[PATCH network v2] fix #6255: snat: update changed bridge IPs in SDN config

[Lukas Sichert <l.sichert@proxmox.com>]

When changing the IP address of an SNAT bridge in a Simple or EVPN zone,
the generated SDN configuration retains the old address. The address is
currently obtained through 'ip route get', which still reports the
previous state before 'ifreload' runs.

Parse the incoming '/etc/network/interfaces' and look up the interface
used by 'ip route'. If it still has a gateway and a changed IP address,
update the SNAT address in the generated SDN configuration and log the
change to the journal.

Signed-off-by: Lukas Sichert <l.sichert@proxmox.com>
Link: https://bugzilla.proxmox.com/show_bug.cgi?id=6255
---

Notes:
    changes from v2 to v3: (thanks @Stefan):
    - simplified the address lookup by selecting the address and gateway key
      based on the IP version
    - add address and gateway check before canonicalzing as canonical_ip
      creates default ip from undef input
    - simplified the fallback logic for changed SNAT bridge addresses
    
    changes from v1 to v2: (thanks @Gabriel, @Stefan)
    - add handling for IPV6 addresses
    - remove warnings for missing ip/gateway, as they might trigger
      in some legitimate scenarios
    - add canonical formatting for IPv4 and IPV6
    - execute make tidy
    - small restructuring of if clauses for earlier exit
    - fix typos

 src/PVE/Network/SDN/Zones/EvpnPlugin.pm   |  5 ++--
 src/PVE/Network/SDN/Zones/Plugin.pm       | 32 +++++++++++++++++++++--
 src/PVE/Network/SDN/Zones/SimplePlugin.pm |  5 ++--
 3 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/src/PVE/Network/SDN/Zones/EvpnPlugin.pm b/src/PVE/Network/SDN/Zones/EvpnPlugin.pm
index dfbd7e9..37bc9f5 100644
--- a/src/PVE/Network/SDN/Zones/EvpnPlugin.pm
+++ b/src/PVE/Network/SDN/Zones/EvpnPlugin.pm
@@ -269,8 +269,9 @@ sub generate_sdn_config {
         if ($subnet->{snat}) {
 
             #find outgoing interface
-            my ($outip, $outiface) =
-                PVE::Network::SDN::Zones::Plugin::get_local_route_ip($checkrouteip);
+            my ($outip, $outiface) = PVE::Network::SDN::Zones::Plugin::get_local_route_ip(
+                $checkrouteip, $interfaces_config,
+            );
             if ($outip && $outiface && $is_evpn_gateway) {
                 #use snat, faster than masquerade
                 push @iface_config,
diff --git a/src/PVE/Network/SDN/Zones/Plugin.pm b/src/PVE/Network/SDN/Zones/Plugin.pm
index 74a3384..5493ec1 100644
--- a/src/PVE/Network/SDN/Zones/Plugin.pm
+++ b/src/PVE/Network/SDN/Zones/Plugin.pm
@@ -9,6 +9,7 @@ use PVE::IPRoute2;
 use PVE::JSONSchema;
 use PVE::Cluster;
 use PVE::Network;
+use PVE::SafeSyslog;
 
 use PVE::JSONSchema qw(get_standard_option);
 use base qw(PVE::SectionConfig);
@@ -306,7 +307,7 @@ sub get_iface_addresses {
 }
 
 sub get_local_route_ip {
-    my ($targetip) = @_;
+    my ($targetip, $interfaces_config) = @_;
 
     my $ip = undef;
     my $interface = undef;
@@ -323,6 +324,33 @@ sub get_local_route_ip {
 
         },
     );
+    my $ipversion = Net::IP::ip_is_ipv6($targetip) ? 6 : 4;
+    my $interface_in_config = $interfaces_config->{ifaces}->{$interface};
+
+    my $address_key = ($ipversion == 6) ? 'address6' : 'address';
+    my $gateway_key = ($ipversion == 6) ? 'gateway6' : 'gateway';
+
+    # check if ip address and gateway exist in config before normalizing, because
+    # canonical_ip will return 0.0.0.0, if called with undef
+    my $ip_address_in_config;
+    if ($ip_address_in_config = $interface_in_config->{$address_key}) {
+        $ip_address_in_config = PVE::Network::canonical_ip($ip_address_in_config);
+    }
+
+    my $gateway_in_config;
+    if ($gateway_in_config = $interface_in_config->{$gateway_key}) {
+        $gateway_in_config = PVE::Network::canonical_ip($gateway_in_config);
+    }
+
+    # if the device currently used for routing still has a valid description in /network/interfaces/, use it
+    if ($interface_in_config && $gateway_in_config && $ip_address_in_config ne $ip) {
+        syslog(
+            "warning",
+            "ip address $ip_address_in_config of interface $interface in /etc/network/interfaces does not match with its ip address reported by ip route: $ip, switching to $ip_address_in_config for SNAT",
+        );
+        return ($ip_address_in_config, $interface);
+    }
+
     return ($ip, $interface);
 }
 
@@ -368,7 +396,7 @@ sub find_local_ip_interface_peers {
 
     #if peer is remote, find source with ip route
     foreach my $address (@{$peers}) {
-        my ($ip, $interface) = get_local_route_ip($address);
+        my ($ip, $interface) = get_local_route_ip($address, $network_config);
         return ($ip, $interface);
     }
 }
diff --git a/src/PVE/Network/SDN/Zones/SimplePlugin.pm b/src/PVE/Network/SDN/Zones/SimplePlugin.pm
index f5cd18e..ac772e7 100644
--- a/src/PVE/Network/SDN/Zones/SimplePlugin.pm
+++ b/src/PVE/Network/SDN/Zones/SimplePlugin.pm
@@ -112,8 +112,9 @@ sub generate_sdn_config {
         push @iface_config, "up ip route add $cidr dev $vnetid" if $mask == 32 && $ipversion == 4;
         if ($subnet->{snat}) {
             #find outgoing interface
-            my ($outip, $outiface) =
-                PVE::Network::SDN::Zones::Plugin::get_local_route_ip($checkrouteip);
+            my ($outip, $outiface) = PVE::Network::SDN::Zones::Plugin::get_local_route_ip(
+                $checkrouteip, $interfaces_config,
+            );
             if ($outip && $outiface) {
                 #use snat, faster than masquerade
                 push @iface_config,
-- 
2.47.3