From 91b4452b3a666cd0f78425313160957b61d761fd Mon Sep 17 00:00:00 2001
From: Las Safin <me@las.rs>
Date: Tue, 16 Jul 2024 19:41:18 +0000
Subject: [PATCH] Avoid accessing uninitialized settings in own init

The default value for the setting was evaluated by
calling a method on the object _being currently constructed_,
so we were using it before all fields were initialized.

This has been fixed by making the called method static,
and not using the previously used fields at all.

But functionality hasn't changed!
The fields were usually always zero (by chance?) anyway,
meaning the conditional path was always taken.

Thus the current logic has been kept, the code simplified,
and UB removed.

This was found with the helper of UBSan.
---
 src/libexpr/eval-settings.cc | 10 ++++------
 src/libexpr/eval-settings.hh |  2 +-
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/libexpr/eval-settings.cc b/src/libexpr/eval-settings.cc
index e2151aa7fc1..eb5761638a7 100644
--- a/src/libexpr/eval-settings.cc
+++ b/src/libexpr/eval-settings.cc
@@ -56,7 +56,7 @@ EvalSettings::EvalSettings(bool & readOnlyMode, EvalSettings::LookupPathHooks lo
         builtinsAbortOnWarn = true;
 }
 
-Strings EvalSettings::getDefaultNixPath() const
+Strings EvalSettings::getDefaultNixPath()
 {
     Strings res;
     auto add = [&](const Path & p, const std::string & s = std::string()) {
@@ -69,11 +69,9 @@ Strings EvalSettings::getDefaultNixPath() const
         }
     };
 
-    if (!restrictEval && !pureEval) {
-        add(getNixDefExpr() + "/channels");
-        add(rootChannelsDir() + "/nixpkgs", "nixpkgs");
-        add(rootChannelsDir());
-    }
+    add(getNixDefExpr() + "/channels");
+    add(rootChannelsDir() + "/nixpkgs", "nixpkgs");
+    add(rootChannelsDir());
 
     return res;
 }
diff --git a/src/libexpr/eval-settings.hh b/src/libexpr/eval-settings.hh
index b915ba530a0..89a42caba5d 100644
--- a/src/libexpr/eval-settings.hh
+++ b/src/libexpr/eval-settings.hh
@@ -43,7 +43,7 @@ struct EvalSettings : Config
 
     bool & readOnlyMode;
 
-    Strings getDefaultNixPath() const;
+    static Strings getDefaultNixPath();
 
     static bool isPseudoUrl(std::string_view s);