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Subject: Re: [PATCH v2] net: rtnetlink: Fix rtnl_dereference may be return
 NULL
To:     Vladimir Oltean <vladimir.oltean@nxp.com>,
        Johannes Berg <johannes@sipsolutions.net>
Cc:     Yajun Deng <yajun.deng@linux.dev>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "ryazanov.s.a@gmail.com" <ryazanov.s.a@gmail.com>,
        "avagin@gmail.com" <avagin@gmail.com>,
        "cong.wang@bytedance.com" <cong.wang@bytedance.com>,
        "roopa@cumulusnetworks.com" <roopa@cumulusnetworks.com>,
        "zhudi21@huawei.com" <zhudi21@huawei.com>,
        "edumazet@google.com" <edumazet@google.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20210708092936.20044-1-yajun.deng@linux.dev>
 <3c160d187382677abe40606a6a88ddac0809c328.camel@sipsolutions.net>
 <20210708111118.kti4jprkz7bus62g@skbuf>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <7e11f410-9a97-c7d8-ee6a-fa776a4d1f0e@gmail.com>
Date:   Thu, 8 Jul 2021 14:26:37 +0200
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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.