linux-kernel - Re: [PATCH] media: qcom: venus: Fix a possible null-pointer dereference in vdec_g

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Message-ID: <0c24a860-7bd7-4f25-3ccf-4c88bdff34c2@xs4all.nl>
Date:   Fri, 13 Mar 2020 12:31:21 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, stanimir.varbanov@...aro.org,
        agross@...nel.org, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: qcom: venus: Fix a possible null-pointer
 dereference in vdec_g_fmt()

This patch fell between the cracks, but while cleaning up patchwork
it popped up again :-)

On 7/27/19 11:15 AM, Jia-Ju Bai wrote:
> In vdec_g_fmt(), fmt is firstly assigned NULL, and it could be never
> assigned before being used on line 223:
>     pixmp->pixelformat = fmt->pixfmt;
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, fmt is checked before being used here.

Actually, this function can only be called for f->type values
V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE or V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE.

The easiest way to fix this is to replace this:

        if (f->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE)
                fmt = inst->fmt_cap;
        else if (f->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
                fmt = inst->fmt_out;

by:

        if (f->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE)
                fmt = inst->fmt_cap;
        else
                fmt = inst->fmt_out;

And the same in a bit lower down in this function.

Regards,

	Hans

> 
> This bug is found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  drivers/media/platform/qcom/venus/vdec.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c
> index e1f998656c07..12c31551f191 100644
> --- a/drivers/media/platform/qcom/venus/vdec.c
> +++ b/drivers/media/platform/qcom/venus/vdec.c
> @@ -211,7 +211,8 @@ static int vdec_g_fmt(struct file *file, void *fh, struct v4l2_format *f)
>  		inst->height = format.fmt.pix_mp.height;
>  	}
>  
> -	pixmp->pixelformat = fmt->pixfmt;
> +	if (fmt)
> +		pixmp->pixelformat = fmt->pixfmt;
>  
>  	if (f->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE) {
>  		pixmp->width = inst->width;
>