vxlan: update default fdb entries when the lower device changes

vxlan_changelink() only refreshed the default fdb entries when the
remote IP changed, but vxlan_config_apply() also updates
default_dst.remote_ifindex when the lower device changes. A changelink
that only swaps the lower device therefore left the all zeros mac rdst
pointing at the old ifindex:

	ip link add vxlan0 type vxlan id 10 group 239.1.1.1 dev eth0
	ip link set dev vxlan0 type vxlan group 239.1.1.1 dev eth1

vxlan_xmit_one() uses rdst->remote_ifindex as the route oif, so traffic
kept leaving eth0.

VNI filter entries have the same problem, and are worse: their fdb
entries are keyed on the device remote_ifindex even when the vni
carries its own group, but vxlan_vnilist_update_group() only visited
the vnis without one. vxlan_vni_delete_group() later looks an entry up
with the current remote_ifindex, and vxlan_fdb_find_rdst() requires an
exact match, so the lookup failed and the entry survived the delete.
Re-adding the same vni then appended a second rdst, duplicating
transmitted BUM traffic.

Likewise, in vxlan_vni_update_group(), oldrip was only set when newrip
was NULL, so changing an existing VNI's group appended the new rdst
without deleting the old one. Set oldrip to the previous effective
remote IP whenever updating an existing VNI (!create).

Pass the old and new ifindex down to vxlan_update_default_fdb_entry()
so the append targets the new lower device and the delete still matches
the entry created for the old one, and refresh every vni rather than
only those inheriting the device group. If updating the vni list fails
partway through, unwind the already updated fdb entries (still deleting
the new rdst even if re-adding the old one fails) so default_dst and
the fdb entries do not diverge.

Also run vxlan_multicast_leave() and vxlan_multicast_join() when
VXLAN_F_VNIFILTER is set so per-VNI multicast memberships are migrated
even when the device default remote_ip is not multicast, and make
vxlan_multicast_leave_vnigrp() skip the default group and ignore
-EADDRNOTAVAIL when multiple VNIs share a multicast group.

The new ifindex is the one vxlan_config_apply() will commit, which is
the current one when lowerdev is NULL, so that default_dst and the fdb
entries can not diverge.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260922181102.3989489-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions