Can AUDIT_LIST_RULES causes kthreadd-spam?

[Tetsuo Handa]

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