295 lines
6.9 KiB
Go
295 lines
6.9 KiB
Go
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// Copyright 2021 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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"runtime"
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"unsafe"
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)
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//sysnb raw_procctl(idtype int, id int64, cmd int, data unsafe.Pointer) (ret int, err Errno)
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//procctl(idtype _C_int, id int64, cmd int, data unsafe.Pointer) _C_int
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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 sets the process group ID of the child to Pgid,
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// or, if Pgid == 0, to the new child's process ID.
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Setpgid bool
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// Setctty sets the controlling terminal of the child to
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// file descriptor Ctty. Ctty must be a descriptor number
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// in the child process: an index into ProcAttr.Files.
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// This is only meaningful if Setsid is true.
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Setctty bool
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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 places the child process group in the foreground.
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// This implies Setpgid. The Ctty field must be set to
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// the descriptor of the controlling TTY.
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// Unlike Setctty, in this case Ctty must be a descriptor
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// number in the parent process.
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Foreground bool
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Pgid int // Child's process group ID if Setpgid.
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Pdeathsig Signal // Signal that the process will get when its parent dies (Linux and FreeBSD only)
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}
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const (
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_P_PID = 0
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_PROC_PDEATHSIG_CTL = 11
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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 Pid_t
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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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// Record parent PID so child can test if it has died.
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ppid := raw_getpid()
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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 = raw_fork()
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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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// Enable tracing if requested.
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if sys.Ptrace {
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err1 = raw_ptrace(_PTRACE_TRACEME, 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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// Session ID
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if sys.Setsid {
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err1 = raw_setsid()
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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 = raw_setpgid(0, sys.Pgid)
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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 := Pid_t(sys.Pgid)
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if pgrp == 0 {
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pgrp = raw_getpid()
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}
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// Place process group in foreground.
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err1 = raw_ioctl(sys.Ctty, TIOCSPGRP, unsafe.Pointner(&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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// Restore the signal mask. We do this after TIOCSPGRP to avoid
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// having the kernel send a SIGTTOU signal to the process group.
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runtime_AfterForkInChild()
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// Chroot
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if chroot != nil {
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err1 = raw_chroot(chroot)
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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 := len(cred.Groups)
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var groups *Gid_t
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if ngroups > 0 {
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gids := make([]Gid_t, ngroups)
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for i, v := range cred.Groups {
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gids[i] = Gid_t(v)
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}
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groups = &gids[0]
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}
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if !cred.NoSetGroups {
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err1 = raw_setgroups(ngroups, groups)
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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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err2 := Setgid(int(cred.Gid))
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if err2 != nil {
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err1 = err2.(Errno)
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goto childerror
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}
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err2 = Setuid(int(cred.Uid))
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if err2 != nil {
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err1 = err2.(Errno)
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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 = raw_chdir(dir)
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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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// Parent death signal
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if sys.Pdeathsig != 0 {
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_, err1 = raw_procctl(_P_PID, 0, _PROC_PDEATHSIG_CTL, unsafe.Pointer(&sys.Pdeathsig))
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if err1 != 0 {
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goto childerror
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}
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// Signal self if parent is already dead. This might cause a
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// duplicate signal in rare cases, but it won't matter when
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// using SIGKILL.
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r1 = raw_getppid()
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if r1 != ppid {
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pid := raw_getpid()
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err1 = raw_kill(pid, sys.Pdeathsig)
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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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}
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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 = raw_fcntl(pipe, _F_DUP2FD_CLOEXEC, nextfd)
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if err1 != 0 {
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goto childerror
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}
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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 = raw_fcntl(fd[i], _F_DUP2FD_CLOEXEC, nextfd)
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if err1 != 0 {
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goto childerror
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}
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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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raw_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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_, err1 = raw_fcntl(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 = raw_dup2(fd[i], i)
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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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raw_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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_, err = raw_ioctl(0, 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 = raw_ioctl(sys.Cty, 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 = raw_execve(argv0, &argv[0], &envv[0])
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childerror:
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// send error code on pipe
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raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
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for {
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raw_exit(253)
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}
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}
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