netdev - Re: [net-next PATCH v1 3/3] net: sched: do not use tcf_proto 'tp' argument from call

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Date:	Mon, 6 Oct 2014 10:05:06 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [net-next PATCH v1 3/3] net: sched: do not use tcf_proto 'tp'
 argument from call_rcu

On Sun, Oct 5, 2014 at 9:28 PM, John Fastabend <john.fastabend@...il.com> wrote:
> Using the tcf_proto pointer 'tp' from inside the classifiers callback
> is not valid because it may have been cleaned up by another call_rcu
> occuring on another CPU.
>
> 'tp' is currently being used by tcf_unbind_filter() in this patch we
> move instances of tcf_unbind_filter outside of the call_rcu() context.
> This is safe to do because any running schedulers will either read the
> valid class field or it will be zeroed.
>
> And all schedulers today when the class is 0 do a lookup using the
> same call used by the tcf_exts_bind(). So even if we have a running
> classifier hit the null class pointer it will do a lookup and get
> to the same result. This is particularly fragile at the moment because
> the only way to verify this is to audit the schedulers call sites.
>
> Reported-by: Cong Wang <xiyou.wangconf@...il.com>
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>

Acked-by: Cong Wang <cwang@...pensource.com>
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