Re: kernel panic: n_tty: init_tty

Greg KH
2017-11-06T12:32:58Z

On Sun, Nov 05, 2017 at 02:04:39PM -0800, Eric Biggers 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. But either way, this is a bug;
> panic() is not an acceptable way of handling kmalloc failure.

That's a well-known issue, it's pretty much impossible to unwind safely
from here. If you don't have enough memory at boot to get a tty_ldisc,
you have bigger problems.

thanks,

greg k-h