Recursively restorecon when SELinux label changes.

PackageManager has been pretty aggressive about asking installd to
restorecon over app data when it thinks something might have
changed.  However, in the vast majority of cases these are no-op
requests, and we waste a bunch of time recursively walking all
private data, easily costing 60+ seconds on dogfooder devices.

This change updates the initial "create_app_data" command to kick off
a recursive restorecon if it detects that the top-level SELinux label
on the app private data directory changes.  The "create_app_data"
command is designed to ensure that an app's storage is ready, so
PackageManager always calls it at least once per boot before apps
can run.  (This change means that PackageManager no longer needs to
make separate "restorecon_app_data" calls.)

Test: booted, verified that a label change triggered restorecon
Bug: 30768146
Change-Id: I0c8d4018cf8ff888d0ae07a82adc3d61a6002aad

1 files changed, 64 insertions, 13 deletions

diff --git a/cmds/installd/commands.cpp b/cmds/installd/commands.cpp
index 5b47b3e500..4ed8997fcb 100644
--- a/cmds/installd/commands.cpp
+++ b/cmds/installd/commands.cpp
@@ -99,23 +99,64 @@ static std::string create_primary_profile(const std::string& profile_dir) {
     return StringPrintf("%s/%s", profile_dir.c_str(), PRIMARY_PROFILE_NAME);
 }
 
-static int prepare_app_dir(const std::string& path, mode_t target_mode, uid_t uid,
-        const char* pkgname, const char* seinfo) {
+/**
+ * Perform restorecon of the given path, but only perform recursive restorecon
+ * if the label of that top-level file actually changed.  This can save us
+ * significant time by avoiding no-op traversals of large filesystem trees.
+ */
+static int restorecon_app_data_lazy(const char* path, const char* seinfo, uid_t uid) {
+    int res = 0;
+    char* before = nullptr;
+    char* after = nullptr;
+
+    // Note that SELINUX_ANDROID_RESTORECON_DATADATA flag is set by
+    // libselinux. Not needed here.
+
+    if (lgetfilecon(path, &before) < 0) {
+        PLOG(ERROR) << "Failed before getfilecon for " << path;
+        goto fail;
+    }
+    if (selinux_android_restorecon_pkgdir(path, seinfo, uid, 0) < 0) {
+        PLOG(ERROR) << "Failed top-level restorecon for " << path;
+        goto fail;
+    }
+    if (lgetfilecon(path, &after) < 0) {
+        PLOG(ERROR) << "Failed after getfilecon for " << path;
+        goto fail;
+    }
+
+    // If the initial top-level restorecon above changed the label, then go
+    // back and restorecon everything recursively
+    if (strcmp(before, after)) {
+        LOG(DEBUG) << "Detected label change from " << before << " to " << after << " at " << path
+                << "; running recursive restorecon";
+        if (selinux_android_restorecon_pkgdir(path, seinfo, uid,
+                SELINUX_ANDROID_RESTORECON_RECURSE) < 0) {
+            PLOG(ERROR) << "Failed recursive restorecon for " << path;
+            goto fail;
+        }
+    }
+
+    goto done;
+fail:
+    res = -1;
+done:
+    free(before);
+    free(after);
+    return res;
+}
+
+static int prepare_app_dir(const std::string& path, mode_t target_mode, uid_t uid) {
     if (fs_prepare_dir_strict(path.c_str(), target_mode, uid, uid) != 0) {
         PLOG(ERROR) << "Failed to prepare " << path;
         return -1;
     }
-    if (selinux_android_setfilecon(path.c_str(), pkgname, seinfo, uid) < 0) {
-        PLOG(ERROR) << "Failed to setfilecon " << path;
-        return -1;
-    }
     return 0;
 }
 
 static int prepare_app_dir(const std::string& parent, const char* name, mode_t target_mode,
-        uid_t uid, const char* pkgname, const char* seinfo) {
-    return prepare_app_dir(StringPrintf("%s/%s", parent.c_str(), name), target_mode, uid, pkgname,
-            seinfo);
+        uid_t uid) {
+    return prepare_app_dir(StringPrintf("%s/%s", parent.c_str(), name), target_mode, uid);
 }
 
 int create_app_data(const char *uuid, const char *pkgname, userid_t userid, int flags,
@@ -124,9 +165,14 @@ int create_app_data(const char *uuid, const char *pkgname, userid_t userid, int
     mode_t target_mode = target_sdk_version >= MIN_RESTRICTED_HOME_SDK_VERSION ? 0700 : 0751;
     if (flags & FLAG_STORAGE_CE) {
         auto path = create_data_user_ce_package_path(uuid, userid, pkgname);
-        if (prepare_app_dir(path, target_mode, uid, pkgname, seinfo) ||
-                prepare_app_dir(path, "cache", 0771, uid, pkgname, seinfo) ||
-                prepare_app_dir(path, "code_cache", 0771, uid, pkgname, seinfo)) {
+        if (prepare_app_dir(path, target_mode, uid) ||
+                prepare_app_dir(path, "cache", 0771, uid) ||
+                prepare_app_dir(path, "code_cache", 0771, uid)) {
+            return -1;
+        }
+
+        // Consider restorecon over contents if label changed
+        if (restorecon_app_data_lazy(path.c_str(), seinfo, uid)) {
             return -1;
         }
 
@@ -139,11 +185,16 @@ int create_app_data(const char *uuid, const char *pkgname, userid_t userid, int
     }
     if (flags & FLAG_STORAGE_DE) {
         auto path = create_data_user_de_package_path(uuid, userid, pkgname);
-        if (prepare_app_dir(path, target_mode, uid, pkgname, seinfo)) {
+        if (prepare_app_dir(path, target_mode, uid)) {
             // TODO: include result once 25796509 is fixed
             return 0;
         }
 
+        // Consider restorecon over contents if label changed
+        if (restorecon_app_data_lazy(path.c_str(), seinfo, uid)) {
+            return -1;
+        }
+
         if (property_get_bool("dalvik.vm.usejitprofiles")) {
             const std::string profile_path = create_data_user_profile_package_path(userid, pkgname);
             // read-write-execute only for the app user.