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

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Date:   Fri, 23 Jul 2021 17:13:59 +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 4:37 PM Johannes Berg <johannes@...solutions.net> wrote:
>
> On Fri, 2021-07-23 at 13:09 +0800, Dongliang Mu wrote:
> > The commit beee24695157 ("cfg80211: Save the regulatory domain when
> > setting custom regulatory") forgets to free the newly allocated regd
> > object.
>
> Not really? It's not forgetting it, it just saves it?

Yes, it saves the regd object in the function wiphy_apply_custom_regulatory.

But its parent function - mac80211_hwsim_new_radio forgets to free
this object when the ieee80211_register_hw fails.

>
> +       new_regd = reg_copy_regd(regd);
> +       if (IS_ERR(new_regd))
> +               return;
> +
> +       tmp = get_wiphy_regdom(wiphy);
> +       rcu_assign_pointer(wiphy->regd, new_regd);
> +       rcu_free_regdom(tmp);
>
> > Fix this by freeing the regd object in the error handling code and
> > deletion function - mac80211_hwsim_del_radio.
>
> This can't be right - the same would affect all other users of that
> function, no?

The problem occurs in the error handling code of
mac80211_hwsim_new_radio, not wiphy_apply_custom_regulatory. My commit
message may be not very clear.

So I think the code in the mac80211_hwsim_del_radio paired with
mac80211_hwsim_new_radio should be changed correspondingly. If I miss
any problems, please let me know.

I have successfully tested my patch in the syzbot dashboard [1].

[1] https://syzkaller.appspot.com/bug?extid=1638e7c770eef6b6c0d0

>
> Perhaps somewhere we have a case where wiphy->regd is leaked, but than
> that should be fixed more generally in cfg80211?
>
> johannes
>