[PATCH 4.4 036/124] PCI: Prevent sysfs disable of device while driver is attached

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@xxxxxx>

[ Upstream commit 6f5cdfa802733dcb561bf664cc89d203f2fd958f ]

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@xxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Acked-by: Keith Busch <keith.busch@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/pci-sysfs.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -180,13 +180,16 @@ static ssize_t enable_store(struct devic
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!val) {
-		if (pci_is_enabled(pdev))
-			pci_disable_device(pdev);
-		else
-			result = -EIO;
-	} else
+	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;
+	device_unlock(dev);
 
 	return result < 0 ? result : count;
 }