[Pkg-samba-maint] Bug#814287: Recent security fix for symlinks renders root filesystem exports unusable

Petr Vandrovec petr at vmware.com
Tue Feb 9 22:27:54 UTC 2016


Package: samba
Version: 2:4.3.3+dfsg-1+b1
Severity: important

Since I updated samba package to latest version, I cannot access my exports:
==
 > net use w: \\petr-dev3\rootfs\bhavesh\home\petr <password> /user:petr
System error 5 has occurred.

Access is denied.
==

It seems to me that there is a thinko in how export of '/' directory is 
handled, ending up with:

check_reduced_name: Bad access attempt: bhavesh/home/petr is a symlink 
outside the share path
conn_rootdir =/
resolved_name=/bhavesh/home/petr

despite there being no symlinks involved, and /bhavesh/home/petr being 
inside / space.

For now I've worked around the problem by setting

follow symlinks = yes
wide links = yes
allow insecure wide links = yes

but I do not think I should be forced to enable 'follow symlinks' to use 
symlink-less share.

							Petr
-------------- next part --------------
[2016/02/09 13:11:33.139038,  5, pid=17936, effective(0, 0), real(0, 0)] ../source3/auth/token_util.c:639(debug_unix_user_token)
  UNIX token of user 884
  Primary group is 201 and contains 20 supplementary groups
  Group[  0]: 201
  Group[  1]: 0
  Group[  2]: 4
  Group[  3]: 5
  Group[  4]: 6
  Group[  5]: 7
  Group[  6]: 15
  Group[  7]: 20
  Group[  8]: 24
  Group[  9]: 25
  Group[ 10]: 26
  Group[ 11]: 27
  Group[ 12]: 29
  Group[ 13]: 44
  Group[ 14]: 46
  Group[ 15]: 50
  Group[ 16]: 118
  Group[ 17]: 1010
  Group[ 18]: 1031
  Group[ 19]: 104310
[2016/02/09 13:11:33.139074,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/uid.c:363(change_to_user_internal)
  Impersonated user: uid=(884,884), gid=(0,201)
[2016/02/09 13:11:33.139081,  4, pid=17936, effective(884, 201), real(884, 0), class=vfs] ../source3/smbd/vfs.c:844(vfs_ChDir)
  vfs_ChDir to /
[2016/02/09 13:11:33.139093,  4, pid=17936, effective(884, 201), real(884, 0), class=vfs] ../source3/smbd/vfs.c:855(vfs_ChDir)
  vfs_ChDir got /
[2016/02/09 13:11:33.139102, 10, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/smb2_create.c:501(smbd_smb2_create_send)
  smbd_smb2_create: name[bhavesh\home\petr]
[2016/02/09 13:11:33.139110, 10, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/smb2_create.c:932(smbd_smb2_create_send)
  smbd_smb2_create_send: open execution phase
[2016/02/09 13:11:33.139121,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/filename.c:257(unix_convert)
  unix_convert called on file "bhavesh/home/petr"
[2016/02/09 13:11:33.139129, 10, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/statcache.c:244(stat_cache_lookup)
  stat_cache_lookup: lookup failed for name [BHAVESH/HOME/PETR]
[2016/02/09 13:11:33.139136, 10, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/statcache.c:244(stat_cache_lookup)
  stat_cache_lookup: lookup failed for name [BHAVESH/HOME]
[2016/02/09 13:11:33.139141, 10, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/statcache.c:244(stat_cache_lookup)
  stat_cache_lookup: lookup failed for name [BHAVESH]
[2016/02/09 13:11:33.139148,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/filename.c:449(unix_convert)
  unix_convert begin: name = bhavesh/home/petr, dirpath = , start = bhavesh/home/petr
[2016/02/09 13:11:33.139158,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/statcache.c:143(stat_cache_add)
  stat_cache_add: Added entry (56549fbbc990:size 11) BHAVESH/HOME/PETR -> bhavesh/home/petr
[2016/02/09 13:11:33.139164,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/filename.c:472(unix_convert)
  conversion of base_name finished bhavesh/home/petr -> bhavesh/home/petr
[2016/02/09 13:11:33.139171, 10, pid=17936, effective(884, 201), real(884, 0), class=vfs] ../source3/smbd/vfs.c:1147(check_reduced_name)
  check_reduced_name [bhavesh/home/petr] [/]
[2016/02/09 13:11:33.139182, 10, pid=17936, effective(884, 201), real(884, 0), class=vfs] ../source3/smbd/vfs.c:1207(check_reduced_name)
  check_reduced_name realpath [bhavesh/home/petr] -> [/bhavesh/home/petr]
[2016/02/09 13:11:33.139189,  2, pid=17936, effective(884, 201), real(884, 0), class=vfs] ../source3/smbd/vfs.c:1240(check_reduced_name)
  check_reduced_name: Bad access attempt: bhavesh/home/petr is a symlink outside the share path
  conn_rootdir =/
  resolved_name=/bhavesh/home/petr
[2016/02/09 13:11:33.139198,  5, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/filename.c:1078(check_name)
  check_name: name bhavesh/home/petr failed with NT_STATUS_ACCESS_DENIED
[2016/02/09 13:11:33.139204,  3, pid=17936, effective(884, 201), real(884, 0)] ../source3/smbd/filename.c:1431(filename_convert_internal)
  filename_convert_internal: check_name failed for name bhavesh/home/petr with NT_STATUS_ACCESS_DENIED

petr-dev3:/bhavesh/home/petr/debian/samba-4.3.3+dfsg$ ls -lad /
drwxr-xr-x 84 root root 4096 Aug 10  2015 /
petr-dev3:/bhavesh/home/petr/debian/samba-4.3.3+dfsg$ ls -lad /bhavesh
drwxr-xr-x 13 root root 4096 Jan  6  2014 /bhavesh
petr-dev3:/bhavesh/home/petr/debian/samba-4.3.3+dfsg$ ls -lad /bhavesh/home
drwxr-sr-x 3 petr mts 4096 Dec  7 12:15 /bhavesh/home
petr-dev3:/bhavesh/home/petr/debian/samba-4.3.3+dfsg$ ls -lad /bhavesh/home/petr
drwxr-sr-x 86 petr mts 12288 Feb  1 22:41 /bhavesh/home/petr
-------------- next part --------------
#
# Sample configuration file for the Samba suite for Debian GNU/Linux.
#
#
# 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 most of which 
# are not shown in this example
#
# 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 commentary 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]

## Browsing/Identification ###

# Change this to the workgroup/NT-domain name your Samba server will part of
   workgroup = WORKGROUP

# server string is the equivalent of the NT Description field
   server string = %h server (Samba %v)

# Windows Internet Name Serving Support Section:
# WINS Support - Tells the NMBD component of Samba to enable its WINS Server
;   wins support = no

# 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

# If we receive WINS server info from DHCP, override the options above. 
   include = /etc/samba/dhcp.conf

# This will prevent nmbd to search for NetBIOS names through DNS.
   dns proxy = no

# What naming service and in what order should we use to resolve host names
# to IP addresses
;   name resolve order = lmhosts host wins bcast

#### Networking ####

# The specific set of interfaces / networks to bind to
# This can be either the interface name or an IP address/netmask;
# interface names are normally preferred
;   interfaces = 127.0.0.0/8 eth0

# Only bind to the named interfaces and/or networks; you must use the
# 'interfaces' option above to use this.
# It is recommended that you enable this feature if your Samba machine is
# not protected by a firewall or is a firewall itself.  However, this
# option cannot handle dynamic or non-broadcast interfaces correctly.
;   bind interfaces only = true

#### Debugging/Accounting ####

# This tells Samba to use a separate log file for each machine
# that connects
   log file = /var/log/samba/log.%m
   log level = 99

# Put a capping on the size of the log files (in Kb).
   max log size = 1000

# If you want Samba to only log through syslog then set the following
# parameter to 'yes'.
;   syslog only = no

# We want Samba to log a minimum amount of information to syslog. Everything
# should go to /var/log/samba/log.{smbd,nmbd} instead. If you want to log
# through syslog you should set the following parameter to something higher.
   syslog = 0

# Do something sensible when Samba crashes: mail the admin a backtrace
   panic action = /bin/sleep 1


####### Authentication #######

# "security = user" is always a good idea. This will require a Unix account
# in this server for every user accessing the server. See
# /usr/share/doc/samba-doc/htmldocs/Samba-HOWTO-Collection/ServerType.html
# in the samba-doc package for details.
;   security = user

# You may wish to use password encryption.  See the section on
# 'encrypt passwords' in the smb.conf(5) manpage before enabling.
   encrypt passwords = true

# If you are using encrypted passwords, Samba will need to know what
# password database type you are using.  
   passdb backend = tdbsam

   obey pam restrictions = no

;   guest account = nobody
   invalid users =

# This boolean parameter controls whether Samba attempts to sync the Unix
# password with the SMB password when the encrypted SMB password in the
# passdb is changed.
;   unix password sync = no

# For Unix password sync to work on a Debian GNU/Linux system, the following
# parameters must be set (thanks to Ian Kahan <<kahan at informatik.tu-muenchen.de> for
# sending the correct chat script for the passwd program in Debian Sarge).
   passwd program = /usr/bin/passwd %u
   passwd chat = *Enter\snew\sUNIX\spassword:* %n\n *Retype\snew\sUNIX\spassword:* %n\n *password\supdated\ssuccessfully* .

# This boolean controls whether PAM will be used for password changes
# when requested by an SMB client instead of the program listed in
# 'passwd program'. The default is 'no'.
;   pam password change = no

client plaintext auth = yes
client use plaintext auth = yes

########## Domains ###########

# Is this machine able to authenticate users. Both PDC and BDC
# must have this setting enabled. If you are the BDC you must
# change the 'domain master' setting to no
#
;   domain logons = yes
#
# The following setting only takes effect if 'domain logons' is set
# It specifies the location of the user's profile directory
# from the client point of view)
# The following required a [profiles] share to be setup on the
# samba server (see below)
;   logon path = \\%N\profiles\%U
# Another common choice is storing the profile in the user's home directory
;   logon path = \\%N\%U\profile

# The following setting only takes effect if 'domain logons' is set
# It specifies the location of a user's home directory (from the client
# point of view)
;   logon drive = H:
;   logon home = \\%N\%U

# The following setting only takes effect if 'domain logons' is set
# It specifies the script to run during logon. The script must be stored
# in the [netlogon] share
# NOTE: Must be store in 'DOS' file format convention
;   logon script = logon.cmd

# This allows Unix users to be created on the domain controller via the SAMR
# RPC pipe.  The example command creates a user account with a disabled Unix
# password; please adapt to your needs
; add user script = /usr/sbin/adduser --quiet --disabled-password --gecos "" %u

########## Printing ##########

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

# lpr(ng) printing. You may wish to override the location of the
# printcap file
;   printing = bsd
;   printcap name = /etc/printcap

# CUPS printing.  See also the cupsaddsmb(8) manpage in the
# cupsys-client package.
;   printing = cups
;   printcap name = cups

# When using [print$], root is implicitly a 'printer admin', but you can
# also give this right to other users to add drivers and set printer
# properties
;   printer admin = @ntadmin


############ Misc ############

# 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
;   include = /home/samba/etc/smb.conf.%m

# Most people will find that this option gives better performance.
# See smb.conf(5) and /usr/share/doc/samba-doc/htmldocs/speed.html
# for details
# You may want to add the following on a Linux system:
#         SO_RCVBUF=8192 SO_SNDBUF=8192
   socket options = TCP_NODELAY

# The following parameter is useful only if you have the linpopup package
# installed. The samba maintainer and the linpopup maintainer are
# working to ease installation and configuration of linpopup and samba.
;   message command = /bin/sh -c '/usr/bin/linpopup "%f" "%m" %s; rm %s' &

# Domain Master specifies Samba to be the Domain Master Browser. If this
# machine will be configured as a BDC (a secondary logon server), you
# must set this to 'no'; otherwise, the default behavior is recommended.
;   domain master = auto

# Some defaults for winbind (make sure you're not using the ranges
# for something else.)
;   idmap uid = 10000-20000
;   idmap gid = 10000-20000
;   template shell = /bin/bash

#======================= Share Definitions =======================

acl allow execute always = True

[homes]
   comment = Home Directories
   browseable = no

# By default, the home directories are exported read-only. Change next
# parameter to 'yes' if you want to be able to write to them.
   writable = yes

# File creation mask is set to 0700 for security reasons. If you want to
# create files with group=rw permissions, set next parameter to 0775.
   create mask = 0775

# Directory creation mask is set to 0700 for security reasons. If you want to
# create dirs. with group=rw permissions, set next parameter to 0775.
   directory mask = 0775

# Un-comment the following and create the netlogon directory for Domain Logons
# (you need to configure Samba to act as a domain controller too.)
;[netlogon]
;   comment = Network Logon Service
;   path = /home/samba/netlogon
;   guest ok = yes
;   writable = no
;   share modes = no

# Un-comment the following and create the profiles directory to store
# users profiles (see the "logon path" option above)
# (you need to configure Samba to act as a domain controller too.)
# The path below should be writable by all users so that their
# profile directory may be created the first time they log on
;[profiles]
;   comment = Users profiles
;   path = /home/samba/profiles
;   guest ok = no
;   browseable = no
;   create mask = 0600
;   directory mask = 0700

[printers]
   comment = All Printers
   browseable = no
   path = /var/spool/samba
   printable = yes
   public = no
   writable = no
   create mode = 0700

# Windows clients look for this share name as a source of downloadable
# printer drivers
[print$]
   comment = Printer Drivers
   path = /var/lib/samba/printers
   browseable = yes
   read only = yes
   guest ok = no
# Uncomment to allow remote administration of Windows print drivers.
# Replace 'ntadmin' with the name of the group your admin users are
# members of.
;   write list = root, @ntadmin

# A sample share for sharing your CD-ROM with others.
;[cdrom]
;   comment = Samba server's CD-ROM
;   writable = no
;   locking = no
;   path = /cdrom
;   public = yes

[rootfs]
	comment = Root FS
	writeable = yes
	locking = yes
	path = /

# The next two parameters show how to auto-mount a CD-ROM when the
#	cdrom share is accesed. For this to work /etc/fstab must contain
#	an entry like this:
#
#       /dev/scd0   /cdrom  iso9660 defaults,noauto,ro,user   0 0
#
# The CD-ROM gets unmounted automatically after the connection to the
#
# If you don't want to use auto-mounting/unmounting make sure the CD
#	is mounted on /cdrom
#
;   preexec = /bin/mount /cdrom
;   postexec = /bin/umount /cdrom



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