app_neverallows.te

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

# Only allow domains in AOSP to use the untrusted_app_all attribute.
neverallow { untrusted_app_all -untrusted_app -untrusted_app_25 } domain:process fork;

define(`all_untrusted_apps',`{ untrusted_app_all untrusted_app_25 untrusted_app ephemeral_app isolated_app }')
# 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 connect to the property service
# or set properties. b/10243159
neverallow all_untrusted_apps property_socket:sock_file write;
neverallow all_untrusted_apps init:unix_stream_socket connectto;
neverallow all_untrusted_apps property_type:property_service set;

# 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;

# Restrict socket ioctls. Either 1. disallow privileged ioctls, 2. disallow the
# ioctl permission, or 3. disallow the socket class.
neverallowxperm all_untrusted_apps domain:{ 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
} *;

# Do not allow untrusted apps access to /cache
neverallow all_untrusted_apps { cache_file cache_recovery_file }:dir ~{ r_dir_perms };
neverallow all_untrusted_apps { 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 {
  fs_type
  -fuse                     # sdcard
  -sdcardfs                 # sdcard
  -vfat
  file_type
  -app_data_file            # The apps sandbox itself
  -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 };

# Do not allow untrusted apps to directly open tun_device
neverallow all_untrusted_apps tun_device:chr_file open;

# 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: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 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.
neverallow all_untrusted_apps {
  hwservice_manager_type
  # Same process services are safe 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
  -same_process_hwservice
  -coredomain_hwservice # neverallows for coredomain HwBinder services are below
  -hal_configstore_ISurfaceFlingerConfigs # Designed for use by any domain
  # These operations are also offered by surfaceflinger Binder service which
  # apps are permitted to access
  -hal_graphics_allocator_hwservice
  # HwBinder version of mediacodec Binder service which apps were permitted to
  # access
  -hal_omx_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;

# 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
    -binder_in_vendor_violators # TODO(b/35870313): Remove once all violations are gone
  }:binder { call transfer };
')