commandconn: set SysProcAttr.Setsid

Setting `Setsid` is needed for SSH connection helper with `ProxyCommand`
config, so as to detach TTY.

e.g.

  $ cat ~/.ssh/config
  Host foo
    Hostname foo
    ProxyCommand ssh -W %h:%p bastion
  $ DOCKER_HOST=ssh://foo docker run -it --rm alpine
  / #

Fix #1707

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cli/connhelper/commandconn/commandconn.go

@@ -41,7 +41,9 @@ func New(ctx context.Context, cmd string, args ...string) (net.Conn, error) {
 	// we assume that args never contains sensitive information
 	logrus.Debugf("commandconn: starting %s with %v", cmd, args)
 	c.cmd.Env = os.Environ()
+	c.cmd.SysProcAttr = &syscall.SysProcAttr{}
 	setPdeathsig(c.cmd)
+	createSession(c.cmd)
 	c.stdin, err = c.cmd.StdinPipe()
 	if err != nil {
 		return nil, err

cli/connhelper/commandconn/pdeathsig_linux.go

@@ -6,7 +6,5 @@ import (
 )
 
 func setPdeathsig(cmd *exec.Cmd) {
-	cmd.SysProcAttr = &syscall.SysProcAttr{
-		Pdeathsig: syscall.SIGKILL,
-	}
+	cmd.SysProcAttr.Pdeathsig = syscall.SIGKILL
 }

cli/connhelper/commandconn/session_unix.go

@@ -0,0 +1,13 @@
+// +build !windows
+
+package commandconn
+
+import (
+	"os/exec"
+)
+
+func createSession(cmd *exec.Cmd) {
+	// for supporting ssh connection helper with ProxyCommand
+	// https://github.com/docker/cli/issues/1707
+	cmd.SysProcAttr.Setsid = true
+}

cli/connhelper/commandconn/session_windows.go

@@ -0,0 +1,8 @@
+package commandconn
+
+import (
+	"os/exec"
+)
+
+func createSession(cmd *exec.Cmd) {
+}