Re: [PATCH] vcodec: mediatek: add check for NULL for vsi->frm_bufs[vsi->new_fb_idx].buf.fb in vp9_swap_frm_bufs

[AngeloGioacchino Del Regno]

Il 28/10/22 15:02, Nicolas Dufresne ha scritto:
> Hi,
>
> Le vendredi 28 octobre 2022 à 15:58 +0300, Anastasia Belova a écrit :
> > If vsi->frm_bufs[vsi->new_fb_idx].buf.fb == NULL while cleaning
> > fb_free_list NULL-pointer is dereferenced.
> >
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Fixes: f77e89854b3e ("[media] vcodec: mediatek: Add Mediatek VP9 Video Decoder Driver")
> >
> > Signed-off-by: Anastasia Belova <abelova@xxxxxxxxxxxxx>
> > ---
> >   drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > 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..b0679aaf6192 100644
> > --- a/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c
> > +++ b/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_if.c
> > @@ -512,7 +512,7 @@ static void vp9_swap_frm_bufs(struct vdec_vp9_inst *inst)
> >   	 * clean fb_free_list
> >   	 */
> >   	if (vsi->frm_bufs[vsi->new_fb_idx].ref_cnt == 0) {
> > -		if (!vp9_is_sf_ref_fb(
> > +		if (vsi->frm_bufs[vsi->new_fb_idx].buf.fb != NULL && !vp9_is_sf_ref_fb(
> >   			inst, vsi->frm_bufs[vsi->new_fb_idx].buf.fb)) {
> >   			struct vdec_fb *fb;
>
> Perhaps we could try and maintain some readability ? I'd suggest to move the
> check into vp9_is_sf_ref_fb() as an early return.

I don't think that this will ever happen, as the check was omitted because of being
totally sure that vsi->frm_bufs[vsi->new_fb_idx].buf.fb is not NULL.

In any case, it doesn't really cost anything to add a check... in which case, I
agree with Nicolas about moving that to vp9_is_sf_ref_fb().

	if (!fb)
		return false
	for .....

Regards,
Angelo