sd_daemon: Fix build on macOS, fix FD leak on Linux

2 files changed, 168 insertions, 1 deletions

diff --git a/sd_daemon/notify.go b/sd_daemon/notify.go
index 62e507f..b0a0d72 100644
--- a/sd_daemon/notify.go
+++ b/sd_daemon/notify.go
@@ -14,6 +14,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build linux
+
 package sd_daemon
 
 import (
@@ -142,8 +144,9 @@ func (msg Notification) Send(unsetEnv bool) error {
 func socketUnixgram(name string) (*net.UnixConn, error) {
 	fd, err := unix.Socket(unix.AF_UNIX, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 	if err != nil {
-		return nil, err
+		return nil, os.NewSyscallError("socket", err)
 	}
+	defer unix.Close(fd)
 	conn, err := net.FileConn(os.NewFile(uintptr(fd), name))
 	if err != nil {
 		return nil, err
diff --git a/sd_daemon/notify_nonlinux.go b/sd_daemon/notify_nonlinux.go
new file mode 100644
index 0000000..5acc5d7
--- /dev/null
+++ b/sd_daemon/notify_nonlinux.go
@@ -0,0 +1,164 @@
+// Copyright 2013-2015 Docker, Inc.
+// Copyright 2014 CoreOS, Inc.
+// Copyright 2015-2018 Luke Shumaker
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !linux
+
+package sd_daemon
+
+import (
+	"bytes"
+	"net"
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// Notification is a message to be sent to the service manager about
+// state changes.
+type Notification struct {
+	// PID specifies which process to send a notification about.
+	// If PID <= 0, or if the current process does not have
+	// privileges to send messages on behalf of other processes,
+	// then the message is simply sent from the current process.
+	PID int
+
+	// State should contain a newline-separated list of variable
+	// assignments.  See the documentation for sd_notify(3) for
+	// well-known variable assignments.
+	//
+	// https://www.freedesktop.org/software/systemd/man/sd_notify.html
+	State string
+
+	// Files is a list of file descriptors to send to the service
+	// manager with the message.  This is useful for keeping files
+	// open across restarts, as it enables the service manager to
+	// pass those files to the new process when it is restarted
+	// (see ListenFds).
+	//
+	// Note: The service manager will only actually store the file
+	// descriptors if you include "FDSTORE=1" in the state (again,
+	// see sd_notify(3) for well-known variable assignments).
+	Files []*os.File
+}
+
+// Send sends the Notification to the service manager.
+//
+// If unsetEnv is true, then (regardless of whether the function call
+// itself succeeds or not) it will unset the environmental variable
+// NOTIFY_SOCKET, which will cause further notify operations to fail.
+//
+// If the service manager is not listening for notifications from this
+// process tree (or a Notification has has already been send with
+// unsetEnv=true), then ErrDisabled is returned.  If the service
+// manager appears to be listening, but there is an error sending the
+// message, then that error is returned.
+//
+// It is generally recommended that you ignore the return value: if
+// there is an error, then this is function no-op; meaning that by
+// calling the function but ignoring the return value, you can easily
+// support both service managers that support these notifications and
+// those that do not.
+func (msg Notification) Send(unsetEnv bool) error {
+	if unsetEnv {
+		defer func() { _ = os.Unsetenv("NOTIFY_SOCKET") }()
+	}
+
+	socketAddr := &net.UnixAddr{
+		Name: os.Getenv("NOTIFY_SOCKET"),
+		Net:  "unixgram",
+	}
+
+	if socketAddr.Name == "" {
+		return ErrDisabled
+	}
+
+	conn, err := socketUnixgram(socketAddr.Name)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = conn.Close() }()
+
+	var cmsgs [][]byte
+
+	if len(msg.Files) > 0 {
+		fds := make([]int, len(msg.Files))
+		for i := range msg.Files {
+			fds[i] = int(msg.Files[i].Fd())
+		}
+		cmsg := unix.UnixRights(fds...)
+		cmsgs = append(cmsgs, cmsg)
+	}
+
+	havePid := msg.PID > 0 && msg.PID != os.Getpid()
+	if havePid {
+		// BUG(lukeshu): Spoofing the socket credentials is
+		// not implemnted on non-Linux kernels.  If you are
+		// knowledgable about how to do this on other kernels,
+		// please let me know at lukeshu@lukeshu.com!
+		havePid = false
+	}
+
+	// If the 2nd argument is empty, this is equivalent to
+	//
+	//    conn, _ := net.DialUnix(socketAddr.Net, nil, socketAddr)
+	//    conn.Write([]byte(msg.State))
+	_, _, err = conn.WriteMsgUnix([]byte(msg.State), bytes.Join(cmsgs, nil), socketAddr)
+
+	if err != nil && havePid {
+		// Maybe it failed because we don't have privileges to
+		// spoof our pid; retry without spoofing the pid.
+		//
+		// I'm not too happy that we do this silently without
+		// notifying the caller, but that's what
+		// sd_pid_notify_with_fds does.
+		cmsgs = cmsgs[:len(cmsgs)-1]
+		_, _, err = conn.WriteMsgUnix([]byte(msg.State), bytes.Join(cmsgs, nil), socketAddr)
+	}
+
+	return err
+}
+
+// socketUnixgram wraps socket(2), but doesn't bind(2) or connect(2)
+// the socket to anything.  This is an ugly hack because none of the
+// functions in "net" actually allow you to get a AF_UNIX socket not
+// bound/connected to anything.
+//
+// At some point you begin to question if it is worth it to keep up
+// the high-level interface of "net", and messing around with FileConn
+// and UnixConn.  Maybe we just drop to using unix.Socket and
+// unix.SendmsgN directly.
+func socketUnixgram(name string) (*net.UnixConn, error) {
+	syscall.ForkLock.RLock()
+	fd, err := unix.Socket(unix.AF_UNIX, unix.SOCK_DGRAM, 0)
+	if err == nil {
+		syscall.CloseOnExec(fd)
+	}
+	syscall.ForkLock.RUnlock()
+	if err != nil {
+		return nil, os.NewSyscallError("socket", err)
+	}
+	defer unix.Close(fd)
+	if err = unix.SetNonblock(fd, true); err != nil {
+		return nil, os.NewSyscallError("setnonblock", err)
+	}
+	conn, err := net.FileConn(os.NewFile(uintptr(fd), name))
+	if err != nil {
+		return nil, err
+	}
+	unixConn := conn.(*net.UnixConn)
+	return unixConn, nil
+}