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[th/local-route-sync] core: don't add dependent local route for addresses

Thomas Haller requested to merge th/local-route-sync into master

When adding an IPv4 address, kernel automatically adds a local route. This is done by fib_add_ifaddr(). Note that if the address is IFA_F_SECONDARY, then the "src" is the primary address. That means, with

  nmcli connection add con-name t type ethernet ifname t autoconnect no \
     ipv4.method manual ipv6.method disabled \
     ipv4.addresses '192.168.77.10/24, 192.168.77.11/24'

we get two addresses:

  "local 192.168.77.10 dev t table local proto kernel scope host src 192.168.77.10"
  "local 192.168.77.11 dev t table local proto kernel scope host src 192.168.77.10"

Our code would only generate instead:

  "local 192.168.77.10 dev t table local proto kernel scope host src 192.168.77.10"
  "local 192.168.77.11 dev t table local proto kernel scope host src 192.168.77.11"

Afterwards, this artificial route can be leaked:

#!/bin/bash

set -vx

nmcli connection delete t || :
ip link delete t || :

ip link add name t type veth peer t-veth

nmcli connection add con-name t type ethernet ifname t autoconnect no ipv4.method manual ipv4.addresses '192.168.77.10/24, 192.168.77.11/24' ipv6.method disabled

nmcli connection up t

ip route show table all dev t | grep --color '^\|192.168.77.11'

sleep 1

nmcli device modify t -ipv4.addresses 192.168.77.11/24

ip route show table all dev t | grep --color '^\|192.168.77.11'

ip route show table all dev t | grep -q 192.168.77.11 && echo "the local route 192.168.77.11 is still there, because NM adds a local route with wrong pref-src"

This was introduced by commit 3e5fc04d ('core: add dependent local routes configured by kernel'), but it's unclear to me why we really need this. Drop it again and effectively revert 3e5fc04d.

https://bugzilla.redhat.com/show_bug.cgi?id=1907661

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