HID: fix race between usb_register_dev() and hiddev_open()

upon further thought this code is still racy.

	retval = usb_register_dev(usbhid->intf, &hiddev_class);

here you open a window during which open can happen

	if (retval) {
		err_hid("Not able to get a minor for this device.");
		hid->hiddev = NULL;
		kfree(hiddev);
		return -1;
	} else {
		hid->minor = usbhid->intf->minor;
		hiddev_table[usbhid->intf->minor - HIDDEV_MINOR_BASE] = hiddev;

and will fail because hiddev_table hasn't been updated

The obvious fix of using a mutex to guard hiddev_table doesn't work because
usb_open() and usb_register_dev() take minor_rwsem and we'd have an AB-BA
deadlock. We need a lock usb_open() also takes in the right order and that leaves
only one option, BKL. I don't like it but I see no alternative.

Once the usb_open() implements something better than lock_kernel(), we could also
do so.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index aa214170baf4..93dcb7e29102 100644
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -875,16 +875,21 @@ int hiddev_connect(struct hid_device *hid, unsigned int force)
         hiddev->hid = hid;
         hiddev->exist = 1;
 
+        /* when lock_kernel() usage is fixed in usb_open(),
+         * we could also fix it here */
+        lock_kernel();
         retval = usb_register_dev(usbhid->intf, &hiddev_class);
         if (retval) {
                 err_hid("Not able to get a minor for this device.");
                 hid->hiddev = NULL;
+                unlock_kernel();
                 kfree(hiddev);
                 return -1;
         } else {
                 hid->minor = usbhid->intf->minor;
                 hiddev_table[usbhid->intf->minor - HIDDEV_MINOR_BASE] = hiddev;
         }
+        unlock_kernel();
 
         return 0;
 }