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 <angelogioacchino.delregno@collabora.com>]

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@astralinux.ru>
>> ---
>>   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