netdev - Re: Crash when receiving FIN-ACK in TCP_FIN

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Date:   Sun, 20 Oct 2019 18:16:04 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Cc:     Netdev <netdev@...r.kernel.org>, Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: Crash when receiving FIN-ACK in TCP_FIN_WAIT1 state

tcp_write_queue_purgeOn Sun, Oct 20, 2019 at 4:25 PM Subash Abhinov
Kasiviswanathan <subashab@...eaurora.org> wrote:
>
> We are seeing a crash in the TCP ACK codepath often in our regression
> racks with an ARM64 device with 4.19 based kernel.
>
> It appears that the tp->highest_ack is invalid when being accessed when
> a
> FIN-ACK is received. In all the instances of the crash, the tcp socket
> is in TCP_FIN_WAIT1 state.

Hmm. Random related thought while searching for a possible cause: I
wonder if tcp_write_queue_purge() should clear tp->highest_sack (and
possibly tp->sacked_out)? The tcp_write_queue_purge() code is careful
to call  tcp_clear_all_retrans_hints(tcp_sk(sk)) and I would imagine
that similar considerations would imply that we should clear at least
tp->highest_sack?

neal