netdev - Re: [PATCH net-next] net/sched: cls_flower: verify root pointer before dereferncing it

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Date:   Tue, 22 Nov 2016 17:13:07 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Miller <davem@...emloft.net>
Cc:     roid@...lanox.com, netdev@...r.kernel.org, jiri@...lanox.com,
        xiyou.wangcong@...il.com, ogerlitz@...lanox.com,
        cwang@...pensource.com
Subject: Re: [PATCH net-next] net/sched: cls_flower: verify root pointer
 before dereferncing it

Tue, Nov 22, 2016 at 04:37:42PM CET, davem@...emloft.net wrote:
>From: Jiri Pirko <jiri@...nulli.us>
>Date: Tue, 22 Nov 2016 15:48:44 +0100
>
>> Tue, Nov 22, 2016 at 03:25:26PM CET, roid@...lanox.com wrote:
>>>tp->root is being allocated in init() time and kfreed in destroy()
>>>however it is being dereferenced in classify() path.
>>>
>>>We could be in classify() path after destroy() was called and thus 
>>>tp->root is null. Verifying if tp->root is null in classify() path 
>>>is enough because it's being freed with kfree_rcu() and classify() 
>>>path is under rcu_read_lock().
>>>
>>>Fixes: 1e052be69d04 ("net_sched: destroy proto tp when all filters are gone")
>>>Signed-off-by: Roi Dayan <roid@...lanox.com>
>>>Cc: Cong Wang <cwang@...pensource.com>
>> 
>> This is correct
>> 
>> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
>> 
>> The other way to fix this would be to move tp->ops->destroy call to
>> call_rcu phase. That would require bigger changes though. net-next
>> perhaps?
>
>This patch is targetted at net-next as per Subj.

Oh, right, then it should be fixed so the tp->head could be never null