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

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Message-ID: <20171105220439.GA11631@zzz.localdomain>
Date:   Sun, 5 Nov 2017 14:04:39 -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 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.

Eric