Re: [PATCH] firmware/sysfb: Fix device reference count leak in sysfb_disable()

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 16.09.26 um 23:06 schrieb Deucher, Alexander:
> Public
>
>> -----Original Message-----
>> From: Wentao Liang <vulab@iscas.ac.cn>
>> Sent: Wednesday, September 16, 2026 3:38 AM
>> To: Deucher, Alexander <Alexander.Deucher@amd.com>
>> Cc: dri-devel@lists.freedesktop.org; javierm@redhat.com; linux-
>> kernel@vger.kernel.org; tzimmermann@suse.de; Wentao Liang
>> <vulab@iscas.ac.cn>; stable@vger.kernel.org
>> Subject: [PATCH] firmware/sysfb: Fix device reference count leak in
>> sysfb_disable()
>>
>> In sysfb_disable(), parent is obtained via sysfb_parent_dev(si), which calls
>> screen_info_pci_dev(si) and returns a pointer to &pdev->dev with an acquired
>> reference count. However, sysfb_disable() does not release this reference
>> before returning, leading to a device reference leak.
>>
>> Fix this by checking if parent is not an ERR_PTR and calling
>> put_device(parent) before releasing the mutex.
>>
>> Fixes: b49420d6a1ae ("video/aperture: optionally match the device in
>> sysfb_disable()")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
>> ---
>>   drivers/firmware/sysfb.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c index
>> 8833582c1883..11c5ce128a6c 100644
>> --- a/drivers/firmware/sysfb.c
>> +++ b/drivers/firmware/sysfb.c
>> @@ -71,9 +71,12 @@ void sysfb_disable(struct device *dev)
>>
>>        mutex_lock(&disable_lock);
>>        parent = sysfb_parent_dev(si);
>> -     if (!dev || !parent || dev == parent) {
>> -             sysfb_unregister();
>> -             disabled = true;
>> +     if (!IS_ERR(parent)) {
> Are there cases where sysfb_unregister() would need to be called even if parent returns an error?

It could be seen as a defensive measure. Usually we want to unregister 
the system framebuffer only if the native driver's device equals the 
parent. But if we fail to retrieve a parent, it might be better to 
unregister unconditionally.  Otherwise the sysfb driver might interfere 
with the native driver.

I think that would be a good idea.

Best regards
Thomas


>
> Alex
>
>> +             if (!dev || !parent || dev == parent) {
>> +                     sysfb_unregister();
>> +                     disabled = true;
>> +             }
>> +             put_device(parent);
>>        }
>>        mutex_unlock(&disable_lock);
>>   }
>> --
>> 2.34.1

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)