Hello everyone, and thank you in advance for any help or information that you can offer me.
I'm configuring a server to run Postfix and Mailman for our development team's test environment. I've installed and configured Apache and Mailman, having no problems with either program. In addition to DISA STIGS, I'm trying to implement some best practices and make better use of the security that SELinux can provide.
My first, and more general question, is can a process started by a user mapped to staff_u could potentially run into any undesirable AVCs?
I've mapped all server administrators to the staff_u SELinux user:
root@DOMAIN-mailman01 in /root >> semanage login -l | grep -i admins
%DOMAIN-LinuxAdmins staff_u s0-s0:c0.c1023
These users are allowed to transition to unconfined_t via sudo:
root@DOMAIN-mailman01 in /home/jyoung_sa >> cat /etc/sudoers.d/linuxadmins
%DOMAIN-LinuxAdmins ALL=(ALL) ROLE=unconfined_r TYPE=unconfined_t ALL
Using "# service $NAME stop|start|restart" as a user in this group, if I perform an action on, let's say auditd, I notice that the service gets started with my user context and not as system_u as I would expect. Am I correct in thinking that since the staff_u SELinux user has the same roles (unconfined_r and system_r) as the system_u user, that this is a non-issue, and the service should perform as normal?
root@DOMAIN-mailman01 in /home/jyoung_sa >> ps auxZ | grep auditd$
staff_u:system_r:auditd_t:s0 root 1830 0.0 0.0 31892 888 ? S<sl 10:12 0:00 auditd
My second question is more specific to Mailman and Apache. I've toggled many of the unnecessary SELinux booleans to off, and am able to view the Apache welcome page with the following being true:
root@DOMAIN-mailman01 in /home/jyoung_sa >> rpm -qa | grep selinux
libselinux-2.0.94-5.3.el6_4.1.x86_64
libselinux-python-2.0.94-5.3.el6_4.1.x86_64
libselinux-utils-2.0.94-5.3.el6_4.1.x86_64
selinux-policy-3.7.19-231.el6_5.1.noarch
selinux-policy-targeted-3.7.19-231.el6_5.1.noarch
root@DOMAIN-mailman01 in /home/jyoung_sa >> sestatus
SELinux status: enabled
SELinuxfs mount: /selinux
Current mode: enforcing
Mode from config file: enforcing
Policy version: 24
Policy from config file: targeted
root@DOMAIN-mailman01 in /home/jyoung_sa >> semanage boolean -l | grep "(on"
allow_staff_exec_content (on , on) allow_staff_exec_content
unconfined_login (on , on) Allow a user to login as an unconfined domain
allow_postfix_local_write_mail_spool (on , on) Allow postfix_local domain full write access to mail_spool directories
init_upstart (on , on) Enable support for upstart as the init program.
allow_kerberos (on , on) Allow confined applications to run with kerberos.
allow_domain_fd_use (on , on) Allow all domains to use other domains file descriptors
When attempting to visit the mailman webpage, however, I would get a 500 error from Apache, producing this AVC in the audit log:
root@DOMAIN-mailman01 in /home/jyoung_sa >> ausearch -m avc -ts recent
----
time->Fri Aug 1 10:03:50 2014
node=DOMAIN-mailman01 type=PATH msg=audit(1406905430.337:1109): item=0 name="/usr/lib/mailman/cgi-bin/listinfo" inode=268184 dev=fd:00 mode=0102755 ouid=0 ogid=41 rdev=00:00 obj=system_u:object_r:lib_t:s0 nametype=NORMAL
node=DOMAIN-mailman01 type=CWD msg=audit(1406905430.337:1109): cwd="/usr/lib/mailman/cgi-bin"
node=DOMAIN-mailman01 type=SYSCALL msg=audit(1406905430.337:1109): arch=c000003e syscall=59 success=no exit=-13 a0=7f9d3732c920 a1=7f9d3732dd98 a2=7f9d3732ddb0 a3=7fffbecc4860 items=1 ppid=1595 pid=1777 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm="httpd" exe="/usr/sbin/httpd" subj=system_u:system_r:httpd_t:s0 key=(null)
node=DOMAIN-mailman01 type=AVC msg=audit(1406905430.337:1109): avc: denied { execute_no_trans } for pid=1777 comm="httpd" path="/usr/lib/mailman/cgi-bin/listinfo" dev=dm-0 ino=268184 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:lib_t:s0 tclass=file
audit2allow generates this module for me:
module mailman 1.0;
require {
type var_log_t;
type lib_t;
type httpd_t;
class file { read execute_no_trans };
}
#============= httpd_t ==============
allow httpd_t lib_t:file execute_no_trans;
allow httpd_t var_log_t:file read;
I tried using "# chcon -t bin_t /usr/lib/mailman/cgi-bin/*" to test, and I got a different denial message:
----
time->Fri Aug 1 10:27:23 2014
node=ues-mailman01 type=PATH msg=audit(1406906843.430:2887): item=1 name=(null) inode=2097286 dev=fd:02 mode=0100664 ouid=41 ogid=41 rdev=00:00 obj=system_u:object_r:var_log_t:s0 nametype=NORMAL
node=ues-mailman01 type=PATH msg=audit(1406906843.430:2887): item=0 name="/var/log/mailman/" inode=2097282 dev=fd:02 mode=042775 ouid=0 ogid=41 rdev=00:00 obj=system_u:object_r:var_log_t:s0 nametype=PARENT
node=ues-mailman01 type=CWD msg=audit(1406906843.430:2887): cwd="/usr/lib/mailman/cgi-bin"
node=ues-mailman01 type=SYSCALL msg=audit(1406906843.430:2887): arch=c000003e syscall=2 success=no exit=-13 a0=7204f0 a1=442 a2=1b6 a3=0 items=2 ppid=1731 pid=1901 auid=4294967295 uid=48 gid=41 euid=48 suid=48 fsuid=48 egid=41 sgid=41 fsgid=41 tty=(none) ses=4294967295 comm="python" exe="/usr/bin/python" subj=system_u:system_r:httpd_t:s0 key=(null)
node=ues-mailman01 type=AVC msg=audit(1406906843.430:2887): avc: denied { read } for pid=1901 comm="python" name="error" dev=dm-2 ino=2097286 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:var_log_t:s0 tclass=file
Because this is a development environment and is not affecting production, I'm not terribly concerned with installing the module. If I'm instructed to perform the same configuration to our production servers, though, the SELinux module would require Federal approval.
Can I have someone's opinion about this module? Is this required, or could I change the context of the files stored in /usr/lib/mailman/cgi-bin to something that Apache is allowed to use? Have I turned off too many booleans that could have prevented this?
Thank you!
--
Jeremy Young, M.S., RHCSA
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