Factor out isRootUser function

src/libstore/globals.cc

@@ -2,7 +2,6 @@
 #include "current-process.hh"
 #include "archive.hh"
 #include "args.hh"
-#include "users.hh"
 #include "abstract-setting-to-json.hh"
 #include "compute-levels.hh"
 
@@ -57,7 +56,7 @@ Settings::Settings()
     , nixManDir(canonPath(NIX_MAN_DIR))
     , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
-    buildUsersGroup = getuid() == 0 ? "nixbld" : "";
+    buildUsersGroup = isRootUser() ? "nixbld" : "";
     allowSymlinkedStore = getEnv("NIX_IGNORE_SYMLINK_STORE") == "1";
 
     auto sslOverride = getEnv("NIX_SSL_CERT_FILE").value_or(getEnv("SSL_CERT_FILE").value_or(""));

src/libstore/globals.hh

@@ -5,6 +5,7 @@
 #include "config.hh"
 #include "environment-variables.hh"
 #include "experimental-features.hh"
+#include "users.hh"
 
 #include <map>
 #include <limits>
@@ -665,7 +666,7 @@ public:
     Setting<bool> sandboxFallback{this, true, "sandbox-fallback",
         "Whether to disable sandboxing when the kernel doesn't allow it."};
 
-    Setting<bool> requireDropSupplementaryGroups{this, getuid() == 0, "require-drop-supplementary-groups",
+    Setting<bool> requireDropSupplementaryGroups{this, isRootUser(), "require-drop-supplementary-groups",
         R"(
           Following the principle of least privilege,
           Nix will attempt to drop supplementary groups when building with sandboxing.

src/libstore/local-store.cc

@@ -16,6 +16,7 @@
 #include "posix-fs-canonicalise.hh"
 #include "posix-source-accessor.hh"
 #include "keys.hh"
+#include "users.hh"
 
 #include <iostream>
 #include <algorithm>
@@ -223,7 +224,7 @@ LocalStore::LocalStore(const Params & params)
 
     /* Optionally, create directories and set permissions for a
        multi-user install. */
-    if (getuid() == 0 && settings.buildUsersGroup != "") {
+    if (isRootUser() && settings.buildUsersGroup != "") {
         mode_t perm = 01775;
 
         struct group * gr = getgrnam(settings.buildUsersGroup.get().c_str());
@@ -573,7 +574,7 @@ void LocalStore::openDB(State & state, bool create)
 void LocalStore::makeStoreWritable()
 {
 #if __linux__
-    if (getuid() != 0) return;
+    if (!isRootUser()) return;
     /* Check if /nix/store is on a read-only mount. */
     struct statvfs stat;
     if (statvfs(realStoreDir.get().c_str(), &stat) != 0)
@@ -1570,7 +1571,7 @@ static void makeMutable(const Path & path)
 /* Upgrade from schema 6 (Nix 0.15) to schema 7 (Nix >= 1.3). */
 void LocalStore::upgradeStore7()
 {
-    if (getuid() != 0) return;
+    if (!isRootUser()) return;
     printInfo("removing immutable bits from the Nix store (this may take a while)...");
     makeMutable(realStoreDir);
 }

src/libstore/lock.cc

@@ -2,6 +2,7 @@
 #include "file-system.hh"
 #include "globals.hh"
 #include "pathlocks.hh"
+#include "users.hh"
 
 #include <pwd.h>
 #include <grp.h>
@@ -192,10 +193,10 @@ std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useUserNamespace)
 bool useBuildUsers()
 {
     #if __linux__
-    static bool b = (settings.buildUsersGroup != "" || settings.autoAllocateUids) && getuid() == 0;
+    static bool b = (settings.buildUsersGroup != "" || settings.autoAllocateUids) && isRootUser();
     return b;
     #elif __APPLE__
-    static bool b = settings.buildUsersGroup != "" && getuid() == 0;
+    static bool b = settings.buildUsersGroup != "" && isRootUser();
     return b;
     #else
     return false;

src/libstore/profiles.cc

@@ -308,7 +308,7 @@ std::string optimisticLockProfile(const Path & profile)
 Path profilesDir()
 {
     auto profileRoot =
-        (getuid() == 0)
+        isRootUser()
         ? rootProfilesDir()
         : createNixStateDir() + "/profiles";
     createDirs(profileRoot);
@@ -332,7 +332,7 @@ Path getDefaultProfile()
         // Backwards compatibiliy measure: Make root's profile available as
         // `.../default` as it's what NixOS and most of the init scripts expect
         Path globalProfileLink = settings.nixStateDir + "/profiles/default";
-        if (getuid() == 0 && !pathExists(globalProfileLink)) {
+        if (isRootUser() && !pathExists(globalProfileLink)) {
             replaceSymlink(profile, globalProfileLink);
         }
         return absPath(readLink(profileLink), dirOf(profileLink));

src/libstore/store-api.cc

@@ -1307,7 +1307,7 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
         #if __linux__
         else if (!pathExists(stateDir)
             && params.empty()
-            && getuid() != 0
+            && !isRootUser()
             && !getEnv("NIX_STORE_DIR").has_value()
             && !getEnv("NIX_STATE_DIR").has_value())
         {

src/libutil/users.cc

@@ -113,4 +113,9 @@ std::string expandTilde(std::string_view path)
         return std::string(path);
 }
 
+
+bool isRootUser() {
+    return getuid() == 0;
+}
+
 }

src/libutil/users.hh

@@ -55,4 +55,10 @@ Path createNixStateDir();
  */
 std::string expandTilde(std::string_view path);
 
+
+/**
+ * Is the current user UID 0 on Unix?
+ */
+bool isRootUser();
+
 }

src/nix-build/nix-build.cc

@@ -24,6 +24,7 @@
 #include "common-eval-args.hh"
 #include "attr-path.hh"
 #include "legacy.hh"
+#include "users.hh"
 
 using namespace nix;
 using namespace std::string_literals;
@@ -572,8 +573,9 @@ static void main_nix_build(int argc, char * * argv)
                 "BASH=%5%; "
                 "set +e; "
                 R"s([ -n "$PS1" -a -z "$NIX_SHELL_PRESERVE_PROMPT" ] && )s" +
-                (getuid() == 0 ? R"s(PS1='\n\[\033[1;31m\][nix-shell:\w]\$\[\033[0m\] '; )s"
-                               : R"s(PS1='\n\[\033[1;32m\][nix-shell:\w]\$\[\033[0m\] '; )s") +
+                (isRootUser()
+                    ? R"s(PS1='\n\[\033[1;31m\][nix-shell:\w]\$\[\033[0m\] '; )s"
+                    : R"s(PS1='\n\[\033[1;32m\][nix-shell:\w]\$\[\033[0m\] '; )s") +
                 "if [ \"$(type -t runHook)\" = function ]; then runHook shellHook; fi; "
                 "unset NIX_ENFORCE_PURITY; "
                 "shopt -u nullglob; "

src/nix-env/nix-env.cc

@@ -1414,7 +1414,7 @@ static int main_nix_env(int argc, char * * argv)
                 replaceSymlink(
                     defaultChannelsDir(),
                     nixExprPath + "/channels");
-                if (getuid() != 0)
+                if (!isRootUser())
                     replaceSymlink(
                         rootChannelsDir(),
                         nixExprPath + "/channels_root");

src/nix/main.cc

@@ -348,7 +348,7 @@ void mainWrapped(int argc, char * * argv)
     initGC();
 
     #if __linux__
-    if (getuid() == 0) {
+    if (isRootUser()) {
         try {
             saveMountNamespace();
             if (unshare(CLONE_NEWNS) == -1)