linux-kernel - Re: [PATCH][next][V2] media: vivid: fix potential integer overflow on left shift

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Message-ID: <8ccbbf10-7af1-b7e3-69ba-a24fe0cda86d@xs4all.nl>
Date:   Thu, 27 Jun 2019 09:22:26 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Colin King <colin.king@...onical.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next][V2] media: vivid: fix potential integer overflow on
 left shift

On 6/26/19 4:47 PM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> There is a potential integer overflow when int 2 is left shifted
> as this is evaluated using 32 bit arithmetic but is being used in
> a context that expects an expression of type s64.  Fix this by
> shifting 2ULL to avoid a 32 bit overflow.
> 
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: 8a99e9faa131 ("media: vivid: add HDMI (dis)connect RX emulation")
> Fixes: 79a792dafac6 ("media: vivid: add HDMI (dis)connect TX emulation")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
> V2: use intermediate variables for the shifted expression to make code
>     a bit more readable.
> ---
>  drivers/media/platform/vivid/vivid-ctrls.c | 24 +++++++++++-----------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/platform/vivid/vivid-ctrls.c b/drivers/media/platform/vivid/vivid-ctrls.c
> index 3e916c8befb7..df1598e81c7a 100644
> --- a/drivers/media/platform/vivid/vivid-ctrls.c
> +++ b/drivers/media/platform/vivid/vivid-ctrls.c
> @@ -1613,6 +1613,8 @@ int vivid_create_controls(struct vivid_dev *dev, bool show_ccs_cap,
>  	}
>  
>  	if (dev->num_hdmi_inputs) {
> +		s64 hdmi_input = (2ULL << (dev->num_hdmi_inputs - 1)) - 1;

Please call this hdmi_input_mask, ditto for the hdmi_output. This is a bitmask,
not an HDMI input index.

We should also use the GENMASK macro here:

	s64 hdmi_input_mask = GENMASK(dev->num_hdmi_inputs - 1, 0);

This is a lot easier to understand.

Regards,

	Hans

> +
>  		dev->ctrl_dv_timings_signal_mode = v4l2_ctrl_new_custom(hdl_vid_cap,
>  					&vivid_ctrl_dv_timings_signal_mode, NULL);
>  
> @@ -1633,12 +1635,13 @@ int vivid_create_controls(struct vivid_dev *dev, bool show_ccs_cap,
>  			V4L2_CID_DV_RX_RGB_RANGE, V4L2_DV_RGB_RANGE_FULL,
>  			0, V4L2_DV_RGB_RANGE_AUTO);
>  		dev->ctrl_rx_power_present = v4l2_ctrl_new_std(hdl_vid_cap,
> -			NULL, V4L2_CID_DV_RX_POWER_PRESENT, 0,
> -			(2 << (dev->num_hdmi_inputs - 1)) - 1, 0,
> -			(2 << (dev->num_hdmi_inputs - 1)) - 1);
> +			NULL, V4L2_CID_DV_RX_POWER_PRESENT, 0, hdmi_input,
> +			0, hdmi_input);
>  
>  	}
>  	if (dev->num_hdmi_outputs) {
> +		s64 hdmi_output = (2ULL << (dev->num_hdmi_outputs - 1)) - 1;
> +
>  		/*
>  		 * We aren't doing anything with this at the moment, but
>  		 * HDMI outputs typically have this controls.
> @@ -1652,17 +1655,14 @@ int vivid_create_controls(struct vivid_dev *dev, bool show_ccs_cap,
>  		dev->ctrl_display_present = v4l2_ctrl_new_custom(hdl_vid_out,
>  			&vivid_ctrl_display_present, NULL);
>  		dev->ctrl_tx_hotplug = v4l2_ctrl_new_std(hdl_vid_out,
> -			NULL, V4L2_CID_DV_TX_HOTPLUG, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1);
> +			NULL, V4L2_CID_DV_TX_HOTPLUG, 0, hdmi_output,
> +			0, hdmi_output);
>  		dev->ctrl_tx_rxsense = v4l2_ctrl_new_std(hdl_vid_out,
> -			NULL, V4L2_CID_DV_TX_RXSENSE, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1);
> +			NULL, V4L2_CID_DV_TX_RXSENSE, 0, hdmi_output,
> +			0, hdmi_output);
>  		dev->ctrl_tx_edid_present = v4l2_ctrl_new_std(hdl_vid_out,
> -			NULL, V4L2_CID_DV_TX_EDID_PRESENT, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1, 0,
> -			(2 << (dev->num_hdmi_outputs - 1)) - 1);
> +			NULL, V4L2_CID_DV_TX_EDID_PRESENT, 0, hdmi_output,
> +			0, hdmi_output);
>  	}
>  	if ((dev->has_vid_cap && dev->has_vid_out) ||
>  	    (dev->has_vbi_cap && dev->has_vbi_out))
>