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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "remoting/host/webauthn/remote_webauthn_caller_security_utils.h"
#include <optional>
#include "base/environment.h"
#include "base/logging.h"
#include "base/notimplemented.h"
#include "base/process/process_handle.h"
#include "base/strings/cstring_view.h"
#include "base/strings/utf_string_conversions.h"
#include "build/build_config.h"
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_WIN)
#include "base/containers/fixed_flat_set.h"
#include "base/files/file_path.h"
#include "remoting/host/base/process_util.h"
#endif
#if BUILDFLAG(IS_WIN)
#include <windows.h>
#include <memory>
#include <string>
#include "base/logging.h"
#include "base/win/scoped_handle.h"
#include "remoting/host/win/trust_util.h"
#endif
#if BUILDFLAG(IS_MAC)
#include <Security/Security.h>
#include <mach/kern_return.h>
#include <unistd.h>
#include <array>
#include "remoting/host/mac/trust_util.h"
#endif
namespace remoting {
namespace {
#if !defined(NDEBUG)
// No static variables needed for debug builds.
#elif BUILDFLAG(IS_LINUX)
constexpr auto kAllowedCallerPrograms =
base::MakeFixedFlatSet<base::FilePath::StringViewType>({
"/opt/google/chrome/chrome",
"/opt/google/chrome-beta/chrome",
"/opt/google/chrome-canary/chrome",
"/opt/google/chrome-unstable/chrome",
});
#elif BUILDFLAG(IS_WIN)
// Names of environment variables that store the path to directories where apps
// are installed.
constexpr auto kAppsDirectoryEnvVars =
base::MakeFixedFlatSet<base::cstring_view>({
"PROGRAMFILES",
// May happen if Chrome is upgraded from a 32-bit version.
"PROGRAMFILES(X86)",
// Refers to "C:\Program Files" if current process is 32-bit.
"ProgramW6432",
// For per-user installations.
"LOCALAPPDATA",
});
// Relative to the Program Files directory.
constexpr auto kAllowedCallerPrograms =
base::MakeFixedFlatSet<base::FilePath::StringViewType>({
L"Google\\Chrome\\Application\\chrome.exe",
L"Google\\Chrome Beta\\Application\\chrome.exe",
L"Google\\Chrome SxS\\Application\\chrome.exe",
L"Google\\Chrome Dev\\Application\\chrome.exe",
});
#elif BUILDFLAG(IS_MAC)
constexpr auto kAllowedIdentifiers = std::to_array<const std::string_view>(
{"com.google.Chrome", "com.google.Chrome.beta", "com.google.Chrome.dev",
"com.google.Chrome.canary"});
#endif
} // namespace
bool IsLaunchedByTrustedProcess() {
#if !defined(NDEBUG)
// Just return true on debug builds for the convenience of development.
return true;
#elif BUILDFLAG(IS_LINUX)
base::ProcessId parent_pid =
base::GetParentProcessId(base::GetCurrentProcessHandle());
// Note that on Linux the process image may no longer exist in its original
// path. This will happen when Chrome has been updated but hasn't been
// relaunched. The path can still be trusted since it's not spoofable even if
// it's no longer pointing to the current Chrome binary.
base::FilePath parent_image_path = GetProcessImagePath(parent_pid);
return kAllowedCallerPrograms.contains(parent_image_path.value());
#elif BUILDFLAG(IS_WIN)
auto environment = base::Environment::Create();
base::ProcessId parent_pid =
base::GetParentProcessId(base::GetCurrentProcessHandle());
base::FilePath parent_image_path = GetProcessImagePath(parent_pid);
// On Windows, Chrome launches native messaging hosts via cmd for stdio
// communication. See:
// chrome/browser/extensions/api/messaging/native_process_launcher_win.cc
// Therefore, we check if the parent is cmd and skip to the grandparent if
// that's the case. It's possible to do stdio communications without cmd, so
// we don't require the parent to always be cmd.
// COMSPEC is generally "C:\WINDOWS\system32\cmd.exe". Note that the casing
// does not match the actual file path's casing.
std::optional<std::string> comspec_utf8 = environment->GetVar("COMSPEC");
if (comspec_utf8.has_value()) {
base::FilePath::StringType comspec = base::UTF8ToWide(comspec_utf8.value());
if (base::FilePath::CompareEqualIgnoreCase(parent_image_path.value(),
comspec)) {
// Skip to the grandparent.
base::win::ScopedHandle parent_handle(
OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, false, parent_pid));
if (parent_handle.is_valid()) {
parent_pid = base::GetParentProcessId(parent_handle.Get());
parent_image_path = GetProcessImagePath(parent_pid);
} else {
PLOG(ERROR) << "Failed to query parent info.";
}
}
} else {
LOG(ERROR) << "COMSPEC is not set";
}
// Check if the caller's image path is allowlisted.
for (base::cstring_view apps_dir_env_var : kAppsDirectoryEnvVars) {
std::optional<std::string> apps_dir_path_utf8 =
environment->GetVar(apps_dir_env_var);
if (!apps_dir_path_utf8.has_value()) {
continue;
}
auto apps_dir_path =
base::FilePath::FromUTF8Unsafe(apps_dir_path_utf8.value());
if (!apps_dir_path.IsParent(parent_image_path)) {
continue;
}
for (const base::FilePath::StringViewType& allowed_caller_program :
kAllowedCallerPrograms) {
base::FilePath allowed_caller_program_full_path =
apps_dir_path.Append(allowed_caller_program);
if (base::FilePath::CompareEqualIgnoreCase(
parent_image_path.value(),
allowed_caller_program_full_path.value())) {
// Caller's path is allowlisted, now also check if it's properly signed.
return IsBinaryTrusted(parent_image_path);
}
}
}
// Caller's path is not allowlisted.
return false;
#elif BUILDFLAG(IS_MAC)
// TODO: crbug.com/410903981 - move away from PID-based security checks, which
// might be susceptible of PID reuse attacks, if Apple provides APIs to query
// parent process audit token without using a PPID.
base::ProcessId parent_pid = getppid();
kern_return_t kern_return;
task_name_t task;
kern_return = task_name_for_pid(mach_task_self(), parent_pid, &task);
if (kern_return != KERN_SUCCESS) {
LOG(ERROR) << "Failed to get task name for parent PID " << parent_pid
<< ": " << kern_return;
return false;
}
mach_msg_type_number_t size = TASK_AUDIT_TOKEN_COUNT;
audit_token_t audit_token;
kern_return =
task_info(task, TASK_AUDIT_TOKEN, (task_info_t)&audit_token, &size);
mach_port_deallocate(mach_task_self(), task);
if (kern_return != KERN_SUCCESS) {
LOG(ERROR) << "Failed to get audit token for parent PID " << parent_pid
<< ": " << kern_return;
return false;
}
return IsProcessTrusted(audit_token, kAllowedIdentifiers);
#else // Unsupported platform
NOTIMPLEMENTED();
return true;
#endif
}
} // namespace remoting
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