Much has been written on SELinux, and a lot of it seems confusing. It's buzzword heavy, involves locking your computer up, has a strange new set of permissions that are obscure in architecture and silently fails where things used to just work. Why use it? Well, for most people, it's not actually that hard to understand. In this talk, Paul Wayper talks about how to make sense of what SELinux does, and how to keep it out of the way and get on with using your computer. In the process Paul will deal with the background to SELinux, what it's main aims are, and why you really do want it turned on.

1. SELinux for everyday users

2. SELinux Don't be afraid!

5. Mandatory Access Control

7. Mandatory Access Control

10. Mandatory Access Control

11. Infested with jargon

13. Applications stop working

14. Can't make it stop

17. Uses Debian

19. Uses Debian

20. Not an everyday user!

21. SELinux Don't be afraid!

27. Fedora since Core 2 (2004)

28. RHEL since version 4 (2005)

30. Fedora since Core 2 (2004)

31. RHEL since version 4 (2005)

32. Debian since Etch (2007)

33. Ubuntu since Hardy Heron 8.04 (2008)

34. SELinux How does it work?

37. Packaged security policy

39. Packaged security policy

40. Checks database of rules on syscalls

42. Packaged security policy

43. Checks database of rules on syscalls

44. Allows or denies based on policy

45. SELinux What does it really do?

49. Policies limit what a daemon can access and how.

51. Policies limit what a daemon can access and how.

52. Prevents daemon compromise affecting other files.

54. Policies limit what a daemon can access and how.

55. Prevents daemon compromise affecting other files / users / ports / etc.

57. User processes are unaffected

62. Firefox still gets to crash your system

65. Firefox still gets to crash your system

66. New policy being written to help that

70. A file has a context

76. netstat -Z

77. ps -Z

79. netstat -Z tcp 0 0 tachyon:54421 upload.pmtpa.wikimedia:http ESTABLISHED 4243/firefox unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcp 1 0 tachyon.tangram.dnsal:46882 media:daap CLOSE_WAIT 1837/rhythmbox unconfined_r:unconfined_execmem_t:s0-s0:c0.c1023

80. ps -Z LABEL PID TTY TIME CMD unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 5950 pts/1 00:00:00 bash unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 6293 pts/1 00:00:00 ps

82. netstat -Z tcp 0 0 tachyon:54421 upload.pmtpa.wikimedia:http ESTABLISHED 4243/firefox unconfined_u:unconfined_r: unconfined_t :s0-s0:c0.c1023 tcp 1 0 tachyon.tangram.dnsal:46882 media:daap CLOSE_WAIT 1837/rhythmbox unconfined_r: unconfined_execmem_t :s0-s0:c0.c1023

83. ps -Z LABEL PID TTY TIME CMD unconfined_u:unconfined_r: unconfined_t :s0-s0:c0.c1023 5950 pts/1 00:00:00 bash unconfined_u:unconfined_r: unconfined_t :s0-s0:c0.c1023 6293 pts/1 00:00:00 ps

84. The type_t is the only thing you need look at

90. Looks up the database of rules and finds the correct context for that file

91. SELinux – how do I use it? [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:etc_t:s0 /etc/group

92. SELinux – how do I use it? [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:etc_t:s0 /etc/group [root@tachyon ~]# cp /etc/group /tmp [root@tachyon ~]# mv /tmp/group /etc [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:user_tmp_t:s0 /etc/group

93. SELinux – how do I use it? [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:etc_t:s0 /etc/group [root@tachyon ~]# cp /etc/group /tmp [root@tachyon ~]# mv /tmp/group /etc [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:user_tmp_t:s0 /etc/group [root@tachyon ~]# restorecon -R -v /etc/group restorecon reset /etc/group context system_u:object_r:user_tmp_t:s0->system_u:object_r:etc_t:s0 [root@tachyon ~]# ls -Z /etc/group -rw-r--r-- root root system_u:object_r:etc_t:s0 /etc/group

107. 2: getsebool and setsebool

109. netstat -Z

112. netstat -Z

114. SELinux – how do I see it? [root@tachyon ~]# tail -4 /var/log/audit/audit.log

115. SELinux – how do I see it? [root@tachyon ~]# tail -4 /var/log/audit/audit.log type=AVC msg=audit(1219408121.814:62): avc: denied { read } for pid=2184 comm="hald" name="group" dev=dm-0 ino=460208 scontext=system_u:system_r:hald_t:s0 tcontext=system_u:object_r:user_tmp_t:s0 tclass=file type=SYSCALL msg=audit(1219408121.814:62): arch=40000003 syscall=5 success=no exit=-13 a0=119f2d a1=80000 a2=1b6 a3=80000 items=0 ppid=1 pid=2184 auid=4294967295 uid=68 gid=68 euid=68 suid=68 fsuid=68 egid=68 sgid=68 fsgid=68 tty=(none) ses=4294967295 comm="hald" exe="/usr/sbin/hald" subj=system_u:system_r:hald_t:s0 key=(null) type=AVC msg=audit(1219408127.814:63): avc: denied { read } for pid=2184 comm="hald" name="group" dev=dm-0 ino=460208 scontext=system_u:system_r:hald_t:s0 tcontext=system_u:object_r:user_tmp_t:s0 tclass=file type=SYSCALL msg=audit(1219408127.814:63): arch=40000003 syscall=5 success=no exit=-13 a0=119f2d a1=80000 a2=1b6 a3=80000 items=0 ppid=1 pid=2184 auid=4294967295 uid=68 gid=68 euid=68 suid=68 fsuid=68 egid=68 sgid=68 fsgid=68 tty=(none) ses=4294967295 comm="hald" exe="/usr/sbin/hald" subj=system_u:system_r:hald_t:s0 key=(null)

116. SELinux – how do I use it? [root@tachyon ~]# grep hald /var/log/audit/audit.log | audit2why type=AVC msg=audit(1219408127.814:63): avc: denied { read } for pid=2184 comm="hald" name="group" dev=dm-0 ino=460208 scontext=system_u:system_r:hald_t:s0 tcontext=system_u:object_r:user_tmp_t:s0 tclass=file Was caused by: Missing type enforcement (TE) allow rule. You can use audit2allow to generate a loadable module to allow this access.

118. 2: getsebool and setsebool

119. 3: audit2why or audit2allow

121. 2: getsebool and setsebool

124. 2: getsebool and setsebool

126. Questions?