Re: [char-misc-next V3] mei: hdcp: fix mei_hdcp_verify_mprime() input paramter

[Gustavo A. R. Silva]

Tomas,

The subject line has a typo: s/paramter/parameter

Please, see more comments below...

On 7/30/20 13:54, Tomas Winkler wrote:
> 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: c56967d674e3 (mei: hdcp: Replace one-element array with flexible-array member)
> Fixes: 0a1af1b5c18d ("misc/mei/hdcp: Verify M_prime")
> Cc: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>
> Cc: Ramalingam C <ramalingam.c@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> v5.1+
> Signed-off-by: Tomas Winkler <tomas.winkler@xxxxxxxxx>
> ---
> V3:
> 1. Fix commit message with more info and another patch it fixes (Gustavo)
> 2. Target stable. (Gustavo)
> V2: Check for allocation failure.
>  drivers/misc/mei/hdcp/mei_hdcp.c | 40 +++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/misc/mei/hdcp/mei_hdcp.c b/drivers/misc/mei/hdcp/mei_hdcp.c
> index d1d3e025ca0e..f1205e0060db 100644
> --- a/drivers/misc/mei/hdcp/mei_hdcp.c
> +++ b/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);

The line above is incorrect, it should be this, instead:

byte = mei_cldev_send(cldev, (u8 *)verify_mprime_in, cmd_size);

otherwise you are passing the address of the object pointer
verify_mprime_in and not the reference to what it points to,
which is what we want in this case.

Thanks
--
Gustavo

> +	kfree(verify_mprime_in);
>  	if (byte < 0) {
>  		dev_dbg(dev, "mei_cldev_send failed. %zd\n", byte);
>  		return byte;
>