linux-kernel - Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init

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Message-ID: <205F52AB-4A5B-4953-B97E-17E7CACBBCD8@gmail.com>
Date:   Tue, 29 Jun 2021 15:17:20 +0800
From:   Nguyen Dinh Phi <phind.uet@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>
CC:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>, kpsingh@...nel.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+f1e24a0594d4e3a895d3@...kaller.appspotmail.com,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.

On June 29, 2021 1:20:19 AM GMT+08:00, Neal Cardwell <ncardwell@...gle.com> wrote:
>)
>
>On Mon, Jun 28, 2021 at 1:15 PM Phi Nguyen <phind.uet@...il.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

I resend my message because I accidently used html format in last one. I am very sorry for the inconvenience caused.
---
Yes, the CC had been initialized by the setsockopt, after that, it was initialized again in function tcp_init_transfer() because of setting isck_ca_initialized to 0.
Regards, 
Phi.