[PATCH] kprobes: disable preempt for module_text_address()

[Lai Jiangshan <laijs@cn.fujitsu.com>]

__register_kprobe() may be preempted after module_text_address()
but before try_module_get(), and in this interval the module may be
unloaded and try_module_get(probed_mod) will access to invalid address.
this patch uses preempt_disable() to protect it.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 8b57a25..8238ec5 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -622,6 +622,7 @@ static int __kprobes __register_kprobe(struct kprobe *p,
 	/*
 	 * Check if are we probing a module.
 	 */
+	preempt_disable();
 	probed_mod = module_text_address((unsigned long) p->addr);
 	if (probed_mod) {
 		struct module *calling_mod = module_text_address(called_from);
@@ -631,12 +632,15 @@ static int __kprobes __register_kprobe(struct kprobe *p,
 		 * unloading of self probing modules.
 		 */
 		if (calling_mod && calling_mod != probed_mod) {
-			if (unlikely(!try_module_get(probed_mod)))
+			if (unlikely(!try_module_get(probed_mod))) {
+				preempt_enable();
 				return -EINVAL;
+			}
 			p->mod_refcounted = 1;
 		} else
 			probed_mod = NULL;
 	}
+	preempt_enable();
 
 	p->nmissed = 0;
 	INIT_LIST_HEAD(&p->list);