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
diff --git a/Android.bp b/Android.bp
index 4032bcc..e7e1938 100644
--- a/Android.bp
+++ b/Android.bp
@@ -72,6 +72,7 @@
],
static_libs: [
+ "libc++fs",
"libinstall",
"librecovery_fastboot",
"libminui",
@@ -94,6 +95,7 @@
],
shared_libs: [
+ "libfusesideload",
"librecovery_ui",
],
}
diff --git a/install/include/install/install.h b/install/include/install/install.h
index 87d43ab..bef23e9 100644
--- a/install/include/install/install.h
+++ b/install/include/install/install.h
@@ -63,3 +63,7 @@
// 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 4bb0903..1c9bf2f 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 @@
}
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;
+}
diff --git a/recovery.cpp b/recovery.cpp
index 9ea616e..526e1a5 100644
--- a/recovery.cpp
+++ b/recovery.cpp
@@ -752,7 +752,11 @@
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(
diff --git a/tests/Android.bp b/tests/Android.bp
index bde1bc5..4c23255 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -92,6 +92,7 @@
"libhidlbase",
"liblp",
"libtinyxml2",
+ "libc++fs",
]
cc_test {
diff --git a/tests/unit/install_test.cpp b/tests/unit/install_test.cpp
index 370fbdc..ee75349 100644
--- a/tests/unit/install_test.cpp
+++ b/tests/unit/install_test.cpp
@@ -35,6 +35,7 @@
#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) {
@@ -513,3 +514,30 @@
"\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));
+}