Re: Can AUDIT_LIST_RULES causes kthreadd-spam?

[Rinat Gadelshin <rgadelsh@gmail.com>]

Hi Tetsuo.

Sorry for my log absence.
The kthread-spam problem has gone when I've switched to using 
unicast-netlink connection (like auditd does).

Do we need to make another test with the additional pr_info() ?

On 10.05.2023 16:30, Tetsuo Handa wrote:
> On 2023/05/10 21:12, Rinat Gadelshin wrote:
>>> Please try to find who is calling audit_send_reply_thread for many times.
>>>
>> I've rebuilt the kernel with 'dump stack()'.
> Oops, I thought dump_stack() shows pid and comm name, but
> it is dump_stack_print_info() that shows pid and comm name.
>
>> As far as I can see, it's the exit of `sendto` syscall.
>> It seems that the kernel just creates a new kthreadd for each sendto syscall.
>> But I think that I'm wrong and just missing something.
> Yes, sendto() on netlink socket calls netlink_sendmsg().
> For some reason, audit_send_reply() is called for many times.
> audit_send_reply() is called by audit_receive_msg() for the following types.
>
>    AUDIT_GET
>    AUDIT_SIGNAL_INFO
>    AUDIT_TTY_GET
>    AUDIT_GET_FEATURE
>
> Would you re-caputure with
>
> -	dump_stack();
> +	pr_info("%s %s:%d type=%d\n", __func__, current->comm, current->pid, type);
>
> ?
>
> Regardless of the result of re-caputure, it seems there is no switch that can
> prevent audit_send_reply() from calling kthread_run(audit_send_reply_thread).
>
> But since kthreadd runs with PID=2 and PPID=0, you might be able to use
> PID=2 and/or PPID=0 in your rules in order to let kernel audit subsystem
> ignore kthreadd. (I can't test because I haven't found how to reproduce
> audit_receive_msg() in my environment...)
>
> # cat /proc/2/status
> Name:   kthreadd
> Umask:  0000
> State:  S (sleeping)
> Tgid:   2
> Ngid:   0
> Pid:    2
> PPid:   0
>

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