March 20, 2025 at 08:34, "Cong Wang" <xiyou.wangcong@xxxxxxxxx> wrote:
>
> 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.
>
Although the Unix domain socket framework does not use RCU locks, the
entire sockmap process protects access to psock via RCU:
'''
rcu_read_lock();
psock = sk_psock(sk_other);
if (psock) {
...
}
rcu_read_unlock(); // `sk_psock_drop` will not execute until the unlock
'''
Therefore, I believe there are no issues with the psock operations here.
Thanks~
