linux-kernel - Re: [RFC][PATCH] media: v4l2-ctrls: add more NULL pointer checks

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Date:   Thu, 16 Apr 2020 14:13:51 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] media: v4l2-ctrls: add more NULL pointer checks

On 16/04/2020 13:32, Sergey Senozhatsky wrote:
> On (20/04/16 10:53), Hans Verkuil wrote:
> [..]
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
>>> @@ -2869,6 +2869,9 @@ EXPORT_SYMBOL(v4l2_ctrl_add_handler);
>>>  
>>>  bool v4l2_ctrl_radio_filter(const struct v4l2_ctrl *ctrl)
>>>  {
>>> +	if (WARN_ON(!ctrl))
>>> +		return false;
>>> +
>>>  	if (V4L2_CTRL_ID2WHICH(ctrl->id) == V4L2_CTRL_CLASS_FM_TX)
>>>  		return true;
>>>  	if (V4L2_CTRL_ID2WHICH(ctrl->id) == V4L2_CTRL_CLASS_FM_RX)
>>> @@ -3794,7 +3797,9 @@ s32 v4l2_ctrl_g_ctrl(struct v4l2_ctrl *ctrl)
>>>  	struct v4l2_ext_control c;
>>>  
>>>  	/* It's a driver bug if this happens. */
>>> -	WARN_ON(!ctrl->is_int);
>>> +	if (WARN_ON(!ctrl || !ctrl->is_int))
>>> +		return -EINVAL;
>>
>> Just return 0 here. The return value is the control's value, not an error code.
>> So all you can do here is return 0 in the absence of anything better.
> 
> OK.
> 
>>> +
>>>  	c.value = 0;
>>>  	get_ctrl(ctrl, &c);
>>>  	return c.value;
>>> @@ -4212,6 +4217,9 @@ EXPORT_SYMBOL(v4l2_s_ctrl);
>>>  
>>>  int __v4l2_ctrl_s_ctrl(struct v4l2_ctrl *ctrl, s32 val)
>>>  {
>>> +	if (!ctrl)
>>
>> Change this to 'if (WARN_ON(!ctrl))'
>>
>> I don't think NULL pointers should be silently ignored: it really
>> indicates a driver bug. It it certainly a good idea to WARN instead.
> 
> Should WARN_ON() be only in unlocked versions of ctrl API? It probably
> would make sense to add WARNs to both - e.g. to v4l2_ctrl_s_ctrl() and

Yes, it should be done for both.

> to __v4l2_ctrl_s_ctrl(). By the way, why don't locked and unlocked
> versions live together in v4l2-ctrls.c file? Any reason for, e.g.,
> v4l2_ctrl_s_ctrl() to be in header and __v4l2_ctrl_s_ctrl() to be C-file?

The v4l2_ctrl_s_ctrl() work fine as a static inline (only compiled if
they are actually used). But with an additional 'if (WARN_ON(!ctrl))'
it becomes a bit questionable. I would not be opposed if these static
inlines are now moved into the source code.

Regards,

	Hans

> 
>> The same is true for the functions below.
> 
> OK.
> 
> 	-ss
>