249 lines
6.8 KiB
Go
249 lines
6.8 KiB
Go
// Copyright 2011 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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package syscall
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import (
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"unsafe"
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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 Pgid, or, if Pgid == 0, to new pid.
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Setctty bool // Set controlling terminal to fd Ctty
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Noctty bool // Detach fd 0 from controlling terminal
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Ctty int // Controlling TTY fd
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Foreground bool // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
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Pgid int // Child's process group ID if Setpgid.
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}
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// Implemented in runtime package.
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func runtime_BeforeFork()
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func runtime_AfterFork()
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func runtime_AfterForkInChild()
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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 error 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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// For the same reason compiler does not race instrument it.
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// The calls to rawSyscall are okay because they are assembly
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// functions that do not grow the stack.
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//go:norace
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func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
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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 (
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r1 uintptr
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err1 Errno
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nextfd int
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i int
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)
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// guard against side effects of shuffling fds below.
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// Make sure that nextfd is beyond any currently open files so
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// that we can't run the risk of overwriting any of them.
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fd := make([]int, len(attr.Files))
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nextfd = len(attr.Files)
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for i, ufd := range attr.Files {
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if nextfd < int(ufd) {
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nextfd = int(ufd)
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}
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fd[i] = int(ufd)
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}
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nextfd++
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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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runtime_BeforeFork()
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r1, _, err1 = rawSyscall(funcPC(libc_fork_trampoline), 0, 0, 0)
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if err1 != 0 {
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runtime_AfterFork()
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return 0, err1
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}
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if r1 != 0 {
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// parent; return PID
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runtime_AfterFork()
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return int(r1), 0
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}
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// Fork succeeded, now in child.
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runtime_AfterForkInChild()
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// Enable tracing if requested.
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if sys.Ptrace {
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if err := ptrace(PTRACE_TRACEME, 0, 0, 0); err != nil {
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err1 = err.(Errno)
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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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_, _, err1 = rawSyscall(funcPC(libc_setsid_trampoline), 0, 0, 0)
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if err1 != 0 {
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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 || sys.Foreground {
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// Place child in process group.
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_, _, err1 = rawSyscall(funcPC(libc_setpgid_trampoline), 0, uintptr(sys.Pgid), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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if sys.Foreground {
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pgrp := sys.Pgid
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if pgrp == 0 {
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r1, _, err1 = rawSyscall(funcPC(libc_getpid_trampoline), 0, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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pgrp = int(r1)
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}
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// Place process group in foreground.
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_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
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if err1 != 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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_, _, err1 = rawSyscall(funcPC(libc_chroot_trampoline), uintptr(unsafe.Pointer(chroot)), 0, 0)
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if err1 != 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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groups := uintptr(0)
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if ngroups > 0 {
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groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
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}
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if !cred.NoSetGroups {
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_, _, err1 = rawSyscall(funcPC(libc_setgroups_trampoline), ngroups, groups, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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_, _, err1 = rawSyscall(funcPC(libc_setgid_trampoline), uintptr(cred.Gid), 0, 0)
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if err1 != 0 {
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goto childerror
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}
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_, _, err1 = rawSyscall(funcPC(libc_setuid_trampoline), uintptr(cred.Uid), 0, 0)
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if err1 != 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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_, _, err1 = rawSyscall(funcPC(libc_chdir_trampoline), uintptr(unsafe.Pointer(dir)), 0, 0)
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if err1 != 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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if pipe < nextfd {
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_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(pipe), uintptr(nextfd), 0)
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if err1 != 0 {
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goto childerror
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}
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rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(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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if nextfd == pipe { // don't stomp on pipe
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nextfd++
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}
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_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(fd[i]), uintptr(nextfd), 0)
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if err1 != 0 {
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goto childerror
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}
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rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
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fd[i] = nextfd
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nextfd++
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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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rawSyscall(funcPC(libc_close_trampoline), uintptr(i), 0, 0)
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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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_, _, err1 = rawSyscall(funcPC(libc_fcntl_trampoline), uintptr(fd[i]), F_SETFD, 0)
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if err1 != 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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_, _, err1 = rawSyscall(funcPC(libc_dup2_trampoline), uintptr(fd[i]), uintptr(i), 0)
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if err1 != 0 {
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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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rawSyscall(funcPC(libc_close_trampoline), uintptr(i), 0, 0)
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}
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// Detach fd 0 from tty
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if sys.Noctty {
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_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), 0, uintptr(TIOCNOTTY), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Set the controlling TTY to Ctty
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if sys.Setctty {
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_, _, err1 = rawSyscall(funcPC(libc_ioctl_trampoline), uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
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if err1 != 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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_, _, err1 = rawSyscall(funcPC(libc_execve_trampoline),
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uintptr(unsafe.Pointer(argv0)),
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uintptr(unsafe.Pointer(&argv[0])),
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uintptr(unsafe.Pointer(&envv[0])))
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childerror:
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// send error code on pipe
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rawSyscall(funcPC(libc_write_trampoline), uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
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for {
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rawSyscall(funcPC(libc_exit_trampoline), 253, 0, 0)
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}
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}
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