diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc index 85f9f0d58..b6bfea8cb 100644 --- a/src/libmain/shared.cc +++ b/src/libmain/shared.cc @@ -15,9 +15,14 @@ #include #include #include -#include -#include -#include +#ifdef __linux__ +#include +#endif +#ifdef __GLIBC__ +#include +#include +#include +#endif #include @@ -121,21 +126,30 @@ static void preloadNSS() { been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to load its lookup libraries in the parent before any child gets a chance to. */ std::call_once(dns_resolve_flag, []() { - struct addrinfo *res = NULL; - - /* nss will only force the "local" (not through nscd) dns resolution if its on the LOCALDOMAIN. - We need the resolution to be done locally, as nscd socket will not be accessible in the - sandbox. */ - char * previous_env = getenv("LOCALDOMAIN"); - setenv("LOCALDOMAIN", "invalid", 1); - if (getaddrinfo("this.pre-initializes.the.dns.resolvers.invalid.", "http", NULL, &res) == 0) { - if (res) freeaddrinfo(res); - } - if (previous_env) { - setenv("LOCALDOMAIN", previous_env, 1); - } else { - unsetenv("LOCALDOMAIN"); +#ifdef __GLIBC__ + /* On linux, glibc will run every lookup through the nss layer. + * That means every lookup goes, by default, through nscd, which acts as a local + * cache. + * Because we run builds in a sandbox, we also remove access to nscd otherwise + * lookups would leak into the sandbox. + * + * But now we have a new problem, we need to make sure the nss_dns backend that + * does the dns lookups when nscd is not available is loaded or available. + * + * We can't make it available without leaking nix's environment, so instead we'll + * load the backend, and configure nss so it does not try to run dns lookups + * through nscd. + * + * This is technically only used for builtins:fetch* functions so we only care + * about dns. + * + * All other platforms are unaffected. + */ + if (dlopen (LIBNSS_DNS_SO, RTLD_NOW) == NULL) { + printMsg(Verbosity::lvlWarn, fmt("Unable to load nss_dns backend")); } + __nss_configure_lookup ("hosts", "dns"); +#endif }); }