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

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

[gregkh]

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 2f86a96be0ccb1302b7eee7855dbee5ce4dc5dfb Mon Sep 17 00:00:00 2001
From: Ajay Kaher <ajay.kaher@samsung.com>
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.

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>
---
 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 e26bd5e773ad..87ad6b6bfee8 100644
--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -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