[Pkg-samba-maint] Bug#873073: samba: smbd starts before interface is ready, listening only on localhost when "bind to interfaces only = yes"

[Timo Sigurdsson]

Package: samba
Version: 2:4.5.8+dfsg-2+deb9u1+b1
Severity: normal

Dear Maintainer,

I noticed that adding the smb.conf options
  interfaces = lo enp2s0
  bind to interfaces only = yes
renders samba unusable.

What happens is that smbd is being started too early (before my ethernet 
interface enp2s0 is ready), so it only listens on the loopback device but
not enp2s0. Thus, smbd won't respond to any connections by clients. My
ethernet interface is configured via DHCP.

The issue is easily resolved by restarting smbd after the system is up and
running, which also shows the configuration itself is ok.

So, as a temporary workaround to the issue I added the following job to my
root crontab to restart smbd after every reboot with a delay of 15 seconds:
  @reboot sleep 15 && systemctl -q restart smbd.service
With this samba works fine and binds to the loopback address as well as the
address of my enp2s0 interface.

This is, however, neither a real nor neat solution to the issue, of course.

First of all, I would have expected the dhclient-scripts to take care of
reloading smbd when the interface is ready. And while I do see in the logs
that smbd is being reloaded via dhclient-scripts, this also happens too early
apparently. Secondly, I'm surprised to see that the systemd unit file for
smbd is set to start after network.target but not network-online.target.
The nmbd unit is set to wait for the latter. In practice, this won't make
much of a difference in most scenarios since smbd waits for nmbd, but there
are setups where you don't need nmbd (see #429429) so having smbd wait for
network-target.online would actually make more sense to me. (Note: On this
installation I do have nmbd running as well.)

So, I tried the following approaches to resolve this issue -  without any
luck:

1) Moving /etc/dhcp/dhclient-enter-hooks.d/samba to the exit-hooks directory,
   as I hoped that would trigger the reload action later. It didn't work.
   It seems the dhclient-exit-hooks are called to early as well and smbd
   can't bind to enp2s0 just yet.

2) I had added "network-online.target" to the "After=" list and into "Wants="
   in the systemd unit file. It didn't help either.
   
Please note that I have encountered this issue on two seperate machines and
even two architectures (amd64 and armhf). In both cases DHCP is used to
configure the network interfaces. Both machines run fresh installs of Debian
Stretch and were not upgraded from Jessie.

Regards,

Timo

-- System Information:
Debian Release: 9.1
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-3-amd64 (SMP w/2 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages samba depends on:
ii  adduser              3.115
ii  dpkg                 1.18.24
ii  init-system-helpers  1.48
ii  libbsd0              0.8.3-1
ii  libc6                2.24-11+deb9u1
ii  libldb1              2:1.1.27-1+b1
ii  libpam-modules       1.1.8-3.6
ii  libpam-runtime       1.1.8-3.6
ii  libpopt0             1.16-10+b2
ii  libpython2.7         2.7.13-2
ii  libtalloc2           2.1.8-1
ii  libtdb1              1.3.11-2
ii  libtevent0           0.9.31-1
ii  libwbclient0         2:4.5.8+dfsg-2+deb9u1+b1
ii  lsb-base             9.20161125
ii  procps               2:3.3.12-3
ii  python               2.7.13-2
ii  python-dnspython     1.15.0-1
ii  python-samba         2:4.5.8+dfsg-2+deb9u1+b1
ii  python2.7            2.7.13-2
ii  samba-common         2:4.5.8+dfsg-2+deb9u1
ii  samba-common-bin     2:4.5.8+dfsg-2+deb9u1+b1
ii  samba-libs           2:4.5.8+dfsg-2+deb9u1+b1
ii  tdb-tools            1.3.11-2
ii  update-inetd         4.44

Versions of packages samba recommends:
ii  attr                1:2.4.47-2+b2
ii  logrotate           3.11.0-0.1
ii  samba-dsdb-modules  2:4.5.8+dfsg-2+deb9u1+b1
ii  samba-vfs-modules   2:4.5.8+dfsg-2+deb9u1+b1

Versions of packages samba suggests:
pn  bind9          <none>
pn  bind9utils     <none>
pn  ctdb           <none>
pn  ldb-tools      <none>
pn  ntp | chrony   <none>
pn  smbldap-tools  <none>
ii  ufw            0.35-4
pn  winbind        <none>