Säkra en Samba fil- och skrivarserver

Samba säkerhetsmetoder

Det finns två säkerhetsnivåer tillgängliga i nätverksprotokollet Common Internet Filesystem (CIFS) användarnivå och delningsnivå. Sambas implementering av säkerhetsmetoder tillåter en högre flexibilitet genom att tillhandahålla fyra sätt att implementera säkerhet på användarnivå och ett sätt att implementera delningsnivå:

  • security = user: kräver att klienter anger ett användarnamn och lösenord för att ansluta till en delning. Användarkonton i Samba är separerade från systemkonton, men paketet libpam-smbpass kan synkronisera systemets användare och lösenord med användardatabasen i Samba.

  • security = domain: det här läget tillåter Sambaservern att för Windowsklienterna framstå som en Primary Domain Controller (PDC), Backup Domain Controller (BDC), eller en Domain Member Server (DMS). Se the section called “Samba som en domänkontrollant” för ytterligare information.

  • security = ADS: tillåter Sambaservern att ansluta till en Active Directory domän som en naturlig medlem. Se the section called “Samba-integrering mot Active Directory” för detaljer.

  • security = server: this mode is left over from before Samba could become a member server, and, due to some security issues, should not be used. See the Server Security section of the Samba guide for more details.

  • security = share: tillåter klienter att ansluta till delningar utan att ange användarnamn och lösenord.

The preferred security mode depends on the environment and what the Samba server needs to accomplish.

Security = User

This section will reconfigure the Samba file and print server, from the section called “Samba-filserver” and the Print Server, to require authentication.

Börja med att installera paketet libpam-smbpass som kommer att synkronisera systemets användare med användardatabasen i Samba:

sudo apt-get install libpam-smbpass

Note

If the Samba Server task was chosen during installation, libpam-smbpass is already installed.

Redigera /etc/samba/smb.conf, och i avsnittet [share] ändra:

guest ok = no

Till sist, starta om Samba för att de nya inställningarna skall få effekt:

sudo /etc/init.d/samba restart

Now when connecting to the shared directories or printers, there will be a prompt for a username and password.

Note

To map a network drive to the share, “Reconnect at Logon” should be checked, which will require the username and password to be entered just once, at least until the password changes.

Delningsäkerhet

Det finns flera möjliga alternativ till att utöka säkerheten för varje enskild delad katalog. Genom att använda modellen [share] kommer detta avsnitt att behandla några av de vanligaste konfigurationsalternativen.

Grupper

Groups define a collection of computers or users which have a common level of access to particular network resources and offer a level of granularity in controlling access to such resources. For example, if a group qa is defined and contains the users freda, danika, and rob and a second group support is defined and consists of users danika, jeremy, and vincent, then certain network resources configured to allow access by the qa group will subsequently enable access by freda, danika, and rob, but not jeremy or vincent. Since the user danika belongs to both the qa and support groups, she will be able to access resources configured for access by both groups, whereas all other users will have only access to resources explicitly allowing the group they are part of.

By default Samba looks for the local system groups defined in /etc/group to determine which users belong to which groups. For more information on adding and removing users from groups see Basics.

When defining groups in the Samba configuration file, /etc/samba/smb.conf, the recognized syntax is to preface the group name with an "@" symbol. For example, to define a group named sysadmin in a certain section of the /etc/samba/smb.conf, the group name would be entered as @sysadmin.

Filrättigheter

Filrättigheter definierar tydliga rättigheter en dator eller användare har till en bestämd fil eller uppsättning filer. Sådana rättigheter kan definieras genom att redigera filen /etc/samba/smb.conf och specificera tydliga rättigheter av en definierad fildelning.

For example, for a defined Samba share called share and the need to give read-only permissions to the group of users known as qa, while allowing write permissions to the share by the group called sysadmin and the user named vincent, then the /etc/samba/smb.conf file could be edited to add the following entries under the [share] entry:

read list = @qa
write list = @sysadmin, vincent

Another possible Samba permission is to declare administrative permissions to a particular shared resource. Users having administrative permissions may read, write, or modify any information contained in the resource where the user has been given explicit administrative permissions.

For example, to give the user melissa administrative permissions to the share example, the /etc/samba/smb.conf file would be edited to add the following line under the [share] entry:

admin users = melissa

Efter redigering av /etc/samba/smb.conf, starta om Samba för att ändringarna skall få effekt:

sudo /etc/init.d/samba restart

Note

Om read list och write list skall fungera skall inte Sambas säkerhetsläge not sättas till security = share

Nu när Samba är konfigurerat till att begränsa vilka grupper som har rättighet att komma åt delade kataloger, måste filsystemets rättigheter uppdateras.

Traditional Linux file permissions do not map well to Windows NT Access Control Lists (ACLs). Fortunately POSIX ACLs are available on Kubuntu servers providing more fine grained control. For example, to enable ACLs on /srv an EXT3 filesystem, edit /etc/fstab adding the acl option:

UUID=66bcdd2e-8861-4fb0-b7e4-e61c569fe17d /srv  ext3    noatime,relatime,acl 0 
    1

Återmontera därefter partitionen

sudo mount -v -o remount /srv

Note

The above example assumes /srv on a separate partition. If /srv, or wherever the share path is configured, is part of the / partition, a reboot may be required.

To match the Samba configuration above, the sysadmin group will be given read, write, and execute permissions to /srv/samba/share, the qa group will be given read and execute permissions, and the files will be owned by the username melissa. Enter the following in a terminal:

sudo chown -R melissa /srv/samba/share/
sudo chgrp -R sysadmin /srv/samba/share/
sudo setfacl -R -m g:qa:rx /srv/samba/share/

Note

The setfacl command above gives execute permissions to all files in the /srv/samba/share directory, which may or may not be desirable.

A Windows client will show that the new file permissions are implemented. See the acl and setfacl man pages for more information on POSIX ACLs.

Samba AppArmor Profil

Kubuntu comes with the AppArmor security module, which provides mandatory access controls. The default AppArmor profile for Samba will need to be adapted to the proper configuration. For more details on using AppArmor, please refer to the wiki

There are default AppArmor profiles for /usr/sbin/smbd and /usr/sbin/nmbd, the Samba daemon binaries, as part of the apparmor-profiles packages. To install the package, from a terminal prompt, enter:

sudo apt-get install apparmor-profiles

Note

Det här paketet innehåller profiler för flera andra binärer.

By default the profiles for smbd and nmbd are in complain mode, allowing Samba to work without modifying the profile, and only logging errors. To place the smbd profile into enforce mode, and have Samba work as expected, the profile will need to be modified to reflect any directories that are shared.

Edit /etc/apparmor.d/usr.sbin.smbd, adding information for [share] from the file server example:

/srv/samba/share/ r,
/srv/samba/share/** rwkix,

Placera nu profilen i enforce och ladda om den:

sudo aa-enforce /usr/sbin/smbd
cat /etc/apparmor.d/usr.sbin.smbd | sudo apparmor_parser -r

It is now possible to read, write, and execute files in the shared directory as normal, and the smbd binary will have access to only the configured files and directories. Be sure to add entries for each directory that Samba is configured to share. Any errors will be logged to /var/log/syslog.

Resurser