Commit 2f86a96b authored Mar 28, 2017 by Ajay Kaher Committed by Greg Kroah-Hartman Mar 29, 2017

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


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.

Signed-off-by: Ajay Kaher <ajay.kaher@samsung.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 041370cc

drivers/usb/core/file.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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)
		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;

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