[PATCH v2] HID: mcp2221: validate report size in raw_event handler

[Sebastian Josue Alba Vives <sebasjosue84@gmail.com>]

mcp2221_raw_event() accesses the data buffer at offsets up to 55
without validating the size parameter. Since __hid_input_report()
invokes the driver's raw_event callback before
hid_report_raw_event() performs its own report-size validation, a
device sending a truncated HID report can cause out-of-bounds heap
reads in the kernel.

The most critical access is the memcpy from data[50] into
mcp->adc_values (6 bytes) when CONFIG_IIO is reachable. Other
unchecked accesses include data[20] and a memcpy at data[22].
Additionally, a memcpy with device-controlled length (data[3],
up to 60 bytes) from data[4] does not verify that size is large
enough to cover the copy.

MCP2221 devices use 64-byte HID reports. Add a check at the top of
the handler to reject any report shorter than expected, and log a
warning to aid debugging.

Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Josue Alba Vives <sebasjosue84@gmail.com>
---
 drivers/hid/hid-mcp2221.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index ef3b5c77c..770c305d8 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -850,6 +850,11 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 {
 	u8 *buf;
 	struct mcp2221 *mcp = hid_get_drvdata(hdev);
+	/* MCP2221 always sends 64-byte reports */
+	if (size < 64) {
+		hid_warn(hdev, "report too short: %d < 64\n", size);
+		return 0;
+	}
 
 	switch (data[0]) {
 
-- 
2.43.0