Add SELinux policy for storage areas

We are adding the ability for apps to create "storage areas", which are transparently encrypted directories that can only be opened when the device is unlocked. This CL makes the required SELinux policy changes. First, assign the type "system_userdir_file" to the new top-level directory /data/storage_area (non-recursively). This is the same type used by the other top-level directories containing app data, such as /data/user, and it restricts access to the directory in the desired way. Second, add new types to represent an app's directory of storage areas, the storage areas themselves, and their contents: `storage_area_app_dir`, `storage_area_dir`, and `storage_area_content_file` respectively. All are `app_data_file_type`s. The directory structure and their associated labels is as follows (note that they also all get the categories of the user+package): /data/storage_area/userId/pkgName storage_area_app_dir /data/storage_area/userId/pkgName/storageAreaName storage_area_dir /data/storage_area/userId/pkgName/storageAreaName/myFile.txt storage_area_content_file /data/storage_area/userId/pkgName/storageAreaName/mySubDir storage_area_content_file These new types allow us to restrict how and which processes interact with storage areas. The new type for the contents of storage areas allows us to add new, desirable restrictions that we cannot add to the more general `app_data_file` type in order to maintain backwards-compatibility, e.g., we block apps from executing any files in their storage areas. Third, allow: -- vold_prepare_subdirs to create and delete storage areas on behalf of apps, and assign them the SElinux type `storage_area_dir` i.e. create directories /data/storage_area/$userId/$pkgName/$storageAreaName -- vold to assign encryption policies to storage area directories -- installd to create an app's directory of storage areas on app install, and delete them on app uninstall, and assign them the SElinux type `storage_area_app_dir`, i.e. directories /data/storage_area/$userId/$pkgName We also add a new SELinux type to represent the storage area encryption keys: `storage_area_key_file`. The keys are created by vold on storage area creation, and deleted either by vold if an app calls the `deleteStorageArea` API function explicitly, or by installd on app uninstall. These keys are stored in `/data/misc_ce/$userId/storage_area_keys`, and only installd and vold have access to them. Bug: 325121608 Test: atest StorageAreaTest Change-Id: I74805d249f59226fc6963693f682c70949bfad93
2024-04-30 20:26:55 +00:00 · 2024-04-30 20:26:55 +00:00 · 27b515e70a
commit 27b515e70a
parent 6543cf9843
13 changed files with 279 additions and 13 deletions
--- a/contexts/plat_file_contexts_test
+++ b/contexts/plat_file_contexts_test
@ -911,6 +911,8 @@
 /data/system_de                                                   system_userdir_file
 /data/user                                                        system_userdir_file
 /data/user_de                                                     system_userdir_file
+/data/storage_area                                                system_userdir_file
+/data/misc_ce/0/storage_area_keys                                 storage_area_key_file

 /data/misc/adb                                                    adb_keys_file
 /data/misc/adb/test                                               adb_keys_file
--- a/flagging/Android.bp
+++ b/flagging/Android.bp
@ -21,6 +21,7 @@ se_flags {
        "RELEASE_AVF_ENABLE_DEVICE_ASSIGNMENT",
        "RELEASE_AVF_ENABLE_LLPVM_CHANGES",
        "RELEASE_HARDWARE_BLUETOOTH_RANGING_SERVICE",
+        "RELEASE_UNLOCKED_STORAGE_API",
    ],
    export_to: ["all_selinux_flags"],
 }
--- a/private/app.te
+++ b/private/app.te
@ -242,12 +242,37 @@ allow appdomain appdomain:fifo_file rw_file_perms;
 allow appdomain surfaceflinger:unix_stream_socket { read write setopt getattr getopt shutdown };

 # App sandbox file accesses.
-allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } { app_data_file privapp_data_file }:dir create_dir_perms;
-allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } { app_data_file privapp_data_file }:file create_file_perms;
-allowxperm { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } { app_data_file privapp_data_file }:file ioctl FS_IOC_MEASURE_VERITY;
+allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir create_dir_perms;
+allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:file create_file_perms;
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  # an app can read but cannot write to its own directory of storage areas
+  allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } storage_area_app_dir:dir r_dir_perms;
+  # an app can write to its storage areas
+  allow { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } storage_area_dir:dir rw_dir_perms;
+')
+
+allowxperm { appdomain -isolated_app_all -mlstrustedsubject -sdk_sandbox_all } {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:file ioctl FS_IOC_MEASURE_VERITY;

 # Access via already open fds is ok even for mlstrustedsubject.
-allow { appdomain -isolated_app_all -sdk_sandbox_all } { app_data_file privapp_data_file system_app_data_file }:file { getattr map read write };
+allow { appdomain -isolated_app_all -sdk_sandbox_all } {
+  app_data_file
+  privapp_data_file
+  system_app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:file { getattr map read write };

 # Access open fds from SDK sandbox
 allow appdomain sdk_sandbox_data_file:file { getattr read };
@ -777,3 +802,13 @@ dontaudit appdomain system_font_fallback_file:file no_rw_file_perms;
 neverallow appdomain system_font_fallback_file:file no_rw_file_perms;

 neverallow { appdomain -shell } tombstone_data_file:file ~{ getattr read };
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  # Files and directories that apps write to their storage areas
+  # should have type storage_area_content_file
+  type_transition {
+    appdomain
+    -isolated_app_all
+    -ephemeral_app
+    -sdk_sandbox_all
+  } storage_area_dir:{ notdevfile_class_set dir } storage_area_content_file;
+')
--- a/private/app_neverallows.te
+++ b/private/app_neverallows.te
@ -68,6 +68,21 @@ neverallow {
  -runas_app
 } { app_data_file privapp_data_file }:file execute_no_trans;

+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  # block apps from executing files in their storage areas
+  # this is a stronger and more desirable guarantee than blocking execute_no_trans, but
+  # execute cannot be blocked on all of app_data_file without causing
+  # backwards compatibility issues (see b/237289679)
+  neverallow appdomain storage_area_content_file:file execute;
+')
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+     # dont allow apps to modify their own directories of storage areas
+    neverallow appdomain storage_area_app_dir:dir_file_class_set {
+        create write setattr relabelfrom relabelto append unlink link rename
+    };
+')
+
 # Do not allow untrusted apps to invoke dex2oat. This was historically required
 # by ART for compiling secondary dex files but has been removed in Q.
 # Exempt legacy apps (targetApi<=28) for compatibility.
@ -156,6 +171,7 @@ neverallow { all_untrusted_apps -mediaprovider } {
  file_type
  -app_data_file            # The apps sandbox itself
  -privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `-storage_area_content_file')
  -app_exec_data_file       # stored within the app sandbox directory
  -media_rw_data_file       # Internal storage. Known that apps can
                            # leave artfacts here after uninstall.
--- a/private/crosvm.te
+++ b/private/crosvm.te
@ -139,6 +139,7 @@ neverallow crosvm {
  apk_data_file
  app_data_file
  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
  userdebug_or_eng(`-shell_data_file')
 }:file open;

--- a/private/domain.te
+++ b/private/domain.te
@ -1594,7 +1594,20 @@ neverallow {
  -appdomain
  -artd # compile secondary dex files
  -installd # creation of sandbox
-} { privapp_data_file app_data_file }:dir_file_class_set { create unlink };
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir_file_class_set { create unlink };
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    domain
+    -artd # compile secondary dex files
+    -installd # creation of sandbox
+    -vold_prepare_subdirs # creation of storage area directories
+  } {storage_area_app_dir storage_area_dir }:dir { create unlink };
+')

 # Only the following processes should be directly accessing private app
 # directories.
@ -1611,7 +1624,38 @@ neverallow {
  -runas
  -system_server
  -zygote
-} { privapp_data_file app_data_file }:dir *;
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir *;
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    domain
+    -appdomain
+    -app_zygote
+    -artd # compile secondary dex files
+    -installd
+    -rs # spawned by appdomain, so carryover the exception above
+    -system_server
+    -vold # encryption of storage area directories
+    -vold_prepare_subdirs # creation of storage area directories
+    -zygote
+  } { storage_area_dir storage_area_app_dir }:dir *;
+')
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  # only vold and installd can access the storage area key files
+  # (and init, in case of a recursive restorecon)
+  neverallow {
+    domain
+    -init
+    -vold
+    -vold_prepare_subdirs
+    -installd
+  } { storage_area_key_file }:dir_file_class_set *;
+')

 # Only apps should be modifying app data. installd is exempted for
 # restorecon and package install/uninstall.
@ -1621,7 +1665,22 @@ neverallow {
  -artd # compile secondary dex files
  -installd
  -rs # spawned by appdomain, so carryover the exception above
-} { privapp_data_file app_data_file }:dir ~r_dir_perms;
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir ~r_dir_perms;
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    domain
+    -appdomain
+    -artd # compile secondary dex files
+    -installd
+    -rs # spawned by appdomain, so carryover the exception above
+    -vold_prepare_subdirs # creation of storage area directories
+  } { storage_area_dir storage_area_app_dir }:dir ~r_dir_perms;
+')

 neverallow {
  domain
@ -1630,20 +1689,41 @@ neverallow {
  -artd # compile secondary dex files
  -installd
  -rs # spawned by appdomain, so carryover the exception above
-} { privapp_data_file app_data_file }:file_class_set open;
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:file_class_set open;

 neverallow {
  domain
  -appdomain
  -artd # compile secondary dex files
  -installd # creation of sandbox
-} { privapp_data_file app_data_file }:dir_file_class_set { create unlink };
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir_file_class_set { create unlink };

 neverallow {
  domain
  -artd # compile secondary dex files
  -installd
-} { privapp_data_file app_data_file }:dir_file_class_set { relabelfrom relabelto };
+} {
+  privapp_data_file
+  app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir_file_class_set { relabelfrom relabelto };
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    domain
+    -artd # compile secondary dex files
+    -installd
+    -vold_prepare_subdirs
+  } { storage_area_dir storage_area_app_dir }:dir { relabelfrom relabelto };
+')

 # The staging directory contains APEX and APK files. It is important to ensure
 # that these files cannot be accessed by other domains to ensure that the files
--- a/private/file.te
+++ b/private/file.te
@ -194,3 +194,12 @@ allow proc_net proc:filesystem associate;
 # Should be:
 #   type apk_data_file, file_type, data_file_type;
 neverallow fs_type file_type:filesystem associate;
+# app directories of storage areas: /data/storage_area/userId/pkgName -- apps cannot write to it
+type storage_area_app_dir, file_type, data_file_type, core_data_file_type, app_data_file_type;
+# app storage areas: /data/storage_area/userId/pkgName/storageAreaName
+type storage_area_dir, file_type, data_file_type, core_data_file_type, app_data_file_type;
+# contents of app storage areas: /data/storage_area/userId/pkgName/storageAreaName/*
+type storage_area_content_file, file_type, data_file_type, core_data_file_type, app_data_file_type;
+
+# /data/misc_ce/userId/storage_area_keys
+type storage_area_key_file, file_type, data_file_type, core_data_file_type;
--- a/private/file_contexts
+++ b/private/file_contexts
@ -624,6 +624,7 @@
 /data/system_de           u:object_r:system_userdir_file:s0
 /data/user                u:object_r:system_userdir_file:s0
 /data/user_de             u:object_r:system_userdir_file:s0
+/data/storage_area        u:object_r:system_userdir_file:s0

 # Misc data
 /data/misc/adb(/.*)?            u:object_r:adb_keys_file:s0
@ -819,6 +820,9 @@
 /data/misc_de/[0-9]+/vold(/.*)?           u:object_r:vold_data_file:s0
 /data/misc_ce/[0-9]+/vold(/.*)?           u:object_r:vold_data_file:s0

+# storage area keys
+/data/misc_ce/[0-9]+/storage_area_keys(/.*)?           u:object_r:storage_area_key_file:s0
+
 # Backup service persistent per-user bookkeeping
 /data/system_ce/[0-9]+/backup(/.*)?		u:object_r:backup_data_file:s0
 # Backup service temporary per-user data for inter-change with apps
--- a/private/init.te
+++ b/private/init.te
@ -300,6 +300,11 @@ allow init self:global_capability_class_set { chown fowner fsetid };
 allow init {
  file_type
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -bpffs_type
  -exec_type
  -misc_logd_file
@ -314,6 +319,11 @@ allow init {
 allow init {
  file_type
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -bpffs_type
  -credstore_data_file
  -exec_type
@ -336,6 +346,11 @@ allow init {
  file_type
  -apex_info_file
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -bpffs_type
  -exec_type
  -gsi_data_file
@ -363,6 +378,11 @@ allow init apex_info_file:file r_file_perms;
 allow init {
  file_type
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -bpffs_type
  -exec_type
  -gsi_data_file
@ -383,6 +403,11 @@ allow init {
  file_type
  -apex_mnt_dir
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -bpffs_type
  -exec_type
  -gsi_data_file
@ -409,6 +434,11 @@ allow init {
  -vendor_file_type
  -exec_type
  -app_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    -storage_area_dir
+    -storage_area_app_dir
+    -storage_area_content_file
+  ')
  -privapp_data_file
 }:dir_file_class_set relabelto;

--- a/private/installd.te
+++ b/private/installd.te
@ -225,6 +225,12 @@ get_prop(installd, storage_config_prop)
 # Accessing files on the Incremental File System uses fds opened in the context of vold.
 allow installd vold:fd use;

+# on app uninstall, installd deletes the storage area keys for the app
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  allow installd storage_area_key_file:dir { open search write remove_name lock };
+  allow installd storage_area_key_file:file unlink;
+')
+
 ###
 ### Neverallow rules
 ###
--- a/private/mlstrustedsubject.te
+++ b/private/mlstrustedsubject.te
@ -8,13 +8,31 @@ neverallow {
  mlstrustedsubject
  -artd # compile secondary dex files
  -installd
-} { app_data_file privapp_data_file }:file ~{ read write map getattr ioctl lock append };
+} {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:file ~{ read write map getattr ioctl lock append };

 neverallow {
  mlstrustedsubject
  -artd # compile secondary dex files
  -installd
-} { app_data_file privapp_data_file }:dir ~{ read getattr search };
+} {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir ~{ read getattr search };
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    mlstrustedsubject
+    -artd # compile secondary dex files
+    -installd
+    -vold # encryption of storage areas
+    -vold_prepare_subdirs # creation of storage area directories
+  } { storage_area_dir storage_area_app_dir }:dir ~{ read getattr search };
+')

 neverallow {
  mlstrustedsubject
@ -24,4 +42,22 @@ neverallow {
  -adbd
  -runas
  -zygote
-} { app_data_file privapp_data_file }:dir { read getattr search };
+} {
+  app_data_file
+  privapp_data_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_content_file')
+}:dir { read getattr search };
+
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  neverallow {
+    mlstrustedsubject
+    -artd # compile secondary dex files
+    -installd
+    -system_server
+    -adbd
+    -runas
+    -vold # encryption of storage area directories
+    -vold_prepare_subdirs # creation of storage area directories
+    -zygote
+  } { storage_area_dir storage_area_app_dir }:dir { read getattr search };
+')
--- a/private/vold.te
+++ b/private/vold.te
@ -62,6 +62,27 @@ allow vold keystore_maintenance_service:service_manager find;
 allow vold keystore:keystore2 early_boot_ended;
 allow vold keystore:keystore2 delete_all_keys;

+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+    # Allow vold to encrypt storage area directories on behalf of apps.
+    allow vold {
+        storage_area_dir
+        storage_area_app_dir
+    }:dir {
+        getattr
+        ioctl # for FS_IOC_SET_ENCRYPTION_POLICY
+        open
+        read # for open(O_RDONLY) for ioctl
+        search
+    };
+')
+
+# when a storage area is created (with `openStorageArea`), vold creates the key
+# and when a storage area is deleted (with `deleteStorageArea`), vold deletes the key
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  allow vold storage_area_key_file:file create_file_perms;
+  allow vold storage_area_key_file:dir create_dir_perms;
+')
+
 # Allow vold to create and delete per-user directories like /data/user/$userId.
 allow vold {
    media_userdir_file
@ -119,6 +140,7 @@ allowxperm vold { fs_type file_type }:dir ioctl FITRIM;
 # and add/remove file-based encryption keys.
 allowxperm vold data_file_type:dir ioctl {
  FS_IOC_GET_ENCRYPTION_POLICY
+  FS_IOC_GET_ENCRYPTION_POLICY_EX
  FS_IOC_SET_ENCRYPTION_POLICY
  FS_IOC_ADD_ENCRYPTION_KEY
  FS_IOC_REMOVE_ENCRYPTION_KEY
@ -131,6 +153,7 @@ allowxperm vold data_file_type:dir ioctl {
 allowxperm vold {
  vold_data_file
  vold_metadata_file
+  is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_key_file')
 }:file ioctl {
  F2FS_IOC_SEC_TRIM_FILE
  FS_IOC_FIEMAP
--- a/private/vold_prepare_subdirs.te
+++ b/private/vold_prepare_subdirs.te
@ -10,6 +10,7 @@ allow vold_prepare_subdirs devpts:chr_file rw_file_perms;
 allow vold_prepare_subdirs vold:fd use;
 allow vold_prepare_subdirs vold:fifo_file { read write };
 allow vold_prepare_subdirs file_contexts_file:file r_file_perms;
+allow vold_prepare_subdirs seapp_contexts_file:file r_file_perms;
 allow vold_prepare_subdirs self:global_capability_class_set { chown dac_override dac_read_search fowner };
 allow vold_prepare_subdirs self:process setfscreate;
 allow vold_prepare_subdirs {
@ -27,6 +28,7 @@ allow vold_prepare_subdirs {
    fingerprint_vendor_data_file
    iris_vendor_data_file
    rollback_data_file
+    is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `storage_area_key_file')
    storaged_data_file
    sdk_sandbox_data_file
    sdk_sandbox_system_data_file
@ -54,6 +56,27 @@ allow vold_prepare_subdirs mnt_expand_file:dir search;
 allow vold_prepare_subdirs user_profile_data_file:dir { search getattr relabelfrom };
 allow vold_prepare_subdirs user_profile_root_file:dir { search getattr relabelfrom relabelto };

+# Allow vold_prepare_subdirs to create storage area directories on behalf of apps.
+is_flag_enabled(RELEASE_UNLOCKED_STORAGE_API, `
+  allow vold_prepare_subdirs {
+      storage_area_dir
+      storage_area_app_dir
+  }:dir {
+      rw_dir_perms
+      create
+      setattr # for chown() and chmod()
+      rmdir
+      unlink
+      relabelfrom # setfilecon
+      relabelto # setfilecon
+  };
+
+  # The storage area directories should have type storage_area_dir
+  type_transition vold_prepare_subdirs storage_area_app_dir:dir storage_area_dir;
+
+  selinux_check_context(vold_prepare_subdirs)
+')
+
 # Migrate legacy labels to apex_system_server_data_file (b/217581286)
 allow vold_prepare_subdirs {
  apex_appsearch_data_file