Hi all,
Quick question is:
In the targeted policy should init run SystemHigh as it does in the mls policy?
The background:
We're setting up a targeted system where we confine all users and remove the unconfined policy module, but we also enable polyinstantiation of /tmp and /var/tmp.
If we ssh in as a staff_u user phil and elevate to root/sysadm_r then we have a context of:
staff_u:sysadm_r:sysadm_t:s0-s0:c0.c1023
And therefore /var/tmp is:
drwxrwxrwt. root root system_u:object_r:tmp_t:s0-s0:c0.c1023 /var/tmp
Which is really:
drwxrwxrwt. root root system_u:object_r:tmp_t:s0-s0:c0.c1023 /var/tmp-inst/system_u:object_r:tmp_t:s0-s0:c0.c1023_phil
The real /var/tmp is:
drwxrwxrwt. root root system_u:object_r:tmp_t:s0 /var/tmp
Now if we use run_init to update an RPM that contains a post install script, rpm can't create the temporary script file:
# run_init bash -c 'rpm -i --force /root/libselinux-2.0.94-7.el6.x86_64.rpm'
Authenticating phil.
Password:
error: error creating temporary file /var/tmp/rpm-tmp.atkHTf: Permission denied
error: Couldn't create temporary file for %post(libselinux-2.0.94-7.el6.x86_64): Permission denied
Note: you need to use run_init as the rpm might restart a service, e.g. the sssd rpm.
We've traced this to the /etc/selinux/targeted/contexts/initrc_context file which contains:
system_u:system_r:initrc_t:s0
So we transition to initrc_t and then to rpm_t without any categories, but because the polyinstantiated /var/tmp directory has c0.c1023 we get denied. Normally in targeted init runs unconfined, but we've removed this.
type=AVC msg=audit(1467342325.016:716): avc: denied { read } for pid=2779 comm="rpm" name="system_u:object_r:tmp_t:s0-s0:c0.c1023_phil" dev=dm-0 ino=1966082 scontext=system_u:system_r:rpm_t:s0 tcontext=system_u:object_r:tmp_t:s0-s0:c0.c1023 tclass=dir
It works if we change initrc_context to:
system_u:system_r:initrc_t:s0-s0:c0.c1023
We don't see the issue under mls because the default initrc_context is:
system_u:system_r:initrc_t:s0-s15:c0.c1023
We've traces this back through the selinux-policy src RPM and to the upstream refpolicy and see that config/appconfig-mcs/initrc_context is:
system_u:system_r:initrc_t:s0
whereas config/appconfig-mls/initrc_context is:
system_u:system_r:initrc_t:s0-mls_systemhigh
So under mls init's context is SystemHigh, but under mcs/targeted it doesn't have any categories.
So the long question is should config/appconfig-mcs/initrc_context really be:
system_u:system_r:initrc_t:mcs_systemhigh
as it seems odd that the more secure mls policy would run init at SystemHigh but targeted doesn't.
Thanks
Phil Seeley
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