blob: 60e88406939fa1a77f1e14d51c26488eb6a28d7d [file] [log] [blame]
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/zygote/zygote_main.h"
#include <dlfcn.h>
#include <fcntl.h>
#include <openssl/crypto.h>
#include <openssl/rand.h>
#include <pthread.h>
#include <signal.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include <memory>
#include <utility>
#include <vector>
#include "base/bind.h"
#include "base/command_line.h"
#include "base/compiler_specific.h"
#include "base/memory/scoped_vector.h"
#include "base/native_library.h"
#include "base/pickle.h"
#include "base/posix/eintr_wrapper.h"
#include "base/posix/unix_domain_socket_linux.h"
#include "base/rand_util.h"
#include "base/strings/safe_sprintf.h"
#include "base/strings/string_number_conversions.h"
#include "base/sys_info.h"
#include "build/build_config.h"
#include "content/common/child_process_sandbox_support_impl_linux.h"
#include "content/common/font_config_ipc_linux.h"
#include "content/common/sandbox_linux/sandbox_debug_handling_linux.h"
#include "content/common/sandbox_linux/sandbox_linux.h"
#include "content/common/zygote_commands_linux.h"
#include "content/public/common/content_switches.h"
#include "content/public/common/main_function_params.h"
#include "content/public/common/sandbox_linux.h"
#include "content/public/common/zygote_fork_delegate_linux.h"
#include "content/zygote/zygote_linux.h"
#include "sandbox/linux/services/credentials.h"
#include "sandbox/linux/services/init_process_reaper.h"
#include "sandbox/linux/services/namespace_sandbox.h"
#include "sandbox/linux/services/thread_helpers.h"
#include "sandbox/linux/suid/client/setuid_sandbox_client.h"
#include "third_party/WebKit/public/web/linux/WebFontRendering.h"
#include "third_party/icu/source/i18n/unicode/timezone.h"
#include "third_party/skia/include/ports/SkFontConfigInterface.h"
#include "third_party/skia/include/ports/SkFontMgr_android.h"
#if defined(OS_LINUX)
#include <sys/prctl.h>
#if defined(ENABLE_PLUGINS)
#include "content/common/pepper_plugin_list.h"
#include "content/public/common/pepper_plugin_info.h"
#if defined(ENABLE_WEBRTC)
#include "third_party/webrtc_overrides/init_webrtc.h"
#include <sanitizer/common_interface_defs.h>
#include <sanitizer/coverage_interface.h>
namespace content {
namespace {
void CloseFds(const std::vector<int>& fds) {
for (const auto& it : fds) {
PCHECK(0 == IGNORE_EINTR(close(it)));
void RunTwoClosures(const base::Closure* first, const base::Closure* second) {
} // namespace
// See
static void ProxyLocaltimeCallToBrowser(time_t input, struct tm* output,
char* timezone_out,
size_t timezone_out_len) {
base::Pickle request;
std::string(reinterpret_cast<char*>(&input), sizeof(input)));
uint8_t reply_buf[512];
const ssize_t r = base::UnixDomainSocket::SendRecvMsg(
GetSandboxFD(), reply_buf, sizeof(reply_buf), NULL, request);
if (r == -1) {
memset(output, 0, sizeof(struct tm));
base::Pickle reply(reinterpret_cast<char*>(reply_buf), r);
base::PickleIterator iter(reply);
std::string result, timezone;
if (!iter.ReadString(&result) ||
!iter.ReadString(&timezone) ||
result.size() != sizeof(struct tm)) {
memset(output, 0, sizeof(struct tm));
memcpy(output,, sizeof(struct tm));
if (timezone_out_len) {
const size_t copy_len = std::min(timezone_out_len - 1, timezone.size());
memcpy(timezone_out,, copy_len);
timezone_out[copy_len] = 0;
output->tm_zone = timezone_out;
} else {
output->tm_zone = NULL;
static bool g_am_zygote_or_renderer = false;
// Sandbox interception of libc calls.
// Because we are running in a sandbox certain libc calls will fail (localtime
// being the motivating example - it needs to read /etc/localtime). We need to
// intercept these calls and proxy them to the browser. However, these calls
// may come from us or from our libraries. In some cases we can't just change
// our code.
// It's for these cases that we have the following setup:
// We define global functions for those functions which we wish to override.
// Since we will be first in the dynamic resolution order, the dynamic linker
// will point callers to our versions of these functions. However, we have the
// same binary for both the browser and the renderers, which means that our
// overrides will apply in the browser too.
// The global |g_am_zygote_or_renderer| is true iff we are in a zygote or
// renderer process. It's set in ZygoteMain and inherited by the renderers when
// they fork. (This means that it'll be incorrect for global constructor
// functions and before ZygoteMain is called - beware).
// Our replacement functions can check this global and either proxy
// the call to the browser over the sandbox IPC
// ( or they can use
// dlsym with RTLD_NEXT to resolve the symbol, ignoring any symbols in the
// current module.
// Other avenues:
// Our first attempt involved some assembly to patch the GOT of the current
// module. This worked, but was platform specific and doesn't catch the case
// where a library makes a call rather than current module.
// We also considered patching the function in place, but this would again by
// platform specific and the above technique seems to work well enough.
typedef struct tm* (*LocaltimeFunction)(const time_t* timep);
typedef struct tm* (*LocaltimeRFunction)(const time_t* timep,
struct tm* result);
static pthread_once_t g_libc_localtime_funcs_guard = PTHREAD_ONCE_INIT;
static LocaltimeFunction g_libc_localtime;
static LocaltimeFunction g_libc_localtime64;
static LocaltimeRFunction g_libc_localtime_r;
static LocaltimeRFunction g_libc_localtime64_r;
static void InitLibcLocaltimeFunctions() {
g_libc_localtime = reinterpret_cast<LocaltimeFunction>(
dlsym(RTLD_NEXT, "localtime"));
g_libc_localtime64 = reinterpret_cast<LocaltimeFunction>(
dlsym(RTLD_NEXT, "localtime64"));
g_libc_localtime_r = reinterpret_cast<LocaltimeRFunction>(
dlsym(RTLD_NEXT, "localtime_r"));
g_libc_localtime64_r = reinterpret_cast<LocaltimeRFunction>(
dlsym(RTLD_NEXT, "localtime64_r"));
if (!g_libc_localtime || !g_libc_localtime_r) {
// Nvidia's overrides dlsym for an unknown reason and replaces
// it with a version which doesn't work. In this case we'll get a NULL
// result. There's not a lot we can do at this point, so we just bodge it!
LOG(ERROR) << "Your system is broken: dlsym doesn't work! This has been "
"reported to be caused by Nvidia's libGL. You should expect"
" time related functions to misbehave. "
if (!g_libc_localtime)
g_libc_localtime = gmtime;
if (!g_libc_localtime64)
g_libc_localtime64 = g_libc_localtime;
if (!g_libc_localtime_r)
g_libc_localtime_r = gmtime_r;
if (!g_libc_localtime64_r)
g_libc_localtime64_r = g_libc_localtime_r;
// Define localtime_override() function with asm name "localtime", so that all
// references to localtime() will resolve to this function. Notice that we need
// to set visibility attribute to "default" to export the symbol, as it is set
// to "hidden" by default in chrome per build/common.gypi.
__attribute__ ((__visibility__("default")))
struct tm* localtime_override(const time_t* timep) __asm__ ("localtime");
__attribute__ ((__visibility__("default")))
struct tm* localtime_override(const time_t* timep) {
if (g_am_zygote_or_renderer) {
static struct tm time_struct;
static char timezone_string[64];
ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
return &time_struct;
} else {
CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
struct tm* res = g_libc_localtime(timep);
if (res) __msan_unpoison(res, sizeof(*res));
if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
return res;
// Use same trick to override localtime64(), localtime_r() and localtime64_r().
__attribute__ ((__visibility__("default")))
struct tm* localtime64_override(const time_t* timep) __asm__ ("localtime64");
__attribute__ ((__visibility__("default")))
struct tm* localtime64_override(const time_t* timep) {
if (g_am_zygote_or_renderer) {
static struct tm time_struct;
static char timezone_string[64];
ProxyLocaltimeCallToBrowser(*timep, &time_struct, timezone_string,
return &time_struct;
} else {
CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
struct tm* res = g_libc_localtime64(timep);
if (res) __msan_unpoison(res, sizeof(*res));
if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
return res;
__attribute__ ((__visibility__("default")))
struct tm* localtime_r_override(const time_t* timep,
struct tm* result) __asm__ ("localtime_r");
__attribute__ ((__visibility__("default")))
struct tm* localtime_r_override(const time_t* timep, struct tm* result) {
if (g_am_zygote_or_renderer) {
ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
return result;
} else {
CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
struct tm* res = g_libc_localtime_r(timep, result);
if (res) __msan_unpoison(res, sizeof(*res));
if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
return res;
__attribute__ ((__visibility__("default")))
struct tm* localtime64_r_override(const time_t* timep,
struct tm* result) __asm__ ("localtime64_r");
__attribute__ ((__visibility__("default")))
struct tm* localtime64_r_override(const time_t* timep, struct tm* result) {
if (g_am_zygote_or_renderer) {
ProxyLocaltimeCallToBrowser(*timep, result, NULL, 0);
return result;
} else {
CHECK_EQ(0, pthread_once(&g_libc_localtime_funcs_guard,
struct tm* res = g_libc_localtime64_r(timep, result);
if (res) __msan_unpoison(res, sizeof(*res));
if (res->tm_zone) __msan_unpoison_string(res->tm_zone);
return res;
#if defined(ENABLE_PLUGINS)
// Loads the (native) libraries but does not initialize them (i.e., does not
// call PPP_InitializeModule). This is needed by the zygote on Linux to get
// access to the plugins before entering the sandbox.
void PreloadPepperPlugins() {
std::vector<PepperPluginInfo> plugins;
for (size_t i = 0; i < plugins.size(); ++i) {
if (!plugins[i].is_internal) {
base::NativeLibraryLoadError error;
base::NativeLibrary library = base::LoadNativeLibrary(plugins[i].path,
VLOG_IF(1, !library) << "Unable to load plugin "
<< plugins[i].path.value() << " "
<< error.ToString();
(void)library; // Prevent release-mode warning.
// This function triggers the static and lazy construction of objects that need
// to be created before imposing the sandbox.
static void ZygotePreSandboxInit() {
// ICU DateFormat class (used in base/ needs to get the
// Olson timezone ID by accessing the zoneinfo files on disk. After
// TimeZone::createDefault is called once here, the timezone ID is
// cached and there's no more need to access the file system.
std::unique_ptr<icu::TimeZone> zone(icu::TimeZone::createDefault());
#if defined(ARCH_CPU_ARM_FAMILY)
// On ARM, BoringSSL requires access to /proc/cpuinfo to determine processor
// features. Query this before entering the sandbox.
// Pass BoringSSL a copy of the /dev/urandom file descriptor so RAND_bytes
// will work inside the sandbox.
#if defined(ENABLE_PLUGINS)
// Ensure access to the Pepper plugins before the sandbox is turned on.
#if defined(ENABLE_WEBRTC)
new FontConfigIPC(GetSandboxFD()))->unref();
// Set the android SkFontMgr for blink. We need to ensure this is done
// before the sandbox is initialized to allow the font manager to access
// font configuration files on disk.
if (base::CommandLine::ForCurrentProcess()->HasSwitch(
switches::kAndroidFontsPath)) {
std::string android_fonts_dir =
if (android_fonts_dir.size() > 0 && android_fonts_dir.back() != '/')
android_fonts_dir += '/';
std::string font_config = android_fonts_dir + "fonts.xml";
SkFontMgr_Android_CustomFonts custom;
custom.fSystemFontUse =
custom.fBasePath = android_fonts_dir.c_str();
custom.fFontsXml = font_config.c_str();
custom.fFallbackFontsXml = nullptr;
custom.fIsolated = true;
static bool CreateInitProcessReaper(base::Closure* post_fork_parent_callback) {
// The current process becomes init(1), this function returns from a
// newly created process.
const bool init_created =
if (!init_created) {
LOG(ERROR) << "Error creating an init process to reap zombies";
return false;
return true;
// Enter the setuid sandbox. This requires the current process to have been
// created through the setuid sandbox.
static bool EnterSuidSandbox(sandbox::SetuidSandboxClient* setuid_sandbox,
base::Closure* post_fork_parent_callback) {
// Use the SUID sandbox. This still allows the seccomp sandbox to
// be enabled by the process later.
if (!setuid_sandbox->IsSuidSandboxUpToDate()) {
"You are using a wrong version of the setuid binary!\n"
"Please read "
if (!setuid_sandbox->ChrootMe())
return false;
if (setuid_sandbox->IsInNewPIDNamespace()) {
CHECK_EQ(1, getpid())
<< "The SUID sandbox created a new PID namespace but Zygote "
"is not the init process. Please, make sure the SUID "
"binary is up to date.";
if (getpid() == 1) {
// The setuid sandbox has created a new PID namespace and we need
// to assume the role of init.
return true;
static void DropAllCapabilities(int proc_fd) {
static void EnterNamespaceSandbox(LinuxSandbox* linux_sandbox,
base::Closure* post_fork_parent_callback) {
if (getpid() == 1) {
base::Closure drop_all_caps_callback =
base::Bind(&DropAllCapabilities, linux_sandbox->proc_fd());
base::Closure callback = base::Bind(
&RunTwoClosures, &drop_all_caps_callback, post_fork_parent_callback);
static int g_sanitizer_message_length = 1 * 1024 * 1024;
// A helper process which collects code coverage data from the renderers over a
// socket and dumps it to a file. See for discussion.
static void SanitizerCoverageHelper(int socket_fd, int file_fd) {
std::unique_ptr<char[]> buffer(new char[g_sanitizer_message_length]);
while (true) {
ssize_t received_size = HANDLE_EINTR(
recv(socket_fd, buffer.get(), g_sanitizer_message_length, 0));
PCHECK(received_size >= 0);
if (received_size == 0)
// All clients have closed the socket. We should die.
PCHECK(file_fd >= 0);
ssize_t written_size = 0;
while (written_size < received_size) {
ssize_t write_res =
HANDLE_EINTR(write(file_fd, buffer.get() + written_size,
received_size - written_size));
PCHECK(write_res >= 0);
written_size += write_res;
PCHECK(0 == HANDLE_EINTR(fsync(file_fd)));
// fds[0] is the read end, fds[1] is the write end.
static void CreateSanitizerCoverageSocketPair(int fds[2]) {
PCHECK(0 == socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds));
PCHECK(0 == shutdown(fds[0], SHUT_WR));
PCHECK(0 == shutdown(fds[1], SHUT_RD));
// Find the right buffer size for sending coverage data.
// The kernel will silently set the buffer size to the allowed maximum when
// the specified size is too large, so we set our desired size and read it
// back.
int* buf_size = &g_sanitizer_message_length;
socklen_t option_length = sizeof(*buf_size);
PCHECK(0 == setsockopt(fds[1], SOL_SOCKET, SO_SNDBUF,
buf_size, option_length));
PCHECK(0 == getsockopt(fds[1], SOL_SOCKET, SO_SNDBUF,
buf_size, &option_length));
DCHECK_EQ(sizeof(*buf_size), option_length);
// The kernel returns the doubled buffer size.
*buf_size /= 2;
PCHECK(*buf_size > 0);
static pid_t ForkSanitizerCoverageHelper(
int child_fd,
int parent_fd,
base::ScopedFD file_fd,
const std::vector<int>& extra_fds_to_close) {
pid_t pid = fork();
PCHECK(pid >= 0);
if (pid == 0) {
// In the child.
PCHECK(0 == IGNORE_EINTR(close(parent_fd)));
SanitizerCoverageHelper(child_fd, file_fd.get());
} else {
// In the parent.
PCHECK(0 == IGNORE_EINTR(close(child_fd)));
return pid;
#endif // defined(SANITIZER_COVERAGE)
static void EnterLayerOneSandbox(LinuxSandbox* linux_sandbox,
const bool using_layer1_sandbox,
base::Closure* post_fork_parent_callback) {
// Check that the pre-sandbox initialization didn't spawn threads.
#if !defined(THREAD_SANITIZER)
sandbox::SetuidSandboxClient* setuid_sandbox =
if (setuid_sandbox->IsSuidSandboxChild()) {
CHECK(EnterSuidSandbox(setuid_sandbox, post_fork_parent_callback))
<< "Failed to enter setuid sandbox";
} else if (sandbox::NamespaceSandbox::InNewUserNamespace()) {
EnterNamespaceSandbox(linux_sandbox, post_fork_parent_callback);
} else {
bool ZygoteMain(const MainFunctionParams& params,
ScopedVector<ZygoteForkDelegate> fork_delegates) {
g_am_zygote_or_renderer = true;
std::vector<int> fds_to_close_post_fork;
LinuxSandbox* linux_sandbox = LinuxSandbox::GetInstance();
const std::string sancov_file_name =
"zygote." + base::Uint64ToString(base::RandUint64());
base::ScopedFD sancov_file_fd(
int sancov_socket_fds[2] = {-1, -1};
linux_sandbox->sanitizer_args()->coverage_sandboxed = 1;
linux_sandbox->sanitizer_args()->coverage_fd = sancov_socket_fds[1];
linux_sandbox->sanitizer_args()->coverage_max_block_size =
// Zygote termination will block until the helper process exits, which will
// not happen until the write end of the socket is closed everywhere. Make
// sure the init process does not hold on to it.
// Skip pre-initializing sandbox under --no-sandbox for
if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
switches::kNoSandbox)) {
// This will pre-initialize the various sandboxes that need it.
const bool using_setuid_sandbox =
const bool using_namespace_sandbox =
const bool using_layer1_sandbox =
using_setuid_sandbox || using_namespace_sandbox;
if (using_setuid_sandbox) {
if (using_layer1_sandbox) {
// Let the ZygoteHost know we're booting up.
VLOG(1) << "ZygoteMain: initializing " << fork_delegates.size()
<< " fork delegates";
for (ZygoteForkDelegate* fork_delegate : fork_delegates) {
fork_delegate->Init(GetSandboxFD(), using_layer1_sandbox);
const std::vector<int> sandbox_fds_to_close_post_fork =
base::Closure post_fork_parent_callback =
base::Bind(&CloseFds, fds_to_close_post_fork);
// Turn on the first layer of the sandbox if the configuration warrants it.
EnterLayerOneSandbox(linux_sandbox, using_layer1_sandbox,
// Extra children and file descriptors created that the Zygote must have
// knowledge of.
std::vector<pid_t> extra_children;
std::vector<int> extra_fds;
pid_t sancov_helper_pid = ForkSanitizerCoverageHelper(
sancov_socket_fds[0], sancov_socket_fds[1], std::move(sancov_file_fd),
// It's important that the zygote reaps the helper before dying. Otherwise,
// the destruction of the PID namespace could kill the helper before it
// completes its I/O tasks. |sancov_helper_pid| will exit once the last
// renderer holding the write end of |sancov_socket_fds| closes it.
// Sanitizer code in the renderers will inherit the write end of the socket
// from the zygote. We must keep it open until the very end of the zygote's
// lifetime, even though we don't explicitly use it.
const int sandbox_flags = linux_sandbox->GetStatus();
const bool setuid_sandbox_engaged = sandbox_flags & kSandboxLinuxSUID;
CHECK_EQ(using_setuid_sandbox, setuid_sandbox_engaged);
const bool namespace_sandbox_engaged = sandbox_flags & kSandboxLinuxUserNS;
CHECK_EQ(using_namespace_sandbox, namespace_sandbox_engaged);
Zygote zygote(sandbox_flags, std::move(fork_delegates), extra_children,
// This function call can return multiple times, once per fork().
return zygote.ProcessRequests();
} // namespace content