linux-kernel - Re: kernel panic: n_tty: init

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Date:   Mon, 6 Nov 2017 13:37:17 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Eric Biggers <ebiggers3@...il.com>,
        syzbot 
        <bot+57840b4d2cc5c46981d5b9e07c9b7b06d5bcf064@...kaller.appspotmail.com>,
        Jiri Slaby <jslaby@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: kernel panic: n_tty: init_tty

On Mon, Nov 06, 2017 at 01:14:00PM +0100, Dmitry Vyukov wrote:
> On Sun, Nov 5, 2017 at 11:04 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> > On Sun, Nov 05, 2017 at 11:34:34AM +0100, Greg KH wrote:
> >> On Sun, Nov 05, 2017 at 01:05:02AM -0800, syzbot wrote:
> >> > Hello,
> >> >
> >> > syzkaller hit the following crash on
> >> > b5ac3beb5a9f0ef0ea64cd85faf94c0dc4de0e42
> >> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
> >> > compiler: gcc (GCC) 7.1.1 20170620
> >> > .config is attached
> >> > Raw console output is attached.
> >>
> >> And again, this would be nicer to provide something that I could
> >> reproduce this with...
> >>
> >> thanks,
> >>
> >> greg k-h
> >>
> >
> > I just saw the same crash running syzkaller.  It was preceded by a fault
> > injection in tty_ldisc_get() here:
> >
> >         ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
> >         if (ld == NULL) {
> >                 put_ldops(ldops);
> >                 return ERR_PTR(-ENOMEM);
> >         }
> >
> > So then it panics at:
> >
> >         if (IS_ERR(ld))
> >                 panic("n_tty: init_tty");
> >
> > It seems that syzkaller needs to do a better job reproducing and reporting bugs
> > that are only reproducible with fault injection.
> 
> Filed https://github.com/google/syzkaller/issues/410 for this.
> We try to reproduce bugs with failure injection, but somehow we failed
> this time.

Ah a big note somewhere saying "We are injecting faults in the system"
might be nice so we can know to ignore them for stuff like startup logic
such as this :)

thanks,

greg k-h