diff options
| -rw-r--r-- | changes/bug21900 | 4 | ||||
| -rw-r--r-- | configure.ac | 2 | ||||
| -rw-r--r-- | doc/tor.1.txt | 3 | ||||
| -rw-r--r-- | src/feature/relay/dns.c | 90 | ||||
| -rw-r--r-- | src/feature/relay/dns.h | 5 | ||||
| -rw-r--r-- | src/test/test_dns.c | 66 |
6 files changed, 152 insertions, 18 deletions
diff --git a/changes/bug21900 b/changes/bug21900 new file mode 100644 index 0000000000..686cb6c584 --- /dev/null +++ b/changes/bug21900 @@ -0,0 +1,4 @@ + o Minor bugfixes (DNS): + - Gracefully handle empty or absent resolve.conf file by falling + back to using localhost DNS service and hoping it works. Fixes + bug 21900; bugfix on 0.2.1.10-alpha. diff --git a/configure.ac b/configure.ac index a7405ec41d..b80aa821ad 100644 --- a/configure.ac +++ b/configure.ac @@ -812,6 +812,8 @@ fi dnl Now check for particular libevent functions. AC_CHECK_FUNCS([evutil_secure_rng_set_urandom_device_file \ evutil_secure_rng_add_bytes \ + evdns_base_get_nameserver_addr \ + ]) LIBS="$save_LIBS" diff --git a/doc/tor.1.txt b/doc/tor.1.txt index 406372433f..8729b8ed50 100644 --- a/doc/tor.1.txt +++ b/doc/tor.1.txt @@ -2211,7 +2211,8 @@ is non-zero): __filename__. The file format is the same as the standard Unix "**resolv.conf**" file (7). This option, like all other ServerDNS options, only affects name lookups that your server does on behalf of clients. - (Defaults to use the system DNS configuration.) + (Defaults to use the system DNS configuration or a localhost DNS service + in case no nameservers are found in a given configuration.) [[ServerDNSAllowBrokenConfig]] **ServerDNSAllowBrokenConfig** **0**|**1**:: If this option is false, Tor exits immediately if there are problems diff --git a/src/feature/relay/dns.c b/src/feature/relay/dns.c index bc507d47f6..371c2f5069 100644 --- a/src/feature/relay/dns.c +++ b/src/feature/relay/dns.c @@ -1357,6 +1357,41 @@ evdns_err_is_transient(int err) } } +/** + * Return number of configured nameservers in <b>the_evdns_base</b>. + */ +size_t +number_of_configured_nameservers(void) +{ + return evdns_base_count_nameservers(the_evdns_base); +} + +#ifdef HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR +/** + * Return address of configured nameserver in <b>the_evdns_base</b> + * at index <b>idx</b>. + */ +tor_addr_t * +configured_nameserver_address(const size_t idx) +{ + struct sockaddr_storage sa; + ev_socklen_t sa_len = sizeof(sa); + + if (evdns_base_get_nameserver_addr(the_evdns_base, (int)idx, + (struct sockaddr *)&sa, + sa_len) > 0) { + tor_addr_t *tor_addr = tor_malloc(sizeof(tor_addr_t)); + if (tor_addr_from_sockaddr(tor_addr, + (const struct sockaddr *)&sa, + NULL) == 0) { + return tor_addr; + } + } + + return NULL; +} +#endif + /** Configure eventdns nameservers if force is true, or if the configuration * has changed since the last time we called this function, or if we failed on * our last attempt. On Unix, this reads from /etc/resolv.conf or @@ -1388,16 +1423,23 @@ 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 +1452,34 @@ 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); } diff --git a/src/feature/relay/dns.h b/src/feature/relay/dns.h index 1dd6f903d1..5758ea4363 100644 --- a/src/feature/relay/dns.h +++ b/src/feature/relay/dns.h @@ -45,6 +45,11 @@ size_t dns_cache_handle_oom(time_t now, size_t min_remove_bytes); #ifdef DNS_PRIVATE #include "feature/relay/dns_structs.h" +size_t number_of_configured_nameservers(void); +#ifdef HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR +tor_addr_t *configured_nameserver_address(const size_t idx); +#endif + MOCK_DECL(STATIC int,dns_resolve_impl,(edge_connection_t *exitconn, int is_resolve,or_circuit_t *oncirc, char **hostname_out, int *made_connection_pending_out, cached_resolve_t **resolve_out)); diff --git a/src/test/test_dns.c b/src/test/test_dns.c index 8369f844f6..ea0fcf8c5e 100644 --- a/src/test/test_dns.c +++ b/src/test/test_dns.c @@ -1,6 +1,7 @@ /* Copyright (c) 2015-2018, The Tor Project, Inc. */ /* See LICENSE for licensing information */ +#include "orconfig.h" #include "core/or/or.h" #include "test/test.h" @@ -13,9 +14,71 @@ #include "core/or/edge_connection_st.h" #include "core/or/or_circuit_st.h" +#include "app/config/or_options_st.h" +#include "app/config/config.h" + +#include <event2/event.h> +#include <event2/dns.h> #define NS_MODULE dns +#ifdef HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR +#define NS_SUBMODULE configure_nameservers_fallback + +static or_options_t options = { + .ORPort_set = 1, +}; + +static const or_options_t * +mock_get_options(void) +{ + return &options; +} + +static void +NS(test_main)(void *arg) +{ + (void)arg; + tor_addr_t *nameserver_addr = NULL; + + MOCK(get_options, mock_get_options); + + options.ServerDNSResolvConfFile = (char *)"no_such_file!!!"; + + dns_init(); // calls configure_nameservers() + + tt_int_op(number_of_configured_nameservers(), OP_EQ, 1); + + nameserver_addr = configured_nameserver_address(0); + + tt_assert(tor_addr_family(nameserver_addr) == AF_INET); + tt_assert(tor_addr_eq_ipv4h(nameserver_addr, 0x7f000001)); + +#ifndef _WIN32 + tor_free(nameserver_addr); + + options.ServerDNSResolvConfFile = (char *)"/dev/null"; + + dns_init(); + + tt_int_op(number_of_configured_nameservers(), OP_EQ, 1); + + nameserver_addr = configured_nameserver_address(0); + + tt_assert(tor_addr_family(nameserver_addr) == AF_INET); + tt_assert(tor_addr_eq_ipv4h(nameserver_addr, 0x7f000001)); +#endif + + UNMOCK(get_options); + + done: + tor_free(nameserver_addr); + return; +} + +#undef NS_SUBMODULE +#endif + #define NS_SUBMODULE clip_ttl static void @@ -736,6 +799,9 @@ NS(test_main)(void *arg) #undef NS_SUBMODULE struct testcase_t dns_tests[] = { +#ifdef HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR + TEST_CASE(configure_nameservers_fallback), +#endif TEST_CASE(clip_ttl), TEST_CASE(resolve), TEST_CASE_ASPECT(resolve_impl, addr_is_ip_no_need_to_resolve), |