netdev - Re: [PATCH] [IPv6]: IPV6_MULTICAST_IF setting is ignored on link-local connect()

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Message-ID: <47696AAA.2010107@hp.com>
Date:	Wed, 19 Dec 2007 14:02:02 -0500
From:	Vlad Yasevich <vladislav.yasevich@...com>
To:	David Stevens <dlstevens@...ibm.com>
Cc:	Brian Haley <brian.haley@...com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	netdev-owner@...r.kernel.org,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH] [IPv6]: IPV6_MULTICAST_IF setting is ignored on link-local
 connect()

David Stevens wrote:
> Vlad Yasevich <vladislav.yasevich@...com> wrote on 12/19/2007 07:20:53 AM:
> 
>> But this still requires either a SO_BINDTODEVICE or sin6_scope_id.  This
>> means the an application can call BINDTODEVICE(eth0), MULTICAST_IF(eth1)
>> issue a connect on a UDP socket an succeed?  Seems wrong to me.
>>
>> Can you check section 6.7 of RFC 3542.
> 
>         No, it requires one of SO_BINDTODEVICE, sin6_scope_id, or 
> IPV6_MULTICAST_IF.
> If you do an SO_BINDTODEVICE(eth0) and then an IPV6_MULTICAST_IF(eth1), 
> the
> IPV6_MULTICAST_IF will fail in setsockopt (EINVAL), because it requires a 
> match
> for bound sockets.

I should have checked that...  so the case I thought off is not possible...


> I'm not sure if SO_BINDTODEVICE resets mcast_oif if you 
> do
> them in the reverse order, but that would be a bug in SO_BINDTODEVICE.

I don't think that would be needed since SO_BINDTODEVICE always wins over
IPV6_MULTICAST_IF, so even if they mismatch, SO_BINDTODEVICE is still used.

>         The precedence order as implemented already is:
> 
>                 SO_BINDTODEVICE is highest and always wins
>                 sin6_scope_id next
>                 IPV6_MULTICAST_IF
> 
> and the existing code has the rule that all link-local addresses require a
> sin6_scope_id. The change (intended) is to relax the sin6_scope_id rule 
> only
> for link-local multicasts that have done either an SO_BINDTODEVICE or
> IPV6_MULTICAST_IF already.
> 

Ok, but I don't think your patch accomplishes that, as Brian pointed out.

-vlad
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