Merge pull request #336 from ijc/configure-unix-socket-group-ownership

buildkitd: allow setting group of /var/run/buildkit/buildkitd.sock

cmd/buildkitd/main.go

@@ -8,8 +8,10 @@ import (
 	"io/ioutil"
 	"net"
 	"os"
+	"os/user"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 
 	"github.com/containerd/containerd/sys"
@@ -80,6 +82,11 @@ func main() {
 			Usage: "listening address (socket or tcp)",
 			Value: &cli.StringSlice{appdefaults.Address},
 		},
+		cli.StringFlag{
+			Name:  "group",
+			Usage: "group (name or gid) which will own all Unix socket listening addresses",
+			Value: "",
+		},
 		cli.StringFlag{
 			Name:  "debugaddr",
 			Usage: "debugging address (eg. 0.0.0.0:6060)",
@@ -142,7 +149,7 @@ func main() {
 		if len(addrs) > 1 {
 			addrs = addrs[1:] // https://github.com/urfave/cli/issues/160
 		}
-		if err := serveGRPC(server, addrs, errCh); err != nil {
+		if err := serveGRPC(c, server, addrs, errCh); err != nil {
 			return err
 		}
 
@@ -181,14 +188,14 @@ func main() {
 	}
 }
 
-func serveGRPC(server *grpc.Server, addrs []string, errCh chan error) error {
+func serveGRPC(c *cli.Context, server *grpc.Server, addrs []string, errCh chan error) error {
 	if len(addrs) == 0 {
 		return errors.New("--addr cannot be empty")
 	}
 	eg, _ := errgroup.WithContext(context.Background())
 	listeners := make([]net.Listener, 0, len(addrs))
 	for _, addr := range addrs {
-		l, err := getListener(addr)
+		l, err := getListener(c, addr)
 		if err != nil {
 			for _, l := range listeners {
 				l.Close()
@@ -212,7 +219,40 @@ func serveGRPC(server *grpc.Server, addrs []string, errCh chan error) error {
 	return nil
 }
 
-func getListener(addr string) (net.Listener, error) {
+// Convert a string containing either a group name or a stringified gid into a numeric id)
+func groupToGid(group string) (int, error) {
+	if group == "" {
+		return os.Getgid(), nil
+	}
+
+	var (
+		err error
+		id  int
+	)
+
+	// Try and parse as a number, if the error is ErrSyntax
+	// (i.e. its not a number) then we carry on and try it as a
+	// name.
+	if id, err = strconv.Atoi(group); err == nil {
+		return id, nil
+	} else if err.(*strconv.NumError).Err != strconv.ErrSyntax {
+		return 0, err
+	}
+
+	ginfo, err := user.LookupGroup(group)
+	if err != nil {
+		return 0, err
+	}
+	group = ginfo.Gid
+
+	if id, err = strconv.Atoi(group); err != nil {
+		return 0, err
+	}
+
+	return id, nil
+}
+
+func getListener(c *cli.Context, addr string) (net.Listener, error) {
 	addrSlice := strings.SplitN(addr, "://", 2)
 	if len(addrSlice) < 2 {
 		return nil, errors.Errorf("address %s does not contain proto, you meant unix://%s ?",
@@ -222,7 +262,12 @@ func getListener(addr string) (net.Listener, error) {
 	listenAddr := addrSlice[1]
 	switch proto {
 	case "unix", "npipe":
-		return sys.GetLocalListener(listenAddr, os.Getuid(), os.Getgid())
+		uid := os.Getuid()
+		gid, err := groupToGid(c.GlobalString("group"))
+		if err != nil {
+			return nil, err
+		}
+		return sys.GetLocalListener(listenAddr, uid, gid)
 	case "tcp":
 		return sockets.NewTCPSocket(listenAddr, nil)
 	default: