Force package installation with FUSE unless the package stores on device

The non-A/B package installation is subject to TOC/TOU flaw if the
attacker can switch the package in the middle of installation. And the
most pratical case is to store the package on an external device, e.g. a
sdcard, and swap the device in the middle.

To prevent that, we can adopt the same protection as used in sideloading
a package with FUSE. Specifically, when we install the package with FUSE,
we read the entire package to cryptographically verify its signature.
The hash for each transfer block is recorded in the memory (TOC), and
the subsequent reads (TOU) will be rejected upon dectecting a mismatch.

This CL forces the package installation with FUSE when the package stays
on a removable media.

Bug: 136498130
Test: Run bin/recovery --update_package with various paths;
and packages are installed from FUSE as expected

Change-Id: Ibc9b095036a2fa624e8edf6c347ed4f12aef072f

Android.bp

@@ -69,6 +69,7 @@ cc_defaults {
     ],
 
     static_libs: [
+        "libc++fs",
         "libinstall",
         "librecovery_fastboot",
         "libminui",

install/include/install/install.h

@@ -67,3 +67,7 @@ bool verify_package_compatibility(ZipArchiveHandle package_zip);
 // pre-device and serial number (if presents). A/B OTA specific checks: pre-build version,
 // fingerprint, timestamp.
 bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, OtaType ota_type);
+
+// Ensures the path to the update package is mounted. Also set the |should_use_fuse| to true if the
+// package stays on a removable media.
+bool SetupPackageMount(const std::string& package_path, bool* should_use_fuse);

install/install.cpp

@@ -30,6 +30,7 @@
 #include <atomic>
 #include <chrono>
 #include <condition_variable>
+#include <filesystem>
 #include <functional>
 #include <limits>
 #include <mutex>
@@ -722,3 +723,49 @@ bool verify_package(Package* package, RecoveryUI* ui) {
   }
   return true;
 }
+
+bool SetupPackageMount(const std::string& package_path, bool* should_use_fuse) {
+  CHECK(should_use_fuse != nullptr);
+
+  if (package_path.empty()) {
+    return false;
+  }
+
+  *should_use_fuse = true;
+  if (package_path[0] == '@') {
+    auto block_map_path = package_path.substr(1);
+    if (ensure_path_mounted(block_map_path) != 0) {
+      LOG(ERROR) << "Failed to mount " << block_map_path;
+      return false;
+    }
+    // uncrypt only produces block map only if the package stays on /data.
+    *should_use_fuse = false;
+    return true;
+  }
+
+  // Package is not a block map file.
+  if (ensure_path_mounted(package_path) != 0) {
+    LOG(ERROR) << "Failed to mount " << package_path;
+    return false;
+  }
+
+  // Reject the package if the input path doesn't equal the canonicalized path.
+  // e.g. /cache/../sdcard/update_package.
+  std::error_code ec;
+  auto canonical_path = std::filesystem::canonical(package_path, ec);
+  if (ec) {
+    LOG(ERROR) << "Failed to get canonical of " << package_path << ", " << ec.message();
+    return false;
+  }
+  if (canonical_path.string() != package_path) {
+    LOG(ERROR) << "Installation aborts. The canonical path " << canonical_path.string()
+               << " doesn't equal the original path " << package_path;
+    return false;
+  }
+
+  constexpr const char* CACHE_ROOT = "/cache";
+  if (android::base::StartsWith(package_path, CACHE_ROOT)) {
+    *should_use_fuse = false;
+  }
+  return true;
+}

recovery.cpp

@@ -733,13 +733,11 @@ Device::BuiltinAction start_recovery(Device* device, const std::vector<std::stri
         set_retry_bootloader_message(retry_count + 1, args);
       }
 
-      if (update_package[0] == '@') {
-        ensure_path_mounted(update_package + 1);
-      } else {
-        ensure_path_mounted(update_package);
-      }
-
-      if (install_with_fuse) {
+      bool should_use_fuse = false;
+      if (!SetupPackageMount(update_package, &should_use_fuse)) {
+        LOG(INFO) << "Failed to set up the package access, skipping installation";
+        status = INSTALL_ERROR;
+      } else if (install_with_fuse || should_use_fuse) {
         LOG(INFO) << "Installing package " << update_package << " with fuse";
         status = InstallWithFuseFromPath(update_package, ui);
       } else if (auto memory_package = Package::CreateMemoryPackage(

tests/Android.bp

@@ -94,6 +94,7 @@ librecovery_static_libs = [
     "liblp",
     "libvndksupport",
     "libtinyxml2",
+    "libc++fs",
 ]
 
 cc_test {

tests/unit/install_test.cpp

@@ -36,6 +36,7 @@
 #include "install/wipe_device.h"
 #include "otautil/paths.h"
 #include "private/setup_commands.h"
+#include "recovery_utils/roots.h"
 
 static void BuildZipArchive(const std::map<std::string, std::string>& file_map, int fd,
                             int compression_type) {
@@ -595,3 +596,30 @@ TEST(InstallTest, CheckPackageMetadata_ab_post_timestamp) {
       "\n");
   TestCheckPackageMetadata(metadata, OtaType::AB, true);
 }
+
+TEST(InstallTest, SetupPackageMount_package_path) {
+  load_volume_table();
+  bool install_with_fuse;
+
+  // Setup should fail if the input path doesn't exist.
+  ASSERT_FALSE(SetupPackageMount("/does_not_exist", &install_with_fuse));
+
+  // Package should be installed with fuse if it's not in /cache.
+  TemporaryDir temp_dir;
+  TemporaryFile update_package(temp_dir.path);
+  ASSERT_TRUE(SetupPackageMount(update_package.path, &install_with_fuse));
+  ASSERT_TRUE(install_with_fuse);
+
+  // Setup should fail if the input path isn't canonicalized.
+  std::string uncanonical_package_path = android::base::Join(
+      std::vector<std::string>{
+          temp_dir.path,
+          "..",
+          android::base::Basename(temp_dir.path),
+          android::base::Basename(update_package.path),
+      },
+      '/');
+
+  ASSERT_EQ(0, access(uncanonical_package_path.c_str(), R_OK));
+  ASSERT_FALSE(SetupPackageMount(uncanonical_package_path, &install_with_fuse));
+}