net: netxen: correct sysfs bin attribute return code

If read() syscall requests unexpected number of bytes from "dimm" binary
attribute file, return EINVAL instead of EPERM.

At the same time pin down sysfs file size to the fixed
sizeof(struct netxen_dimm_cfg), which allows to exploit some missing
sanity checks from kernfs (file boundary checks vs offset etc.)

Signed-off-by: Vladimir Zapolskiy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/qlogic/netxen/netxen_nic_main.c

···
 	u8 dw, rows, cols, banks, ranks;
 	u32 val;
 
-	if (size != sizeof(struct netxen_dimm_cfg)) {
+	if (size < attr->size) {
 		netdev_err(netdev, "Invalid size\n");
-		return -1;
+		return -EINVAL;
 	}
 
 	memset(&dimm, 0, sizeof(struct netxen_dimm_cfg));
···
 
 static struct bin_attribute bin_attr_dimm = {
 	.attr = { .name = "dimm", .mode = (S_IRUGO | S_IWUSR) },
-	.size = 0,
+	.size = sizeof(struct netxen_dimm_cfg),
 	.read = netxen_sysfs_read_dimm,
 };