Walk config path symlinks when verifying Containerd configuration

CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - [#535](https://github.com/spegel-org/spegel/pull/535) Fix Docker build casing checks.
+- [#571](https://github.com/spegel-org/spegel/pull/571) Walk config path symlinks when verifying Containerd configuration.
 
 ### Security
 

pkg/oci/containerd.go

@@ -126,16 +126,41 @@ func verifyStatusResponse(resp *runtimeapi.StatusResponse, configPath string) er
 	if cfg.Registry.ConfigPath == "" {
 		return errors.New("Containerd registry config path needs to be set for mirror configuration to take effect")
 	}
+	linkPaths, err := walkSymbolicLinks(configPath)
+	if err != nil {
+		return err
+	}
 	paths := filepath.SplitList(cfg.Registry.ConfigPath)
 	for _, path := range paths {
-		if path != configPath {
-			continue
+		for _, linkedPath := range linkPaths {
+			if linkedPath == path {
+				return nil
+			}
 		}
-		return nil
 	}
 	return fmt.Errorf("Containerd registry config path is %s but needs to contain path %s for mirror configuration to take effect", cfg.Registry.ConfigPath, configPath)
 }
 
+func walkSymbolicLinks(path string) ([]string, error) {
+	fi, err := os.Lstat(path)
+	if err != nil {
+		return nil, err
+	}
+	if fi.Mode()&os.ModeSymlink != os.ModeSymlink {
+		return []string{path}, nil
+	}
+	linkPath, err := os.Readlink(path)
+	if err != nil {
+		return nil, err
+	}
+	paths, err := walkSymbolicLinks(linkPath)
+	if err != nil {
+		return nil, err
+	}
+	paths = append(paths, path)
+	return paths, nil
+}
+
 func (c *Containerd) Subscribe(ctx context.Context) (<-chan ImageEvent, <-chan error, error) {
 	imgCh := make(chan ImageEvent)
 	errCh := make(chan error)

pkg/oci/containerd_test.go

@@ -5,6 +5,9 @@ import (
 	"fmt"
 	iofs "io/fs"
 	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 
 	eventtypes "github.com/containerd/containerd/api/events"
@@ -31,40 +34,54 @@ func TestNewContainerd(t *testing.T) {
 func TestVerifyStatusResponse(t *testing.T) {
 	t.Parallel()
 
+	tmpDir := t.TempDir()
+
+	err := os.MkdirAll(filepath.Join(tmpDir, "etc", "target", "certs.d"), 0o777)
+	require.NoError(t, err)
+	err = os.MkdirAll(filepath.Join(tmpDir, "etc", "symlink"), 0o777)
+	require.NoError(t, err)
+	err = os.Symlink(filepath.Join(tmpDir, "etc", "target", "certs.d"), filepath.Join(tmpDir, "etc", "symlink", "certs.d"))
+	require.NoError(t, err)
+
 	tests := []struct {
 		name                  string
-		configPath            string
+		configPaths           []string
 		requiredConfigPath    string
 		expectedErrMsg        string
 		discardUnpackedLayers bool
 	}{
 		{
-			name:               "empty config path",
-			configPath:         "",
+			name:               "single config path",
+			configPaths:        []string{"/etc/containerd/certs.d"},
 			requiredConfigPath: "/etc/containerd/certs.d",
-			expectedErrMsg:     "Containerd registry config path needs to be set for mirror configuration to take effect",
 		},
 		{
-			name:               "single config path",
-			configPath:         "/etc/containerd/certs.d",
+			name:               "multiple config paths",
+			configPaths:        []string{"/etc/containerd/certs.d", "/etc/docker/certs.d"},
 			requiredConfigPath: "/etc/containerd/certs.d",
 		},
 		{
-			name:               "missing single config path",
-			configPath:         "/etc/containerd/certs.d",
-			requiredConfigPath: "/var/lib/containerd/certs.d",
-			expectedErrMsg:     "Containerd registry config path is /etc/containerd/certs.d but needs to contain path /var/lib/containerd/certs.d for mirror configuration to take effect",
+			name:               "symlinked config path",
+			configPaths:        []string{"/etc/target/certs.d"},
+			requiredConfigPath: "/etc/symlink/certs.d",
 		},
 		{
-			name:               "multiple config paths",
-			configPath:         "/etc/containerd/certs.d:/etc/docker/certs.d",
+			name:               "empty config path",
+			configPaths:        nil,
 			requiredConfigPath: "/etc/containerd/certs.d",
+			expectedErrMsg:     "Containerd registry config path needs to be set for mirror configuration to take effect",
+		},
+		{
+			name:               "missing single config path",
+			configPaths:        []string{"/etc/containerd/certs.d"},
+			requiredConfigPath: "/var/lib/containerd/certs.d",
+			expectedErrMsg:     fmt.Sprintf("Containerd registry config path is %[1]s/etc/containerd/certs.d but needs to contain path %[1]s/var/lib/containerd/certs.d for mirror configuration to take effect", tmpDir),
 		},
 		{
 			name:               "missing multiple config paths",
-			configPath:         "/etc/containerd/certs.d:/etc/docker/certs.d",
+			configPaths:        []string{"/etc/containerd/certs.d", "/etc/docker/certs.d"},
 			requiredConfigPath: "/var/lib/containerd/certs.d",
-			expectedErrMsg:     "Containerd registry config path is /etc/containerd/certs.d:/etc/docker/certs.d but needs to contain path /var/lib/containerd/certs.d for mirror configuration to take effect",
+			expectedErrMsg:     fmt.Sprintf("Containerd registry config path is %[1]s/etc/containerd/certs.d:%[1]s/etc/docker/certs.d but needs to contain path %[1]s/var/lib/containerd/certs.d for mirror configuration to take effect", tmpDir),
 		},
 		{
 			name:                  "discard unpacked layers enabled",
@@ -76,12 +93,21 @@ func TestVerifyStatusResponse(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 
+			tmpConfigPaths := []string{}
+			for _, configPath := range tt.configPaths {
+				tmpConfigPaths = append(tmpConfigPaths, filepath.Join(tmpDir, configPath))
+			}
+			tmpConfigPath := strings.Join(tmpConfigPaths, string(os.PathListSeparator))
+			tmpRequiredPath := filepath.Join(tmpDir, tt.requiredConfigPath)
+			err := os.MkdirAll(tmpRequiredPath, 0o777)
+			require.NoError(t, err)
+
 			resp := &runtimeapi.StatusResponse{
 				Info: map[string]string{
-					"config": fmt.Sprintf(`{"registry": {"configPath": %q}, "containerd": {"runtimes":{"discardUnpackedLayers": %v}}}`, tt.configPath, tt.discardUnpackedLayers),
+					"config": fmt.Sprintf(`{"registry": {"configPath": %q}, "containerd": {"runtimes":{"discardUnpackedLayers": %v}}}`, tmpConfigPath, tt.discardUnpackedLayers),
 				},
 			}
-			err := verifyStatusResponse(resp, tt.requiredConfigPath)
+			err = verifyStatusResponse(resp, tmpRequiredPath)
 			if tt.expectedErrMsg != "" {
 				require.EqualError(t, err, tt.expectedErrMsg)
 				return
@@ -91,6 +117,36 @@ func TestVerifyStatusResponse(t *testing.T) {
 	}
 }
 
+func TestWalkSymbolicLinks(t *testing.T) {
+	t.Parallel()
+
+	tmpDir := t.TempDir()
+	targetPath := filepath.Join(tmpDir, "data.txt")
+	err := os.WriteFile(targetPath, []byte("hello world"), 0o777)
+	require.NoError(t, err)
+	firstOrderPath := filepath.Join(tmpDir, "first.txt")
+	err = os.Symlink(targetPath, firstOrderPath)
+	require.NoError(t, err)
+	secondOrderPath := filepath.Join(tmpDir, "second.txt")
+	err = os.Symlink(firstOrderPath, secondOrderPath)
+	require.NoError(t, err)
+
+	// Second order symlink
+	paths, err := walkSymbolicLinks(secondOrderPath)
+	require.NoError(t, err)
+	require.Equal(t, paths, []string{targetPath, firstOrderPath, secondOrderPath})
+
+	// First order symlink
+	paths, err = walkSymbolicLinks(firstOrderPath)
+	require.NoError(t, err)
+	require.Equal(t, paths, []string{targetPath, firstOrderPath})
+
+	// No symnlink
+	paths, err = walkSymbolicLinks(targetPath)
+	require.NoError(t, err)
+	require.Equal(t, paths, []string{targetPath})
+}
+
 func TestCreateFilter(t *testing.T) {
 	t.Parallel()