netdev - Re: Comment on nf_queue NF

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Message-ID: <1318997435.19139.16.camel@edumazet-laptop>
Date:	Wed, 19 Oct 2011 06:10:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jim Sansing <jjsansing@...izon.net>
Cc:	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

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 :)




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