libnvdimm, tools/testing/nvdimm: fix 'ars_status' output buffer sizing

Use the output length specified in the command to size the receive
buffer rather than the arbitrary 4K limit.

This bug was hiding the fact that the ndctl implementation of
ndctl_bus_cmd_new_ars_status() was not specifying an output buffer size.

Cc: <stable@vger.kernel.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
index 424b362..1d4b9c6 100644
--- a/drivers/acpi/nfit.c
+++ b/drivers/acpi/nfit.c
@@ -1516,13 +1516,13 @@
 }
 
 static int ars_get_status(struct nvdimm_bus_descriptor *nd_desc,
-		struct nd_cmd_ars_status *cmd)
+		struct nd_cmd_ars_status *cmd, u32 size)
 {
 	int rc;
 
 	while (1) {
 		rc = nd_desc->ndctl(nd_desc, NULL, ND_CMD_ARS_STATUS, cmd,
-			sizeof(*cmd));
+			size);
 		if (rc || cmd->status & 0xffff)
 			return -ENXIO;
 
@@ -1580,6 +1580,7 @@
 	struct nd_cmd_ars_start *ars_start = NULL;
 	struct nd_cmd_ars_cap *ars_cap = NULL;
 	u64 start, len, cur, remaining;
+	u32 ars_status_size;
 	int rc;
 
 	ars_cap = kzalloc(sizeof(*ars_cap), GFP_KERNEL);
@@ -1609,14 +1610,14 @@
 	 * Check if a full-range ARS has been run. If so, use those results
 	 * without having to start a new ARS.
 	 */
-	ars_status = kzalloc(ars_cap->max_ars_out + sizeof(*ars_status),
-			GFP_KERNEL);
+	ars_status_size = ars_cap->max_ars_out;
+	ars_status = kzalloc(ars_status_size, GFP_KERNEL);
 	if (!ars_status) {
 		rc = -ENOMEM;
 		goto out;
 	}
 
-	rc = ars_get_status(nd_desc, ars_status);
+	rc = ars_get_status(nd_desc, ars_status, ars_status_size);
 	if (rc)
 		goto out;
 
@@ -1646,7 +1647,7 @@
 		if (rc)
 			goto out;
 
-		rc = ars_get_status(nd_desc, ars_status);
+		rc = ars_get_status(nd_desc, ars_status, ars_status_size);
 		if (rc)
 			goto out;