linux-kernel - Re: [PATCH v3] vcodec: mediatek: add check for NULL for vsi->frm_bufs[vsi->new_fb_idx].buf.fb in vp9_swap_frm

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Date:   Fri, 18 Nov 2022 15:39:46 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Anastasia Belova <abelova@...ralinux.ru>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Tiffany Lin <tiffany.lin@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Yunfei Dong <yunfei.dong@...iatek.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v3] vcodec: mediatek: add check for NULL for
 vsi->frm_bufs[vsi->new_fb_idx].buf.fb in vp9_swap_frm_bufs

On 11/11/22 10:06, Anastasia Belova wrote:
> Any time calling vp9_is_sf_ref_fb we need fb != NULL after checks.

This doesn't match the subject line at all!

> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: f77e89854b3e ("[media] vcodec: mediatek: Add Mediatek VP9 Video Decoder Driver")

Drop this, it's not a fix, it just attempts to make things more robust.

> 
> Signed-off-by: Anastasia Belova <abelova@...ralinux.ru>
> ---
>  drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c b/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c
> index 70b8383f7c8e..776468cd834a 100644
> --- a/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c
> +++ b/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c
> @@ -208,6 +208,9 @@ static bool vp9_is_sf_ref_fb(struct vdec_vp9_inst *inst, struct vdec_fb *fb)
>  	int i;
>  	struct vdec_vp9_vsi *vsi = inst->vsi;
>  
> +	if (!fb)
> +		return true;
> +
>  	for (i = 0; i < ARRAY_SIZE(vsi->sf_ref_fb); i++) {
>  		if (fb == &vsi->sf_ref_fb[i].fb)
>  			return true;

This won't work: if fb == NULL, then depending on whether
this function returns true or false, the code in vp9_swap_frm_bufs()
will crash in either vsi->frm_bufs[vsi->new_fb_idx].buf.fb->base_y.va
or in vp9_free_sf_ref_fb().

Unless you can show there really is a path through which fb can be NULL,
I don't think it is worth continuing with this.

Regards,

	Hans