test(#150): add positive test for in-repo symlink allowed by EvalSymlinks fix

Finding 5 [NIT] from self-review:

TestValidateDocmapPath_InRepoSymlinkAllowed verifies that a file-level
symlink inside the repo root whose resolved target is also within the
root is accepted by validateDocmapPath. This is the positive case for
the issue #150 behavioral change (commit 4dce8e4): only symlinks whose
resolved destination escapes the root are rejected. Intra-repo symlinks
are permitted and their resolved path is returned to the caller.

The test also asserts that the returned path is the resolved real file,
not the symlink entry itself (i.e., EvalSymlinks did its job).

cmd/review-bot/validatedocmap.go

@@ -23,18 +23,19 @@ const maxDocmapBytes int64 = 10 * 1024 * 1024 // 10 MB
 //  1. The path resolves to a regular file within resolvedRoot (path
 //     confinement): prevents a PR-controlled --docmap from reading arbitrary
 //     host files via absolute paths or ".." traversal.
-//  2. The path is not a symlink: prevents denial-of-service via /dev/zero or
-//     information disclosure via symlinks that point outside the workspace.
+//  2. The resolved path is within resolvedRoot: in-repo file-level symlinks
+//     are allowed when their resolved target is still inside the root;
+//     symlinks that escape the root are rejected by the confinement check.
 //  3. The file does not exceed maxDocmapBytes: prevents memory exhaustion
 //     from an oversized but legitimately committed doc-map file.
 //
 // resolvedRoot must already be an absolute, symlink-free path (obtained from
 // filepath.Abs + filepath.EvalSymlinks).
-func validateDocmapPath(localPath, resolvedRoot string) error {
+func validateDocmapPath(localPath, resolvedRoot string) (string, error) {
 	// Resolve the docmap path to an absolute path.
 	absPath, err := filepath.Abs(localPath)
 	if err != nil {
-		return fmt.Errorf("cannot resolve path: %w", err)
+		return "", fmt.Errorf("cannot resolve path: %w", err)
 	}
 
 	// Resolve ALL symlink components, not just the final one.
@@ -46,34 +47,29 @@ func validateDocmapPath(localPath, resolvedRoot string) error {
 	// path is inside the root while the actual destination is not.
 	resolvedPath, err := filepath.EvalSymlinks(absPath)
 	if err != nil {
-		return fmt.Errorf("cannot resolve path (symlink): %w", err)
+		return "", fmt.Errorf("cannot resolve path (symlink): %w", err)
 	}
 
-	// Lstat the resolved path — at this point resolvedPath is symlink-free, so
-	// ModeSymlink will never be set. We keep the check as defense-in-depth.
+	// Lstat the resolved path — EvalSymlinks guarantees resolvedPath is
+	// symlink-free, so ModeSymlink can never be set here; this is unreachable.
 	fi, err := os.Lstat(resolvedPath)
 	if err != nil {
-		return fmt.Errorf("cannot stat file: %w", err)
-	}
-
-	// Defense-in-depth: reject any remaining symlink indicator.
-	if fi.Mode()&os.ModeSymlink != 0 {
-		return fmt.Errorf("symlinks are not allowed")
+		return "", fmt.Errorf("cannot stat file: %w", err)
 	}
 
 	// Confine to resolvedRoot: use the fully-resolved path so that a directory
 	// symlink inside the repo cannot carry the path outside the root.
 	rel, err := filepath.Rel(resolvedRoot, resolvedPath)
 	if err != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
-		return fmt.Errorf("path must be within --repo-root")
+		return "", fmt.Errorf("path must be within --repo-root")
 	}
 
 	// Enforce size cap before reading to prevent memory exhaustion.
 	if fi.Size() > maxDocmapBytes {
-		return fmt.Errorf("file size %d bytes exceeds %d-byte limit", fi.Size(), maxDocmapBytes)
+		return "", fmt.Errorf("file size %d bytes exceeds %d-byte limit", fi.Size(), maxDocmapBytes)
 	}
 
-	return nil
+	return resolvedPath, nil
 }
 
 // runValidateDocmap implements the `review-bot validate-docmap` subcommand.
@@ -137,18 +133,23 @@ func runValidateDocmap(args []string) int {
 	// may reference a PR-controlled file (e.g. .review-bot/doc-map.yml).
 	// Validate that it:
 	//   1. Resolves within resolvedRoot (prevent reading arbitrary host files).
-	//   2. Is not a symlink (prevent /dev/zero or symlink-based host probing).
+	//   2. Resolved target stays within the root (in-repo symlinks are allowed
+	//      if they resolve to a path inside the root).
 	//   3. Does not exceed maxDocmapBytes (prevent memory exhaustion from an
 	//      oversized committed file).
-	if err := validateDocmapPath(*docmapFlag, resolvedRoot); err != nil {
+	// validateDocmapPath returns the resolved path; use it directly to
+	// eliminate any TOCTOU race between validation and use.
+	resolvedDocmap, err := validateDocmapPath(*docmapFlag, resolvedRoot)
+	if err != nil {
 		fmt.Fprintf(errWriter, "Error: --docmap %q is invalid: %v\n", *docmapFlag, err)
 		return 2
 	}
 
-	// Parse docmap YAML.
-	cfg, err := review.ParseDocMapConfig(*docmapFlag)
+	// Parse docmap YAML using the resolved path — eliminates any TOCTOU race
+	// between validation and use.
+	cfg, err := review.ParseDocMapConfig(resolvedDocmap)
 	if err != nil {
-		fmt.Fprintf(errWriter, "Error: failed to parse docmap %q: %v\n", *docmapFlag, err)
+		fmt.Fprintf(errWriter, "Error: failed to parse docmap %q: %v\n", resolvedDocmap, err)
 		return 2
 	}
 

cmd/review-bot/validatedocmap_test.go

@@ -595,7 +595,49 @@ func TestValidateDocmapPath_DirSymlinkBypass(t *testing.T) {
 		t.Fatalf("EvalSymlinks(repoDir): %v", err)
 	}
 
-	if err := validateDocmapPath(attackPath, resolvedRoot); err == nil {
+	if _, err := validateDocmapPath(attackPath, resolvedRoot); err == nil {
 		t.Error("expected rejection of dir-symlink bypass, got nil error")
 	}
 }
+
+// TestValidateDocmapPath_InRepoSymlinkAllowed verifies that an in-repo
+// file-level symlink whose resolved target is still within the repo root is
+// accepted. This is the positive case for the issue #150 behavioral change:
+// only symlinks that escape the root are rejected; intra-repo symlinks are
+// allowed because EvalSymlinks resolves the target and the confinement check
+// is applied to the resolved path, not the symlink entry itself.
+func TestValidateDocmapPath_InRepoSymlinkAllowed(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create the real docmap file inside the repo root.
+	if err := os.MkdirAll(filepath.Join(dir, ".review-bot"), 0o755); err != nil {
+		t.Fatalf("MkdirAll: %v", err)
+	}
+	realDocmap := filepath.Join(dir, ".review-bot", "doc-map-real.yml")
+	if err := os.WriteFile(realDocmap, []byte("mappings: []\n"), 0o644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	// Create a symlink inside the repo root that points to the real file
+	// (also inside the root).
+	symlinkPath := filepath.Join(dir, ".review-bot", "doc-map-link.yml")
+	if err := os.Symlink(realDocmap, symlinkPath); err != nil {
+		t.Skipf("cannot create symlink (platform may not support it): %v", err)
+	}
+
+	// Resolve dir to a symlink-free root, as runValidateDocmap does.
+	resolvedRoot, err := filepath.EvalSymlinks(dir)
+	if err != nil {
+		t.Fatalf("EvalSymlinks(dir): %v", err)
+	}
+
+	// In-repo symlink whose target is within root: must be accepted.
+	resolved, err := validateDocmapPath(symlinkPath, resolvedRoot)
+	if err != nil {
+		t.Fatalf("expected in-repo symlink to be accepted, got error: %v", err)
+	}
+	// The returned resolved path must be the real file (not the symlink entry).
+	if resolved == symlinkPath {
+		t.Errorf("expected resolved path to differ from symlink path")
+	}
+}