adelton

Confining Spacewalk with SELinux

Jan Pazdziora

Principal Software Engineer
Satellite Engineering, Red Hat
Developer Conference 2011
12th February 2011
Brno, Czech Republic

Copyright © 2011 Jan Pazdziora

This text is also available as slides in PDF format. See also a newer version of the talk.

What is Spacewalk?

  • System management system, with WebUI and XMLRPC API.

  • The project is the upstream for Red Hat Network Satellite product (and SuSE Manager).

  • Written in Java, Python, and Perl.

  • Daemons running are tomcat, httpd with mod_perl and mod_python/mod_wsgi, monitoring, cobbler, database, jabberd, osa-dispatcher.

  • 700+ thousand lines of code.

  • http://spacewalk.redhat.com/

  • https://fedorahosted.org/spacewalk/

What is SELinux?

  • Another access control mechanism.

  • Orthogonal to Un*x users, groups, and access rights.

    • You can have Unix user adelton run process as unconfined_t.

    • You can have root's process run as httpd_t.

  • We use targeted policy, so we only care about types.

  • What is not explicitly allowed is denied.

The goal

  • All daemons should run in their domains or just use domains native in the OS.

    • httpd_t

    • java_t

    • spacewalk_monitoring_t (swmon_t)

    • oracle_db_t

    • osa_dispatcher_t

  • And there should be no AVC denials.

    • Yes, we will see one in a minute.

  • You get to love Z. You get to love iterative work.

Make things run in their domains

policy_module(swmon,1.0)

type swmon_t;
domain_type(swmon_t);
type swmon_exec_t;
files_type(swmon_exec_t);

init_daemon_domain(swmon_t, swmon_exec_t)

/etc/rc\.d/np\.d/step                             ⏎
  gen_context(system_u:object_r:swmon_exec_t,s0)

Check the transition

# cp /bin/sleep .
# chcon -t swmon_exec_t sleep
# cat init.sh 
#!/bin/bash
./sleep 10 &
ps --no-headers -Zp $! | awk '{print $1}'
# chmod a+x init.sh
# chcon -t initrc_exec_t init.sh
# ./init.sh 
unconfined_u:system_r:swmon_t:s0
#

Make it possible to restart

require {
    type java_t;
    type initrc_t;
}
 
type sw_initrc_exec_t;
domain_entry_file(initrc_t, sw_initrc_exec_t)
domain_auto_trans(java_t, sw_initrc_exec_t,       ⏎
                                          initrc_t)

/sbin/rhn-sat-restart-silent                      ⏎
  gen_context(system_u:object_r:sw_initrc_exec_t,s0)

Oracle RDBMS

  • Source not available.

  • Prime target for confining.

  • Oracle SELinux policy module written by Rob Myers.

  • We ended up splitting the file contexts .fc to separate module:

    # semodule -l | grep oracle
oracle-nofcontext	1.1.2
oracle-port	1.1.2
oracle-xe	10.2.0.19.1

AVC denial

  • In /var/log/audit/audit.log

avc:  denied  { append } for  pid=3941
comm="httpd"
path="/var/log/rhn/rhn-installation.log"
dev=dm-0 ino=774447
scontext=root:system_r:httpd_t:s0
tcontext=root:object_r:var_log_t:s0
tclass=file

Addressing AVC denials

  • Not always is the solution to allow.

  • Only run audit2allow to get nicer overview:

    allow httpd_t var_log_t:file { ioctl append };

  • Even audit2allow -R might not be correct:

    logging_write_generic_logs(httpd_t)

  • Often it's correct that SELinux stopped us from doing what we shouldn't have done.

  • Maybe there is already a boolean for our problem:

    getsebool -a | grep http

Tackle them one by one

  • New types might be needed for files:

    require {
 type httpd_t;
}
type sw_install_log_t;
logging_log_file(sw_install_log_t)
allow httpd_t sw_install_log_t:file {append ioctl};

    /var/log/rhn/rhn-installation\.log             ⏎
  gen_context(system_u:object_r:sw_install_log_t,s0)

  • Do not forget to restorecon:

    # The following is simply a touch
local *X;
open X, '>', INSTALL_LOG_FILE and close X;
system('/sbin/restorecon', INSTALL_LOG_FILE);

More AVC examples

Script in /etc

avc:  denied  { execute } for  pid=6322
comm="httpd" name="satidmap.pl"
dev=dm-0 ino=742377
scontext=root:system_r:httpd_t:s0
tcontext=root:object_r:etc_t:s0 tclass=file

Connect to port

avc:  denied  { name_connect } for  pid=5587
comm="httpd" dest=1521
scontext=root:system_r:httpd_t:s0
tcontext=system_u:object_r:oracle_port_t:s0
tclass=tcp_socket

Restart Spacewalk via WebUI

avc:  denied  { read } for  pid=9882
comm="httpd" path="pipe:[30334]" dev=pipefs ino=30334
scontext=root:system_r:httpd_t:s0
tcontext=root:system_r:java_t:s0
tclass=fifo_file

Sendmail run to send error mail

avc:  denied  { read } for  pid=9737
comm="sendmail"
path="/var/log/rhn/rhn_upload_package_push.log"
dev=dm-0 ino=516406
scontext=root:system_r:system_mail_t:s0
tcontext=root:object_r:spacewalk_httpd_log_t:s0
tclass=file

A daemon wants to read /proc/meminfo

avc:  denied  { read } for  pid=15987
comm="jabberd" name="meminfo" dev=proc
ino=-268435454 scontext=root:system_r:jabberd_t:s0
tcontext=system_u:object_r:proc_t:s0 tclass=file

Process cannot read its own pid file

avc:  denied  { read } for  pid=3169
comm="osa-dispatcher" name="osa-dispatcher.pid"
dev=dm-0 ino=516358
scontext=unconfined_u:system_r:osa_dispatcher_t:s0
tcontext=unconfined_u:object_r:osa_dispatcher_var_run_t:s0
tclass=file

Daemon wants to connect to the PostgreSQL database

avc:  denied  { write } for  pid=28271
comm="osa-dispatcher" name=".s.PGSQL.5432"
dev=dm-0 ino=28622
scontext=unconfined_u:system_r:osa_dispatcher_t:s0
tcontext=unconfined_u:object_r:postgresql_tmp_t:s0
tclass=sock_file
avc:  denied  { connectto } for  pid=28271
comm="osa-dispatcher" path="/tmp/.s.PGSQL.5432"
scontext=unconfined_u:system_r:osa_dispatcher_t:s0
tcontext=unconfined_u:system_r:postgresql_t:s0
tclass=unix_stream_socket

Possible solutions

Script in /etc

Mark is as CGI script:

/etc/rhn/satellite-httpd/conf/satidmap\.pl     ⏎
  gen_context(system_u:object_r:httpd_sys_script_exec_t,s0)

restorecon -vv /etc/rhn/satellite-httpd/conf/satidmap.pl
setsebool -P httpd_enable_cgi 1

Connect to port

Just allow it:

allow httpd_t oracle_port_t:tcp_socket name_connect;

But also consider putting it to a boolean.


Restart Spacewalk via WebUI

-/sbin/rhn-satellite restart &> /dev/null
+/sbin/rhn-satellite restart &> /dev/null < /dev/null

Do not give it the stdin filehandle.


Sendmail run to send error mail

Close the filehandle on exec:

+def set_close_on_exec(fd):
+    s = fcntl.fcntl(fd, fcntl.F_GETFD)
+    fcntl.fcntl(fd, fcntl.F_SETFD, \
+                         s | fcntl.FD_CLOEXEC)
[...] 
             self.fd = open(self.file, "a+", 1)
+            set_close_on_exec(self.fd)

A daemon wants to read /proc/meminfo

Just allow it, with a macro:

kernel_read_system_state(jabberd_t)

Process cannot read its own pid file

It does not need to read it:

- fd = os.open(pid_file, \
-                  os.O_RDWR | os.O_CREAT, 0644)
+ fd = os.open(pid_file, \
+   os.O_WRONLY| os.O_APPEND | os.O_CREAT, 0644)

Daemon wants to connect to the PostgreSQL database

Allow, with nice macro:

postgresql_stream_connect(osa_dispatcher_t)

Closing remarks

  • https://fedorahosted.org/spacewalk/wiki/Features/SELinux

  • We put the exact AVC denial to commit message which addresses the problem in Spacewalk git repo.

    • For our reference.

    • It also makes it easy for you to search through our fixes.

    • Comments and patches most welcome.

  • Thank you for your attention.