[PATCH] HID: mcp2221: Fix heap buffer overflow in mcp2221_raw_event()

[Benoit Sevens]

From: Benoît Sevens <bsevens@xxxxxxxxxx>

A heap buffer overflow can occur in the mcp2221_raw_event() function
when handling I2C read responses. The driver failed to check if the
total incoming data length fits within the originally allocated buffer
`mcp->rxbuf`.

Fix this by introducing `rxbuf_len` to `struct mcp2221` to keep track
of the allocated buffer size. Initialize it in `mcp_i2c_smbus_read()`
and `mcp_smbus_xfer()`, and ensure the copied data length combined with
the current index does not exceed this length in `mcp2221_raw_event()`.

Signed-off-by: Benoît Sevens <bsevens@xxxxxxxxxx>
---
 drivers/hid/hid-mcp2221.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index ef3b5c77c38e..744561e65079 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -119,6 +119,7 @@ struct mcp2221 {
 	struct completion wait_in_report;
 	struct delayed_work init_work;
 	u8 *rxbuf;
+	int rxbuf_len;
 	u8 txbuf[64];
 	int rxbuf_idx;
 	int status;
@@ -323,12 +324,14 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 		mcp->txbuf[3] = (u8)(msg->addr << 1);
 		total_len = msg->len;
 		mcp->rxbuf = msg->buf;
+		mcp->rxbuf_len = msg->len;
 	} else {
 		mcp->txbuf[1] = smbus_len;
 		mcp->txbuf[2] = 0;
 		mcp->txbuf[3] = (u8)(smbus_addr << 1);
 		total_len = smbus_len;
 		mcp->rxbuf = smbus_buf;
+		mcp->rxbuf_len = smbus_len;
 	}
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);
@@ -538,6 +541,7 @@ static int mcp_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 
 			mcp->rxbuf_idx = 0;
 			mcp->rxbuf = data->block;
+			mcp->rxbuf_len = sizeof(data->block);
 			mcp->txbuf[0] = MCP2221_I2C_GET_DATA;
 			ret = mcp_send_data_req_status(mcp, mcp->txbuf, 1);
 			if (ret)
@@ -561,6 +565,7 @@ static int mcp_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 
 			mcp->rxbuf_idx = 0;
 			mcp->rxbuf = data->block;
+			mcp->rxbuf_len = sizeof(data->block);
 			mcp->txbuf[0] = MCP2221_I2C_GET_DATA;
 			ret = mcp_send_data_req_status(mcp, mcp->txbuf, 1);
 			if (ret)
@@ -908,7 +913,9 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 			}
 			if (data[2] == MCP2221_I2C_READ_COMPL ||
 			    data[2] == MCP2221_I2C_READ_PARTIAL) {
-				if (!mcp->rxbuf || mcp->rxbuf_idx < 0 || data[3] > 60) {
+				if (!mcp->rxbuf || mcp->rxbuf_idx < 0 ||
+				    data[3] > 60 ||
+				    mcp->rxbuf_idx + data[3] > mcp->rxbuf_len) {
 					mcp->status = -EINVAL;
 					break;
 				}
-- 
2.54.0.rc0.605.g598a273b03-goog