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

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Date:   Mon, 6 Nov 2017 13:14:00 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        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 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.


> But either way, this is a bug;
> panic() is not an acceptable way of handling kmalloc failure.
>
> Eric
>
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