tomoyo: recognize kernel threads correctly

Commit db68ce10 ("new helper: uaccess_kernel()") replaced
segment_eq(get_fs(), KERNEL_DS) with uaccess_kernel(). But the correct
method for tomoyo to check whether current is a kernel thread in order
to assume that kernel threads are privileged for socket operations was
(current->flags & PF_KTHREAD). Now that uaccess_kernel() became 0 on x86,
tomoyo has to fix this problem. Do like commit 942cb357 ("Smack:
Handle io_uring kernel thread privileges") does.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

security/tomoyo/network.c

@@ -613,7 +613,7 @@ static int tomoyo_check_unix_address(struct sockaddr *addr,
 static bool tomoyo_kernel_service(void)
 {
 	/* Nothing to do if I am a kernel service. */
-	return uaccess_kernel();
+	return (current->flags & (PF_KTHREAD | PF_IO_WORKER)) == PF_KTHREAD;
 }
 
 /**