linux-kernel - Re: Boot regression caused by kauditd

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Date:   Thu, 27 Apr 2017 16:41:24 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: Boot regression caused by kauditd

On Thu, Apr 27, 2017 at 3:38 PM, Paul Moore <paul@...l-moore.com> wrote:
> On Thu, Apr 27, 2017 at 5:45 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>> On Thu, Apr 27, 2017 at 2:35 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>> On Thu, Apr 27, 2017 at 1:31 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>> On Wed, Apr 26, 2017 at 2:20 PM, Paul Moore <paul@...l-moore.com> wrote:
>>>>> Thanks for the report, this is the only one like it that I've seen.
>>>>> I'm looking at the code in Linus' tree and I'm not seeing anything
>>>>> obvious ... looking at the trace above it appears that the problem is
>>>>> when get_net() goes to bump the refcount and the passed net pointer is
>>>>> NULL; unless I'm missing something, the only way this would happen in
>>>>> kauditd_thread() is if the auditd_conn.pid value is non-zero but the
>>>>> auditd_conn.net pointer is NULL.
>>>>>
>>>>> That shouldn't happen.
>>>>>
>>>>
>>>> Looking at the code that reads/writes the global auditd_conn,
>>>> I don't see how it even works with RCU+spinlock, RCU plays
>>>> with pointers and you have to make a copy as its name implies.
>>>> But it looks like you simply use RCU+spinlock as a traditional
>>>> rwlock, it doesn't work.
>>>
>>> The attached patch seems working for me, I tried to boot my
>>> VM for 4 times, so far no crash or warning.
>>>
>>
>> Or even better, save a memory allocation for reset path...
>
> I need to step away from my laptop for the evening so I can't give
> this a proper review until tomorrow (sending patches as attachments
> makes it difficult to review), but on quick glance I did notice a few
> small things I would like to see changed.  However, since there is no
> normal commit description and sign-off, I'm guessing you sent these
> out as a suggestion and not a proper patch submission, yes/no?  If
> that's the case, I'll work up a proper fix tomorrow and share it with
> you for comment/review, but if you were planning on sending a proper
> patch let me know and I'll wait until I see something in my inbox from
> you.

I want you to give it sanity check before I submit a formal one. ;)
If you don't reject it, I will send a formal one with description and SoB.

Thanks.