Validate HCL for SSHHelper too

api/ssh_agent.go

@@ -8,18 +8,22 @@ import (
 	"os"
 
 	"github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/hcl"
+	"github.com/hashicorp/hcl/hcl/ast"
 	"github.com/mitchellh/mapstructure"
 )
 
 const (
-	// Default path at which SSH backend will be mounted in Vault server
+	// SSHHelperDefaultMountPoint is the default path at which SSH backend will be
+	// mounted in the Vault server.
 	SSHHelperDefaultMountPoint = "ssh"
 
-	// Echo request message sent as OTP by the vault-ssh-helper
+	// VerifyEchoRequest is the echo request message sent as OTP by the helper.
 	VerifyEchoRequest = "verify-echo-request"
 
-	// Echo response message sent as a response to OTP matching echo request
+	// VerifyEchoResponse is the echo response message sent as a response to OTP
+	// matching echo request.
 	VerifyEchoResponse = "verify-echo-response"
 )
 
@@ -55,8 +59,7 @@ type SSHHelperConfig struct {
 	TLSSkipVerify   bool   `hcl:"tls_skip_verify"`
 }
 
-// TLSClient returns a HTTP client that uses TLS verification (TLS 1.2) for a given
-// certificate pool.
+// SetTLSParameters sets the TLS parameters for this SSH agent.
 func (c *SSHHelperConfig) SetTLSParameters(clientConfig *Config, certPool *x509.CertPool) {
 	tlsConfig := &tls.Config{
 		InsecureSkipVerify: c.TLSSkipVerify,
@@ -112,29 +115,48 @@ func (c *SSHHelperConfig) NewClient() (*Client, error) {
 // Vault address is a required parameter.
 // Mount point defaults to "ssh".
 func LoadSSHHelperConfig(path string) (*SSHHelperConfig, error) {
-	var config SSHHelperConfig
 	contents, err := ioutil.ReadFile(path)
-	if !os.IsNotExist(err) {
-		obj, err := hcl.Parse(string(contents))
-		if err != nil {
-			return nil, err
-		}
+	if err != nil && !os.IsNotExist(err) {
+		return nil, multierror.Prefix(err, "ssh_helper:")
+	}
+	return ParseSSHHelperConfig(string(contents))
+}
 
-		if err := hcl.DecodeObject(&config, obj); err != nil {
-			return nil, err
-		}
-	} else {
-		return nil, err
+// ParseSSHHelperConfig parses the given contents as a string for the SSHHelper
+// configuration.
+func ParseSSHHelperConfig(contents string) (*SSHHelperConfig, error) {
+	root, err := hcl.Parse(string(contents))
+	if err != nil {
+		return nil, fmt.Errorf("ssh_helper: error parsing config: %s", err)
 	}
 
-	if config.VaultAddr == "" {
-		return nil, fmt.Errorf("config missing vault_addr")
-	}
-	if config.SSHMountPoint == "" {
-		config.SSHMountPoint = SSHHelperDefaultMountPoint
+	list, ok := root.Node.(*ast.ObjectList)
+	if !ok {
+		return nil, fmt.Errorf("ssh_helper: error parsing config: file doesn't contain a root object")
 	}
 
-	return &config, nil
+	valid := []string{
+		"vault_addr",
+		"ssh_mount_point",
+		"ca_cert",
+		"ca_path",
+		"allowed_cidr_list",
+		"tls_skip_verify",
+	}
+	if err := checkHCLKeys(list, valid); err != nil {
+		return nil, multierror.Prefix(err, "ssh_helper:")
+	}
+
+	var c SSHHelperConfig
+	c.SSHMountPoint = SSHHelperDefaultMountPoint
+	if err := hcl.DecodeObject(&c, list); err != nil {
+		return nil, multierror.Prefix(err, "ssh_helper:")
+	}
+
+	if c.VaultAddr == "" {
+		return nil, fmt.Errorf("ssh_helper: missing config 'vault_addr'")
+	}
+	return &c, nil
 }
 
 // SSHHelper creates an SSHHelper object which can talk to Vault server with SSH backend
@@ -189,3 +211,31 @@ func (c *SSHHelper) Verify(otp string) (*SSHVerifyResponse, error) {
 	}
 	return &verifyResp, nil
 }
+
+func checkHCLKeys(node ast.Node, valid []string) error {
+	var list *ast.ObjectList
+	switch n := node.(type) {
+	case *ast.ObjectList:
+		list = n
+	case *ast.ObjectType:
+		list = n.List
+	default:
+		return fmt.Errorf("cannot check HCL keys of type %T", n)
+	}
+
+	validMap := make(map[string]struct{}, len(valid))
+	for _, v := range valid {
+		validMap[v] = struct{}{}
+	}
+
+	var result error
+	for _, item := range list.Items {
+		key := item.Keys[0].Token.Value().(string)
+		if _, ok := validMap[key]; !ok {
+			result = multierror.Append(result, fmt.Errorf(
+				"invalid key '%s' on line %d", key, item.Assign.Line))
+		}
+	}
+
+	return result
+}

api/ssh_agent_test.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -28,3 +29,41 @@ func TestSSH_CreateTLSClient(t *testing.T) {
 		panic(fmt.Sprintf("error creating client with TLS transport"))
 	}
 }
+
+func TestParseSSHHelperConfig(t *testing.T) {
+	config, err := ParseSSHHelperConfig(`
+		vault_addr = "1.2.3.4"
+`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if config.SSHMountPoint != SSHHelperDefaultMountPoint {
+		t.Errorf("expected %q to be %q", config.SSHMountPoint, SSHHelperDefaultMountPoint)
+	}
+}
+
+func TestParseSSHHelperConfig_missingVaultAddr(t *testing.T) {
+	_, err := ParseSSHHelperConfig("")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+
+	if !strings.Contains(err.Error(), "ssh_helper: missing config 'vault_addr'") {
+		t.Errorf("bad error: %s", err)
+	}
+}
+
+func TestParseSSHHelperConfig_badKeys(t *testing.T) {
+	_, err := ParseSSHHelperConfig(`
+vault_addr = "1.2.3.4"
+nope = "bad"
+`)
+	if err == nil {
+		t.Fatal("expected error")
+	}
+
+	if !strings.Contains(err.Error(), "ssh_helper: invalid key 'nope' on line 3") {
+		t.Errorf("bad error: %s", err)
+	}
+}