linux-kernel - Re: [PATCH 2/2 v2] mtd: ubi: use put_device() if device

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Date:   Thu, 15 Mar 2018 23:11:58 +0530
From:   arvindY <arvind.yadav.cs@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     dwmw2@...radead.org, computersforpeace@...il.com,
        boris.brezillon@...e-electrons.com, marek.vasut@...il.com,
        cyrille.pitchen@...ev4u.fr, dedekind1@...il.com,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH 2/2 v2] mtd: ubi: use put_device() if device_register fail



On Thursday 15 March 2018 02:17 PM, Arvind Yadav wrote:
>
>
> On Thursday 15 March 2018 01:25 PM, Richard Weinberger wrote:
>> Am Donnerstag, 15. März 2018, 08:20:31 CET schrieb Arvind Yadav:
>>> if device_register() returned an error! Always use put_device()
>>> to give up the reference initialized.
>> Like DaveM said, there is no need to shout and use "!".
>
> I will fix this and send you update patch.
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>> ---
>>> change in v2:
>>>          Fix use-after-free bug. move put_device() after cdev_del().
>>>
>>>   drivers/mtd/ubi/vmt.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
>>> index 3fd8d7f..93c6163 100644
>>> --- a/drivers/mtd/ubi/vmt.c
>>> +++ b/drivers/mtd/ubi/vmt.c
>>> @@ -610,6 +610,7 @@ int ubi_add_volume(struct ubi_device *ubi, struct
>>> ubi_volume *vol)
>>>
>>>   out_cdev:
>>>       cdev_del(&vol->cdev);
>>> +    put_device(&vol->dev);
>>>       return err;
>> The more I dig into device code, the more questions I have.
>> Why is cdev_del() not part of the release function?
>>
>> Thanks,
>> //richard
>
> Yes, It's should be a part release function.
>
> ~arvind

I was wrong, We can not add cdev_del() in release(vol_release)
function.
Function's ubi_create_volume and ubi_add_volume both are using
same release function to release a volume devices.
ubi_add_volume is registering character device for the volume.
So we will have to release character device here.

~arvind