platform/wmi: Extend wmidev_invoke_method() to reject undersized data

WMI drivers using the buffer-based WMI API are expected to reject
undersized method return values. Extend wmidev_invoke_method() to
enable the WMI driver core to perform this size check internally.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260406203237.2970-5-W_Armin@gmx.de
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: Wer-Wolf

drivers/platform/wmi/core.c

@@ -364,20 +364,23 @@ acpi_status wmidev_evaluate_method(struct wmi_device *wdev, u8 instance, u32 met
 EXPORT_SYMBOL_GPL(wmidev_evaluate_method);
 
 /**
- * wmidev_invoke_method - Invoke a WMI method
+ * wmidev_invoke_method - Invoke a WMI method that returns values
  * @wdev: A wmi bus device from a driver
  * @instance: Instance index
  * @method_id: Method ID to call
  * @in: Mandatory WMI buffer containing input for the method call
- * @out: Optional WMI buffer to return the method results
+ * @out: Mandatory WMI buffer to return the method results
+ * @min_size: Minimum size of the method result data in bytes
  *
- * Invoke a WMI method, the caller must free the resulting data inside @out.
- * Said data is guaranteed to be aligned on a 8-byte boundary.
+ * Invoke a WMI method that returns values, the caller must free the resulting
+ * data inside @out using kfree(). Said data is guaranteed to be aligned on a
+ * 8-byte boundary. Use wmidev_invoke_procedure() for WMI methods that
+ * return no values.
  *
  * Return: 0 on success or negative error code on failure.
  */
 int wmidev_invoke_method(struct wmi_device *wdev, u8 instance, u32 method_id,
-			 const struct wmi_buffer *in, struct wmi_buffer *out)
+			 const struct wmi_buffer *in, struct wmi_buffer *out, size_t min_size)
 {
 	struct wmi_block *wblock = container_of(wdev, struct wmi_block, dev);
 	struct acpi_buffer aout = { ACPI_ALLOCATE_BUFFER, NULL };
@@ -398,20 +401,14 @@ int wmidev_invoke_method(struct wmi_device *wdev, u8 instance, u32 method_id,
 		ain.pointer = in->data;
 	}
 
-	if (out)
-		status = wmidev_evaluate_method(wdev, instance, method_id, &ain, &aout);
-	else
-		status = wmidev_evaluate_method(wdev, instance, method_id, &ain, NULL);
+	status = wmidev_evaluate_method(wdev, instance, method_id, &ain, &aout);
 
 	if (wblock->gblock.flags & ACPI_WMI_STRING)
 		kfree(ain.pointer);
 
 	if (ACPI_FAILURE(status))
 		return -EIO;
 
-	if (!out)
-		return 0;
-
 	obj = aout.pointer;
 	if (!obj) {
 		out->length = 0;
@@ -420,7 +417,7 @@ int wmidev_invoke_method(struct wmi_device *wdev, u8 instance, u32 method_id,
 		return 0;
 	}
 
-	ret = wmi_unmarshal_acpi_object(obj, out, 0);
+	ret = wmi_unmarshal_acpi_object(obj, out, min_size);
 	kfree(obj);
 
 	return ret;

drivers/platform/x86/bitland-mifs-wmi.c

@@ -10,7 +10,6 @@
 #include <linux/acpi.h>
 #include <linux/array_size.h>
 #include <linux/bits.h>
-#include <linux/cleanup.h>
 #include <linux/container_of.h>
 #include <linux/dev_printk.h>
 #include <linux/device.h>
@@ -167,7 +166,6 @@ static int bitland_mifs_wmi_call(struct bitland_mifs_wmi_data *data,
 				 struct bitland_mifs_output *output)
 {
 	struct wmi_buffer in_buf = { .length = sizeof(*input), .data = (void *)input };
-	void *out_data __free(kfree) = NULL;
 	struct wmi_buffer out_buf = { 0 };
 	int ret;
 
@@ -176,15 +174,12 @@ static int bitland_mifs_wmi_call(struct bitland_mifs_wmi_data *data,
 	if (!output)
 		return wmidev_invoke_procedure(data->wdev, 0, 1, &in_buf);
 
-	ret = wmidev_invoke_method(data->wdev, 0, 1, &in_buf, &out_buf);
+	ret = wmidev_invoke_method(data->wdev, 0, 1, &in_buf, &out_buf, sizeof(*output));
 	if (ret)
 		return ret;
 
-	out_data = out_buf.data;
-	if (out_buf.length < sizeof(*output))
-		return -EIO;
-
-	memcpy(output, out_data, sizeof(*output));
+	memcpy(output, out_buf.data, sizeof(*output));
+	kfree(out_buf.data);
 
 	return 0;
 }

include/linux/wmi.h

@@ -68,7 +68,7 @@ ssize_t wmi_string_from_utf8s(struct wmi_string *str, size_t max_chars, const u8
 			      size_t src_length);
 
 int wmidev_invoke_method(struct wmi_device *wdev, u8 instance, u32 method_id,
-			 const struct wmi_buffer *in, struct wmi_buffer *out);
+			 const struct wmi_buffer *in, struct wmi_buffer *out, size_t min_size);
 
 int wmidev_invoke_procedure(struct wmi_device *wdev, u8 instance, u32 method_id,
 			    const struct wmi_buffer *in);