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From:   Neal Cardwell <ncardwell@google.com>
Date:   Mon, 28 Jun 2021 13:20:19 -0400
Message-ID: <CADVnQynqMQhO4cBON=xUCkne9-E1hze3naMZZ8tQ-a0k71kh8g@mail.gmail.com>
Subject: Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.
To:     Phi Nguyen <phind.uet@gmail.com>
Cc:     Eric Dumazet <edumazet@google.com>,
        David Miller <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        John Fastabend <john.fastabend@gmail.com>, kpsingh@kernel.org,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+f1e24a0594d4e3a895d3@syzkaller.appspotmail.com,
        Yuchung Cheng <ycheng@google.com>
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On Mon, Jun 28, 2021 at 1:15 PM Phi Nguyen <phind.uet@gmail.com> wrote:
>
> On 6/29/2021 12:24 AM, Neal Cardwell wrote:
>
> > Thanks.
> >
> > Can you also please provide a summary of the event sequence that
> > triggers the bug? Based on your Reported-by tag, I guess this is based
> > on the syzbot reproducer:
> >
> >   https://groups.google.com/g/syzkaller-bugs/c/VbHoSsBz0hk/m/cOxOoTgPCAAJ
> >
> > but perhaps you can give a summary of the event sequence that causes
> > the bug? Is it that the call:
> >
> > setsockopt$inet_tcp_TCP_CONGESTION(r0, 0x6, 0xd,
> > &(0x7f0000000000)='cdg\x00', 0x4)
> >
> > initializes the CC and happens before the connection is established,
> > and then when the connection is established, the line that sets:
> >    icsk->icsk_ca_initialized = 0;
> > is incorrect, causing the CC to be initialized again without first
> > calling the cleanup code that deallocates the CDG-allocated memory?
> >
> > thanks,
> > neal
> >
>
> Hi Neal,
>
> The gdb stack trace that lead to init_transfer_input() is as bellow, the
> current sock state is TCP_SYN_RECV.

Thanks. That makes sense as a snapshot of time for
tcp_init_transfer(), but I think what would be more useful would be a
description of the sequence of events, including when the CC was
initialized previous to that point (as noted above, was it that the
setsockopt(TCP_CONGESTION) completed before that point?).

thanks,
neal