Restrict the ability to set usermodehelpers and proc security settings.

Limit the ability to write to the files that configure kernel
usermodehelpers and security-sensitive proc settings to the init domain.
Permissive domains can also continue to set these values.

The current list is not exhaustive, just an initial set.
Not all of these files will exist on all kernels/devices.
Controlling access to certain kernel usermodehelpers, e.g. cgroup
release_agent, will require kernel changes to support and cannot be
addressed here.

Expected output on e.g. flo after the change:
ls -Z /sys/kernel/uevent_helper /proc/sys/fs/suid_dumpable /proc/sys/kernel/core_pattern /proc/sys/kernel/dmesg_restrict /proc/sys/kernel/hotplug /proc/sys/kernel/kptr_restrict /proc/sys/kernel/poweroff_cmd /proc/sys/kernel/randomize_va_space /proc/sys/kernel/usermodehelper
-rw-r--r-- root     root              u:object_r:usermodehelper:s0 uevent_helper
-rw-r--r-- root     root              u:object_r:proc_security:s0 suid_dumpable
-rw-r--r-- root     root              u:object_r:usermodehelper:s0 core_pattern
-rw-r--r-- root     root              u:object_r:proc_security:s0 dmesg_restrict
-rw-r--r-- root     root              u:object_r:usermodehelper:s0 hotplug
-rw-r--r-- root     root              u:object_r:proc_security:s0 kptr_restrict
-rw-r--r-- root     root              u:object_r:usermodehelper:s0 poweroff_cmd
-rw-r--r-- root     root              u:object_r:proc_security:s0 randomize_va_space
-rw------- root     root              u:object_r:usermodehelper:s0 bset
-rw------- root     root              u:object_r:usermodehelper:s0 inheritable

Change-Id: I3f24b4bb90f0916ead863be6afd66d15ac5e8de0
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

domain.te

@@ -142,3 +142,8 @@ neverallow domain { file_type -exec_type }:file entrypoint;
 # Ensure that nothing in userspace can access /dev/mem or /dev/kmem
 neverallow { domain -kernel -ueventd -init } kmem_device:chr_file *;
 neverallow domain kmem_device:chr_file ~{ create relabelto unlink setattr };
+
+# Only init should be able to configure kernel usermodehelpers or
+# security-sensitive proc settings.
+neverallow { domain -init } usermodehelper:file { append write };
+neverallow { domain -init } proc_security:file { append write };

file.te

@@ -4,6 +4,10 @@ type pipefs, fs_type;
 type sockfs, fs_type;
 type rootfs, fs_type;
 type proc, fs_type;
+# Security-sensitive proc nodes that should not be writable to most.
+type proc_security, fs_type;
+# proc, sysfs, or other nodes that permit configuration of kernel usermodehelpers.
+type usermodehelper, fs_type, sysfs_type;
 type qtaguid_proc, fs_type, mlstrustedobject;
 type proc_bluetooth_writable, fs_type;
 type selinuxfs, fs_type;

file_contexts

@@ -206,6 +206,7 @@
 /sys/devices/system/cpu(/.*)?    u:object_r:sysfs_devices_system_cpu:s0
 /sys/power/wake_lock -- u:object_r:sysfs_wake_lock:s0
 /sys/power/wake_unlock -- u:object_r:sysfs_wake_lock:s0
+/sys/kernel/uevent_helper --	u:object_r:usermodehelper:s0
 #############################
 # asec containers
 /mnt/asec(/.*)?         u:object_r:asec_apk_file:s0

genfs_contexts

@@ -3,6 +3,18 @@ genfscon rootfs / u:object_r:rootfs:s0
 # proc labeling can be further refined (longest matching prefix).
 genfscon proc / u:object_r:proc:s0
 genfscon proc /net/xt_qtaguid/ctrl u:object_r:qtaguid_proc:s0
+genfscon proc /sys/fs/protected_hardlinks u:object_r:proc_security:s0
+genfscon proc /sys/fs/protected_symlinks u:object_r:proc_security:s0
+genfscon proc /sys/fs/suid_dumpable u:object_r:proc_security:s0
+genfscon proc /sys/kernel/core_pattern u:object_r:usermodehelper:s0
+genfscon proc /sys/kernel/dmesg_restrict u:object_r:proc_security:s0
+genfscon proc /sys/kernel/hotplug u:object_r:usermodehelper:s0
+genfscon proc /sys/kernel/kptr_restrict u:object_r:proc_security:s0
+genfscon proc /sys/kernel/modprobe u:object_r:usermodehelper:s0
+genfscon proc /sys/kernel/modules_disabled u:object_r:proc_security:s0
+genfscon proc /sys/kernel/poweroff_cmd u:object_r:usermodehelper:s0
+genfscon proc /sys/kernel/randomize_va_space u:object_r:proc_security:s0
+genfscon proc /sys/kernel/usermodehelper u:object_r:usermodehelper:s0
 # selinuxfs booleans can be individually labeled.
 genfscon selinuxfs / u:object_r:selinuxfs:s0
 genfscon cgroup / u:object_r:cgroup:s0

init.te

@@ -9,3 +9,5 @@ allow init unlabeled:filesystem mount;
 
 allow init {fs_type dev_type file_type}:dir_file_class_set relabelto;
 allow init kernel:security { load_policy setenforce };
+allow init usermodehelper:file rw_file_perms;
+allow init proc_security:file rw_file_perms;

unconfined.te

@@ -30,7 +30,9 @@ allow unconfineddomain domain:ipc_class_set *;
 allow unconfineddomain domain:key *;
 allow unconfineddomain fs_type:filesystem *;
 allow unconfineddomain {fs_type dev_type file_type}:{ dir blk_file lnk_file sock_file fifo_file } ~relabelto;
-allow unconfineddomain {fs_type dev_type file_type -kmem_device}:{ chr_file file } ~{entrypoint relabelto};
+allow unconfineddomain {fs_type -usermodehelper -proc_security}:{ chr_file file } ~{entrypoint relabelto};
+allow unconfineddomain {dev_type -kmem_device}:{ chr_file file } ~{entrypoint relabelto};
+allow unconfineddomain file_type:{ chr_file file } ~{entrypoint relabelto};
 allow unconfineddomain node_type:node *;
 allow unconfineddomain node_type:{ tcp_socket udp_socket rawip_socket } node_bind;
 allow unconfineddomain netif_type:netif *;