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

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Date:   Thu, 08 Jul 2021 11:43:20 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Yajun Deng <yajun.deng@...ux.dev>, davem@...emloft.net,
        kuba@...nel.org, ryazanov.s.a@...il.com, avagin@...il.com,
        vladimir.oltean@....com, cong.wang@...edance.com,
        roopa@...ulusnetworks.com, zhudi21@...wei.com, edumazet@...gle.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: rtnetlink: Fix rtnl_dereference may be return
 NULL

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.

>  And modify the return
> value to 'void' in rtnl_unregister(). there is no case using it.
> 
> Fixes: addf9b90de22 (net: rtnetlink: use rcu to free rtnl message handlers)
> Fixes: 51e13685bd93 (rtnetlink: RCU-annotate both dimensions of rtnl_msg_handlers)

It certainly fixes nothing in those patches.

johannes