EvalState::realiseContext(): Allow access to the entire closure (backport #12045)

src/libexpr/eval.cc

@@ -347,6 +347,16 @@ void EvalState::allowPath(const StorePath & storePath)
         rootFS2->allowPrefix(CanonPath(store->toRealPath(storePath)));
 }
 
+void EvalState::allowClosure(const StorePath & storePath)
+{
+    if (!rootFS.dynamic_pointer_cast<AllowListSourceAccessor>()) return;
+
+    StorePathSet closure;
+    store->computeFSClosure(storePath, closure);
+    for (auto & p : closure)
+        allowPath(p);
+}
+
 void EvalState::allowAndSetStorePathString(const StorePath & storePath, Value & v)
 {
     allowPath(storePath);
@@ -3090,10 +3100,7 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
             allowPath(path);
             if (store->isInStore(path)) {
                 try {
-                    StorePathSet closure;
-                    store->computeFSClosure(store->toStorePath(path).first, closure);
-                    for (auto & p : closure)
-                        allowPath(p);
+                    allowClosure(store->toStorePath(path).first);
                 } catch (InvalidPath &) { }
             }
         }

src/libexpr/eval.hh

@@ -400,6 +400,11 @@ public:
      */
     void allowPath(const StorePath & storePath);
 
+    /**
+     * Allow access to the closure of a store path.
+     */
+    void allowClosure(const StorePath & storePath);
+
     /**
      * Allow access to a store path and return it as a string.
      */

src/libexpr/primops.cc

@@ -121,11 +121,9 @@ StringMap EvalState::realiseContext(const NixStringContext & context, StorePathS
     if (store != buildStore) copyClosure(*buildStore, *store, outputsToCopyAndAllow);
 
     if (isIFD) {
-        for (auto & outputPath : outputsToCopyAndAllow) {
-            /* Add the output of this derivations to the allowed
-            paths. */
-            allowPath(outputPath);
-        }
+        /* Allow access to the output closures of this derivation. */
+        for (auto & outputPath : outputsToCopyAndAllow)
+            allowClosure(outputPath);
     }
 
     return res;

tests/functional/import-from-derivation.nix

@@ -30,4 +30,23 @@ rec {
         echo -n BLA$(cat $src) > $out
       '';
   };
+
+  step1 = mkDerivation {
+    name = "step1";
+    buildCommand = ''
+      mkdir -p $out
+      echo 'foo' > $out/bla
+    '';
+  };
+
+  addPathExpr = mkDerivation {
+    name = "add-path";
+    inherit step1;
+    buildCommand = ''
+      mkdir -p $out
+      echo "builtins.path { path = \"$step1\"; sha256 = \"7ptL+pnrZXnSa5hwwB+2SXTLkcSb5264WGGokN8OXto=\"; }" > $out/default.nix
+    '';
+  };
+
+  importAddPathExpr = import addPathExpr;
 }

tests/functional/import-from-derivation.sh

@@ -6,6 +6,8 @@ TODO_NixOS
 
 clearStoreIfPossible
 
+export NIX_PATH=config="${config_nix}"
+
 if nix-instantiate --readonly-mode ./import-from-derivation.nix -A result; then
     echo "read-only evaluation of an imported derivation unexpectedly failed"
     exit 1
@@ -15,6 +17,9 @@ outPath=$(nix-build ./import-from-derivation.nix -A result --no-out-link)
 
 [ "$(cat "$outPath")" = FOO579 ]
 
+# Check that we can have access to the entire closure of a derivation output.
+nix build --no-link --restrict-eval -I src=. -f ./import-from-derivation.nix importAddPathExpr -v
+
 # FIXME: the next tests are broken on CA.
 if [[ -n "${NIX_TESTS_CA_BY_DEFAULT:-}" ]]; then
     exit 0