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

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Message-ID: <20191213160700.GA2632926@kroah.com>
Date:   Fri, 13 Dec 2019 17:07:00 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+f4f1e871965064ae689e@...kaller.appspotmail.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asierra@...-inc.com, ext-kimmo.rautkoski@...sala.com,
        Jiri Slaby <jslaby@...e.com>,
        kai heng feng <kai.heng.feng@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        mika.westerberg@...ux.intel.com, o.barta89@...il.com,
        paulburton@...nel.org, sr@...x.de,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        yegorslists@...glemail.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in
 mem_serial_out

On Fri, Dec 13, 2019 at 11:31:08PM +0900, Tetsuo Handa wrote:
> On 2019/12/13 19:00, Dmitry Vyukov wrote:
> > Easier said than done. "normal user of the serial port" is not really
> > a thing in Linux, right? You either have CAP_SYS_ADMIN or not, that's
> > not per-device...
> > As far as I remember +Tetsuo proposed a config along the lines of
> > "restrict only things that legitimately cause damage under a fuzzer
> > workload", e.g. freezing filesystems, disabling console output, etc.
> > This may be another candidate. But I can't find where that proposal is
> > now.
> 
> That suggestion got no response for two months.
> 
>   https://lkml.kernel.org/r/3e4e2b6b-7828-54ab-cf28-db1a396d7e20@i-love.sakura.ne.jp
> 
> Unless we add such kernel config option to upstream kernels, it will become
> a whack-a-mole game.

It will be a whack-a-mole game no matter what.

Yes, /dev/mem/ makes no sense to fuzz.  Neither does other things (like
serial port memory addresses.)

You just will have a list of things that you "do not fuzz as these are
dangerous".  Nothing new here, any os will have that.

thanks,

greg k-h