linux-kernel - Re: [PATCH RESENT] MEDIA CODA: Fix NULL ptr dereference in the encoder.

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Date:   Tue, 08 Jun 2021 11:55:03 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Krzysztof Halasa <khalasa@...p.pl>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESENT] MEDIA CODA: Fix NULL ptr dereference in the
 encoder.

Hi Krzysztof,

thank you for the patch.

On Mon, 2021-06-07 at 13:05 +0200, Krzysztof Halasa wrote:
> ctx->mb_err_cnt_ctrl could be NULL in case of failed initialization
> (on decoders), and encoders don't use it at all.
> 
> Fixes: b2d3bef1aa78 ("media: coda: Add a V4L2 user for control error macroblocks count")
> Signed-off-by: Krzysztof Halasa <khalasa@...p.pl>
> Cc: stable@...r.kernel.org # 5.11+
> 
> diff --git a/drivers/media/platform/coda/coda-bit.c b/drivers/media/platform/coda/coda-bit.c
> index 2f42808c43a4..26e37cbfe8dd 100644
> --- a/drivers/media/platform/coda/coda-bit.c
> +++ b/drivers/media/platform/coda/coda-bit.c
> @@ -2373,8 +2373,10 @@ static void coda_finish_decode(struct coda_ctx *ctx)
>  	if (err_mb > 0) {
>  		if (__ratelimit(&dev->mb_err_rs))
>  			coda_dbg(1, ctx, "errors in %d macroblocks\n", err_mb);
> -		v4l2_ctrl_s_ctrl(ctx->mb_err_cnt_ctrl,
> -				 v4l2_ctrl_g_ctrl(ctx->mb_err_cnt_ctrl) + err_mb);
> +		if (ctx->mb_err_cnt_ctrl)
> +			v4l2_ctrl_s_ctrl(ctx->mb_err_cnt_ctrl,
> +					 v4l2_ctrl_g_ctrl(ctx->mb_err_cnt_ctrl)
> +					 + err_mb);
>  	}
>  
>  	if (dev->devtype->product == CODA_HX4 ||

I don't think this is required though. If v4l2_ctrl_new_custom() fails
in coda_ctrls_setup(), ctx->ctrls.error is set and the function returns
-EINVAL, causing coda_open() to fail with the error message "failed to
setup coda controls". I see no way to reach coda_finish_decode() without
ctx->mb_err_cnt_ctrl being set correctly.

> diff --git a/drivers/media/platform/coda/coda-common.c b/drivers/media/platform/coda/coda-common.c
> index 96802b8f47ea..285c80f87b65 100644
> --- a/drivers/media/platform/coda/coda-common.c
> +++ b/drivers/media/platform/coda/coda-common.c
> @@ -2062,7 +2062,8 @@ static int coda_start_streaming(struct vb2_queue *q, unsigned int count)
>  	if (q_data_dst->fourcc == V4L2_PIX_FMT_JPEG)
>  		ctx->params.gop_size = 1;
>  	ctx->gopcounter = ctx->params.gop_size - 1;
> -	v4l2_ctrl_s_ctrl(ctx->mb_err_cnt_ctrl, 0);
> +	if (ctx->mb_err_cnt_ctrl)
> +		v4l2_ctrl_s_ctrl(ctx->mb_err_cnt_ctrl, 0);
>  
>  	ret = ctx->ops->start_streaming(ctx);
>  	if (ctx->inst_type == CODA_INST_DECODER) {

This is already fixed by [1] in media-tree/master.

[1] 0b276e470a4d ("media: coda: fix macroblocks count control usage")

regards
Philipp