tests: validate that flakes do path traversal checking

Apparently we had zero test coverage of this, let's fix that.

Change-Id: I00c906daf5acfc01913562036ca88abbf63dd3d9

tests/functional2/flakes/test_pure.py

@@ -0,0 +1,67 @@
+from pathlib import Path
+from textwrap import dedent
+from functional2.testlib.fixtures import Nix
+import re
+
+
+def test_purity_traversal(nix: Nix, tmp_path: Path):
+    ERROR_RE = re.compile(r"error: access to absolute path '.+' is forbidden in pure eval mode")
+
+    flake_dir = tmp_path / 'flake'
+    flake_dir.mkdir()
+
+    evilpath = tmp_path / 'sekrit.txt'
+    evilpath.write_text('kitty kitty')
+
+    evilnix = tmp_path / 'default.nix'
+    evilnix.write_text('"woof"')
+
+    goodnix = flake_dir / 'good.nix'
+    goodnix.write_text("1")
+
+    nested_dir = flake_dir / 'nested' / 'nested2'
+    nested_dir.mkdir(parents=True)
+    (nested_dir / 'good.nix').write_text("1")
+
+    (flake_dir / 'evil-link').symlink_to(evilpath)
+    (flake_dir / 'evil-default-nix').symlink_to(tmp_path)
+    (flake_dir / 'less-evil-link').symlink_to(tmp_path / 'link-to-flake')
+    (tmp_path / 'link-to-flake').symlink_to(flake_dir / 'flake.nix')
+
+    (flake_dir / 'nested-good.nix').symlink_to('nested/nested2/good.nix')
+    (flake_dir / 'nested-bad.nix').symlink_to('nested/../../nested2/good.nix')
+
+    (flake_dir / 'flake.nix').write_text(dedent("""
+        {
+            inputs = {};
+            outputs = inputs: {
+                bad1 = "${@ABSPATH@}";
+                bad2 = builtins.readFile "${@ABSPATH@}";
+                bad3 = builtins.readFile @ABSPATH@;
+                bad4 = builtins.readFile ./evil-link;
+                bad5 = builtins.readFile "${./evil-link}";
+                bad6 = builtins.readFile ./less-evil-link;
+                bad7 = builtins.readFile "${./less-evil-link}";
+                bad8 = import ./evil-default-nix;
+                bad9 = import ./nested-bad.nix;
+
+                good1 = builtins.readFile "${inputs.self.outPath}/good.nix";
+                good2 = builtins.readFile ./good.nix;
+                good3 = builtins.readFile "${./good.nix}";
+                good4 = toString (import ./good.nix);
+                good5 = toString (import ./nested-good.nix);
+            };
+        }
+    """).replace('@ABSPATH@', str(evilpath.absolute())))
+
+    for idx in range(1, 10):
+        cmd = nix.nix(['eval', f'.#bad{idx}'], flake=True)
+        cmd.cwd = flake_dir
+        res = cmd.run().expect(1)
+        print(res.stderr_plain)
+        assert ERROR_RE.search(res.stderr_plain)
+    for idx in range(1, 6):
+        cmd = nix.nix(['eval', f'.#good{idx}'], flake=True)
+        cmd.cwd = flake_dir
+        res = cmd.run().expect(0)
+        assert res.stdout_plain == '"1"'

tests/functional2/testlib/fixtures.py

@@ -3,7 +3,7 @@ import json
 import subprocess
 from typing import Any
 from pathlib import Path
-from functools import partial, partialmethod
+from functools import partialmethod
 from functional2.testlib.terminal_code_eater import eat_terminal_codes
 import dataclasses
 
@@ -198,17 +198,21 @@ class Nix:
             settings.store = str(store_path)
         return settings
 
-    def nix_cmd(self, argv: list[str], allow_builds: bool = False):
+    def nix_cmd(self, argv: list[str], flake: bool = False):
         """
         Constructs a NixCommand with the appropriate settings.
         """
+        settings = self.settings()
+        if flake:
+            settings.feature('nix-command', 'flakes')
+
         return NixCommand(argv=argv,
                           cwd=self.test_root,
                           env=self.make_env(),
-                          settings=self.settings())
+                          settings=settings)
 
-    def nix(self, cmd: list[str], nix_exe: str = 'nix') -> NixCommand:
-        return self.nix_cmd([nix_exe, *cmd])
+    def nix(self, cmd: list[str], nix_exe: str = 'nix', flake: bool = False) -> NixCommand:
+        return self.nix_cmd([nix_exe, *cmd], flake=flake)
 
     nix_build = partialmethod(nix, nix_exe='nix-build')
     nix_shell = partialmethod(nix, nix_exe='nix-shell')