PCI: Prevent sysfs disable of device while driver is attached

Manipulating the enable_cnt behind the back of the driver will wreak
complete havoc with the kernel state, so disallow it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Acked-by: Keith Busch <keith.busch@intel.com>

drivers/pci/pci-sysfs.c

@@ -288,13 +288,16 @@ static ssize_t enable_store(struct device *dev, struct device_attribute *attr,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!val) {
-		if (pci_is_enabled(pdev))
+	device_lock(dev);
+	if (dev->driver)
+		result = -EBUSY;
+	else if (val)
+		result = pci_enable_device(pdev);
+	else if (pci_is_enabled(pdev))
 		pci_disable_device(pdev);
 	else
 		result = -EIO;
-	} else
-		result = pci_enable_device(pdev);
+	device_unlock(dev);
 
 	return result < 0 ? result : count;
 }