How to restrict "sftp only" user into your home dir and subdir

Question

Hi OTN forums members
Question : I want restrict a sftp only user to browse ONLY in your home directory and subdirectory . I don't want sftp user access into other directory.
Details : I want use a "ssh bundle package" on s10(only package on SUNWCXall installation cluster). I don't want to use the "extrernal package", as "ProFTP", "Chroot", sunfreeware OpenSSH package,ecc. It's possible?
Technical Details of my system(test) : the hostname and username it's fantasy name, not real ;-)
root@sunlab1:/[1]$ cat /etc/release
                       Solaris 10 5/09 s10s_u7wos_08 SPARC
           Copyright 2009 Sun Microsystems, Inc.  All Rights Reserved.
                        Use is subject to license terms.
                             Assembled 30 March 2009
root@sunlab1:/[2]$ uname -a
SunOS sunlab1 5.10 Generic_142909-17 sun4u sparc SUNW,Sun-Blade-100
root@sunlab1:/[3]$ grep explorer /etc/group
explorer::111:
root@sunlab1:/[4]$ grep explorer /etc/passwd
explorer:x:111:111:Sun Explorer Data Collector sftp only user:/export/home/explorer:/usr/lib/ssh/sftp-server
root@sunlab1:/[5]$ zfs list
NAME                       USED  AVAIL  REFER  MOUNTPOINT
rpool                     27.3G  9.33G    96K  /rpool
rpool/ROOT                11.6G  9.33G    18K  legacy
rpool/ROOT/s10s_u7wos_08  11.6G  9.33G  11.6G  /
rpool/cfengine            73.7M   950M  73.7M  /var/cfengine
rpool/dump                1.00G  9.33G  1.00G  -
rpool/export              5.01G  9.33G  11.8M  /export
rpool/export/home         1.40G  3.60G  1.40G  /export/home
rpool/mp3                 2.65G  2.35G  2.65G  /mp3
rpool/patches              206M  2.80G   206M  /var/patches
rpool/swap                 768M  9.58G   514M  -
root@sunlab1:/[6]$
root@sunlab1:/[7]$ cd /export/home
root@sunlab1:/export/home[9]$ ls -la
total 47
drwxr-xr-x   5 root     root           9 Oct  7 09:51 .
drwxr-xr-x   4 root     sys            6 Jun  7 09:44 ..
drwxr-x---  11 explorer explorer      11 Oct  7 11:30 explorer
root@sunlab1:/[8]$ sftp explorer@sunlab1
Connecting to sunlab1...
Password:
sftp> dir
[...more output...]
sftp> pwd
Remote working directory: /export/home/explorer
sftp> cd /var/adm
sftp> dir
[...more output...]
sftp> get messages
Fetching /var/adm/messages to messages
sftp> pwd
Remote working directory: /var/adm
sftp> bye
root@sunlab1:/[9]$
root@sunlab1:/[10]$ pkginfo -l SUNWsshr
   PKGINST:  SUNWsshr
      NAME:  SSH Client and utilities, (Root)
  CATEGORY:  system
      ARCH:  sparc
   VERSION:  11.10.0,REV=2005.01.21.15.53
   BASEDIR:  /
    VENDOR:  Sun Microsystems, Inc.
      DESC:  Secure Shell protocol Client and associated Utilities
[...snip...]
root@sunlab1:/[11]$ pca -l installed --pattern=[Ss]sh
[...snip...]
Using /var/patches/pca/patchdiag.xref from Oct/14/10
Host: sunlab1 (SunOS 5.10/Generic_142909-17/sparc/sun4u)
List: installed (3/584)
Patch  IR   CR RSB Age Synopsis
141742 04 = 04 -S- 427 Obsoleted by: 141444-09 SunOS 5.10: sshd patch
143140 04 = 04 RS- 119 Obsoleted by: 143559-03 SunOS 5.10: ssh patch
143559 03 = 03 RS-  38 SunOS 5.10: ssh scp patch
root@sunlab1:/[12]$ pca -l 141444 143559
Using /var/patches/pca/patchdiag.xref from Oct/14/10
Host: sunlab1 (SunOS 5.10/Generic_142909-17/sparc/sun4u)
List: 141444 143559 (2/405)
Patch  IR   CR RSB Age Synopsis
141444 09 = 09 RS- 367 SunOS 5.10: kernel patch
143559 03 = 03 RS-  38 SunOS 5.10: ssh scp patch
root@sunlab1:/[13]$Legenda:
PCA = [url http://www.par.univie.ac.at/solaris/pca/] Patch Check Advanced  , PCA is 3PP free and fast tool for Analyze, download and install patches for Solaris
IR =Installed Rev. CR = Current Rev. (published on patchdiag.xref from Oct/14/10)
RSB =[R]eccommended,[S]ecurity, [\B]ab patches
Not helpful reading "<tt>man sshd_config</tt>" and "<tt>man sftp-server</tt>", and Google searching. Nothing by MOS Community search.
Any idea?
Best Regards
Michele V.
P.S.: Excuse me for my bad English.

Answer 1

Hi OTN forums members,
     I find the solution. Thanks Andrea Manganaro (aka Amanga) for the help.
1) Download and install OpenSSH for Solaris 10/SPARC and all dependencies(Please read the http://www.sunfreeware.com/openssh.html note):
     - [url ftp://ftp.sunfreeware.com/pub/freeware/sparc/10/openssh-5.6p1-sol10-sparc-local.gz]openssh-5.6p1-sol10-sparc-local.gz
     - [url ftp://ftp.sunfreeware.com/pub/freeware/sparc/10/openssl-1.0.0a-sol10-sparc-local.gz]openssl-1.0.0a-sol10-sparc-local.gz
     - [url ftp://ftp.sunfreeware.com/pub/freeware/sparc/10/zlib-1.2.5-sol10-sparc-local.gz]zlib-1.2.5-sol10-sparc-local.gz
     - [url ftp://ftp.sunfreeware.com/pub/freeware/sparc/10/libgcc-3.4.6-sol10-sparc-local.gz]ibgcc-3.4.6-sol10-sparc-local.gz
2) Configure <tt>/usr/local/etc/sshd_config</tt> file with the "+<tt>ChrootDirectory</tt>+" directive. For me:
# override default of no subsystems
#Subsystem      sftp    /usr/local/libexec/sftp-server
Subsystem       sftp    internal-sftp[...]
# Example of overriding settings on a per-user basis
Match Group sftponly
        ChrootDirectory %h
        ForceCommand internal-sftp
        AllowTcpForwarding no3) Create group and user for sftp-only account. For me:
root@taurus # groupadd sftponly
root@taurus # grep sftponly /etc/group
sftponly::202:
root@taurus # useradd -g sftponly -c "Sftp only user" -d /export/home/explorer -s /bin/false -m explorer
explorer:x:1002:202:Sftp only user:/export/home/explorer:/bin/false
root@taurus # passwd explorer
New Password:
Re-enter new Password:
passwd: password successfully changed for explorer
root@taurus # 4) Change home directory permission and create a r/w direcorty (uploads) for sftponly user account.
root@taurus # cd /export/home
root@taurus # ls -la
total 14
drwxr-xr-x   4 root     root           4 Oct 29 15:28 .
drwxr-xr-x   3 root     sys            3 Jan 22  2009 ..
drwxr-xr-x   3 explorer sftponly       3 Oct 29 15:41 explorer
root@taurus # chown root:sftponly explorer; chmod 750 explorer
root@taurus # ls -la
total 14
drwxr-xr-x   4 root     root           4 Oct 29 15:28 .
drwxr-xr-x   3 root     sys            3 Jan 22  2009 ..
drwxr-x---   3 root     sftponly       3 Oct 29 15:41 explorer
root@taurus # This will make a read-only, chrooted directory perfect for people to come in and get stuff, but never write.
For example, you could make a directory explorer/uploads that allow people to write in.Then you can moderate what gets copied into the read-only /explorer area. Remember that if a user can write in a directory then they can also delete anything in that directory.
root@taurus # cd explorer
root@taurus # mkdir uploads && chown -R explorer:sftponly uploads && chmod 0755 uploads
root@taurus # ls -al
total 9
drwxr-x---   3 root     sftponly       3 Oct 29 15:41 .
drwxr-xr-x   4 root     root           4 Oct 29 15:28 ..
drwxr-xr-x   2 explorer sftponly       2 Oct 29 15:56 uploads
root@taurus # 5) Disable SunSSH "service" and enable OpenSSH "service" (with SMF):
root@taurus # svcadm disable sshSee [url http://www.sunfreeware.com/sshsol10.html]here for Running openssh vis SMF on Solaris 10 Systems
root@taurus # svcadm disable ossh
root@taurus # svcs -a | grep ssh
disabled       12:37:51 svc:/network/ssh:default
online         15:29:41 svc:/network/ossh:default
root@taurus # 6) Test your job :-)
Helpful links:
==============
http://www.sunfreeware.com
http://www.openssh.org
http://calomel.org/sftp_chroot.html
HTH
Michele Vecchiato