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Date: Tue, 24 Feb 2026 13:52:19 +0100
From: Florian Westphal <fw@strlen.de>
To: Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Jozsef Kadlecsik <kadlec@netfilter.org>, netdev@vger.kernel.org,
	netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
	eric.dumazet@gmail.com
Subject: Re: [PATCH net-next] netfilter: xt_owner: no longer acquire
 sk_callback_lock in mt_owner()
Message-ID: <aZ2fA2x5nHsnQoBu@strlen.de>
References: <20260224122856.3152608-1-edumazet@google.com>
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In-Reply-To: <20260224122856.3152608-1-edumazet@google.com>

Eric Dumazet <edumazet@google.com> wrote:
> After commit 983512f3a87f ("net: Drop the lock in skb_may_tx_timestamp()")
> from Sebastian Andrzej Siewior, apply the same logic in mt_owner()
> to avoid touching sk_callback_lock.
> -	read_lock_bh(&sk->sk_callback_lock);
> -	filp = sk->sk_socket ? sk->sk_socket->file : NULL;
> +	/* The sk pointer remains valid as long as the skb is. The sk_socket and
> +	 * file pointer may become NULL if the socket is closed. Both structures
> +	 * (including file->cred) are RCU freed which means they can be accessed
> +	 * within a RCU read section.
> +	 */
> +	rcu_read_lock();
> +	sock = READ_ONCE(sk->sk_socket);
> +	filp = sock ? READ_ONCE(sock->file) : NULL;

Thanks for doing this Eric!

Minor nit: rcu_read_lock is already acquired from nf_hook() helper, so
we aleays have it in both iptables and nftables.

Reviewed-by: Florian Westphal <fw@strlen.de>