linux-kernel - Re: [PATCH] media: em28xx: return error on media_device

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Message-ID: <b7ca60c4-2392-448e-90e4-5078051d7af6@fintech.ru>
Date: Thu, 11 Jan 2024 07:10:10 -0800
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Mauro Carvalho Chehab <mchehab@...nel.org>
CC: <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: em28xx: return error on media_device_register()
 failure


On 1/10/24 22:49, Mauro Carvalho Chehab wrote:
> Em Wed, 10 Jan 2024 09:39:58 -0800
> Nikita Zhandarovich <n.zhandarovich@...tech.ru> escreveu:
> 
>> In an unlikely case of failure in media_device_register(), release
>> resources and return the erroneous value. Otherwise, possible issues
>> with registering the device will continue to be ignored.
>>
>> Found by Linux Verification Center (linuxtesting.org) with static
>> analysis tool SVACE.
>>
>> Fixes: 37ecc7b1278f ("[media] em28xx: add media controller support")
>> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
>> ---
>>  drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
>> index 4d037c92af7c..dae731dfc569 100644
>> --- a/drivers/media/usb/em28xx/em28xx-cards.c
>> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
>> @@ -4095,6 +4095,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
>>  	 */
>>  #ifdef CONFIG_MEDIA_CONTROLLER
>>  	retval = media_device_register(dev->media_dev);
>> +	if (retval)
>> +		goto err_free;
> 
> Not freeing resources here is intentional. See, the media controller 
> API is optional on this driver. It will just provide a way to identify
> the device's topology, but the device is completely usable without
> it.
> 
> Perhaps we need, instead, a patch documenting it, and preventing
> static analysis tools to point it as an issue.
> 
> Thanks,
> Mauro

Thank you for your feedback, however I had a few questions...

While I understand what you mean about optional nature of media
controller registration in this case, a quick glance into other calls to
media_device_register() across the source code shows that usually
failure with registering is handled as a proper error regardless of
whether the device is still usable. But if you think that we can make an
exception here, I'll happily oblige.

Then if I am to continue on this path, would the following comment above
the call to media_device_register() suffice?

 #ifdef CONFIG_MEDIA_CONTROLLER
+	/*
+	 * No need to check the return value, the device will still be 	     +
 * usable without media controller API.
+	 */
 	retval = media_device_register(dev->media_dev);

Thanks,
Nikita