347 lines
8.1 KiB
Go
347 lines
8.1 KiB
Go
// exec.go -- fork/exec syscall support.
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Fork, exec, wait, etc.
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package syscall
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import "unsafe"
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func libc_fcntl(fd int, cmd int, arg int) int __asm__ ("fcntl")
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func libc_fork() Pid_t __asm__ ("fork")
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func libc_setsid() Pid_t __asm__ ("setsid")
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func libc_setpgid(Pid_t, Pid_t) int __asm__ ("setpgid")
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func libc_chroot(path *byte) int __asm__ ("chroot")
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func libc_setuid(Uid_t) int __asm__ ("setuid")
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func libc_setgid(Gid_t) int __asm__ ("setgid")
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func libc_setgroups(Size_t, *Gid_t) int __asm__ ("setgroups")
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func libc_chdir(name *byte) int __asm__ ("chdir")
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func libc_dup2(int, int) int __asm__ ("dup2")
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func libc_ioctl(int, int) int __asm__ ("ioctl")
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func libc_execve(*byte, **byte, **byte) int __asm__ ("execve")
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func libc_sysexit(int) __asm__ ("_exit")
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// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
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// If a dup or exec fails, write the errno int to pipe.
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// (Pipe is close-on-exec so if exec succeeds, it will be closed.)
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// In the child, this function must not acquire any locks, because
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// they might have been locked at the time of the fork. This means
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// no rescheduling, no malloc calls, and no new stack segments.
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func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err int) {
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// Declare all variables at top in case any
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// declarations require heap allocation (e.g., err1).
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var r1, r2, err1 uintptr
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var nextfd int
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var i int
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// guard against side effects of shuffling fds below.
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fd := append([]int(nil), attr.Files...)
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darwin := OS == "darwin"
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// About to call fork.
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// No more allocation or calls of non-assembly functions.
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child := libc_fork()
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if child == -1 {
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return 0, GetErrno()
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}
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if child != 0 {
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// parent; return PID
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return int(child), 0
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}
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// Fork succeeded, now in child.
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// Enable tracing if requested.
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if sys.Ptrace {
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if libc_ptrace(_PTRACE_TRACEME, 0, 0, nil) < 0 {
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goto childerror
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}
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}
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// Session ID
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if sys.Setsid {
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if libc_setsid() == Pid_t(-1) {
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goto childerror
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}
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}
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// Set process group
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if sys.Setpgid {
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if libc_setpgid(0, 0) < 0 {
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goto childerror
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}
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}
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// Chroot
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if chroot != nil {
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if libc_chroot(chroot) < 0 {
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goto childerror
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}
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}
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// User and groups
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if cred := sys.Credential; cred != nil {
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ngroups := uintptr(len(cred.Groups))
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var groups *Gid_t
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if ngroups > 0 {
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groups = (*Gid_t)(unsafe.Pointer(&cred.Groups[0]))
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}
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if libc_setgroups(Size_t(ngroups), groups) < 0 {
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goto childerror
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}
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if libc_setgid(Gid_t(cred.Gid)) < 0 {
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goto childerror
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}
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if libc_setuid(Uid_t(cred.Uid)) < 0 {
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goto childerror
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}
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}
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// Chdir
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if dir != nil {
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if libc_chdir(dir) < 0 {
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goto childerror
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}
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}
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// Pass 1: look for fd[i] < i and move those up above len(fd)
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// so that pass 2 won't stomp on an fd it needs later.
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nextfd = int(len(fd))
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if pipe < nextfd {
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r := libc_dup2(pipe, nextfd)
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if r == -1 {
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goto childerror
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}
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libc_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
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pipe = nextfd
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nextfd++
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}
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for i = 0; i < len(fd); i++ {
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if fd[i] >= 0 && fd[i] < int(i) {
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r := libc_dup2(fd[i], nextfd)
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if r == -1 {
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goto childerror
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}
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libc_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
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fd[i] = nextfd
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nextfd++
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if nextfd == pipe { // don't stomp on pipe
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nextfd++
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}
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}
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}
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// Pass 2: dup fd[i] down onto i.
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for i = 0; i < len(fd); i++ {
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if fd[i] == -1 {
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libc_close(i)
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continue
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}
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if fd[i] == int(i) {
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// dup2(i, i) won't clear close-on-exec flag on Linux,
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// probably not elsewhere either.
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r := libc_fcntl(fd[i], F_SETFD, 0)
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if r != 0 {
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goto childerror
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}
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continue
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}
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// The new fd is created NOT close-on-exec,
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// which is exactly what we want.
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r := libc_dup2(fd[i], i)
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if r == -1 {
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goto childerror
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}
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}
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// By convention, we don't close-on-exec the fds we are
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// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
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// Programs that know they inherit fds >= 3 will need
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// to set them close-on-exec.
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for i = len(fd); i < 3; i++ {
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libc_close(i)
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}
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// Detach fd 0 from tty
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if sys.Noctty {
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if libc_ioctl(0, TIOCNOTTY) < 0 {
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goto childerror
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}
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}
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// Make fd 0 the tty
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if sys.Setctty {
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if libc_ioctl(0, TIOCSCTTY) < 0 {
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goto childerror
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}
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}
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// Time to exec.
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libc_execve(argv0, &argv[0], &envv[0])
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childerror:
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// send error code on pipe
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var e uintptr = uintptr(GetErrno())
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libc_write(pipe, (*byte)(unsafe.Pointer(&e)),
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Size_t(unsafe.Sizeof(err1)))
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for {
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libc_sysexit(253)
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}
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// Calling panic is not actually safe,
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// but the for loop above won't break
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// and this shuts up the compiler.
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panic("unreached")
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}
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// Credential holds user and group identities to be assumed
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// by a child process started by StartProcess.
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type Credential struct {
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Uid uint32 // User ID.
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Gid uint32 // Group ID.
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Groups []uint32 // Supplementary group IDs.
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}
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// ProcAttr holds attributes that will be applied to a new process started
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// by StartProcess.
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type ProcAttr struct {
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Dir string // Current working directory.
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Env []string // Environment.
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Files []int // File descriptors.
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Sys *SysProcAttr
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}
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type SysProcAttr struct {
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Chroot string // Chroot.
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Credential *Credential // Credential.
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Ptrace bool // Enable tracing.
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Setsid bool // Create session.
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Setpgid bool // Set process group ID to new pid (SYSV setpgrp)
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Setctty bool // Set controlling terminal to fd 0
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Noctty bool // Detach fd 0 from controlling terminal
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}
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var zeroProcAttr ProcAttr
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var zeroSysProcAttr SysProcAttr
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func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err int) {
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var p [2]int
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var n Ssize_t
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var r1 int
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var err1 uintptr
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var wstatus WaitStatus
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if attr == nil {
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attr = &zeroProcAttr
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}
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sys := attr.Sys
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if sys == nil {
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sys = &zeroSysProcAttr
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}
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p[0] = -1
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p[1] = -1
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// Convert args to C form.
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argv0p := StringBytePtr(argv0)
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argvp := StringArrayPtr(argv)
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envvp := StringArrayPtr(attr.Env)
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if OS == "freebsd" && len(argv[0]) > len(argv0) {
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argvp[0] = argv0p
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}
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var chroot *byte
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if sys.Chroot != "" {
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chroot = StringBytePtr(sys.Chroot)
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}
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var dir *byte
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if attr.Dir != "" {
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dir = StringBytePtr(attr.Dir)
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}
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// Acquire the fork lock so that no other threads
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// create new fds that are not yet close-on-exec
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// before we fork.
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ForkLock.Lock()
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// Allocate child status pipe close on exec.
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if err = Pipe(p[0:]); err != 0 {
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goto error
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}
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if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != 0 {
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goto error
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}
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if _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC); err != 0 {
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goto error
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}
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// Kick off child.
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pid, err = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1])
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if err != 0 {
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goto error
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}
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ForkLock.Unlock()
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// Read child error status from pipe.
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Close(p[1])
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n = libc_read(p[0], (*byte)(unsafe.Pointer(&err1)),
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Size_t(unsafe.Sizeof(err1)))
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err = 0
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if n < 0 {
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err = GetErrno()
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}
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Close(p[0])
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if err != 0 || n != 0 {
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if int(n) == unsafe.Sizeof(err1) {
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err = int(err1)
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}
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if err == 0 {
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err = EPIPE
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}
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// Child failed; wait for it to exit, to make sure
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// the zombies don't accumulate.
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_, err1 := Wait4(pid, &wstatus, 0, nil)
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for err1 == EINTR {
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_, err1 = Wait4(pid, &wstatus, 0, nil)
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}
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return 0, err
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}
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// Read got EOF, so pipe closed on exec, so exec succeeded.
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return pid, 0
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error:
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if p[0] >= 0 {
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Close(p[0])
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Close(p[1])
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}
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ForkLock.Unlock()
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return 0, err
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}
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// Combination of fork and exec, careful to be thread safe.
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func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err int) {
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return forkExec(argv0, argv, attr)
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}
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// StartProcess wraps ForkExec for package os.
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func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid, handle int, err int) {
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pid, err = forkExec(argv0, argv, attr)
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return pid, 0, err
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}
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// Ordinary exec.
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func Exec(argv0 string, argv []string, envv []string) (err int) {
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argv_arg := StringArrayPtr(argv)
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envv_arg := StringArrayPtr(envv)
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libc_execve(StringBytePtr(argv0), &argv_arg[0], &envv_arg[0])
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return GetErrno()
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}
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