enable ssh agent

cmd/drone-docker/main.go

@@ -264,6 +264,11 @@ func main() {
 			Usage:  "secret key value pairs eg secret_name=/path/to/secret",
 			EnvVar: "PLUGIN_SECRETS_FROM_FILE",
 		},
+		cli.StringFlag{
+			Name:   "ssh-agent",
+			Usage:  "mount ssh agent",
+			EnvVar: "PLUGIN_SSH_AGENT",
+		},
 		cli.StringFlag{
 			Name:   "drone-card-path",
 			Usage:  "card path location to write to",
@@ -310,6 +315,7 @@ func run(c *cli.Context) error {
 			Secret:      c.String("secret"),
 			SecretEnvs:  c.StringSlice("secrets-from-env"),
 			SecretFiles: c.StringSlice("secrets-from-file"),
+			SSHAgent:    c.String("ssh-agent"),
 			AddHost:     c.StringSlice("add-host"),
 			Quiet:       c.Bool("quiet"),
 		},

docker.go

@@ -1,8 +1,10 @@
 package docker
 
 import (
+	"encoding/base64"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -11,6 +13,11 @@ import (
 	"time"
 )
 
+const (
+	SSHAgentSockPath     = "/tmp/drone-ssh-agent-sock"
+	SSHPrivateKeyFromEnv = "SSH_KEY"
+)
+
 type (
 	// Daemon defines Docker daemon parameters.
 	Daemon struct {
@@ -63,6 +70,7 @@ type (
 		SecretFiles []string // Docker build secrets with file as source
 		AddHost     []string // Docker build add-host
 		Quiet       bool     // Docker build quiet
+		SSHAgent    string   // Docker build ssh
 	}
 
 	// Plugin defines the Docker plugin parameters.
@@ -105,6 +113,7 @@ type (
 
 // Exec executes the plugin step
 func (p Plugin) Exec() error {
+
 	// start the Docker daemon server
 	if !p.Daemon.Disabled {
 		p.startDaemon()
@@ -178,6 +187,16 @@ func (p Plugin) Exec() error {
 		cmds = append(cmds, commandPull(img))
 	}
 
+	// setup for using ssh agent (https://docs.docker.com/develop/develop-images/build_enhancements/#using-ssh-to-access-private-data-in-builds)
+	if p.Build.SSHAgent != "" {
+		// TODO check in with one of the drone devs...this should not be necessary. I'm probably doing something
+		// wrong with the cli framework
+		p.Build.SSHAgent = strings.TrimSuffix(p.Build.SSHAgent, "]")
+		p.Build.SSHAgent = strings.TrimPrefix(p.Build.SSHAgent, "[")
+		fmt.Printf("ssh agent set to \"%s\"\n", p.Build.SSHAgent)
+		cmds = append(cmds, commandSSHAgentForwardingSetup(p.Build)...)
+	}
+
 	cmds = append(cmds, commandBuild(p.Build)) // docker build
 
 	for _, tag := range p.Build.Tags {
@@ -324,6 +343,9 @@ func commandBuild(build Build) *exec.Cmd {
 	if build.Quiet {
 		args = append(args, "--quiet")
 	}
+	if build.SSHAgent != "" {
+		args = append(args, "--ssh", build.SSHAgent)
+	}
 
 	if build.AutoLabel {
 		labelSchema := []string{
@@ -349,8 +371,8 @@ func commandBuild(build Build) *exec.Cmd {
 		}
 	}
 
-	// we need to enable buildkit, for secret support
-	if build.Secret != "" || len(build.SecretEnvs) > 0 || len(build.SecretFiles) > 0 {
+	// we need to enable buildkit, for secret support and ssh agent support
+	if build.Secret != "" || len(build.SecretEnvs) > 0 || len(build.SecretFiles) > 0 || build.SSHAgent != "" {
 		os.Setenv("DOCKER_BUILDKIT", "1")
 	}
 	return exec.Command(dockerExe, args...)
@@ -503,6 +525,40 @@ func commandRmi(tag string) *exec.Cmd {
 	return exec.Command(dockerExe, "rmi", tag)
 }
 
+func commandSSHAgentForwardingSetup(build Build) []*exec.Cmd {
+	cmds := make([]*exec.Cmd, 0)
+	if err := writeSSHPrivateKey(); err != nil {
+		log.Fatalf("unable to setup ssh agent forwarding: %s", err)
+	}
+	os.Setenv("SSH_AUTH_SOCK", SSHAgentSockPath)
+	cmds = append(cmds, exec.Command("ssh-agent", "-a", SSHAgentSockPath))
+	cmds = append(cmds, exec.Command("ssh-add"))
+	return cmds
+}
+
+func writeSSHPrivateKey() error {
+	privateKeyBase64 := os.Getenv(SSHPrivateKeyFromEnv)
+	if privateKeyBase64 == "" {
+		return fmt.Errorf("%s must be defined and contain the base64 encoded private key to use for ssh agent forwarding", SSHPrivateKeyFromEnv)
+	}
+	var err error
+	privateKey, err := base64.StdEncoding.DecodeString(privateKeyBase64)
+	if err != nil {
+		return fmt.Errorf("unable to base64 decode private key")
+	}
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("unable to determine home directory: %s", err)
+	}
+	if err := os.MkdirAll(filepath.Join(home, ".ssh"), 0700); err != nil {
+		return fmt.Errorf("unable to create .ssh directory: %s", err)
+	}
+	if err := os.WriteFile(filepath.Join(home, ".ssh", "id_rsa"), privateKey, 0400); err != nil {
+		return fmt.Errorf("unable to write ssh key: %s", err)
+	}
+	return nil
+}
+
 // trace writes each command to stdout with the command wrapped in an xml
 // tag so that it can be extracted and displayed in the logs.
 func trace(cmd *exec.Cmd) {

docker_test.go

@@ -114,6 +114,26 @@ func TestCommandBuild(t *testing.T) {
 				".",
 			),
 		},
+		{
+			name: "ssh agent",
+			build: Build{
+				Name:       "plugins/drone-docker:latest",
+				Dockerfile: "Dockerfile",
+				Context:    ".",
+				SSHAgent:   "default",
+			},
+			want: exec.Command(
+				dockerExe,
+				"build",
+				"--rm=true",
+				"-f",
+				"Dockerfile",
+				"-t",
+				"plugins/drone-docker:latest",
+				".",
+				"--ssh default",
+			),
+		},
 	}
 
 	for _, tc := range tcs {