src/os/user/cgo_lookup_unix.go - go - Git at Google

 // 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.

 //go:build (aix || darwin || dragonfly || freebsd || (!android && linux) || netbsd || openbsd || solaris) && cgo && !osusergo
 // +build aix darwin dragonfly freebsd !android,linux netbsd openbsd solaris
 // +build cgo
 // +build !osusergo

 package user

 import (
 	"fmt"
 	"strconv"
 	"strings"
 	"syscall"
 	"unsafe"
 )

 /*
 #cgo solaris CFLAGS: -D_POSIX_PTHREAD_SEMANTICS
 #include <unistd.h>
 #include <sys/types.h>
 #include <pwd.h>
 #include <grp.h>
 #include <stdlib.h>

 static int mygetpwuid_r(int uid, struct passwd *pwd,
 	char *buf, size_t buflen, struct passwd **result) {
 	return getpwuid_r(uid, pwd, buf, buflen, result);
 }

 static int mygetpwnam_r(const char *name, struct passwd *pwd,
 	char *buf, size_t buflen, struct passwd **result) {
 	return getpwnam_r(name, pwd, buf, buflen, result);
 }

 static int mygetgrgid_r(int gid, struct group *grp,
 	char *buf, size_t buflen, struct group **result) {
  return getgrgid_r(gid, grp, buf, buflen, result);
 }

 static int mygetgrnam_r(const char *name, struct group *grp,
 	char *buf, size_t buflen, struct group **result) {
  return getgrnam_r(name, grp, buf, buflen, result);
 }
 */
 import "C"

 func current() (*User, error) {
 	return lookupUnixUid(syscall.Getuid())
 }

 func lookupUser(username string) (*User, error) {
 	var pwd C.struct_passwd
 	var result *C.struct_passwd
 	nameC := make([]byte, len(username)+1)
 	copy(nameC, username)

 	buf := alloc(userBuffer)
 	defer buf.free()

 	err := retryWithBuffer(buf, func() syscall.Errno {
 		// mygetpwnam_r is a wrapper around getpwnam_r to avoid
 		// passing a size_t to getpwnam_r, because for unknown
 		// reasons passing a size_t to getpwnam_r doesn't work on
 		// Solaris.
 		return syscall.Errno(C.mygetpwnam_r((*C.char)(unsafe.Pointer(&nameC[0])),
 			&pwd,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),
 			&result))
 	})
 	if err != nil {
 		return nil, fmt.Errorf("user: lookup username %s: %v", username, err)
 	}
 	if result == nil {
 		return nil, UnknownUserError(username)
 	}
 	return buildUser(&pwd), err
 }

 func lookupUserId(uid string) (*User, error) {
 	i, e := strconv.Atoi(uid)
 	if e != nil {
 		return nil, e
 	}
 	return lookupUnixUid(i)
 }

 func lookupUnixUid(uid int) (*User, error) {
 	var pwd C.struct_passwd
 	var result *C.struct_passwd

 	buf := alloc(userBuffer)
 	defer buf.free()

 	err := retryWithBuffer(buf, func() syscall.Errno {
 		// mygetpwuid_r is a wrapper around getpwuid_r to avoid using uid_t
 		// because C.uid_t(uid) for unknown reasons doesn't work on linux.
 		return syscall.Errno(C.mygetpwuid_r(C.int(uid),
 			&pwd,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),
 			&result))
 	})
 	if err != nil {
 		return nil, fmt.Errorf("user: lookup userid %d: %v", uid, err)
 	}
 	if result == nil {
 		return nil, UnknownUserIdError(uid)
 	}
 	return buildUser(&pwd), nil
 }

 func buildUser(pwd *C.struct_passwd) *User {
 	u := &User{
 		Uid:      strconv.FormatUint(uint64(pwd.pw_uid), 10),
 		Gid:      strconv.FormatUint(uint64(pwd.pw_gid), 10),
 		Username: C.GoString(pwd.pw_name),
 		Name:     C.GoString(pwd.pw_gecos),
 		HomeDir:  C.GoString(pwd.pw_dir),
 	}
 	// The pw_gecos field isn't quite standardized. Some docs
 	// say: "It is expected to be a comma separated list of
 	// personal data where the first item is the full name of the
 	// user."
 	u.Name, _, _ = strings.Cut(u.Name, ",")
 	return u
 }

 func lookupGroup(groupname string) (*Group, error) {
 	var grp C.struct_group
 	var result *C.struct_group

 	buf := alloc(groupBuffer)
 	defer buf.free()
 	cname := make([]byte, len(groupname)+1)
 	copy(cname, groupname)

 	err := retryWithBuffer(buf, func() syscall.Errno {
 		return syscall.Errno(C.mygetgrnam_r((*C.char)(unsafe.Pointer(&cname[0])),
 			&grp,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),
 			&result))
 	})
 	if err != nil {
 		return nil, fmt.Errorf("user: lookup groupname %s: %v", groupname, err)
 	}
 	if result == nil {
 		return nil, UnknownGroupError(groupname)
 	}
 	return buildGroup(&grp), nil
 }

 func lookupGroupId(gid string) (*Group, error) {
 	i, e := strconv.Atoi(gid)
 	if e != nil {
 		return nil, e
 	}
 	return lookupUnixGid(i)
 }

 func lookupUnixGid(gid int) (*Group, error) {
 	var grp C.struct_group
 	var result *C.struct_group

 	buf := alloc(groupBuffer)
 	defer buf.free()

 	err := retryWithBuffer(buf, func() syscall.Errno {
 		// mygetgrgid_r is a wrapper around getgrgid_r to avoid using gid_t
 		// because C.gid_t(gid) for unknown reasons doesn't work on linux.
 		return syscall.Errno(C.mygetgrgid_r(C.int(gid),
 			&grp,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),
 			&result))
 	})
 	if err != nil {
 		return nil, fmt.Errorf("user: lookup groupid %d: %v", gid, err)
 	}
 	if result == nil {
 		return nil, UnknownGroupIdError(strconv.Itoa(gid))
 	}
 	return buildGroup(&grp), nil
 }

 func buildGroup(grp *C.struct_group) *Group {
 	g := &Group{
 		Gid:  strconv.Itoa(int(grp.gr_gid)),
 		Name: C.GoString(grp.gr_name),
 	}
 	return g
 }

 type bufferKind C.int

 const (
 	userBuffer  = bufferKind(C._SC_GETPW_R_SIZE_MAX)
 	groupBuffer = bufferKind(C._SC_GETGR_R_SIZE_MAX)
 )

 func (k bufferKind) initialSize() C.size_t {
 	sz := C.sysconf(C.int(k))
 	if sz == -1 {
 		// DragonFly and FreeBSD do not have _SC_GETPW_R_SIZE_MAX.
 		// Additionally, not all Linux systems have it, either. For
 		// example, the musl libc returns -1.
 		return 1024
 	}
 	if !isSizeReasonable(int64(sz)) {
 		// Truncate.  If this truly isn't enough, retryWithBuffer will error on the first run.
 		return maxBufferSize
 	}
 	return C.size_t(sz)
 }

 type memBuffer struct {
 	ptr  unsafe.Pointer
 	size C.size_t
 }

 func alloc(kind bufferKind) *memBuffer {
 	sz := kind.initialSize()
 	return &memBuffer{
 		ptr:  C.malloc(sz),
 		size: sz,
 	}
 }

 func (mb *memBuffer) resize(newSize C.size_t) {
 	mb.ptr = C.realloc(mb.ptr, newSize)
 	mb.size = newSize
 }

 func (mb *memBuffer) free() {
 	C.free(mb.ptr)
 }

 // retryWithBuffer repeatedly calls f(), increasing the size of the
 // buffer each time, until f succeeds, fails with a non-ERANGE error,
 // or the buffer exceeds a reasonable limit.
 func retryWithBuffer(buf *memBuffer, f func() syscall.Errno) error {
 	for {
 		errno := f()
 		if errno == 0 {
 			return nil
 		} else if errno != syscall.ERANGE {
 			return errno
 		}
 		newSize := buf.size * 2
 		if !isSizeReasonable(int64(newSize)) {
 			return fmt.Errorf("internal buffer exceeds %d bytes", maxBufferSize)
 		}
 		buf.resize(newSize)
 	}
 }

 const maxBufferSize = 1 << 20

 func isSizeReasonable(sz int64) bool {
 	return sz > 0 && sz <= maxBufferSize
 }

 // Because we can't use cgo in tests:
 func structPasswdForNegativeTest() C.struct_passwd {
 	sp := C.struct_passwd{}
 	sp.pw_uid = 1<<32 - 2
 	sp.pw_gid = 1<<32 - 3
 	return sp
 }
	// 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.

	//go:build (aix \|\| darwin \|\| dragonfly \|\| freebsd \|\| (!android && linux) \|\| netbsd \|\| openbsd \|\| solaris) && cgo && !osusergo
	// +build aix darwin dragonfly freebsd !android,linux netbsd openbsd solaris
	// +build cgo
	// +build !osusergo

	package user

	import (
	"fmt"
	"strconv"
	"strings"
	"syscall"
	"unsafe"
	)

	/*
	#cgo solaris CFLAGS: -D_POSIX_PTHREAD_SEMANTICS
	#include <unistd.h>
	#include <sys/types.h>
	#include <pwd.h>
	#include <grp.h>
	#include <stdlib.h>

	static int mygetpwuid_r(int uid, struct passwd *pwd,
	char buf, size_t buflen, struct passwd *result) {
	return getpwuid_r(uid, pwd, buf, buflen, result);
	}

	static int mygetpwnam_r(const char name, struct passwd pwd,
	char buf, size_t buflen, struct passwd *result) {
	return getpwnam_r(name, pwd, buf, buflen, result);
	}

	static int mygetgrgid_r(int gid, struct group *grp,
	char buf, size_t buflen, struct group *result) {
	return getgrgid_r(gid, grp, buf, buflen, result);
	}

	static int mygetgrnam_r(const char name, struct group grp,
	char buf, size_t buflen, struct group *result) {
	return getgrnam_r(name, grp, buf, buflen, result);
	}
	*/
	import "C"

	func current() (*User, error) {
	return lookupUnixUid(syscall.Getuid())
	}

	func lookupUser(username string) (*User, error) {
	var pwd C.struct_passwd
	var result *C.struct_passwd
	nameC := make([]byte, len(username)+1)
	copy(nameC, username)

	buf := alloc(userBuffer)
	defer buf.free()

	err := retryWithBuffer(buf, func() syscall.Errno {
	// mygetpwnam_r is a wrapper around getpwnam_r to avoid
	// passing a size_t to getpwnam_r, because for unknown
	// reasons passing a size_t to getpwnam_r doesn't work on
	// Solaris.
	return syscall.Errno(C.mygetpwnam_r((*C.char)(unsafe.Pointer(&nameC[0])),
	&pwd,
	(*C.char)(buf.ptr),
	C.size_t(buf.size),
	&result))
	})
	if err != nil {
	return nil, fmt.Errorf("user: lookup username %s: %v", username, err)
	}
	if result == nil {
	return nil, UnknownUserError(username)
	}
	return buildUser(&pwd), err
	}

	func lookupUserId(uid string) (*User, error) {
	i, e := strconv.Atoi(uid)
	if e != nil {
	return nil, e
	}
	return lookupUnixUid(i)
	}

	func lookupUnixUid(uid int) (*User, error) {
	var pwd C.struct_passwd
	var result *C.struct_passwd

	buf := alloc(userBuffer)
	defer buf.free()

	err := retryWithBuffer(buf, func() syscall.Errno {
	// mygetpwuid_r is a wrapper around getpwuid_r to avoid using uid_t
	// because C.uid_t(uid) for unknown reasons doesn't work on linux.
	return syscall.Errno(C.mygetpwuid_r(C.int(uid),
	&pwd,
	(*C.char)(buf.ptr),
	C.size_t(buf.size),
	&result))
	})
	if err != nil {
	return nil, fmt.Errorf("user: lookup userid %d: %v", uid, err)
	}
	if result == nil {
	return nil, UnknownUserIdError(uid)
	}
	return buildUser(&pwd), nil
	}

	func buildUser(pwd C.struct_passwd) User {
	u := &User{
	Uid: strconv.FormatUint(uint64(pwd.pw_uid), 10),
	Gid: strconv.FormatUint(uint64(pwd.pw_gid), 10),
	Username: C.GoString(pwd.pw_name),
	Name: C.GoString(pwd.pw_gecos),
	HomeDir: C.GoString(pwd.pw_dir),
	}
	// The pw_gecos field isn't quite standardized. Some docs
	// say: "It is expected to be a comma separated list of
	// personal data where the first item is the full name of the
	// user."
	u.Name, _, _ = strings.Cut(u.Name, ",")
	return u
	}

	func lookupGroup(groupname string) (*Group, error) {
	var grp C.struct_group
	var result *C.struct_group

	buf := alloc(groupBuffer)
	defer buf.free()
	cname := make([]byte, len(groupname)+1)
	copy(cname, groupname)

	err := retryWithBuffer(buf, func() syscall.Errno {
	return syscall.Errno(C.mygetgrnam_r((*C.char)(unsafe.Pointer(&cname[0])),
	&grp,
	(*C.char)(buf.ptr),
	C.size_t(buf.size),
	&result))
	})
	if err != nil {
	return nil, fmt.Errorf("user: lookup groupname %s: %v", groupname, err)
	}
	if result == nil {
	return nil, UnknownGroupError(groupname)
	}
	return buildGroup(&grp), nil
	}

	func lookupGroupId(gid string) (*Group, error) {
	i, e := strconv.Atoi(gid)
	if e != nil {
	return nil, e
	}
	return lookupUnixGid(i)
	}

	func lookupUnixGid(gid int) (*Group, error) {
	var grp C.struct_group
	var result *C.struct_group

	buf := alloc(groupBuffer)
	defer buf.free()

	err := retryWithBuffer(buf, func() syscall.Errno {
	// mygetgrgid_r is a wrapper around getgrgid_r to avoid using gid_t
	// because C.gid_t(gid) for unknown reasons doesn't work on linux.
	return syscall.Errno(C.mygetgrgid_r(C.int(gid),
	&grp,
	(*C.char)(buf.ptr),
	C.size_t(buf.size),
	&result))
	})
	if err != nil {
	return nil, fmt.Errorf("user: lookup groupid %d: %v", gid, err)
	}
	if result == nil {
	return nil, UnknownGroupIdError(strconv.Itoa(gid))
	}
	return buildGroup(&grp), nil
	}

	func buildGroup(grp C.struct_group) Group {
	g := &Group{
	Gid: strconv.Itoa(int(grp.gr_gid)),
	Name: C.GoString(grp.gr_name),
	}
	return g
	}

	type bufferKind C.int

	const (
	userBuffer = bufferKind(C._SC_GETPW_R_SIZE_MAX)
	groupBuffer = bufferKind(C._SC_GETGR_R_SIZE_MAX)
	)

	func (k bufferKind) initialSize() C.size_t {
	sz := C.sysconf(C.int(k))
	if sz == -1 {
	// DragonFly and FreeBSD do not have _SC_GETPW_R_SIZE_MAX.
	// Additionally, not all Linux systems have it, either. For
	// example, the musl libc returns -1.
	return 1024
	}
	if !isSizeReasonable(int64(sz)) {
	// Truncate. If this truly isn't enough, retryWithBuffer will error on the first run.
	return maxBufferSize
	}
	return C.size_t(sz)
	}

	type memBuffer struct {
	ptr unsafe.Pointer
	size C.size_t
	}

	func alloc(kind bufferKind) *memBuffer {
	sz := kind.initialSize()
	return &memBuffer{
	ptr: C.malloc(sz),
	size: sz,
	}
	}

	func (mb *memBuffer) resize(newSize C.size_t) {
	mb.ptr = C.realloc(mb.ptr, newSize)
	mb.size = newSize
	}

	func (mb *memBuffer) free() {
	C.free(mb.ptr)
	}

	// retryWithBuffer repeatedly calls f(), increasing the size of the
	// buffer each time, until f succeeds, fails with a non-ERANGE error,
	// or the buffer exceeds a reasonable limit.
	func retryWithBuffer(buf *memBuffer, f func() syscall.Errno) error {
	for {
	errno := f()
	if errno == 0 {
	return nil
	} else if errno != syscall.ERANGE {
	return errno
	}
	newSize := buf.size * 2
	if !isSizeReasonable(int64(newSize)) {
	return fmt.Errorf("internal buffer exceeds %d bytes", maxBufferSize)
	}
	buf.resize(newSize)
	}
	}

	const maxBufferSize = 1 << 20

	func isSizeReasonable(sz int64) bool {
	return sz > 0 && sz <= maxBufferSize
	}

	// Because we can't use cgo in tests:
	func structPasswdForNegativeTest() C.struct_passwd {
	sp := C.struct_passwd{}
	sp.pw_uid = 1<<32 - 2
	sp.pw_gid = 1<<32 - 3
	return sp
	}