netdev - Re: [PATCH net] net: read dev->needs_free_netdev before potentially freeing dev

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Message-ID: <20200825082437.GQ5493@kadam>
Date:   Tue, 25 Aug 2020 11:24:37 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] net: read dev->needs_free_netdev before potentially
 freeing dev

On Mon, Aug 24, 2020 at 10:06:50PM +0200, Jason A. Donenfeld wrote:
> If dev->needs_free_netdev is true, it means that netdev_run_todo should
> call free_netdev(dev) after it calls dev->priv_destructor. If
> dev->needs_free_netdev is false, then it means that either
> dev->priv_destructor is taking care of calling free_netdev(dev), or
> something else, elsewhere, is doing that. In this case, branching on
> "if (dev->needs_free_netdev)" after calling dev->priv_destructor is a
> potential UaF. This patch fixes the issue by reading
> dev->needs_free_netdev before calling dev->priv_destructor.
> 

No, I misread the code.  Sorry.  This patch is not required.  We can
use "dev" up to the end of the function where we do:

		/* Free network device */
		kobject_put(&dev->dev.kobj);

That's where the final reference is released.

regards,
dan carpenter