fix(tools): normalize whitelist path checks for symlinked allowed roots (#1660)

- keep regex whitelist matching for existing configs
- add normalized directory-prefix checks for literal allow-path patterns
- support allowed roots that resolve through symlinks
- add regression coverage for symlink-backed whitelist paths

pkg/tools/filesystem.go

@@ -98,14 +98,115 @@ func isAllowedPath(path string, patterns []*regexp.Regexp) bool {
 }
 
 func matchesAllowedPath(path string, patterns []*regexp.Regexp) bool {
+	cleaned := filepath.Clean(path)
 	for _, pattern := range patterns {
-		if pattern.MatchString(path) {
+		if pattern.MatchString(cleaned) {
+			return true
+		}
+		if root, ok := extractAllowedPathRoot(pattern); ok && isWithinAllowedRoot(cleaned, root) {
 			return true
 		}
 	}
 	return false
 }
 
+func extractAllowedPathRoot(pattern *regexp.Regexp) (string, bool) {
+	raw := pattern.String()
+	if !strings.HasPrefix(raw, "^") {
+		return "", false
+	}
+
+	literal := strings.TrimPrefix(raw, "^")
+
+	// Recognize the common "directory prefix" form: ^<literal>(?:/|$)
+	literal = strings.TrimSuffix(literal, "(?:/|$)")
+	literal = strings.TrimSuffix(literal, `(?:\\|$)`)
+
+	// Reject patterns that still contain regex operators after removing the
+	// optional anchored-directory suffix. That keeps arbitrary regex behavior
+	// unchanged and only enables normalized prefix matching for literal paths.
+	if containsUnescapedRegexMeta(literal) {
+		return "", false
+	}
+
+	unescaped, ok := unescapeRegexLiteral(literal)
+	if !ok || unescaped == "" {
+		return "", false
+	}
+
+	return filepath.Clean(unescaped), filepath.IsAbs(unescaped)
+}
+
+func appendUniquePath(paths []string, path string) []string {
+	for _, existing := range paths {
+		if existing == path {
+			return paths
+		}
+	}
+	return append(paths, path)
+}
+
+func containsUnescapedRegexMeta(s string) bool {
+	escaped := false
+	for _, r := range s {
+		if escaped {
+			escaped = false
+			continue
+		}
+		if r == '\\' {
+			escaped = true
+			continue
+		}
+		switch r {
+		case '.', '+', '*', '?', '(', ')', '[', ']', '{', '}', '|':
+			return true
+		}
+	}
+	return escaped
+}
+
+func unescapeRegexLiteral(s string) (string, bool) {
+	var b strings.Builder
+	b.Grow(len(s))
+
+	escaped := false
+	for _, r := range s {
+		if escaped {
+			b.WriteRune(r)
+			escaped = false
+			continue
+		}
+		if r == '\\' {
+			escaped = true
+			continue
+		}
+		b.WriteRune(r)
+	}
+
+	if escaped {
+		return "", false
+	}
+
+	return b.String(), true
+}
+
+func isWithinAllowedRoot(path, root string) bool {
+	candidate := filepath.Clean(path)
+	allowedVariants := []string{filepath.Clean(root)}
+
+	if resolvedRoot, err := resolvePathAgainstExistingAncestor(root); err == nil {
+		allowedVariants = appendUniquePath(allowedVariants, filepath.Clean(resolvedRoot))
+	}
+
+	for _, allowedRoot := range allowedVariants {
+		if isWithinWorkspace(candidate, allowedRoot) {
+			return true
+		}
+	}
+
+	return false
+}
+
 func resolveExistingAncestor(path string) (string, error) {
 	for current := filepath.Clean(path); ; current = filepath.Dir(current) {
 		if resolved, err := filepath.EvalSymlinks(current); err == nil {
@@ -144,7 +245,7 @@ func resolvePathAgainstExistingAncestor(path string) (string, error) {
 
 func isWithinWorkspace(candidate, workspace string) bool {
 	rel, err := filepath.Rel(filepath.Clean(workspace), filepath.Clean(candidate))
-	return err == nil && filepath.IsLocal(rel)
+	return err == nil && (rel == "." || filepath.IsLocal(rel))
 }
 
 type ReadFileTool struct {

pkg/tools/filesystem_test.go

@@ -570,6 +570,41 @@ func TestWhitelistFs_WriteAllowsNewFileUnderAllowedDir(t *testing.T) {
 	}
 }
 
+func TestWhitelistFs_AllowsResolvedAllowedRootAlias(t *testing.T) {
+	workspace := t.TempDir()
+	realDir := t.TempDir()
+	linkParent := t.TempDir()
+	allowedAlias := filepath.Join(linkParent, "allowed-link")
+
+	if err := os.Symlink(realDir, allowedAlias); err != nil {
+		t.Skipf("symlink not supported in this environment: %v", err)
+	}
+
+	targetFile := filepath.Join(allowedAlias, "nested", "alias.txt")
+	if err := os.MkdirAll(filepath.Dir(targetFile), 0o755); err != nil {
+		t.Fatalf("MkdirAll(targetFile dir) error = %v", err)
+	}
+	if err := os.WriteFile(targetFile, []byte("through alias"), 0o644); err != nil {
+		t.Fatalf("WriteFile(targetFile) error = %v", err)
+	}
+
+	patterns := []*regexp.Regexp{
+		regexp.MustCompile(
+			"^" + regexp.QuoteMeta(filepath.Clean(allowedAlias)) +
+				"(?:" + regexp.QuoteMeta(string(os.PathSeparator)) + "|$)",
+		),
+	}
+	tool := NewReadFileTool(workspace, true, MaxReadFileSize, patterns)
+
+	result := tool.Execute(context.Background(), map[string]any{"path": targetFile})
+	if result.IsError {
+		t.Fatalf("expected symlink-backed allowed root to be readable, got: %s", result.ForLLM)
+	}
+	if !strings.Contains(result.ForLLM, "through alias") {
+		t.Fatalf("expected file content, got: %s", result.ForLLM)
+	}
+}
+
 // TestReadFileTool_ChunkedReading verifies the pagination logic of the tool
 // by reading a file in multiple chunks using 'offset' and 'length'.
 func TestReadFileTool_ChunkedReading(t *testing.T) {