Clean up old file-based OTA SELinux rules
Remove a number of SELinux rules which were required to support file
based OTA. After this, we can have a much stronger assertion that files
on /system are immutable. Tighten up the neverallow rules at the same
time.
Bug: 35853185
Bug: 15575013
Test: adb reboot recovery && adb sideload [file]
Change-Id: I4238d17808bed6a81f47e14eb1797496c07642e2
diff --git a/public/domain.te b/public/domain.te
index f4d5c68..f544cd1 100644
--- a/public/domain.te
+++ b/public/domain.te
@@ -238,8 +238,8 @@
# http://www.openwall.com/lists/oss-security/2016/09/26/14
neverallowxperm * devpts:chr_file ioctl TIOCSTI;
-# Do not allow any domain other than init or recovery to create unlabeled files.
-neverallow { domain -init -recovery } unlabeled:dir_file_class_set create;
+# Do not allow any domain other than init to create unlabeled files.
+neverallow { domain -init } unlabeled:dir_file_class_set create;
# Limit device node creation to these whitelisted domains.
neverallow {
@@ -269,8 +269,10 @@
# No domain needs mac_override as it is unused by SELinux.
neverallow * self:global_capability2_class_set mac_override;
-# Only recovery needs mac_admin to set contexts not defined in current policy.
-neverallow { domain -recovery } self:global_capability2_class_set mac_admin;
+# Disallow attempts to set contexts not defined in current policy
+# This helps guarantee that unknown or dangerous contents will not ever
+# be set.
+neverallow * self:global_capability2_class_set mac_admin;
# Once the policy has been loaded there shall be none to modify the policy.
# It is sealed.
@@ -376,6 +378,7 @@
-bootanim # for oemfs
-recovery # for /tmp/update_binary in tmpfs
} { fs_type -rootfs }:file execute;
+
# Files from cache should never be executed
neverallow domain { cache_file cache_backup_file cache_private_backup_file cache_recovery_file }:file execute;
@@ -399,10 +402,12 @@
neverallow { domain -init } properties_device:file { no_w_file_perms no_x_file_perms };
neverallow { domain -init } properties_serial:file { no_w_file_perms no_x_file_perms };
-# Only recovery should be doing writes to /system & /vendor
+# Nobody should be doing writes to /system & /vendor
+# These partitions are intended to be read-only and must never be
+# modified. Doing so would violate important Android security guarantees
+# and invalidate dm-verity signatures.
neverallow {
domain
- -recovery
with_asan(`-asan_extract')
} {
system_file
@@ -410,7 +415,7 @@
exec_type
}:dir_file_class_set { create write setattr relabelfrom append unlink link rename };
-neverallow { domain -recovery -kernel with_asan(`-asan_extract') } { system_file vendor_file_type exec_type }:dir_file_class_set relabelto;
+neverallow { domain -kernel with_asan(`-asan_extract') } { system_file vendor_file_type exec_type }:dir_file_class_set relabelto;
# Don't allow mounting on top of /system files or directories
neverallow * exec_type:dir_file_class_set mounton;
@@ -426,7 +431,7 @@
# Ensure that context mount types are not writable, to ensure that
# the write to /system restriction above is not bypassed via context=
# mount to another type.
-neverallow { domain -recovery } contextmount_type:dir_file_class_set
+neverallow * contextmount_type:dir_file_class_set
{ create write setattr relabelfrom relabelto append unlink link rename };
# Do not allow service_manager add for default service labels.
@@ -1091,12 +1096,9 @@
# vendor, and boot partitions.
neverallow * ~{ system_file vendor_file rootfs }:system module_load;
-# Only allow filesystem caps to be set at build time or
-# during upgrade by recovery.
-neverallow {
- domain
- -recovery
-} self:global_capability_class_set setfcap;
+# Only allow filesystem caps to be set at build time. Runtime changes
+# to filesystem capabilities are not permitted.
+neverallow * self:global_capability_class_set setfcap;
# Enforce AT_SECURE for executing crash_dump.
neverallow domain crash_dump:process noatsecure;
diff --git a/public/recovery.te b/public/recovery.te
index 3e3c28e..f6ad47f 100644
--- a/public/recovery.te
+++ b/public/recovery.te
@@ -12,10 +12,7 @@
# Recovery can only use HALs in passthrough mode
passthrough_hal_client_domain(recovery, hal_bootctl)
- allow recovery self:global_capability_class_set { chown dac_override fowner fsetid setfcap setuid setgid sys_admin sys_tty_config };
-
- # Set security contexts on files that are not known to the loaded policy.
- allow recovery self:global_capability2_class_set mac_admin;
+ allow recovery self:global_capability_class_set { dac_override fowner setuid setgid sys_admin sys_tty_config };
# Run helpers from / or /system without changing domain.
r_dir_file(recovery, rootfs)
@@ -29,26 +26,9 @@
allow recovery unlabeled:filesystem ~relabelto;
allow recovery contextmount_type:filesystem relabelto;
- # Create and relabel files and directories under /system.
- allow recovery exec_type:{ file lnk_file } { create_file_perms relabelfrom relabelto };
- allow recovery { system_file }:{ file lnk_file } { create_file_perms relabelfrom relabelto };
- allow recovery system_file:dir { create_dir_perms relabelfrom relabelto };
-
- # We may be asked to set an SELinux label for a type not known to the
- # currently loaded policy. Allow it.
- allow recovery unlabeled:{ file lnk_file } { create_file_perms relabelfrom relabelto };
- allow recovery unlabeled:dir { create_dir_perms relabelfrom relabelto };
# Get file contexts
allow recovery file_contexts_file:file r_file_perms;
- # 0eb17d944704b3eb140bb9dded299d3be3aed77e in build/ added SELinux
- # support to OTAs. However, that code has a bug. When an update occurs,
- # some directories are inappropriately labeled as exec_type. This is
- # only transient, and subsequent steps in the OTA script correct this
- # mistake. New devices are moving to block based OTAs, so this is not
- # worth fixing. b/15575013
- allow recovery exec_type:dir { create_dir_perms relabelfrom relabelto };
-
# Write to /proc/sys/vm/drop_caches
allow recovery proc_drop_caches:file w_file_perms;