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

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Date:	Wed, 19 Dec 2007 10:18:24 -0800
From:	David Stevens <dlstevens@...ibm.com>
To:	Vlad Yasevich <vladislav.yasevich@...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()

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'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.
        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.

 +-DLS

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