From de9d2d297ebe4d591efd41902c568e3ef4774c43 Mon Sep 17 00:00:00 2001 From: Ajay Kaher Date: Tue, 28 Mar 2017 08:09:32 -0400 Subject: [PATCH] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously 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 Acked-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/file.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c index ea337a718cc1..b3de806085f0 100644 --- 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 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) @@ -171,7 +173,10 @@ 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; -- 2.20.1