netdev - Re: [PATCH net] tcp: purge write queue in tcp_connect

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Message-ID: <CADVnQykhb97fS3kqAwgQL-mRdTjJo2c3NoSfgnTRmx+QeMuFEg@mail.gmail.com>
Date:   Tue, 15 May 2018 12:42:31 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net] tcp: purge write queue in tcp_connect_init()

On Tue, May 15, 2018 at 12:14 AM Eric Dumazet <edumazet@...gle.com> wrote:

> syzkaller found a reliable way to crash the host, hitting a BUG()
> in __tcp_retransmit_skb()

> Malicous MSG_FASTOPEN is the root cause. We need to purge write queue
> in tcp_connect_init() at the point we init snd_una/write_seq.

> This patch also replaces the BUG() by a less intrusive WARN_ON_ONCE()

> kernel BUG at net/ipv4/tcp_output.c:2837!
...

> Fixes: cf60af03ca4e ("net-tcp: Fast Open client - sendmsg(MSG_FASTOPEN)")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>

Thanks, Eric!

neal