netdev - Re: [PATCH net-next v2 1/2] Add a helper function to get socket cookie in eBPF

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Message-ID: <CAKD1Yr0Jdj=KZ+MOs8V1WVYg_j3BkWQ6Ncmu9u4YYYu_pxS77A@mail.gmail.com>
Date:   Mon, 6 Feb 2017 12:01:47 +0900
From:   Lorenzo Colitti <lorenzo@...gle.com>
To:     Chenbo Feng <chenbofeng.kernel@...il.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Chenbo Feng <fengc@...gle.com>
Subject: Re: [PATCH net-next v2 1/2] Add a helper function to get socket
 cookie in eBPF

On Mon, Feb 6, 2017 at 11:17 AM, Chenbo Feng
<chenbofeng.kernel@...il.com> wrote:
> +BPF_CALL_1(bpf_get_socket_cookie, struct sk_buff *, skb)
> +{
> +       return skb->sk ? sock_gen_cookie(skb->sk) : 0;
> +}
> +

Does this code need to increment the socket refcount, or call
ACCESS_ONCE to get skb->sk? The socket filter codepath should be safe,
but if this function is called in xt_ebpf, could it race with
something that sets skb->sk to null?