netdev - Re: Comment on nf_queue NF

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Date:	Thu, 20 Oct 2011 12:30:15 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jim Sansing <jjsansing@...izon.net>,
	Linux Network Development list <netdev@...r.kernel.org>,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>, Florian Westphal <fw@...len.de>
Subject: Re: Comment on nf_queue NF_STOLEN patch

On Wed, Oct 19, 2011 at 06:10:35AM +0200, Eric Dumazet wrote:
> Le mardi 18 octobre 2011 à 17:34 -0400, Jim Sansing a écrit :
> > Eric Dumazet wrote:
> > > Le mardi 18 octobre 2011 à 15:08 -0400, Jim Sansing a écrit :
> > >   
> > >> I have been working on a kernel module that registers with netfilter,
> > >> and I noticed that a patch was added to nf_queue that changed the
> > >> handling of return code NF_FILTER from 'do nothing' to 'free the skb'. 
> > >> I'm not sure which kernel version this went in, but the date of the
> > >> patch is Feb, 19, 2010.
> > >>
> > >> Everything I have read about netfilter states that it is up to the
> > >> netfilter hook to free the skb if NF_STOLEN is returned.  The
> > >> implications of this patch from a hook programming perspective are:
> > >>
> > >> 1) If the skb is used after the return from the hook, it must be cloned.
> > >> 2) The original skb must not be freed.
> > >>
> > >> I suggest that a comment be added to include/linux/netfilter.h that says
> > >> explicitly the skb will be freed if NF_STOLEN is returned.
> > >>     
> > >
> > > But its not true. Just read the code.
> > >
> > > If you are working on this stuff I recommend you take a look at
> > > commits :
> > >
> > > c6675233f9015d3c0460c8aab53ed9b99d915c64
> > > (netfilter: nf_queue: reject NF_STOLEN verdicts from userspace)
> > >
> > > fad54440438a7c231a6ae347738423cbabc936d9
> > > (netfilter: avoid double free in nf_reinject)
> > >
> > > 64507fdbc29c3a622180378210ecea8659b14e40
> > > (netfilter: nf_queue: fix NF_STOLEN skb leak)
> > >
> > > 3bc38712e3a6e0596ccb6f8299043a826f983701
> > > ([NETFILTER]: nf_queue: handle NF_STOP and unknown verdicts in
> > > nf_reinject)
> > >
> > >   
> > 
> > I see that fad54440438a7c231a6ae347738423cbabc936d9 (netfilter: avoid
> > double free in nf_reinject) returns the switch case for NF_STOLEN back
> > to the original state, but I just downloaded 3.0.4, and the skb is still
> > freed.  So for some versions of the kernel, the situation exists. 
> > Hopefully anyone who runs into it will find this thread.
> > 
> 
> Hopefully netfilter guys (CCed) will sort out the problem and ask stable
> submissions, if not already done. 3.0.4 is quite old :)

Not done yet, sorry. I'll do it asap.
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