[Samba] permissions, and maybe a violation of the least surprise principle

L.P.H. van Belle belle at bazuin.nl
Mon Nov 8 22:50:28 UTC 2021

I'll add my view on it. 

Windows can only hold 1 primary group for a user, which is by "Domain Users". 
So,yes, every file holds the "domain users" by default. Lets say GID 10000 is assigned. 

By example. 
We have 2 users, bugger and bogger. 
Bugger is member of "domain users" (GID 10000) and SomeUseless group. (GID 10001)
Bogger is member of "domain users" (GID 10000) and Staff group. (GID 10002) 

>From a windows machine, default rights are set as you see in you output.
Which is all correct as far is see. 

Now, let remove the windows thoughts and just use POSIX. 
You change the default group in windows for both users to its group with GID.

Bogger places a file in the SomeUseless group, so bugger can open it. 
But the file owner now is bogger:staff, bugger isnt a member, 
so to bad he cant open/change it, even if its in the right folder.

This is why, i use in a  "linux with mixed windows" rights setup the windows defaults

So, all "file rights" are "domain users" as group and every member kan open/change it.
The fixes the above rights problem. 

On the "folder part". 
The acl is obeyed from windows and linux users cant enter it.
You use a group as security group to allow access only. 

Only one important part, or you need to change rights later on. 
Set the UID/GIDS first thing in the objectes, before you create folders, or the GID doesnt show/is set.
Still need to look better into that, only so little time currently. 

Use from windows to posix are key "Creator Owner" and "Creator Group" (mainly creator group)

Windows		: Posix
( Creator owner ) : 1770 (through sticky bit) ( normaly chmod 4770)
( creator group ) : chmod 2770
( creator owner and group ) : chmod 3770

https://chmodcommand.com/ has a nice explantion on the i at sticky bit and SetGid.

And you can use getacl and setacl to copy right from windows to linux if you like command prompt.

I hope this helped a bit. 



> -----Oorspronkelijk bericht-----
> Van: samba [mailto:samba-bounces at lists.samba.org] Namens 
> Patrick Goetz via samba
> Verzonden: maandag 8 november 2021 16:38
> Aan: Samba listserv
> Onderwerp: [Samba] permissions, and maybe a violation of the 
> least surprise principle
> I'm down to the last step of my current re-implementation of Samba, 
> namely getting the permissions to work right.
> Here is the share section (+ some general) from my smb.conf file:
>     winbind refresh tickets = Yes
>     vfs objects = acl_xattr
> [share]
>     comment = Share Directory
>     path = /data/share
>     guest ok = no
>     browseable = yes
>     writeable = yes
>     create mask = 0770
>     directory mask = 0770
>     # inherit permissions = yes
>     follow symlinks = yes
> Here are the filesystem permissions on the directory:
> root at data2:/data# ls -ld share
> drwxrws---+ 3 root ea-staff 4096 Nov  6 16:31 share
> root at data2:/data# getfacl share
> # file: share
> # owner: root
> # group: ea-staff
> # flags: -s-
> user::rwx
> group::rwx
> other::---
> default:user::rwx
> default:group::rwx
> default:group:ea-staff:rwx
> default:mask::rwx
> default:other::---
> Notice that the setgid bit is set, with group = (security 
> group) ea-staff
> So, I login on a Windows machine as a member of the ea-staff 
> group, and 
> save a document to the share:
> root at data2:/data/share# ls -l top*
> -rwxrwx---+ 1 dhales domain users 227 Nov  8 09:12 
> top-secret_document_only_staff_should_see.rtf
> Notice that the setgid bit on the parent folder was ignored, and the 
> primary group assignment to the file is Domain Users.  Worse, 
> anyone in 
> Domain Users has access to write this file, although I 
> suppose the lack 
> of other  "x" permission on the parent folder might prevent access.
> I think I read that if you are using Windows ACLs, then the 
> Windows ACLs 
> are checked and honored first; however this seems like a violation of 
> the least surprise principle, since I'm getting user rights  
> elevations 
> (namely Domain Users read/write access) that I don't want.
> These Wiki pages talk about using POSIX and Windows ACLs respectively:
> https://wiki.samba.org/index.php/Setting_up_a_Share_Using_POSIX_ACLs
> https://wiki.samba.org/index.php/Setting_up_a_Share_Using_Windows_ACLs
>   but I can't figure out how to tell the system I would 
> prefer to base 
> ACLs on POSIX rather than Windows ACLs.
> Now, for the "it gets worse" category.  There is an awful lot of 
> misinformation about configuring a Home share, perhaps because the 
> Windows people seem to see this as something you use for backup only. 
> The Home folder Wiki page also suggests that you can use GPO drive 
> mapping for this rather than setting it in the user's 
> Profile. Looking 
> online I see Windows admins stating that one should *not* use 
> GPO file 
> sharing to configure the home directory and that only the 
> user's Profile 
> tab should be used for this.  In any case, Folder Redirection 
> does not 
> appear to work unless you set up a home directory under Profile.
> Otherwise, using /home for this purpose appears to work fine 
> and means 
> the user will have immediate access to all their files when they ssh 
> into the linux fileserver.  However:
> [home]
>     comment = Home Directories
>     path = /data/home
>     guest ok = no
>     browseable = no
>     writeable = yes
>     create mask = 0700
>     directory mask = 0700
>     follow symlinks = yes
> root at data2:/data# ls -ld home
> drwxr-xr-x+ 8 root root 4096 Nov  6 08:27 home
> root at data2:/data# getfacl home
> # file: home
> # owner: root
> # group: root
> user::rwx
> group::r-x
> group:domain\040admins:rwx	#effective:r-x
> mask::r-x
> other::r-x
> /home is a bind mount to /data/home
> The same user logs in on a W10 client and saves a file to his 
> Documents 
> folder:
> root at data2:~# cd /home/dhales/Documents/
> root at data2:/home/dhales/Documents# ls -l my*
> -rwxrwx---+ 1 dhales domain users 222 Nov  8 09:25 
> my-super-secret-file.rtf
> So looks like the create mask is being ignored as well?
> I spend a lot of time adjusting permissions for users.  Most of them 
> can't figure out how to do this themselves, and letting a 
> user loose in 
> the Windows ACL zoo seems like a recipe for disaster anyway.
> Consequently I'd prefer to manage POSIX ACLs via the 
> filesystem and ssh 
> and then have the Windows ACL's approximated from that. Is 
> there a way 
> to do this?
> It also seems to me that the filesystem permissions should *never* be 
> bypassed under any circumstances.
> Final question if anyone in the know has read this far. By 
> default the 
> Windows ACLs are stored in a TDB database on the fileserver's 
> filesystem?  What happens to these permissions if I migrate the data 
> (say, via rsync) to another server? Seems like all the 
> Windows ACLs will 
> be lost unless I transfer the relevant database as well.
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