PCI: Allow access to VPD attributes with size 0

It is not always possible to determine the actual size of the VPD
data, so allow access to them if the size is set to '0'.

Tested-by: Shane Seymour <shane.seymour@hpe.com>
Tested-by: Babu Moger <babu.moger@oracle.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>

drivers/pci/pci-sysfs.c

@@ -769,10 +769,12 @@ static ssize_t read_vpd_attr(struct file *filp, struct kobject *kobj,
 {
 	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
 
-	if (off > bin_attr->size)
-		count = 0;
-	else if (count > bin_attr->size - off)
-		count = bin_attr->size - off;
+	if (bin_attr->size > 0) {
+		if (off > bin_attr->size)
+			count = 0;
+		else if (count > bin_attr->size - off)
+			count = bin_attr->size - off;
+	}
 
 	return pci_read_vpd(dev, off, count, buf);
 }
@@ -783,10 +785,12 @@ static ssize_t write_vpd_attr(struct file *filp, struct kobject *kobj,
 {
 	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
 
-	if (off > bin_attr->size)
-		count = 0;
-	else if (count > bin_attr->size - off)
-		count = bin_attr->size - off;
+	if (bin_attr->size > 0) {
+		if (off > bin_attr->size)
+			count = 0;
+		else if (count > bin_attr->size - off)
+			count = bin_attr->size - off;
+	}
 
 	return pci_write_vpd(dev, off, count, buf);
 }