mei: hdcp: fix mei_hdcp_verify_mprime() input parameter

wired_cmd_repeater_auth_stream_req_in has a variable
length array at the end. we use struct_size() overflow
macro to determine the size for the allocation and sending
size.
This also fixes bug in case number of streams is > 0 in the original
submission. This bug was not triggered as the number of streams is
always one.

Fixes: c56967d6 (mei: hdcp: Replace one-element array with flexible-array member)
Fixes: 0a1af1b5 (misc/mei/hdcp: Verify M_prime)
Cc: <stable@vger.kernel.org> # v5.1+: c56967d6 (mei: hdcp: Replace one-element array with flexible-array member)
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200818075406.2532605-1-tomas.winkler@intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/hdcp/mei_hdcp.c

@@ -546,38 +546,46 @@ static int mei_hdcp_verify_mprime(struct device *dev,
 				  struct hdcp_port_data *data,
 				  struct hdcp2_rep_stream_ready *stream_ready)
 {
-	struct wired_cmd_repeater_auth_stream_req_in
-					verify_mprime_in = { { 0 } };
+	struct wired_cmd_repeater_auth_stream_req_in *verify_mprime_in;
 	struct wired_cmd_repeater_auth_stream_req_out
 					verify_mprime_out = { { 0 } };
 	struct mei_cl_device *cldev;
 	ssize_t byte;
+	size_t cmd_size;
 
 	if (!dev || !stream_ready || !data)
 		return -EINVAL;
 
 	cldev = to_mei_cl_device(dev);
 
-	verify_mprime_in.header.api_version = HDCP_API_VERSION;
-	verify_mprime_in.header.command_id = WIRED_REPEATER_AUTH_STREAM_REQ;
-	verify_mprime_in.header.status = ME_HDCP_STATUS_SUCCESS;
-	verify_mprime_in.header.buffer_len =
+	cmd_size = struct_size(verify_mprime_in, streams, data->k);
+	if (cmd_size == SIZE_MAX)
+		return -EINVAL;
+
+	verify_mprime_in = kzalloc(cmd_size, GFP_KERNEL);
+	if (!verify_mprime_in)
+		return -ENOMEM;
+
+	verify_mprime_in->header.api_version = HDCP_API_VERSION;
+	verify_mprime_in->header.command_id = WIRED_REPEATER_AUTH_STREAM_REQ;
+	verify_mprime_in->header.status = ME_HDCP_STATUS_SUCCESS;
+	verify_mprime_in->header.buffer_len =
 			WIRED_CMD_BUF_LEN_REPEATER_AUTH_STREAM_REQ_MIN_IN;
 
-	verify_mprime_in.port.integrated_port_type = data->port_type;
-	verify_mprime_in.port.physical_port = (u8)data->fw_ddi;
-	verify_mprime_in.port.attached_transcoder = (u8)data->fw_tc;
+	verify_mprime_in->port.integrated_port_type = data->port_type;
+	verify_mprime_in->port.physical_port = (u8)data->fw_ddi;
+	verify_mprime_in->port.attached_transcoder = (u8)data->fw_tc;
+
+	memcpy(verify_mprime_in->m_prime, stream_ready->m_prime, HDCP_2_2_MPRIME_LEN);
+	drm_hdcp_cpu_to_be24(verify_mprime_in->seq_num_m, data->seq_num_m);
 
-	memcpy(verify_mprime_in.m_prime, stream_ready->m_prime,
-	       HDCP_2_2_MPRIME_LEN);
-	drm_hdcp_cpu_to_be24(verify_mprime_in.seq_num_m, data->seq_num_m);
-	memcpy(verify_mprime_in.streams, data->streams,
+	memcpy(verify_mprime_in->streams, data->streams,
 	       array_size(data->k, sizeof(*data->streams)));
 
-	verify_mprime_in.k = cpu_to_be16(data->k);
+	verify_mprime_in->k = cpu_to_be16(data->k);
 
-	byte = mei_cldev_send(cldev, (u8 *)&verify_mprime_in,
-			      sizeof(verify_mprime_in));
+	byte = mei_cldev_send(cldev, (u8 *)verify_mprime_in, cmd_size);
+	kfree(verify_mprime_in);
 	if (byte < 0) {
 		dev_dbg(dev, "mei_cldev_send failed. %zd\n", byte);
 		return byte;