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Commit 2f86a96b authored by Ajay Kaher's avatar Ajay Kaher Committed by Greg Kroah-Hartman
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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: default avatarAjay Kaher <ajay.kaher@samsung.com>
Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg 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;