linux-kernel - Re: [PATCH] media: dvb_vb2: fix possible out of bound access

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Date:   Wed, 18 May 2022 12:44:20 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Hangyu Hua <hbh25y@...il.com>, mchehab@...nel.org,
        senozhatsky@...omium.org, caihuoqing@...du.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: dvb_vb2: fix possible out of bound access

Hi Hangyu,

It appears this patch fell through the cracks. It's certainly useful to
have.

On 3/24/22 09:01, Hangyu Hua wrote:
> vb2_core_qbuf and vb2_core_querybuf don't check the range of b->index
> controlled by the user.
> 
> Fix this by adding range checking code before using them.
> 
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>  drivers/media/dvb-core/dvb_vb2.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
> index a1bd6d9c9223..f410800b92e7 100644
> --- a/drivers/media/dvb-core/dvb_vb2.c
> +++ b/drivers/media/dvb-core/dvb_vb2.c
> @@ -354,6 +354,12 @@ int dvb_vb2_reqbufs(struct dvb_vb2_ctx *ctx, struct dmx_requestbuffers *req)
>  
>  int dvb_vb2_querybuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
>  {
> +	struct vb2_queue *q = &ctx->vb_q;
> +
> +	if (b->index >= q->num_buffers) {
> +		dprintk(q, 1, "buffer index out of range\n");

However, this patch doesn't compile: dprintk in this source doesn't
have a 'q' argument!

> +		return -EINVAL;
> +	}
>  	vb2_core_querybuf(&ctx->vb_q, b->index, b);
>  	dprintk(3, "[%s] index=%d\n", ctx->name, b->index);

Also, to help debugging it prefixes the warnings with the ctx-name.

Can you post a v2 of this patch?

Regards,

	Hans

>  	return 0;
> @@ -378,8 +384,13 @@ int dvb_vb2_expbuf(struct dvb_vb2_ctx *ctx, struct dmx_exportbuffer *exp)
>  
>  int dvb_vb2_qbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
>  {
> +	struct vb2_queue *q = &ctx->vb_q;
>  	int ret;
>  
> +	if (b->index >= q->num_buffers) {
> +		dprintk(q, 1, "buffer index out of range\n");
> +		return -EINVAL;
> +	}
>  	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b, NULL);
>  	if (ret) {
>  		dprintk(1, "[%s] index=%d errno=%d\n", ctx->name,