private/app_neverallows.te

###
### neverallow rules for untrusted app domains
###

define(`all_untrusted_apps',`{
  ephemeral_app
  isolated_app
  mediaprovider
  untrusted_app
  untrusted_app_25
  untrusted_app_27
  untrusted_app_all
}')
# Receive or send uevent messages.
neverallow all_untrusted_apps domain:netlink_kobject_uevent_socket *;

# Receive or send generic netlink messages
neverallow all_untrusted_apps domain:netlink_socket *;

# Too much leaky information in debugfs. It's a security
# best practice to ensure these files aren't readable.
neverallow all_untrusted_apps debugfs_type:file read;

# Do not allow untrusted apps to register services.
# Only trusted components of Android should be registering
# services.
neverallow all_untrusted_apps service_manager_type:service_manager add;

# Do not allow untrusted apps to use VendorBinder
neverallow all_untrusted_apps vndbinder_device:chr_file *;
neverallow all_untrusted_apps vndservice_manager_type:service_manager *;

# Do not allow untrusted apps to connect to the property service
# or set properties. b/10243159
neverallow { all_untrusted_apps -mediaprovider } property_socket:sock_file write;
neverallow { all_untrusted_apps -mediaprovider } init:unix_stream_socket connectto;
neverallow { all_untrusted_apps -mediaprovider } property_type:property_service set;

# net.dns properties are not a public API. Temporarily exempt pre-Oreo apps,
# but otherwise disallow untrusted apps from reading this property.
neverallow { all_untrusted_apps -untrusted_app_25 } net_dns_prop:file read;

# Block calling execve() on files in an apps home directory.
# This is a W^X violation (loading executable code from a writable
# home directory). For compatibility, allow for targetApi <= 28.
# b/112357170
neverallow {
  all_untrusted_apps
  -untrusted_app_25
  -untrusted_app_27
  -runas_app
} { app_data_file privapp_data_file }:file execute_no_trans;

# Do not allow untrusted apps to be assigned mlstrustedsubject.
# This would undermine the per-user isolation model being
# enforced via levelFrom=user in seapp_contexts and the mls
# constraints.  As there is no direct way to specify a neverallow
# on attribute assignment, this relies on the fact that fork
# permission only makes sense within a domain (hence should
# never be granted to any other domain within mlstrustedsubject)
# and an untrusted app is allowed fork permission to itself.
neverallow all_untrusted_apps mlstrustedsubject:process fork;

# Do not allow untrusted apps to hard link to any files.
# In particular, if an untrusted app links to other app data
# files, installd will not be able to guarantee the deletion
# of the linked to file. Hard links also contribute to security
# bugs, so we want to ensure untrusted apps never have this
# capability.
neverallow all_untrusted_apps file_type:file link;

# Do not allow untrusted apps to access network MAC address file
neverallow all_untrusted_apps sysfs_mac_address:file no_rw_file_perms;

# Do not allow any write access to files in /sys
neverallow all_untrusted_apps sysfs_type:file { no_w_file_perms no_x_file_perms };

# Apps may never access the default sysfs label.
neverallow all_untrusted_apps sysfs:file no_rw_file_perms;

# Restrict socket ioctls. Either 1. disallow privileged ioctls, 2. disallow the
# ioctl permission, or 3. disallow the socket class.
neverallowxperm all_untrusted_apps domain:{ icmp_socket rawip_socket tcp_socket udp_socket } ioctl priv_sock_ioctls;
neverallow all_untrusted_apps *:{ netlink_route_socket netlink_selinux_socket } ioctl;
neverallow all_untrusted_apps *:{
  socket netlink_socket packet_socket key_socket appletalk_socket
  netlink_tcpdiag_socket netlink_nflog_socket
  netlink_xfrm_socket netlink_audit_socket
  netlink_dnrt_socket netlink_kobject_uevent_socket tun_socket
  netlink_iscsi_socket netlink_fib_lookup_socket netlink_connector_socket
  netlink_netfilter_socket netlink_generic_socket netlink_scsitransport_socket
  netlink_rdma_socket netlink_crypto_socket sctp_socket
  ax25_socket ipx_socket netrom_socket atmpvc_socket x25_socket rose_socket decnet_socket
  atmsvc_socket rds_socket irda_socket pppox_socket llc_socket can_socket tipc_socket
  bluetooth_socket iucv_socket rxrpc_socket isdn_socket phonet_socket ieee802154_socket caif_socket
  alg_socket nfc_socket vsock_socket kcm_socket qipcrtr_socket smc_socket
} *;

# Do not allow untrusted apps access to /cache
neverallow { all_untrusted_apps -mediaprovider } { cache_file cache_recovery_file }:dir ~{ r_dir_perms };
neverallow { all_untrusted_apps -mediaprovider } { cache_file cache_recovery_file }:file ~{ read getattr };

# Do not allow untrusted apps to create/unlink files outside of its sandbox,
# internal storage or sdcard.
# World accessible data locations allow application to fill the device
# with unaccounted for data. This data will not get removed during
# application un-installation.
neverallow { all_untrusted_apps -mediaprovider } {
  fs_type
  -sdcard_type
  file_type
  -app_data_file            # The apps sandbox itself
  -privapp_data_file
  -media_rw_data_file       # Internal storage. Known that apps can
                            # leave artfacts here after uninstall.
  -user_profile_data_file   # Access to profile files
  userdebug_or_eng(`
    -method_trace_data_file # only on ro.debuggable=1
    -coredump_file          # userdebug/eng only
  ')
}:dir_file_class_set { create unlink };

# No untrusted component should be touching /dev/fuse
neverallow all_untrusted_apps fuse_device:chr_file *;

# Do not allow untrusted apps to directly open or
# issue ioctls to the tun_device
neverallow all_untrusted_apps tun_device:chr_file { open ioctl };
# Additionally, assert that the following ioctls are never reachable.
# This should already be blocked by the neverallow rule above, but this
# is added for robustness, and to prove equivalence to the kernel patch at
# https://android.googlesource.com/kernel/common/+/11cee2be0c2062ba88f04eb51196506f870a3b5d%5E%21
neverallowxperm all_untrusted_apps tun_device:chr_file ioctl {
  SIOCGIFHWADDR
  SIOCSIFHWADDR
  TUNATTACHFILTER
  TUNDETACHFILTER
  TUNGETFEATURES
  TUNGETFILTER
  TUNGETSNDBUF
  TUNGETVNETHDRSZ
  TUNSETDEBUG
  TUNSETGROUP
  TUNSETIFF
  TUNSETLINK
  TUNSETNOCSUM
  TUNSETOFFLOAD
  TUNSETOWNER
  TUNSETPERSIST
  TUNSETQUEUE
  TUNSETSNDBUF
  TUNSETTXFILTER
  TUNSETVNETHDRSZ
};

# Only allow appending to /data/anr/traces.txt (b/27853304, b/18340553)
neverallow all_untrusted_apps anr_data_file:file ~{ open append };
neverallow all_untrusted_apps anr_data_file:dir ~search;

# Avoid reads from generically labeled /proc files
# Create a more specific label if needed
neverallow all_untrusted_apps {
  proc
  proc_asound
  proc_filesystems
  proc_kmsg
  proc_loadavg
  proc_mounts
  proc_pagetypeinfo
  proc_slabinfo
  proc_stat
  proc_swaps
  proc_uptime
  proc_version
  proc_vmallocinfo
  proc_vmstat
}:file { no_rw_file_perms no_x_file_perms };

# Avoid all access to kernel configuration
neverallow all_untrusted_apps config_gz:file { no_rw_file_perms no_x_file_perms };

# Do not allow untrusted apps access to preloads data files
neverallow all_untrusted_apps preloads_data_file:file no_rw_file_perms;

# Locking of files on /system could lead to denial of service attacks
# against privileged system components
neverallow all_untrusted_apps system_file:file lock;

# Do not permit untrusted apps to perform actions on HwBinder service_manager
# other than find actions for services listed below
neverallow all_untrusted_apps *:hwservice_manager ~find;

# Do not permit access from apps which host arbitrary code to HwBinder services,
# except those considered sufficiently safe for access from such apps.
# The two main reasons for this are:
# 1. HwBinder servers do not perform client authentication because HIDL
#    currently does not expose caller UID information and, even if it did, many
#    HwBinder services either operate at a level below that of apps (e.g., HALs)
#    or must not rely on app identity for authorization. Thus, to be safe, the
#    default assumption is that every HwBinder service treats all its clients as
#    equally authorized to perform operations offered by the service.
# 2. HAL servers (a subset of HwBinder services) contain code with higher
#    incidence rate of security issues than system/core components and have
#    access to lower layes of the stack (all the way down to hardware) thus
#    increasing opportunities for bypassing the Android security model.
#
# Safe services include:
# - same process services: because they by definition run in the process
#   of the client and thus have the same access as the client domain in which
#   the process runs
# - coredomain_hwservice: are considered safe because they do not pose risks
#   associated with reason #2 above.
# - hal_configstore_ISurfaceFlingerConfigs:  becuase it has specifically been
#   designed for use by any domain.
# - hal_graphics_allocator_hwservice: because these operations are also offered
#   by surfaceflinger Binder service, which apps are permitted to access
# - hal_omx_hwservice: because this is a HwBinder version of the mediacodec
#   Binder service which apps were permitted to access.
# - hal_codec2_hwservice: because this is a newer version of hal_omx_hwservice.
neverallow all_untrusted_apps {
  hwservice_manager_type
  -same_process_hwservice
  -coredomain_hwservice
  -hal_codec2_hwservice
  -hal_configstore_ISurfaceFlingerConfigs
  -hal_graphics_allocator_hwservice
  -hal_omx_hwservice
  -hal_cas_hwservice
  -hal_neuralnetworks_hwservice
  -untrusted_app_visible_hwservice_violators
}:hwservice_manager find;

# Make sure that the following services are never accessible by untrusted_apps
neverallow all_untrusted_apps {
  default_android_hwservice
  hal_atrace_hwservice
  hal_audio_hwservice
  hal_authsecret_hwservice
  hal_bluetooth_hwservice
  hal_bootctl_hwservice
  hal_camera_hwservice
  hal_confirmationui_hwservice
  hal_contexthub_hwservice
  hal_drm_hwservice
  hal_dumpstate_hwservice
  hal_fingerprint_hwservice
  hal_gatekeeper_hwservice
  hal_gnss_hwservice
  hal_graphics_composer_hwservice
  hal_health_hwservice
  hal_ir_hwservice
  hal_keymaster_hwservice
  hal_light_hwservice
  hal_memtrack_hwservice
  hal_nfc_hwservice
  hal_oemlock_hwservice
  hal_power_hwservice
  hal_secure_element_hwservice
  hal_sensors_hwservice
  hal_telephony_hwservice
  hal_thermal_hwservice
  hal_tv_cec_hwservice
  hal_tv_input_hwservice
  hal_usb_hwservice
  hal_vibrator_hwservice
  hal_vr_hwservice
  hal_weaver_hwservice
  hal_wifi_hwservice
  hal_wifi_offload_hwservice
  hal_wifi_supplicant_hwservice
  hidl_base_hwservice
  system_net_netd_hwservice
  thermalcallback_hwservice
}:hwservice_manager find;
# HwBinder services offered by core components (as opposed to vendor components)
# are considered somewhat safer due to point #2 above.
neverallow all_untrusted_apps {
  coredomain_hwservice
  -same_process_hwservice
  -hidl_allocator_hwservice # Designed for use by any domain
  -hidl_manager_hwservice # Designed for use by any domain
  -hidl_memory_hwservice # Designed for use by any domain
  -hidl_token_hwservice # Designed for use by any domain
}:hwservice_manager find;

# SELinux is not an API for untrusted apps to use
neverallow all_untrusted_apps selinuxfs:file no_rw_file_perms;

# Restrict *Binder access from apps to HAL domains. We can only do this on full
# Treble devices where *Binder communications between apps and HALs are tightly
# restricted.
full_treble_only(`
  neverallow all_untrusted_apps {
    halserverdomain
    -coredomain
    -hal_configstore_server
    -hal_graphics_allocator_server
    -hal_cas_server
    -hal_neuralnetworks_server
    -hal_omx_server
    -binder_in_vendor_violators # TODO(b/35870313): Remove once all violations are gone
    -untrusted_app_visible_halserver_violators
  }:binder { call transfer };
')

# Untrusted apps are not allowed to find mediaextractor update service.
neverallow all_untrusted_apps mediaextractor_update_service:service_manager find;

# Access to /proc/tty/drivers, to allow apps to determine if they
# are running in an emulated environment.
# b/33214085 b/33814662 b/33791054 b/33211769
# https://github.com/strazzere/anti-emulator/blob/master/AntiEmulator/src/diff/strazzere/anti/emulator/FindEmulator.java
# This will go away in a future Android release
neverallow { all_untrusted_apps -untrusted_app_25 } proc_tty_drivers:file r_file_perms;
neverallow all_untrusted_apps proc_tty_drivers:file ~r_file_perms;

# Untrusted apps are not allowed to use cgroups.
neverallow all_untrusted_apps cgroup:file *;