linux-kernel - Re: [PATCH v4 1/4] uacce: fix for cdev memory leak

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Message-ID: <12a8a634-f256-45e8-be74-a283e8edce9c@hisilicon.com>
Date: Tue, 4 Nov 2025 20:41:02 +0800
From: "linwenkai (C)" <linwenkai6@...ilicon.com>
To: Zhangfei Gao <zhangfei.gao@...aro.org>, Chenghai Huang
	<huangchenghai2@...wei.com>
CC: <gregkh@...uxfoundation.org>, <wangzhou1@...ilicon.com>,
	<linux-kernel@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
	<fanghao11@...wei.com>, <shenyang39@...wei.com>, <liulongfang@...wei.com>,
	<qianweili@...wei.com>
Subject: Re: [PATCH v4 1/4] uacce: fix for cdev memory leak


在 2025/10/22 14:17, Zhangfei Gao 写道:
> On Wed, 22 Oct 2025 at 10:12, Chenghai Huang <huangchenghai2@...wei.com> wrote:
>> From: Wenkai Lin <linwenkai6@...ilicon.com>
>>
>> In uacce_register(), if cdev_device_add() fails, we should properly
>> decrease the reference count of the cdev kobject and set uacce->cdev
>> to NULL to avoid potential use-after-free or double free issues.
>>
>> This change adds proper error handling after cdev_device_add() fails,
>> ensuring that kobject_put() is called and uacce->cdev is cleared.
>>
>> Fixes: 015d239ac014 ("uacce: add uacce driver")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Wenkai Lin <linwenkai6@...ilicon.com>
>> Signed-off-by: Chenghai Huang <huangchenghai2@...wei.com>
>> ---
>>   drivers/misc/uacce/uacce.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
>> index 42e7d2a2a90c..9b82a6731832 100644
>> --- a/drivers/misc/uacce/uacce.c
>> +++ b/drivers/misc/uacce/uacce.c
>> @@ -519,6 +519,8 @@ EXPORT_SYMBOL_GPL(uacce_alloc);
>>    */
>>   int uacce_register(struct uacce_device *uacce)
>>   {
>> +       int ret;
>> +
>>          if (!uacce)
>>                  return -ENODEV;
>>
>> @@ -529,7 +531,14 @@ int uacce_register(struct uacce_device *uacce)
>>          uacce->cdev->ops = &uacce_fops;
>>          uacce->cdev->owner = THIS_MODULE;
>>
>> -       return cdev_device_add(uacce->cdev, &uacce->dev);
>> +       ret = cdev_device_add(uacce->cdev, &uacce->dev);
>> +       if (ret) {
>> +               kobject_put(&uacce->cdev->kobj);
> Not understanding this,
> What if kobject_put(&p->kobj) is called twice?
> cdev_device_add would call cdev_del->kobject_put(&p->kobj) as well.
>
> If you think cdev_device_add has an issue, maybe fixing
> cdev_device_add itself is better?
>
> Thanks
After more testing, a new conclusion was reached.

After the cdev_set_parent function in cdev_device_add is called,
the cdev and the device will share the same lifetime and the memory
of the cdev is managed by the device.
So when put_device is called in the uacce_remove, the memory of the cdev
will also be released, so there is no memory leak issue in the code.

In addition, when cdev_device_add fails, a flag should be set to detect
this situation to prevent the uacce_remove from incorrectly calling
cdev_device_del to release the unallocated resources.
This issue will be fixed in the next patch.

Thanks,
Wenkai