun 2024 16:18:55 +0100
From: Simon Horman <horms@...nel.org>
To: Yan Zhai <yan@...udflare.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	David Ahern <dsahern@...nel.org>,
	Abhishek Chauhan <quic_abchauha@...cinc.com>,
	Mina Almasry <almasrymina@...gle.com>,
	Florian Westphal <fw@...len.de>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	David Howells <dhowells@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
	Daniel Borkmann <daniel@...earbox.net>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Pavel Begunkov <asml.silence@...il.com>,
	linux-kernel@...r.kernel.org, kernel-team@...udflare.com,
	Jesper Dangaard Brouer <hawk@...nel.org>
Subject: Re: [RFC v2 net-next 7/7] af_packet: use sk_skb_reason_drop to free
 rx packets

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 <yan@...udflare.com>
> ---
>  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
> 
>