Don’t use entire /etc/nsswitch.conf file

The default nsswitch.conf(5) file in most distros can handle many
different things including host name, user names, groups, etc. In Nix,
we want to limit the amount of impurities that come from these things.
As a result, we should only allow nss to be used for gethostbyname(3)
and getservent(3).

/cc @Ericson2314

1 files changed, 7 insertions, 1 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 5b38bcf3c5ec..813d7e2c2d08 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2728,7 +2728,13 @@ void DerivationGoal::runChild()
                on. */
             if (fixedOutput) {
                 ss.push_back("/etc/resolv.conf");
-                ss.push_back("/etc/nsswitch.conf");
+
+                // Only use nss functions to resolve hosts and
+                // services. Don’t use it for anything else that may
+                // be configured for this system. This limits the
+                // potential impurities introduced in fixed outputs.
+                writeFile(chrootRootDir + "/etc/nsswitch.conf", "hosts: files dns\nservices: files\n");
+
                 ss.push_back("/etc/services");
                 ss.push_back("/etc/hosts");
                 if (pathExists("/var/run/nscd/socket"))