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References: <20211229085547.206008-1-imagedong@tencent.com>
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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 29 Dec 2021 08:44:08 -0800
Message-ID: <CAADnVQLiqRdE0iqSFM7za2g5UVNDE-ZZmS7+pca176_ePKsZvA@mail.gmail.com>
Subject: Re: [PATCH net-next] net: bpf: hook for inet port bind conflict check
To:     menglong8.dong@gmail.com
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Menglong Dong <imagedong@tencent.com>
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On Wed, Dec 29, 2021 at 12:56 AM <menglong8.dong@gmail.com> wrote:
>
> From: Menglong Dong <imagedong@tencent.com>
>
> This hook of cgroup is called while TCP/UDP local port bind conflict
> check. This is different from the 'commit aac3fc320d94 ("bpf: Post-hooks
> for sys_bind")', as it is also called in autobind case.
>
> For TCP, this hook is called during sys_bind() and autobind. And it
> is also called during tcp_v4_connect() before hash the sock to ehash,
> during which src ip, src port, dst ip, and dst port is already
> allocated, means that we have a chance to determine whether this
> connect should continue.
>
> This can be useful when we want some applications not to use some
> port (include auto bind port). For autobind, the kernel has the chance
> to choose another port.

The use case is too vague to consider adding a new hook.
Also there are no selftests.