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

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Message-ID: <20171106172604.GB50562@gmail.com>
Date:   Mon, 6 Nov 2017 09:26:04 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     syzbot 
        <bot+57840b4d2cc5c46981d5b9e07c9b7b06d5bcf064@...kaller.appspotmail.com>,
        jslaby@...e.com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: kernel panic: n_tty: init_tty

On Mon, Nov 06, 2017 at 01:33:09PM +0100, Greg KH wrote:
> > 
> > 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

It's not just running at boot though.  It's also being hit by the fuzzer at
runtime, via ptmx_open().

Eric