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Date:   Thu, 3 Aug 2023 14:53:38 +0200
From:   Simon Horman <horms@kernel.org>
To:     Geliang Tang <geliang.tang@suse.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Florent Revest <revest@chromium.org>,
        Brendan Jackman <jackmanb@chromium.org>,
        Matthieu Baerts <matthieu.baerts@tessares.net>,
        Mat Martineau <martineau@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
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        "Serge E. Hallyn" <serge@hallyn.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Eric Paris <eparis@parisplace.org>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        bpf@vger.kernel.org, netdev@vger.kernel.org, mptcp@lists.linux.dev,
        apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org,
        selinux@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next v8 1/4] bpf: Add update_socket_protocol hook
Message-ID: <ZMujUofDnb8wMb36@kernel.org>
References: <cover.1691047403.git.geliang.tang@suse.com>
 <120b307aacd1791fac016d33e112069ffb7db21a.1691047403.git.geliang.tang@suse.com>
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List-ID: <linux-security-module.vger.kernel.org>

On Thu, Aug 03, 2023 at 03:30:39PM +0800, Geliang Tang wrote:
> Add a hook named update_socket_protocol in __sys_socket(), for bpf
> progs to attach to and update socket protocol. One user case is to
> force legacy TCP apps to create and use MPTCP sockets instead of
> TCP ones.
> 
> Define a mod_ret set named bpf_mptcp_fmodret_ids, add the hook
> update_socket_protocol into this set, and register it in
> bpf_mptcp_kfunc_init().
> 
> Signed-off-by: Geliang Tang <geliang.tang@suse.com>

...

> diff --git a/net/socket.c b/net/socket.c
> index 2b0e54b2405c..586a437d7a5e 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1644,11 +1644,36 @@ struct file *__sys_socket_file(int family, int type, int protocol)
>  	return sock_alloc_file(sock, flags, NULL);
>  }
>  
> +/**

Hi Geliang Tang,

nit: The format of the text below is not in kernel doc format,
     so it is probably better if the comment begins with '/*'
     rather than '/**'.

> + *	A hook for bpf progs to attach to and update socket protocol.
> + *
> + *	A static noinline declaration here could cause the compiler to
> + *	optimize away the function. A global noinline declaration will
> + *	keep the definition, but may optimize away the callsite.
> + *	Therefore, __weak is needed to ensure that the call is still
> + *	emitted, by telling the compiler that we don't know what the
> + *	function might eventually be.
> + *
> + *	__diag_* below are needed to dismiss the missing prototype warning.
> + */

...