linux-kernel - Re: KASAN: use-after-free Read in alloc

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Date:   Mon, 02 Apr 2018 18:00:57 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     syzbot <syzbot+7a1cff37dbbef9e7ba4c@...kaller.appspotmail.com>
Cc:     akpm@...ux-foundation.org, dhowells@...hat.com, gs051095@...il.com,
        linux-kernel@...r.kernel.org, oleg@...hat.com,
        pasha.tatashin@...cle.com, riel@...hat.com,
        rppt@...ux.vnet.ibm.com, syzkaller-bugs@...glegroups.com,
        wangkefeng.wang@...wei.com
Subject: Re: KASAN: use-after-free Read in alloc_pid

syzbot <syzbot+7a1cff37dbbef9e7ba4c@...kaller.appspotmail.com> writes:

> Hello,
>
> syzbot hit the following crash on upstream commit
> 9dd2326890d89a5179967c947dab2bab34d7ddee (Fri Mar 30 17:29:47 2018 +0000)
> Merge tag 'ceph-for-4.16-rc8' of git://github.com/ceph/ceph-client
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=7a1cff37dbbef9e7ba4c
>
> So far this crash happened 4 times on upstream.
>
> Unfortunately, I don't have any reproducer for this crash yet.

Do you have any of the other traces?  This looks like a something is
calling put_pid_ns more than it is calling get_pid_ns causing a
reference count mismatch.

If this is not: 9ee332d99e4d5a97548943b81c54668450ce641b

I could use a few more hints to help narrow down what is going wrong.

It would be nice to know what the other 3 crashes looked like and
exactly which upstream they were on.

Eric