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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package syscall
import (
"unsafe"
)
type SysProcAttr struct {
Chroot string // Chroot.
Credential *Credential // Credential.
Ptrace bool // Enable tracing.
Setsid bool // Create session.
Setpgid bool // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
Setctty bool // Set controlling terminal to fd Ctty
Noctty bool // Detach fd 0 from controlling terminal
Ctty int // Controlling TTY fd
Foreground bool // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
Pgid int // Child's process group ID if Setpgid.
}
// Implemented in runtime package.
func runtime_BeforeFork()
func runtime_AfterFork()
func runtime_AfterForkInChild()
// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
// If a dup or exec fails, write the errno error to pipe.
// (Pipe is close-on-exec so if exec succeeds, it will be closed.)
// In the child, this function must not acquire any locks, because
// they might have been locked at the time of the fork. This means
// no rescheduling, no malloc calls, and no new stack segments.
// For the same reason compiler does not race instrument it.
// The calls to rawSyscall are okay because they are assembly
// functions that do not grow the stack.
//go:norace
func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
// Declare all variables at top in case any
// declarations require heap allocation (e.g., err1).
var (
r1 uintptr
err1 Errno
nextfd int
i int
)
// guard against side effects of shuffling fds below.
// Make sure that nextfd is beyond any currently open files so
// that we can't run the risk of overwriting any of them.
fd := make([]int, len(attr.Files))
nextfd = len(attr.Files)
for i, ufd := range attr.Files {
if nextfd < int(ufd) {
nextfd = int(ufd)
}
fd[i] = int(ufd)
}
nextfd++
// About to call fork.
// No more allocation or calls of non-assembly functions.
runtime_BeforeFork()
r1, _, err1 = rawSyscall(funcPC(libc_fork_trampoline), 0, 0, 0)
if err1 != 0 {
runtime_AfterFork()
return 0, err1
}
if r1 != 0 {
// parent; return PID
runtime_AfterFork()
return int(r1), 0
}
// Fork succeeded, now in child.
runtime_AfterForkInChild()
// Enable tracing if requested.
if sys.Ptrace {
if err := ptrace(PTRACE_TRACEME, 0, 0, 0); err != nil {
err1 = err.(Errno)
goto childerror
}
}
// Session ID
if sys.Setsid {
_, _, err1 = rawSyscall(funcPC(libc_setsid_trampoline), 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
// Set process group
if sys.Setpgid || sys.Foreground {
// Place child in process group.
_, _, err1 = rawSyscall(funcPC(libc_setpgid_trampoline), 0, uintptr(sys.Pgid), 0)
if err1 != 0 {
goto childerror
}
}
if sys.Foreground {
pgrp := sys.Pgid
if pgrp == 0 {
r1, _, err1 = rawSyscall(funcPC(libc_getpid_trampoline), 0, 0, 0)
if err1 != 0 {
goto childerror
}
pgrp = int(r1)
}
// Place process group in foreground.
_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
if err1 != 0 {
goto childerror
}
}
// Chroot
if chroot != nil {
_, _, err1 = rawSyscall(funcPC(libc_chroot_trampoline), uintptr(unsafe.Pointer(chroot)), 0, 0)
if err1 != 0 {
goto childerror
}
}
// User and groups
if cred := sys.Credential; cred != nil {
ngroups := uintptr(len(cred.Groups))
groups := uintptr(0)
if ngroups > 0 {
groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
}
if !cred.NoSetGroups {
_, _, err1 = rawSyscall(funcPC(libc_setgroups_trampoline), ngroups, groups, 0)
if err1 != 0 {
goto childerror
}
}
_, _, err1 = rawSyscall(funcPC(libc_setgid_trampoline), uintptr(cred.Gid), 0, 0)
if err1 != 0 {
goto childerror
}
_, _, err1 = rawSyscall(funcPC(libc_setuid_trampoline), uintptr(cred.Uid), 0, 0)
if err1 != 0 {
goto childerror
}
}
// Chdir
if dir != nil {
_, _, err1 = rawSyscall(funcPC(libc_chdir_trampoline), uintptr(unsafe.Pointer(dir)), 0, 0)
if err1 != 0 {
goto childerror
}
}
// Pass 1: look for fd[i] < i and move those up above len(fd)
// so that pass 2 won't stomp on an fd it needs later.
if pipe < nextfd {
_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(pipe), uintptr(nextfd), 0)
if err1 != 0 {
goto childerror
}
rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
pipe = nextfd
nextfd++
}
for i = 0; i < len(fd); i++ {
if fd[i] >= 0 && fd[i] < int(i) {
if nextfd == pipe { // don't stomp on pipe
nextfd++
}
_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(fd[i]), uintptr(nextfd), 0)
if err1 != 0 {
goto childerror
}
rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
fd[i] = nextfd
nextfd++
}
}
// Pass 2: dup fd[i] down onto i.
for i = 0; i < len(fd); i++ {
if fd[i] == -1 {
rawSyscall(funcPC(libc_close_trampoline), uintptr(i), 0, 0)
continue
}
if fd[i] == int(i) {
// dup2(i, i) won't clear close-on-exec flag on Linux,
// probably not elsewhere either.
_, _, err1 = rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(fd[i]), F_SETFD, 0)
if err1 != 0 {
goto childerror
}
continue
}
// The new fd is created NOT close-on-exec,
// which is exactly what we want.
_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(fd[i]), uintptr(i), 0)
if err1 != 0 {
goto childerror
}
}
// By convention, we don't close-on-exec the fds we are
// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
// Programs that know they inherit fds >= 3 will need
// to set them close-on-exec.
for i = len(fd); i < 3; i++ {
rawSyscall(funcPC(libc_close_trampoline), uintptr(i), 0, 0)
}
// Detach fd 0 from tty
if sys.Noctty {
_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), 0, uintptr(TIOCNOTTY), 0)
if err1 != 0 {
goto childerror
}
}
// Set the controlling TTY to Ctty
if sys.Setctty {
_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
if err1 != 0 {
goto childerror
}
}
// Time to exec.
_, _, err1 = rawSyscall(funcPC(libc_execve_trampoline),
uintptr(unsafe.Pointer(argv0)),
uintptr(unsafe.Pointer(&argv[0])),
uintptr(unsafe.Pointer(&envv[0])))
childerror:
// send error code on pipe
rawSyscall(funcPC(libc_write_trampoline), uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
for {
rawSyscall(funcPC(libc_exit_trampoline), 253, 0, 0)
}
}
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