Consistently apply Unix socket settings (#277)

Previously, we only supported setting the group for the server-side
socket. This change makes it possible to set it on the client side as
well. Also fixes a bug where the gRPC broker on the server side would
previously not consume the directory/group environment variables.

client.go

@@ -101,7 +101,7 @@ type Client struct {
 	// forcefully killed.
 	processKilled bool
 
-	hostSocketDir string
+	unixSocketCfg UnixSocketConfig
 }
 
 // NegotiatedVersion returns the protocol version negotiated with the server.
@@ -240,6 +240,28 @@ type ClientConfig struct {
 	// SkipHostEnv allows plugins to run without inheriting the parent process'
 	// environment variables.
 	SkipHostEnv bool
+
+	// UnixSocketConfig configures additional options for any Unix sockets
+	// that are created. Not normally required. Not supported on Windows.
+	UnixSocketConfig *UnixSocketConfig
+}
+
+type UnixSocketConfig struct {
+	// If set, go-plugin will change the owner of any Unix sockets created to
+	// this group, and set them as group-writable. Can be a name or gid. The
+	// client process must be a member of this group or chown will fail.
+	Group string
+
+	// The directory to create Unix sockets in. Internally managed by go-plugin
+	// and deleted when the plugin is killed.
+	directory string
+}
+
+func unixSocketConfigFromEnv() UnixSocketConfig {
+	return UnixSocketConfig{
+		Group:     os.Getenv(EnvUnixSocketGroup),
+		directory: os.Getenv(EnvUnixSocketDir),
+	}
 }
 
 // ReattachConfig is used to configure a client to reattach to an
@@ -445,7 +467,7 @@ func (c *Client) Kill() {
 	c.l.Lock()
 	runner := c.runner
 	addr := c.address
-	hostSocketDir := c.hostSocketDir
+	hostSocketDir := c.unixSocketCfg.directory
 	c.l.Unlock()
 
 	// If there is no runner or ID, there is nothing to kill.
@@ -629,15 +651,33 @@ func (c *Client) Start() (addr net.Addr, err error) {
 		}
 	}
 
+	if c.config.UnixSocketConfig != nil {
+		c.unixSocketCfg.Group = c.config.UnixSocketConfig.Group
+	}
+
+	if c.unixSocketCfg.Group != "" {
+		cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", EnvUnixSocketGroup, c.unixSocketCfg.Group))
+	}
+
 	var runner runner.Runner
 	switch {
 	case c.config.RunnerFunc != nil:
-		c.hostSocketDir, err = os.MkdirTemp("", "")
+		c.unixSocketCfg.directory, err = os.MkdirTemp("", "plugin-dir")
 		if err != nil {
 			return nil, err
 		}
-		c.logger.Trace("created temporary directory for unix sockets", "dir", c.hostSocketDir)
-		runner, err = c.config.RunnerFunc(c.logger, cmd, c.hostSocketDir)
+		// os.MkdirTemp creates folders with 0o700, so if we have a group
+		// configured we need to make it group-writable.
+		if c.unixSocketCfg.Group != "" {
+			err = setGroupWritable(c.unixSocketCfg.directory, c.unixSocketCfg.Group, 0o770)
+			if err != nil {
+				return nil, err
+			}
+		}
+		cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", EnvUnixSocketDir, c.unixSocketCfg.directory))
+		c.logger.Trace("created temporary directory for unix sockets", "dir", c.unixSocketCfg.directory)
+
+		runner, err = c.config.RunnerFunc(c.logger, cmd, c.unixSocketCfg.directory)
 		if err != nil {
 			return nil, err
 		}

client_unix_test.go

@@ -0,0 +1,97 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+//go:build !windows
+// +build !windows
+
+package plugin
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"os/user"
+	"runtime"
+	"syscall"
+	"testing"
+
+	"github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/go-plugin/internal/cmdrunner"
+	"github.com/hashicorp/go-plugin/runner"
+)
+
+func TestSetGroup(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("go-plugin doesn't support unix sockets on Windows")
+	}
+
+	group, err := user.LookupGroupId(fmt.Sprintf("%d", os.Getgid()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for name, tc := range map[string]struct {
+		group string
+	}{
+		"as integer": {fmt.Sprintf("%d", os.Getgid())},
+		"as name":    {group.Name},
+	} {
+		t.Run(name, func(t *testing.T) {
+			process := helperProcess("mock")
+			c := NewClient(&ClientConfig{
+				HandshakeConfig: testHandshake,
+				Plugins:         testPluginMap,
+				UnixSocketConfig: &UnixSocketConfig{
+					Group: tc.group,
+				},
+				RunnerFunc: func(l hclog.Logger, cmd *exec.Cmd, tmpDir string) (runner.Runner, error) {
+					// Run tests inside the RunnerFunc to ensure we don't race
+					// with the code that deletes tmpDir when the client fails
+					// to start properly.
+
+					// Test that it creates a directory with the proper owners and permissions.
+					info, err := os.Lstat(tmpDir)
+					if err != nil {
+						t.Fatal(err)
+					}
+					if info.Mode()&os.ModePerm != 0o770 {
+						t.Fatal(info.Mode())
+					}
+					stat, ok := info.Sys().(*syscall.Stat_t)
+					if !ok {
+						t.Fatal()
+					}
+					if stat.Gid != uint32(os.Getgid()) {
+						t.Fatalf("Expected %d, but got %d", os.Getgid(), stat.Gid)
+					}
+
+					// Check the correct environment variables were set to forward
+					// Unix socket config onto the plugin.
+					var foundUnixSocketDir, foundUnixSocketGroup bool
+					for _, env := range cmd.Env {
+						if env == fmt.Sprintf("%s=%s", EnvUnixSocketDir, tmpDir) {
+							foundUnixSocketDir = true
+						}
+						if env == fmt.Sprintf("%s=%s", EnvUnixSocketGroup, tc.group) {
+							foundUnixSocketGroup = true
+						}
+					}
+					if !foundUnixSocketDir {
+						t.Errorf("Did not find correct %s env in %v", EnvUnixSocketDir, cmd.Env)
+					}
+					if !foundUnixSocketGroup {
+						t.Errorf("Did not find correct %s env in %v", EnvUnixSocketGroup, cmd.Env)
+					}
+
+					process.Env = append(process.Env, cmd.Env...)
+					return cmdrunner.NewCmdRunner(l, process)
+				},
+			})
+			defer c.Kill()
+
+			_, err := c.Start()
+			if err != nil {
+				t.Fatalf("err should be nil, got %s", err)
+			}
+		})
+	}
+}

grpc_broker.go

@@ -268,7 +268,7 @@ type GRPCBroker struct {
 	doneCh   chan struct{}
 	o        sync.Once
 
-	socketDir      string
+	unixSocketCfg  UnixSocketConfig
 	addrTranslator runner.AddrTranslator
 
 	sync.Mutex
@@ -279,14 +279,14 @@ type gRPCBrokerPending struct {
 	doneCh chan struct{}
 }
 
-func newGRPCBroker(s streamer, tls *tls.Config, socketDir string, addrTranslator runner.AddrTranslator) *GRPCBroker {
+func newGRPCBroker(s streamer, tls *tls.Config, unixSocketCfg UnixSocketConfig, addrTranslator runner.AddrTranslator) *GRPCBroker {
 	return &GRPCBroker{
 		streamer: s,
 		streams:  make(map[uint32]*gRPCBrokerPending),
 		tls:      tls,
 		doneCh:   make(chan struct{}),
 
-		socketDir:      socketDir,
+		unixSocketCfg:  unixSocketCfg,
 		addrTranslator: addrTranslator,
 	}
 }
@@ -295,7 +295,7 @@ func newGRPCBroker(s streamer, tls *tls.Config, socketDir string, addrTranslator
 //
 // This should not be called multiple times with the same ID at one time.
 func (b *GRPCBroker) Accept(id uint32) (net.Listener, error) {
-	listener, err := serverListener(b.socketDir)
+	listener, err := serverListener(b.unixSocketCfg)
 	if err != nil {
 		return nil, err
 	}

grpc_client.go

@@ -63,7 +63,7 @@ func newGRPCClient(doneCtx context.Context, c *Client) (*GRPCClient, error) {
 
 	// Start the broker.
 	brokerGRPCClient := newGRPCBrokerClient(conn)
-	broker := newGRPCBroker(brokerGRPCClient, c.config.TLSConfig, c.hostSocketDir, c.runner)
+	broker := newGRPCBroker(brokerGRPCClient, c.config.TLSConfig, c.unixSocketCfg, c.runner)
 	go broker.Run()
 	go brokerGRPCClient.StartStream()
 

grpc_server.go

@@ -84,7 +84,7 @@ func (s *GRPCServer) Init() error {
 	// Register the broker service
 	brokerServer := newGRPCBrokerServer()
 	plugin.RegisterGRPCBrokerServer(s.server, brokerServer)
-	s.broker = newGRPCBroker(brokerServer, s.TLS, "", nil)
+	s.broker = newGRPCBroker(brokerServer, s.TLS, unixSocketConfigFromEnv(), nil)
 	go s.broker.Run()
 
 	// Register the controller

server.go

@@ -273,7 +273,7 @@ func Serve(opts *ServeConfig) {
 	}
 
 	// Register a listener so we can accept a connection
-	listener, err := serverListener(os.Getenv(EnvUnixSocketDir))
+	listener, err := serverListener(unixSocketConfigFromEnv())
 	if err != nil {
 		logger.Error("plugin init error", "error", err)
 		return
@@ -496,12 +496,12 @@ func Serve(opts *ServeConfig) {
 	}
 }
 
-func serverListener(dir string) (net.Listener, error) {
+func serverListener(unixSocketCfg UnixSocketConfig) (net.Listener, error) {
 	if runtime.GOOS == "windows" {
 		return serverListener_tcp()
 	}
 
-	return serverListener_unix(dir)
+	return serverListener_unix(unixSocketCfg)
 }
 
 func serverListener_tcp() (net.Listener, error) {
@@ -546,8 +546,8 @@ func serverListener_tcp() (net.Listener, error) {
 	return nil, errors.New("Couldn't bind plugin TCP listener")
 }
 
-func serverListener_unix(dir string) (net.Listener, error) {
-	tf, err := os.CreateTemp(dir, "plugin")
+func serverListener_unix(unixSocketCfg UnixSocketConfig) (net.Listener, error) {
+	tf, err := os.CreateTemp(unixSocketCfg.directory, "plugin")
 	if err != nil {
 		return nil, err
 	}
@@ -569,25 +569,8 @@ func serverListener_unix(dir string) (net.Listener, error) {
 
 	// By default, unix sockets are only writable by the owner. Set up a custom
 	// group owner and group write permissions if configured.
-	if groupString := os.Getenv(EnvUnixSocketGroup); groupString != "" {
-		groupID, err := strconv.Atoi(groupString)
-		if err != nil {
-			group, err := user.LookupGroup(groupString)
-			if err != nil {
-				return nil, fmt.Errorf("failed to find group ID from %s=%s environment variable: %w", EnvUnixSocketGroup, groupString, err)
-			}
-			groupID, err = strconv.Atoi(group.Gid)
-			if err != nil {
-				return nil, fmt.Errorf("failed to parse %q group's Gid as an integer: %w", groupString, err)
-			}
-		}
-
-		err = os.Chown(path, -1, groupID)
-		if err != nil {
-			return nil, err
-		}
-
-		err = os.Chmod(path, 0o660)
+	if unixSocketCfg.Group != "" {
+		err = setGroupWritable(path, unixSocketCfg.Group, 0o660)
 		if err != nil {
 			return nil, err
 		}
@@ -601,6 +584,32 @@ func serverListener_unix(dir string) (net.Listener, error) {
 	}, nil
 }
 
+func setGroupWritable(path, groupString string, mode os.FileMode) error {
+	groupID, err := strconv.Atoi(groupString)
+	if err != nil {
+		group, err := user.LookupGroup(groupString)
+		if err != nil {
+			return fmt.Errorf("failed to find gid from %q: %w", groupString, err)
+		}
+		groupID, err = strconv.Atoi(group.Gid)
+		if err != nil {
+			return fmt.Errorf("failed to parse %q group's gid as an integer: %w", groupString, err)
+		}
+	}
+
+	err = os.Chown(path, -1, groupID)
+	if err != nil {
+		return err
+	}
+
+	err = os.Chmod(path, mode)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // rmListener is an implementation of net.Listener that forwards most
 // calls to the listener but also removes a file as part of the close. We
 // use this to cleanup the unix domain socket on close.

server_unix_test.go

@@ -25,15 +25,13 @@ func TestUnixSocketGroupPermissions(t *testing.T) {
 		t.Fatal(err)
 	}
 	for name, tc := range map[string]struct {
-		gid string
+		group string
 	}{
 		"as integer": {fmt.Sprintf("%d", os.Getgid())},
 		"as name":    {group.Name},
 	} {
 		t.Run(name, func(t *testing.T) {
-			t.Setenv(EnvUnixSocketGroup, tc.gid)
-
-			ln, err := serverListener_unix("")
+			ln, err := serverListener_unix(UnixSocketConfig{Group: tc.group})
 			if err != nil {
 				t.Fatal(err)
 			}

testing.go

@@ -166,7 +166,7 @@ func TestPluginGRPCConn(t testing.T, ps map[string]Plugin) (*GRPCClient, *GRPCSe
 	}
 
 	brokerGRPCClient := newGRPCBrokerClient(conn)
-	broker := newGRPCBroker(brokerGRPCClient, nil, "", nil)
+	broker := newGRPCBroker(brokerGRPCClient, nil, UnixSocketConfig{}, nil)
 	go broker.Run()
 	go brokerGRPCClient.StartStream()