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).

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+### Security
+
+- **`validateDocmapPath`: add `EvalSymlinks` to close directory-symlink bypass** ([#150](https://gitea.weiker.me/rodin/review-bot/issues/150)): The previous implementation used `os.Lstat` which only avoids following the *final* path component. An intermediate directory symlink (e.g. `.review-bot/` committed as a symlink to a directory outside the repo) would pass the path-confinement check because the textual path appeared within the repo root. `filepath.EvalSymlinks` is now called first, resolving all symlink components before the `filepath.Rel` confinement check. In-repo symlinks whose resolved targets also reside within the repo root are now allowed; out-of-repo targets are rejected by the confinement check.
+
+### Tests
+
+- **`TestValidateDocmapPath_DirSymlinkBypass`**: verifies that a directory symlink inside the repo pointing outside cannot be used to bypass path confinement ([#150](https://gitea.weiker.me/rodin/review-bot/issues/150)).
+
 ### Added
 
 - **`doc-map` input** (`--doc-map` flag / `DOC_MAP_FILE` env var): Path to a YAML file mapping source path globs to governing design docs. review-bot intersects the map with changed PR paths and injects matching docs into the system prompt under a `## Design Documents` heading. ([#137](https://gitea.weiker.me/rodin/review-bot/issues/137))

cmd/review-bot/main_test.go

@@ -1506,3 +1506,4 @@ func TestMainSubprocess_DeprecatedGiteaURLEnv(t *testing.T) {
 		t.Errorf("expected deprecation warning for GITEA_URL, got: %s", out)
 	}
 }
+

cmd/review-bot/validatedocmap.go

@@ -23,46 +23,53 @@ 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)
 	}
 
-	// Lstat: do NOT follow symlinks. We want to inspect the entry itself.
-	fi, err := os.Lstat(absPath)
+	// Resolve ALL symlink components, not just the final one.
+	// os.Lstat only avoids following the *final* path component; intermediate
+	// directory symlinks are still followed. EvalSymlinks resolves every
+	// component, closing the directory-symlink bypass: a PR that commits
+	// .review-bot/ as a directory symlink pointing outside the repo would
+	// otherwise pass the filepath.Rel confinement check because the textual
+	// path is inside the root while the actual destination is not.
+	resolvedPath, err := filepath.EvalSymlinks(absPath)
 	if err != nil {
-		return fmt.Errorf("cannot stat file: %w", err)
+		return "", fmt.Errorf("cannot resolve path (symlink): %w", err)
 	}
 
-	// Reject symlinks outright — a symlink can point to /dev/zero or arbitrary
-	// host paths, bypassing both the confinement check and the size check.
-	if fi.Mode()&os.ModeSymlink != 0 {
-		return fmt.Errorf("symlinks are not allowed")
+	// 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)
 	}
 
-	// Confine to resolvedRoot: the cleaned absolute path must be a descendant
-	// of the repo root. This catches paths that escaped via "..", absolute
-	// paths that happen to be outside the root, etc.
-	rel, err := filepath.Rel(resolvedRoot, absPath)
+	// 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.
@@ -126,18 +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

@@ -465,23 +465,34 @@ mappings:
 }
 
 // TestValidateDocmapPath_Symlink verifies that --docmap pointing at a symlink
-// is rejected before the file is read (prevents /dev/zero DOS or arbitrary
-// host-file reads via PR-controlled symlinks).
+// whose resolved target is outside --repo-root is rejected (prevents reading
+// arbitrary host files via PR-controlled symlinks).
+//
+// Note: after the EvalSymlinks fix (issue #150), in-repo symlinks whose
+// targets also reside within the repo root are now allowed — the confinement
+// check is applied to the resolved path, not the symlink entry itself. The
+// security invariant is: the resolved destination must be within the root.
 func TestValidateDocmapPath_Symlink(t *testing.T) {
 	dir := t.TempDir()
+	outside := t.TempDir()
 
-	// Create a real docmap file to serve as the symlink target.
-	realDocmap := makeDocmapInDir(t, dir, `
-mappings:
-  - paths:
-      - "lib/**"
-    docs:
-      - docs/foo.md
-`)
+	// Create a docmap file OUTSIDE the repo root to serve as the symlink
+	// target. EvalSymlinks will resolve to this path, which the Rel check
+	// must then reject.
+	if err := os.MkdirAll(filepath.Join(outside, ".review-bot"), 0o755); err != nil {
+		t.Fatalf("MkdirAll: %v", err)
+	}
+	outsideDocmap := filepath.Join(outside, ".review-bot", "doc-map.yml")
+	if err := os.WriteFile(outsideDocmap, []byte("mappings: []\n"), 0o644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
 
-	// Create a symlink inside dir pointing to the real docmap.
+	// Create a symlink inside dir pointing to the file outside the repo.
+	if err := os.MkdirAll(filepath.Join(dir, ".review-bot"), 0o755); err != nil {
+		t.Fatalf("MkdirAll: %v", err)
+	}
 	symlinkPath := filepath.Join(dir, ".review-bot", "doc-map-link.yml")
-	if err := os.Symlink(realDocmap, symlinkPath); err != nil {
+	if err := os.Symlink(outsideDocmap, symlinkPath); err != nil {
 		t.Fatalf("Symlink: %v", err)
 	}
 
@@ -490,10 +501,10 @@ mappings:
 		[]string{"--docmap", symlinkPath, "--repo-root", dir},
 	)
 	if code != 2 {
-		t.Errorf("expected exit 2 for symlink docmap, got %d; stderr: %q", code, stderr)
+		t.Errorf("expected exit 2 for out-of-repo symlink docmap, got %d; stderr: %q", code, stderr)
 	}
-	if !strings.Contains(stderr, "symlink") && !strings.Contains(stderr, "invalid") {
-		t.Errorf("expected symlink rejection in stderr, got %q", stderr)
+	if !strings.Contains(stderr, "invalid") && !strings.Contains(stderr, "repo-root") {
+		t.Errorf("expected confinement rejection in stderr, got %q", stderr)
 	}
 }
 
@@ -550,3 +561,83 @@ func TestValidateDocmapPath_SizeLimit(t *testing.T) {
 		t.Errorf("expected size limit error in stderr, got %q", stderr)
 	}
 }
+
+// TestValidateDocmapPath_DirSymlinkBypass verifies that a directory-symlink
+// inside the repo pointing outside cannot be used to read arbitrary host files.
+//
+// Attack vector: a PR commits .review-bot/ as a directory symlink targeting a
+// directory outside the repo. The textual path of the docmap file is inside
+// the repo root, so the old Rel-only check passed — but the actual file is
+// outside. This is closed by calling EvalSymlinks on the full path before the
+// confinement check.
+func TestValidateDocmapPath_DirSymlinkBypass(t *testing.T) {
+	repoDir := t.TempDir()
+	outsideDir := t.TempDir()
+
+	// Secret file outside the repo.
+	secretPath := filepath.Join(outsideDir, "secret.yml")
+	if err := os.WriteFile(secretPath, []byte("mappings: []\n"), 0o644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	// Create .review-bot/ as a directory symlink pointing outside the repo.
+	reviewBotDir := filepath.Join(repoDir, ".review-bot")
+	if err := os.Symlink(outsideDir, reviewBotDir); err != nil {
+		t.Skipf("cannot create dir symlink (platform may not support it): %v", err)
+	}
+
+	// Textually inside repo — .review-bot/secret.yml — but resolves outside.
+	attackPath := filepath.Join(repoDir, ".review-bot", "secret.yml")
+
+	// Resolve repoDir to a symlink-free path, as runValidateDocmap does.
+	resolvedRoot, err := filepath.EvalSymlinks(repoDir)
+	if err != nil {
+		t.Fatalf("EvalSymlinks(repoDir): %v", err)
+	}
+
+	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")
+	}
+}