patch "USB: Proper handling of Race Condition when two USB class drivers try" added to usb-testing

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 my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the usb-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

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

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(-)

index e26bd5e773ad..87ad6b6bfee8 100644
@@ -29,6 +29,7 @@
 #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)
 {

@@ -111,8 +112,9 @@ static void release_usb_class(struct kref *kref)
 
 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)

@@ -173,7 +175,10 @@ int usb_register_dev(struct usb_interface *intf,
 	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;
 

2.12.1