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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "apex_shim.h"
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <openssl/sha.h>
#include <filesystem>
#include <fstream>
#include <sstream>
#include <unordered_set>
#include "apex_constants.h"
#include "apex_file.h"
#include "string_log.h"
using android::base::ErrnoError;
using android::base::Error;
using android::base::Result;
namespace android {
namespace apex {
namespace shim {
namespace fs = std::filesystem;
namespace {
static constexpr const char* kApexCtsShimPackage = "com.android.apex.cts.shim";
static constexpr const char* kHashFilePath = "etc/hash.txt";
static constexpr const int kBufSize = 1024;
static constexpr const fs::perms kForbiddenFilePermissions =
fs::perms::owner_exec | fs::perms::group_exec | fs::perms::others_exec;
static constexpr const char* kExpectedCtsShimFiles[] = {
"apex_manifest.json",
"apex_manifest.pb",
"etc/hash.txt",
"app/CtsShimPrebuilt/CtsShimPrebuilt.apk",
"priv-app/CtsShimPrivPrebuilt/CtsShimPrivPrebuilt.apk",
};
Result<std::string> CalculateSha512(const std::string& path) {
LOG(DEBUG) << "Calculating SHA512 of " << path;
SHA512_CTX ctx;
SHA512_Init(&ctx);
std::ifstream apex(path, std::ios::binary);
if (apex.bad()) {
return Error() << "Failed to open " << path;
}
char buf[kBufSize];
while (!apex.eof()) {
apex.read(buf, kBufSize);
if (apex.bad()) {
return Error() << "Failed to read " << path;
}
int bytes_read = apex.gcount();
SHA512_Update(&ctx, buf, bytes_read);
}
uint8_t hash[SHA512_DIGEST_LENGTH];
SHA512_Final(hash, &ctx);
std::stringstream ss;
ss << std::hex;
for (int i = 0; i < SHA512_DIGEST_LENGTH; i++) {
ss << std::setw(2) << std::setfill('0') << static_cast<int>(hash[i]);
}
return ss.str();
}
Result<std::vector<std::string>> GetAllowedHashes(const std::string& path) {
using android::base::ReadFileToString;
using android::base::StringPrintf;
const std::string& file_path =
StringPrintf("%s/%s", path.c_str(), kHashFilePath);
LOG(DEBUG) << "Reading SHA512 from " << file_path;
std::string hash;
if (!ReadFileToString(file_path, &hash, false /* follows symlinks */)) {
return ErrnoError() << "Failed to read " << file_path;
}
std::vector<std::string> allowed_hashes = android::base::Split(hash, "\n");
auto system_shim_hash = CalculateSha512(
StringPrintf("%s/%s", kApexPackageSystemDir, shim::kSystemShimApexName));
if (!system_shim_hash.ok()) {
return system_shim_hash.error();
}
allowed_hashes.push_back(std::move(*system_shim_hash));
return allowed_hashes;
}
} // namespace
bool IsShimApex(const ApexFile& apex_file) {
return apex_file.GetManifest().name() == kApexCtsShimPackage;
}
Result<void> ValidateShimApex(const std::string& mount_point,
const ApexFile& apex_file) {
LOG(DEBUG) << "Validating shim apex " << mount_point;
const ApexManifest& manifest = apex_file.GetManifest();
if (!manifest.preinstallhook().empty() ||
!manifest.postinstallhook().empty()) {
return Errorf("Shim apex is not allowed to have pre or post install hooks");
}
std::error_code ec;
std::unordered_set<std::string> expected_files;
for (auto file : kExpectedCtsShimFiles) {
expected_files.insert(file);
}
auto iter = fs::recursive_directory_iterator(mount_point, ec);
// Unfortunately fs::recursive_directory_iterator::operator++ can throw an
// exception, which means that it's impossible to use range-based for loop
// here.
// TODO: wrap into a non-throwing iterator to support range-based for loop.
while (iter != fs::end(iter)) {
auto path = iter->path();
// Resolve the mount point to ensure any trailing slash is removed.
auto resolved_mount_point = fs::path(mount_point).string();
auto local_path = path.string().substr(resolved_mount_point.length() + 1);
fs::file_status status = iter->status(ec);
if (fs::is_symlink(status)) {
return Error()
<< "Shim apex is not allowed to contain symbolic links, found "
<< path;
} else if (fs::is_regular_file(status)) {
if ((status.permissions() & kForbiddenFilePermissions) !=
fs::perms::none) {
return Error() << path << " has illegal permissions";
}
auto ex = expected_files.find(local_path);
if (ex != expected_files.end()) {
expected_files.erase(local_path);
} else {
return Error() << path << " is an unexpected file inside the shim apex";
}
} else if (!fs::is_directory(status)) {
// If this is not a symlink, a file or a directory, fail.
return Error() << "Unexpected file entry in shim apex: " << iter->path();
}
iter = iter.increment(ec);
if (ec) {
return Error() << "Failed to scan " << mount_point << " : "
<< ec.message();
}
}
return {};
}
Result<void> ValidateUpdate(const std::string& system_apex_path,
const std::string& new_apex_path) {
LOG(DEBUG) << "Validating update of shim apex to " << new_apex_path
<< " using system shim apex " << system_apex_path;
auto allowed = GetAllowedHashes(system_apex_path);
if (!allowed.ok()) {
return allowed.error();
}
auto actual = CalculateSha512(new_apex_path);
if (!actual.ok()) {
return actual.error();
}
auto it = std::find(allowed->begin(), allowed->end(), *actual);
if (it == allowed->end()) {
return Error() << new_apex_path << " has unexpected SHA512 hash "
<< *actual;
}
return {};
}
} // namespace shim
} // namespace apex
} // namespace android