actions/config: improve config file related errors

ErrBadConfig:
	Fix backwards wrapping, include the bad config, and make it
	clear that this is an internal error.

ErrBadConfigFile:
	Fix backwards wrapping, include the config file location, and
	adjust the suggestion slightly.

ErrConfigFileExists:
	Include the config file location.

ErrNoConfigFile:
	Include the config file location, and adjust the suggestion
	slightly.

4 files changed, 59 insertions, 23 deletions

diff --git a/actions/config.go b/actions/config.go
index 2463b95..b848d92 100644
--- a/actions/config.go
+++ b/actions/config.go
@@ -22,12 +22,12 @@ package actions
 
 import (
 	"bytes"
+	"fmt"
 	"log"
 	"os"
 	"runtime"
 	"time"
 
-	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
 
 	"github.com/google/fscrypt/crypto"
@@ -40,6 +40,46 @@ import (
 // overridden by the user of this package.
 var ConfigFileLocation = "/etc/fscrypt.conf"
 
+// ErrBadConfig is an internal error that indicates that the config struct is invalid.
+type ErrBadConfig struct {
+	Config          *metadata.Config
+	UnderlyingError error
+}
+
+func (err *ErrBadConfig) Error() string {
+	return fmt.Sprintf(`internal error: config is invalid: %s
+
+	The invalid config is %s`, err.UnderlyingError, err.Config)
+}
+
+// ErrBadConfigFile indicates that the config file is invalid.
+type ErrBadConfigFile struct {
+	Path            string
+	UnderlyingError error
+}
+
+func (err *ErrBadConfigFile) Error() string {
+	return fmt.Sprintf("%q is invalid: %s", err.Path, err.UnderlyingError)
+}
+
+// ErrConfigFileExists indicates that the config file already exists.
+type ErrConfigFileExists struct {
+	Path string
+}
+
+func (err *ErrConfigFileExists) Error() string {
+	return fmt.Sprintf("%q already exists", err.Path)
+}
+
+// ErrNoConfigFile indicates that the config file doesn't exist.
+type ErrNoConfigFile struct {
+	Path string
+}
+
+func (err *ErrNoConfigFile) Error() string {
+	return fmt.Sprintf("%q doesn't exist", err.Path)
+}
+
 const (
 	// Permissions of the config file (global readable)
 	configPermissions = 0644
@@ -67,7 +107,7 @@ func CreateConfigFile(target time.Duration, policyVersion int64) error {
 		createFlags, configPermissions)
 	switch {
 	case os.IsExist(err):
-		return ErrConfigFileExists
+		return &ErrConfigFileExists{ConfigFileLocation}
 	case err != nil:
 		return err
 	}
@@ -98,7 +138,7 @@ func getConfig() (*metadata.Config, error) {
 	configFile, err := os.Open(ConfigFileLocation)
 	switch {
 	case os.IsNotExist(err):
-		return nil, ErrNoConfigFile
+		return nil, &ErrNoConfigFile{ConfigFileLocation}
 	case err != nil:
 		return nil, err
 	}
@@ -107,7 +147,7 @@ func getConfig() (*metadata.Config, error) {
 	log.Printf("Reading config from %q\n", ConfigFileLocation)
 	config, err := metadata.ReadConfig(configFile)
 	if err != nil {
-		return nil, errors.Wrap(ErrBadConfigFile, err.Error())
+		return nil, &ErrBadConfigFile{ConfigFileLocation, err}
 	}
 
 	// Use system defaults if not specified
@@ -133,7 +173,7 @@ func getConfig() (*metadata.Config, error) {
 	}
 
 	if err := config.CheckValidity(); err != nil {
-		return nil, errors.Wrap(ErrBadConfigFile, err.Error())
+		return nil, &ErrBadConfigFile{ConfigFileLocation, err}
 	}
 
 	return config, nil
diff --git a/actions/context.go b/actions/context.go
index 0db0671..26295ec 100644
--- a/actions/context.go
+++ b/actions/context.go
@@ -40,14 +40,8 @@ import (
 	"github.com/google/fscrypt/util"
 )
 
-// Errors relating to Config files or Config structures.
-var (
-	ErrNoConfigFile     = errors.New("global config file does not exist")
-	ErrBadConfigFile    = errors.New("global config file has invalid data")
-	ErrConfigFileExists = errors.New("global config file already exists")
-	ErrBadConfig        = errors.New("invalid Config structure provided")
-	ErrLocked           = errors.New("key needs to be unlocked first")
-)
+// ErrLocked indicates that the key hasn't been unwrapped yet.
+var ErrLocked = errors.New("key needs to be unlocked first")
 
 // Context contains the necessary global state to perform most of fscrypt's
 // actions.
@@ -126,7 +120,7 @@ func newContextFromUser(targetUser *user.User) (*Context, error) {
 // which is being used with fscrypt.
 func (ctx *Context) checkContext() error {
 	if err := ctx.Config.CheckValidity(); err != nil {
-		return errors.Wrap(ErrBadConfig, err.Error())
+		return &ErrBadConfig{ctx.Config, err}
 	}
 	return ctx.Mount.CheckSetup()
 }
diff --git a/cli-tests/t_setup.out b/cli-tests/t_setup.out
index e1606ba..7d597bd 100644
--- a/cli-tests/t_setup.out
+++ b/cli-tests/t_setup.out
@@ -38,12 +38,12 @@ Metadata directories created at "MNT/.fscrypt".
                        with fscrypt
 
 # no config file
-[ERROR] fscrypt setup: global config file does not exist
+[ERROR] fscrypt setup: "FSCRYPT_CONF" doesn't exist
 
-Run "sudo fscrypt setup" to create the file.
+Run "sudo fscrypt setup" to create this file.
 
 # bad config file
-[ERROR] fscrypt setup: invalid character 'b' looking for beginning of value:
-                       global config file has invalid data
+[ERROR] fscrypt setup: "FSCRYPT_CONF" is invalid: invalid
+                       character 'b' looking for beginning of value
 
-Run "sudo fscrypt setup" to recreate the file.
+Either fix this file manually, or run "sudo fscrypt setup" to recreate it.
diff --git a/cmd/fscrypt/errors.go b/cmd/fscrypt/errors.go
index 8bda921..e7c025f 100644
--- a/cmd/fscrypt/errors.go
+++ b/cmd/fscrypt/errors.go
@@ -79,6 +79,12 @@ func getFullName(c *cli.Context) string {
 // getErrorSuggestions returns a string containing suggestions about how to fix
 // an error. If no suggestion is necessary or available, return empty string.
 func getErrorSuggestions(err error) string {
+	switch err.(type) {
+	case *actions.ErrBadConfigFile:
+		return `Either fix this file manually, or run "sudo fscrypt setup" to recreate it.`
+	case *actions.ErrNoConfigFile:
+		return `Run "sudo fscrypt setup" to create this file.`
+	}
 	switch errors.Cause(err) {
 	case filesystem.ErrNotSetup:
 		return fmt.Sprintf(`Run "fscrypt setup %s" to use fscrypt on this filesystem.`, mountpointArg)
@@ -117,10 +123,6 @@ func getErrorSuggestions(err error) string {
 		return fmt.Sprintf(`v2 encryption policies are only supported by kernel
 		version 5.4 and later. Either use a newer kernel, or change
 		policy_version to 1 in %s.`, actions.ConfigFileLocation)
-	case actions.ErrBadConfigFile:
-		return `Run "sudo fscrypt setup" to recreate the file.`
-	case actions.ErrNoConfigFile:
-		return `Run "sudo fscrypt setup" to create the file.`
 	case actions.ErrMissingPolicyMetadata:
 		return `This file or directory has either been encrypted with
 			another tool (such as e4crypt) or the corresponding