lib/resolver.c

   1 /* C-Ares integration to Quagga mainloop
   2  * Copyright (c) 2014-2015 Timo Teräs
   3  *
   4  * This file is free software: you may copy, redistribute and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 2 of the License, or
   7  * (at your option) any later version.
   8  */
   9
  10 #ifdef HAVE_CONFIG_H
  11 #include "config.h"
  12 #endif
  13
  14 #include <ares.h>
  15 #include <ares_version.h>
  16
  17 #include "typesafe.h"
  18 #include "jhash.h"
  19 #include "thread.h"
  20 #include "lib_errors.h"
  21 #include "resolver.h"
  22 #include "command.h"
  23 #include "xref.h"
  24 #include "vrf.h"
  25
  26 XREF_SETUP();
  27
  28 struct resolver_state {
  29         ares_channel channel;
  30         struct thread_master *master;
  31         struct thread *timeout;
  32 };
  33
  34 static struct resolver_state state;
  35 static bool resolver_debug;
  36
  37 /* a FD doesn't necessarily map 1:1 to a request;  we could be talking to
  38  * multiple caches simultaneously, to see which responds fastest.
  39  * Theoretically we could also be using the same fd for multiple lookups,
  40  * but the c-ares API guarantees an n:1 mapping for fd => channel.
  41  *
  42  * Either way c-ares makes that decision and we just need to deal with
  43  * whatever FDs it gives us.
  44  */
  45
  46 DEFINE_MTYPE_STATIC(LIB, ARES_FD, "c-ares (DNS) file descriptor information");
  47 PREDECL_HASH(resolver_fds);
  48
  49 struct resolver_fd {
  50         struct resolver_fds_item itm;
  51
  52         int fd;
  53         struct resolver_state *state;
  54         struct thread *t_read, *t_write;
  55 };
  56
  57 static int resolver_fd_cmp(const struct resolver_fd *a,
  58                            const struct resolver_fd *b)
  59 {
  60         return numcmp(a->fd, b->fd);
  61 }
  62
  63 static uint32_t resolver_fd_hash(const struct resolver_fd *item)
  64 {
  65         return jhash_1word(item->fd, 0xacd04c9e);
  66 }
  67
  68 DECLARE_HASH(resolver_fds, struct resolver_fd, itm, resolver_fd_cmp,
  69              resolver_fd_hash);
  70
  71 static struct resolver_fds_head resfds[1] = {INIT_HASH(resfds[0])};
  72
  73 static struct resolver_fd *resolver_fd_get(int fd,
  74                                            struct resolver_state *newstate)
  75 {
  76         struct resolver_fd ref = {.fd = fd}, *res;
  77
  78         res = resolver_fds_find(resfds, &ref);
  79         if (!res && newstate) {
  80                 res = XCALLOC(MTYPE_ARES_FD, sizeof(*res));
  81                 res->fd = fd;
  82                 res->state = newstate;
  83                 resolver_fds_add(resfds, res);
  84
  85                 if (resolver_debug)
  86                         zlog_debug("c-ares registered FD %d", fd);
  87         }
  88         return res;
  89 }
  90
  91 static void resolver_fd_drop_maybe(struct resolver_fd *resfd)
  92 {
  93         if (resfd->t_read || resfd->t_write)
  94                 return;
  95
  96         if (resolver_debug)
  97                 zlog_debug("c-ares unregistered FD %d", resfd->fd);
  98
  99         resolver_fds_del(resfds, resfd);
 100         XFREE(MTYPE_ARES_FD, resfd);
 101 }
 102
 103 /* end of FD housekeeping */
 104
 105 static void resolver_update_timeouts(struct resolver_state *r);
 106
 107 static void resolver_cb_timeout(struct thread *t)
 108 {
 109         struct resolver_state *r = THREAD_ARG(t);
 110
 111         ares_process(r->channel, NULL, NULL);
 112         resolver_update_timeouts(r);
 113 }
 114
 115 static void resolver_cb_socket_readable(struct thread *t)
 116 {
 117         struct resolver_fd *resfd = THREAD_ARG(t);
 118         struct resolver_state *r = resfd->state;
 119
 120         thread_add_read(r->master, resolver_cb_socket_readable, resfd,
 121                         resfd->fd, &resfd->t_read);
 122         /* ^ ordering important:
 123          * ares_process_fd may transitively call THREAD_OFF(resfd->t_read)
 124          * combined with resolver_fd_drop_maybe, so resfd may be free'd after!
 125          */
 126         ares_process_fd(r->channel, resfd->fd, ARES_SOCKET_BAD);
 127         resolver_update_timeouts(r);
 128 }
 129
 130 static void resolver_cb_socket_writable(struct thread *t)
 131 {
 132         struct resolver_fd *resfd = THREAD_ARG(t);
 133         struct resolver_state *r = resfd->state;
 134
 135         thread_add_write(r->master, resolver_cb_socket_writable, resfd,
 136                          resfd->fd, &resfd->t_write);
 137         /* ^ ordering important:
 138          * ares_process_fd may transitively call THREAD_OFF(resfd->t_write)
 139          * combined with resolver_fd_drop_maybe, so resfd may be free'd after!
 140          */
 141         ares_process_fd(r->channel, ARES_SOCKET_BAD, resfd->fd);
 142         resolver_update_timeouts(r);
 143 }
 144
 145 static void resolver_update_timeouts(struct resolver_state *r)
 146 {
 147         struct timeval *tv, tvbuf;
 148
 149         THREAD_OFF(r->timeout);
 150         tv = ares_timeout(r->channel, NULL, &tvbuf);
 151         if (tv) {
 152                 unsigned int timeoutms = tv->tv_sec * 1000 + tv->tv_usec / 1000;
 153
 154                 thread_add_timer_msec(r->master, resolver_cb_timeout, r,
 155                                       timeoutms, &r->timeout);
 156         }
 157 }
 158
 159 static void ares_socket_cb(void *data, ares_socket_t fd, int readable,
 160                            int writable)
 161 {
 162         struct resolver_state *r = (struct resolver_state *)data;
 163         struct resolver_fd *resfd;
 164
 165         resfd = resolver_fd_get(fd, (readable || writable) ? r : NULL);
 166         if (!resfd)
 167                 return;
 168
 169         assert(resfd->state == r);
 170
 171         if (!readable)
 172                 THREAD_OFF(resfd->t_read);
 173         else if (!resfd->t_read)
 174                 thread_add_read(r->master, resolver_cb_socket_readable, resfd,
 175                                 fd, &resfd->t_read);
 176
 177         if (!writable)
 178                 THREAD_OFF(resfd->t_write);
 179         else if (!resfd->t_write)
 180                 thread_add_write(r->master, resolver_cb_socket_writable, resfd,
 181                                  fd, &resfd->t_write);
 182
 183         resolver_fd_drop_maybe(resfd);
 184 }
 185
 186
 187 static void ares_address_cb(void *arg, int status, int timeouts,
 188                             struct hostent *he)
 189 {
 190         struct resolver_query *query = (struct resolver_query *)arg;
 191         union sockunion addr[16];
 192         void (*callback)(struct resolver_query *, const char *, int,
 193                          union sockunion *);
 194         size_t i;
 195
 196         callback = query->callback;
 197         query->callback = NULL;
 198
 199         if (status != ARES_SUCCESS) {
 200                 if (resolver_debug)
 201                         zlog_debug("[%p] Resolving failed (%s)",
 202                                    query, ares_strerror(status));
 203
 204                 callback(query, ares_strerror(status), -1, NULL);
 205                 return;
 206         }
 207
 208         for (i = 0; i < array_size(addr) && he->h_addr_list[i] != NULL; i++) {
 209                 memset(&addr[i], 0, sizeof(addr[i]));
 210                 addr[i].sa.sa_family = he->h_addrtype;
 211                 switch (he->h_addrtype) {
 212                 case AF_INET:
 213                         memcpy(&addr[i].sin.sin_addr,
 214                                (uint8_t *)he->h_addr_list[i], he->h_length);
 215                         break;
 216                 case AF_INET6:
 217                         memcpy(&addr[i].sin6.sin6_addr,
 218                                (uint8_t *)he->h_addr_list[i], he->h_length);
 219                         break;
 220                 }
 221         }
 222
 223         if (resolver_debug)
 224                 zlog_debug("[%p] Resolved with %d results", query, (int)i);
 225
 226         callback(query, NULL, i, &addr[0]);
 227 }
 228
 229 static void resolver_cb_literal(struct thread *t)
 230 {
 231         struct resolver_query *query = THREAD_ARG(t);
 232         void (*callback)(struct resolver_query *, const char *, int,
 233                          union sockunion *);
 234
 235         callback = query->callback;
 236         query->callback = NULL;
 237
 238         callback(query, ARES_SUCCESS, 1, &query->literal_addr);
 239 }
 240
 241 void resolver_resolve(struct resolver_query *query, int af, vrf_id_t vrf_id,
 242                       const char *hostname,
 243                       void (*callback)(struct resolver_query *, const char *,
 244                                        int, union sockunion *))
 245 {
 246         int ret;
 247
 248         if (hostname == NULL)
 249                 return;
 250
 251         if (query->callback != NULL) {
 252                 flog_err(
 253                         EC_LIB_RESOLVER,
 254                         "Trying to resolve '%s', but previous query was not finished yet",
 255                         hostname);
 256                 return;
 257         }
 258
 259         query->callback = callback;
 260         query->literal_cb = NULL;
 261
 262         ret = str2sockunion(hostname, &query->literal_addr);
 263         if (ret == 0) {
 264                 if (resolver_debug)
 265                         zlog_debug("[%p] Resolving '%s' (IP literal)",
 266                                    query, hostname);
 267
 268                 /* for consistency with proper name lookup, don't call the
 269                  * callback immediately; defer to thread loop
 270                  */
 271                 thread_add_timer_msec(state.master, resolver_cb_literal,
 272                                       query, 0, &query->literal_cb);
 273                 return;
 274         }
 275
 276         if (resolver_debug)
 277                 zlog_debug("[%p] Resolving '%s'", query, hostname);
 278
 279         ret = vrf_switch_to_netns(vrf_id);
 280         if (ret < 0) {
 281                 flog_err_sys(EC_LIB_SOCKET, "%s: Can't switch to VRF %u (%s)",
 282                              __func__, vrf_id, safe_strerror(errno));
 283                 return;
 284         }
 285         ares_gethostbyname(state.channel, hostname, af, ares_address_cb, query);
 286         ret = vrf_switchback_to_initial();
 287         if (ret < 0)
 288                 flog_err_sys(EC_LIB_SOCKET,
 289                              "%s: Can't switchback from VRF %u (%s)", __func__,
 290                              vrf_id, safe_strerror(errno));
 291         resolver_update_timeouts(&state);
 292 }
 293
 294 DEFUN(debug_resolver,
 295       debug_resolver_cmd,
 296       "[no] debug resolver",
 297       NO_STR
 298       DEBUG_STR
 299       "Debug DNS resolver actions\n")
 300 {
 301         resolver_debug = (argc == 2);
 302         return CMD_SUCCESS;
 303 }
 304
 305 static int resolver_config_write_debug(struct vty *vty);
 306 static struct cmd_node resolver_debug_node = {
 307         .name = "resolver debug",
 308         .node = RESOLVER_DEBUG_NODE,
 309         .prompt = "",
 310         .config_write = resolver_config_write_debug,
 311 };
 312
 313 static int resolver_config_write_debug(struct vty *vty)
 314 {
 315         if (resolver_debug)
 316                 vty_out(vty, "debug resolver\n");
 317         return 1;
 318 }
 319
 320
 321 void resolver_init(struct thread_master *tm)
 322 {
 323         struct ares_options ares_opts;
 324
 325         state.master = tm;
 326
 327         ares_opts = (struct ares_options){
 328                 .sock_state_cb = &ares_socket_cb,
 329                 .sock_state_cb_data = &state,
 330                 .timeout = 2,
 331                 .tries = 3,
 332         };
 333
 334         ares_init_options(&state.channel, &ares_opts,
 335                           ARES_OPT_SOCK_STATE_CB | ARES_OPT_TIMEOUT
 336                                   | ARES_OPT_TRIES);
 337
 338         install_node(&resolver_debug_node);
 339         install_element(CONFIG_NODE, &debug_resolver_cmd);
 340         install_element(ENABLE_NODE, &debug_resolver_cmd);
 341 }