PCI: Don't read past the end of sysfs "driver_override" buffer

When printing the driver_override parameter when it is 4095 and 4094 bytes
long, the printing code would access invalid memory because we need count+1
bytes for printing.

Fixes: 782a985d7a ("PCI: Introduce new device binding path using pci_dev.driver_override")
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Acked-by: Alex Williamson <[email protected]>
CC: [email protected]	# v3.16+
CC: Konrad Rzeszutek Wilk <[email protected]>
CC: Alexander Graf <[email protected]>
CC: Greg Kroah-Hartman <[email protected]>

drivers/pci/pci-sysfs.c

@@ -521,7 +521,8 @@ static ssize_t driver_override_store(struct device *dev,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	char *driver_override, *old = pdev->driver_override, *cp;
 
-	if (count > PATH_MAX)
+	/* We need to keep extra room for a newline */
+	if (count >= (PAGE_SIZE - 1))
 		return -EINVAL;
 
 	driver_override = kstrndup(buf, count, GFP_KERNEL);
@@ -549,7 +550,7 @@ static ssize_t driver_override_show(struct device *dev,
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 
-	return sprintf(buf, "%s\n", pdev->driver_override);
+	return snprintf(buf, PAGE_SIZE, "%s\n", pdev->driver_override);
 }
 static DEVICE_ATTR_RW(driver_override);