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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef SANDBOX_LINUX_SYSCALL_BROKER_BROKER_PROCESS_H_
#define SANDBOX_LINUX_SYSCALL_BROKER_BROKER_PROCESS_H_
#include <sys/stat.h>
#include <memory>
#include <optional>
#include <string>
#include <vector>
#include "base/functional/callback_forward.h"
#include "sandbox/linux/syscall_broker/broker_sandbox_config.h"
#include "sandbox/sandbox_export.h"
namespace sandbox {
namespace syscall_broker {
class BrokerClient;
// Create a new "broker" process to which we can send requests via an IPC
// channel by forking the current process.
// This is a low level IPC mechanism that is suitable to be called from a
// signal handler.
// A process would typically create a broker process before entering
// sandboxing.
// 1. BrokerProcess open_broker(read_allowlist, write_allowlist);
// 2. CHECK(open_broker.Init(NULL));
// 3. Enable sandbox.
// 4. Use open_broker.Open() to open files.
class SANDBOX_EXPORT BrokerProcess {
public:
enum class BrokerType { SIGNAL_BASED };
using BrokerSideCallback =
base::OnceCallback<bool(const BrokerSandboxConfig&)>;
// |policy| is the policy for the broker process.
//
// |denied_errno| is the error code returned when methods such as Open() or
// Access() are invoked on a file which is not in the allowlist (EACCESS would
// be a typical value).
//
// |fast_check_in_client| controls whether requests are
// first filtered on the client side before being proxied. Apart from tests,
// this should always be true since our main clients are not always
// well-behaved. They may have third party libraries that don't know about
// sandboxing, and typically try to open all sorts of stuff they don't really
// need. It's important to reduce this load given that there is only one
// pipeline to the broker process, and it is not multi-threaded.
//
// |quiet_failures_for_tests| is reserved for unit tests, don't use it.
BrokerProcess(std::optional<BrokerSandboxConfig> policy,
BrokerType broker_type,
bool fast_check_in_client = true,
bool quiet_failures_for_tests = false);
BrokerProcess(const BrokerProcess&) = delete;
BrokerProcess& operator=(const BrokerProcess&) = delete;
~BrokerProcess();
// Will initialize the broker process. There should be no threads at this
// point, since we need to fork().
// broker_process_init_callback will be called in the new broker process,
// after fork() returns.
bool Fork(BrokerSideCallback broker_process_init_callback);
// Return the PID of the child created by Fork().
int broker_pid() const { return broker_pid_; }
// Can be used in bpf_dsl::Policy::EvaluateSyscall() implementations to
// determine if the system call |sysno| should be trapped and forwarded
// to the broker process for handling. This examines the
// |policy_->allowed_command_set| iff |fast_check_in_client_| is true. If
// the fast checks are disabled, then all possible brokerable system
// calls are forwarded to the broker process for handling.
bool IsSyscallAllowed(int sysno) const;
// Gets the signal-based BrokerClient created by Fork().
syscall_broker::BrokerClient* GetBrokerClientSignalBased() const {
return broker_client_.get();
}
private:
friend class BrokerProcessTestHelper;
friend class HandleFilesystemViaBrokerPolicy;
// IsSyscallBrokerable() answers the same question as IsSyscallAllowed(),
// but takes |fast_check| as a parameter. If |fast_check| is false, do not
// check |policy_->allowed_command_set| before returning true for a syscall
// that is brokerable.
bool IsSyscallBrokerable(int sysno, bool fast_check) const;
// Close the IPC channel with the other party. This should only be used
// by tests and none of the class methods should be used afterwards.
void CloseChannel();
// Forks the signal-based broker, where syscall emulation is performed using
// signals in the sandboxed process that connect to the broker via Unix
// socket.
bool ForkSignalBasedBroker(BrokerSideCallback broker_process_init_callback);
// Variables initialized by the constructor.
std::optional<BrokerSandboxConfig>
policy_; // Can also be created by SendPolicy().
const BrokerType broker_type_;
const bool fast_check_in_client_;
const bool quiet_failures_for_tests_;
bool initialized_ = false; // Whether we've been through Fork() yet.
pid_t broker_pid_ = -1; // The PID of the broker (child) created in Fork().
// Created in the parent process.
std::unique_ptr<syscall_broker::BrokerClient> broker_client_;
};
} // namespace syscall_broker
} // namespace sandbox
#endif // SANDBOX_LINUX_SYSCALL_BROKER_BROKER_PROCESS_H_
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