linux-kernel - Re: [PATCH] net: mdiobus: Fix memory leak in __mdiobus

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Date:   Tue, 28 Sep 2021 23:48:23 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Pavel Skripkin <paskripkin@...il.com>,
        Yanfei Xu <yanfei.xu@...driver.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        andrew@...n.ch, hkallweit1@...il.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, p.zabel@...gutronix.de,
        syzbot <syzbot+398e7dc692ddbbb4cfec@...kaller.appspotmail.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: mdiobus: Fix memory leak in __mdiobus_register

On Tue, Sep 28, 2021 at 11:41 PM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Tue, Sep 28, 2021 at 04:52:07PM +0300, Dan Carpenter wrote:
> > On Tue, Sep 28, 2021 at 01:58:00PM +0100, Russell King (Oracle) wrote:
> > >
> > > This thread seems to be getting out of hand.
> >
> > The thread was closed.  We need to revert Yanfei's patch and apply
> > Pavel's patch.  He's going to resend.
> >
> > > So, I would suggest a simple fix is to set bus->state to
> > > MDIOBUS_UNREGISTERED immediately _after_ the successful
> > > device_register().
> >
> > Not after.  It has to be set to MDIOBUS_UNREGISTERED if device_register()
> > fails, otherwise there will still be a leak.
>
> Ah yes, you are correct - the device name may not be freed. Also...
>
>  * NOTE: _Never_ directly free @dev after calling this function, even
>  * if it returned an error! Always use put_device() to give up your
>  * reference instead.
>
> So yes, we must set to MDIOBUS_UNREGISTERED even if device_register()
> fails.
>

So we have reached an agreement. Pavel's patch fixes the syzbot link
[1], other than Yanfei's patch. However, Yanfei's patch also fixes
another memory link nearby.

Right?

[1] https://syzkaller.appspot.com/bug?id=fa99459691911a0369622248e0f4e3285fcedd97

> --
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