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
diff --git a/install/install.cpp b/install/install.cpp
index 9166f9c..43916b3 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>
@@ -722,3 +723,49 @@
}
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;
+}