netdev - [PATCH net] af_packet: do not use READ_ONCE() in packet

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Date: Fri, 26 May 2023 09:23:20 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <kuba@...nel.org>,
	<kuniyu@...zon.com>, <netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<willemb@...gle.com>
Subject: [PATCH net] af_packet: do not use READ_ONCE() in packet_bind()

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 26 May 2023 15:43:42 +0000
> A recent patch added READ_ONCE() in packet_bind() and packet_bind_spkt()
> 
> This is better handled by reading pkt_sk(sk)->num later
> in packet_do_bind() while appropriate lock is held.
> 
> READ_ONCE() in writers are often an evidence of something being wrong.
> 
> Fixes: 822b5a1c17df ("af_packet: Fix data-races of pkt_sk(sk)->num.")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
> Cc: Willem de Bruijn <willemb@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Thanks!


> ---
>  net/packet/af_packet.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index a1f9a0e9f3c8a72e5a95f96473b7b6c63f893935..a2dbeb264f260e5b8923ece9aac99fe19ddfeb62 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -3201,6 +3201,9 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
>  
>  	lock_sock(sk);
>  	spin_lock(&po->bind_lock);
> +	if (!proto)
> +		proto = po->num;
> +
>  	rcu_read_lock();
>  
>  	if (po->fanout) {
> @@ -3299,7 +3302,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
>  	memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data_min));
>  	name[sizeof(uaddr->sa_data_min)] = 0;
>  
> -	return packet_do_bind(sk, name, 0, READ_ONCE(pkt_sk(sk)->num));
> +	return packet_do_bind(sk, name, 0, 0);
>  }
>  
>  static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
> @@ -3316,8 +3319,7 @@ static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len
>  	if (sll->sll_family != AF_PACKET)
>  		return -EINVAL;
>  
> -	return packet_do_bind(sk, NULL, sll->sll_ifindex,
> -			      sll->sll_protocol ? : READ_ONCE(pkt_sk(sk)->num));
> +	return packet_do_bind(sk, NULL, sll->sll_ifindex, sll->sll_protocol);
>  }
>  
>  static struct proto packet_proto = {
> -- 
> 2.41.0.rc0.172.g3f132b7071-goog