Restrict use of context= mount options.
Prior to this change, the init and recovery domains were
allowed unrestricted use of context= mount options to force
all files within a given filesystem to be treated as having a
security context specified at mount time. The context= mount
option can be used in device-specific fstab.<board> files
to assign a context to filesystems that do not support labeling
such as vfat where the default label of sdcard_external is not
appropriate (e.g. /firmware on hammerhead).
Restrict the use of context= mount options to types marked with the
contextmount_type attribute, and then remove write access from
such types from unconfineddomain and prohibit write access to such
types via neverallow. This ensures that the no write to /system
restriction cannot be bypassed via context= mount.
Change-Id: I4e773fadc9e11328d13a0acec164124ad6e840c1
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
diff --git a/domain.te b/domain.te
index b161467..6c800ab 100644
--- a/domain.te
+++ b/domain.te
@@ -259,3 +259,13 @@
# Only recovery should be doing writes to /system
neverallow { domain -recovery } { system_file exec_type }:dir_file_class_set
{ create write setattr relabelfrom relabelto append unlink link rename };
+
+# Restrict context mounts to specific types marked with
+# the contextmount_type attribute.
+neverallow domain {fs_type -contextmount_type}:filesystem relabelto;
+
+# 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
+ { create write setattr relabelfrom relabelto append unlink link rename };