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

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Date:   Fri, 16 Mar 2018 08:50:06 +0100
From:   Richard Weinberger <richard@....at>
To:     arvindY <arvind.yadav.cs@...il.com>
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

Arvind,

Am Donnerstag, 15. März 2018, 18:41:58 CET schrieb arvindY:
> 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.

This is not what I meant.
The question was whether we should free all this data structures from the 
device model's point of view.
That we have to massage UBI code for that is clear.

Thanks,
//richard