linux-kernel - Re: [PATCH] cfg80211: free the object allocated in wiphy_apply_custom

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Date:   Fri, 23 Jul 2021 17:59:39 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Luca Coelho <luciano.coelho@...el.com>,
        Ilan Peer <ilan.peer@...el.com>,
        syzbot+1638e7c770eef6b6c0d0@...kaller.appspotmail.com,
        linux-wireless@...r.kernel.org,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] cfg80211: free the object allocated in wiphy_apply_custom_regulatory

On Fri, Jul 23, 2021 at 5:42 PM Johannes Berg <johannes@...solutions.net> wrote:
>
> Hi,
>
> On Fri, 2021-07-23 at 17:30 +0800, Dongliang Mu wrote:
> > if zhao in the thread is right, we don't need to add this free
> > operation to wiphy_free().
>
> Actually, no, that statement is not true.
>
> All that zhao claimed was that the free happens correctly during
> unregister (or later), and that is indeed true, since it happens from
>
> ieee80211_unregister_hw()
>  -> wiphy_unregister()
>  -> wiphy_regulatory_deregister()
>

Thanks for your explanation. Now the situation is more clear.

>
> However, syzbot of course is also correct. Abstracting a bit and
> ignoring mac80211, the problem is that here we assign it before
> wiphy_register(), then wiphy_register() doesn't get called or fails, and
> therefore we don't call wiphy_unregister(), only wiphy_free().

Yes, you're right. In this case, wiphy_register is not called. We
should not call wiphy_unregister() to clean up anything.

>
> Hence the leak.
>
> But you can also easily see from that description that it's not related
> to hwsim - we should add a secondary round of cleanups in wiphy_free()
> or even move the call to wiphy_regulatory_deregister() into
> wiphy_free(), we need to look what else this does to see if we can move
> it or not.

I agree to move the cleanup operation of regd to wiphy_free API.
That's the partial functionability of this function.

>
> johannes
>