Poojan's Tech Blog

My latest security schemees that I’ve mapped the Samba guest user to a new user “samba_guest”. I’ve made nobody the owner of public shares. I’ve removed the allow settings for the “nobody” user. I then enable everyone to read:

owner@:————–:——:deny
group@:-w-p———-:——:deny
group@:r-x———–:——:allow
everyone@:—-Dd-A-W-Co-:f—–:deny
everyone@:rwxp–a-R-c–s:-d—-:allow


Note that I’ve set up Samba with the ZFS ACL module. For each share, I’ve added the following entries:


vfs objects = zfsacl
nfs4:mode = special
nfs4:acedup = merge
nfs4:chown = yes


I’ve installed a FreeBSD system using gmirror onto a couple of USB drives. I’ve noticed that there’s a considerable lag when I’m doing certain things (running top for example). I’ve narrowed it down to the /tmp and /var file systems. These two file systems get written to often during normal system operation. I’ve recently aleviated this problem using the md facility–which creates a ramdisk.

Since I’m using USB drives for the root (a d the default /tmp and /var), the write latency is higher than read latency. In addition, gmirror exacerbates this tendency.

Update 2011-03-05 (again)

I now have everything contained within /etc/fstab. /tmp exists in memory (md), /var sits on USB, but a few key subdirectories of [/var] exist in memory as well. My /etc/fstab looks like so:

I’ve commented out all the md-related lines in /etc/rc.conf:

Update 2011-03-05

I’ve since this concluded that most of FreeBSD expects certain things within /var to be persistent across boots (namely /var/db). I’ve since put /var back on my USB drives. However, I’ve followed the advice given here: http://www.cabstand.com/usbflash.html#flash_parts and set noatime on my mounts, so that a read access doesn’t require a write. The system generally seems pretty responsive. My fstab now looks like:

I may go forward and make /var/run and /var/log md files as advised in the above link.

Update 2011-02-14

The below procedure had problems with samba. Unfortunately, samba puts a bunch of stuff in /var/log/samba, /var/run/samba and /var/db/samba. Not sure why you’d want another level of indirection below each of these directories. Unfortunately, this behavior is hard-coded into the samba ports Makefile. To get around it, you can either follow the original instructions using fstab below and modify /usr/local/etc/rc.d/samba with:

[cce_bash]
samba_start_precmd() {
mkdir -p /var/log/samba /var/run/samba /var/run/samba
# XXX: Never delete winbindd_idmap, winbindd_cache and group_mapping
[/cce_bash]

Which ensures that the directories are created before samba is started. Or, you can use the method with rc.conf. Either way, you’re editing two files: A)/usr/local/etc/rc.d/samba and /etc/fstab; or B)/etc/rc.conf and /etc/fstab.

Original Instructions (using fstab)

So, moving the /tmp and /var file systems into RAM makes things go much faster. It’s pretty easy to do so. You only have to edit /etc/fstab.

Here’s my /etc/fstab:

You can see that I labeled two new USB drives (4G each) to contain swap. I called them swap0 and swap1. The memory-based file system will use swap as a backing store (it’ll spill over into the swap space if the system runs low on RAM).

Alternative method using /etc/rc.conf and /etc/fstab

Edit /etc/rc.conf to look like so:

[cce_bash]
mdconfig_md0=”-t swap -s 32m”
mdconfig_md1=”-t swap -s 512m”
mdconfig_md1_cmd=”mkdir -p /var/log/samba /var/db/samba /var/run/samba”
[/cce_bash]

This instructs rc.conf (really mdconfig and mdconfig2 startup scripts) to create a md0 of size 32 MB and md1 of size 512MB. It also runs a command to create the directories samba expects (but does not create).

Unfortunately, you also have to add entries to fstab to mount the md devices as file systems:

Fixing portsnap

One problem with the above is that portsnap tends to dump things to /var/db/portsnap. Since /var is now in a memory file system, it’ll get cleared on each reboot. Instead, I now store portsnap fetches in /usr/local/portsnap. (This is the default if you install portsnap from the ports collection, but the base install of FreeBSD includes a portsnap which stores it in /var/db/portsnap.)

To make this change, I edited /etc/portsnap.conf:

[cc_bash]
# Default directory where compressed snapshots are stored.
# WORKDIR=/var/db/portsnap
WORKDIR=/usr/local/portsnap
[/cc_bash]

This time, I’m going to to try using FreeBSD’s support for NFS ACL’s, using http://forums.freebsd.org/showthread.php?t=17627 as a reference:


server# zfs set aclmode=passthrough tank/Users
server# zfs set aclinherit=passthrough tank/Users


I created ZFS filesystems within tank/Users/Public like so:

[cce_bash]
server% cat add_pub.sh
#!/bin/sh

u=”$1″
zfs create tank/Users/$u
chown nobody:nogroup /tank/Users/$u
for d in “Documents” “Music” “Videos” “Pictures”; do
zfs create tank/Users/$u/$d
zfs set aclmode=passthrough tank/Users/$u/$d
zfs set aclinherit=passthrough tank/Users/$u/$d
chown nobody:nogroup “/tank/Users/$u/$d”
done
zfs set compression=gzip tank/Users/$u/Documents
[/cce_bash]

Note the zfs set aclmode and zfs set aclinherit lines. These prevent a calculation of effective permissions based on the umask which pretty much renders the ACL commands useless (documented here). Now, to let myself read/write/etc tank/Users/Public:


server# setfacl -m "user:Poojan:rwxp:fd:allow" /tank/Users/Public


Or, more generally:

[cce_bash]
server% cat prm_pub.sh
#!/bin/sh

u=”$1″
for d in “Documents” “Music” “Videos” “Pictures”; do
setfacl -m “user:${u}:rwxp:fd:allow” “/tank/Users/Public/$d”
done
[/cce_bash]

I’ll admit that I have no idea how this works, but it looks like it does.

For samba, here’s my smb.conf:
[cce_ini]
# This is the main Samba configuration file. You should read the
# smb.conf(5) manual page in order to understand the options listed
# here. Samba has a huge number of configurable options (perhaps too
# many!) most of which are not shown in this example
#
# For a step to step guide on installing, configuring and using samba,
# read the Samba-HOWTO-Collection. This may be obtained from:
# http://www.samba.org/samba/docs/Samba-HOWTO-Collection.pdf
#
# Many working examples of smb.conf files can be found in the
# Samba-Guide which is generated daily and can be downloaded from:
# http://www.samba.org/samba/docs/Samba-Guide.pdf
#
# Any line which starts with a ; (semi-colon) or a # (hash)
# is a comment and is ignored. In this example we will use a #
# for commentry and a ; for parts of the config file that you
# may wish to enable
#
# NOTE: Whenever you modify this file you should run the command “testparm”
# to check that you have not made any basic syntactic errors.
#
#======================= Global Settings =====================================
[global]

# workgroup = NT-Domain-Name or Workgroup-Name, eg: MIDEARTH
workgroup = MYGROUP

# server string is the equivalent of the NT Description field
server string = Samba Server

# Security mode. Defines in which mode Samba will operate. Possible
# values are share, user, server, domain and ads. Most people will want
# user level security. See the Samba-HOWTO-Collection for details.
security = user

# This option is important for security. It allows you to restrict
# connections to machines which are on your local network. The
# following example restricts access to two C class networks and
# the “loopback” interface. For more examples of the syntax see
# the smb.conf man page
; hosts allow = 192.168.1. 192.168.2. 127.

# If you want to automatically load your printer list rather
# than setting them up individually then you’ll need this
load printers = yes

# you may wish to override the location of the printcap file
; printcap name = /etc/printcap

# on SystemV system setting printcap name to lpstat should allow
# you to automatically obtain a printer list from the SystemV spool
# system
; printcap name = lpstat

# It should not be necessary to specify the print system type unless
# it is non-standard. Currently supported print systems include:
# bsd, cups, sysv, plp, lprng, aix, hpux, qnx
; printing = cups

# Uncomment this if you want a guest account, you must add this to /etc/passwd
# otherwise the user “nobody” is used
; guest account = pcguest

# this tells Samba to use a separate log file for each machine
# that connects
log file = /var/log/samba/log.%m

# Put a capping on the size of the log files (in Kb).
max log size = 50

# Use password server option only with security = server
# The argument list may include:
# password server = My_PDC_Name [My_BDC_Name] [My_Next_BDC_Name]
# or to auto-locate the domain controller/s
# password server = *
; password server =

# Use the realm option only with security = ads
# Specifies the Active Directory realm the host is part of
; realm = MY_REALM

# Backend to store user information in. New installations should
# use either tdbsam or ldapsam. smbpasswd is available for backwards
# compatibility. tdbsam requires no further configuration.
; passdb backend = tdbsam

# Using the following line enables you to customise your configuration
# on a per machine basis. The %m gets replaced with the netbios name
# of the machine that is connecting.
# Note: Consider carefully the location in the configuration file of
# this line. The included file is read at that point.
; include = /usr/local/etc/smb.conf.%m

# Most people will find that this option gives better performance.
# See the chapter ‘Samba performance issues’ in the Samba HOWTO Collection
# and the manual pages for details.
# You may want to add the following on a Linux system:
; socket options = SO_RCVBUF=8192 SO_SNDBUF=8192

# Configure Samba to use multiple interfaces
# If you have multiple network interfaces then you must list them
# here. See the man page for details.
; interfaces = 192.168.12.2/24 192.168.13.2/24

# Browser Control Options:
# set local master to no if you don’t want Samba to become a master
# browser on your network. Otherwise the normal election rules apply
; local master = no

# OS Level determines the precedence of this server in master browser
# elections. The default value should be reasonable
; os level = 33

# Domain Master specifies Samba to be the Domain Master Browser. This
# allows Samba to collate browse lists between subnets. Don’t use this
# if you already have a Windows NT domain controller doing this job
; domain master = yes

# Preferred Master causes Samba to force a local browser election on startup
# and gives it a slightly higher chance of winning the election
; preferred master = yes

# Enable this if you want Samba to be a domain logon server for
# Windows95 workstations.
; domain logons = yes

# if you enable domain logons then you may want a per-machine or
# per user logon script
# run a specific logon batch file per workstation (machine)
; logon script = %m.bat
# run a specific logon batch file per username
; logon script = %U.bat

# Where to store roving profiles (only for Win95 and WinNT)
# %L substitutes for this servers netbios name, %U is username
# You must uncomment the [Profiles] share below
; logon path = \\%L\Profiles\%U

# Windows Internet Name Serving Support Section:
# WINS Support – Tells the NMBD component of Samba to enable it’s WINS Server
; wins support = yes

# WINS Server – Tells the NMBD components of Samba to be a WINS Client
# Note: Samba can be either a WINS Server, or a WINS Client, but NOT both
; wins server = w.x.y.z

# WINS Proxy – Tells Samba to answer name resolution queries on
# behalf of a non WINS capable client, for this to work there must be
# at least one WINS Server on the network. The default is NO.
; wins proxy = yes

# DNS Proxy – tells Samba whether or not to try to resolve NetBIOS names
# via DNS nslookups. The default is NO.
dns proxy = no

# Charset settings
; display charset = koi8-r
; unix charset = koi8-r
; dos charset = cp866

# Use extended attributes to store file modes
; store dos attributes = yes
; map hidden = no
; map system = no
; map archive = no

# Use inherited ACLs for directories
; nt acl support = yes
; inherit acls = yes
; map acl inherit = yes

# These scripts are used on a domain controller or stand-alone
# machine to add or delete corresponding unix accounts
; add user script = /usr/sbin/useradd %u
; add group script = /usr/sbin/groupadd %g
; add machine script = /usr/sbin/adduser -n -g machines -c Machine -d /dev/null -s /bin/false %u
; delete user script = /usr/sbin/userdel %u
; delete user from group script = /usr/sbin/deluser %u %g
; delete group script = /usr/sbin/groupdel %g

# This is a DRAFT sample configuration for the ACLs on the ZFS partition.
#
nt acl support = yes
inherit acls = no
map acl inherit = yes

#============================ Share Definitions ==============================
[homes]
comment = Home Directories
browseable = no
writable = yes
path = /tank/Users/%S

# Un-comment the following and create the netlogon directory for Domain Logons
; [netlogon]
; comment = Network Logon Service
; path = /usr/local/samba/lib/netlogon
; guest ok = yes
; writable = no
; share modes = no

# Un-comment the following to provide a specific roving profile share
# the default is to use the user’s home directory
;[Profiles]
; path = /usr/local/samba/profiles
; browseable = no
; guest ok = yes

# NOTE: If you have a BSD-style print system there is no need to
# specifically define each individual printer
[printers]
comment = All Printers
path = /var/spool/samba
browseable = no
# Set public = yes to allow user ‘guest account’ to print
guest ok = no
writable = no
printable = yes

# This one is useful for people to share files
;[tmp]
; comment = Temporary file space
; path = /tmp
; read only = no
; public = yes

# A publicly accessible directory, but read only, except for people in
# the “staff” group
;[public]
; comment = Public Stuff
; path = /home/samba
; public = yes
; writable = yes
; printable = no
; write list = @staff

# Other examples.
#
# A private printer, usable only by fred. Spool data will be placed in fred’s
# home directory. Note that fred must have write access to the spool directory,
# wherever it is.
;[fredsprn]
; comment = Fred’s Printer
; valid users = fred
; path = /homes/fred
; printer = freds_printer
; public = no
; writable = no
; printable = yes

# A private directory, usable only by fred. Note that fred requires write
# access to the directory.
;[fredsdir]
; comment = Fred’s Service
; path = /usr/somewhere/private
; valid users = fred
; public = no
; writable = yes
; printable = no

# a service which has a different directory for each machine that connects
# this allows you to tailor configurations to incoming machines. You could
# also use the %U option to tailor it by user name.
# The %m gets replaced with the machine name that is connecting.
;[pchome]
; comment = PC Directories
; path = /usr/pc/%m
; public = no
; writable = yes

# A publicly accessible directory, read/write to all users. Note that all files
# created in the directory by users will be owned by the default user, so
# any user with access can delete any other user’s files. Obviously this
# directory must be writable by the default user. Another user could of course
# be specified, in which case all files would be owned by that user instead.
;[public]
; path = /usr/somewhere/else/public
; public = yes
; only guest = yes
; writable = yes
; printable = no

# The following two entries demonstrate how to share a directory so that two
# users can place files there that will be owned by the specific users. In this
# setup, the directory should be writable by both users and should have the
# sticky bit set on it to prevent abuse. Obviously this could be extended to
# as many users as required.
;[myshare]
; comment = Mary’s and Fred’s stuff
; path = /usr/somewhere/shared
; valid users = mary fred
; public = no
; writable = yes
; printable = no
; create mask = 0765
;

# This is a DRAFT sample configuration for the ACLs on the ZFS partition.
#
; nt acl support = yes
; inherit acls = no
; map acl inherit = yes
;
;[zpool]
; path = /tank/zpool
; unix extensions = no
; vfs objects = zfsacl
; nfs4:mode = special
; nfs4:acedup = merge
; nfs4:chown = yes

[Public]
comment = Public (user-wide) directories
browseable = yes
read only = no
path = /tank/Users/Public
vfs objects = zfsacl
nfs4:mode = special
nfs4:acedup = merge
nfs4:chown = yes
[/cce_ini]

Have 3 drives: 1.5 TB WD15EARS, 1 TB Fantom Green (eSATA), 2 TB WD20EARS.
First, did a:

server# gpart add -b 2048 -s 2929865452 -t freebsd-zfs -l WD15EARS ada0
ada0p1 added
server# gpart add -b 2048 -s 1953113452 -t freebsd-zfs -l FANTOM1TB ada1
ada1p1 added
server# gpart add -b 2048 -s 3906617452 -t freebsd-zfs -l WD20EARS ada2
ada2p1 added

Now, I have:

server# gpart show ada0
=> 34 2930277101 ada0 GPT (1.4T)
34 2014 - free - (1.0M)
2048 2929865452 1 freebsd-zfs (1.4T)
2929867500 409635 - free - (200M)

server# gpart show ada1
=> 34 1953525101 ada1 GPT (932G)
34 2014 - free - (1.0M)
2048 1953113452 1 freebsd-zfs (931G)
1953115500 409635 - free - (200M)

server# gpart show ada2
=> 34 3907029101 ada2 GPT (1.8T)
34 2014 - free - (1.0M)
2048 3906617452 1 freebsd-zfs (1.8T)
3906619500 409635 - free - (200M)

You’ll note that I’m leaving 200M free in case I replace the drive with a slightly smaller drive.
Next step: set up ZFS pools.