Revert "plugins: run plugin with new process group ID"

This reverts commit ef5e5fa03f.

Running new plugins under a new pgid isn't a viable solution due to
it causing issues with plugin processes attempting to read from the
TTY (see: https://github.com/moby/moby/issues/47073).

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli-plugins/manager/manager.go

@@ -233,7 +233,6 @@ func PluginRunCommand(dockerCli command.Cli, name string, rootcmd *cobra.Command
 		cmd.Stdin = os.Stdin
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
-		configureOSSpecificCommand(cmd)
 
 		cmd.Env = os.Environ()
 		cmd.Env = append(cmd.Env, ReexecEnvvar+"="+os.Args[0])

cli-plugins/manager/manager_unix.go

@@ -2,21 +2,7 @@
 
 package manager
 
-import (
-	"os/exec"
-	"syscall"
-)
-
 var defaultSystemPluginDirs = []string{
 	"/usr/local/lib/docker/cli-plugins", "/usr/local/libexec/docker/cli-plugins",
 	"/usr/lib/docker/cli-plugins", "/usr/libexec/docker/cli-plugins",
 }
-
-func configureOSSpecificCommand(cmd *exec.Cmd) {
-	// Spawn the plugin process in a new process group, so that signals are not forwarded by the OS.
-	// The foreground process group is e.g. sent a SIGINT when Ctrl-C is input to the TTY, but we
-	// implement our own job control for the plugin.
-	cmd.SysProcAttr = &syscall.SysProcAttr{
-		Setpgid: true,
-	}
-}

cli-plugins/manager/manager_windows.go

@@ -2,7 +2,6 @@ package manager
 
 import (
 	"os"
-	"os/exec"
 	"path/filepath"
 )
 
@@ -10,7 +9,3 @@ var defaultSystemPluginDirs = []string{
 	filepath.Join(os.Getenv("ProgramData"), "Docker", "cli-plugins"),
 	filepath.Join(os.Getenv("ProgramFiles"), "Docker", "cli-plugins"),
 }
-
-func configureOSSpecificCommand(cmd *exec.Cmd) {
-	// no-op
-}

cmd/docker/docker.go

@@ -240,16 +240,12 @@ func tryPluginRun(dockerCli command.Cli, cmd *cobra.Command, subcommand string,
 	// we send a SIGKILL to the plugin process and exit
 	go func() {
 		retries := 0
-		for s := range signals {
+		for range signals {
 			if conn != nil {
 				if err := conn.Close(); err != nil {
 					_, _ = fmt.Fprintf(dockerCli.Err(), "failed to signal plugin to close: %v\n", err)
 				}
 				conn = nil
-			} else {
-				// When the plugin is communicating via socket with the host CLI, we perform job control via the socket.
-				// However, if the plugin is an old version that is not socket-aware, we need to explicitly forward termination signals.
-				plugincmd.Process.Signal(s)
 			}
 			retries++
 			if retries >= exitLimit {