[PATCH 6.1.y 2/2] HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes

[Sasha Levin <sashal@kernel.org>]

From: Jiangshan Yi <yijiangshan@kylinos.cn>

[ Upstream commit db2333f88729c8aae062cb171ed058725ff5c901 ]

mcp_i2c_smbus_read() stores the caller-supplied buffer pointer in
mcp->rxbuf for the duration of a transfer but never clears it when the
transfer finishes or times out. Once the caller frees or reuses the
buffer, mcp->rxbuf becomes a dangling pointer. A delayed or spurious
MCP2221_I2C_GET_DATA report can then drive mcp2221_raw_event() to
memcpy device data into the freed memory, causing a write
use-after-free.

Route all return paths through a single exit point that clears
mcp->rxbuf and mcp->rxbuf_size, so that the existing !mcp->rxbuf guard
in the raw_event handler can reject any report arriving after the
transfer has ended.

Fixes: 67a95c21463d ("HID: mcp2221: add usb to i2c-smbus host bridge")
Cc: stable@vger.kernel.org
Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hid/hid-mcp2221.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index f041e47ffba1e..2332ce6cf5cc5 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -302,7 +302,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);
 	if (ret)
-		return ret;
+		goto out;
 
 	mcp->rxbuf_idx = 0;
 
@@ -324,7 +324,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 			} else {
 				usleep_range(980, 1000);
 				mcp_cancel_last_cmd(mcp);
-				return ret;
+				goto out;
 			}
 		} else {
 			retries = 0;
@@ -334,6 +334,10 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 	usleep_range(980, 1000);
 	ret = mcp_chk_last_cmd_status_free_bus(mcp);
 
+out:
+	mcp->rxbuf = NULL;
+	mcp->rxbuf_size = 0;
+
 	return ret;
 }
 
-- 
2.53.0