linux-kernel - Re: 6.0 tty regression, NULL pointer deref in flush_to

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Date:   Mon, 29 Aug 2022 12:36:24 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux regressions mailing list <regressions@...ts.linux.dev>
Subject: Re: 6.0 tty regression, NULL pointer deref in flush_to_ldisc

On Mon, 29 Aug 2022, Hans de Goede wrote:

> Hi All,
> 
> This weekend I noticed that on various Bay Trail based systems which have
> their bluetooth HCI connected over an uart (using hci_uart driver /
> using the drivers/tty/serial bus) there is a NULL pointer deref in
> flush_to_ldisc, see below for the full backtrace.
> 
> I *suspect* that this is caused by commit 6bb6fa6908eb
> ("tty: Implement lookahead to process XON/XOFF timely").
> 
> I can cleanly revert this by reverting the following commits:
> 
> ab24a01b2765 ("tty: Add closing marker into comment in tty_ldisc.h")
> 65534736d9a5 ("tty: Use flow-control char function on closing path")
> 6bb6fa6908eb ("tty: Implement lookahead to process XON/XOFF timely")
> 
> ATM I don't have one of the affected systems handy. I will give
> a 6.0-rc3 kernel with these 3 commits reverted a try tonight (CEST)
> and I'll let you know the results.
> 
> Note I can NOT confirm yet that these reverts fix things, so please
> don't revert anything yet. I just wanted to give people a headsup
> about this issue.
> 
> Also maybe we can fix the new lookahead code instead of reverting.
> I would be happy to add a patch adding some debugging prints the
> systems run fine after the backtrace as long as I don't suspend them
> so gathering logs is easy.

I guess this will help:

https://lore.kernel.org/linux-kernel/20220818115026.2237893-1-vincent.whitchurch@axis.com/

-- 
 i.