netdev - Re:Re: [PATCH net] driver: vrf: Fix one possible use-after-free issue

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Date:   Tue, 9 May 2017 17:41:57 +0800 (CST)
From:   "Gao Feng" <gfree.wind@....163.com>
To:     "Florian Westphal" <fw@...len.de>
Cc:     dsa@...ulusnetworks.com, shm@...ulusnetworks.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        "gfree.wind@...mail.com" <gfree.wind@...mail.com>
Subject: Re:Re: [PATCH net] driver: vrf: Fix one possible use-after-free
 issue

At 2017-05-09 17:21:02, "Florian Westphal" <fw@...len.de> wrote:
>gfree.wind@....163.com <gfree.wind@....163.com> wrote:
>> When one netfilter rule or hook stoles the skb and return NF_STOLEN,
>> it means the skb is taken by the rule, and other modules should not
>> touch this skb ever. Maybe the skb is queued or freed directly by the
>> rule.
>> 
>> Now uses the nf_hook instead of NF_HOOK to get the result of netfilter,
>> and check the return value of nf_hook. Only when its value equals 1, it
>> means the skb could go ahead. Or reset the skb as NULL.
>> 
>> BTW, because vrf_rcv_finish is empty function, so needn't invoke it
>> even though nf_hook returns 1.
>
>Thats a bug then.
>
>The okfn (if called) takes ownership of skb and must free it eventually.
>Otherwise userspace queueing leaks skb on reinjection.
>
>(see nf_reinject() and its use of okfn()).

Thanks, I only thought about the stolen case like synproxy which would free the skb directly,
and forget the userspace could reinject the skb.

I would update the patch.

Best Regards
Feng