lix/src/libutil/processes.cc
eldritch horrors 4162a66cee libutil: return sources from runProgram2
this much more closely mimics what is actually happening: we're reading
data from somewhere else, actively, rather than passively waiting. with
the data flow matching the underlying system interactions better we can
remove a few sinkToSource calls that merely exists to undo the mismatch
caused by not treating subprocess output as a data source to begin with

Change-Id: If4abfc2f8398fb5e88c9b91a8bdefd5504bb2d11
2024-07-06 12:36:36 +02:00

378 lines
9.7 KiB
C++

#include "current-process.hh"
#include "environment-variables.hh"
#include "finally.hh"
#include "logging.hh"
#include "processes.hh"
#include "serialise.hh"
#include "signals.hh"
#include <cerrno>
#include <cstdlib>
#include <cstring>
#include <future>
#include <iostream>
#include <thread>
#include <grp.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#ifdef __APPLE__
# include <sys/syscall.h>
#endif
#ifdef __linux__
# include <sys/prctl.h>
# include <sys/mman.h>
#endif
namespace nix {
Pid::Pid()
{
}
Pid::Pid(Pid && other) : pid(other.pid), separatePG(other.separatePG), killSignal(other.killSignal)
{
other.pid = -1;
}
Pid & Pid::operator=(Pid && other)
{
Pid tmp(std::move(other));
std::swap(pid, tmp.pid);
std::swap(separatePG, tmp.separatePG);
std::swap(killSignal, tmp.killSignal);
return *this;
}
Pid::~Pid() noexcept(false)
{
if (pid != -1) kill();
}
int Pid::kill()
{
assert(pid != -1);
debug("killing process %1%", pid);
/* Send the requested signal to the child. If it has its own
process group, send the signal to every process in the child
process group (which hopefully includes *all* its children). */
if (::kill(separatePG ? -pid : pid, killSignal) != 0) {
/* On BSDs, killing a process group will return EPERM if all
processes in the group are zombies (or something like
that). So try to detect and ignore that situation. */
#if __FreeBSD__ || __APPLE__
if (errno != EPERM || ::kill(pid, 0) != 0)
#endif
logError(SysError("killing process %d", pid).info());
}
return wait();
}
int Pid::wait()
{
assert(pid != -1);
while (1) {
int status;
int res = waitpid(pid, &status, 0);
if (res == pid) {
pid = -1;
return status;
}
if (errno != EINTR)
throw SysError("cannot get exit status of PID %d", pid);
checkInterrupt();
}
}
void Pid::setSeparatePG(bool separatePG)
{
this->separatePG = separatePG;
}
void Pid::setKillSignal(int signal)
{
this->killSignal = signal;
}
pid_t Pid::release()
{
pid_t p = pid;
pid = -1;
return p;
}
void killUser(uid_t uid)
{
debug("killing all processes running under uid '%1%'", uid);
assert(uid != 0); /* just to be safe... */
/* The system call kill(-1, sig) sends the signal `sig' to all
users to which the current process can send signals. So we
fork a process, switch to uid, and send a mass kill. */
Pid pid{startProcess([&]() {
if (setuid(uid) == -1)
throw SysError("setting uid");
while (true) {
#ifdef __APPLE__
/* OSX's kill syscall takes a third parameter that, among
other things, determines if kill(-1, signo) affects the
calling process. In the OSX libc, it's set to true,
which means "follow POSIX", which we don't want here
*/
if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
#else
if (kill(-1, SIGKILL) == 0) break;
#endif
if (errno == ESRCH || errno == EPERM) break; /* no more processes */
if (errno != EINTR)
throw SysError("cannot kill processes for uid '%1%'", uid);
}
_exit(0);
})};
int status = pid.wait();
if (status != 0)
throw Error("cannot kill processes for uid '%1%': %2%", uid, statusToString(status));
/* !!! We should really do some check to make sure that there are
no processes left running under `uid', but there is no portable
way to do so (I think). The most reliable way may be `ps -eo
uid | grep -q $uid'. */
}
//////////////////////////////////////////////////////////////////////
static pid_t doFork(std::function<void()> fun)
{
pid_t pid = fork();
if (pid != 0) return pid;
fun();
abort();
}
#if __linux__
static int childEntry(void * arg)
{
auto main = (std::function<void()> *) arg;
(*main)();
return 1;
}
#endif
Pid startProcess(std::function<void()> fun, const ProcessOptions & options)
{
std::function<void()> wrapper = [&]() {
logger = makeSimpleLogger();
try {
#if __linux__
if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1)
throw SysError("setting death signal");
#endif
fun();
} catch (std::exception & e) {
try {
std::cerr << options.errorPrefix << e.what() << "\n";
} catch (...) { }
} catch (...) { }
if (options.runExitHandlers)
exit(1);
else
_exit(1);
};
pid_t pid = -1;
if (options.cloneFlags) {
#ifdef __linux__
// Not supported, since then we don't know when to free the stack.
assert(!(options.cloneFlags & CLONE_VM));
size_t stackSize = 1 * 1024 * 1024;
auto stack = (char *) mmap(0, stackSize,
PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
if (stack == MAP_FAILED) throw SysError("allocating stack");
Finally freeStack([&]() { munmap(stack, stackSize); });
pid = clone(childEntry, stack + stackSize, options.cloneFlags | SIGCHLD, &wrapper);
#else
throw Error("clone flags are only supported on Linux");
#endif
} else
pid = doFork(wrapper);
if (pid == -1) throw SysError("unable to fork");
return Pid{pid};
}
std::string runProgram(Path program, bool searchPath, const Strings & args, bool isInteractive)
{
auto res = runProgram(RunOptions {.program = program, .searchPath = searchPath, .args = args, .isInteractive = isInteractive});
if (!statusOk(res.first))
throw ExecError(res.first, "program '%1%' %2%", program, statusToString(res.first));
return res.second;
}
// Output = error code + "standard out" output stream
std::pair<int, std::string> runProgram(RunOptions && options)
{
options.captureStdout = true;
int status = 0;
std::string stdout;
try {
auto proc = runProgram2(options);
Finally const _wait([&] { proc.wait(); });
stdout = proc.stdout()->drain();
} catch (ExecError & e) {
status = e.status;
}
return {status, std::move(stdout)};
}
RunningProgram::RunningProgram(PathView program, Pid pid, AutoCloseFD stdout)
: program(program)
, pid(std::move(pid))
, stdoutSource(stdout ? std::make_unique<FdSource>(stdout.get()) : nullptr)
, stdout_(std::move(stdout))
{
}
RunningProgram::~RunningProgram()
{
if (pid) {
// we will not kill a subprocess because we *can't* kill a subprocess
// reliably without placing it in its own process group, and cleaning
// up a subprocess only when `separatePG` is set is a loaded footgun.
assert(false && "destroying un-wait()ed running process");
std::terminate();
}
}
void RunningProgram::wait()
{
int status = pid.wait();
if (status)
throw ExecError(status, "program '%1%' %2%", program, statusToString(status));
}
RunningProgram runProgram2(const RunOptions & options)
{
checkInterrupt();
/* Create a pipe. */
Pipe out;
if (options.captureStdout) out.create();
ProcessOptions processOptions;
std::optional<Finally<std::function<void()>>> resumeLoggerDefer;
if (options.isInteractive) {
logger->pause();
resumeLoggerDefer.emplace(
[]() {
logger->resume();
}
);
}
/* Fork. */
Pid pid{startProcess([&]() {
if (options.environment)
replaceEnv(*options.environment);
if (options.captureStdout && dup2(out.writeSide.get(), STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
if (options.mergeStderrToStdout)
if (dup2(STDOUT_FILENO, STDERR_FILENO) == -1)
throw SysError("cannot dup stdout into stderr");
if (options.chdir && chdir((*options.chdir).c_str()) == -1)
throw SysError("chdir failed");
if (options.gid && setgid(*options.gid) == -1)
throw SysError("setgid failed");
/* Drop all other groups if we're setgid. */
if (options.gid && setgroups(0, 0) == -1)
throw SysError("setgroups failed");
if (options.uid && setuid(*options.uid) == -1)
throw SysError("setuid failed");
Strings args_(options.args);
args_.push_front(options.program);
restoreProcessContext();
if (options.searchPath)
execvp(options.program.c_str(), stringsToCharPtrs(args_).data());
// This allows you to refer to a program with a pathname relative
// to the PATH variable.
else
execv(options.program.c_str(), stringsToCharPtrs(args_).data());
throw SysError("executing '%1%'", options.program);
}, processOptions)};
out.writeSide.close();
return RunningProgram{
options.program,
std::move(pid),
options.captureStdout ? std::move(out.readSide) : AutoCloseFD{}
};
}
std::string statusToString(int status)
{
if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
if (WIFEXITED(status))
return fmt("failed with exit code %1%", WEXITSTATUS(status));
else if (WIFSIGNALED(status)) {
int sig = WTERMSIG(status);
#if HAVE_STRSIGNAL
const char * description = strsignal(sig);
return fmt("failed due to signal %1% (%2%)", sig, description);
#else
return fmt("failed due to signal %1%", sig);
#endif
}
else
return "died abnormally";
} else return "succeeded";
}
bool statusOk(int status)
{
return WIFEXITED(status) && WEXITSTATUS(status) == 0;
}
}