netdev - Re: [PATCH 13/13] TProxy: use the interface primary IP address as a default value for --on-ip

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Message-Id: <1253601509.6883.5.camel@bzorp.balabit>
Date:	Tue, 22 Sep 2009 08:38:29 +0200
From:	Balazs Scheidler <bazsi@...abit.hu>
To:	Brian Haley <brian.haley@...com>
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 13/13] TProxy: use the interface primary IP address as
 a default value for --on-ip

On Mon, 2009-09-21 at 14:00 -0400, Brian Haley wrote:
> Balazs Scheidler wrote: 
> >  #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
> > +
> > +static inline const struct in6_addr *
> > +tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr, const struct in6_addr *daddr)
> > +{
> > +	struct inet6_dev *indev;
> > +	struct inet6_ifaddr *ifa;
> > +	struct in6_addr *laddr;
> > +	
> > +        if (!ipv6_addr_any(user_laddr))
> > +                return user_laddr;
> > +	
> > +        laddr = NULL;
> > +        rcu_read_lock();
> > +        indev = __in6_dev_get(skb->dev);
> > +        if (indev && (ifa = indev->addr_list)) {
> > +		laddr = &ifa->addr;
> > +	}
> > +        rcu_read_unlock();
> > +        
> > +        return laddr ? laddr : daddr;
> > +}
> 
> You should call ipv6_dev_get_saddr() to get a source address based on the target
> destination address.

Thanks for this hint, however this is not selecting a source address for
a given destination, rather it selects the address where tproxy is
redirecting the connection in case the user specified no --on-ip
parameter.

e.g. 

ip6tables -A PREROUTING -p tcp --dport 80 -j TPROXY --on-port 50080

This should redirect the connection to the primary IP address of the
incoming interface. In fact I spent 2 hours to figure out how to find
the proper address, and at the end I used the first IP address
configured to the interface, seeing that those addresses are sorted in
'scope' order, e.g. link-local and site-local addresses are at the end
of the list, thus the front should be ok.

Since I'm not that much into IPv6, I'd appreciate some help, is
ipv6_dev_get_saddr(client_ip_address) indeed the best solution here?

-- 
Bazsi

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