[Samba] smbpasswd stops working post-upgrade

[J Martin Rushton]

Background

I have a network of machines behind an air-gap, therefore upgrades are a 
tedious business normally performed four times per year.  The systems 
run various versions of CentOS and I use the Samba that is distributed 
with CentOS.  Last weekend I updated the 5.7 machines with updates to 18 
April 2016, not the current 5.8.  Those of my users who run Windows 
boxes (Windows 7 Enterprise) map Samba shares on my machines to a drive 
letter on their PCs. In order to do this they need to keep their Samba 
passwords updated. Samba passwords are held in /etc/samba/passdb.tdb.

Problem

Users are reporting that password setting fails. This seems to be a 
fairly solid issue (see below).  Attempting to use "smbpasswd" or 
"smbclient -L YYYY" fails with an error "cli_negprot: SMB signing is 
mandatory and the server doesn't support it" which I've not seen before. 
  smbpasswd the incoreectly states that the password has been changed, 
which it hasn't.

In the transcript below I show the basic command (as seen by the users), 
smbclient used to find the error, versions and finally a -D3 which 
confirms the error.  All work was done on the local machine. XXXX is my 
username YYYY is the machine's simple name. IP addresses have been 
stripped of meaningful information but were consistent. No other network 
problems are apparent.

I'm sure there is a simple tweak required to the smb.conf file (which 
has not been changed), can anyone tell be what to tweak?

Regards,
Martin

Transcript

$ smbpasswd
Old SMB password:
New SMB password:
Retype new SMB password:
machine 127.0.0.1 rejected the negotiate protocol. Error was : 
NT_STATUS_ACCESS_DENIED.
Password changed for user XXXX

$ smbclient -L YYYY
Enter XXXX's password:
cli_negprot: SMB signing is mandatory and the server doesn't support it.
protocol negotiation failed: NT_STATUS_ACCESS_DENIED

$ smbclient -V
Version 3.6.23-12.el5_11
$ uname -a
Linux YYYY 2.6.18-409.el5 #1 SMP Tue Mar 15 18:13:50 EDT 2016 x86_64 
x86_64 x86_64 GNU/Linux

$ smbpasswd -D3
added interface ib0 ip=:::::%ib0 bcast=::ffff:ffff:ffff:ffff%ib0 
netmask=ffff:ffff:ffff:ffff::
added interface eth2 ip=:::::%eth2 bcast=::ffff:ffff:ffff:ffff%eth2 
netmask=ffff:ffff:ffff:ffff::
added interface eth1 ip=:::::fe%eth1 bcast=::ffff:ffff:ffff:ffff%eth1 
netmask=ffff:ffff:ffff:ffff::
added interface ib0 ip=... bcast=...255 netmask=255.255.255.0
added interface eth1 ip=... bcast=...255 netmask=255.255.255.0
added interface eth2 ip=... bcast=...255 netmask=255.255.255.0
Old SMB password:
New SMB password:
Retype new SMB password:
Connecting to 127.0.0.1 at port 445
cli_negprot: SMB signing is mandatory and the server doesn't support it.
machine 127.0.0.1 rejected the negotiate protocol. Error was : 
NT_STATUS_ACCESS_DENIED.
Password changed for user XXXX