netdev - Re: [Patch bpf-next v8 10/16] sock: introduce sk->sk_prot->psock_update_sk

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Date:   Mon, 5 Apr 2021 10:25:27 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, duanxiongchun@...edance.com,
        wangdongdong.6@...edance.com, jiang.wang@...edance.com,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v8 10/16] sock: introduce
 sk->sk_prot->psock_update_sk_prot()



On 3/31/21 4:32 AM, Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> Currently sockmap calls into each protocol to update the struct
> proto and replace it. This certainly won't work when the protocol
> is implemented as a module, for example, AF_UNIX.
> 
> Introduce a new ops sk->sk_prot->psock_update_sk_prot(), so each
> protocol can implement its own way to replace the struct proto.
> This also helps get rid of symbol dependencies on CONFIG_INET.

[...]


>  
> -struct proto *tcp_bpf_get_proto(struct sock *sk, struct sk_psock *psock)
> +int tcp_bpf_update_proto(struct sock *sk, bool restore)
>  {
> +	struct sk_psock *psock = sk_psock(sk);

I do not think RCU is held here ?

sk_psock() is using rcu_dereference_sk_user_data()

>  	int family = sk->sk_family == AF_INET6 ? TCP_BPF_IPV6 : TCP_BPF_IPV4;
>  	int config = psock->progs.msg_parser   ? TCP_BPF_TX   : TCP_BPF_BASE;
>  

Same issue in udp_bpf_update_proto() of course.