netdev - Re: [PATCH] bpf: Add bpf_skb_get_sock

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Date:   Mon, 10 Aug 2020 10:56:14 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Jiang Yu <jyu.jiang@...o.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        zhanglin <zhang.lin16@....com.cn>,
        Kees Cook <keescook@...omium.org>,
        Andrey Ignatov <rdna@...com>,
        Quentin Monnet <quentin@...valent.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <bpf@...r.kernel.org>, <opensource.kernel@...o.com>
Subject: Re: [PATCH] bpf: Add bpf_skb_get_sock_comm() helper

On Mon, Aug 10, 2020 at 06:09:48AM -0700, Jiang Yu wrote:
> skb distinguished by uid can only recorded to user who consume them.
> in many case, skb should been recorded more specific to process who
> consume them. E.g, the unexpected large data traffic of illegal process
> in metered network.
> 
> this helper is used in tracing task comm of the sock to which a skb
> belongs.
> 
> Signed-off-by: Jiang Yu <jyu.jiang@...o.com>
> ---
>  include/net/sock.h             |  1 +
>  include/uapi/linux/bpf.h       |  1 +
>  net/core/filter.c              | 32 ++++++++++++++++++++++++++++++++
>  net/core/sock.c                | 20 ++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  1 +
>  5 files changed, 55 insertions(+)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 064637d1ddf6..9c6e8e61940f 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -519,6 +519,7 @@ struct sock {
>  #ifdef CONFIG_BPF_SYSCALL
>  	struct bpf_sk_storage __rcu	*sk_bpf_storage;
>  #endif
> +	char sk_task_com[TASK_COMM_LEN];
One possibility is to use the "sk_bpf_storage" member immediately above
instead of adding "sk_task_com[]".

It is an extensible sk storage for bpf.  There are examples in selftests,
e.g tools/testing/selftests/bpf/progs/udp_limits.c which creates sk storage
at socket creation time.  Another hook point option could be "connect()"
for tcp, i.e. "cgroup/connect[46]".

Search "BPF_MAP_TYPE_SK_STORAGE" under the selftests/bpf for other examples.

It seems there is already a "bpf_get_current_comm()" helper which
could be used to initialize the task comm string in the bpf sk storage.

btw, bpf-next is still closed.