[PATCH 03/15] flask/policy: move user definitions and constraints into modules

From: Daniel De Graaf <dgdegra@tycho.nsa.gov>
To: xen-devel@lists.xen.org
Cc: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Subject: [PATCH 03/15] flask/policy: move user definitions and constraints into modules
Date: Thu,  9 Jun 2016 10:47:06 -0400	[thread overview]
Message-ID: <1465483638-9489-4-git-send-email-dgdegra@tycho.nsa.gov> (raw)
In-Reply-To: <1465483638-9489-1-git-send-email-dgdegra@tycho.nsa.gov>

This also renames the example users created by vm_role.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
---
 docs/misc/xsm-flask.txt                            | 34 +++++++++++-----------
 tools/flask/policy/Makefile                        |  9 ++++--
 tools/flask/policy/modules/all_system_role.te      |  5 ----
 tools/flask/policy/modules/modules.conf            | 11 +++++--
 .../{policy/constraints => modules/vm_role.cons}   |  6 ++--
 tools/flask/policy/modules/vm_role.te              | 16 ++++++++++
 tools/flask/policy/modules/xen.te                  |  9 ++++--
 tools/flask/policy/policy/support/misc_macros.spt  |  6 ++--
 tools/flask/policy/policy/users                    | 12 +-------
 9 files changed, 63 insertions(+), 45 deletions(-)
 rename tools/flask/policy/{policy/constraints => modules/vm_role.cons} (78%)
 create mode 100644 tools/flask/policy/modules/vm_role.te

diff --git a/docs/misc/xsm-flask.txt b/docs/misc/xsm-flask.txt
index d3015ca..2f42585 100644
--- a/docs/misc/xsm-flask.txt
+++ b/docs/misc/xsm-flask.txt
@@ -147,9 +147,11 @@ it relies on the SELinux compiler "checkpolicy"; run
 	make -C tools/flask/policy
 
 to compile the example policy included with Xen. The policy is generated from
-definition files under this directory. When creating or modifying security
-policy, most modifications will be made to the xen type enforcement (.te) file
-tools/flask/policy/policy/modules/xen/xen.te or the macro definitions in xen.if.
+definition files under this directory. Most changes to security policy will
+involve creating or modifying modules found in tools/flask/policy/modules/.  The
+modules.conf file there defines what modules are enabled and has short
+descriptions of each module.
+
 The XSM policy file needs to be copied to /boot and loaded as a module by grub.
 The exact position of the module does not matter as long as it is after the Xen
 kernel; it is normally placed either just above the dom0 kernel or at the end.
@@ -210,17 +212,16 @@ Type transitions are also used to compute the labels of event channels.
 Users and roles
 ---------------
 
-Users are defined in tools/flask/policy/policy/users. The example policy defines
-two users (customer_1 and customer_2) in addition to the system user system_u.
-Users are visible in the labels of domains and associated objects (event
-channels); in the example policy, "customer_1:vm_r:domU_t" is a valid label for
-the customer_1 user.
+The default user and role used for domains is system_u and system_r.  Users are
+visible in the labels of domains and associated objects (event channels); when
+the vm_role module is enabled, "user_1:vm_r:domU_t" is a valid label for a
+domain created by the user_1 user.
 
-Access control rules involving users and roles are defined in the policy
-constraints file (tools/flask/policy/policy/constraints). The example policy
-provides constraints that prevent different users from communicating using
-grants or event channels, while still allowing communication with the system_u
-user where dom0 resides.
+Access control rules involving users and roles are defined in a module's
+constraints file (for example, vm_rule.cons). The vm_role module defines one
+role (vm_r) and three users (user_1 .. user_3), along with constraints that
+prevent different users from communicating using grants or event channels, while
+still allowing communication with the system_u user where dom0 resides.
 
 Resource Policy
 ---------------
@@ -268,10 +269,9 @@ declare_domain and create_domain interfaces:
 Existing SELinux tools such as audit2allow can be applied to these denials, e.g.
 xl dmesg | audit2allow
 
-The generated allow rules can then be fed back into the policy by
-adding them to xen.te, although manual review is advised and will
-often lead to adding parameterized rules to the interfaces in xen.if
-to address the general case.
+The generated allow rules can then be fed back into the policy by adding them to
+a module, although manual review is advised and will often lead to adding
+parameterized rules to the interfaces in xen.if to address the general case.
 
 
 Device Labeling in Policy
diff --git a/tools/flask/policy/Makefile b/tools/flask/policy/Makefile
index b2c2d06..693eb10 100644
--- a/tools/flask/policy/Makefile
+++ b/tools/flask/policy/Makefile
@@ -54,7 +54,6 @@ AVS += $(POLDIR)/access_vectors
 M4SUPPORT := $(wildcard $(POLDIR)/support/*.spt)
 MLSSUPPORT := $(POLDIR)/mls
 USERS := $(POLDIR)/users
-CONSTRAINTS := $(POLDIR)/constraints
 ISID_DEFS := $(POLDIR)/initial_sids
 DEV_OCONS := $(POLDIR)/device_contexts
 
@@ -90,8 +89,12 @@ MODENABLED := on
 # extract settings from modules.conf
 ENABLED_LIST := $(shell awk '/^[ \t]*[a-z]/{ if ($$3 == "$(MODENABLED)") print $$1 }' $(MOD_CONF) 2> /dev/null)
 
+# Modules must provide a .te file, although it could be empty
 ALL_MODULES := $(foreach mod,$(ENABLED_LIST),$(MODDIR)/$(mod).te)
+
+# Modules may also provide interfaces and constraint definitions
 ALL_INTERFACES := $(wildcard $(ALL_MODULES:.te=.if))
+ALL_CONSTRAINTS := $(wildcard $(ALL_MODULES:.te=.cons))
 
 # The order of these files is important
 POLICY_SECTIONS := $(SECCLASS) $(ISID_DECLS) $(AVS)
@@ -99,7 +102,9 @@ POLICY_SECTIONS += $(M4SUPPORT) $(MLSSUPPORT)
 POLICY_SECTIONS += $(ALL_INTERFACES)
 POLICY_SECTIONS += $(GLOBALTUN)
 POLICY_SECTIONS += $(ALL_MODULES)
-POLICY_SECTIONS += $(USERS) $(CONSTRAINTS) $(ISID_DEFS) $(DEV_OCONS)
+POLICY_SECTIONS += $(USERS)
+POLICY_SECTIONS += $(ALL_CONSTRAINTS)
+POLICY_SECTIONS += $(ISID_DEFS) $(DEV_OCONS)
 
 all: $(POLICY_FILENAME)
 
diff --git a/tools/flask/policy/modules/all_system_role.te b/tools/flask/policy/modules/all_system_role.te
index 74f870f..3018540 100644
--- a/tools/flask/policy/modules/all_system_role.te
+++ b/tools/flask/policy/modules/all_system_role.te
@@ -1,8 +1,3 @@
 # Allow all domains to use system_r so that systems that are not using the
 # user/role separation feature will work properly.
 role system_r types domain_type;
-
-# The vm role is used as part of user separation.  Allow all domain types to use
-# this role except dom0.
-role vm_r;
-role vm_r types { domain_type -dom0_t };
diff --git a/tools/flask/policy/modules/modules.conf b/tools/flask/policy/modules/modules.conf
index d875dbf..9aac6a0 100644
--- a/tools/flask/policy/modules/modules.conf
+++ b/tools/flask/policy/modules/modules.conf
@@ -34,6 +34,13 @@ nomigrate = on
 nic_dev = on
 
 # This allows any domain type to be created using the system_r role.  When it is
-# disabled, domains not using the default types (dom0_t and domU_t) must use
-# another role (such as vm_r) from the vm_role module.
+# disabled, domains not using the default types (dom0_t, domU_t, dm_dom_t) must
+# use another role (such as vm_r from the vm_role module below).
 all_system_role = on
+
+# Example users, roles, and constraints for user-based separation.
+# 
+# The three users defined here can set up grant/event channel communication
+# (vchan, device frontend/backend) between their own VMs, but cannot set up a
+# channel to a VM under a different user.
+vm_role = on
diff --git a/tools/flask/policy/policy/constraints b/tools/flask/policy/modules/vm_role.cons
similarity index 78%
rename from tools/flask/policy/policy/constraints
rename to tools/flask/policy/modules/vm_role.cons
index 765ed4d..3847ec1 100644
--- a/tools/flask/policy/policy/constraints
+++ b/tools/flask/policy/modules/vm_role.cons
@@ -1,6 +1,5 @@
-
 #
-# Define the constraints
+# Constraints are defined by:
 #
 # constrain class_set perm_set expression ;
 #
@@ -25,8 +24,9 @@
 # name_list : name | name_list name
 #
 
-# Prevent event channels and grants between different customers
 
+# Prevent event channels and grants between different users.  This could be
+# further limited to only restricting those domains using the vm_r role.
 constrain event bind (
 	u1 == system_u or
 	u2 == system_u or
diff --git a/tools/flask/policy/modules/vm_role.te b/tools/flask/policy/modules/vm_role.te
new file mode 100644
index 0000000..f816de1
--- /dev/null
+++ b/tools/flask/policy/modules/vm_role.te
@@ -0,0 +1,16 @@
+# The vm role is used as part of user separation.  Allow all domain types to use
+# this role except dom0.
+role vm_r;
+role vm_r types { domain_type -dom0_t };
+
+# Define some users that must use this role (full type "user_1:vm_r:domU_t").
+gen_user(user_1,, vm_r, s0, s0)
+gen_user(user_2,, vm_r, s0, s0)
+gen_user(user_3,, vm_r, s0, s0)
+
+# Alternate: define and use a macro to generate 1000 users
+define(`def_vm_users',`gen_user(user_$1,, vm_r, s0, s0)
+ifelse(`$1',`$2',,`def_vm_users(incr($1),$2)')dnl
+')
+
+# def_vm_users(0,999)
diff --git a/tools/flask/policy/modules/xen.te b/tools/flask/policy/modules/xen.te
index f374dc5..b52edc2 100644
--- a/tools/flask/policy/modules/xen.te
+++ b/tools/flask/policy/modules/xen.te
@@ -71,14 +71,17 @@ neverallow * ~event_type:event { create send status };
 
 ################################################################################
 #
-# Roles
+# Users and Roles
 #
 ################################################################################
 
 # The object role (object_r) is used for devices, resources, and event channels;
 # it does not need to be defined here and should not be used for domains.
 
-# The system role is used for utility domains and pseudo-domains.  If roles are
-# not being used for separation, all domains can use the system role.
+# The system user and role are used for utility domains and pseudo-domains.  In
+# systems where users and roles are not being used for separation, all domains
+# can use the system user and role.
+gen_user(system_u,, system_r, s0, s0 - mls_systemhigh)
+
 role system_r;
 role system_r types { xen_type dom0_t };
diff --git a/tools/flask/policy/policy/support/misc_macros.spt b/tools/flask/policy/policy/support/misc_macros.spt
index 2b27955..344f5c4 100644
--- a/tools/flask/policy/policy/support/misc_macros.spt
+++ b/tools/flask/policy/policy/support/misc_macros.spt
@@ -49,9 +49,11 @@ define(`refpolicyerr',`errprint(__file__:__line__: Error: `$1'__endline__)')
 #
 # gen_user(username, prefix, role_set, mls_defaultlevel, mls_range)
 #
-define(`gen_user',`dnl
+define(`gen_user',`define(`gen_all_users', gen_all_users `dnl
 user $1 roles { $3 }`'ifdef(`enable_mls', ` level $4 range $5')`';
-')
+')')
+
+define(`gen_all_users',`')
 
 ########################################
 #
diff --git a/tools/flask/policy/policy/users b/tools/flask/policy/policy/users
index 35ed8a9..af6acbd 100644
--- a/tools/flask/policy/policy/users
+++ b/tools/flask/policy/policy/users
@@ -1,11 +1 @@
-##################################
-#
-# System User configuration.
-#
-
-# system_u is the user identity for system domains and objects
-gen_user(system_u,, system_r, s0, s0 - mls_systemhigh)
-
-# Other users are defined using the vm role
-gen_user(customer_1,, vm_r, s0, s0)
-gen_user(customer_2,, vm_r, s0, s0)
+gen_all_users()
-- 
2.5.5


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