security: confine the browser connector's file tools to the session roots

coworker/connectors/browser_automation.py

@@ -17,9 +17,44 @@
 
 import aisuite as ai
 
+from ..roots import RootDir
 from ..web.guard import check_url
 
 
+def _resolve_in_roots(
+    path: str, roots: Optional[list[RootDir]], *, need_write: bool
+) -> tuple[Optional[Path], Optional[dict[str, Any]]]:
+    """Resolve a local path and require it to sit inside a granted session root.
+
+    The permission engine only path-scopes the built-in ``WRITE_TOOLS`` by inspecting
+    ``arguments["path"]``, so a connector tool that touches the filesystem is invisible to
+    it. These two do, in both directions: ``browser_upload_file`` reads a file and hands it
+    to whatever page is loaded, and ``browser_screenshot`` writes one. Without this check
+    they reach anything the OS lets the process reach — ``~/.ssh/id_rsa``, the secret store
+    itself — regardless of which folders the user actually granted the session.
+
+    Mirrors the confinement ``email_tools`` already applies to outgoing attachments.
+    Returns ``(resolved_path, None)`` on success or ``(None, error_dict)`` for the tool to
+    return verbatim.
+    """
+    candidates = [r for r in (roots or []) if r.writable or not need_write]
+    if not candidates:
+        return None, {
+            "error": (
+                "no writable session directory is available"
+                if need_write
+                else "this session has no granted directories"
+            )
+        }
+    resolved = Path(str(path)).expanduser().resolve()
+    if not any(resolved.is_relative_to(r.path) for r in candidates):
+        verb = "writable " if need_write else ""
+        return None, {
+            "error": f"{path} is outside the session's {verb}directories"
+        }
+    return resolved, None
+
+
 def _meta(
     name: str, *, approval: bool = False, capabilities: Optional[list[str]] = None
 ):
@@ -326,7 +361,9 @@ def _snapshot(page, max_chars: int) -> dict[str, Any]:
     }
 
 
-def make_browser_automation_tools() -> list[Callable[..., Any]]:
+def make_browser_automation_tools(
+    roots: Optional[list[RootDir]] = None,
+) -> list[Callable[..., Any]]:
     tools: list[Callable[..., Any]] = []
 
     def browser_open_url(
@@ -484,9 +521,11 @@ def browser_select(target: str, value: str) -> dict[str, Any]:
     )
 
     def browser_upload_file(target: str, path: str) -> dict[str, Any]:
-        file_path = Path(path).expanduser().resolve()
+        file_path, err = _resolve_in_roots(path, roots, need_write=False)
+        if err:
+            return err
         if not file_path.exists():
-            return {"error": f"file not found: {file_path}"}
+            return {"error": f"file not found: {path}"}
         return _BROWSER.call(
             "upload_file",
             lambda page: (
@@ -538,13 +577,16 @@ def run(page):
     )
 
     def browser_screenshot(path: str = "") -> dict[str, Any]:
-        def run(page):
+        if path:
+            out, err = _resolve_in_roots(path, roots, need_write=True)
+            if err:
+                return err
+        else:
             out = (
-                Path(path).expanduser()
-                if path
-                else Path(tempfile.gettempdir()) / "coworker-browser-screenshot.png"
-            )
-            out = out.resolve()
+                Path(tempfile.gettempdir()) / "coworker-browser-screenshot.png"
+            ).resolve()
+
+        def run(page):
             out.parent.mkdir(parents=True, exist_ok=True)
             page.screenshot(path=str(out), full_page=True)
             return {"ok": True, "path": str(out), "url": page.url}

coworker/connectors/integration_tools.py

@@ -550,7 +550,7 @@ def make_integration_tools(
     enabled_tools: Optional[set[str]] = None,
     roots: Optional[list[Any]] = None,
 ) -> list[Callable[..., Any]]:
-    tools: list[Callable[..., Any]] = make_browser_automation_tools()
+    tools: list[Callable[..., Any]] = make_browser_automation_tools(roots=roots)
     # Email needs the session roots: attachment downloads land in the primary scratch
     # and outgoing attachments must resolve inside a granted directory.
     tools.extend(make_email_tools(secrets, roots=roots))

tests/test_browser_path_confinement.py

@@ -0,0 +1,134 @@
+"""The browser connector's two filesystem tools must stay inside the session's roots.
+
+The permission engine path-scopes only the built-in ``WRITE_TOOLS``, and only by reading
+``arguments["path"]`` (``permissions.PermissionEngine.evaluate``). A connector tool that
+touches local files is therefore invisible to it, in both directions:
+
+  browser_upload_file   reads any readable path and hands it to the loaded page
+  browser_screenshot    writes a PNG to any writable path, creating parent dirs
+
+``email_tools`` already confines outgoing attachments to the granted roots; these tests pin
+the same rule for the browser tools.
+"""
+
+from pathlib import Path
+
+import pytest
+
+from coworker.connectors.browser_automation import (
+    _resolve_in_roots,
+    make_browser_automation_tools,
+)
+from coworker.roots import RootDir
+
+
+def _tools(roots):
+    return {t.__name__: t for t in make_browser_automation_tools(roots=roots)}
+
+
+@pytest.fixture
+def session(tmp_path):
+    scratch = tmp_path / "scratch"
+    readonly = tmp_path / "readonly"
+    outside = tmp_path / "outside"
+    for d in (scratch, readonly, outside):
+        d.mkdir()
+    (readonly / "notes.txt").write_text("granted, read-only")
+    (outside / "id_rsa").write_text("PRIVATE KEY")
+    return {
+        "roots": [RootDir(path=scratch, writable=True),
+                  RootDir(path=readonly, writable=False)],
+        "scratch": scratch,
+        "readonly": readonly,
+        "outside": outside,
+    }
+
+
+# -- the helper ---------------------------------------------------------------
+
+def test_read_is_allowed_from_any_granted_root(session):
+    resolved, err = _resolve_in_roots(
+        str(session["readonly"] / "notes.txt"), session["roots"], need_write=False)
+    assert err is None
+    assert resolved == (session["readonly"] / "notes.txt").resolve()
+
+
+def test_write_is_refused_into_a_read_only_root(session):
+    resolved, err = _resolve_in_roots(
+        str(session["readonly"] / "shot.png"), session["roots"], need_write=True)
+    assert resolved is None
+    assert "outside the session's writable directories" in err["error"]
+
+
+def test_ungranted_path_is_refused(session):
+    _, err = _resolve_in_roots(
+        str(session["outside"] / "id_rsa"), session["roots"], need_write=False)
+    assert err and "outside the session's directories" in err["error"]
+
+
+def test_traversal_out_of_a_root_is_refused(session):
+    escape = str(session["scratch"] / ".." / "outside" / "id_rsa")
+    _, err = _resolve_in_roots(escape, session["roots"], need_write=False)
+    assert err, "`..` must be resolved before the containment check, not after"
+
+
+def test_symlink_pointing_out_of_a_root_is_refused(session):
+    link = session["scratch"] / "innocent.txt"
+    try:
+        link.symlink_to(session["outside"] / "id_rsa")
+    except (OSError, NotImplementedError):  # Windows without developer mode
+        pytest.skip("symlinks unavailable")
+    _, err = _resolve_in_roots(str(link), session["roots"], need_write=False)
+    assert err, "resolve() must follow the symlink before containment is decided"
+
+
+def test_no_roots_means_no_filesystem_access(session):
+    _, err = _resolve_in_roots(str(session["outside"] / "id_rsa"), [], need_write=False)
+    assert err and "no granted directories" in err["error"]
+
+
+# -- the tools ----------------------------------------------------------------
+
+def test_upload_refuses_a_path_outside_the_session(session):
+    upload = _tools(session["roots"])["browser_upload_file"]
+    out = upload("input[type=file]", str(session["outside"] / "id_rsa"))
+    assert "error" in out and "outside the session" in out["error"]
+
+
+def test_upload_refuses_before_reporting_whether_the_file_exists(session):
+    """The refusal must not double as an existence oracle for ungranted paths."""
+    upload = _tools(session["roots"])["browser_upload_file"]
+    missing = upload("input", str(session["outside"] / "nope.txt"))
+    present = upload("input", str(session["outside"] / "id_rsa"))
+    # Same refusal for both: containment is decided before the file is stat'd, so the
+    # error never distinguishes "exists but ungranted" from "does not exist".
+    assert "outside the session" in missing["error"]
+    assert "outside the session" in present["error"]
+    assert "not found" not in missing["error"]
+
+
+def test_screenshot_refuses_a_path_outside_the_session(session):
+    shot = _tools(session["roots"])["browser_screenshot"]
+    out = shot(str(session["outside"] / "evil.png"))
+    assert "error" in out and "outside the session" in out["error"]
+
+
+def test_screenshot_is_refused_before_the_browser_is_touched(session):
+    """Containment must be decided by the tool, not incidentally by the browser layer.
+
+    Previously the check did not exist and `out.parent.mkdir(parents=True)` sat inside the
+    Playwright callback, so on a machine with Playwright installed a refused path still had
+    its directory tree created. The refusal now happens first, which is observable here
+    because the error is the containment error rather than Playwright's.
+    """
+    shot = _tools(session["roots"])["browser_screenshot"]
+    out = shot(str(session["outside"] / "a" / "b" / "c.png"))
+    assert "outside the session" in out["error"]
+    assert "laywright" not in out["error"]
+    assert not (session["outside"] / "a").exists()
+
+
+def test_tools_are_constructible_without_roots(session):
+    """CLI/direct callers pass no roots; construction must still work (and deny)."""
+    upload = _tools(None)["browser_upload_file"]
+    assert "error" in upload("input", str(session["outside"] / "id_rsa"))