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// Copyright 2017 The Crashpad Authors
//
// 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.
#include "util/posix/spawn_subprocess.h"
#include <errno.h>
#include <spawn.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
#include "base/check.h"
#include "base/check_op.h"
#include "base/logging.h"
#include "base/posix/eintr_wrapper.h"
#include "base/strings/stringprintf.h"
#include "build/build_config.h"
#include "util/posix/close_multiple.h"
#if BUILDFLAG(IS_ANDROID)
#include <android/api-level.h>
#endif
extern char** environ;
namespace crashpad {
namespace {
#if BUILDFLAG(IS_APPLE)
class PosixSpawnAttr {
public:
PosixSpawnAttr() {
PCHECK((errno = posix_spawnattr_init(&attr_)) == 0)
<< "posix_spawnattr_init";
}
PosixSpawnAttr(const PosixSpawnAttr&) = delete;
PosixSpawnAttr& operator=(const PosixSpawnAttr&) = delete;
~PosixSpawnAttr() {
PCHECK((errno = posix_spawnattr_destroy(&attr_)) == 0)
<< "posix_spawnattr_destroy";
}
void SetFlags(short flags) {
PCHECK((errno = posix_spawnattr_setflags(&attr_, flags)) == 0)
<< "posix_spawnattr_setflags";
}
const posix_spawnattr_t* Get() const { return &attr_; }
private:
posix_spawnattr_t attr_;
};
class PosixSpawnFileActions {
public:
PosixSpawnFileActions() {
PCHECK((errno = posix_spawn_file_actions_init(&file_actions_)) == 0)
<< "posix_spawn_file_actions_init";
}
PosixSpawnFileActions(const PosixSpawnFileActions&) = delete;
PosixSpawnFileActions& operator=(const PosixSpawnFileActions&) = delete;
~PosixSpawnFileActions() {
PCHECK((errno = posix_spawn_file_actions_destroy(&file_actions_)) == 0)
<< "posix_spawn_file_actions_destroy";
}
void AddInheritedFileDescriptor(int fd) {
PCHECK((errno = posix_spawn_file_actions_addinherit_np(&file_actions_,
fd)) == 0)
<< "posix_spawn_file_actions_addinherit_np";
}
const posix_spawn_file_actions_t* Get() const { return &file_actions_; }
private:
posix_spawn_file_actions_t file_actions_;
};
#endif
} // namespace
bool SpawnSubprocess(const std::vector<std::string>& argv,
const std::vector<std::string>* envp,
int preserve_fd,
bool use_path,
void (*child_function)()) {
// argv_c contains const char* pointers and is terminated by nullptr. This is
// suitable for passing to posix_spawn*() and execv*(). Although argv_c is not
// used in the parent process, it must be built in the parent process because
// it’s unsafe to do so in the child or grandchild process.
std::vector<const char*> argv_c;
argv_c.reserve(argv.size() + 1);
for (const std::string& argument : argv) {
argv_c.push_back(argument.c_str());
}
argv_c.push_back(nullptr);
std::vector<const char*> envp_c;
if (envp) {
envp_c.reserve(envp->size() + 1);
for (const std::string& variable : *envp) {
envp_c.push_back(variable.c_str());
}
envp_c.push_back(nullptr);
}
// The three processes involved are parent, child, and grandchild. The child
// exits immediately after spawning the grandchild, so the grandchild becomes
// an orphan and its parent process ID becomes 1. This relieves the parent and
// child of the responsibility to reap the grandchild with waitpid() or
// similar. The grandchild is expected to outlive the parent process, so the
// parent shouldn’t be concerned with reaping it. This approach means that
// accidental early termination of the handler process will not result in a
// zombie process.
pid_t pid = fork();
if (pid < 0) {
PLOG(ERROR) << "fork";
return false;
}
if (pid == 0) {
// Child process.
if (child_function) {
child_function();
}
// Call setsid(), creating a new process group and a new session, both led
// by this process. The new process group has no controlling terminal. This
// disconnects it from signals generated by the parent process’ terminal.
//
// setsid() is done in the child instead of the grandchild so that the
// grandchild will not be a session leader. If it were a session leader, an
// accidental open() of a terminal device without O_NOCTTY would make that
// terminal the controlling terminal.
//
// It’s not desirable for the grandchild to have a controlling terminal. The
// grandchild manages its own lifetime, such as by monitoring clients on its
// own and exiting when it loses all clients and when it deems it
// appropraite to do so. It may serve clients in different process groups or
// sessions than its original client, and receiving signals intended for its
// original client’s process group could be harmful in that case.
PCHECK(setsid() != -1) << "setsid";
// &argv_c[0] is a pointer to a pointer to const char data, but because of
// how C (not C++) works, posix_spawn*() and execv*() want a pointer to
// a const pointer to char data. They modify neither the data nor the
// pointers, so the const_cast is safe.
char* const* argv_for_spawn = const_cast<char* const*>(argv_c.data());
// This cast is safe for the same reason that the argv_for_spawn cast is.
char* const* envp_for_spawn =
envp ? const_cast<char* const*>(envp_c.data()) : environ;
#if BUILDFLAG(IS_ANDROID) && __ANDROID_API__ < 28
pid = fork();
if (pid < 0) {
PLOG(FATAL) << "fork";
}
if (pid > 0) {
// Child process.
// _exit() instead of exit(), because fork() was called.
_exit(EXIT_SUCCESS);
}
// Grandchild process.
CloseMultipleNowOrOnExec(STDERR_FILENO + 1, preserve_fd);
auto execve_fp = use_path ? execvpe : execve;
execve_fp(argv_for_spawn[0], argv_for_spawn, envp_for_spawn);
PLOG(FATAL) << (use_path ? "execvpe" : "execve");
#else
#if BUILDFLAG(IS_APPLE)
PosixSpawnAttr attr;
attr.SetFlags(POSIX_SPAWN_CLOEXEC_DEFAULT);
PosixSpawnFileActions file_actions;
for (int fd = 0; fd <= STDERR_FILENO; ++fd) {
file_actions.AddInheritedFileDescriptor(fd);
}
file_actions.AddInheritedFileDescriptor(preserve_fd);
const posix_spawnattr_t* attr_p = attr.Get();
const posix_spawn_file_actions_t* file_actions_p = file_actions.Get();
#else
CloseMultipleNowOrOnExec(STDERR_FILENO + 1, preserve_fd);
const posix_spawnattr_t* attr_p = nullptr;
const posix_spawn_file_actions_t* file_actions_p = nullptr;
#endif
auto posix_spawn_fp = use_path ? posix_spawnp : posix_spawn;
if ((errno = posix_spawn_fp(nullptr,
argv_for_spawn[0],
file_actions_p,
attr_p,
argv_for_spawn,
envp_for_spawn)) != 0) {
PLOG(FATAL) << (use_path ? "posix_spawnp" : "posix_spawn");
}
// _exit() instead of exit(), because fork() was called.
_exit(EXIT_SUCCESS);
#endif
}
// waitpid() for the child, so that it does not become a zombie process. The
// child normally exits quickly.
//
// Failures from this point on may result in the accumulation of a zombie, but
// should not be considered fatal. Log only warnings, but don’t treat these
// failures as a failure of the function overall.
int status;
pid_t wait_pid = HANDLE_EINTR(waitpid(pid, &status, 0));
if (wait_pid == -1) {
PLOG(WARNING) << "waitpid";
return true;
}
DCHECK_EQ(wait_pid, pid);
if (WIFSIGNALED(status)) {
int sig = WTERMSIG(status);
LOG(WARNING) << base::StringPrintf(
"intermediate process terminated by signal %d (%s)%s",
sig,
strsignal(sig),
WCOREDUMP(status) ? " (core dumped)" : "");
} else if (!WIFEXITED(status)) {
LOG(WARNING) << base::StringPrintf(
"intermediate process: unknown termination 0x%x", status);
} else if (WEXITSTATUS(status) != EXIT_SUCCESS) {
LOG(WARNING) << "intermediate process exited with code "
<< WEXITSTATUS(status);
}
return true;
}
} // namespace crashpad