[PATCH] platform/chrome: sensorhub: Fix memory overread in ring handler

`max_response` and `sensor_num` are read from different EC commands:

- `max_response` is from cros_ec_get_proto_info().
    ec_dev->max_response = info->max_response_packet_size -
                                    sizeof(struct ec_host_response);

- `sensor_num` is from cros_ec_get_sensor_count().
    sensor_num = cros_ec_get_sensor_count(ec);

With a malfunctioning EC firmware, it is possible that the `msg->insize`
(i.e., `fifo_info_length` in the context) could be clamped in
cros_ec_cmd_xfer() because `msg->insize` is greater than `max_response`.

    int fifo_info_length =
            sizeof(struct ec_response_motion_sense_fifo_info) +
            sizeof(u16) * sensorhub->sensor_num;

This means the number of read bytes could be less than expected.  As a
result, the subsequent memcpy() in cros_ec_sensorhub_ring_handler()
overreads the `resp->fifo_info` buffer.

Check the return value of cros_ec_cmd_xfer_status() and clamp the length
passed to memcpy() to the actual number of bytes read.

Fixes: 145d59baff59 ("platform/chrome: cros_ec_sensorhub: Add FIFO support")
Signed-off-by: Tzung-Bi Shih <[email protected]>
---
 drivers/platform/chrome/cros_ec_sensorhub_ring.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
index 64e9615ed6f4..4b4adc38485c 100644
--- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
+++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
@@ -825,11 +825,19 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
 		sensorhub->msg->outsize = 1;
 		sensorhub->msg->insize = fifo_info_length;
 
-		if (cros_ec_cmd_xfer_status(ec->ec_dev, sensorhub->msg) < 0)
+		ret = cros_ec_cmd_xfer_status(ec->ec_dev, sensorhub->msg);
+		if (ret < 0)
 			goto error;
 
 		memcpy(fifo_info, &sensorhub->resp->fifo_info,
-		       fifo_info_length);
+		       min(fifo_info_length, ret));
+
+		if (ret < fifo_info_length) {
+			dev_info_ratelimited(sensorhub->dev,
+					     "Read less FIFO info: size %d - expected %d\n",
+					     ret, fifo_info_length);
+			memset((u8 *)fifo_info + ret, 0, fifo_info_length - ret);
+		}
 
 		/*
 		 * Update collection time, will not be as precise as the
-- 
2.55.0.rc0.799.gd6f94ed593-goog