linux-kernel - [PATCH] driver core: Fix possible use after free on name

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Date:   Sun,  5 Apr 2020 09:05:49 -0700
From:   zhangfeionline@...il.com
To:     gregkh@...uxfoundation.org
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com, PengfeiZhang <zhangfeionline@...il.com>
Subject: [PATCH] driver core: Fix possible use after free on name

From: PengfeiZhang <zhangfeionline@...il.com>

__class_create() copies the pointer to the name passed as an
argument only to be used later. But there's a chance the caller
could immediately free the passed string(e.g., local variable).
This could trigger a use after free when we use class name(e.g.,
dev_uevent_name()called by device_destroy(),class_create_release()).

To be on the safe side: duplicate the string with kstrdup_const()
so that if an unaware user passes an address to a stack-allocated
buffer, we won't get the arbitrary name and crash.

Signed-off-by: PengfeiZhang <zhangfeionline@...il.com>
---
 drivers/base/class.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index bcd410e..770b3b3 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -206,6 +206,7 @@ void class_unregister(struct class *cls)
 static void class_create_release(struct class *cls)
 {
 	pr_debug("%s called for %s\n", __func__, cls->name);
+	kfree_const(cls->name);
 	kfree(cls);
 }
 
@@ -227,7 +228,10 @@ struct class *__class_create(struct module *owner, const char *name,
 			     struct lock_class_key *key)
 {
 	struct class *cls;
-	int retval;
+	int retval = -EINVAL;
+
+	if (!name)
+		goto done;
 
 	cls = kzalloc(sizeof(*cls), GFP_KERNEL);
 	if (!cls) {
@@ -235,18 +239,27 @@ struct class *__class_create(struct module *owner, const char *name,
 		goto error;
 	}
 
+	name = kstrdup_const(name, GFP_KERNEL);
+	if (!name) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
 	cls->name = name;
 	cls->owner = owner;
 	cls->class_release = class_create_release;
 
 	retval = __class_register(cls, key);
 	if (retval)
-		goto error;
+		goto error_class_register;
 
 	return cls;
 
+error_class_register:
+	kfree(cls->name);
 error:
 	kfree(cls);
+done:
 	return ERR_PTR(retval);
 }
 EXPORT_SYMBOL_GPL(__class_create);
-- 
2.7.4