[PATCH] HID: mcp2221: validate raw report length

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

HID calls a driver raw_event() callback before it performs the generic
report-length validation. mcp2221_raw_event() subsequently reads fixed
response fields up to byte 55 and can copy a response payload through byte
63.

A short input report can therefore be interpreted using bytes beyond the
current report length before the HID core rejects it. Validate the
descriptor-derived report length at the beginning of the driver callback.

Complete the pending command with -EINVAL for a truncated report so that a
malformed response does not turn into an unrelated timeout.

Fixes: 67a95c21463d ("HID: mcp2221: add usb to i2c-smbus host bridge")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 drivers/hid/hid-mcp2221.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index e4ddd8e9293b..67afef1a275f 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -861,6 +861,17 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 	u8 *buf;
 	struct mcp2221 *mcp = hid_get_drvdata(hdev);
 
+	/*
+	 * HID invokes .raw_event() before its generic report-length check.
+	 * The response handlers below read fixed offsets from @data, so reject
+	 * a truncated current report before interpreting any of its fields.
+	 */
+	if (size < hid_report_len(report)) {
+		mcp->status = -EINVAL;
+		complete(&mcp->wait_in_report);
+		return 1;
+	}
+
 	switch (data[0]) {
 
 	case MCP2221_I2C_WR_DATA:
-- 
2.43.0