netdev - Re: [PATCH net-next v3 07/15] bpf: Add setsockopt helper function to bpf

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Date:   Tue, 20 Jun 2017 17:25:46 -0400
From:   Craig Gallek <kraigatgoog@...il.com>
To:     Lawrence Brakmo <brakmo@...com>
Cc:     netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        Blake Matheny <bmatheny@...com>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [PATCH net-next v3 07/15] bpf: Add setsockopt helper function to bpf

On Mon, Jun 19, 2017 at 11:00 PM, Lawrence Brakmo <brakmo@...com> wrote:
> Added support for calling a subset of socket setsockopts from
> BPF_PROG_TYPE_SOCK_OPS programs. The code was duplicated rather
> than making the changes to call the socket setsockopt function because
> the changes required would have been larger.
>
> @@ -2671,6 +2672,69 @@ static const struct bpf_func_proto bpf_get_socket_uid_proto = {
>         .arg1_type      = ARG_PTR_TO_CTX,
>  };
>
> +BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
> +          int, level, int, optname, char *, optval, int, optlen)
> +{
> +       struct sock *sk = bpf_sock->sk;
> +       int ret = 0;
> +       int val;
> +
> +       if (bpf_sock->is_req_sock)
> +               return -EINVAL;
> +
> +       if (level == SOL_SOCKET) {
> +               /* Only some socketops are supported */
> +               val = *((int *)optval);
> +
> +               switch (optname) {
> +               case SO_RCVBUF:
> +                       sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
> +                       sk->sk_rcvbuf = max_t(int, val * 2, SOCK_MIN_RCVBUF);
> +                       break;
> +               case SO_SNDBUF:
> +                       sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
> +                       sk->sk_sndbuf = max_t(int, val * 2, SOCK_MIN_SNDBUF);
> +                       break;
> +               case SO_MAX_PACING_RATE:
> +                       sk->sk_max_pacing_rate = val;
> +                       sk->sk_pacing_rate = min(sk->sk_pacing_rate,
> +                                                sk->sk_max_pacing_rate);
> +                       break;
> +               case SO_PRIORITY:
> +                       sk->sk_priority = val;
> +                       break;
> +               case SO_RCVLOWAT:
> +                       if (val < 0)
> +                               val = INT_MAX;
> +                       sk->sk_rcvlowat = val ? : 1;
> +                       break;
> +               case SO_MARK:
> +                       sk->sk_mark = val;
> +                       break;

Isn't the socket lock required when manipulating these fields?  It's
not obvious that the lock is held from every bpf hook point that could
trigger this function...