[v2,01/13] media: v4l2-ctrls-api: fix error handling for v4l2_g_ctrl()

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@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
---
 drivers/media/v4l2-core/v4l2-ctrls-api.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

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@vger.kernel.org
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.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

Hi Mauro,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Mauro-Carvalho-Chehab/media-v4l2-ctrls-api-fix-error-handling-for-v4l2_g_ctrl/20241018-181159
base:   https://git.linuxtv.org/media_stage.git master
patch link:    https://lore.kernel.org/r/4d36ccf66f48a870c9bc0f7e9fda595505c4d342.1729230718.git.mchehab%2Bhuawei%40kernel.org
patch subject: [PATCH v2 01/13] media: v4l2-ctrls-api: fix error handling for v4l2_g_ctrl()
config: i386-randconfig-141-20241021 (https://download.01.org/0day-ci/archive/20241022/202410220105.oP6D4QD7-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202410220105.oP6D4QD7-lkp@intel.com/

smatch warnings:
drivers/media/v4l2-core/v4l2-ctrls-api.c:825 set_ctrl_lock() warn: inconsistent returns 'ctrl->handler->lock'.

vim +825 drivers/media/v4l2-core/v4l2-ctrls-api.c

71c689dc2e732d4 Hans Verkuil          2021-04-27  812  static int set_ctrl_lock(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
71c689dc2e732d4 Hans Verkuil          2021-04-27  813  			 struct v4l2_ext_control *c)
71c689dc2e732d4 Hans Verkuil          2021-04-27  814  {
71c689dc2e732d4 Hans Verkuil          2021-04-27  815  	int ret;
71c689dc2e732d4 Hans Verkuil          2021-04-27  816  
71c689dc2e732d4 Hans Verkuil          2021-04-27  817  	v4l2_ctrl_lock(ctrl);
54c5e2c49a4358b Mauro Carvalho Chehab 2024-10-18  818  	ret = user_to_new(c, ctrl);
54c5e2c49a4358b Mauro Carvalho Chehab 2024-10-18  819  	if (ret)
54c5e2c49a4358b Mauro Carvalho Chehab 2024-10-18  820  		return ret;

v4l2_ctrl_unlock() before returning

71c689dc2e732d4 Hans Verkuil          2021-04-27  821  	ret = set_ctrl(fh, ctrl, 0);
71c689dc2e732d4 Hans Verkuil          2021-04-27  822  	if (!ret)
54c5e2c49a4358b Mauro Carvalho Chehab 2024-10-18  823  		ret = cur_to_user(c, ctrl);
71c689dc2e732d4 Hans Verkuil          2021-04-27  824  	v4l2_ctrl_unlock(ctrl);
71c689dc2e732d4 Hans Verkuil          2021-04-27 @825  	return ret;
71c689dc2e732d4 Hans Verkuil          2021-04-27  826  }