linux-kernel - Re: [PATCH bpf-next v3 2/3] bpf, sockmap: avoid using sk

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Message-ID: <Z9tiqkSOH9vuOOJL@pop-os.localdomain>
Date: Wed, 19 Mar 2025 17:34:50 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: john.fastabend@...il.com, jakub@...udflare.com, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
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	jolsa@...nel.org, shuah@...nel.org, mhal@...x.co,
	sgarzare@...hat.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	syzbot+dd90a702f518e0eac072@...kaller.appspotmail.com
Subject: Re: [PATCH bpf-next v3 2/3] bpf, sockmap: avoid using sk_socket
 after free when reading

On Mon, Mar 17, 2025 at 05:22:55PM +0800, Jiayuan Chen wrote:
> There are potential concurrency issues, as shown below.
> '''
> CPU0                               CPU1
> sk_psock_verdict_data_ready:
>   socket *sock = sk->sk_socket
>   if (!sock) return
>                                    close(fd):
>                                      ...
>                                      ops->release()
>   if (!sock->ops) return
>                                      sock->ops = NULL
>                                      rcu_call(sock)
>                                      free(sock)
>   READ_ONCE(sock->ops)
>   ^
>   use 'sock' after free
> '''
> 
> RCU is not applicable to Unix sockets read path, because the Unix socket
> implementation itself assumes it's always in process context and heavily
> uses mutex_lock, so, we can't call read_skb within rcu lock.

Hm, I guess the RCU work in sk_psock_drop() does not work for Unix
domain sockets either?

Thanks.