linux-kernel - [PATCH] livepatch: Prevent to enable uninitialized patch

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Date:	Mon, 11 May 2015 10:57:46 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	jpoimboe@...hat.com, sjenning@...hat.com, jkosina@...e.cz,
	vojtech@...e.cz
Cc:	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <minfei.huang@...mail.com>
Subject: [PATCH] livepatch: Prevent to enable uninitialized patch

From: Minfei Huang <minfei.huang@...mail.com>

The previous patches can be applied, while the corresponding module is
loaded. Now the code cannot handle correct behavior to deal with the
case that the patch fail to be initialized when the module is being
loaded.

In general, the patch will do relocation (if necessary) and
obtain/verify function address before we start to enable patch. But we
can still trigger to enable the patch (disable the patch firstly, then
enable it), although the patch fail to be initialized in the function
klp_module_notify_coming.

To fix it, we can make obj->mod to NULL, if the object fails to be
initialized.

Signed-off-by: Minfei Huang <minfei.huang@...mail.com>
---
 kernel/livepatch/core.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 284e269..4bbcdda 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -883,30 +883,30 @@ int klp_register_patch(struct klp_patch *patch)
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
-static void klp_module_notify_coming(struct klp_patch *patch,
+static int klp_module_notify_coming(struct klp_patch *patch,
 				     struct klp_object *obj)
 {
 	struct module *pmod = patch->mod;
 	struct module *mod = obj->mod;
-	int ret;
+	int ret = 0;
 
 	ret = klp_init_object_loaded(patch, obj);
 	if (ret)
-		goto err;
+		goto out;
 
 	if (patch->state == KLP_DISABLED)
-		return;
+		goto out;
 
 	pr_notice("applying patch '%s' to loading module '%s'\n",
 		  pmod->name, mod->name);
 
 	ret = klp_enable_object(obj);
-	if (!ret)
-		return;
 
-err:
-	pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
-		pmod->name, mod->name, ret);
+out:
+	if (ret)
+		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+				pmod->name, mod->name, ret);
+	return ret;
 }
 
 static void klp_module_notify_going(struct klp_patch *patch,
@@ -930,6 +930,7 @@ disabled:
 static int klp_module_notify(struct notifier_block *nb, unsigned long action,
 			     void *data)
 {
+	int ret = 0;
 	struct module *mod = data;
 	struct klp_patch *patch;
 	struct klp_object *obj;
@@ -955,7 +956,9 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
 
 			if (action == MODULE_STATE_COMING) {
 				obj->mod = mod;
-				klp_module_notify_coming(patch, obj);
+				ret = klp_module_notify_coming(patch, obj);
+				if (ret)
+					obj->mod = NULL;
 			} else /* MODULE_STATE_GOING */
 				klp_module_notify_going(patch, obj);
 
-- 
2.2.2

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