B.7. Chroot environment for SSH

Creating a restricted environment for SSH is a tough job due to its dependencies and the fact that, unlike other servers, SSH provides a remote shell to users. Thus, you will also have to consider the applications users will be allowed to use in the environment.

You have two options to setup a restricted remote shell:

Chrooting the ssh users, by properly configuring the ssh daemon you can ask it to chroot a user after authentication just before it is provided a shell. Each user can have their own environment.
Chrooting the ssh server, since you chroot the ssh application itself all users are chrooted to the defined environment.

The first option has the advantage of making it possible to have both non-chrooted and chrooted users, if you don't introduce any setuid application in the user's chroots it is more difficult to break out of it. However, you might need to setup individual chroots for each user and it is more difficult to setup (as it requires cooperation from the SSH server). The second option is more easy to setup, and protects from an exploitation of the ssh server itself (since it's also in the chroot) but it will have the limitation that all users will share the same chroot environment (you cannot setup a per-user chroot environment).

B.7.1. Chrooting the ssh users

You can setup the ssh server so that it will chroot a set of defined users into a shell with a limited set of applications available.

B.7.1.1. Using libpam-chroot

Probably the easiest way is to use the libpam-chroot package provided in Debian. Once you install it you need to:

Modify /etc/pam.d/ssh to use this PAM module, add as its last line^[78]:
```
session    required   pam_chroot.so
```
set a proper chroot environment for the user. You can try using the scripts available at /usr/share/doc/libpam-chroot/examples/, use the makejail ^[79] program or setup a minimum Debian environment with debootstrap. Make sure the environment includes the needed devices ^[80].
Configure /etc/security/chroot.conf so that the users you determine are chrooted to the directory you setup previously. You might want to have independent directories for different users so that they will not be able to see neither the whole system nor each other's.
Configure SSH: Depending on your OpenSSH version the chroot environment might work straight of the box or not. Since 3.6.1p2 the do_pam_session() function is called after sshd has dropped privileges, since chroot() needs root priviledges it will not work with Privilege separation on. In newer OpenSSH versions, however, the PAM code has been modified and do_pam_session is called before dropping priviledges so it will work even with Privilege separation is on. If you have to disable it modify /etc/ssh/sshd_config like this:
```
UsePrivilegeSeparation no
```
Notice that this will lower the security of your system since the OpenSSH server will then run as root user. This means that if a remote attack is found against OpenSSH an attacker will get root privileges instead of sshd, thus compromising the whole system. ^[81]

If you don't disable Privilege Separation you will need an /etc/passwd which includes the user's UID inside the chroot for Privilege Separation to work properly.

If you have Privilege Separation set to yes and your OpenSSH version does not behave properly you will need to disable it. If you don't, users that try to connect to your server and would be chrooted by this module will see this:

$ ssh -l user server
user@server's password:
Connection to server closed by remote host.
Connection to server closed.

This is because the ssh daemon, which is running as 'sshd', is not be able to make the chroot() system call. To disable Privilege separation you have to modify the /etc/ssh/sshd_config configuration file as described above.

Notice that if any of the following is missing the users will not be able to logon to the chroot:

The /proc filesystem needs to be mounted in the users' chroot.
The necessary /dev/pts/ devices need to exist. If the files are generated by your running kernel automatically then you have to manually create them on the chroot's /dev/.
The user's home directory has to exist in the chroot, otherwise the ssh daemon will not continue.

You can debug all these issues if you use the debug keyword in the /etc/pam.d/ssh PAM definition. If you encounter issues you might find it useful to enable the debugging mode on the ssh client too.

Note: This information is also available (and maybe more up to date) in /usr/share/doc/libpam-chroot/README.Debian.gz, please review it for updated information before taking the above steps.

B.7.1.2. Patching the `ssh` server

Debian's sshd does not allow restriction of a user's movement through the server, since it lacks the chroot function that the commercial program sshd2 includes (using 'ChrootGroups' or 'ChrootUsers', see sshd2_config(5)). However, there is a patch available to add this functionality available from http://chrootssh.sourceforge.net (requested and available in http://bugs.debian.org/139047 in Debian). The patch may be included in future releases of the OpenSSH package. Emmanuel Lacour has ssh deb packages for sarge with this feature. They are available at http://debian.home-dn.net/sarge/ssh/. Notice that those might not be up to date so completing the compilation step is recommended.

After applying the patch, modify /etc/passwd by changing the home path of the users (with the special /./ token):

  joeuser:x:1099:1099:Joe Random User:/home/joe/./:/bin/bash

Isto irá restringir ambos o acesso remoto ao shell, como também a cópia remota através do canal ssh.

Tenha certeza de ter todos os binários e bibliotecas necessárias dentro do caminho que está enjaulado para os usuários. Estes arquivos devem pertencer ao root para evitar tampering pelo usuário (como sair da jaula chroot'ed). Um exemplo possível inclue:

./bin:
total 660
drwxr-xr-x    2 root     root         4096 Mar 18 13:36 .
drwxr-xr-x    8 guest    guest        4096 Mar 15 16:53 ..
-r-xr-xr-x    1 root     root       531160 Feb  6 22:36 bash
-r-xr-xr-x    1 root     root        43916 Nov 29 13:19 ls
-r-xr-xr-x    1 root     root        16684 Nov 29 13:19 mkdir
-rwxr-xr-x    1 root     root        23960 Mar 18 13:36 more
-r-xr-xr-x    1 root     root         9916 Jul 26  2001 pwd
-r-xr-xr-x    1 root     root        24780 Nov 29 13:19 rm
lrwxrwxrwx    1 root     root            4 Mar 30 16:29 sh -> bash

./etc:
total 24
drwxr-xr-x    2 root     root         4096 Mar 15 16:13 .
drwxr-xr-x    8 guest    guest        4096 Mar 15 16:53 ..
-rw-r--r--    1 root     root           54 Mar 15 13:23 group
-rw-r--r--    1 root     root          428 Mar 15 15:56 hosts
-rw-r--r--    1 root     root           44 Mar 15 15:53 passwd
-rw-r--r--    1 root     root           52 Mar 15 13:23 shells

./lib:
total 1848
drwxr-xr-x    2 root     root         4096 Mar 18 13:37 .
drwxr-xr-x    8 guest    guest        4096 Mar 15 16:53 ..
-rwxr-xr-x    1 root     root        92511 Mar 15 12:49 ld-linux.so.2
-rwxr-xr-x    1 root     root      1170812 Mar 15 12:49 libc.so.6
-rw-r--r--    1 root     root        20900 Mar 15 13:01 libcrypt.so.1
-rw-r--r--    1 root     root         9436 Mar 15 12:49 libdl.so.2
-rw-r--r--    1 root     root       248132 Mar 15 12:48 libncurses.so.5
-rw-r--r--    1 root     root        71332 Mar 15 13:00 libnsl.so.1
-rw-r--r--    1 root     root        34144 Mar 15 16:10
libnss_files.so.2
-rw-r--r--    1 root     root        29420 Mar 15 12:57 libpam.so.0
-rw-r--r--    1 root     root       105498 Mar 15 12:51 libpthread.so.0
-rw-r--r--    1 root     root        25596 Mar 15 12:51 librt.so.1
-rw-r--r--    1 root     root         7760 Mar 15 12:59 libutil.so.1
-rw-r--r--    1 root     root        24328 Mar 15 12:57 libwrap.so.0

./usr:
total 16
drwxr-xr-x    4 root     root         4096 Mar 15 13:00 .
drwxr-xr-x    8 guest    guest        4096 Mar 15 16:53 ..
drwxr-xr-x    2 root     root         4096 Mar 15 15:55 bin
drwxr-xr-x    2 root     root         4096 Mar 15 15:37 lib

./usr/bin:
total 340
drwxr-xr-x    2 root     root         4096 Mar 15 15:55 .
drwxr-xr-x    4 root     root         4096 Mar 15 13:00 ..
-rwxr-xr-x    1 root     root        10332 Mar 15 15:55 env
-rwxr-xr-x    1 root     root        13052 Mar 15 13:13 id
-r-xr-xr-x    1 root     root        25432 Mar 15 12:40 scp
-rwxr-xr-x    1 root     root        43768 Mar 15 15:15 sftp
-r-sr-xr-x    1 root     root       218456 Mar 15 12:40 ssh
-rwxr-xr-x    1 root     root         9692 Mar 15 13:17 tty

./usr/lib:
total 852
drwxr-xr-x    2 root     root         4096 Mar 15 15:37 .
drwxr-xr-x    4 root     root         4096 Mar 15 13:00 ..
-rw-r--r--    1 root     root       771088 Mar 15 13:01
libcrypto.so.0.9.6
-rw-r--r--    1 root     root        54548 Mar 15 13:00 libz.so.1
-rwxr-xr-x    1 root     root        23096 Mar 15 15:37 sftp-server

B.7.2. Chrooting the ssh server

If you create a chroot which includes the SSH server files in, for example /var/chroot/ssh, you would start the ssh server chroot'ed with this command:

  # chroot /var/chroot/ssh /sbin/sshd -f /etc/sshd_config

That would make startup the sshd daemon inside the chroot. In order to do that you have to first prepare the contents of the /var/chroot/ssh directory so that it includes both the SSH server and all the utilities that the users connecting to that server might need. If you are doing this you should make certain that OpenSSH uses Privilege Separation (which is the default) having the following line in the configuration file /etc/ssh/sshd_config:

UsePrivilegeSeparation yes

That way the remote daemon will do as few things as possible as the root user so even if there is a bug in it it will not compromise the chroot. Notice that, unlike the case in which you setup a per-user chroot, the ssh daemon is running in the same chroot as the users so there is at least one potential process running as root which could break out of the chroot.

Notice, also, that in order for SSH to work in that location, the partition where the chroot directory resides cannot be mounted with the nodev option. If you use that option, then you will get the following error: PRNG is not seeded, because /dev/urandom does not work in the chroot.

B.7.2.1. Setup a minimal system (the really easy way)

You can use debootstrap to setup a minimal environment that just includes the ssh server. In order to do this you just have to create a chroot as described in the http://www.debian.org/doc/manuals/reference/ch09#_chroot_system document. This method is bound to work (you will get all the necessary componentes for the chroot) but at the cost of disk space (a minimal installation of Debian will amount to several hundred megabytes). This minimal system might also include setuid files that a user in the chroot could use to break out of the chroot if any of those could be use for a privilege escalation.

B.7.2.2. Configurando automaticamente o ambiente (a maneira fácil)

Você pode facilmente criar um ambiente restrito com o pacote makejail, já que ele automaticamente segue as trilhas do servidor daemon (com strace) e faz com que ele execute em um ambiente restrito.

A vantagem de programas que automaticamente geram um ambiente chroot é que eles são capazes de copiar qualquer pacote para o ambiente chroot (mesmo seguindo as dependências do pacote e certificar que foi completada). Então, fornecer as aplicações dos usuários é bem mais fácil.

To set up the environment using makejail's provided examples, just create /var/chroot/sshd and use the command:

  # makejail /usr/share/doc/makejail/examples/sshd.py

This will setup the chroot in the /var/chroot/sshd directory. Notice that this chroot will not fully work unless you:

Mount the procfs filesystem in /var/chroot/sshd/proc. Makejail will mount it for you but if the system reboots you need to remount it running:
```
# mount -t proc proc /var/chroot/sshd/proc
```
You can also have it be mounted automatically by editing /etc/fstab and including this line:
```
proc-ssh /var/chroot/sshd/proc  proc none 0 0
```
Have syslog listen to the device /dev/log inside the chroot. In order to do this you have modify /etc/default/syslogd and add -a /var/chroot/sshd/dev/log to the SYSLOGD variable definition.

Leia o arquivo exemplo para ver que outras mudanças devem ser feitas para o ambiente. Algumas dessas mudanças, como copiar os diretórios home do usuário, não podem ser feitas automaticamente. Também limite a exposição de informações sensíveis, copiando os dados de um certo número de usuários dos arquivos /etc/shadow ou /etc/group.

O seguinte exemplo de ambiente tem sido (levemente) testado, foi construído com o arquivo de configuração fornecido no pacote e inclue o pacote fileutils:

.
|-- bin
|   |-- ash
|   |-- bash
|   |-- chgrp
|   |-- chmod
|   |-- chown
|   |-- cp
|   |-- csh -> /etc/alternatives/csh
|   |-- dd
|   |-- df
|   |-- dir
|   |-- fdflush
|   |-- ksh
|   |-- ln
|   |-- ls
|   |-- mkdir
|   |-- mknod
|   |-- mv
|   |-- rbash -> bash
|   |-- rm
|   |-- rmdir
|   |-- sh -> bash
|   |-- sync
|   |-- tcsh
|   |-- touch
|   |-- vdir
|   |-- zsh -> /etc/alternatives/zsh
|   `-- zsh4
|-- dev
|   |-- null
|   |-- ptmx
|   |-- pts
|   |-- ptya0
(...)
|   |-- tty
|   |-- tty0
(...)
|   `-- urandom
|-- etc
|   |-- alternatives
|   |   |-- csh -> /bin/tcsh
|   |   `-- zsh -> /bin/zsh4
|   |-- environment
|   |-- hosts
|   |-- hosts.allow
|   |-- hosts.deny
|   |-- ld.so.conf
|   |-- localtime -> /usr/share/zoneinfo/Europe/Madrid
|   |-- motd
|   |-- nsswitch.conf
|   |-- pam.conf
|   |-- pam.d
|   |   |-- other
|   |   `-- ssh
|   |-- passwd
|   |-- resolv.conf
|   |-- security
|   |   |-- access.conf
|   |   |-- chroot.conf
|   |   |-- group.conf
|   |   |-- limits.conf
|   |   |-- pam_env.conf
|   |   `-- time.conf
|   |-- shadow
|   |-- shells
|   `-- ssh
|       |-- moduli
|       |-- ssh_host_dsa_key
|       |-- ssh_host_dsa_key.pub
|       |-- ssh_host_rsa_key
|       |-- ssh_host_rsa_key.pub
|       `-- sshd_config
|-- home
|   `-- userX
|-- lib
|   |-- ld-2.2.5.so
|   |-- ld-linux.so.2 -> ld-2.2.5.so
|   |-- libc-2.2.5.so
|   |-- libc.so.6 -> libc-2.2.5.so
|   |-- libcap.so.1 -> libcap.so.1.10
|   |-- libcap.so.1.10
|   |-- libcrypt-2.2.5.so
|   |-- libcrypt.so.1 -> libcrypt-2.2.5.so
|   |-- libdl-2.2.5.so
|   |-- libdl.so.2 -> libdl-2.2.5.so
|   |-- libm-2.2.5.so
|   |-- libm.so.6 -> libm-2.2.5.so
|   |-- libncurses.so.5 -> libncurses.so.5.2
|   |-- libncurses.so.5.2
|   |-- libnsl-2.2.5.so
|   |-- libnsl.so.1 -> libnsl-2.2.5.so
|   |-- libnss_compat-2.2.5.so
|   |-- libnss_compat.so.2 -> libnss_compat-2.2.5.so
|   |-- libnss_db-2.2.so
|   |-- libnss_db.so.2 -> libnss_db-2.2.so
|   |-- libnss_dns-2.2.5.so
|   |-- libnss_dns.so.2 -> libnss_dns-2.2.5.so
|   |-- libnss_files-2.2.5.so
|   |-- libnss_files.so.2 -> libnss_files-2.2.5.so
|   |-- libnss_hesiod-2.2.5.so
|   |-- libnss_hesiod.so.2 -> libnss_hesiod-2.2.5.so
|   |-- libnss_nis-2.2.5.so
|   |-- libnss_nis.so.2 -> libnss_nis-2.2.5.so
|   |-- libnss_nisplus-2.2.5.so
|   |-- libnss_nisplus.so.2 -> libnss_nisplus-2.2.5.so
|   |-- libpam.so.0 -> libpam.so.0.72
|   |-- libpam.so.0.72
|   |-- libpthread-0.9.so
|   |-- libpthread.so.0 -> libpthread-0.9.so
|   |-- libresolv-2.2.5.so
|   |-- libresolv.so.2 -> libresolv-2.2.5.so
|   |-- librt-2.2.5.so
|   |-- librt.so.1 -> librt-2.2.5.so
|   |-- libutil-2.2.5.so
|   |-- libutil.so.1 -> libutil-2.2.5.so
|   |-- libwrap.so.0 -> libwrap.so.0.7.6
|   |-- libwrap.so.0.7.6
|   `-- security
|       |-- pam_access.so
|       |-- pam_chroot.so
|       |-- pam_deny.so
|       |-- pam_env.so
|       |-- pam_filter.so
|       |-- pam_ftp.so
|       |-- pam_group.so
|       |-- pam_issue.so
|       |-- pam_lastlog.so
|       |-- pam_limits.so
|       |-- pam_listfile.so
|       |-- pam_mail.so
|       |-- pam_mkhomedir.so
|       |-- pam_motd.so
|       |-- pam_nologin.so
|       |-- pam_permit.so
|       |-- pam_rhosts_auth.so
|       |-- pam_rootok.so
|       |-- pam_securetty.so
|       |-- pam_shells.so
|       |-- pam_stress.so
|       |-- pam_tally.so
|       |-- pam_time.so
|       |-- pam_unix.so
|       |-- pam_unix_acct.so -> pam_unix.so
|       |-- pam_unix_auth.so -> pam_unix.so
|       |-- pam_unix_passwd.so -> pam_unix.so
|       |-- pam_unix_session.so -> pam_unix.so
|       |-- pam_userdb.so
|       |-- pam_warn.so
|       `-- pam_wheel.so
|-- sbin
|   `-- start-stop-daemon
|-- usr
|   |-- bin
|   |   |-- dircolors
|   |   |-- du
|   |   |-- install
|   |   |-- link
|   |   |-- mkfifo
|   |   |-- shred
|   |   |-- touch -> /bin/touch
|   |   `-- unlink
|   |-- lib
|   |   |-- libcrypto.so.0.9.6
|   |   |-- libdb3.so.3 -> libdb3.so.3.0.2
|   |   |-- libdb3.so.3.0.2
|   |   |-- libz.so.1 -> libz.so.1.1.4
|   |   `-- libz.so.1.1.4
|   |-- sbin
|   |   `-- sshd
|   `-- share
|       |-- locale
|       |   `-- es
|       |       |-- LC_MESSAGES
|       |       |   |-- fileutils.mo
|       |       |   |-- libc.mo
|       |       |   `-- sh-utils.mo
|       |       `-- LC_TIME -> LC_MESSAGES
|       `-- zoneinfo
|           `-- Europe
|               `-- Madrid
`-- var
    `-- run
        |-- sshd
        `-- sshd.pid

27 directories, 733 files

For Debian release 3.1 you have to make sure that the environment includes also the common files for PAM. The following files need to be copied over to the chroot if makejail did not do it for you:

$ ls /etc/pam.d/common-*
/etc/pam.d/common-account  /etc/pam.d/common-password
/etc/pam.d/common-auth     /etc/pam.d/common-session

B.7.2.3. Manually creating the environment (the hard way)

É possível criar um ambiente, usando o método de tentativa e erro, seguindo a execução do servidor sshd e arquivos de log para determinar os arquivos necessários. O seguinte ambiente, contribuído por José Luis Ledesma, é uma listagem amostral do arquivos que estão no ambiente chroot para o ssh: ^[82]

.:
total 36
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ./
drwxr-xr-x 11 root root 4096 Jun 3 13:43 ../
drwxr-xr-x 2 root root 4096 Jun 4 12:13 bin/
drwxr-xr-x 2 root root 4096 Jun 4 12:16 dev/
drwxr-xr-x 4 root root 4096 Jun 4 12:35 etc/
drwxr-xr-x 3 root root 4096 Jun 4 12:13 lib/
drwxr-xr-x 2 root root 4096 Jun 4 12:35 sbin/
drwxr-xr-x 2 root root 4096 Jun 4 12:32 tmp/
drwxr-xr-x 2 root root 4096 Jun 4 12:16 usr/
./bin:
total 8368
drwxr-xr-x 2 root root 4096 Jun 4 12:13 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
-rwxr-xr-x 1 root root 109855 Jun 3 13:45 a2p*
-rwxr-xr-x 1 root root 387764 Jun 3 13:45 bash*
-rwxr-xr-x 1 root root 36365 Jun 3 13:45 c2ph*
-rwxr-xr-x 1 root root 20629 Jun 3 13:45 dprofpp*
-rwxr-xr-x 1 root root 6956 Jun 3 13:46 env*
-rwxr-xr-x 1 root root 158116 Jun 3 13:45 fax2ps*
-rwxr-xr-x 1 root root 104008 Jun 3 13:45 faxalter*
-rwxr-xr-x 1 root root 89340 Jun 3 13:45 faxcover*
-rwxr-xr-x 1 root root 441584 Jun 3 13:45 faxmail*
-rwxr-xr-x 1 root root 96036 Jun 3 13:45 faxrm*
-rwxr-xr-x 1 root root 107000 Jun 3 13:45 faxstat*
-rwxr-xr-x 1 root root 77832 Jun 4 11:46 grep*
-rwxr-xr-x 1 root root 19597 Jun 3 13:45 h2ph*
-rwxr-xr-x 1 root root 46979 Jun 3 13:45 h2xs*
-rwxr-xr-x 1 root root 10420 Jun 3 13:46 id*
-rwxr-xr-x 1 root root 4528 Jun 3 13:46 ldd*
-rwxr-xr-x 1 root root 111386 Jun 4 11:46 less*
-r-xr-xr-x 1 root root 26168 Jun 3 13:45 login*
-rwxr-xr-x 1 root root 49164 Jun 3 13:45 ls*
-rwxr-xr-x 1 root root 11600 Jun 3 13:45 mkdir*
-rwxr-xr-x 1 root root 24780 Jun 3 13:45 more*
-rwxr-xr-x 1 root root 154980 Jun 3 13:45 pal2rgb*
-rwxr-xr-x 1 root root 27920 Jun 3 13:46 passwd*
-rwxr-xr-x 1 root root 4241 Jun 3 13:45 pl2pm*
-rwxr-xr-x 1 root root 2350 Jun 3 13:45 pod2html*
-rwxr-xr-x 1 root root 7875 Jun 3 13:45 pod2latex*
-rwxr-xr-x 1 root root 17587 Jun 3 13:45 pod2man*
-rwxr-xr-x 1 root root 6877 Jun 3 13:45 pod2text*
-rwxr-xr-x 1 root root 3300 Jun 3 13:45 pod2usage*
-rwxr-xr-x 1 root root 3341 Jun 3 13:45 podchecker*
-rwxr-xr-x 1 root root 2483 Jun 3 13:45 podselect*
-r-xr-xr-x 1 root root 82412 Jun 4 11:46 ps*
-rwxr-xr-x 1 root root 36365 Jun 3 13:45 pstruct*
-rwxr-xr-x 1 root root 7120 Jun 3 13:45 pwd*
-rwxr-xr-x 1 root root 179884 Jun 3 13:45 rgb2ycbcr*
-rwxr-xr-x 1 root root 20532 Jun 3 13:45 rm*
-rwxr-xr-x 1 root root 6720 Jun 4 10:15 rmdir*
-rwxr-xr-x 1 root root 14705 Jun 3 13:45 s2p*
-rwxr-xr-x 1 root root 28764 Jun 3 13:46 scp*
-rwxr-xr-x 1 root root 385000 Jun 3 13:45 sendfax*
-rwxr-xr-x 1 root root 67548 Jun 3 13:45 sendpage*
-rwxr-xr-x 1 root root 88632 Jun 3 13:46 sftp*
-rwxr-xr-x 1 root root 387764 Jun 3 13:45 sh*
-rws--x--x 1 root root 744500 Jun 3 13:46 slogin*
-rwxr-xr-x 1 root root 14523 Jun 3 13:46 splain*
-rws--x--x 1 root root 744500 Jun 3 13:46 ssh*
-rwxr-xr-x 1 root root 570960 Jun 3 13:46 ssh-add*
-rwxr-xr-x 1 root root 502952 Jun 3 13:46 ssh-agent*
-rwxr-xr-x 1 root root 575740 Jun 3 13:46 ssh-keygen*
-rwxr-xr-x 1 root root 383480 Jun 3 13:46 ssh-keyscan*
-rwxr-xr-x 1 root root 39 Jun 3 13:46 ssh_europa*
-rwxr-xr-x 1 root root 107252 Jun 4 10:14 strace*
-rwxr-xr-x 1 root root 8323 Jun 4 10:14 strace-graph*
-rwxr-xr-x 1 root root 158088 Jun 3 13:46 thumbnail*
-rwxr-xr-x 1 root root 6312 Jun 3 13:46 tty*
-rwxr-xr-x 1 root root 55904 Jun 4 11:46 useradd*
-rwxr-xr-x 1 root root 585656 Jun 4 11:47 vi*
-rwxr-xr-x 1 root root 6444 Jun 4 11:45 whoami*
./dev:
total 8
drwxr-xr-x 2 root root 4096 Jun 4 12:16 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
crw-r--r-- 1 root root 1, 9 Jun 3 13:43 urandom
./etc:
total 208
drwxr-xr-x 4 root root 4096 Jun 4 12:35 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
-rw------- 1 root root 0 Jun 4 11:46 .pwd.lock
-rw-r--r-- 1 root root 653 Jun 3 13:46 group
-rw-r--r-- 1 root root 242 Jun 4 11:33 host.conf
-rw-r--r-- 1 root root 857 Jun 4 12:04 hosts
-rw-r--r-- 1 root root 1050 Jun 4 11:29 ld.so.cache
-rw-r--r-- 1 root root 304 Jun 4 11:28 ld.so.conf
-rw-r--r-- 1 root root 235 Jun 4 11:27 ld.so.conf~
-rw-r--r-- 1 root root 88039 Jun 3 13:46 moduli
-rw-r--r-- 1 root root 1342 Jun 4 11:34 nsswitch.conf
drwxr-xr-x 2 root root 4096 Jun 4 12:02 pam.d/
-rw-r--r-- 1 root root 28 Jun 4 12:00 pam_smb.conf
-rw-r--r-- 1 root root 2520 Jun 4 11:57 passwd
-rw-r--r-- 1 root root 7228 Jun 3 13:48 profile
-rw-r--r-- 1 root root 1339 Jun 4 11:33 protocols
-rw-r--r-- 1 root root 274 Jun 4 11:44 resolv.conf
drwxr-xr-x 2 root root 4096 Jun 3 13:43 security/
-rw-r----- 1 root root 1178 Jun 4 11:51 shadow
-rw------- 1 root root 80 Jun 4 11:45 shadow-
-rw-r----- 1 root root 1178 Jun 4 11:48 shadow.old
-rw-r--r-- 1 root root 161 Jun 3 13:46 shells
-rw-r--r-- 1 root root 1144 Jun 3 13:46 ssh_config
-rw------- 1 root root 668 Jun 3 13:46 ssh_host_dsa_key
-rw-r--r-- 1 root root 602 Jun 3 13:46 ssh_host_dsa_key.pub
-rw------- 1 root root 527 Jun 3 13:46 ssh_host_key
-rw-r--r-- 1 root root 331 Jun 3 13:46 ssh_host_key.pub
-rw------- 1 root root 883 Jun 3 13:46 ssh_host_rsa_key
-rw-r--r-- 1 root root 222 Jun 3 13:46 ssh_host_rsa_key.pub
-rw-r--r-- 1 root root 2471 Jun 4 12:15 sshd_config
./etc/pam.d:
total 24
drwxr-xr-x 2 root root 4096 Jun 4 12:02 ./
drwxr-xr-x 4 root root 4096 Jun 4 12:35 ../
lrwxrwxrwx 1 root root 4 Jun 4 12:02 other -> sshd
-rw-r--r-- 1 root root 318 Jun 3 13:46 passwd
-rw-r--r-- 1 root root 546 Jun 4 11:36 ssh
-rw-r--r-- 1 root root 479 Jun 4 12:02 sshd
-rw-r--r-- 1 root root 370 Jun 3 13:46 su
./etc/security:
total 32
drwxr-xr-x 2 root root 4096 Jun 3 13:43 ./
drwxr-xr-x 4 root root 4096 Jun 4 12:35 ../
-rw-r--r-- 1 root root 1971 Jun 3 13:46 access.conf
-rw-r--r-- 1 root root 184 Jun 3 13:46 chroot.conf
-rw-r--r-- 1 root root 2145 Jun 3 13:46 group.conf
-rw-r--r-- 1 root root 1356 Jun 3 13:46 limits.conf
-rw-r--r-- 1 root root 2858 Jun 3 13:46 pam_env.conf
-rw-r--r-- 1 root root 2154 Jun 3 13:46 time.conf
./lib:
total 8316
drwxr-xr-x 3 root root 4096 Jun 4 12:13 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
-rw-r--r-- 1 root root 1024 Jun 4 11:51 cracklib_dict.hwm
-rw-r--r-- 1 root root 214324 Jun 4 11:51 cracklib_dict.pwd
-rw-r--r-- 1 root root 11360 Jun 4 11:51 cracklib_dict.pwi
-rwxr-xr-x 1 root root 342427 Jun 3 13:46 ld-linux.so.2*
-rwxr-xr-x 1 root root 4061504 Jun 3 13:46 libc.so.6*
lrwxrwxrwx 1 root root 15 Jun 4 12:11 libcrack.so -> libcrack.so.2.7*
lrwxrwxrwx 1 root root 15 Jun 4 12:11 libcrack.so.2 -> libcrack.so.2.7*
-rwxr-xr-x 1 root root 33291 Jun 4 11:39 libcrack.so.2.7*
-rwxr-xr-x 1 root root 60988 Jun 3 13:46 libcrypt.so.1*
-rwxr-xr-x 1 root root 71846 Jun 3 13:46 libdl.so.2*
-rwxr-xr-x 1 root root 27762 Jun 3 13:46 libhistory.so.4.0*
lrwxrwxrwx 1 root root 17 Jun 4 12:12 libncurses.so.4 -> libncurses.so.4.2*
-rwxr-xr-x 1 root root 503903 Jun 3 13:46 libncurses.so.4.2*
lrwxrwxrwx 1 root root 17 Jun 4 12:12 libncurses.so.5 -> libncurses.so.5.0*
-rwxr-xr-x 1 root root 549429 Jun 3 13:46 libncurses.so.5.0*
-rwxr-xr-x 1 root root 369801 Jun 3 13:46 libnsl.so.1*
-rwxr-xr-x 1 root root 142563 Jun 4 11:49 libnss_compat.so.1*
-rwxr-xr-x 1 root root 215569 Jun 4 11:49 libnss_compat.so.2*
-rwxr-xr-x 1 root root 61648 Jun 4 11:34 libnss_dns.so.1*
-rwxr-xr-x 1 root root 63453 Jun 4 11:34 libnss_dns.so.2*
-rwxr-xr-x 1 root root 63782 Jun 4 11:34 libnss_dns6.so.2*
-rwxr-xr-x 1 root root 205715 Jun 3 13:46 libnss_files.so.1*
-rwxr-xr-x 1 root root 235932 Jun 3 13:49 libnss_files.so.2*
-rwxr-xr-x 1 root root 204383 Jun 4 11:33 libnss_nis.so.1*
-rwxr-xr-x 1 root root 254023 Jun 4 11:33 libnss_nis.so.2*
-rwxr-xr-x 1 root root 256465 Jun 4 11:33 libnss_nisplus.so.2*
lrwxrwxrwx 1 root root 14 Jun 4 12:12 libpam.so.0 -> libpam.so.0.72*
-rwxr-xr-x 1 root root 31449 Jun 3 13:46 libpam.so.0.72*
lrwxrwxrwx 1 root root 19 Jun 4 12:12 libpam_misc.so.0 ->
libpam_misc.so.0.72*
-rwxr-xr-x 1 root root 8125 Jun 3 13:46 libpam_misc.so.0.72*
lrwxrwxrwx 1 root root 15 Jun 4 12:12 libpamc.so.0 -> libpamc.so.0.72*
-rwxr-xr-x 1 root root 10499 Jun 3 13:46 libpamc.so.0.72*
-rwxr-xr-x 1 root root 176427 Jun 3 13:46 libreadline.so.4.0*
-rwxr-xr-x 1 root root 44729 Jun 3 13:46 libutil.so.1*
-rwxr-xr-x 1 root root 70254 Jun 3 13:46 libz.a*
lrwxrwxrwx 1 root root 13 Jun 4 12:13 libz.so -> libz.so.1.1.3*
lrwxrwxrwx 1 root root 13 Jun 4 12:13 libz.so.1 -> libz.so.1.1.3*
-rwxr-xr-x 1 root root 63312 Jun 3 13:46 libz.so.1.1.3*
drwxr-xr-x 2 root root 4096 Jun 4 12:00 security/
./lib/security:
total 668
drwxr-xr-x 2 root root 4096 Jun 4 12:00 ./
drwxr-xr-x 3 root root 4096 Jun 4 12:13 ../
-rwxr-xr-x 1 root root 10067 Jun 3 13:46 pam_access.so*
-rwxr-xr-x 1 root root 8300 Jun 3 13:46 pam_chroot.so*
-rwxr-xr-x 1 root root 14397 Jun 3 13:46 pam_cracklib.so*
-rwxr-xr-x 1 root root 5082 Jun 3 13:46 pam_deny.so*
-rwxr-xr-x 1 root root 13153 Jun 3 13:46 pam_env.so*
-rwxr-xr-x 1 root root 13371 Jun 3 13:46 pam_filter.so*
-rwxr-xr-x 1 root root 7957 Jun 3 13:46 pam_ftp.so*
-rwxr-xr-x 1 root root 12771 Jun 3 13:46 pam_group.so*
-rwxr-xr-x 1 root root 10174 Jun 3 13:46 pam_issue.so*
-rwxr-xr-x 1 root root 9774 Jun 3 13:46 pam_lastlog.so*
-rwxr-xr-x 1 root root 13591 Jun 3 13:46 pam_limits.so*
-rwxr-xr-x 1 root root 11268 Jun 3 13:46 pam_listfile.so*
-rwxr-xr-x 1 root root 11182 Jun 3 13:46 pam_mail.so*
-rwxr-xr-x 1 root root 5923 Jun 3 13:46 pam_nologin.so*
-rwxr-xr-x 1 root root 5460 Jun 3 13:46 pam_permit.so*
-rwxr-xr-x 1 root root 18226 Jun 3 13:46 pam_pwcheck.so*
-rwxr-xr-x 1 root root 12590 Jun 3 13:46 pam_rhosts_auth.so*
-rwxr-xr-x 1 root root 5551 Jun 3 13:46 pam_rootok.so*
-rwxr-xr-x 1 root root 7239 Jun 3 13:46 pam_securetty.so*
-rwxr-xr-x 1 root root 6551 Jun 3 13:46 pam_shells.so*
-rwxr-xr-x 1 root root 55925 Jun 4 12:00 pam_smb_auth.so*
-rwxr-xr-x 1 root root 12678 Jun 3 13:46 pam_stress.so*
-rwxr-xr-x 1 root root 11170 Jun 3 13:46 pam_tally.so*
-rwxr-xr-x 1 root root 11124 Jun 3 13:46 pam_time.so*
-rwxr-xr-x 1 root root 45703 Jun 3 13:46 pam_unix.so*
-rwxr-xr-x 1 root root 45703 Jun 3 13:46 pam_unix2.so*
-rwxr-xr-x 1 root root 45386 Jun 3 13:46 pam_unix_acct.so*
-rwxr-xr-x 1 root root 45386 Jun 3 13:46 pam_unix_auth.so*
-rwxr-xr-x 1 root root 45386 Jun 3 13:46 pam_unix_passwd.so*
-rwxr-xr-x 1 root root 45386 Jun 3 13:46 pam_unix_session.so*
-rwxr-xr-x 1 root root 9726 Jun 3 13:46 pam_userdb.so*
-rwxr-xr-x 1 root root 6424 Jun 3 13:46 pam_warn.so*
-rwxr-xr-x 1 root root 7460 Jun 3 13:46 pam_wheel.so*
./sbin:
total 3132
drwxr-xr-x 2 root root 4096 Jun 4 12:35 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
-rwxr-xr-x 1 root root 178256 Jun 3 13:46 choptest*
-rwxr-xr-x 1 root root 184032 Jun 3 13:46 cqtest*
-rwxr-xr-x 1 root root 81096 Jun 3 13:46 dialtest*
-rwxr-xr-x 1 root root 1142128 Jun 4 11:28 ldconfig*
-rwxr-xr-x 1 root root 2868 Jun 3 13:46 lockname*
-rwxr-xr-x 1 root root 3340 Jun 3 13:46 ondelay*
-rwxr-xr-x 1 root root 376796 Jun 3 13:46 pagesend*
-rwxr-xr-x 1 root root 13950 Jun 3 13:46 probemodem*
-rwxr-xr-x 1 root root 9234 Jun 3 13:46 recvstats*
-rwxr-xr-x 1 root root 64480 Jun 3 13:46 sftp-server*
-rwxr-xr-x 1 root root 744412 Jun 3 13:46 sshd*
-rwxr-xr-x 1 root root 30750 Jun 4 11:46 su*
-rwxr-xr-x 1 root root 194632 Jun 3 13:46 tagtest*
-rwxr-xr-x 1 root root 69892 Jun 3 13:46 tsitest*
-rwxr-xr-x 1 root root 43792 Jun 3 13:46 typetest*
./tmp:
total 8
drwxr-xr-x 2 root root 4096 Jun 4 12:32 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
./usr:
total 8
drwxr-xr-x 2 root root 4096 Jun 4 12:16 ./
drwxr-xr-x 9 root root 4096 Jun 5 10:05 ../
lrwxrwxrwx 1 root root 7 Jun 4 12:14 bin -> ../bin//
lrwxrwxrwx 1 root root 7 Jun 4 11:33 lib -> ../lib//
lrwxrwxrwx 1 root root 8 Jun 4 12:13 sbin -> ../sbin//

B.7.3. Chroot environment for Apache

B.7.3.1. Introduçao

O utilitário chroot é muitas vezes usado para enjaular um daemon dentro de uma estrutura restrita. Voce pode usá-lo para isolar um serviço do outro, desta forma um problema de segurança em um pacote de software específico não interfere em todo o servidor. A utilização do script makejail torna a configuração e atualização da árvore enjaulada muito mais fácil.

FIXME: Apache também pode ser enjaulado usando http://www.modsecurity.org que está disponível em libapache-mod-security (para Apache 1.x) e libapache2-mod-security (para Apache 2.x).

B.7.3.1.1. Licença

This document is copyright 2002 Alexandre Ratti. It has been dual-licensed and released under the GPL version 2 (GNU General Public License) the GNU-FDL 1.2 (GNU Free Documentation Licence) and is included in this manual with his explicit permission.

B.7.3.2. Instalando o servidor

Este procedimento foi testado no Debian GNU/Linux 3.0 (Woody) com makejail 0.0.4-1 (em Debian/testing).

Efetue o login como root e crie um novo diretório para jaula:
```
$ mkdir -p /var/chroot/apache
```
Crie um novo usuário e novo grupo. O servidor Apache enjaulado irá executar com este usuário/grupo, que não é utilizado para mais nada no sistema. Neste exemplo, ambos usuário e grupo são chamados de chrapach.
```
 
 $ adduser --home /var/chroot/apache --shell /bin/false \
 --no-create-home --system --group chrapach
```
FIXME: é preciso um novo usuário? (Apache já executa como usuário apache)
Instale o Apache normalmente no Debian: apt-get install apache
Configure o Apache (por exemplo defina seus subdomínios e etc.). No arquivo de configuração /etc/apache/httpd.conf, altere as opções Group e User para chrapach. Reinicie o Apache e tenha certeza que o servidor está funcionando corretamente. Agora, pare o daemon do Apache.
Instale o makejail (disponível agora no Debian/testing). Você também deve instalar wget e lynx, pois eles serão usados pelo makejail para testar o servidor enjaulado: apt-get install makejail wget lynx
Copie o arquivo de configuração de exemplo para o Apache para o diretório /etc/makejail:
```
 
 # cp /usr/share/doc/makejail/examples/apache.py /etc/makejail/
```

Edit /etc/makejail/apache.py. You need to change the chroot, users and groups options. To run this version of makejail, you can also add a packages option. See the http://www.floc.net/makejail/current/doc/. A sample is shown here:

chroot="/var/chroot/apache"
testCommandsInsideJail=["/usr/sbin/apachectl start"]
processNames=["apache"]
testCommandsOutsideJail=["wget -r --spider http://localhost/",
                         "lynx --source https://localhost/"]
preserve=["/var/www",
          "/var/log/apache",
          "/dev/log"]
users=["chrapach"]
groups=["chrapach"]
packages=["apache", "apache-common"]
userFiles=["/etc/password",
           "/etc/shadow"]
groupFiles=["/etc/group",
            "/etc/gshadow"]
forceCopy=["/etc/hosts",
           "/etc/mime.types"]

FIXME: algumas opções parecem não funcionar corretamente. Por exemplo, /etc/shadow e /etc/gshadow não são copiados, visto que /etc/password e /etc/group são copiados em vez de serem filtrados.

Crie a árvore da jaula: makejail /etc/makejail/apache.py

Se /etc/password e /etc/group forem copiados completamente, digite:

      $ grep chrapach /etc/passwd > /var/chroot/apache/etc/passwd
      $ grep chrapach /etc/group > /var/chroot/apache/etc/group

para substituí-los com as cópias filtradas.

Copie as páginas e os logs do site Web dentro da jaula. Estes arquivos não são copiados automaticamente (veja a opção preserve no arquivo de configuração do makejail).
```
      # cp -Rp /var/www /var/chroot/apache/var
      # cp -Rp /var/log/apache/*.log /var/chroot/apache/var/log/apache
```
Edite o script de inicialização para que o daemon de logging do sistema também ouça do socket /var/chroot/apache/dev/log. No arquivo /etc/init.d/sysklogd, substitua: SYSLOGD="" com SYSLOGD=" -a /var/chroot/apache/dev/log" e reinicie o daemon (/etc/init.d/sysklogd restart).

Edite o script de inicialização do Apache (/etc/init.d/apache). Você pode precisar fazer algumas alterações no script de inicialização padrão para que ele funcione apropriadamente com a árvore enjaulada. Como:

configure uma nova variável CHRDIR no início do arquivo;
edite as seções start, stop, reload, etc.;
adicione uma linha para montar e desmontar o sistema de arquivo /proc que está dentro da jaula.

#! /bin/bash
#
# apache\tStart the apache HTTP server.
#

CHRDIR=/var/chroot/apache

NAME=apache
PATH=/bin:/usr/bin:/sbin:/usr/sbin
DAEMON=/usr/sbin/apache
SUEXEC=/usr/lib/apache/suexec
PIDFILE=/var/run/$NAME.pid
CONF=/etc/apache/httpd.conf
APACHECTL=/usr/sbin/apachectl 

trap "" 1
export LANG=C
export PATH

test -f $DAEMON || exit 0
test -f $APACHECTL || exit 0

# ensure we don't leak environment vars into apachectl
APACHECTL="env -i LANG=${LANG} PATH=${PATH} chroot $CHRDIR $APACHECTL"

if egrep -q -i "^[[:space:]]*ServerType[[:space:]]+inet" $CONF
then
    exit 0
fi

case "$1" in
  start)
    echo -n "Starting web server: $NAME"
    mount -t proc proc /var/chroot/apache/proc
    start-stop-daemon --start --pidfile $PIDFILE --exec $DAEMON \
\t--chroot $CHRDIR
    ;;

  stop)
    echo -n "Stopping web server: $NAME"
    start-stop-daemon --stop --pidfile "$CHRDIR/$PIDFILE" --oknodo
    umount /var/chroot/apache/proc
    ;;

  reload)
    echo -n "Reloading $NAME configuration"
    start-stop-daemon --stop --pidfile "$CHRDIR/$PIDFILE" \
\t--signal USR1 --startas $DAEMON --chroot $CHRDIR
    ;;

  reload-modules)
    echo -n "Reloading $NAME modules"
    start-stop-daemon --stop --pidfile "$CHRDIR/$PIDFILE" --oknodo \
\t--retry 30
    start-stop-daemon --start --pidfile $PIDFILE \
\t--exec $DAEMON --chroot $CHRDIR
    ;;

  restart)
    $0 reload-modules
    exit $?
    ;;

  force-reload)
    $0 reload-modules
    exit $?
    ;;

  *)
    echo "Usage: /etc/init.d/$NAME {start|stop|reload|reload-modules|force-reload|restart}"
    exit 1
    ;;
esac

if [ $? == 0 ]; then
\techo .
\texit 0
else
\techo failed
\texit 1
fi

FIXME: should the first Apache process be run as another user than root (i.e. add --chuid chrapach:chrapach)? Cons: chrapach will need write access to the logs, which is awkward.

Substitua no /etc/logrotate.d/apache o /var/log/apache/*.log com /var/chroot/apache/var/log/apache/*.log
Inicialize o Apache (/etc/init.d/apache start) e verifique o que está sendo reportado no log da jaula (/var/chroot/apache/var/log/apache/error.log). Se a sua configuração for mais complexa (exemplo: se também utiliza PHP e MySQL), alguns arquivos provavelmente estarão faltando. Se estes arquivos não são copiados automaticamente pelo makejail, você pode listá-los com a opção forceCopy (para copiar os arquivos diretamente) ou packages (para copiar pacotes completos e suas dependências) no arquivo de configuração /etc/makejail/apache.py.

Digite ps aux | grep apache para ter certeza que o Apache está rodando. Você deve ver algo do tipo:

      root 180 0.0 1.1 2936 1436 ? S 04:03 0:00 /usr/sbin/apache
      chrapach 189 0.0 1.1 2960 1456 ? S 04:03 0:00 /usr/sbin/apache
      chrapach 190 0.0 1.1 2960 1456 ? S 04:03 0:00 /usr/sbin/apache
      chrapach 191 0.0 1.1 2960 1456 ? S 04:03 0:00 /usr/sbin/apache
      chrapach 192 0.0 1.1 2960 1456 ? S 04:03 0:00 /usr/sbin/apache
      chrapach 193 0.0 1.1 2960 1456 ? S 04:03 0:00 /usr/sbin/apache

Certifique-se que os processos do Apache estão sendo executados na jaula chroot procurando no sistema de arquivo /proc: ls -la /proc/process_number/root/. onde process_number é um dos PID listados acima (por exemplo: segunda coluna; PID 189). As entradas para a árvore restrita devem ser listadas:
```
    drwxr-sr-x 10 root staff 240 Dec 2 16:06 .
    drwxrwsr-x 4 root staff 72 Dec 2 08:07 ..
    drwxr-xr-x 2 root root 144 Dec 2 16:05 bin
    drwxr-xr-x 2 root root 120 Dec 3 04:03 dev
    drwxr-xr-x 5 root root 408 Dec 3 04:03 etc
    drwxr-xr-x 2 root root 800 Dec 2 16:06 lib
    dr-xr-xr-x 43 root root 0 Dec 3 05:03 proc
    drwxr-xr-x 2 root root 48 Dec 2 16:06 sbin
    drwxr-xr-x 6 root root 144 Dec 2 16:04 usr
    drwxr-xr-x 7 root root 168 Dec 2 16:06 var
```
Para automatizar este teste, você pode digitar:ls -la /proc/`cat /var/chroot/apache/var/run/apache.pid`/root/.
FIXME: Add other tests that can be run to make sure the jail is closed?

A razão pela qual eu gosto disso é que a configuração da jaula não é tão complicada e o servidor pode ser atualizado em somente duas linhas:

 
apt-get update && apt-get install apache
makejail /etc/makejail/apache.py

B.7.4. Veja também

If you are looking for more information you can consider these sources of information in which the information presented is based: http://www.floc.net/makejail/, this program was written by Alain Tesio

^[78] You can use the debug option to have it send the progress of the module to the authpriv.notice facility

^[79] You can create a very limited bash environment with the following python definition for makejail, just create the directory /var/chroots/users/foo and a file with the following contents and call it bash.py:

chroot="/var/chroots/users/foo"
cleanJailFirst=1
testCommandsInsideJail=["bash ls"]

And then run makejail bash.py to create the user environment at /var/chroots/users/foo. To test the environment run:

# chroot /var/chroots/users/foo/ ls
bin  dev  etc  lib  proc  sbin  usr

^[80] In some occasions you might need the /dev/ptmx and /dev/pty* devices and the /dev/pts/ subdirectory. Running MAKEDEV in the /dev directory of the chrooted environment should be sufficient to create them if they do not exist. If you are using kernels (version 2.6) which dynamically create device files you will need to create the /dev/pts/ files yourself and grant them the proper privileges.

^[81] If you are using a kernel that implements Mandatory Access Control (RSBAC/SElinux) you can avoid changing this configuration just by granting the sshd user privileges to make the chroot() system call.

^[82] Observe que não existem arquivos SETUID. Isso torna mais difícil para usuários remotos fugir o ambiente chroot. Entretanto, isso também previne que os usuários alterem suas senhas, já que o programa passwd não pode modificar os arquivos /etc/passwd ou /etc/shadow.