linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference in mem16_serial

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Date:   Fri, 13 Dec 2019 10:05:11 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     syzbot <syzbot+92f32d4e21fb246d31a2@...kaller.appspotmail.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asierra@...-inc.com, Jonathan Corbet <corbet@....net>,
        ext-kimmo.rautkoski@...sala.com, Jiri Slaby <jslaby@...e.com>,
        kai heng feng <kai.heng.feng@...onical.com>,
        Linux API <linux-api@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        mika.westerberg@...ux.intel.com, paulburton@...nel.org,
        Peter Hurley <peter@...leysoftware.com>, sr@...x.de,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        yegorslists@...glemail.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out

On Thu, Dec 12, 2019 at 11:57 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Mon, Dec 09, 2019 at 05:38:01PM -0800, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit bd94c4077a0b2ecc35562c294f80f3659ecd8499
> > Author: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > Date:   Wed Oct 28 03:46:05 2015 +0000
> >
> >     serial: support 16-bit register interface for console
>
> That would be because that is when this function was added to the kernel
> :)
>
> Again, you are asking the kernel to write to a bad place in memory, and
> then crash when that happens.  That sounds like the correct
> functionality to me...

This looks like:

#syz dup:
BUG: unable to handle kernel NULL pointer dereference in mem_serial_out

Let's continue in that thread.