fix: make sandbox uid configurable across all languages

.env.example

@@ -27,7 +27,9 @@ MINIO_SECRET_KEY=minioadmin
 # ── Sandbox Pool (Python REPL) ─────────────────────────────────
 # SANDBOX_POOL_ENABLED=true
 # SANDBOX_POOL_PY=5        # Number of pre-warmed Python REPLs
+# SANDBOX_POOL_PARALLEL_BATCH=1  # Safer on busy multi-tenant hosts
 # REPL_ENABLED=true
+# SANDBOX_UID=1002         # Shared host UID for all sandbox languages
 
 # ── Port ──────────────────────────────────────────────────────
 # PORT=8000                # External port the API is reachable on

README.md

@@ -136,7 +136,7 @@ For comprehensive testing details, see [TESTING.md](docs/TESTING.md).
 - Seccomp syscall filtering restricts available system calls
 - Cgroup-based resource limits prevent CPU, memory, and process exhaustion
 - rlimits restrict file sizes, open file descriptors, etc.
-- Code runs as non-root user (uid 1001)
+- Code runs as a shared non-root sandbox user (default uid `1001`, configurable with `SANDBOX_UID`)
 - Read-only bind mounts for language runtimes and libraries
 - API key authentication protects all endpoints
 - Input validation prevents injection attacks

docs/ARCHITECTURE.md

@@ -363,7 +363,7 @@ settings.max_memory_mb
 │   4. Seccomp Filtering    : Restricted syscalls                            │
 │   5. Cgroup Limits        : Memory, CPU, pids                              │
 │   6. rlimits              : File size, open files, stack size              │
-│   7. Non-root Execution   : Code runs as uid 1001 (codeuser)              │
+│   7. Non-root Execution   : Code runs as shared uid 1001 by default       │
 │                                                                             │
 └─────────────────────────────────────────────────────────────────────────────┘
 ```

docs/CONFIGURATION.md

@@ -147,7 +147,8 @@ nsjail is used for secure code execution in isolated sandboxes.
 **Security Notes:**
 
 - nsjail provides PID, mount, and network namespace isolation
-- Code runs as non-root user (uid 1001) inside the sandbox
+- Code runs as a shared non-root UID inside the sandbox
+- All sandbox languages default to UID `1001`, and can be moved with `SANDBOX_UID`
 - The API container requires `SYS_ADMIN` capability for nsjail namespace creation
 
 ### Resource Limits
@@ -184,6 +185,8 @@ Pre-warmed Python REPL sandboxes reduce execution latency by eliminating interpr
 | `SANDBOX_POOL_ENABLED`             | `true`  | Enable Python REPL pool                |
 | `SANDBOX_POOL_WARMUP_ON_STARTUP`   | `true`  | Pre-warm Python REPLs at startup       |
 | `SANDBOX_POOL_PY`                  | `5`     | Number of pre-warmed Python REPLs      |
+| `SANDBOX_POOL_PARALLEL_BATCH`      | `5`     | Number of warmup sandboxes started concurrently |
+| `SANDBOX_UID`                      | `1001`  | Shared host UID used by all sandbox languages |
 
 **Note:** Sandboxes are destroyed immediately after execution. The pool is automatically replenished in the background. Non-Python languages do not use pooling.
 

docs/SECURITY.md

@@ -106,7 +106,7 @@ Code is analyzed for potentially dangerous patterns:
 - **Seccomp filtering**: Restricts available system calls
 - **Cgroup limits**: Memory, CPU, and PID limits enforced
 - **rlimits**: File size, open files, and stack size restricted
-- **Non-root execution**: Code runs as uid 1001 (codeuser)
+- **Non-root execution**: Code runs as a shared non-root sandbox UID (default `1001`, configurable with `SANDBOX_UID`)
 
 **Note**: The API container requires `SYS_ADMIN` capability for nsjail to create namespaces and cgroups. No Docker socket is mounted.
 

src/config/languages.py

@@ -4,6 +4,7 @@
 execution settings (commands, resource multipliers, user IDs, etc.).
 """
 
+import os
 from dataclasses import dataclass, field
 from typing import Dict, Optional
 
@@ -26,12 +27,33 @@ class LanguageConfig:
     environment: Dict[str, str] = field(default_factory=dict)
 
 
+def _get_sandbox_user_id(default: int = 1001) -> int:
+    """Read the shared sandbox UID override from the environment."""
+    raw_value = os.getenv("SANDBOX_UID")
+    if raw_value in (None, ""):
+        return default
+    assert raw_value is not None
+
+    try:
+        user_id = int(raw_value)
+    except ValueError as exc:
+        raise ValueError(f"SANDBOX_UID must be an integer, got: {raw_value}") from exc
+
+    if user_id < 0:
+        raise ValueError(f"SANDBOX_UID must be >= 0, got: {user_id}")
+
+    return user_id
+
+
+SANDBOX_USER_ID = _get_sandbox_user_id()
+
+
 # All 13 supported languages with complete configuration
 LANGUAGES: Dict[str, LanguageConfig] = {
     "py": LanguageConfig(
         code="py",
         name="Python",
-        user_id=999,
+        user_id=SANDBOX_USER_ID,
         file_extension="py",
         execution_command="python3 -",
         uses_stdin=True,
@@ -41,7 +63,7 @@ class LanguageConfig:
     "js": LanguageConfig(
         code="js",
         name="JavaScript",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="js",
         execution_command="node",
         uses_stdin=True,
@@ -51,7 +73,7 @@ class LanguageConfig:
     "ts": LanguageConfig(
         code="ts",
         name="TypeScript",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="ts",
         execution_command="tsc code.ts --outDir . --module commonjs "
         "--target ES2019 && node code.js",
@@ -62,7 +84,7 @@ class LanguageConfig:
     "go": LanguageConfig(
         code="go",
         name="Go",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="go",
         execution_command="go build -o code code.go && ./code",
         uses_stdin=False,
@@ -72,7 +94,7 @@ class LanguageConfig:
     "java": LanguageConfig(
         code="java",
         name="Java",
-        user_id=999,
+        user_id=SANDBOX_USER_ID,
         file_extension="java",
         execution_command="javac Code.java && java Code",
         uses_stdin=False,
@@ -82,7 +104,7 @@ class LanguageConfig:
     "c": LanguageConfig(
         code="c",
         name="C",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="c",
         execution_command="gcc -o code code.c && ./code",
         uses_stdin=False,
@@ -92,7 +114,7 @@ class LanguageConfig:
     "cpp": LanguageConfig(
         code="cpp",
         name="C++",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="cpp",
         execution_command="g++ -o code code.cpp && ./code",
         uses_stdin=False,
@@ -102,7 +124,7 @@ class LanguageConfig:
     "php": LanguageConfig(
         code="php",
         name="PHP",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="php",
         execution_command="php",
         uses_stdin=True,
@@ -112,7 +134,7 @@ class LanguageConfig:
     "rs": LanguageConfig(
         code="rs",
         name="Rust",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="rs",
         execution_command="rustc code.rs -o code && ./code",
         uses_stdin=False,
@@ -122,7 +144,7 @@ class LanguageConfig:
     "r": LanguageConfig(
         code="r",
         name="R",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="r",
         execution_command="Rscript code.r",
         uses_stdin=False,
@@ -132,7 +154,7 @@ class LanguageConfig:
     "f90": LanguageConfig(
         code="f90",
         name="Fortran",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="f90",
         execution_command="gfortran -o code code.f90 && ./code",
         uses_stdin=False,
@@ -142,7 +164,7 @@ class LanguageConfig:
     "d": LanguageConfig(
         code="d",
         name="D",
-        user_id=0,
+        user_id=SANDBOX_USER_ID,
         file_extension="d",
         execution_command="ldc2 code.d -of=code && ./code",
         uses_stdin=False,
@@ -152,7 +174,7 @@ class LanguageConfig:
     "bash": LanguageConfig(
         code="bash",
         name="Bash",
-        user_id=1001,
+        user_id=SANDBOX_USER_ID,
         file_extension="sh",
         execution_command="bash",
         uses_stdin=True,

tests/unit/test_language_config.py

@@ -4,11 +4,12 @@
 functions, and correctness of all 13 supported languages.
 """
 
+import importlib
 import pytest
+import src.config.languages as languages_module
 
 from src.config.languages import (
     LANGUAGES,
-    LanguageConfig,
     get_language,
     get_supported_languages,
     is_supported_language,
@@ -52,7 +53,7 @@ def test_language_code_present(self, code):
     def test_language_config_is_frozen_dataclass(self, code):
         """Each language config must be a frozen LanguageConfig dataclass."""
         lang = LANGUAGES[code]
-        assert isinstance(lang, LanguageConfig)
+        assert isinstance(lang, languages_module.LanguageConfig)
         with pytest.raises(AttributeError):
             lang.code = "modified"
 
@@ -104,14 +105,24 @@ class TestPythonLanguage:
 
     def test_python_user_id(self):
         lang = get_language("py")
-        assert lang.user_id == 999
+        assert lang.user_id == 1001
 
     def test_python_uses_stdin(self):
         assert uses_stdin("py") is True
 
     def test_python_extension(self):
         assert get_file_extension("py") == "py"
 
+    def test_python_user_id_can_be_overridden(self, monkeypatch):
+        monkeypatch.setenv("SANDBOX_UID", "1002")
+        reloaded = importlib.reload(languages_module)
+        try:
+            assert reloaded.get_user_id_for_language("py") == 1002
+            assert reloaded.get_user_id_for_language("js") == 1002
+        finally:
+            monkeypatch.delenv("SANDBOX_UID", raising=False)
+            importlib.reload(languages_module)
+
 
 class TestStdinVsFileLanguages:
     """Test that stdin and file-based language sets are correct."""
@@ -137,7 +148,7 @@ class TestGetLanguage:
     def test_returns_config_for_known_code(self, code):
         result = get_language(code)
         assert result is not None
-        assert isinstance(result, LanguageConfig)
+        assert isinstance(result, languages_module.LanguageConfig)
         assert result.code == code
 
     def test_returns_none_for_unknown(self):
@@ -187,16 +198,28 @@ class TestGetUserIdForLanguage:
     """Test get_user_id_for_language() function."""
 
     def test_python_user_id(self):
-        assert get_user_id_for_language("py") == 999
+        assert get_user_id_for_language("py") == 1001
 
     def test_java_user_id(self):
-        assert get_user_id_for_language("java") == 999
+        assert get_user_id_for_language("java") == 1001
+
+    def test_all_languages_share_overridden_user_id(self, monkeypatch):
+        monkeypatch.setenv("SANDBOX_UID", "1003")
+        reloaded = importlib.reload(languages_module)
+        try:
+            assert reloaded.get_user_id_for_language("py") == 1003
+            assert reloaded.get_user_id_for_language("java") == 1003
+            assert reloaded.get_user_id_for_language("bash") == 1003
+            assert reloaded.get_user_id_for_language("d") == 1003
+        finally:
+            monkeypatch.delenv("SANDBOX_UID", raising=False)
+            importlib.reload(languages_module)
 
     def test_bash_user_id(self):
         assert get_user_id_for_language("bash") == 1001
 
     def test_d_user_id(self):
-        assert get_user_id_for_language("d") == 0
+        assert get_user_id_for_language("d") == 1001
 
     def test_raises_for_unknown(self):
         with pytest.raises(ValueError, match="Unsupported language"):

tests/unit/test_sandbox_manager.py

@@ -291,9 +291,8 @@ def test_get_user_id_for_language(self):
                 manager._base_dir = Path("/tmp/test")
                 manager._initialization_error = None
 
-                # Python user ID is 999
-                assert manager.get_user_id_for_language("py") == 999
-                # JS user ID is 1001
+                # All sandbox languages share the same non-root UID by default
+                assert manager.get_user_id_for_language("py") == 1001
                 assert manager.get_user_id_for_language("js") == 1001
 
     def test_close_is_noop(self):