list fdb issue on ubuntu-xenial, kernel 4.15.0, reproduction steps

main.go

package main

import (
	"fmt"
	"os"
	"strconv"
	"syscall"

	"github.com/vishvananda/netlink"
)
// Call as `./listfdb ${link_index}` to see the entries for the link
func main() {
	if len(os.Args) != 2 {
		panic(fmt.Errorf("you must provide a single index number for the interface you are listing fdb rules for"))
	}

	index, err := strconv.Atoi(os.Args[1])
	if err != nil {
		panic(fmt.Errorf("you must provide an valid index number: %s", err))
	}

	neighs, err := netlink.NeighList(index, syscall.AF_BRIDGE)
	if err != nil {
		panic(fmt.Errorf("list fdb failed: %s", err))
	}

	for _, neigh := range neighs {
		fmt.Printf("%#v\n", neigh)
	}
}

Makefile

all: deps build

deps:
	go get github.com/vishvananda/netlink

build:
	GOOS=linux GOARCH=amd64 go build

usage.md

We have discovered an potential regression on ubuntu-xenial when upgrading our environments from ubuntu-trusty. The change appears to manifest somewhere between 4.4.0 and 4.15.0 kernel versions.

When listing bridge fdb entries via syscalls, we do not receive any data.

We have made a binary that makes the same calls, stripped down to only make the affected calls. We are making use of a library to wrap the netlink logic, https://github.com/vishvananda/netlink.

Steps to reproduce:

1. install golang and vagrant
2. place the main.go, Makefile, and Vagrantfile in ${GOPATH}/src/listfdb
3. cd ${GOPATH}/src/listfdb
4. make
5. vagrant up to deploy ubuntu-xenial
6. vagrant ssh
7. uname -a and see that kernel version is 4.4.0
8. bridge fdb and see that there are entries for enp0s3
9. ip link to get the index for enp0s3
10. /vagrant/listfdb ${link_index}, 2 should be the index for the enp0s3 device which has 3 fdb entries by default
11. sudo apt-get install linux-image-4.15.0-33-generic -y
12. exit
13. vagrant reload to restart with 4.15 kernel
14. vagrant ssh
15. uname -a and see that kernel version is 4.15.0
16. bridge fdb and see that there are entries for enp0s3
17. ip link to get the index for enp0s3
18. /vagrant/listfdb ${link_index}, 2 should be the index for the enp0s3 device, note that no results are returned

No entries are listed, despite being able to see them with bridge fdb.

Vagrantfile

# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant.configure("2") do |config|
  config.vm.box = "ubuntu/xenial64"
end