danwalsh

Hi Dan,

To be very precise I'm working on: Scientific Linux SL release 5.1(2.6.18-53.1.4.el5), I think SELinux implementation in this release is equivalent to FC9 (In earlier post I mistyped FC9 as FC5, apology for that...)

I'm running SELinux STRICT policy in enforcing mode. Semanage command output is as follows:-

[root@xyz ~]# semanage login -l

Login Name SELinux User MLS/MCS Range

__default__ user_u s0
admin staff_u s0
root root s0-s0:c0.c1023
system_u system_u s0-s0:c0.c1023


[root@xyz ~]# semanage user -l

Labeling MLS/ MLS/
SELinux User Prefix MCS Level MCS Range SELinux Roles

root sysadm s0 s0-s0:c0.c1023 system_r sysadm_r staff_r
staff_u staff s0 s0-s0:c0.c1023 staff_r
sysadm_u sysadm s0 s0-s0:c0.c1023 sysadm_r
system_u user s0 s0-s0:c0.c1023 system_r
user_u user s0 s0 user_r

I've put 'admin' user in sudoers list and allowed him to reboot, shutdown the machine.

OK when I start executing the command "sudo /sbin/reboot" I got lot of avc's. When I used audit2allow utility on these messages I got following "type-enforcement" file :-

module test 1.0;

require {
type staff_t;
type root_t;
type sysadm_home_t;
type staff_devpts_t;
type init_exec_t;
type var_run_t;
type pam_var_run_t;
type kernel_t;
type pam_var_run_t;
type sysadm_devpts_t;
type initctl_t;
class system syslog_mod;
class chr_file { relabelfrom relabelto setattr };
class capability { setuid sys_resource dac_override };
class fifo_file write;
class key search;
class file { rename setattr read create execute_no_trans execute write relabelfrom getattr relabelto unlink append };
class dir { read write search getattr setattr remove_name add_name };
}

#============= staff_t ==============
allow staff_t init_exec_t:file { read execute_no_trans execute };
allow staff_t initctl_t:fifo_file write;
allow staff_t kernel_t:key search;
allow staff_t kernel_t:system syslog_mod;
allow staff_t pam_var_run_t:dir { write setattr };
allow staff_t root_t:dir { write add_name };
allow staff_t root_t:file { read write create };
allow staff_t self:capability { setuid sys_resource dac_override };
allow staff_t staff_devpts_t:chr_file relabelfrom;
allow staff_t sysadm_devpts_t:chr_file relabelto;
allow staff_t sysadm_home_t:file { read write append };
allow staff_t var_run_t:dir { write remove_name add_name };
allow staff_t var_run_t:file { write read create unlink };
allow staff_t pam_var_run_t:dir { write remove_name add_name search getattr };
allow staff_t pam_var_run_t:file { write read create unlink };

On loading this file as policy using semodule, I'm able to reboot the machine from admin account. Now the question is: Is the above mentioned 'allow' rules cause some kind of security threat/flaw??? as lot of things are now allowed for "staff_t" type...for example: allow staff_t root_t:dir { write add_name };

How to make sure that user 'admin' in 'staff_r' role is not going to harm my machine in any way???

Your help will be highly appreciated.

Thanks in advance.

Well there is no Strict policy as of Fedora 9, If you are using confined users:
Why not setup sudo with a rule for the reboot command that has this access rather then adding all of these privs to staff_t

admin ALL=(ALL) TYPE=unconfined_t ROLE=unconfined_r /sbin/reboot
or
admin ALL=(ALL) TYPE=sysadm_t ROLE=sysadm_r /sbin/reboot

This way you are relying on sudo as the only mechanism for getting access to those privs.

From a minimum security point of view you could design a user admin role whose only privs is the ability to reboot. reboot_t and reboot_r.

If you do any of the above you will also need to modify the staff_u user to include the role required for transition

semanage user -m -R"staff_r sysadm_r" staff_u for example

Or create a new user admin_u

# semanage user -m -P user -R"staff_r sysadm_r" -rs0-s0:c0.c1023 admin_u
# semanage login -m -s admin_u admin

Hi Dan,

I've created admin_u selinux user, with staff_r and sysadm_r roles assigned:

[root@xyz ~]# semanage login -l

Login Name SELinux User MLS/MCS Range

__default__ user_u s0
admin admin_u s0
root root s0-s0:c0.c1023
system_u system_u s0-s0:c0.c1023


[root@xyz ~]# semanage user -l

Labeling MLS/ MLS/
SELinux User Prefix MCS Level MCS Range SELinux Roles

admin_u staff s0 s0-s0:c0.c1023 sysadm_r staff_r
root sysadm s0 s0-s0:c0.c1023 system_r sysadm_r staff_r
staff_u staff s0 s0-s0:c0.c1023 staff_r
sysadm_u sysadm s0 s0-s0:c0.c1023 sysadm_r
system_u user s0 s0-s0:c0.c1023 system_r
user_u user s0 s0 user_r


I've set up sudoers as follows for admin user:-

ADMIN ALL=(ALL) TYPE=sysadm_t ROLE=sysadm_r /sbin/reboot


Now when I issue reboot command:-

[admin@xyz ~]$ id -Z
admin_u:staff_r:staff_t:s0
[admin@xyz ~]$ sudo /sbin/reboot

A lot of avc message were generated. When I used audit2allow utility on these messages I got following "type-enforcement" file :-

module test 1.0;

require {
type sysadm_t;
type staff_t;
type sysadm_devpts_t;
type staff_devpts_t;
type staff_tty_device_t;
type tty_device_t;
type sysadm_tty_device_t;
type pam_var_run_t;
type usr_t;
type proc_t;
type kernel_t;
class process { siginh transition setexec noatsecure rlimitinh };
class capability { setuid sys_resource dac_override };
class key search;
class chr_file { relabelfrom relabelto getattr write };
class file { read getattr write create entrypoint unlink execute execute_no_trans };
class dir { write remove_name add_name search getattr };
}

#============= staff_t ==============
allow staff_t kernel_t:key search;
allow staff_t self:capability { setuid sys_resource dac_override };
allow staff_t staff_tty_device_t:chr_file { relabelfrom relabelto };
allow staff_t tty_device_t:chr_file { write getattr };
allow staff_t sysadm_tty_device_t:chr_file { relabelto relabelfrom getattr };
allow staff_t staff_devpts_t:chr_file { relabelto relabelfrom };
allow staff_t sysadm_devpts_t:chr_file { relabelto relabelfrom};
allow staff_t pam_var_run_t:dir { write remove_name add_name search getattr };
allow staff_t pam_var_run_t:file { write read create unlink };
allow staff_t self:process setexec;
allow staff_t sysadm_t:process { siginh rlimitinh transition noatsecure };

#============= sysadm_t ==============
allow sysadm_t sysadm_devpts_t:chr_file { relabelto relabelfrom };
allow sysadm_t usr_t:file { entrypoint execute execute_no_trans } ;


Still admin user is not able to reboot the machine. Following avc message keeps on coming:-

Aug 13 14:39:55 xyz kernel: audit(1218618595.898:5): avc: denied { transition } for pid=2058 comm="sudo" path="/usr/local/libexec/sesh" dev=hda9 ino=96888 scontext=admin_u:staff_r:staff_t:s0 tcontext=admin_u:sysadm_r:sysadm_t:s0 tclass=process


This avc is translated into :-

allow staff_t sysadm_t:process transition;

I've already allowed this in last line of "staff_t" rules in .te file above.

Is there something I'm missing???


Thanks,Regards

I think you have a problem in your policy. I tried what you explained above on Fedora 9 and it worked fine.

I think you might be getting a constraint violation

Run the transition rule through audit2why and I think you will see what the problem is.

Fedora has these calls in it
userdom_role_change_template(staff, sysadm)
userdom_dontaudit_use_sysadm_terms(staff_t)

Added following lines to my .te file :
userdom_role_change_template(staff, sysadm)
userdom_dontaudit_use_sysadm_terms(staff_t)

But when tried to make module, got following error:

[root@xyz ~]# checkmodule -M -m test.te -o test.mod
checkmodule: loading policy configuration from test.te
(unknown source)::ERROR 'syntax error' at token 'userdom_role_change_template' on line 42:
userdom_role_change_template(staff, sysadm)

checkmodule: error(s) encountered while parsing configuration

[root@xyz ~]# checkmodule -V
Module versions 4-6

I think checkmodule policy compiler is not recognizing "userdom_role_change_template".


any ideas why????

You don't have the interface defined.

template(`userdom_role_change_template',`
gen_require(`
role $1_r, $2_r;
type $1_t, $2_t;
type $1_devpts_t, $2_devpts_t;
type $1_tty_device_t, $2_tty_device_t;
')

allow $1_r $2_r;
type_change $2_t $1_devpts_t:chr_file $2_devpts_t;
type_change $2_t $1_tty_device_t:chr_file $2_tty_device_t;
# avoid annoying messages on terminal hangup
dontaudit $1_t { $2_devpts_t $2_tty_device_t }:chr_file ioctl;
')

Aug 13 14:39:55 xyz kernel: audit(1218618595.898:5): avc: denied { transition } for pid=2058 comm="sudo" path="/usr/local/libexec/sesh" dev=hda9 ino=96888 scontext=admin_u:staff_r:staff_t:s0 tcontext=admin_u:sysadm_r:sysadm_t:s0 tclass=process

audit2why on above avc gives:-

Was caused by:
Constraint violation.
Check policy/constraints.
Typically, you just need to add a type attribute to the domain to satisfy the constraint.


With correct interface file defined I added

userdom_role_change_template(staff, sysadm)
userdom_dontaudit_use_sysadm_terms(staff_t)

to my .te file and loaded the resultant policy.

Still I don't have any success... When I issue "sudo /sbin/reboot" as admin user, the terminal logout happens..(but no reboot!)

Are you seeing an additional AVC? Do you see anything in the log files?

Hi Dan,

The same avc is still coming: -

Aug 18 15:56:34 xyz kernel: audit(1219055194.331:6): avc: denied { transition } for pid=2128 comm="sudo" path="/usr/local/libexec/sesh" dev=hda9 ino=96888 scontext=admin_u:staff_r:staff_t:s0 tcontext=admin_u:sysadm_r:sysadm_t:s0 tclass=process

I'm wondering why the following type-enforcement rule is still not working????

allow staff_t sysadm_t:process { siginh rlimitinh transition noatsecure };

Well there is something wrong with your policy.

I just setup everything you are describing in Fedora 10 and it worked correctly.

I created an admin_u account.

# semanage user -a -R"staff_r sysadm_r" admin_u
# useradd -Z admin_u admin
# cp /etc/selinux/context/users/staff_u /etc/selinux/contexts/users/admin_u
# visudo
admin ALL=(ALL) ROLE=sysadm_r TYPE=sysadm_t ALL

Login as admin
> id -Z
admin_u:staff_r:staff_t:s0
> sudo sh
[sudo] password for admin:
# id -Z
admin_u:sysadm_r:sysadm_t:s0

I would look at your definition of sysadm and see if it is missing some attribute. It might not see sysadm_t as a domain?

Since this is not a RHEL or Fedora policy please bring up discussion on the NSA list