Re: [BUG][PATCH] audit: audit_log_start running on auditd should not stop

Toshiyuki Okajima
2013-10-28T09:20:25Z

Hi.

(2013/10/26 0:12), Eric Paris wrote:
> On Fri, 2013-10-25 at 10:36 +0900, Toshiyuki Okajima wrote:
>
>> systemd |auditd
>> -------------------------------------------+-----------------------------------
>> ... |
>> -> audit_receive |...
>> -> mutex_lock(&audit_cmd_mutex) |-> audit_receive
>> ... -> audit_log_start | -> mutex_lock(&audit_cmd_mutex)
>> -> wait_for_auditd | // wait for systemd
>> -> schedule_timeout(60*HZ) |
>

> Ugggh, definitely a problem. Adding a similar hack to systemd really
> does not seem like an acceptable answer. It seems to me that in
I think so, too. We should fix it against the various cases.

> audit_receive_msg()
>
> case AUDIT_USER:
> case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
> case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
>
> we do not need to hold the audit_cmd_mutex. So a quick and dirty patch
> should be to just drop the mutex there (and we need to verify there
> aren't issues running the audit_filter_user() without the lock). That
> will take care of systemd and anything USING audit. It still means that
> you could race with something configuring audit and auditd shutting
> down. Seems like a good quick and dirty 'fix' while we work on a better
> fix...
>
> To take care of that I think maybe we could drop the cmd_mutex every
> time we call audit_log_start. That's not necessarily going to be
> pretty. Maybe make a new switch at the top of the function which knows
> which operations we are going to have to allocate an audit_buffer. Drop
> the lock, allocate the buffer, then retake the lock to finish running
> audit_receive_msg()....
>

> Maybe that second option isn't so hard and we can go directly after that
> instead of just dealing with userspace audit messages?
>
> Thoughts?
Does it mean that we can also fix the problem only in the userspace?

Even if we fix userspace process (auditd, readahead-collector and systemd) only,
the problem would happen again if a new userspace audit process is implemented.
Therefore, I think we should fix only in the kernel.
Sorry, but I don't have clear method to fix it.

Regards,
Toshiyuki Okajima

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