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Add execve/posix_spawn fallbacks for older kernels

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This commit is contained in:
Luke Street 2025-10-08 18:42:22 -06:00
parent cac944400f
commit 9cd15e9be8
1 changed files with 60 additions and 23 deletions
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83
src/processes.cpp
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@ -5,6 +5,7 @@
#include "kernel32/internal.h"
#include <algorithm>
#include <cassert>
#include <cerrno>
#include <cstdio>
#include <cstdlib>
#include <fcntl.h>
@ -372,6 +373,55 @@ std::optional<std::filesystem::path> resolveExecutable(const std::string &comman
return std::nullopt;
}
static int spawnClone3(pid_t &pid, int &pidfd, int &tid, char **argv, char **envp) {
int exefd = open("/proc/self/exe", O_PATH | O_CLOEXEC);
if (exefd < 0) {
int err = errno;
perror("open /proc/self/exe");
return err;
}
struct clone_args ca = {};
ca.flags = CLONE_PIDFD | CLONE_PARENT_SETTID | CLONE_CLEAR_SIGHAND;
ca.pidfd = reinterpret_cast<uintptr_t>(&pidfd);
ca.parent_tid = reinterpret_cast<uintptr_t>(&tid);
pid = static_cast<pid_t>(syscall(SYS_clone3, &ca, sizeof(ca)));
if (pid < 0) {
int err = errno;
close(exefd);
return err;
} else if (pid == 0) {
prctl(PR_SET_PDEATHSIG, SIGKILL);
// First, attempt to execveat using the open fd (atomic)
syscall(SYS_execveat, exefd, "", argv, envp, AT_EMPTY_PATH);
// Otherwise, fall back to direct execve
execve("/proc/self/exe", argv, envp);
// If we're still here, something went wrong
perror("execve");
_exit(127);
}
close(exefd);
return 0;
}
static int spawnPosixSpawn(pid_t &pid, int &pidfd, char **argv, char **envp) {
std::error_code ec;
auto resolved = std::filesystem::read_symlink("/proc/self/exe", ec);
if (ec) {
return ec.value();
}
int rc = posix_spawn(&pid, resolved.c_str(), nullptr, nullptr, argv, envp);
if (rc != 0) {
return rc;
}
pidfd = static_cast<int>(syscall(SYS_pidfd_open, pid, 0));
if (pidfd < 0) {
int err = errno;
perror("pidfd_open");
return err;
}
return 0;
}
static int spawnInternal(const std::vector<std::string> &args, Pin<kernel32::ProcessObject> &pinOut) {
std::vector<char *> argv;
argv.reserve(args.size() + 2);
@ -408,32 +458,19 @@ static int spawnInternal(const std::vector<std::string> &args, Pin<kernel32::Pro
envp.push_back(const_cast<char *>(s.c_str()));
envp.push_back(nullptr);
int exefd = open("/proc/self/exe", O_PATH | O_CLOEXEC);
if (exefd < 0) {
int err = errno;
perror("open /proc/self/exe");
return err;
}
pid_t pid = -1;
int pidfd = -1;
int tid = -1;
struct clone_args ca = {};
ca.flags = CLONE_PIDFD | CLONE_PARENT_SETTID | CLONE_CLEAR_SIGHAND;
ca.pidfd = reinterpret_cast<uintptr_t>(&pidfd);
ca.parent_tid = reinterpret_cast<uintptr_t>(&tid);
pid_t pid = static_cast<pid_t>(syscall(SYS_clone3, &ca, sizeof(ca)));
if (pid < 0) {
close(exefd);
int err = errno;
perror("clone3");
return err;
} else if (pid == 0) {
prctl(PR_SET_PDEATHSIG, SIGKILL);
int rc = execveat(exefd, "", argv.data(), envp.data(), AT_EMPTY_PATH);
fprintf(stderr, "execveat failed: %s\n", strerror(rc));
_exit(127);
int rc = spawnClone3(pid, pidfd, tid, argv.data(), envp.data());
if (rc != 0) {
if (rc == ENOSYS) {
rc = spawnPosixSpawn(pid, pidfd, argv.data(), envp.data());
}
if (rc != 0) {
return rc;
}
tid = pid;
}
close(exefd);
DEBUG_LOG("Spawned process with PID %d (pidfd=%d, tid=%d)\n", pid, pidfd, tid);