Samba share doesn’t have write permissions

This might help. I do something similar, but only one share is open to the group's users. Other shares are read-only except for a single maintainer user. The [global] section of my smb.conf is almost identical to yours, except I don't use the force create/directory mode directives (in my case, they'd interfere with the other shares).

Here's the share definition:

[shared stuff]
        comment = blah, blah, etc
        path = /path/to/share
        write list = @sambagroup
        force group = +sambagroup
        read only = yes
        directory mask = 0775
        create mask = 0664
        guest ok = yes
        invalid users = root
        case sensitive = True
        default case = lower
        preserve case = yes
        short preserve case = yes

The important stuff here are these:

• read only = yes -- by default, read only.
• guest ok = yes -- guests can browse.
• write list = @sambagroup -- Authenticated members of sambagroup can write.
• force group = +sambagroup -- The + means that the force only applies to existing members of sambagroup. They're already the only ones who can write. I think, without the +, guest is given sambagroup credentials, which is not wanted (particularly with the write list directive above).
• directory mask = 0775
• create mask = 0664

These do exactly what you want yours to do: "drwxrwxr-x" on directories, "rwxrwxr-x" on files, and newly created files are owned by the user and sambagroup. The maintainers of the other shares get the same permissions as everyone else when working in shared stuff, and permissions & groups are normal when they work in the other shares.

My smb.conf has been working with only minor tweaks through several different versions of Samba, and currently is used with Samba 3.2.5. I never had it running on Ubuntu 8.04, but it ran on Ubuntu 7.04 for a long time before getting migrated to a recent Debian Lenny install.

From http://blog.realcomputerguy.com/2010/12/samba-and-guest-shares-with-security.html?spref=tw

In a nutshell you need:

• A username map file.
• A valid 'nix "guest" user mapped to the Windows guest account ("nobody" in most distros).
• Proper smb.conf configuration.

In this example our username map file is /etc/samba/smbusers. It maps a 'nix user to a Windows user.

In /etc/samba/smbusers (many distros include this file, but with the default commented out):

nobody = guest

In /etc/samba/smb.conf:

[global]
   ...
   security = user
   Map to guest = Bad User
   username map = /etc/samba/smbusers
   ...
-- no 'valid users =' line --

[theshare]
   ...
   guest ok = yes
-- no 'valid users =' line --