[PATCH 2/2] HID: hyperv: add KUnit coverage for device info bounds

[Michael Bommarito <michael.bommarito@gmail.com>]

Add KUnit coverage for Hyper-V synthetic HID initial device-info parsing.
The tests cover zero bLength, a valid descriptor plus report descriptor,
and a malformed report descriptor length that exceeds the received
message.

The same-translation-unit test uses a KUnit-only ACK bypass so parser
coverage does not require a live VMBus channel.

Assisted-by: Codex:gpt-5-5-xhigh
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 drivers/hid/Kconfig      |  10 ++++
 drivers/hid/hid-hyperv.c | 117 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 120 insertions(+), 7 deletions(-)

diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index c1d9f7c6a5f23..41ca48d9adc9e 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -1183,6 +1183,16 @@ config HID_HYPERV_MOUSE
 	help
 	Select this option to enable the Hyper-V mouse driver.
 
+config HID_HYPERV_MOUSE_KUNIT_TEST
+	bool "KUnit tests for Hyper-V mouse driver" if !KUNIT_ALL_TESTS
+	depends on KUNIT && HID_HYPERV_MOUSE
+	default KUNIT_ALL_TESTS
+	help
+	  Builds unit tests for the Hyper-V synthetic HID driver.
+	  These tests exercise the initial device-info parser with
+	  malformed host-provided HID descriptors and are only useful
+	  for kernel developers running KUnit.
+
 config HID_SMARTJOYPLUS
 	tristate "SmartJoy PLUS PS2/USB adapter support"
 	help
diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
index fd90196430e29..6579bd19da13a 100644
--- a/drivers/hid/hid-hyperv.c
+++ b/drivers/hid/hid-hyperv.c
@@ -13,6 +13,9 @@
 #include <linux/hiddev.h>
 #include <linux/hyperv.h>
 
+#if IS_ENABLED(CONFIG_HID_HYPERV_MOUSE_KUNIT_TEST)
+#include <kunit/test.h>
+#endif
 
 struct hv_input_dev_info {
 	unsigned int size;
@@ -240,13 +243,18 @@ static void mousevsc_on_receive_device_info(struct mousevsc_dev *input_device,
 	ack.ack.header.size = 1;
 	ack.ack.reserved = 0;
 
-	ret = vmbus_sendpacket(input_device->device->channel,
-			&ack,
-			sizeof(struct pipe_prt_msg) +
-			sizeof(struct synthhid_device_info_ack),
-			(unsigned long)&ack,
-			VM_PKT_DATA_INBAND,
-			VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (IS_ENABLED(CONFIG_HID_HYPERV_MOUSE_KUNIT_TEST) &&
+	    !input_device->device) {
+		ret = 0;
+	} else {
+		ret = vmbus_sendpacket(input_device->device->channel,
+				       &ack,
+				       sizeof(struct pipe_prt_msg) +
+				       sizeof(struct synthhid_device_info_ack),
+				       (unsigned long)&ack,
+				       VM_PKT_DATA_INBAND,
+				       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	}
 
 	if (!ret)
 		input_device->dev_info_status = 0;
@@ -635,5 +643,100 @@ static void __exit mousevsc_exit(void)
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Microsoft Hyper-V Synthetic HID Driver");
 
+#if IS_ENABLED(CONFIG_HID_HYPERV_MOUSE_KUNIT_TEST)
+static struct mousevsc_dev *mousevsc_kunit_alloc_dev(struct kunit *test)
+{
+	struct mousevsc_dev *input_dev;
+
+	input_dev = kunit_kzalloc(test, sizeof(*input_dev), GFP_KERNEL);
+	if (!input_dev)
+		return NULL;
+
+	init_completion(&input_dev->wait_event);
+
+	return input_dev;
+}
+
+static void mousevsc_device_info_zero_blength(struct kunit *test)
+{
+	struct synthhid_device_info *info;
+	struct mousevsc_dev *input_dev;
+
+	input_dev = mousevsc_kunit_alloc_dev(test);
+	KUNIT_ASSERT_NOT_NULL(test, input_dev);
+	info = kunit_kzalloc(test, sizeof(*info), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, info);
+
+	info->hid_descriptor.bLength = 0;
+
+	mousevsc_on_receive_device_info(input_dev, info, sizeof(*info));
+
+	KUNIT_EXPECT_EQ(test, input_dev->dev_info_status, -ENOMEM);
+}
+
+static void mousevsc_device_info_valid_descriptor(struct kunit *test)
+{
+	struct synthhid_device_info *info;
+	struct mousevsc_dev *input_dev;
+	u8 *report;
+
+	input_dev = mousevsc_kunit_alloc_dev(test);
+	KUNIT_ASSERT_NOT_NULL(test, input_dev);
+	info = kunit_kzalloc(test, sizeof(*info) + 4, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, info);
+
+	info->hid_descriptor.bLength = sizeof(struct hid_descriptor);
+	info->hid_descriptor.rpt_desc.wDescriptorLength = cpu_to_le16(4);
+	report = ((u8 *)&info->hid_descriptor) + info->hid_descriptor.bLength;
+	memset(report, 0x42, 4);
+
+	mousevsc_on_receive_device_info(input_dev, info, sizeof(*info) + 4);
+
+	KUNIT_EXPECT_EQ(test, input_dev->dev_info_status, 0);
+	KUNIT_EXPECT_EQ(test, input_dev->report_desc_size, 4);
+	KUNIT_EXPECT_MEMEQ(test, input_dev->report_desc, report, 4);
+
+	kfree(input_dev->hid_desc);
+	kfree(input_dev->report_desc);
+}
+
+static void mousevsc_device_info_report_desc_oob(struct kunit *test)
+{
+	struct synthhid_device_info *info;
+	struct mousevsc_dev *input_dev;
+	u8 *report;
+
+	input_dev = mousevsc_kunit_alloc_dev(test);
+	KUNIT_ASSERT_NOT_NULL(test, input_dev);
+	info = kunit_kzalloc(test, sizeof(*info) + 8, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, info);
+
+	info->hid_descriptor.bLength = sizeof(struct hid_descriptor);
+	info->hid_descriptor.rpt_desc.wDescriptorLength = cpu_to_le16(64);
+	report = ((u8 *)&info->hid_descriptor) + info->hid_descriptor.bLength;
+	memset(report, 0x42, 8);
+
+	mousevsc_on_receive_device_info(input_dev, info, sizeof(*info) + 8);
+
+	KUNIT_EXPECT_EQ(test, input_dev->dev_info_status, -EINVAL);
+
+	kfree(input_dev->hid_desc);
+}
+
+static struct kunit_case mousevsc_test_cases[] = {
+	KUNIT_CASE(mousevsc_device_info_zero_blength),
+	KUNIT_CASE(mousevsc_device_info_valid_descriptor),
+	KUNIT_CASE(mousevsc_device_info_report_desc_oob),
+	{}
+};
+
+static struct kunit_suite mousevsc_test_suite = {
+	.name = "hid_hyperv_mouse",
+	.test_cases = mousevsc_test_cases,
+};
+
+kunit_test_suite(mousevsc_test_suite);
+#endif
+
 module_init(mousevsc_init);
 module_exit(mousevsc_exit);
-- 
2.53.0