recovery: Fix recursive rm wipe of data

Android 6 re-introduced MCS/MLS SELinux contexts.  Unforunately,
this broke our previous SELinux model for walking /data and unlinking
everything but media.  Fix this by mounting /data with a temporary
SELinux context that works with the previous model.

Ticket: CYNGNOS-1747
Change-Id: Id87ad3bb357102c3a8bd7c1417183d788ef858a0

2 files changed, 30 insertions, 0 deletions

diff --git a/roots.cpp b/roots.cpp
index ceafed9..4586c42 100644
--- a/roots.cpp
+++ b/roots.cpp
@@ -253,6 +253,32 @@ int ensure_volume_mounted(Volume* v, bool force_rw) {
     return ensure_path_mounted_at(v->mount_point, nullptr, force_rw);
 }
 
+int remount_for_wipe(const char* path) {
+    int ret;
+
+    char *old_fs_options;
+    char *new_fs_options;
+
+    char se_context[] = ",context=u:object_r:app_data_file:s0";
+    Volume *v;
+
+    // Backup original mount options
+    v = volume_for_path(path);
+    old_fs_options = v->fs_options;
+
+    // Add SELinux mount override
+    asprintf(&new_fs_options, "%s%s", v->fs_options, se_context);
+
+    ensure_path_unmounted(path);
+    ret = ensure_path_mounted(path);
+
+    // Restore original mount options
+    v->fs_options = old_fs_options;
+    free(new_fs_options);
+
+    return ret;
+}
+
 int ensure_path_mounted(const char* path, bool force_rw) {
     // Mount at the default mount point.
     return ensure_path_mounted_at(path, nullptr, force_rw);
@@ -379,6 +405,7 @@ int format_volume(const char* volume, bool force) {
             LOGE("format_volume failed to mount /data\n");
             return -1;
         }
+        remount_for_wipe("/data");
         int rc = 0;
         rc = rmtree_except("/data/media", NULL);
         ensure_path_unmounted("/data");
@@ -402,6 +429,7 @@ int format_volume(const char* volume, bool force) {
 
     if (!force && strcmp(volume, "/data") == 0 && vdc->isEmulatedStorage()) {
         if (ensure_path_mounted("/data") == 0) {
+            remount_for_wipe("/data");
             // Preserve .layout_version to avoid "nesting bug"
             LOGI("Preserving layout version\n");
             unsigned char layout_buf[256];
diff --git a/roots.h b/roots.h
index addb142..2140363 100644
--- a/roots.h
+++ b/roots.h
@@ -30,6 +30,8 @@ Volume* volume_for_path(const char* path);
 // success (volume is mounted).
 int ensure_volume_mounted(Volume* v, bool force_rw=false);
 int ensure_path_mounted(const char* path, bool force_rw=false);
+// Above, plus override SELinux default context
+int remount_for_wipe(const char* path);
 
 // Similar to ensure_path_mounted, but allows one to specify the mount_point.
 int ensure_path_mounted_at(const char* path, const char* mount_point, bool force_rw=false);