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

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Message-ID: <20170509092102.GB16263@breakpoint.cc>
Date:   Tue, 9 May 2017 11:21:02 +0200
From:   Florian Westphal <fw@...len.de>
To:     gfree.wind@....163.com
Cc:     dsa@...ulusnetworks.com, shm@...ulusnetworks.com,
        davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net] driver: vrf: Fix one possible use-after-free issue

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()).