Date: Fri, 2 Jun 2017 09:06:33 +0900
From: Greg KH <gregkh@linuxfoundation.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Vegard Nossum <vegard.nossum@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jiri Slaby <jslaby@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-serial <linux-serial@vger.kernel.org>
Subject: Re: [GIT PULL] TTY/Serial driver fixes for 4.11-rc4
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On Thu, Jun 01, 2017 at 02:06:08PM +0200, Dmitry Vyukov wrote:
> On Wed, May 31, 2017 at 5:04 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
> > On Wed, 31 May 2017 20:16:12 +0900
> > Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> >> On Wed, May 31, 2017 at 10:39:23AM +0200, Dmitry Vyukov wrote:
> >> > On Tue, May 30, 2017 at 2:09 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
> >> > >> >> I'll think about possible solutions, but I have no prior experience
> >> > >> >> with the tty code. In the meantime syzkaller also hit a couple of
> >> > >> >> other fun tty/pty bugs including a write/ioctl race that results in
> >> > >> >> buffer overflow :-/
> >> > >
> >> > > There are several of those, including some of that have been documented
> >> > > for years but nobody ever volunteered to fix - in particular all the
> >> > > interfaces that push characters to the tty other than via the normal
> >> > > interrupt receive path are dodgy (console selection in particular)
> >> > >
> >> > > The original tty model btw was that setting the ldisc to n_tty cannot
> >> > > fail, and the structure allocated was smaller than a page size so was
> >> > > safe.
> >> > >
> >> > > The simple way to fix it is to restore that behaviour by adding a 'null'
> >> > > ldisc that we can fail to instead of N_TTY since the N_TTY failback path
> >> > > is long broken.
> >> >
> >> > Greg, what do you think about this patch? Are you ready to accept
> >> > something like this?
> >> > Definitely shorter than changing all drivers.
> >>
> >> Yes, it looks reasonable to me.
> >
> >
> >
> > Ok try this
> 
> 
> I've applied the patch and run syzkaller with it. I don't see kernel
> panics in tty_ldisc_restore any more. Also don't see any new
> tty-related crashes.
> 
> Greg, will you take it from here?

I can if Alan sends it to me in a form I can apply it in (i.e. it has a
siged-off-by line...)

thanks,

greg k-h