netdev - Re: [PATCH bpf-next] flow_dissector: lookup netns by skb->sk if skb->dev is NULL

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Message-ID: <CAPhsuW4VGft08QbAK7sKs4xkFq7P+JzZMYdSi-47mh0gyw8SnQ@mail.gmail.com>
Date:   Mon, 24 Sep 2018 23:13:52 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next] flow_dissector: lookup netns by skb->sk if
 skb->dev is NULL

On Mon, Sep 24, 2018 at 1:52 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> From: Willem de Bruijn <willemb@...gle.com>
>
> BPF flow dissectors are configured per network namespace.
> __skb_flow_dissect looks up the netns through dev_net(skb->dev).
>
> In some dissector paths skb->dev is NULL, such as for Unix sockets.
> In these cases fall back to looking up the netns by socket.
>
> Analyzing the codepaths leading to __skb_flow_dissect I did not find
> a case where both skb->dev and skb->sk are NULL. Warn and fall back to
> standard flow dissector if one is found.
>
> Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  net/core/flow_dissector.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 5c5dd74b5b3b..738c7562e1e0 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -714,7 +714,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>         struct flow_dissector_key_vlan *key_vlan;
>         enum flow_dissect_ret fdret;
>         enum flow_dissector_key_id dissector_vlan = FLOW_DISSECTOR_KEY_MAX;
> -       struct bpf_prog *attached;
> +       struct bpf_prog *attached = NULL;
>         int num_hdrs = 0;
>         u8 ip_proto = 0;
>         bool ret;
> @@ -755,8 +755,14 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>                                               target_container);
>
>         rcu_read_lock();
> -       attached = skb ? rcu_dereference(dev_net(skb->dev)->flow_dissector_prog)
> -                      : NULL;
> +       if (skb) {
> +               if (skb->dev)
> +                       attached = rcu_dereference(dev_net(skb->dev)->flow_dissector_prog);
> +               else if (skb->sk)
> +                       attached = rcu_dereference(sock_net(skb->sk)->flow_dissector_prog);
> +               else
> +                       WARN_ON_ONCE(1);
> +       }
>         if (attached) {
>                 /* Note that even though the const qualifier is discarded
>                  * throughout the execution of the BPF program, all changes(the
> --
> 2.19.0.444.g18242da7ef-goog
>