[PATCH 3.16 018/134] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

Ben Hutchings
2017-08-18T13:15:42Z

From: Ajay Kaher <ajay.kaher@samsung.com>

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.

Signed-off-by: Ajay Kaher <ajay.kaher@samsung.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/usb/core/file.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -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;