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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <2523f498-3723-48a1-8594-83bac35a4ead@hisilicon.com>
Date: Wed, 22 Oct 2025 15:37:26 +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
Regarding your concern, cdev_device_add() use cdev_del rolls back
its cdev_add operations (add the refcount to 2) upon failure when
dev->devt is not null, the refcount of cdev is still 1 after the
rollback, so it does not free the memory of the cdev structure itself.

Therefore, in the error path of uacce_register, we still need to
manually call kobject_put to decrement the refcount of the kobject to
zero within cdev and free it.

Thanks,
Wenkai