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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "mozilla/ipc/ForkServer.h"
#include "chrome/common/chrome_switches.h"
#include "ipc/IPCMessageUtilsSpecializations.h"
#include "mozilla/BlockingResourceBase.h"
#include "mozilla/Logging.h"
#include "mozilla/Omnijar.h"
#include "mozilla/ipc/FileDescriptor.h"
#include "mozilla/ipc/IPDLParamTraits.h"
#include "mozilla/ipc/ProtocolMessageUtils.h"
#include "mozilla/ipc/SetProcessTitle.h"
#include "nsTraceRefcnt.h"
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#if defined(XP_LINUX) && defined(MOZ_SANDBOX)
# include "mozilla/SandboxLaunch.h"
#include <algorithm>
namespace mozilla {
namespace ipc {
LazyLogModule gForkServiceLog("ForkService");
ForkServer::ForkServer() {}
* Prepare an environment for running a fork server.
void ForkServer::InitProcess(int* aArgc, char*** aArgv) {
mTcver = MakeUnique<MiniTransceiver>(kClientPipeFd,
* Preload any resources that the forked child processes might need,
* and which might change incompatibly or become unavailable by the
* time they're started. For example: the omnijar files, or certain
* shared libraries.
static void ForkServerPreload(int& aArgc, char** aArgv) {
Omnijar::ChildProcessInit(aArgc, aArgv);
* Start providing the service at the IPC channel.
bool ForkServer::HandleMessages() {
while (true) {
UniquePtr<IPC::Message> msg;
if (!mTcver->Recv(msg)) {
if (mAppProcBuilder) {
// New process - child
return false;
// Stop the server
return true;
inline void CleanCString(nsCString& str) {
char* data;
int sz = str.GetMutableData(&data);
memset(data, ' ', sz);
inline void CleanString(std::string& str) {
const char deadbeef[] =
int pos = 0;
size_t sz = str.size();
while (sz > 0) {
int toclean = std::min(sz, sizeof(deadbeef) - 1);
str.replace(pos, toclean, deadbeef);
sz -= toclean;
pos += toclean;
inline void PrepareArguments(std::vector<std::string>& aArgv,
nsTArray<nsCString>& aArgvArray) {
for (auto& elt : aArgvArray) {
// Prepare aOptions->env_map
inline void PrepareEnv(base::LaunchOptions* aOptions,
nsTArray<EnvVar>& aEnvMap) {
for (auto& elt : aEnvMap) {
nsCString& var = std::get<0>(elt);
nsCString& val = std::get<1>(elt);
aOptions->env_map[var.get()] = val.get();
// Prepare aOptions->fds_to_remap
inline void PrepareFdsRemap(base::LaunchOptions* aOptions,
nsTArray<FdMapping>& aFdsRemap) {
MOZ_LOG(gForkServiceLog, LogLevel::Verbose, ("fds mapping:"));
for (auto& elt : aFdsRemap) {
// FDs are duplicated here.
int fd = std::get<0>(elt).ClonePlatformHandle().release();
std::pair<int, int> fdmap(fd, std::get<1>(elt));
MOZ_LOG(gForkServiceLog, LogLevel::Verbose,
("\t%d => %d", fdmap.first, fdmap.second));
template <class P>
static void ReadParamInfallible(IPC::MessageReader* aReader, P* aResult,
const char* aCrashMessage) {
if (!IPC::ReadParam(aReader, aResult)) {
* Parse a Message to get a list of arguments and fill a LaunchOptions.
inline bool ParseForkNewSubprocess(IPC::Message& aMsg,
std::vector<std::string>& aArgv,
base::LaunchOptions* aOptions) {
if (aMsg.type() != Msg_ForkNewSubprocess__ID) {
MOZ_LOG(gForkServiceLog, LogLevel::Verbose,
("unknown message type %d\n", aMsg.type()));
return false;
IPC::MessageReader reader(aMsg);
nsTArray<nsCString> argv_array;
nsTArray<EnvVar> env_map;
nsTArray<FdMapping> fds_remap;
#if defined(XP_LINUX) && defined(MOZ_SANDBOX)
ReadParamInfallible(&reader, &aOptions->fork_flags,
"Error deserializing 'int'");
ReadParamInfallible(&reader, &aOptions->sandbox_chroot,
"Error deserializing 'bool'");
ReadParamInfallible(&reader, &argv_array,
"Error deserializing 'nsCString[]'");
ReadParamInfallible(&reader, &env_map, "Error deserializing 'EnvVar[]'");
ReadParamInfallible(&reader, &fds_remap, "Error deserializing 'FdMapping[]'");
PrepareArguments(aArgv, argv_array);
PrepareEnv(aOptions, env_map);
PrepareFdsRemap(aOptions, fds_remap);
return true;
inline void SanitizeBuffers(IPC::Message& aMsg, std::vector<std::string>& aArgv,
base::LaunchOptions& aOptions) {
// Clean all buffers in the message to make sure content processes
// not peeking others.
auto& blist = aMsg.Buffers();
for (auto itr = blist.Iter(); !itr.Done();
itr.Advance(blist, itr.RemainingInSegment())) {
memset(itr.Data(), 0, itr.RemainingInSegment());
// clean all data string made from the message.
for (auto& var : aOptions.env_map) {
// Do it anyway since it is not going to be used anymore.
for (auto& arg : aArgv) {
* Extract parameters from the |Message| to create a
* |base::AppProcessBuilder| as |mAppProcBuilder|.
* It will return in both the fork server process and the new content
* process. |mAppProcBuilder| is null for the fork server.
void ForkServer::OnMessageReceived(UniquePtr<IPC::Message> message) {
std::vector<std::string> argv;
base::LaunchOptions options;
if (!ParseForkNewSubprocess(*message, argv, &options)) {
base::ProcessHandle child_pid = -1;
mAppProcBuilder = MakeUnique<base::AppProcessBuilder>();
if (!mAppProcBuilder->ForkProcess(argv, std::move(options), &child_pid)) {
MOZ_CRASH("fail to fork");
MOZ_ASSERT(child_pid >= 0);
if (child_pid == 0) {
// Content process
// Fork server process
mAppProcBuilder = nullptr;
IPC::Message reply(MSG_ROUTING_CONTROL, Reply_ForkNewSubprocess__ID);
IPC::MessageWriter writer(reply);
WriteIPDLParam(&writer, nullptr, child_pid);
mTcver->SendInfallible(reply, "failed to send a reply message");
// Without this, the content processes that is forked later are
// able to read the content of buffers even the buffers have been
// released.
SanitizeBuffers(*message, argv, options);
* Setup and run a fork server at the main thread.
* This function returns for two reasons:
* - the fork server is stopped normally, or
* - a new process is forked from the fork server and this function
* returned in the child, the new process.
* For the later case, aArgc and aArgv are modified to pass the
* arguments from the chrome process.
bool ForkServer::RunForkServer(int* aArgc, char*** aArgv) {
#ifdef DEBUG
if (getenv("MOZ_FORKSERVER_WAIT_GDB")) {
"Waiting for 30 seconds."
" Attach the fork server with gdb %s %d\n",
(*aArgv)[0], base::GetCurrentProcId());
bool sleep_newproc = !!getenv("MOZ_FORKSERVER_WAIT_GDB_NEWPROC");
// Do this before NS_LogInit() to avoid log files taking lower
// FDs.
ForkServer forkserver;
forkserver.InitProcess(aArgc, aArgv);
mozilla::LogModule::Init(0, nullptr);
ForkServerPreload(*aArgc, *aArgv);
MOZ_LOG(gForkServiceLog, LogLevel::Verbose, ("Start a fork server"));
DebugOnly<base::ProcessHandle> forkserver_pid = base::GetCurrentProcId();
if (forkserver.HandleMessages()) {
// In the fork server process
// The server has stopped.
MOZ_LOG(gForkServiceLog, LogLevel::Verbose,
("Terminate the fork server"));
return true;
// Now, we are running in a content process just forked from
// the fork server process.
MOZ_ASSERT(base::GetCurrentProcId() != forkserver_pid);
MOZ_LOG(gForkServiceLog, LogLevel::Verbose, ("Fork a new content process"));
#ifdef DEBUG
if (sleep_newproc) {
"Waiting for 30 seconds."
" Attach the new process with gdb %s %d\n",
(*aArgv)[0], base::GetCurrentProcId());
// |messageloop| has been destroyed. So, we can intialized the
// process safely. Message loops may allocates some file
// descriptors. If it is destroyed later, it may mess up this
// content process by closing wrong file descriptors.
forkserver.mAppProcBuilder->InitAppProcess(aArgc, aArgv);
// Open log files again with right names and the new PID.
nsTraceRefcnt::ResetLogFiles((*aArgv)[*aArgc - 1]);
return false;
} // namespace ipc
} // namespace mozilla