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H A Din_mcast.cdiff 206452 Sat Apr 10 10:08:09 MDT 2010 bms Fix a few issues related to the legacy 4.4 BSD multicast APIs.

IPv4 addresses can and do change during normal operation. Testing by
pfSense developers exposed an issue where OpenOSPFD was using the IPv4
address to leave the OSPF link-scope multicast groups on a dynamic
OpenVPN tun interface, rather than using RFC 3678 with the interface
index, which won't be raced when the interface's addresses change.

In inp_join_group():
If we are already a member of an ASM group, and IP_ADD_MEMBERSHIP or
MCAST_JOIN_GROUP ioctls are re-issued, return EADDRINUSE as per the
legacy 4.4BSD multicast API. This bends RFC 3678 slightly, but does
not violate POLA for apps using the old API.
It also stops us falling through to kicking IGMP state transactions
in what is otherwise a no-op case.
[This has already been dealt with in HEAD, but make it explicit before
we MFC the change to 8.]

In inp_leave_group():
Fix a bogus conditional.
Move the ifp null check to ioctls MCAST_LEAVE* in the switch..case
where it actually belongs.
If an interface was specified, by primary IPv4 address, for ioctl
IP_DROP_MEMBERSHIP or MCAST_LEAVE_GROUP (an ASM full leave operation),
then and only then should we look up the ifp from the IPv4 address in
mreqs.imr_interface.
If not, we fall through to imo_match_group() as before, but only in
the IP_DROP_MEMBERSHIP case.

With these changes, the legacy 4.4BSD multicast API idempotence should
be mostly preserved in the SSM enabled IPv4 stack.

Found by: ermal (with pfSense)
MFC after: 3 days

Completed in 70 milliseconds