sandboxed-api/sandboxed_api/sandbox2/executor.cc

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// Copyright 2019 Google LLC
//
// 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
//
// https://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.
// Implementation of the sandbox2::Executor class
#include "sandboxed_api/sandbox2/executor.h"
#include <fcntl.h>
#include <libgen.h>
#include <sys/socket.h>
#include <unistd.h>
#include <climits>
#include <cstddef>
#include "absl/memory/memory.h"
#include "absl/strings/str_cat.h"
#include "sandboxed_api/sandbox2/fork_client.h"
#include "sandboxed_api/sandbox2/forkserver.pb.h"
#include "sandboxed_api/sandbox2/global_forkclient.h"
#include "sandboxed_api/sandbox2/ipc.h"
#include "sandboxed_api/sandbox2/util.h"
#include "sandboxed_api/util/fileops.h"
namespace sandbox2 {
namespace file_util = ::sapi::file_util;
std::vector<std::string> Executor::CopyEnviron() {
return util::CharPtrArray(environ).ToStringVector();
}
pid_t Executor::StartSubProcess(int32_t clone_flags, const Namespace* ns,
const std::vector<int>& caps,
pid_t* init_pid_out) {
if (started_) {
LOG(ERROR) << "This executor has already been started";
return -1;
}
if (!path_.empty()) {
exec_fd_ = file_util::fileops::FDCloser(open(path_.c_str(), O_PATH));
if (exec_fd_.get() < 0) {
PLOG(ERROR) << "Could not open file " << path_;
return -1;
}
}
if (libunwind_sbox_for_pid_ != 0) {
VLOG(1) << "StartSubProcces, starting libunwind";
} else if (exec_fd_.get() < 0) {
VLOG(1) << "StartSubProcess, with [Fork-Server]";
} else if (!path_.empty()) {
VLOG(1) << "StartSubProcess, with file " << path_;
} else {
VLOG(1) << "StartSubProcess, with fd " << exec_fd_.get();
}
ForkRequest request;
*request.mutable_args() = {argv_.begin(), argv_.end()};
*request.mutable_envs() = {envp_.begin(), envp_.end()};
// Add LD_ORIGIN_PATH to envs, as it'll make the amount of syscalls invoked by
// ld.so smaller.
if (!path_.empty()) {
request.add_envs(absl::StrCat("LD_ORIGIN_PATH=",
file_util::fileops::StripBasename(path_)));
}
// If neither the path, nor exec_fd is specified, just assume that we need to
// send a fork request.
//
// Otherwise, it's either sandboxing pre- or post-execve with the global
// Fork-Server.
if (libunwind_sbox_for_pid_ != 0) {
request.set_mode(FORKSERVER_FORK_JOIN_SANDBOX_UNWIND);
} else if (exec_fd_.get() == -1) {
request.set_mode(FORKSERVER_FORK);
} else if (enable_sandboxing_pre_execve_) {
request.set_mode(FORKSERVER_FORK_EXECVE_SANDBOX);
} else {
request.set_mode(FORKSERVER_FORK_EXECVE);
}
if (ns) {
clone_flags |= ns->GetCloneFlags();
*request.mutable_mount_tree() = ns->mounts().GetMountTree();
request.set_hostname(ns->hostname());
}
request.set_clone_flags(clone_flags);
for (auto cap : caps) {
request.add_capabilities(cap);
}
file_util::fileops::FDCloser ns_fd;
if (libunwind_sbox_for_pid_ != 0) {
const std::string ns_path =
absl::StrCat("/proc/", libunwind_sbox_for_pid_, "/ns/user");
ns_fd = file_util::fileops::FDCloser(open(ns_path.c_str(), O_RDONLY));
PCHECK(ns_fd.get() != -1)
<< "Could not open user ns fd (" << ns_path << ")";
}
pid_t init_pid = -1;
pid_t sandboxee_pid;
if (fork_client_) {
sandboxee_pid = fork_client_->SendRequest(request, exec_fd_.get(),
client_comms_fd_.get(),
ns_fd.get(), &init_pid);
} else {
sandboxee_pid = GlobalForkClient::SendRequest(request, exec_fd_.get(),
client_comms_fd_.get(),
ns_fd.get(), &init_pid);
}
if (init_pid < 0) {
LOG(ERROR) << "Could not obtain init PID";
} else if (init_pid == 0 && request.clone_flags() & CLONE_NEWPID) {
LOG(FATAL)
<< "No init process was spawned even though a PID NS was created, "
<< "potential logic bug";
}
if (init_pid_out) {
*init_pid_out = init_pid;
}
started_ = true;
client_comms_fd_.Close();
exec_fd_.Close();
VLOG(1) << "StartSubProcess returned with: " << sandboxee_pid;
return sandboxee_pid;
}
std::unique_ptr<ForkClient> Executor::StartForkServer() {
// This flag is set explicitly to 'true' during object instantiation, and
// custom fork-servers should never be sandboxed.
set_enable_sandbox_before_exec(false);
pid_t pid = StartSubProcess(0);
if (pid == -1) {
return nullptr;
}
return absl::make_unique<ForkClient>(pid, ipc_.comms());
}
void Executor::SetUpServerSideCommsFd() {
int sv[2];
if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) == -1) {
PLOG(FATAL) << "socketpair(AF_UNIX, SOCK_STREAM) failed";
}
client_comms_fd_ = file_util::fileops::FDCloser(sv[0]);
ipc_.SetUpServerSideComms(sv[1]);
}
} // namespace sandbox2