commit 91fa12aedc5f30e0f3703bed252e5b30ce374c5c Author: rl1987 rl1987@sdf.lonestar.org Date: Mon Aug 13 18:31:27 2018 +0300
Fallback to local DNS when no other nameservers are known --- src/feature/relay/dns.c | 55 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 38 insertions(+), 17 deletions(-)
diff --git a/src/feature/relay/dns.c b/src/feature/relay/dns.c index bc507d47f..f056629b8 100644 --- a/src/feature/relay/dns.c +++ b/src/feature/relay/dns.c @@ -1388,16 +1388,23 @@ configure_nameservers(int force) evdns_set_log_fn(evdns_log_cb); if (conf_fname) { log_debug(LD_FS, "stat()ing %s", conf_fname); - if (stat(sandbox_intern_string(conf_fname), &st)) { + int missing_resolv_conf = 0; + int stat_res = stat(sandbox_intern_string(conf_fname), &st); + + if (stat_res) { log_warn(LD_EXIT, "Unable to stat resolver configuration in '%s': %s", conf_fname, strerror(errno)); - goto err; - } - if (!force && resolv_conf_fname && !strcmp(conf_fname,resolv_conf_fname) + missing_resolv_conf = 1; + } else if (!force && resolv_conf_fname && + !strcmp(conf_fname,resolv_conf_fname) && st.st_mtime == resolv_conf_mtime) { log_info(LD_EXIT, "No change to '%s'", conf_fname); return 0; } + + if (stat_res == 0 && st.st_size == 0) + missing_resolv_conf = 1; + if (nameservers_configured) { evdns_base_search_clear(the_evdns_base); evdns_base_clear_nameservers_and_suspend(the_evdns_base); @@ -1410,20 +1417,34 @@ configure_nameservers(int force) sandbox_intern_string("/etc/hosts")); } #endif /* defined(DNS_OPTION_HOSTSFILE) && defined(USE_LIBSECCOMP) */ - log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname); - if ((r = evdns_base_resolv_conf_parse(the_evdns_base, flags, - sandbox_intern_string(conf_fname)))) { - log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers in '%s' (%d)", - conf_fname, conf_fname, r); - goto err; - } - if (evdns_base_count_nameservers(the_evdns_base) == 0) { - log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", conf_fname); - goto err; + + if (!missing_resolv_conf) { + log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname); + if ((r = evdns_base_resolv_conf_parse(the_evdns_base, flags, + sandbox_intern_string(conf_fname)))) { + log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers " + "in '%s' (%d)", conf_fname, conf_fname, r); + + if (r != 6) // "r = 6" means "no DNS servers were in resolv.conf" - + goto err; // in which case we expect libevent to add 127.0.0.1 as + // fallback. + } + if (evdns_base_count_nameservers(the_evdns_base) == 0) { + log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", + conf_fname); + } + + tor_free(resolv_conf_fname); + resolv_conf_fname = tor_strdup(conf_fname); + resolv_conf_mtime = st.st_mtime; + } else { + log_warn(LD_EXIT, "Could not read your DNS config from '%s' - " + "please investigate your DNS configuration. " + "This is possibly a problem. Meanwhile, falling" + " back to local DNS at 127.0.0.1.", conf_fname); + evdns_base_nameserver_ip_add(the_evdns_base, "127.0.0.1"); } - tor_free(resolv_conf_fname); - resolv_conf_fname = tor_strdup(conf_fname); - resolv_conf_mtime = st.st_mtime; + if (nameservers_configured) evdns_base_resume(the_evdns_base); }