src/syscall/exec_unix.go - go - Git at Google

 // Copyright 2009 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.

 // +build darwin dragonfly freebsd linux netbsd openbsd solaris

 // Fork, exec, wait, etc.

 package syscall

 import (
 	"runtime"
 	"sync"
 	"unsafe"
 )

 // Lock synchronizing creation of new file descriptors with fork.
 //
 // We want the child in a fork/exec sequence to inherit only the
 // file descriptors we intend.  To do that, we mark all file
 // descriptors close-on-exec and then, in the child, explicitly
 // unmark the ones we want the exec'ed program to keep.
 // Unix doesn't make this easy: there is, in general, no way to
 // allocate a new file descriptor close-on-exec.  Instead you
 // have to allocate the descriptor and then mark it close-on-exec.
 // If a fork happens between those two events, the child's exec
 // will inherit an unwanted file descriptor.
 //
 // This lock solves that race: the create new fd/mark close-on-exec
 // operation is done holding ForkLock for reading, and the fork itself
 // is done holding ForkLock for writing.  At least, that's the idea.
 // There are some complications.
 //
 // Some system calls that create new file descriptors can block
 // for arbitrarily long times: open on a hung NFS server or named
 // pipe, accept on a socket, and so on.  We can't reasonably grab
 // the lock across those operations.
 //
 // It is worse to inherit some file descriptors than others.
 // If a non-malicious child accidentally inherits an open ordinary file,
 // that's not a big deal.  On the other hand, if a long-lived child
 // accidentally inherits the write end of a pipe, then the reader
 // of that pipe will not see EOF until that child exits, potentially
 // causing the parent program to hang.  This is a common problem
 // in threaded C programs that use popen.
 //
 // Luckily, the file descriptors that are most important not to
 // inherit are not the ones that can take an arbitrarily long time
 // to create: pipe returns instantly, and the net package uses
 // non-blocking I/O to accept on a listening socket.
 // The rules for which file descriptor-creating operations use the
 // ForkLock are as follows:
 //
 // 1) Pipe.    Does not block.  Use the ForkLock.
 // 2) Socket.  Does not block.  Use the ForkLock.
 // 3) Accept.  If using non-blocking mode, use the ForkLock.
 //             Otherwise, live with the race.
 // 4) Open.    Can block.  Use O_CLOEXEC if available (Linux).
 //             Otherwise, live with the race.
 // 5) Dup.     Does not block.  Use the ForkLock.
 //             On Linux, could use fcntl F_DUPFD_CLOEXEC
 //             instead of the ForkLock, but only for dup(fd, -1).

 var ForkLock sync.RWMutex

 // StringSlicePtr is deprecated. Use SlicePtrFromStrings instead.
 // If any string contains a NUL byte this function panics instead
 // of returning an error.
 func StringSlicePtr(ss []string) []*byte {
 	bb := make([]*byte, len(ss)+1)
 	for i := 0; i < len(ss); i++ {
 		bb[i] = StringBytePtr(ss[i])
 	}
 	bb[len(ss)] = nil
 	return bb
 }

 // SlicePtrFromStrings converts a slice of strings to a slice of
 // pointers to NUL-terminated byte slices. If any string contains
 // a NUL byte, it returns (nil, EINVAL).
 func SlicePtrFromStrings(ss []string) ([]*byte, error) {
 	var err error
 	bb := make([]*byte, len(ss)+1)
 	for i := 0; i < len(ss); i++ {
 		bb[i], err = BytePtrFromString(ss[i])
 		if err != nil {
 			return nil, err
 		}
 	}
 	bb[len(ss)] = nil
 	return bb, nil
 }

 func CloseOnExec(fd int) { fcntl(fd, F_SETFD, FD_CLOEXEC) }

 func SetNonblock(fd int, nonblocking bool) (err error) {
 	flag, err := fcntl(fd, F_GETFL, 0)
 	if err != nil {
 		return err
 	}
 	if nonblocking {
 		flag |= O_NONBLOCK
 	} else {
 		flag &= ^O_NONBLOCK
 	}
 	_, err = fcntl(fd, F_SETFL, flag)
 	return err
 }

 // Credential holds user and group identities to be assumed
 // by a child process started by StartProcess.
 type Credential struct {
 	Uid    uint32   // User ID.
 	Gid    uint32   // Group ID.
 	Groups []uint32 // Supplementary group IDs.
 }

 // ProcAttr holds attributes that will be applied to a new process started
 // by StartProcess.
 type ProcAttr struct {
 	Dir   string    // Current working directory.
 	Env   []string  // Environment.
 	Files []uintptr // File descriptors.
 	Sys   *SysProcAttr
 }

 var zeroProcAttr ProcAttr
 var zeroSysProcAttr SysProcAttr

 func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
 	var p [2]int
 	var n int
 	var err1 Errno
 	var wstatus WaitStatus

 	if attr == nil {
 		attr = &zeroProcAttr
 	}
 	sys := attr.Sys
 	if sys == nil {
 		sys = &zeroSysProcAttr
 	}

 	p[0] = -1
 	p[1] = -1

 	// Convert args to C form.
 	argv0p, err := BytePtrFromString(argv0)
 	if err != nil {
 		return 0, err
 	}
 	argvp, err := SlicePtrFromStrings(argv)
 	if err != nil {
 		return 0, err
 	}
 	envvp, err := SlicePtrFromStrings(attr.Env)
 	if err != nil {
 		return 0, err
 	}

 	if (runtime.GOOS == "freebsd" || runtime.GOOS == "dragonfly") && len(argv[0]) > len(argv0) {
 		argvp[0] = argv0p
 	}

 	var chroot *byte
 	if sys.Chroot != "" {
 		chroot, err = BytePtrFromString(sys.Chroot)
 		if err != nil {
 			return 0, err
 		}
 	}
 	var dir *byte
 	if attr.Dir != "" {
 		dir, err = BytePtrFromString(attr.Dir)
 		if err != nil {
 			return 0, err
 		}
 	}

 	// Acquire the fork lock so that no other threads
 	// create new fds that are not yet close-on-exec
 	// before we fork.
 	ForkLock.Lock()

 	// Allocate child status pipe close on exec.
 	if err = forkExecPipe(p[:]); err != nil {
 		goto error
 	}

 	// Kick off child.
 	pid, err1 = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1])
 	if err1 != 0 {
 		err = Errno(err1)
 		goto error
 	}
 	ForkLock.Unlock()

 	// Read child error status from pipe.
 	Close(p[1])
 	n, err = readlen(p[0], (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
 	Close(p[0])
 	if err != nil || n != 0 {
 		if n == int(unsafe.Sizeof(err1)) {
 			err = Errno(err1)
 		}
 		if err == nil {
 			err = EPIPE
 		}

 		// Child failed; wait for it to exit, to make sure
 		// the zombies don't accumulate.
 		_, err1 := Wait4(pid, &wstatus, 0, nil)
 		for err1 == EINTR {
 			_, err1 = Wait4(pid, &wstatus, 0, nil)
 		}
 		return 0, err
 	}

 	// Read got EOF, so pipe closed on exec, so exec succeeded.
 	return pid, nil

 error:
 	if p[0] >= 0 {
 		Close(p[0])
 		Close(p[1])
 	}
 	ForkLock.Unlock()
 	return 0, err
 }

 // Combination of fork and exec, careful to be thread safe.
 func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
 	return forkExec(argv0, argv, attr)
 }

 // StartProcess wraps ForkExec for package os.
 func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {
 	pid, err = forkExec(argv0, argv, attr)
 	return pid, 0, err
 }

 // Ordinary exec.
 func Exec(argv0 string, argv []string, envv []string) (err error) {
 	argv0p, err := BytePtrFromString(argv0)
 	if err != nil {
 		return err
 	}
 	argvp, err := SlicePtrFromStrings(argv)
 	if err != nil {
 		return err
 	}
 	envvp, err := SlicePtrFromStrings(envv)
 	if err != nil {
 		return err
 	}
 	_, _, err1 := RawSyscall(SYS_EXECVE,
 		uintptr(unsafe.Pointer(argv0p)),
 		uintptr(unsafe.Pointer(&argvp[0])),
 		uintptr(unsafe.Pointer(&envvp[0])))
 	return Errno(err1)
 }
	// Copyright 2009 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.

	// +build darwin dragonfly freebsd linux netbsd openbsd solaris

	// Fork, exec, wait, etc.

	package syscall

	import (
	"runtime"
	"sync"
	"unsafe"
	)

	// Lock synchronizing creation of new file descriptors with fork.
	//
	// We want the child in a fork/exec sequence to inherit only the
	// file descriptors we intend. To do that, we mark all file
	// descriptors close-on-exec and then, in the child, explicitly
	// unmark the ones we want the exec'ed program to keep.
	// Unix doesn't make this easy: there is, in general, no way to
	// allocate a new file descriptor close-on-exec. Instead you
	// have to allocate the descriptor and then mark it close-on-exec.
	// If a fork happens between those two events, the child's exec
	// will inherit an unwanted file descriptor.
	//
	// This lock solves that race: the create new fd/mark close-on-exec
	// operation is done holding ForkLock for reading, and the fork itself
	// is done holding ForkLock for writing. At least, that's the idea.
	// There are some complications.
	//
	// Some system calls that create new file descriptors can block
	// for arbitrarily long times: open on a hung NFS server or named
	// pipe, accept on a socket, and so on. We can't reasonably grab
	// the lock across those operations.
	//
	// It is worse to inherit some file descriptors than others.
	// If a non-malicious child accidentally inherits an open ordinary file,
	// that's not a big deal. On the other hand, if a long-lived child
	// accidentally inherits the write end of a pipe, then the reader
	// of that pipe will not see EOF until that child exits, potentially
	// causing the parent program to hang. This is a common problem
	// in threaded C programs that use popen.
	//
	// Luckily, the file descriptors that are most important not to
	// inherit are not the ones that can take an arbitrarily long time
	// to create: pipe returns instantly, and the net package uses
	// non-blocking I/O to accept on a listening socket.
	// The rules for which file descriptor-creating operations use the
	// ForkLock are as follows:
	//
	// 1) Pipe. Does not block. Use the ForkLock.
	// 2) Socket. Does not block. Use the ForkLock.
	// 3) Accept. If using non-blocking mode, use the ForkLock.
	// Otherwise, live with the race.
	// 4) Open. Can block. Use O_CLOEXEC if available (Linux).
	// Otherwise, live with the race.
	// 5) Dup. Does not block. Use the ForkLock.
	// On Linux, could use fcntl F_DUPFD_CLOEXEC
	// instead of the ForkLock, but only for dup(fd, -1).

	var ForkLock sync.RWMutex

	// StringSlicePtr is deprecated. Use SlicePtrFromStrings instead.
	// If any string contains a NUL byte this function panics instead
	// of returning an error.
	func StringSlicePtr(ss []string) []*byte {
	bb := make([]*byte, len(ss)+1)
	for i := 0; i < len(ss); i++ {
	bb[i] = StringBytePtr(ss[i])
	}
	bb[len(ss)] = nil
	return bb
	}

	// SlicePtrFromStrings converts a slice of strings to a slice of
	// pointers to NUL-terminated byte slices. If any string contains
	// a NUL byte, it returns (nil, EINVAL).
	func SlicePtrFromStrings(ss []string) ([]*byte, error) {
	var err error
	bb := make([]*byte, len(ss)+1)
	for i := 0; i < len(ss); i++ {
	bb[i], err = BytePtrFromString(ss[i])
	if err != nil {
	return nil, err
	}
	}
	bb[len(ss)] = nil
	return bb, nil
	}

	func CloseOnExec(fd int) { fcntl(fd, F_SETFD, FD_CLOEXEC) }

	func SetNonblock(fd int, nonblocking bool) (err error) {
	flag, err := fcntl(fd, F_GETFL, 0)
	if err != nil {
	return err
	}
	if nonblocking {
	flag \|= O_NONBLOCK
	} else {
	flag &= ^O_NONBLOCK
	}
	_, err = fcntl(fd, F_SETFL, flag)
	return err
	}

	// Credential holds user and group identities to be assumed
	// by a child process started by StartProcess.
	type Credential struct {
	Uid uint32 // User ID.
	Gid uint32 // Group ID.
	Groups []uint32 // Supplementary group IDs.
	}

	// ProcAttr holds attributes that will be applied to a new process started
	// by StartProcess.
	type ProcAttr struct {
	Dir string // Current working directory.
	Env []string // Environment.
	Files []uintptr // File descriptors.
	Sys *SysProcAttr
	}

	var zeroProcAttr ProcAttr
	var zeroSysProcAttr SysProcAttr

	func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
	var p [2]int
	var n int
	var err1 Errno
	var wstatus WaitStatus

	if attr == nil {
	attr = &zeroProcAttr
	}
	sys := attr.Sys
	if sys == nil {
	sys = &zeroSysProcAttr
	}

	p[0] = -1
	p[1] = -1

	// Convert args to C form.
	argv0p, err := BytePtrFromString(argv0)
	if err != nil {
	return 0, err
	}
	argvp, err := SlicePtrFromStrings(argv)
	if err != nil {
	return 0, err
	}
	envvp, err := SlicePtrFromStrings(attr.Env)
	if err != nil {
	return 0, err
	}

	if (runtime.GOOS == "freebsd" \|\| runtime.GOOS == "dragonfly") && len(argv[0]) > len(argv0) {
	argvp[0] = argv0p
	}

	var chroot *byte
	if sys.Chroot != "" {
	chroot, err = BytePtrFromString(sys.Chroot)
	if err != nil {
	return 0, err
	}
	}
	var dir *byte
	if attr.Dir != "" {
	dir, err = BytePtrFromString(attr.Dir)
	if err != nil {
	return 0, err
	}
	}

	// Acquire the fork lock so that no other threads
	// create new fds that are not yet close-on-exec
	// before we fork.
	ForkLock.Lock()

	// Allocate child status pipe close on exec.
	if err = forkExecPipe(p[:]); err != nil {
	goto error
	}

	// Kick off child.
	pid, err1 = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1])
	if err1 != 0 {
	err = Errno(err1)
	goto error
	}
	ForkLock.Unlock()

	// Read child error status from pipe.
	Close(p[1])
	n, err = readlen(p[0], (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
	Close(p[0])
	if err != nil \|\| n != 0 {
	if n == int(unsafe.Sizeof(err1)) {
	err = Errno(err1)
	}
	if err == nil {
	err = EPIPE
	}

	// Child failed; wait for it to exit, to make sure
	// the zombies don't accumulate.
	_, err1 := Wait4(pid, &wstatus, 0, nil)
	for err1 == EINTR {
	_, err1 = Wait4(pid, &wstatus, 0, nil)
	}
	return 0, err
	}

	// Read got EOF, so pipe closed on exec, so exec succeeded.
	return pid, nil

	error:
	if p[0] >= 0 {
	Close(p[0])
	Close(p[1])
	}
	ForkLock.Unlock()
	return 0, err
	}

	// Combination of fork and exec, careful to be thread safe.
	func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
	return forkExec(argv0, argv, attr)
	}

	// StartProcess wraps ForkExec for package os.
	func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {
	pid, err = forkExec(argv0, argv, attr)
	return pid, 0, err
	}

	// Ordinary exec.
	func Exec(argv0 string, argv []string, envv []string) (err error) {
	argv0p, err := BytePtrFromString(argv0)
	if err != nil {
	return err
	}
	argvp, err := SlicePtrFromStrings(argv)
	if err != nil {
	return err
	}
	envvp, err := SlicePtrFromStrings(envv)
	if err != nil {
	return err
	}
	_, _, err1 := RawSyscall(SYS_EXECVE,
	uintptr(unsafe.Pointer(argv0p)),
	uintptr(unsafe.Pointer(&argvp[0])),
	uintptr(unsafe.Pointer(&envvp[0])))
	return Errno(err1)
	}