lib/tevent/tevent_signal.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    common events code for signal events
   5
   6    Copyright (C) Andrew Tridgell        2007
   7
   8      ** NOTE! The following LGPL license applies to the tevent
   9      ** library. This does NOT imply that all of Samba is released
  10      ** under the LGPL
  11
  12    This library is free software; you can redistribute it and/or
  13    modify it under the terms of the GNU Lesser General Public
  14    License as published by the Free Software Foundation; either
  15    version 3 of the License, or (at your option) any later version.
  16
  17    This library is distributed in the hope that it will be useful,
  18    but WITHOUT ANY WARRANTY; without even the implied warranty of
  19    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20    Lesser General Public License for more details.
  21
  22    You should have received a copy of the GNU Lesser General Public
  23    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  24 */
  25
  26 #include "replace.h"
  27 #include "system/filesys.h"
  28 #include "system/wait.h"
  29 #include "tevent.h"
  30 #include "tevent_internal.h"
  31 #include "tevent_util.h"
  32
  33 /* maximum number of SA_SIGINFO signals to hold in the queue.
  34   NB. This *MUST* be a power of 2, in order for the ring buffer
  35   wrap to work correctly. Thanks to Petr Vandrovec <petr@vandrovec.name>
  36   for this. */
  37
  38 #define TEVENT_SA_INFO_QUEUE_COUNT 256
  39
  40 size_t tevent_num_signals(void)
  41 {
  42         return TEVENT_NUM_SIGNALS;
  43 }
  44
  45 size_t tevent_sa_info_queue_count(void)
  46 {
  47         return TEVENT_SA_INFO_QUEUE_COUNT;
  48 }
  49
  50 struct tevent_sigcounter {
  51         uint32_t count;
  52         uint32_t seen;
  53 };
  54
  55 #if defined(HAVE___SYNC_FETCH_AND_ADD)
  56 #define TEVENT_SIG_INCREMENT(s) __sync_fetch_and_add(&((s).count), 1)
  57 #elif defined(HAVE_ATOMIC_ADD_32)
  58 #define TEVENT_SIG_INCREMENT(s) atomic_add_32(&((s).count), 1)
  59 #else
  60 #define TEVENT_SIG_INCREMENT(s) (s).count++
  61 #endif
  62 #define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
  63 #define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)
  64
  65 struct tevent_common_signal_list {
  66         struct tevent_common_signal_list *prev, *next;
  67         struct tevent_signal *se;
  68 };
  69
  70 /*
  71   the poor design of signals means that this table must be static global
  72 */
  73 static struct tevent_sig_state {
  74         struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
  75         struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
  76         struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
  77         struct tevent_sigcounter got_signal;
  78 #ifdef SA_SIGINFO
  79         /* with SA_SIGINFO we get quite a lot of info per signal */
  80         siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
  81         struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
  82 #endif
  83 } *sig_state;
  84
  85 /*
  86   return number of sigcounter events not processed yet
  87 */
  88 static uint32_t tevent_sig_count(struct tevent_sigcounter s)
  89 {
  90         return s.count - s.seen;
  91 }
  92
  93 /*
  94   signal handler - redirects to registered signals
  95 */
  96 static void tevent_common_signal_handler(int signum)
  97 {
  98         char c = 0;
  99         struct tevent_common_signal_list *sl;
 100         struct tevent_context *ev = NULL;
 101         int saved_errno = errno;
 102
 103         TEVENT_SIG_INCREMENT(sig_state->signal_count[signum]);
 104         TEVENT_SIG_INCREMENT(sig_state->got_signal);
 105
 106         /* Write to each unique event context. */
 107         for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
 108                 if (sl->se->event_ctx && sl->se->event_ctx != ev) {
 109                         ev = sl->se->event_ctx;
 110                         /* doesn't matter if this pipe overflows */
 111                         (void) write(ev->pipe_fds[1], &c, 1);
 112                 }
 113         }
 114
 115         errno = saved_errno;
 116 }
 117
 118 #ifdef SA_SIGINFO
 119 /*
 120   signal handler with SA_SIGINFO - redirects to registered signals
 121 */
 122 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 123                                               void *uctx)
 124 {
 125         uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
 126         /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
 127          * is the base of the unprocessed signals in the ringbuffer. */
 128         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 129                                 TEVENT_SA_INFO_QUEUE_COUNT;
 130         sig_state->sig_info[signum][ofs] = *info;
 131
 132         tevent_common_signal_handler(signum);
 133
 134         /* handle SA_SIGINFO */
 135         if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
 136                 /* we've filled the info array - block this signal until
 137                    these ones are delivered */
 138 #ifdef HAVE_UCONTEXT_T
 139                 /*
 140                  * This is the only way for this to work.
 141                  * By default signum is blocked inside this
 142                  * signal handler using a temporary mask,
 143                  * but what we really need to do now is
 144                  * block it in the callers mask, so it
 145                  * stays blocked when the temporary signal
 146                  * handler mask is replaced when we return
 147                  * from here. The callers mask can be found
 148                  * in the ucontext_t passed in as the
 149                  * void *uctx argument.
 150                  */
 151                 ucontext_t *ucp = (ucontext_t *)uctx;
 152                 sigaddset(&ucp->uc_sigmask, signum);
 153 #else
 154                 /*
 155                  * WARNING !!! WARNING !!!!
 156                  *
 157                  * This code doesn't work.
 158                  * By default signum is blocked inside this
 159                  * signal handler, but calling sigprocmask
 160                  * modifies the temporary signal mask being
 161                  * used *inside* this handler, which will be
 162                  * replaced by the callers signal mask once
 163                  * we return from here. See Samba
 164                  * bug #9550 for details.
 165                  */
 166                 sigset_t set;
 167                 sigemptyset(&set);
 168                 sigaddset(&set, signum);
 169                 sigprocmask(SIG_BLOCK, &set, NULL);
 170 #endif
 171                 TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
 172         }
 173 }
 174 #endif
 175
 176 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 177 {
 178         if (sig_state->sig_handlers[sl->se->signum]) {
 179                 DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 180         }
 181         return 0;
 182 }
 183
 184 /*
 185   destroy a signal event
 186 */
 187 static int tevent_signal_destructor(struct tevent_signal *se)
 188 {
 189         struct tevent_common_signal_list *sl =
 190                 talloc_get_type_abort(se->additional_data,
 191                 struct tevent_common_signal_list);
 192
 193         if (se->event_ctx) {
 194                 struct tevent_context *ev = se->event_ctx;
 195
 196                 DLIST_REMOVE(ev->signal_events, se);
 197
 198                 if (ev->signal_events == NULL && ev->pipe_fde != NULL) {
 199                         /*
 200                          * This was the last signal. Destroy the pipe.
 201                          */
 202                         TALLOC_FREE(ev->pipe_fde);
 203
 204                         close(ev->pipe_fds[0]);
 205                         close(ev->pipe_fds[1]);
 206                 }
 207         }
 208
 209         talloc_free(sl);
 210
 211         if (sig_state->sig_handlers[se->signum] == NULL) {
 212                 /* restore old handler, if any */
 213                 if (sig_state->oldact[se->signum]) {
 214                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 215                         sig_state->oldact[se->signum] = NULL;
 216                 }
 217 #ifdef SA_SIGINFO
 218                 if (se->sa_flags & SA_SIGINFO) {
 219                         if (sig_state->sig_info[se->signum]) {
 220                                 talloc_free(sig_state->sig_info[se->signum]);
 221                                 sig_state->sig_info[se->signum] = NULL;
 222                         }
 223                 }
 224 #endif
 225         }
 226
 227         return 0;
 228 }
 229
 230 /*
 231   this is part of the pipe hack needed to avoid the signal race condition
 232 */
 233 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 234                                 uint16_t flags, void *_private)
 235 {
 236         char c[16];
 237         /* its non-blocking, doesn't matter if we read too much */
 238         (void) read(fde->fd, c, sizeof(c));
 239 }
 240
 241 /*
 242   add a signal event
 243   return NULL on failure (memory allocation error)
 244 */
 245 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 246                                                TALLOC_CTX *mem_ctx,
 247                                                int signum,
 248                                                int sa_flags,
 249                                                tevent_signal_handler_t handler,
 250                                                void *private_data,
 251                                                const char *handler_name,
 252                                                const char *location)
 253 {
 254         struct tevent_signal *se;
 255         struct tevent_common_signal_list *sl;
 256         sigset_t set, oldset;
 257
 258         if (signum >= TEVENT_NUM_SIGNALS) {
 259                 errno = EINVAL;
 260                 return NULL;
 261         }
 262
 263         /* the sig_state needs to be on a global context as it can last across
 264            multiple event contexts */
 265         if (sig_state == NULL) {
 266                 sig_state = talloc_zero(NULL, struct tevent_sig_state);
 267                 if (sig_state == NULL) {
 268                         return NULL;
 269                 }
 270         }
 271
 272         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 273         if (se == NULL) return NULL;
 274
 275         se->event_ctx           = ev;
 276         se->signum              = signum;
 277         se->sa_flags            = sa_flags;
 278         se->handler             = handler;
 279         se->private_data        = private_data;
 280         se->handler_name        = handler_name;
 281         se->location            = location;
 282         se->additional_data     = NULL;
 283
 284         sl = talloc(se, struct tevent_common_signal_list);
 285         if (!sl) {
 286                 talloc_free(se);
 287                 return NULL;
 288         }
 289         sl->se = se;
 290         se->additional_data     = sl;
 291
 292         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 293         if (!talloc_reference(se, sig_state)) {
 294                 talloc_free(se);
 295                 return NULL;
 296         }
 297
 298         /* we need to setup the pipe hack handler if not already
 299            setup */
 300         if (ev->pipe_fde == NULL) {
 301                 if (pipe(ev->pipe_fds) == -1) {
 302                         talloc_free(se);
 303                         return NULL;
 304                 }
 305                 ev_set_blocking(ev->pipe_fds[0], false);
 306                 ev_set_blocking(ev->pipe_fds[1], false);
 307                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 308                                              TEVENT_FD_READ,
 309                                              signal_pipe_handler, NULL);
 310                 if (!ev->pipe_fde) {
 311                         close(ev->pipe_fds[0]);
 312                         close(ev->pipe_fds[1]);
 313                         talloc_free(se);
 314                         return NULL;
 315                 }
 316         }
 317
 318         /* only install a signal handler if not already installed */
 319         if (sig_state->sig_handlers[signum] == NULL) {
 320                 struct sigaction act;
 321                 ZERO_STRUCT(act);
 322                 act.sa_handler = tevent_common_signal_handler;
 323                 act.sa_flags = sa_flags;
 324 #ifdef SA_SIGINFO
 325                 if (sa_flags & SA_SIGINFO) {
 326                         act.sa_handler   = NULL;
 327                         act.sa_sigaction = tevent_common_signal_handler_info;
 328                         if (sig_state->sig_info[signum] == NULL) {
 329                                 sig_state->sig_info[signum] =
 330                                         talloc_zero_array(sig_state, siginfo_t,
 331                                                           TEVENT_SA_INFO_QUEUE_COUNT);
 332                                 if (sig_state->sig_info[signum] == NULL) {
 333                                         talloc_free(se);
 334                                         return NULL;
 335                                 }
 336                         }
 337                 }
 338 #endif
 339                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 340                 if (sig_state->oldact[signum] == NULL) {
 341                         talloc_free(se);
 342                         return NULL;
 343                 }
 344                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 345                         talloc_free(se);
 346                         return NULL;
 347                 }
 348         }
 349
 350         DLIST_ADD(se->event_ctx->signal_events, se);
 351
 352         /* Make sure the signal doesn't come in while we're mangling list. */
 353         sigemptyset(&set);
 354         sigaddset(&set, signum);
 355         sigprocmask(SIG_BLOCK, &set, &oldset);
 356         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 357         sigprocmask(SIG_SETMASK, &oldset, NULL);
 358
 359         talloc_set_destructor(se, tevent_signal_destructor);
 360         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 361
 362         return se;
 363 }
 364
 365 struct tevent_se_exists {
 366         struct tevent_se_exists **myself;
 367 };
 368
 369 static int tevent_se_exists_destructor(struct tevent_se_exists *s)
 370 {
 371         *s->myself = NULL;
 372         return 0;
 373 }
 374
 375 /*
 376   check if a signal is pending
 377   return != 0 if a signal was pending
 378 */
 379 int tevent_common_check_signal(struct tevent_context *ev)
 380 {
 381         int i;
 382
 383         if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
 384                 return 0;
 385         }
 386
 387         for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
 388                 struct tevent_common_signal_list *sl, *next;
 389                 struct tevent_sigcounter counter = sig_state->signal_count[i];
 390                 uint32_t count = tevent_sig_count(counter);
 391 #ifdef SA_SIGINFO
 392                 /* Ensure we null out any stored siginfo_t entries
 393                  * after processing for debugging purposes. */
 394                 bool clear_processed_siginfo = false;
 395 #endif
 396
 397                 if (count == 0) {
 398                         continue;
 399                 }
 400                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 401                         struct tevent_signal *se = sl->se;
 402                         struct tevent_se_exists *exists;
 403
 404                         next = sl->next;
 405
 406                         /*
 407                          * We have to be careful to not touch "se"
 408                          * after it was deleted in its handler. Thus
 409                          * we allocate a child whose destructor will
 410                          * tell by nulling out itself that its parent
 411                          * is gone.
 412                          */
 413                         exists = talloc(se, struct tevent_se_exists);
 414                         if (exists == NULL) {
 415                                 continue;
 416                         }
 417                         exists->myself = &exists;
 418                         talloc_set_destructor(
 419                                 exists, tevent_se_exists_destructor);
 420
 421 #ifdef SA_SIGINFO
 422                         if (se->sa_flags & SA_SIGINFO) {
 423                                 uint32_t j;
 424
 425                                 clear_processed_siginfo = true;
 426
 427                                 for (j=0;j<count;j++) {
 428                                         /* sig_state->signal_count[i].seen
 429                                          * % TEVENT_SA_INFO_QUEUE_COUNT is
 430                                          * the base position of the unprocessed
 431                                          * signals in the ringbuffer. */
 432                                         uint32_t ofs = (counter.seen + j)
 433                                                 % TEVENT_SA_INFO_QUEUE_COUNT;
 434                                         se->handler(ev, se, i, 1,
 435                                                     (void*)&sig_state->sig_info[i][ofs],
 436                                                     se->private_data);
 437                                         if (!exists) {
 438                                                 break;
 439                                         }
 440                                 }
 441 #ifdef SA_RESETHAND
 442                                 if (exists && (se->sa_flags & SA_RESETHAND)) {
 443                                         talloc_free(se);
 444                                 }
 445 #endif
 446                                 talloc_free(exists);
 447                                 continue;
 448                         }
 449 #endif
 450                         se->handler(ev, se, i, count, NULL, se->private_data);
 451 #ifdef SA_RESETHAND
 452                         if (exists && (se->sa_flags & SA_RESETHAND)) {
 453                                 talloc_free(se);
 454                         }
 455 #endif
 456                         talloc_free(exists);
 457                 }
 458
 459 #ifdef SA_SIGINFO
 460                 if (clear_processed_siginfo) {
 461                         uint32_t j;
 462                         for (j=0;j<count;j++) {
 463                                 uint32_t ofs = (counter.seen + j)
 464                                         % TEVENT_SA_INFO_QUEUE_COUNT;
 465                                 memset((void*)&sig_state->sig_info[i][ofs],
 466                                         '\0',
 467                                         sizeof(siginfo_t));
 468                         }
 469                 }
 470 #endif
 471
 472                 TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
 473                 TEVENT_SIG_SEEN(sig_state->got_signal, count);
 474
 475 #ifdef SA_SIGINFO
 476                 if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
 477                         /* We'd filled the queue, unblock the
 478                            signal now the queue is empty again.
 479                            Note we MUST do this after the
 480                            TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
 481                            call to prevent a new signal running
 482                            out of room in the sig_state->sig_info[i][]
 483                            ring buffer. */
 484                         sigset_t set;
 485                         sigemptyset(&set);
 486                         sigaddset(&set, i);
 487                         TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
 488                                  tevent_sig_count(sig_state->sig_blocked[i]));
 489                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 490                 }
 491 #endif
 492         }
 493
 494         return 1;
 495 }
 496
 497 void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
 498 {
 499         struct tevent_common_signal_list *sl =
 500                 talloc_get_type_abort(se->additional_data,
 501                 struct tevent_common_signal_list);
 502
 503         tevent_common_signal_list_destructor(sl);
 504
 505         if (sig_state->sig_handlers[se->signum] == NULL) {
 506                 if (sig_state->oldact[se->signum]) {
 507                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 508                         sig_state->oldact[se->signum] = NULL;
 509                 }
 510         }
 511         return;
 512 }