From 58a27693b22da9b93c634d053a53deb4c4a71e4e Mon Sep 17 00:00:00 2001 From: Tianjie Xu Date: Tue, 6 Aug 2019 12:32:05 -0700 Subject: [PATCH] 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 | 1 + install/include/install/install.h | 4 +++ install/install.cpp | 47 +++++++++++++++++++++++++++++++ recovery.cpp | 12 ++++---- tests/Android.bp | 1 + tests/unit/install_test.cpp | 28 ++++++++++++++++++ 6 files changed, 86 insertions(+), 7 deletions(-) diff --git a/Android.bp b/Android.bp index 0759e08d..a9a08a1a 100644 --- a/Android.bp +++ b/Android.bp @@ -69,6 +69,7 @@ cc_defaults { ], static_libs: [ + "libc++fs", "libinstall", "librecovery_fastboot", "libminui", diff --git a/install/include/install/install.h b/install/include/install/install.h index b4b3a914..c3331c8b 100644 --- a/install/include/install/install.h +++ b/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& 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 9166f9cf..43916b3d 100644 --- a/install/install.cpp +++ b/install/install.cpp @@ -30,6 +30,7 @@ #include #include #include +#include #include #include #include @@ -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; +} diff --git a/recovery.cpp b/recovery.cpp index 682ddbc4..8f8f7dc0 100644 --- a/recovery.cpp +++ b/recovery.cpp @@ -733,13 +733,11 @@ Device::BuiltinAction start_recovery(Device* device, const std::vector& 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{ + 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)); +}