linux-kernel - Re: [PATCH net,v2] team: fix possible deadlock in team_port_change

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Message-Id: <4E6F3146-AE8D-4C70-A068-A6EE8588F13D@gmail.com>
Date: Sat, 3 Aug 2024 10:36:48 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: edumazet@...gle.com, davem@...emloft.net, kuba@...nel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com,
 syzbot+b668da2bc4cb9670bf58@...kaller.appspotmail.com
Subject: Re: [PATCH net,v2] team: fix possible deadlock in team_port_change_check



> Jiri Pirko wrote:
> 
> Fri, Aug 02, 2024 at 06:25:31PM CEST, aha310510@...il.com wrote:
>> Eric Dumazet wrote:
>>> 
>>>> On Fri, Aug 2, 2024 at 5:00 PM Jeongjun Park <aha310510@...il.com> wrote:
>>>>> 
>> 
>> [..]
>> 
>> @@ -2501,6 +2470,11 @@ int team_nl_options_get_doit(struct sk_buff *skb, struct genl_info *info)
>>    int err;
>>    LIST_HEAD(sel_opt_inst_list);
>> 
>> +    if (!rtnl_is_locked()) {
> 
> This is completely wrong, other thread may hold the lock.
> 
> 
>> +        rtnl_lock();
> 
> NACK! I wrote it in the other thread. Don't take rtnl for get options
> command. It is used for repeated fetch of stats. It's read only. Should
> be converted to RCU.
> 

I see. But, in the current, when called through the following path:
team_nl_send_event_options_get()->
team_nl_send_options_get()->
team_nl_fill_one_option_get()
, it was protected through rtnl. Does this mean that rcu should be 
used instead of rtnl in this case as well?

> Why are you so obsessed by this hypothetical syzcaller bug? Are you
> hitting this in real? If not, please let it go. I will fix it myself
> when I find some spare cycles.

Sorry for the inconvenience, but I don't want to give up on this bug 
so easily since it is a valid bug that we have started analyzing 
anyway and the direction of how to fix it is clear. I hope you 
understand and I will send you a patch that uses rcu instead 
of rtnl soon.

Regards,
Jeongjun Park