samba - Apr 2025 - If a NetBIOS name used within a week is reused, an incorrect owner is returned.

Rowland,

Thank you for the information.

I would like to know when to execute net cache flush. Are there any other
necessary timings besides hostname changes?

We propose an amendment.
I believe that if "net cache flush" is executed when Samba starts with
systemctl, the problem will not occur.

Best regards,
Hiroshi Chiba

-----Original Message-----
From: samba <samba-bounces at lists.samba.org> On Behalf Of Rowland Penny
via samba
Sent: Wednesday, March 12, 2025 6:50 PM
To: samba at lists.samba.org
Cc: Rowland Penny <rpenny at samba.org>
Subject: Re: [Samba] If a NetBIOS name used within a week is reused, an
incorrect owner is returned.

On Wed, 12 Mar 2025 08:19:29 +0000
CHIBA HIROSHI(????) via samba <samba at lists.samba.org> wrote:
> Hi,
> 
>  
> 
> I suspect this behavior comes from a bug. If the behavior is as 
> designed, I'd like to know the background of the design.
> 
> - Bug information
> 
> Version: 4.20.2
> 
> When a shared guest account is enabled and a NetBIOS name that was 
> used within the past week is reassigned, the owner of the guest 
> account becomes Account Unknown (S-1-5-21-*-501), and WRITE returns 
> ACCESS_DENIED. (For example, this issue occurs when the NetBIOS name 
> is changed from "AAAA" to "BBBB" and then back to
"AAAA" again.)
> 
> This behavior seems to be caused by the idmap cache.  
Well, yes, but only because you are failing to do something.

Every time you change the computers hostname, Samba issues a new SID.
Which means that your 'Account Unknown' (which actually is known, it is
'Guest') gets a new SID and when someone connects to Samba, this is
stored in the cache.

The cache is just that, it is a cache, it is not permanent.
The fix for your problem is very easy, every time you change the hostname, clear
the cache with 'net cache flush'.

Can I close your bug report ?

Rowland


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On Tue, 1 Apr 2025 08:41:07 +0000
CHIBA HIROSHI(????) via samba <samba at lists.samba.org> wrote:
> Rowland,
> 
> Thank you for the information.
> 
> I would like to know when to execute net cache flush. Are there any
> other necessary timings besides hostname changes?
> 
> We propose an amendment.
> I believe that if "net cache flush" is executed when Samba starts
> with systemctl, the problem will not occur.
> 
If you are running Samba, there is normally no need to have the
'netbios name' parameter in the smb.conf file, Samba will use the
computers hostname.

So, when you change a computers hostname and restart Samba or reload
the Samba configuration with smbcontrol, you should also run 'net cache
flush', this will remove any cached records.

How you do this is up to you, but because it isn't normal to keep
changing a computers hostname, I suppose running 'net cache flush'
should be part of changing the hostname procedure.

Rowland