sandboxed-api/sandboxed_api/sandbox2/forkserver.h
Wiktor Garbacz 035965060a Create initial namespaces on demand
PiperOrigin-RevId: 283321826
Change-Id: I746ce726b834273fd8a8e0de36b311c46e42d57a
2019-12-02 05:31:42 -08:00

114 lines
3.9 KiB
C++

// Copyright 2019 Google LLC. All Rights Reserved.
//
// 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.
// sandbox2::ForkServer is a class which serves fork()ing request for the
// clients.
#ifndef SANDBOXED_API_SANDBOX2_FORKSERVER_H_
#define SANDBOXED_API_SANDBOX2_FORKSERVER_H_
#include <sys/types.h>
#include <string>
#include <vector>
#include <glog/logging.h>
#include "absl/synchronization/mutex.h"
namespace sandbox2 {
class Comms;
class ForkRequest;
// Envvar indicating that this process should not start the fork-server.
static constexpr const char* kForkServerDisableEnv = "SANDBOX2_NOFORKSERVER";
class ForkClient {
public:
ForkClient(const ForkClient&) = delete;
ForkClient& operator=(const ForkClient&) = delete;
explicit ForkClient(Comms* comms) : comms_(comms) {}
// Sends the fork request over the supplied Comms channel.
pid_t SendRequest(const ForkRequest& request, int exec_fd, int comms_fd,
int user_ns_fd = -1, pid_t* init_pid = nullptr);
private:
// Comms channel connecting with the ForkServer. Not owned by the object.
Comms* comms_;
// Mutex locking transactions (requests) over the Comms channel.
absl::Mutex comms_mutex_;
};
class ForkServer {
public:
ForkServer(const ForkServer&) = delete;
ForkServer& operator=(const ForkServer&) = delete;
explicit ForkServer(Comms* comms) : comms_(comms) {
if (!Initialize()) {
LOG(FATAL) << "Could not initialize the ForkServer";
}
}
// Receives a fork request from the master process. The started process does
// not need to be waited for (with waitid/waitpid/wait3/wait4) as the current
// process will have the SIGCHLD set to sa_flags=SA_NOCLDWAIT.
// Returns values defined as with fork() (-1 means error).
pid_t ServeRequest();
private:
// Creates and launched the child process.
void LaunchChild(const ForkRequest& request, int execve_fd, int client_fd,
uid_t uid, gid_t gid, int user_ns_fd, int signaling_fd,
bool avoid_pivot_root) const;
// Prepares the Fork-Server (worker side, not the requester side) for work by
// sanitizing the environment:
// - go down if the parent goes down,
// - become subreaper - PR_SET_CHILD_SUBREAPER (man prctl),
// - don't convert children processes into zombies if they terminate.
bool Initialize();
// Creates initial namespaces used as a template for namespaced sandboxees
void CreateInitialNamespaces();
// Prepares arguments for the upcoming execve (if execve was requested).
static void PrepareExecveArgs(const ForkRequest& request,
std::vector<std::string>* args,
std::vector<std::string>* envp);
// Ensures that no unnecessary file descriptors are lingering after execve().
static void SanitizeEnvironment(int client_fd);
// Executes the sandboxee, or exit with Executor::kFailedExecve.
static void ExecuteProcess(int execve_fd, const char** argv,
const char** envp);
// Runs namespace initializers for a sandboxee.
static void InitializeNamespaces(const ForkRequest& request, uid_t uid,
gid_t gid, bool avoid_pivot_root);
// Comms channel which is used to send requests to this class. Not owned by
// the object.
Comms* comms_;
int initial_mntns_fd_ = -1;
int initial_userns_fd_ = -1;
};
} // namespace sandbox2
#endif // SANDBOXED_API_SANDBOX2_FORKSERVER_H_