netdev - Re: [bpf PATCH 1/2] bpf, sockmap: fix sk->prot unhash op reset

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Message-ID: <CAM_iQpUNUE8cmyNaALG1dZtCfJGah2pggDNk-eVbyxexnA4o_g@mail.gmail.com>
Date:   Wed, 24 Mar 2021 17:11:22 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>, bpf <bpf@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [bpf PATCH 1/2] bpf, sockmap: fix sk->prot unhash op reset

On Wed, Mar 24, 2021 at 1:59 PM John Fastabend <john.fastabend@...il.com> wrote:
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> index 47b7c5334c34..ecb5634b4c4a 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -754,6 +754,12 @@ static void tls_update(struct sock *sk, struct proto *p,
>
>         ctx = tls_get_ctx(sk);
>         if (likely(ctx)) {
> +               /* TLS does not have an unhash proto in SW cases, but we need
> +                * to ensure we stop using the sock_map unhash routine because
> +                * the associated psock is being removed. So use the original
> +                * unhash handler.
> +                */
> +               WRITE_ONCE(sk->sk_prot->unhash, p->unhash);
>                 ctx->sk_write_space = write_space;
>                 ctx->sk_proto = p;

It looks awkward to update sk->sk_proto inside tls_update(),
at least when ctx!=NULL.

What is wrong with updating it in sk_psock_restore_proto()
when inet_csk_has_ulp() is true? It looks better to me.

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 6c09d94be2e9..da5dc3ef0ee3 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -360,8 +360,8 @@ static inline void sk_psock_update_proto(struct sock *sk,
 static inline void sk_psock_restore_proto(struct sock *sk,
                                          struct sk_psock *psock)
 {
-       sk->sk_prot->unhash = psock->saved_unhash;
        if (inet_csk_has_ulp(sk)) {
+               sk->sk_prot->unhash = psock->sk_proto->unhash;
                tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
        } else {
                sk->sk_write_space = psock->saved_write_space;


sk_psock_restore_proto() is the only caller of tcp_update_ulp()
so should be equivalent.

Thanks.