--- /dev/null
+// Copyright 2021 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 sets the process group ID of the child to Pgid,
+ // or, if Pgid == 0, to the new child's process ID.
+ Setpgid bool
+ // Setctty sets the controlling terminal of the child to
+ // file descriptor Ctty. Ctty must be a descriptor number
+ // in the child process: an index into ProcAttr.Files.
+ // This is only meaningful if Setsid is true.
+ Setctty bool
+ Noctty bool // Detach fd 0 from controlling terminal
+ Ctty int // Controlling TTY fd
+ // Foreground places the child process group in the foreground.
+ // This implies Setpgid. The Ctty field must be set to
+ // the descriptor of the controlling TTY.
+ // Unlike Setctty, in this case Ctty must be a descriptor
+ // number in the parent process.
+ Foreground bool
+ 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(SYS_FORK, 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.
+
+ // Enable tracing if requested.
+ if sys.Ptrace {
+ _, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Session ID
+ if sys.Setsid {
+ _, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Set process group
+ if sys.Setpgid || sys.Foreground {
+ // Place child in process group.
+ _, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ if sys.Foreground {
+ // This should really be pid_t, however _C_int (aka int32) is
+ // generally equivalent.
+ pgrp := _C_int(sys.Pgid)
+ if pgrp == 0 {
+ r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+
+ pgrp = _C_int(r1)
+ }
+
+ // Place process group in foreground.
+ _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Restore the signal mask. We do this after TIOCSPGRP to avoid
+ // having the kernel send a SIGTTOU signal to the process group.
+ runtime_AfterForkInChild()
+
+ // Chroot
+ if chroot != nil {
+ _, _, err1 = RawSyscall(SYS_CHROOT, 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(SYS_SETGROUPS, ngroups, groups, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+ _, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ _, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Chdir
+ if dir != nil {
+ _, _, err1 = RawSyscall(SYS_CHDIR, 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(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ RawSyscall(SYS_FCNTL, 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(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ RawSyscall(SYS_FCNTL, 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(SYS_CLOSE, 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(SYS_FCNTL, 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(SYS_DUP2, 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(SYS_CLOSE, uintptr(i), 0, 0)
+ }
+
+ // Detach fd 0 from tty
+ if sys.Noctty {
+ _, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Set the controlling TTY to Ctty
+ if sys.Setctty {
+ _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
+ if err1 != 0 {
+ goto childerror
+ }
+ }
+
+ // Time to exec.
+ _, _, err1 = RawSyscall(SYS_EXECVE,
+ uintptr(unsafe.Pointer(argv0)),
+ uintptr(unsafe.Pointer(&argv[0])),
+ uintptr(unsafe.Pointer(&envv[0])))
+
+childerror:
+ // send error code on pipe
+ RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
+ for {
+ RawSyscall(SYS_EXIT, 253, 0, 0)
+ }
+}