Re: [PATCH] net: mdiobus: Fix memory leak in __mdiobus_register

From: Pavel Skripkin
Date: Tue Sep 28 2021 - 07:45:46 EST

On 9/28/21 14:30, Dan Carpenter wrote:
On Tue, Sep 28, 2021 at 02:09:06PM +0300, Pavel Skripkin wrote:
On 9/28/21 14:06, Pavel Skripkin wrote:
> > It's not actually the same. The state has to be set before the
> > device_register() or there is still a leak.
> > > Ah, I see... I forgot to handle possible device_register() error. Will
> send v2 soon, thank you
> > > Wait... Yanfei's patch is already applied to net tree and if I understand
correctly, calling put_device() 2 times will cause UAF or smth else.

Yes. It causes a UAF.

Huh... You're right that the log should say "failed to register". But
I don't think that's the correct syzbot link for your patch either
because I don't think anyone calls mdiobus_free() if
__devm_mdiobus_register() fails. I have looked at these callers. It
would be a bug as well.

mdiobus_free() is called in case of ->probe() failure, because devres clean up function for bus is devm_mdiobus_free(). It simply calls mdiobus_free().

So, i imagine following calltrace:

devm_mdiobus_alloc() <- bus registered as devres
devm_mdiobus_register() <- fail (->probe failure)



Also, syzbot has tested my patch :)

Anyway, your patch is required and the __devm_mdiobus_register()
function has leaks as well. And perhaps there are more bugs we have not

dan carpenter

With regards,
Pavel Skripkin