linux-kernel - Re: [PATCH v2] net: rtnetlink: Fix rtnl

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Date:   Thu, 8 Jul 2021 14:26:37 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>,
        Johannes Berg <johannes@...solutions.net>
Cc:     Yajun Deng <yajun.deng@...ux.dev>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "ryazanov.s.a@...il.com" <ryazanov.s.a@...il.com>,
        "avagin@...il.com" <avagin@...il.com>,
        "cong.wang@...edance.com" <cong.wang@...edance.com>,
        "roopa@...ulusnetworks.com" <roopa@...ulusnetworks.com>,
        "zhudi21@...wei.com" <zhudi21@...wei.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: rtnetlink: Fix rtnl_dereference may be return
 NULL



On 7/8/21 1:11 PM, Vladimir Oltean wrote:
> On Thu, Jul 08, 2021 at 11:43:20AM +0200, Johannes Berg wrote:
>> On Thu, 2021-07-08 at 17:29 +0800, Yajun Deng wrote:
>>> The value 'link' may be NULL in rtnl_unregister(), this leads to
>>> kfree_rcu(NULL, xxx), so add this case handling.
>>>
>>
>> I don't see how. It would require the caller to unregister something
>> they never registered. That would be a bug there, but I don't see that
>> it's very useful to actually be defensive about bugs there.
> 
> Besides, isn't kfree_rcu(NULL) safe anyway?
> 

Only from linux-5.3 I think.
(commit 12edff045bc6dd3ab1565cc02fa4841803c2a633 was not backported to old kernels)

But yes, this patch is not solving any bug, as I suspected.