feat(agent): report and refuse Compose services built from source; honour --env-file (#7)

internal/agent/updater/override.go

@@ -136,6 +136,16 @@ func MountRoots(ctx context.Context, cli SelfInspector, selfID string) ([]string
 // override last so it wins. Every file, and the real location of its
 // directory after resolving symlinks, must be inside one of roots.
 func composeFiles(roots []string, configFilesLabel string) (files []string, dir string, err error) {
+	files, dir, err = stackFiles(roots, configFilesLabel)
+	if err != nil {
+		return nil, "", err
+	}
+	return append(files, filepath.Join(dir, OverrideName)), dir, nil
+}
+
+// stackFiles is composeFiles without the override: the operator's own config
+// files, checked against roots. dir is the first file's directory.
+func stackFiles(roots []string, configFilesLabel string) (files []string, dir string, err error) {
 	if len(roots) == 0 {
 		return nil, "", errNoRoots
 	}
@@ -150,16 +160,7 @@ func composeFiles(roots []string, configFilesLabel string) (files []string, dir
 	dir = filepath.Dir(files[0])
 	override := filepath.Join(dir, OverrideName)
 
-	// Only directories count once resolved: this drops a same-path mount of
-	// a single file such as /var/run/docker.sock.
-	var realRoots []string
-	for _, r := range roots {
-		if rr, err := filepath.EvalSymlinks(r); err == nil {
-			if fi, err := os.Stat(rr); err == nil && fi.IsDir() {
-				realRoots = append(realRoots, rr)
-			}
-		}
-	}
+	realRoots := realDirs(roots)
 	out := files[:0]
 	for _, f := range files {
 		if !filepath.IsAbs(f) || !insideAny(roots, f) {
@@ -176,7 +177,48 @@ func composeFiles(roots []string, configFilesLabel string) (files []string, dir
 			out = append(out, f)
 		}
 	}
-	return append(out, override), dir, nil
+	return out, dir, nil
+}
+
+// envFiles returns the --env-file paths from the container's
+// com.docker.compose.project.environment_file label (empty label: none).
+// Like config files, each must be inside one of roots, also after resolving
+// symlinks of the file itself.
+func envFiles(roots []string, label string) ([]string, error) {
+	var files []string
+	realRoots := realDirs(roots)
+	for _, f := range strings.Split(label, ",") {
+		if f = strings.TrimSpace(f); f == "" {
+			continue
+		}
+		if !filepath.IsAbs(f) || !insideAny(roots, f) {
+			return nil, fmt.Errorf("env file %s is not inside a directory mounted into the agent at the same path (read-write)", f)
+		}
+		real, err := filepath.EvalSymlinks(f)
+		if err != nil {
+			return nil, fmt.Errorf("resolve env file %s: %w", f, err)
+		}
+		if !insideAny(realRoots, real) {
+			return nil, fmt.Errorf("env file %s is not inside a directory mounted into the agent at the same path (read-write)", f)
+		}
+		files = append(files, f)
+	}
+	return files, nil
+}
+
+// realDirs returns roots with symlinks resolved. Only directories count once
+// resolved: this drops a same-path mount of a single file such as
+// /var/run/docker.sock.
+func realDirs(roots []string) []string {
+	var out []string
+	for _, r := range roots {
+		if rr, err := filepath.EvalSymlinks(r); err == nil {
+			if fi, err := os.Stat(rr); err == nil && fi.IsDir() {
+				out = append(out, rr)
+			}
+		}
+	}
+	return out
 }
 
 func insideAny(roots []string, path string) bool {