Force off-device package installation with FUSE

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
Test: recovery_unit_test - no new failures

Change-Id: Ia5afd19854c3737110339fd59491b96708926ae5
Merged-In: I35119c2334895aa0ef4ed71b3ddd08f280c0c031

2 files changed, 51 insertions, 0 deletions

diff --git a/install/include/install/install.h b/install/include/install/install.h
index 87d43ab0..bef23e9c 100644
--- a/install/include/install/install.h
+++ b/install/include/install/install.h
@@ -63,3 +63,7 @@ bool ReadMetadataFromPackage(ZipArchiveHandle zip, std::map<std::string, std::st
 // 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);
diff --git a/install/install.cpp b/install/install.cpp
index 4bb0903c..1c9bf2fd 100644
--- a/install/install.cpp
+++ b/install/install.cpp
@@ -30,6 +30,7 @@
 #include <atomic>
 #include <chrono>
 #include <condition_variable>
+#include <filesystem>
 #include <functional>
 #include <limits>
 #include <mutex>
@@ -641,3 +642,49 @@ 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;
+}