kprobes: Fix to check probe enabled before disarm_kprobe_ftrace()

Commit:

  0cb2f1372b ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")

fixed one bug but the underlying bugs are not completely fixed yet.

If we run a kprobe_module.tc of ftracetest, a warning triggers:

  # ./ftracetest test.d/kprobe/kprobe_module.tc
  === Ftrace unit tests ===
  [1] Kprobe dynamic event - probing module
  ...
   ------------[ cut here ]------------
   Failed to disarm kprobe-ftrace at trace_printk_irq_work+0x0/0x7e [trace_printk] (-2)
   WARNING: CPU: 7 PID: 200 at kernel/kprobes.c:1091 __disarm_kprobe_ftrace.isra.0+0x7e/0xa0

This is because the kill_kprobe() calls disarm_kprobe_ftrace() even
if the given probe is not enabled. In that case, ftrace_set_filter_ip()
fails because the given probe point is not registered to ftrace.

Fix to check the given (going) probe is enabled before invoking
disarm_kprobe_ftrace().

Fixes: 0cb2f1372b ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/159888672694.1411785.5987998076694782591.stgit@devnote2

kernel/kprobes.c

@@ -2235,9 +2235,10 @@ static void kill_kprobe(struct kprobe *p)
 
 	/*
 	 * The module is going away. We should disarm the kprobe which
-	 * is using ftrace.
+	 * is using ftrace, because ftrace framework is still available at
+	 * MODULE_STATE_GOING notification.
 	 */
-	if (kprobe_ftrace(p))
+	if (kprobe_ftrace(p) && !kprobe_disabled(p) && !kprobes_all_disarmed)
 		disarm_kprobe_ftrace(p);
 }