linux-kernel - Re: [PATCH v2 01/13] media: v4l2-ctrls-api: fix error handling for v4l2_g

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Message-ID: <2caf0dfc-6d7c-4561-b126-4f3c654706fe@xs4all.nl>
Date: Fri, 18 Oct 2024 08:13:01 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Ricardo Ribalda <ribalda@...omium.org>, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 01/13] media: v4l2-ctrls-api: fix error handling for
 v4l2_g_ctrl()

On 18/10/2024 07:53, Mauro Carvalho Chehab wrote:
> As detected by Coverity, the error check logic at get_ctrl() is
> broken: if ptr_to_user() fails to fill a control due to an error,
> no errors are returned and v4l2_g_ctrl() returns success on a
> failed operation, which may cause applications to fail.
> 
> Add an error check at get_ctrl() and ensure that it will
> be returned to userspace without filling the control value if
> get_ctrl() fails.
> 
> Fixes: 71c689dc2e73 ("media: v4l2-ctrls: split up into four source files")
> Cc: stable@...r.kernel.org
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> ---
>  drivers/media/v4l2-core/v4l2-ctrls-api.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> index e5a364efd5e6..a0de7eeaf085 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> @@ -753,9 +753,10 @@ static int get_ctrl(struct v4l2_ctrl *ctrl, struct v4l2_ext_control *c)
>  		for (i = 0; i < master->ncontrols; i++)
>  			cur_to_new(master->cluster[i]);
>  		ret = call_op(master, g_volatile_ctrl);
> -		new_to_user(c, ctrl);
> +		if (!ret)
> +			ret = new_to_user(c, ctrl);
>  	} else {
> -		cur_to_user(c, ctrl);
> +		ret = cur_to_user(c, ctrl);
>  	}
>  	v4l2_ctrl_unlock(master);
>  	return ret;
> @@ -770,7 +771,10 @@ int v4l2_g_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *control)
>  	if (!ctrl || !ctrl->is_int)
>  		return -EINVAL;
>  	ret = get_ctrl(ctrl, &c);
> -	control->value = c.value;
> +
> +	if (!ret)
> +		control->value = c.value;
> +
>  	return ret;
>  }
>  EXPORT_SYMBOL(v4l2_g_ctrl);
> @@ -811,10 +815,12 @@ static int set_ctrl_lock(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
>  	int ret;
>  
>  	v4l2_ctrl_lock(ctrl);
> -	user_to_new(c, ctrl);
> +	ret = user_to_new(c, ctrl);
> +	if (ret)
> +		return ret;

A lock was taken above and that isn't unlocked here.

It is better to write this as:

	if (!ret)
		ret = set_ctrl(fh, ctrl, 0);

>  	ret = set_ctrl(fh, ctrl, 0);
>  	if (!ret)
> -		cur_to_user(c, ctrl);
> +		ret = cur_to_user(c, ctrl);
>  	v4l2_ctrl_unlock(ctrl);
>  	return ret;
>  }

Regards,

	Hans