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

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Date:   Tue, 25 Jun 2019 09:57:34 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     wharms@....de, Colin King <colin.king@...onical.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] media: vivid: fix potential integer overflow on
 left shift

On 6/25/19 9:48 AM, walter harms wrote:
> 
> 
> Am 24.06.2019 23:58, schrieb Colin King:
>> 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>
>> ---
>>  drivers/media/platform/vivid/vivid-ctrls.c | 16 ++++++++--------
>>  1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/media/platform/vivid/vivid-ctrls.c b/drivers/media/platform/vivid/vivid-ctrls.c
>> index 3e916c8befb7..8f340cfd6993 100644
>> --- a/drivers/media/platform/vivid/vivid-ctrls.c
>> +++ b/drivers/media/platform/vivid/vivid-ctrls.c
>> @@ -1634,8 +1634,8 @@ int vivid_create_controls(struct vivid_dev *dev, bool show_ccs_cap,
>>  			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);
>> +			(2ULL << (dev->num_hdmi_inputs - 1)) - 1, 0,
>> +			(2ULL << (dev->num_hdmi_inputs - 1)) - 1);
>>  
>>  	}
>>  	if (dev->num_hdmi_outputs) {
>> @@ -1653,16 +1653,16 @@ int vivid_create_controls(struct vivid_dev *dev, bool show_ccs_cap,
>>  			&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);
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1, 0,
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1);
>>  		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);
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1, 0,
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1);
>>  		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);
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1, 0,
>> +			(2ULL << (dev->num_hdmi_outputs - 1)) - 1);
>>  	}
>>  	if ((dev->has_vid_cap && dev->has_vid_out) ||
>>  	    (dev->has_vbi_cap && dev->has_vbi_out))
> 
> 
> To make this more readable for humans, it could help to store
>  (2ULL << (dev->num_hdmi_outputs - 1)) - 1 in an intermediate.
> like:
> s64 hdmi=(2ULL << (dev->num_hdmi_outputs - 1)) - 1;
> 
>   		dev->ctrl_tx_edid_present = v4l2_ctrl_new_std(hdl_vid_out,
>   			NULL, V4L2_CID_DV_TX_EDID_PRESENT, 0,
> 			hdmi, 0,hdmi);
> 
> 
> just my 2 cents,

I agree. Call it hdmi_output/input_mask, that is a good name for it.

Regards,

	Hans