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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 10 Nov 2020 08:32:52 +0100
Message-ID: <CANn89iL6UW9mG6hW7f3Yv+32Pe_i9F-5cQhfo2uV68wdcgSuZA@mail.gmail.com>
Subject: Re: [PATCH net v5] net: Update window_clamp if SOCK_RCVBUF is set
To:     Mao Wenan <wenan.mao@linux.alibaba.com>
Cc:     David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-janitors@vger.kernel.org
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On Tue, Nov 10, 2020 at 1:16 AM Mao Wenan <wenan.mao@linux.alibaba.com> wrote:
>
> When net.ipv4.tcp_syncookies=1 and syn flood is happened,
> cookie_v4_check or cookie_v6_check tries to redo what
> tcp_v4_send_synack or tcp_v6_send_synack did,
> rsk_window_clamp will be changed if SOCK_RCVBUF is set,
> which will make rcv_wscale is different, the client
> still operates with initial window scale and can overshot
> granted window, the client use the initial scale but local
> server use new scale to advertise window value, and session
> work abnormally.
>
> Fixes: e88c64f0a425 ("tcp: allow effective reduction of TCP's rcv-buffer via setsockopt")
> Signed-off-by: Mao Wenan <wenan.mao@linux.alibaba.com>

Signed-off-by: Eric Dumazet <edumazet@google.com>

Thanks !