Patch "USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-proper-handling-of-race-condition-when-two-usb-class-drivers-try-to-call-init_usb_class-simultaneously.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ajay Kaher <[email protected]>
Date: Tue, 28 Mar 2017 08:09:32 -0400
Subject: USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

From: Ajay Kaher <[email protected]>

commit 2f86a96be0ccb1302b7eee7855dbee5ce4dc5dfb upstream.

There is race condition when two USB class drivers try to call init_usb_class at the same time and leads to crash. code path: probe->usb_register_dev->init_usb_class

To solve this, mutex locking has been added in init_usb_class() and destroy_usb_class().

As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class() because usb_class can never be NULL there.

---
 drivers/usb/core/file.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -26,6 +26,7 @@
 #define MAX_USB_MINORS	256
 static const struct file_operations *usb_minors[MAX_USB_MINORS];
 static DECLARE_RWSEM(minor_rwsem);
+static DEFINE_MUTEX(init_usb_class_mutex);
 
 static int usb_open(struct inode *inode, struct file *file)
 {

@@ -108,8 +109,9 @@ static void release_usb_class(struct kre
 
 static void destroy_usb_class(void)
 {
-	if (usb_class)
-		kref_put(&usb_class->kref, release_usb_class);
+	mutex_lock(&init_usb_class_mutex);
+	kref_put(&usb_class->kref, release_usb_class);
+	mutex_unlock(&init_usb_class_mutex);
 }
 
 int usb_major_init(void)

@@ -171,7 +173,10 @@ int usb_register_dev(struct usb_interfac
 	if (intf->minor >= 0)
 		return -EADDRINUSE;
 
+	mutex_lock(&init_usb_class_mutex);
 	retval = init_usb_class();
+	mutex_unlock(&init_usb_class_mutex);
+
 	if (retval)
 		return retval;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/usb-proper-handling-of-race-condition-when-two-usb-class-drivers-try-to-call-init_usb_class-simultaneously.patch