bond: T7571: fix inconsistent MAC address behaviour

After upgrading from VyOS 1.3 to 1.4, there is an inconsistent behavior with
MAC address assignment on bonded interfaces. In VyOS 1.3, bond interfaces used
a hardware MAC address from one of the member interfaces. In 1.4, a synthetic
MAC is used by default - generated by the Linux Kernel.

Oddly, setting mode 802.3ad (which is also the default) temporarily causes the
hardware MAC to be used again - until a reboot, after which the synthetic MAC
returns.

Deleting the mode config again causes the hardware MAC to be used. This
inconsistent behavior has caused issues with MAC-based filtering in networks.

The fix is to retrive the hardware MAC address from the first bond member
interface and use set it explicitly for the bond interface.

2 files changed, 35 insertions, 4 deletions

diff --git a/python/vyos/ifconfig/bond.py b/python/vyos/ifconfig/bond.py
index 8a97243c5..ba31ae0c9 100644
--- a/python/vyos/ifconfig/bond.py
+++ b/python/vyos/ifconfig/bond.py
@@ -485,11 +485,25 @@ class BondIf(Interface):
 
             # Add (enslave) interfaces to bond
             value = dict_search('member.interface', config)
+            is_first = True
             for interface in (value or []):
-                # if we've come here we already verified the interface
-                # does not have an addresses configured so just flush
-                # any remaining ones
-                Interface(interface).flush_addrs()
+                # Physical bond member interface instance
+                tmp_if = Interface(interface)
+                # At this point, we've confirmed that the interface has no
+                # configured addresses, so we can safely flush any remaining ones.
+                tmp_if.flush_addrs()
+
+                # T7571: This behavior changed from Linux Kernel 5.4 (used in VyOS 1.3)
+                # to Kernel 6.6 (starting with VyOS 1.4). Previously, the MAC address of
+                # the first member interface in a bond was adopted as the bond's default MAC.
+                # In newer versions, a synthetic MAC address is assigned instead.
+                #
+                # Re-assign first underlay MAC address to the bond
+                if is_first:
+                    self.set_mac(tmp_if.get_mac())
+                    is_first = False
+
+                # Assign underlaying interface to logical bond
                 self.add_port(interface)
 
         # Add system mac address for 802.3ad - default address is all zero
diff --git a/smoketest/scripts/cli/test_interfaces_bonding.py b/smoketest/scripts/cli/test_interfaces_bonding.py
index 2473bc732..57d245ae6 100755
--- a/smoketest/scripts/cli/test_interfaces_bonding.py
+++ b/smoketest/scripts/cli/test_interfaces_bonding.py
@@ -62,6 +62,23 @@ class BondingInterfaceTest(BasicInterfaceTest.TestCase):
             slaves = read_file(f'/sys/class/net/{interface}/bonding/slaves').split()
             self.assertListEqual(slaves, self._members)
 
+    def test_bonding_keep_mac(self):
+        # T7571: A bond interface should always run from the physical interfaces
+        # MAC address and not a synthetic one.
+        base_mac = Interface(self._members[0]).get_mac()
+
+        # configure member interfaces
+        for interface in self._interfaces:
+            for option in self._options.get(interface, []):
+                self.cli_set(self._base_path + [interface] + option.split())
+
+        self.cli_commit()
+
+        # Verify bond interface MAC address matches the address of it's first member
+        for interface in self._interfaces:
+            mac = Interface(interface).get_mac()
+            self.assertEqual(mac, base_mac)
+
     def test_bonding_remove_member(self):
         # T2515: when removing a bond member the previously enslaved/member
         # interface must be in its former admin-up/down state. Here we ensure