Managing Usershares properly, under SAMBA (meaning, under the SMB emulation given by Linux).

Just to encapsulate the subject of this posting… ‘SMB’ is a file-sharing protocol which is really Windows-owned. Granted, ‘SMB1‘ cannot be fully Windows-owned, but, on the assumption that a ‘SAMBA’ server is being used to emulate ‘SMB2′ and ‘SMB3′ (under Linux), there are many ways in which the (root-owned) configuration file at ‘/etc/samba/smb.conf’ could be faulty, and could result in weird error messages. The fixes which are highlighted in this posting worked for me, but my reader could be suffering from mistakes of an entirely different nature. I am posting this, in case the reader happens to be suffering from the same configuration mistakes which I was.

Also, my configuration issues arose partially, because I’ve switched this configuration file from a configuration in which Home Directories are being shared out in their entirety, to a configuration in which individual users can decide to share out specific folders they own. This system is one of ‘Usershares’.

What I was eventually doing was, to give the command ‘net usershare add <Share-Name> "<Path-Name>" "<Comment>" Host\\user1:f,Host\\user2:f‘. The comma and the absence of spaces in the Access Control List are important. I was getting the error-message stating, that these user-names, part of the ACL, could not be converted into SIDs. What I found was, that I had the following error in my ‘smb.conf’ file:

 


   map to guest = bad user
   guest account = nobody

(...)

   server max protocol = SMB3
   server min protocol = SMB2


 

Amazingly, the error message went away, if I changed that last detail to:

 


   client max protocol = SMB3
   server min protocol = SMB2

 

But, there is more to be known about my configuration:

 


usershare allow guests = no
usershare max shares = 10
usershare owner only = false
usershare path = /var/lib/samba/usershares

 

What this last set of parameters actually requests is, that individual users should not be able to grant Guest Access – unauthenticated access – to any of their folders, but potentially, to grant access which is authenticated by another SAMBA username, with their enabled password, as existing on the server.

Again to my amazement, I found that, if the server is massaged adequately, it will implement the settings exactly as requested. But it will do so with a crucial limitation. Locally on the server, the non-owner username must already have access to the exact folder named in the usershare. What level of access that username has (to the named folder itself), will cap whatever level of control is granted by way of a SAMBA client.

This observation could also be rephrased as follows: Even though (Linux) SAMBA has an impressive-looking feature in “Usershares”, while that creates rule-files in the folder ‘/var/lib/samba/usershares’, which even possess Access-Control Lists, those ACLs finally disappoint, in NOT guaranteeing what the behaviour of the SAMBA server will be, once a usershare has finally granted access (to a folder, for the client). (:2)

Usually, in order to grant such access locally on the server, some strategy with group memberships and permission-bits gets used. Which exact arrangement of groups and permission-bits gets used, is not set in stone. Any arrangement will work that grants full access. But, because it’s usually unwieldy for users to set up such local sharing of their folders, they are also not likely to succeed – without compromising their security completely – unless they also have the help of someone with root access. Therefore, the ability to give this feature to users in user-space, is theoretical at best. (:1)  And, if the user wants to activate this extension, he or she must use the CLI, and cannot count on the GUI within ‘Dolphin’ to do so. But, the final command given via the CLI can be given as user.

By default,  declaring a usershare ‘the easy way, via the GUI’, remains owner-only.


 

There is one more caveat to mention. According to my recent experiences, if ‘Dolphin’ is being used as the SAMBA client, and if it’s to authenticate with the server, using any username other than the current username on the local client-computer, then the credentials need to be specified under ‘System settings -> Network -> Connectivity’ (where the Plasma 5.8 Desktop manager puts them). If there is a set of credentials there, they will not be stored encrypted, but only stored with casual obfuscation, and Dolphin will use them. If the user wants the credentials to be stored in the ‘kwallet’ (and thus encrypted), he needs to make his username, to log into the server with, identical to his username on the local client. Otherwise, illogical error messages will appear again, this time, from the Dolphin file-browser not being consistent, in whether to try to authenticate at all. And, if an attempt is made to access the share without authenticating, then Dolphin generates an illogical error message, which can be paraphrased as a ‘File Exists’ error message.

With enough effort, and, sacrificing some security, it can all be done.

(Updated 3/29/2021, 15h10… )

Continue reading Managing Usershares properly, under SAMBA (meaning, under the SMB emulation given by Linux).

File-Sharing under Linux, using Usershares – the Modernistic Way.

One concept which readers may already know, is that under Linux, we can set up a Samba-server, which makes the sharing-out of our home directories possible, and that if we fiddle with the ‘smb.conf’ configuration file thoroughly enough, it becomes possible to browse the available shares on a LAN, in a way semi-compatible with Windows computers that also reside on the same LAN.

Traditionally, this has always been a bit of a PITA, especially since the ‘/etc/samba/smb.conf’ configuration files have been finicky, and since each share practically needs to be configured individually, by a person with the ‘root’ password.

Well an alternative exists under Linux as well, which is the concept of ‘Usershares’. With this concept, each user who belongs to a specific group has the privilege, of designating a folder within his desktop manager, to share out, pointing-and-clicking. This is closer in ease-of-use, to how the process works under Windows. But, it needs to be set up correctly once, by the sysadmin, before it will work as often as simple users wish it to work.

I think that an existing Web-article on the subject, already explains well, what the settings in the ‘smb.conf’ file need to be, as well as what directories need to exist, in order for usershares to work. Except that the article I just linked to, refers to Fedora and SELinux systems and their norms. I happen to be based on Debian and KDE 4 or Plasma 5. And so I have a few observations to add:

Firstly, the following packages should be installed, under Debian also:

 


#apt-get install kdenetwork samba

 

Secondly, ‘/etc/samba/smb.conf’ needs to be edited like so:

 

screenshot_20180324_205625

 

Under Debian, the directory ‘/var/lib/samba/usershares’ already exists, If the relevant packages are installed. And its permission-bits have already been set as they should be set. Only, the feature is not configured in ‘smb.conf’ by default. And, the additional package named ‘kdenetwork-filesharing’ needs to be installed, in order for the tab to appear in Dolphin’s File-Properties box, that enables sharing from the GUI. Aside from that, enabled users need to be added to the ‘sambashare’ group, after which this membership only goes into effect, once the user in question has started a new session…

(Info Corrected 03/25/2018, 17h10,

Updated again 03/28/2018 … )

Continue reading File-Sharing under Linux, using Usershares – the Modernistic Way.