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Fallback to local DNS when no other nameservers are known

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This commit is contained in:
rl1987 2018-08-13 18:31:27 +03:00
parent 275e831cea
commit 91fa12aedc
1 changed files with 38 additions and 17 deletions
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39
src/feature/relay/dns.c
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@ -1388,16 +1388,23 @@ configure_nameservers(int force)
evdns_set_log_fn(evdns_log_cb); evdns_set_log_fn(evdns_log_cb);
if (conf_fname) { if (conf_fname) {
log_debug(LD_FS, "stat()ing %s", 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", log_warn(LD_EXIT, "Unable to stat resolver configuration in '%s': %s",
conf_fname, strerror(errno)); conf_fname, strerror(errno));
goto err; missing_resolv_conf = 1;
} } else if (!force && resolv_conf_fname &&
if (!force && resolv_conf_fname && !strcmp(conf_fname,resolv_conf_fname) !strcmp(conf_fname,resolv_conf_fname)
&& st.st_mtime == resolv_conf_mtime) { && st.st_mtime == resolv_conf_mtime) {
log_info(LD_EXIT, "No change to '%s'", conf_fname); log_info(LD_EXIT, "No change to '%s'", conf_fname);
return 0; return 0;
} }
if (stat_res == 0 && st.st_size == 0)
missing_resolv_conf = 1;
if (nameservers_configured) { if (nameservers_configured) {
evdns_base_search_clear(the_evdns_base); evdns_base_search_clear(the_evdns_base);
evdns_base_clear_nameservers_and_suspend(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")); sandbox_intern_string("/etc/hosts"));
} }
#endif /* defined(DNS_OPTION_HOSTSFILE) && defined(USE_LIBSECCOMP) */ #endif /* defined(DNS_OPTION_HOSTSFILE) && defined(USE_LIBSECCOMP) */
if (!missing_resolv_conf) {
log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname); log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname);
if ((r = evdns_base_resolv_conf_parse(the_evdns_base, flags, if ((r = evdns_base_resolv_conf_parse(the_evdns_base, flags,
sandbox_intern_string(conf_fname)))) { sandbox_intern_string(conf_fname)))) {
log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers in '%s' (%d)", log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers "
conf_fname, conf_fname, r); "in '%s' (%d)", conf_fname, conf_fname, r);
goto err;
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) { if (evdns_base_count_nameservers(the_evdns_base) == 0) {
log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", conf_fname); log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.",
goto err; conf_fname);
} }
tor_free(resolv_conf_fname); tor_free(resolv_conf_fname);
resolv_conf_fname = tor_strdup(conf_fname); resolv_conf_fname = tor_strdup(conf_fname);
resolv_conf_mtime = st.st_mtime; 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");
}
if (nameservers_configured) if (nameservers_configured)
evdns_base_resume(the_evdns_base); evdns_base_resume(the_evdns_base);
} }