fix(sandbox): prevent local custom mount symlink escapes (bytedance#2558)

* fix(sandbox): prevent local custom mount symlink escapes

Fixes bytedance#2506

* fix(sandbox): harden custom mount symlink handling

* fix(sandbox): format internal symlink directory listings

Author: hetaoBackend

backend/packages/harness/deerflow/sandbox/local/list_dir.py

@@ -22,6 +22,13 @@ def list_dir(path: str, max_depth: int = 2) -> list[str]:
     if not root_path.is_dir():
         return result
 
+    def _is_within_root(candidate: Path) -> bool:
+        try:
+            candidate.relative_to(root_path)
+            return True
+        except ValueError:
+            return False
+
     def _traverse(current_path: Path, current_depth: int) -> None:
         """Recursively traverse directories up to max_depth."""
         if current_depth > max_depth:
@@ -32,8 +39,23 @@ def _traverse(current_path: Path, current_depth: int) -> None:
                 if should_ignore_name(item.name):
                     continue
 
+                if item.is_symlink():
+                    try:
+                        item_resolved = item.resolve()
+                        if not _is_within_root(item_resolved):
+                            continue
+                    except OSError:
+                        continue
+                    post_fix = "/" if item_resolved.is_dir() else ""
+                    result.append(str(item_resolved) + post_fix)
+                    continue
+
+                item_resolved = item.resolve()
+                if not _is_within_root(item_resolved):
+                    continue
+
                 post_fix = "/" if item.is_dir() else ""
-                result.append(str(item.resolve()) + post_fix)
+                result.append(str(item_resolved) + post_fix)
 
                 # Recurse into subdirectories if not at max depth
                 if item.is_dir() and current_depth < max_depth:

backend/packages/harness/deerflow/sandbox/local/local_sandbox.py

@@ -5,6 +5,7 @@
 import subprocess
 from dataclasses import dataclass
 from pathlib import Path
+from typing import NamedTuple
 
 from deerflow.sandbox.local.list_dir import list_dir
 from deerflow.sandbox.sandbox import Sandbox
@@ -20,6 +21,11 @@ class PathMapping:
     read_only: bool = False
 
 
+class ResolvedPath(NamedTuple):
+    path: str
+    mapping: PathMapping | None
+
+
 class LocalSandbox(Sandbox):
     @staticmethod
     def _shell_name(shell: str) -> str:
@@ -91,30 +97,54 @@ def _is_read_only_path(self, resolved_path: str) -> bool:
 
         return best_mapping.read_only
 
-    def _resolve_path(self, path: str) -> str:
+    def _find_path_mapping(self, path: str) -> tuple[PathMapping, str] | None:
+        path_str = str(path)
+
+        for mapping in sorted(self.path_mappings, key=lambda m: len(m.container_path.rstrip("/") or "/"), reverse=True):
+            container_path = mapping.container_path.rstrip("/") or "/"
+            if container_path == "/":
+                if path_str.startswith("/"):
+                    return mapping, path_str.lstrip("/")
+                continue
+
+            if path_str == container_path or path_str.startswith(container_path + "/"):
+                relative = path_str[len(container_path) :].lstrip("/")
+                return mapping, relative
+
+        return None
+
+    def _resolve_path_with_mapping(self, path: str) -> ResolvedPath:
         """
         Resolve container path to actual local path using mappings.
 
         Args:
             path: Path that might be a container path
 
         Returns:
-            Resolved local path
+            Resolved local path and the matched mapping, if any
         """
         path_str = str(path)
 
-        # Try each mapping (longest prefix first for more specific matches)
-        for mapping in sorted(self.path_mappings, key=lambda m: len(m.container_path), reverse=True):
-            container_path = mapping.container_path
-            local_path = mapping.local_path
-            if path_str == container_path or path_str.startswith(container_path + "/"):
-                # Replace the container path prefix with local path
-                relative = path_str[len(container_path) :].lstrip("/")
-                resolved = str(Path(local_path) / relative) if relative else local_path
-                return resolved
+        mapping_match = self._find_path_mapping(path_str)
+        if mapping_match is None:
+            return ResolvedPath(path_str, None)
 
-        # No mapping found, return original path
-        return path_str
+        mapping, relative = mapping_match
+        local_root = Path(mapping.local_path).resolve()
+        resolved_path = (local_root / relative).resolve() if relative else local_root
+
+        try:
+            resolved_path.relative_to(local_root)
+        except ValueError as exc:
+            raise PermissionError(errno.EACCES, "Access denied: path escapes mounted directory", path_str) from exc
+
+        return ResolvedPath(str(resolved_path), mapping)
+
+    def _resolve_path(self, path: str) -> str:
+        return self._resolve_path_with_mapping(path).path
+
+    def _is_resolved_path_read_only(self, resolved: ResolvedPath) -> bool:
+        return bool(resolved.mapping and resolved.mapping.read_only) or self._is_read_only_path(resolved.path)
 
     def _reverse_resolve_path(self, path: str) -> str:
         """
@@ -309,8 +339,14 @@ def execute_command(self, command: str) -> str:
     def list_dir(self, path: str, max_depth=2) -> list[str]:
         resolved_path = self._resolve_path(path)
         entries = list_dir(resolved_path, max_depth)
-        # Reverse resolve local paths back to container paths in output
-        return [self._reverse_resolve_paths_in_output(entry) for entry in entries]
+        # Reverse resolve local paths back to container paths and preserve
+        # list_dir's trailing "/" marker for directories.
+        result: list[str] = []
+        for entry in entries:
+            is_dir = entry.endswith(("/", "\\"))
+            reversed_entry = self._reverse_resolve_path(entry.rstrip("/\\")) if is_dir else self._reverse_resolve_path(entry)
+            result.append(f"{reversed_entry}/" if is_dir and not reversed_entry.endswith("/") else reversed_entry)
+        return result
 
     def read_file(self, path: str) -> str:
         resolved_path = self._resolve_path(path)
@@ -329,8 +365,9 @@ def read_file(self, path: str) -> str:
             raise type(e)(e.errno, e.strerror, path) from None
 
     def write_file(self, path: str, content: str, append: bool = False) -> None:
-        resolved_path = self._resolve_path(path)
-        if self._is_read_only_path(resolved_path):
+        resolved = self._resolve_path_with_mapping(path)
+        resolved_path = resolved.path
+        if self._is_resolved_path_read_only(resolved):
             raise OSError(errno.EROFS, "Read-only file system", path)
         try:
             dir_path = os.path.dirname(resolved_path)
@@ -384,8 +421,9 @@ def grep(
         ], truncated
 
     def update_file(self, path: str, content: bytes) -> None:
-        resolved_path = self._resolve_path(path)
-        if self._is_read_only_path(resolved_path):
+        resolved = self._resolve_path_with_mapping(path)
+        resolved_path = resolved.path
+        if self._is_resolved_path_read_only(resolved):
             raise OSError(errno.EROFS, "Read-only file system", path)
         try:
             dir_path = os.path.dirname(resolved_path)

backend/tests/test_local_sandbox_provider_mounts.py

@@ -1,4 +1,5 @@
 import errno
+from pathlib import Path
 from types import SimpleNamespace
 from unittest.mock import patch
 
@@ -8,6 +9,13 @@
 from deerflow.sandbox.local.local_sandbox_provider import LocalSandboxProvider
 
 
+def _symlink_to(target, link, *, target_is_directory=False):
+    try:
+        link.symlink_to(target, target_is_directory=target_is_directory)
+    except (NotImplementedError, OSError) as exc:
+        pytest.skip(f"symlinks are not available: {exc}")
+
+
 class TestPathMapping:
     def test_path_mapping_dataclass(self):
         mapping = PathMapping(container_path="/mnt/skills", local_path="/home/user/skills", read_only=True)
@@ -29,7 +37,7 @@ def test_resolve_path_exact_match(self):
             ],
         )
         resolved = sandbox._resolve_path("/mnt/skills")
-        assert resolved == "/home/user/skills"
+        assert resolved == str(Path("/home/user/skills").resolve())
 
     def test_resolve_path_nested_path(self):
         sandbox = LocalSandbox(
@@ -39,7 +47,7 @@ def test_resolve_path_nested_path(self):
             ],
         )
         resolved = sandbox._resolve_path("/mnt/skills/agent/prompt.py")
-        assert resolved == "/home/user/skills/agent/prompt.py"
+        assert resolved == str(Path("/home/user/skills/agent/prompt.py").resolve())
 
     def test_resolve_path_no_mapping(self):
         sandbox = LocalSandbox(
@@ -61,7 +69,7 @@ def test_resolve_path_longest_prefix_first(self):
         )
         resolved = sandbox._resolve_path("/mnt/skills/file.py")
         # Should match /mnt/skills first (longer prefix)
-        assert resolved == "/home/user/skills/file.py"
+        assert resolved == str(Path("/home/user/skills/file.py").resolve())
 
     def test_reverse_resolve_path_exact_match(self, tmp_path):
         skills_dir = tmp_path / "skills"
@@ -175,6 +183,157 @@ def test_update_file_blocked_on_read_only(self, tmp_path):
         assert exc_info.value.errno == errno.EROFS
 
 
+class TestSymlinkEscapes:
+    def test_read_file_blocks_symlink_escape_from_mount(self, tmp_path):
+        mount_dir = tmp_path / "mount"
+        mount_dir.mkdir()
+        outside_dir = tmp_path / "outside"
+        outside_dir.mkdir()
+        (outside_dir / "secret.txt").write_text("secret")
+        _symlink_to(outside_dir, mount_dir / "escape", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/data", local_path=str(mount_dir), read_only=False),
+            ],
+        )
+
+        with pytest.raises(PermissionError) as exc_info:
+            sandbox.read_file("/mnt/data/escape/secret.txt")
+
+        assert exc_info.value.errno == errno.EACCES
+
+    def test_write_file_blocks_symlink_escape_from_mount(self, tmp_path):
+        mount_dir = tmp_path / "mount"
+        mount_dir.mkdir()
+        outside_dir = tmp_path / "outside"
+        outside_dir.mkdir()
+        victim = outside_dir / "victim.txt"
+        victim.write_text("original")
+        _symlink_to(outside_dir, mount_dir / "escape", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/data", local_path=str(mount_dir), read_only=False),
+            ],
+        )
+
+        with pytest.raises(PermissionError) as exc_info:
+            sandbox.write_file("/mnt/data/escape/victim.txt", "changed")
+
+        assert exc_info.value.errno == errno.EACCES
+        assert victim.read_text() == "original"
+
+    def test_write_file_uses_matched_read_only_mount_for_symlink_target(self, tmp_path):
+        repo_dir = tmp_path / "repo"
+        repo_dir.mkdir()
+        writable_dir = repo_dir / "writable"
+        writable_dir.mkdir()
+        _symlink_to(writable_dir, repo_dir / "link-to-writable", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/repo", local_path=str(repo_dir), read_only=True),
+                PathMapping(container_path="/mnt/repo/writable", local_path=str(writable_dir), read_only=False),
+            ],
+        )
+
+        with pytest.raises(OSError) as exc_info:
+            sandbox.write_file("/mnt/repo/link-to-writable/file.txt", "bypass")
+
+        assert exc_info.value.errno == errno.EROFS
+        assert not (writable_dir / "file.txt").exists()
+
+    def test_list_dir_does_not_follow_symlink_escape_from_mount(self, tmp_path):
+        mount_dir = tmp_path / "mount"
+        mount_dir.mkdir()
+        outside_dir = tmp_path / "outside"
+        outside_dir.mkdir()
+        (outside_dir / "secret.txt").write_text("secret")
+        _symlink_to(outside_dir, mount_dir / "escape", target_is_directory=True)
+        (mount_dir / "visible.txt").write_text("visible")
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/data", local_path=str(mount_dir), read_only=False),
+            ],
+        )
+
+        entries = sandbox.list_dir("/mnt/data", max_depth=2)
+
+        assert "/mnt/data/visible.txt" in entries
+        assert all("secret.txt" not in entry for entry in entries)
+        assert all("outside" not in entry for entry in entries)
+
+    def test_list_dir_formats_internal_directory_symlink_like_directory(self, tmp_path):
+        mount_dir = tmp_path / "mount"
+        nested_dir = mount_dir / "nested"
+        linked_dir = nested_dir / "linked-dir"
+        linked_dir.mkdir(parents=True)
+        _symlink_to(linked_dir, mount_dir / "dir-link", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/data", local_path=str(mount_dir), read_only=False),
+            ],
+        )
+
+        entries = sandbox.list_dir("/mnt/data", max_depth=1)
+
+        assert "/mnt/data/nested/" in entries
+        assert "/mnt/data/nested/linked-dir/" in entries
+        assert "/mnt/data/dir-link" not in entries
+
+    def test_write_file_blocks_symlink_into_nested_read_only_mount(self, tmp_path):
+        repo_dir = tmp_path / "repo"
+        repo_dir.mkdir()
+        protected_dir = repo_dir / "protected"
+        protected_dir.mkdir()
+        _symlink_to(protected_dir, repo_dir / "link-to-protected", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/repo", local_path=str(repo_dir), read_only=False),
+                PathMapping(container_path="/mnt/repo/protected", local_path=str(protected_dir), read_only=True),
+            ],
+        )
+
+        with pytest.raises(OSError) as exc_info:
+            sandbox.write_file("/mnt/repo/link-to-protected/file.txt", "bypass")
+
+        assert exc_info.value.errno == errno.EROFS
+        assert not (protected_dir / "file.txt").exists()
+
+    def test_update_file_blocks_symlink_into_nested_read_only_mount(self, tmp_path):
+        repo_dir = tmp_path / "repo"
+        repo_dir.mkdir()
+        protected_dir = repo_dir / "protected"
+        protected_dir.mkdir()
+        existing = protected_dir / "file.txt"
+        existing.write_bytes(b"original")
+        _symlink_to(protected_dir, repo_dir / "link-to-protected", target_is_directory=True)
+
+        sandbox = LocalSandbox(
+            "test",
+            [
+                PathMapping(container_path="/mnt/repo", local_path=str(repo_dir), read_only=False),
+                PathMapping(container_path="/mnt/repo/protected", local_path=str(protected_dir), read_only=True),
+            ],
+        )
+
+        with pytest.raises(OSError) as exc_info:
+            sandbox.update_file("/mnt/repo/link-to-protected/file.txt", b"changed")
+
+        assert exc_info.value.errno == errno.EROFS
+        assert existing.read_bytes() == b"original"
+
+
 class TestMultipleMounts:
     def test_multiple_read_write_mounts(self, tmp_path):
         skills_dir = tmp_path / "skills"