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114 lines
3.9 KiB
C++
114 lines
3.9 KiB
C++
// Copyright 2019 Google LLC. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// sandbox2::ForkServer is a class which serves fork()ing request for the
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// clients.
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#ifndef SANDBOXED_API_SANDBOX2_FORKSERVER_H_
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#define SANDBOXED_API_SANDBOX2_FORKSERVER_H_
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#include <sys/types.h>
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#include <string>
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#include <vector>
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#include <glog/logging.h>
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#include "absl/synchronization/mutex.h"
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namespace sandbox2 {
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class Comms;
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class ForkRequest;
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// Envvar indicating that this process should not start the fork-server.
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static constexpr const char* kForkServerDisableEnv = "SANDBOX2_NOFORKSERVER";
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class ForkClient {
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public:
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ForkClient(const ForkClient&) = delete;
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ForkClient& operator=(const ForkClient&) = delete;
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explicit ForkClient(Comms* comms) : comms_(comms) {}
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// Sends the fork request over the supplied Comms channel.
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pid_t SendRequest(const ForkRequest& request, int exec_fd, int comms_fd,
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int user_ns_fd = -1, pid_t* init_pid = nullptr);
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private:
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// Comms channel connecting with the ForkServer. Not owned by the object.
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Comms* comms_;
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// Mutex locking transactions (requests) over the Comms channel.
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absl::Mutex comms_mutex_;
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};
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class ForkServer {
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public:
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ForkServer(const ForkServer&) = delete;
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ForkServer& operator=(const ForkServer&) = delete;
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explicit ForkServer(Comms* comms) : comms_(comms) {
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if (!Initialize()) {
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LOG(FATAL) << "Could not initialize the ForkServer";
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}
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}
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// Receives a fork request from the master process. The started process does
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// not need to be waited for (with waitid/waitpid/wait3/wait4) as the current
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// process will have the SIGCHLD set to sa_flags=SA_NOCLDWAIT.
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// Returns values defined as with fork() (-1 means error).
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pid_t ServeRequest();
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private:
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// Creates and launched the child process.
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void LaunchChild(const ForkRequest& request, int execve_fd, int client_fd,
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uid_t uid, gid_t gid, int user_ns_fd, int signaling_fd,
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bool avoid_pivot_root) const;
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// Prepares the Fork-Server (worker side, not the requester side) for work by
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// sanitizing the environment:
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// - go down if the parent goes down,
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// - become subreaper - PR_SET_CHILD_SUBREAPER (man prctl),
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// - don't convert children processes into zombies if they terminate.
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bool Initialize();
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// Creates initial namespaces used as a template for namespaced sandboxees
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void CreateInitialNamespaces();
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// Prepares arguments for the upcoming execve (if execve was requested).
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static void PrepareExecveArgs(const ForkRequest& request,
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std::vector<std::string>* args,
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std::vector<std::string>* envp);
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// Ensures that no unnecessary file descriptors are lingering after execve().
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static void SanitizeEnvironment(int client_fd);
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// Executes the sandboxee, or exit with Executor::kFailedExecve.
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static void ExecuteProcess(int execve_fd, const char** argv,
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const char** envp);
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// Runs namespace initializers for a sandboxee.
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static void InitializeNamespaces(const ForkRequest& request, uid_t uid,
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gid_t gid, bool avoid_pivot_root);
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// Comms channel which is used to send requests to this class. Not owned by
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// the object.
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Comms* comms_;
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int initial_mntns_fd_ = -1;
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int initial_userns_fd_ = -1;
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};
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} // namespace sandbox2
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#endif // SANDBOXED_API_SANDBOX2_FORKSERVER_H_
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