gotd/listen.c

   1 /*
   2  * Copyright (c) 2022 Stefan Sperling <stsp@openbsd.org>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 #include "got_compat.h"
  18
  19 #include <sys/types.h>
  20 #include <sys/queue.h>
  21 #include <sys/socket.h>
  22 #include <sys/uio.h>
  23
  24 #include <errno.h>
  25 #include <event.h>
  26 #include <stdint.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <imsg.h>
  31 #include <limits.h>
  32 #include <signal.h>
  33 #include <unistd.h>
  34
  35 #include "got_error.h"
  36 #include "got_path.h"
  37
  38 #include "got_compat.h"
  39
  40 #include "gotd.h"
  41 #include "log.h"
  42 #include "listen.h"
  43
  44 #ifndef nitems
  45 #define nitems(_a)      (sizeof((_a)) / sizeof((_a)[0]))
  46 #endif
  47
  48 struct gotd_listen_client {
  49         STAILQ_ENTRY(gotd_listen_client)         entry;
  50         uint32_t                         id;
  51         int                              fd;
  52         uid_t                            euid;
  53 };
  54 STAILQ_HEAD(gotd_listen_clients, gotd_listen_client);
  55
  56 static struct gotd_listen_clients gotd_listen_clients[GOTD_CLIENT_TABLE_SIZE];
  57 static SIPHASH_KEY clients_hash_key;
  58 static volatile int listen_client_cnt;
  59 static int inflight;
  60
  61 struct gotd_uid_connection_counter {
  62         STAILQ_ENTRY(gotd_uid_connection_counter) entry;
  63         uid_t euid;
  64         int nconnections;
  65 };
  66 STAILQ_HEAD(gotd_client_uids, gotd_uid_connection_counter);
  67 static struct gotd_client_uids gotd_client_uids[GOTD_CLIENT_TABLE_SIZE];
  68 static SIPHASH_KEY uid_hash_key;
  69
  70 static struct {
  71         pid_t pid;
  72         const char *title;
  73         int fd;
  74         struct gotd_imsgev iev;
  75         struct gotd_imsgev pause;
  76         struct gotd_uid_connection_limit *connection_limits;
  77         size_t nconnection_limits;
  78 } gotd_listen;
  79
  80 static int inflight;
  81
  82 static void listen_shutdown(void);
  83
  84 static void
  85 listen_sighdlr(int sig, short event, void *arg)
  86 {
  87         /*
  88          * Normal signal handler rules don't apply because libevent
  89          * decouples for us.
  90          */
  91
  92         switch (sig) {
  93         case SIGHUP:
  94                 break;
  95         case SIGUSR1:
  96                 break;
  97         case SIGTERM:
  98         case SIGINT:
  99                 listen_shutdown();
 100                 /* NOTREACHED */
 101                 break;
 102         default:
 103                 fatalx("unexpected signal");
 104         }
 105 }
 106
 107 static uint64_t
 108 client_hash(uint32_t client_id)
 109 {
 110         return SipHash24(&clients_hash_key, &client_id, sizeof(client_id));
 111 }
 112
 113 static void
 114 add_client(struct gotd_listen_client *client)
 115 {
 116         uint64_t slot = client_hash(client->id) % nitems(gotd_listen_clients);
 117         STAILQ_INSERT_HEAD(&gotd_listen_clients[slot], client, entry);
 118         listen_client_cnt++;
 119 }
 120
 121 static struct gotd_listen_client *
 122 find_client(uint32_t client_id)
 123 {
 124         uint64_t slot;
 125         struct gotd_listen_client *c;
 126
 127         slot = client_hash(client_id) % nitems(gotd_listen_clients);
 128         STAILQ_FOREACH(c, &gotd_listen_clients[slot], entry) {
 129                 if (c->id == client_id)
 130                         return c;
 131         }
 132
 133         return NULL;
 134 }
 135
 136 static uint32_t
 137 get_client_id(void)
 138 {
 139         int duplicate = 0;
 140         uint32_t id;
 141
 142         do {
 143                 id = arc4random();
 144                 duplicate = (find_client(id) != NULL);
 145         } while (duplicate || id == 0);
 146
 147         return id;
 148 }
 149
 150 static uint64_t
 151 uid_hash(uid_t euid)
 152 {
 153         return SipHash24(&uid_hash_key, &euid, sizeof(euid));
 154 }
 155
 156 static void
 157 add_uid_connection_counter(struct gotd_uid_connection_counter *counter)
 158 {
 159         uint64_t slot = uid_hash(counter->euid) % nitems(gotd_client_uids);
 160         STAILQ_INSERT_HEAD(&gotd_client_uids[slot], counter, entry);
 161 }
 162
 163 static void
 164 remove_uid_connection_counter(struct gotd_uid_connection_counter *counter)
 165 {
 166         uint64_t slot = uid_hash(counter->euid) % nitems(gotd_client_uids);
 167         STAILQ_REMOVE(&gotd_client_uids[slot], counter,
 168             gotd_uid_connection_counter, entry);
 169 }
 170
 171 static struct gotd_uid_connection_counter *
 172 find_uid_connection_counter(uid_t euid)
 173 {
 174         uint64_t slot;
 175         struct gotd_uid_connection_counter *c;
 176
 177         slot = uid_hash(euid) % nitems(gotd_client_uids);
 178         STAILQ_FOREACH(c, &gotd_client_uids[slot], entry) {
 179                 if (c->euid == euid)
 180                         return c;
 181         }
 182
 183         return NULL;
 184 }
 185
 186 static const struct got_error *
 187 disconnect(struct gotd_listen_client *client)
 188 {
 189         struct gotd_uid_connection_counter *counter;
 190         uint64_t slot;
 191         int client_fd;
 192
 193         log_debug("client on fd %d disconnecting", client->fd);
 194
 195         slot = client_hash(client->id) % nitems(gotd_listen_clients);
 196         STAILQ_REMOVE(&gotd_listen_clients[slot], client,
 197             gotd_listen_client, entry);
 198
 199         counter = find_uid_connection_counter(client->euid);
 200         if (counter) {
 201                 if (counter->nconnections > 0)
 202                         counter->nconnections--;
 203                 if (counter->nconnections == 0) {
 204                         remove_uid_connection_counter(counter);
 205                         free(counter);
 206                 }
 207         }
 208
 209         client_fd = client->fd;
 210         free(client);
 211         inflight--;
 212         listen_client_cnt--;
 213         if (close(client_fd) == -1)
 214                 return got_error_from_errno("close");
 215
 216         return NULL;
 217 }
 218
 219 static int
 220 accept_reserve(int fd, struct sockaddr *addr, socklen_t *addrlen,
 221     int reserve, volatile int *counter)
 222 {
 223         int ret;
 224         int sock_flags = SOCK_NONBLOCK;
 225
 226 #ifdef SOCK_CLOEXEC
 227         sock_flags |= SOCK_CLOEXEC;
 228 #endif
 229
 230         if (getdtablecount() + reserve +
 231             ((*counter + 1) * GOTD_FD_NEEDED) >= getdtablesize()) {
 232                 log_debug("inflight fds exceeded");
 233                 errno = EMFILE;
 234                 return -1;
 235         }
 236 #ifdef __APPLE__
 237         /* TA:  silence warning from GCC. */
 238         (void)sock_flags;
 239         ret = accept(fd, addr, addrlen);
 240 #else
 241         ret = accept4(fd, addr, addrlen, sock_flags);
 242 #endif
 243
 244         if (ret > -1) {
 245                 (*counter)++;
 246         }
 247
 248         return ret;
 249 }
 250
 251 static void
 252 gotd_accept_paused(int fd, short event, void *arg)
 253 {
 254         event_add(&gotd_listen.iev.ev, NULL);
 255 }
 256
 257 static void
 258 gotd_accept(int fd, short event, void *arg)
 259 {
 260         struct gotd_imsgev *iev = arg;
 261         struct sockaddr_storage ss;
 262         struct timeval backoff;
 263         socklen_t len;
 264         int s = -1;
 265         struct gotd_listen_client *client = NULL;
 266         struct gotd_uid_connection_counter *counter = NULL;
 267         struct gotd_imsg_connect iconn;
 268         uid_t euid;
 269         gid_t egid;
 270
 271         backoff.tv_sec = 1;
 272         backoff.tv_usec = 0;
 273
 274         if (event_add(&gotd_listen.iev.ev, NULL) == -1) {
 275                 log_warn("event_add");
 276                 return;
 277         }
 278         if (event & EV_TIMEOUT)
 279                 return;
 280
 281         len = sizeof(ss);
 282
 283         /* Other backoff conditions apart from EMFILE/ENFILE? */
 284         s = accept_reserve(fd, (struct sockaddr *)&ss, &len, GOTD_FD_RESERVE,
 285             &inflight);
 286         if (s == -1) {
 287                 switch (errno) {
 288                 case EINTR:
 289                 case EWOULDBLOCK:
 290                 case ECONNABORTED:
 291                         return;
 292                 case EMFILE:
 293                 case ENFILE:
 294                         event_del(&gotd_listen.iev.ev);
 295                         evtimer_add(&gotd_listen.pause.ev, &backoff);
 296                         return;
 297                 default:
 298                         log_warn("accept");
 299                         return;
 300                 }
 301         }
 302
 303         if (listen_client_cnt >= GOTD_MAXCLIENTS)
 304                 goto err;
 305
 306         if (getpeereid(s, &euid, &egid) == -1) {
 307                 log_warn("getpeerid");
 308                 goto err;
 309         }
 310
 311         counter = find_uid_connection_counter(euid);
 312         if (counter == NULL) {
 313                 counter = calloc(1, sizeof(*counter));
 314                 if (counter == NULL) {
 315                         log_warn("%s: calloc", __func__);
 316                         goto err;
 317                 }
 318                 counter->euid = euid;
 319                 counter->nconnections = 1;
 320                 add_uid_connection_counter(counter);
 321         } else {
 322                 int max_connections = GOTD_MAX_CONN_PER_UID;
 323                 struct gotd_uid_connection_limit *limit;
 324
 325                 limit = gotd_find_uid_connection_limit(
 326                     gotd_listen.connection_limits,
 327                     gotd_listen.nconnection_limits, euid);
 328                 if (limit)
 329                         max_connections = limit->max_connections;
 330
 331                 if (counter->nconnections >= max_connections) {
 332                         log_warnx("maximum connections exceeded for uid %d",
 333                             euid);
 334                         goto err;
 335                 }
 336                 counter->nconnections++;
 337         }
 338
 339         client = calloc(1, sizeof(*client));
 340         if (client == NULL) {
 341                 log_warn("%s: calloc", __func__);
 342                 goto err;
 343         }
 344         client->id = get_client_id();
 345         client->fd = s;
 346         client->euid = euid;
 347         s = -1;
 348         add_client(client);
 349         log_debug("%s: new client connected on fd %d uid %d gid %d", __func__,
 350             client->fd, euid, egid);
 351
 352         memset(&iconn, 0, sizeof(iconn));
 353         iconn.client_id = client->id;
 354         iconn.euid = euid;
 355         iconn.egid = egid;
 356         s = dup(client->fd);
 357         if (s == -1) {
 358                 log_warn("%s: dup", __func__);
 359                 goto err;
 360         }
 361         if (gotd_imsg_compose_event(iev, GOTD_IMSG_CONNECT, PROC_LISTEN, s,
 362             &iconn, sizeof(iconn)) == -1) {
 363                 log_warn("imsg compose CONNECT");
 364                 goto err;
 365         }
 366
 367         return;
 368 err:
 369         inflight--;
 370         if (client)
 371                 disconnect(client);
 372         if (s != -1)
 373                 close(s);
 374 }
 375
 376 static const struct got_error *
 377 recv_disconnect(struct imsg *imsg)
 378 {
 379         struct gotd_imsg_disconnect idisconnect;
 380         size_t datalen;
 381         struct gotd_listen_client *client = NULL;
 382
 383         datalen = imsg->hdr.len - IMSG_HEADER_SIZE;
 384         if (datalen != sizeof(idisconnect))
 385                 return got_error(GOT_ERR_PRIVSEP_LEN);
 386         memcpy(&idisconnect, imsg->data, sizeof(idisconnect));
 387
 388         log_debug("client disconnecting");
 389
 390         client = find_client(idisconnect.client_id);
 391         if (client == NULL)
 392                 return got_error(GOT_ERR_CLIENT_ID);
 393
 394         return disconnect(client);
 395 }
 396
 397 static void
 398 listen_dispatch(int fd, short event, void *arg)
 399 {
 400         const struct got_error *err = NULL;
 401         struct gotd_imsgev *iev = arg;
 402         struct imsgbuf *ibuf = &iev->ibuf;
 403         struct imsg imsg;
 404         ssize_t n;
 405         int shut = 0;
 406
 407         if (event & EV_READ) {
 408                 if ((n = imsg_read(ibuf)) == -1 && errno != EAGAIN)
 409                         fatal("imsg_read error");
 410                 if (n == 0)     /* Connection closed. */
 411                         shut = 1;
 412         }
 413
 414         if (event & EV_WRITE) {
 415                 n = msgbuf_write(&ibuf->w);
 416                 if (n == -1 && errno != EAGAIN)
 417                         fatal("msgbuf_write");
 418                 if (n == 0)     /* Connection closed. */
 419                         shut = 1;
 420         }
 421
 422         for (;;) {
 423                 if ((n = imsg_get(ibuf, &imsg)) == -1)
 424                         fatal("%s: imsg_get", __func__);
 425                 if (n == 0)     /* No more messages. */
 426                         break;
 427
 428                 switch (imsg.hdr.type) {
 429                 case GOTD_IMSG_DISCONNECT:
 430                         err = recv_disconnect(&imsg);
 431                         if (err)
 432                                 log_warnx("disconnect: %s", err->msg);
 433                         break;
 434                 default:
 435                         log_debug("unexpected imsg %d", imsg.hdr.type);
 436                         break;
 437                 }
 438
 439                 imsg_free(&imsg);
 440         }
 441
 442         if (!shut) {
 443                 gotd_imsg_event_add(iev);
 444         } else {
 445                 /* This pipe is dead. Remove its event handler */
 446                 event_del(&iev->ev);
 447                 event_loopexit(NULL);
 448         }
 449 }
 450
 451 void
 452 listen_main(const char *title, int gotd_socket,
 453     struct gotd_uid_connection_limit *connection_limits,
 454     size_t nconnection_limits)
 455 {
 456         struct gotd_imsgev iev;
 457         struct event evsigint, evsigterm, evsighup, evsigusr1;
 458
 459         arc4random_buf(&clients_hash_key, sizeof(clients_hash_key));
 460         arc4random_buf(&uid_hash_key, sizeof(uid_hash_key));
 461
 462         gotd_listen.title = title;
 463         gotd_listen.pid = getpid();
 464         gotd_listen.fd = gotd_socket;
 465         gotd_listen.connection_limits = connection_limits;
 466         gotd_listen.nconnection_limits = nconnection_limits;
 467
 468         signal_set(&evsigint, SIGINT, listen_sighdlr, NULL);
 469         signal_set(&evsigterm, SIGTERM, listen_sighdlr, NULL);
 470         signal_set(&evsighup, SIGHUP, listen_sighdlr, NULL);
 471         signal_set(&evsigusr1, SIGUSR1, listen_sighdlr, NULL);
 472         signal(SIGPIPE, SIG_IGN);
 473
 474         signal_add(&evsigint, NULL);
 475         signal_add(&evsigterm, NULL);
 476         signal_add(&evsighup, NULL);
 477         signal_add(&evsigusr1, NULL);
 478
 479         imsg_init(&iev.ibuf, GOTD_FILENO_MSG_PIPE);
 480         iev.handler = listen_dispatch;
 481         iev.events = EV_READ;
 482         iev.handler_arg = NULL;
 483         event_set(&iev.ev, iev.ibuf.fd, EV_READ, listen_dispatch, &iev);
 484         if (event_add(&iev.ev, NULL) == -1)
 485                 fatalx("event add");
 486
 487         event_set(&gotd_listen.iev.ev, gotd_listen.fd, EV_READ | EV_PERSIST,
 488             gotd_accept, &iev);
 489         if (event_add(&gotd_listen.iev.ev, NULL))
 490                 fatalx("event add");
 491         evtimer_set(&gotd_listen.pause.ev, gotd_accept_paused, NULL);
 492
 493         event_dispatch();
 494
 495         listen_shutdown();
 496 }
 497
 498 static void
 499 listen_shutdown(void)
 500 {
 501         log_debug("shutting down");
 502
 503         free(gotd_listen.connection_limits);
 504         if (gotd_listen.fd != -1)
 505                 close(gotd_listen.fd);
 506
 507         exit(0);
 508 }