USB: usb-skeleton.c: fix open/disconnect race

If usb device is disconnected between usb_get_intfdata()
and kref_get() in skel_open(), kref_get may access a freed
object.

Also check if device is disconnected in ->open.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 32d6fc953904..3635f9e37559 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -27,6 +27,8 @@
 #define USB_SKEL_VENDOR_ID      0xfff0
 #define USB_SKEL_PRODUCT_ID     0xfff0
 
+static DEFINE_MUTEX(skel_mutex);
+
 /* table of devices that work with this driver */
 static const struct usb_device_id skel_table[] = {
         { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
@@ -100,18 +102,25 @@ static int skel_open(struct inode *inode, struct file *file)
                 goto exit;
         }
 
+        mutex_lock(&skel_mutex);
         dev = usb_get_intfdata(interface);
         if (!dev) {
+                mutex_unlock(&skel_mutex);
                 retval = -ENODEV;
                 goto exit;
         }
 
         /* increment our usage count for the device */
         kref_get(&dev->kref);
+        mutex_unlock(&skel_mutex);
 
         /* lock the device to allow correctly handling errors
          * in resumption */
         mutex_lock(&dev->io_mutex);
+        if (!dev->interface) {
+                retval = -ENODEV;
+                goto out_err;
+        }
 
         if (!dev->open_count++) {
                 retval = usb_autopm_get_interface(interface);
@@ -132,7 +141,11 @@ static int skel_open(struct inode *inode, struct file *file)
 
         /* save our object in the file's private structure */
         file->private_data = dev;
+
+out_err:
         mutex_unlock(&dev->io_mutex);
+        if (retval)
+                kref_put(&dev->kref, skel_delete);
 
 exit:
         return retval;
@@ -612,7 +625,6 @@ static void skel_disconnect(struct usb_interface *interface)
         int minor = interface->minor;
 
         dev = usb_get_intfdata(interface);
-        usb_set_intfdata(interface, NULL);
 
         /* give back our minor */
         usb_deregister_dev(interface, &skel_class);
@@ -624,8 +636,12 @@ static void skel_disconnect(struct usb_interface *interface)
 
         usb_kill_anchored_urbs(&dev->submitted);
 
+        mutex_lock(&skel_mutex);
+        usb_set_intfdata(interface, NULL);
+
         /* decrement our usage count */
         kref_put(&dev->kref, skel_delete);
+        mutex_unlock(&skel_mutex);
 
         dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
 }