[PATCH 6.1.y 1/2] HID: mcp2221: fix OOB write in mcp2221_raw_event()

[Sasha Levin <sashal@kernel.org>]

From: Florian Pradines <florian.pradines@gmail.com>

[ Upstream commit f097d246677b03db814c5862f368cea341b76a00 ]

mcp2221_raw_event() copies device-supplied data into mcp->rxbuf at
offset rxbuf_idx without checking that the copy fits within the
destination buffer. A device responding with up to 60 bytes to a
small I2C/SMBus read can overflow the buffer.

Add a rxbuf_size field to struct mcp2221, set it alongside rxbuf in
mcp_i2c_smbus_read(), and check rxbuf_idx + data[3] <= rxbuf_size
before the memcpy.

Reported-by: Benoît Sevens <bsevens@google.com>
Signed-off-by: Florian Pradines <florian.pradines@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Stable-dep-of: db2333f88729 ("HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hid/hid-mcp2221.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index e1bd1744bf307..f041e47ffba1e 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -93,6 +93,7 @@ struct mcp2221 {
 	u8 *rxbuf;
 	u8 txbuf[64];
 	int rxbuf_idx;
+	int rxbuf_size;
 	int status;
 	u8 cur_i2c_clk_div;
 	struct gpio_chip *gc;
@@ -289,12 +290,14 @@ 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_size = 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_size = smbus_len;
 	}
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);
@@ -797,6 +800,10 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 					mcp->status = -EINVAL;
 					break;
 				}
+				if (mcp->rxbuf_idx + data[3] > mcp->rxbuf_size) {
+					mcp->status = -EINVAL;
+					break;
+				}
 				buf = mcp->rxbuf;
 				memcpy(&buf[mcp->rxbuf_idx], &data[4], data[3]);
 				mcp->rxbuf_idx = mcp->rxbuf_idx + data[3];
-- 
2.53.0