[PATCH] Kprobes: Reference count the modules when probed on it

When a Kprobes are inserted/removed on a modules, the modules must be ref
counted so as not to allow to unload while probes are registered on that
module.

Without this patch, the probed module is free to unload, and when the
probing module unregister the probe, the kpobes code while trying to
replace the original instruction might crash.
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Mao Bibo <bibo.mao@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/kprobes.c

@@ -462,9 +462,16 @@ int __kprobes register_kprobe(struct kprobe *p)
 	int ret = 0;
 	unsigned long flags = 0;
 	struct kprobe *old_p;
+	struct module *mod;
+
+	if ((!kernel_text_address((unsigned long) p->addr)) ||
+		in_kprobes_functions((unsigned long) p->addr))
+		return -EINVAL;
+
+	if ((mod = module_text_address((unsigned long) p->addr)) &&
+			(unlikely(!try_module_get(mod))))
+		return -EINVAL;
 
-	if ((ret = in_kprobes_functions((unsigned long) p->addr)) != 0)
-		return ret;
 	if ((ret = arch_prepare_kprobe(p)) != 0)
 		goto rm_kprobe;
 
@@ -488,6 +495,8 @@ int __kprobes register_kprobe(struct kprobe *p)
 rm_kprobe:
 	if (ret == -EEXIST)
 		arch_remove_kprobe(p);
+	if (ret && mod)
+		module_put(mod);
 	return ret;
 }
 
@@ -495,6 +504,7 @@ void __kprobes unregister_kprobe(struct kprobe *p)
 {
 	unsigned long flags;
 	struct kprobe *old_p;
+	struct module *mod;
 
 	spin_lock_irqsave(&kprobe_lock, flags);
 	old_p = get_kprobe(p->addr);
@@ -506,6 +516,10 @@ void __kprobes unregister_kprobe(struct kprobe *p)
 			cleanup_kprobe(p, flags);
 
 		synchronize_sched();
+
+		if ((mod = module_text_address((unsigned long)p->addr)))
+			module_put(mod);
+
 		if (old_p->pre_handler == aggr_pre_handler &&
 				list_empty(&old_p->list))
 			kfree(old_p);