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                         ssize_t ret;
 110
 111                         ev = sl->se->event_ctx;
 112                         /* doesn't matter if this pipe overflows */
 113                         do {
 114                                 ret = write(ev->pipe_fds[1], &c, 1);
 115                         } while (ret == -1 && errno == EINTR);
 116                 }
 117         }
 118
 119         errno = saved_errno;
 120 }
 121
 122 #ifdef SA_SIGINFO
 123 /*
 124   signal handler with SA_SIGINFO - redirects to registered signals
 125 */
 126 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 127                                               void *uctx)
 128 {
 129         uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
 130         /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
 131          * is the base of the unprocessed signals in the ringbuffer. */
 132         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 133                                 TEVENT_SA_INFO_QUEUE_COUNT;
 134         sig_state->sig_info[signum][ofs] = *info;
 135
 136         tevent_common_signal_handler(signum);
 137
 138         /* handle SA_SIGINFO */
 139         if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
 140                 /* we've filled the info array - block this signal until
 141                    these ones are delivered */
 142 #ifdef HAVE_UCONTEXT_T
 143                 /*
 144                  * This is the only way for this to work.
 145                  * By default signum is blocked inside this
 146                  * signal handler using a temporary mask,
 147                  * but what we really need to do now is
 148                  * block it in the callers mask, so it
 149                  * stays blocked when the temporary signal
 150                  * handler mask is replaced when we return
 151                  * from here. The callers mask can be found
 152                  * in the ucontext_t passed in as the
 153                  * void *uctx argument.
 154                  */
 155                 ucontext_t *ucp = (ucontext_t *)uctx;
 156                 sigaddset(&ucp->uc_sigmask, signum);
 157 #else
 158                 /*
 159                  * WARNING !!! WARNING !!!!
 160                  *
 161                  * This code doesn't work.
 162                  * By default signum is blocked inside this
 163                  * signal handler, but calling sigprocmask
 164                  * modifies the temporary signal mask being
 165                  * used *inside* this handler, which will be
 166                  * replaced by the callers signal mask once
 167                  * we return from here. See Samba
 168                  * bug #9550 for details.
 169                  */
 170                 sigset_t set;
 171                 sigemptyset(&set);
 172                 sigaddset(&set, signum);
 173                 sigprocmask(SIG_BLOCK, &set, NULL);
 174 #endif
 175                 TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
 176         }
 177 }
 178 #endif
 179
 180 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 181 {
 182         if (sig_state->sig_handlers[sl->se->signum]) {
 183                 DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 184         }
 185         return 0;
 186 }
 187
 188 /*
 189   destroy a signal event
 190 */
 191 static int tevent_signal_destructor(struct tevent_signal *se)
 192 {
 193         struct tevent_common_signal_list *sl =
 194                 talloc_get_type_abort(se->additional_data,
 195                 struct tevent_common_signal_list);
 196
 197         if (se->event_ctx) {
 198                 struct tevent_context *ev = se->event_ctx;
 199
 200                 DLIST_REMOVE(ev->signal_events, se);
 201
 202                 if (ev->signal_events == NULL && ev->pipe_fde != NULL) {
 203                         /*
 204                          * This was the last signal. Destroy the pipe.
 205                          */
 206                         TALLOC_FREE(ev->pipe_fde);
 207
 208                         close(ev->pipe_fds[0]);
 209                         close(ev->pipe_fds[1]);
 210                 }
 211         }
 212
 213         talloc_free(sl);
 214
 215         if (sig_state->sig_handlers[se->signum] == NULL) {
 216                 /* restore old handler, if any */
 217                 if (sig_state->oldact[se->signum]) {
 218                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 219                         talloc_free(sig_state->oldact[se->signum]);
 220                         sig_state->oldact[se->signum] = NULL;
 221                 }
 222 #ifdef SA_SIGINFO
 223                 if (se->sa_flags & SA_SIGINFO) {
 224                         if (sig_state->sig_info[se->signum]) {
 225                                 talloc_free(sig_state->sig_info[se->signum]);
 226                                 sig_state->sig_info[se->signum] = NULL;
 227                         }
 228                 }
 229 #endif
 230         }
 231
 232         return 0;
 233 }
 234
 235 /*
 236   this is part of the pipe hack needed to avoid the signal race condition
 237 */
 238 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 239                                 uint16_t flags, void *_private)
 240 {
 241         char c[16];
 242         /* its non-blocking, doesn't matter if we read too much */
 243         (void) read(fde->fd, c, sizeof(c));
 244 }
 245
 246 /*
 247   add a signal event
 248   return NULL on failure (memory allocation error)
 249 */
 250 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 251                                                TALLOC_CTX *mem_ctx,
 252                                                int signum,
 253                                                int sa_flags,
 254                                                tevent_signal_handler_t handler,
 255                                                void *private_data,
 256                                                const char *handler_name,
 257                                                const char *location)
 258 {
 259         struct tevent_signal *se;
 260         struct tevent_common_signal_list *sl;
 261         sigset_t set, oldset;
 262
 263         if (signum >= TEVENT_NUM_SIGNALS) {
 264                 errno = EINVAL;
 265                 return NULL;
 266         }
 267
 268         /* the sig_state needs to be on a global context as it can last across
 269            multiple event contexts */
 270         if (sig_state == NULL) {
 271                 sig_state = talloc_zero(NULL, struct tevent_sig_state);
 272                 if (sig_state == NULL) {
 273                         return NULL;
 274                 }
 275         }
 276
 277         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 278         if (se == NULL) return NULL;
 279
 280         se->event_ctx           = ev;
 281         se->signum              = signum;
 282         se->sa_flags            = sa_flags;
 283         se->handler             = handler;
 284         se->private_data        = private_data;
 285         se->handler_name        = handler_name;
 286         se->location            = location;
 287         se->additional_data     = NULL;
 288
 289         sl = talloc(se, struct tevent_common_signal_list);
 290         if (!sl) {
 291                 talloc_free(se);
 292                 return NULL;
 293         }
 294         sl->se = se;
 295         se->additional_data     = sl;
 296
 297         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 298         if (!talloc_reference(se, sig_state)) {
 299                 talloc_free(se);
 300                 return NULL;
 301         }
 302
 303         /* we need to setup the pipe hack handler if not already
 304            setup */
 305         if (ev->pipe_fde == NULL) {
 306                 if (pipe(ev->pipe_fds) == -1) {
 307                         talloc_free(se);
 308                         return NULL;
 309                 }
 310                 ev_set_blocking(ev->pipe_fds[0], false);
 311                 ev_set_blocking(ev->pipe_fds[1], false);
 312                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 313                                              TEVENT_FD_READ,
 314                                              signal_pipe_handler, NULL);
 315                 if (!ev->pipe_fde) {
 316                         close(ev->pipe_fds[0]);
 317                         close(ev->pipe_fds[1]);
 318                         talloc_free(se);
 319                         return NULL;
 320                 }
 321         }
 322
 323         /* only install a signal handler if not already installed */
 324         if (sig_state->sig_handlers[signum] == NULL) {
 325                 struct sigaction act;
 326                 ZERO_STRUCT(act);
 327                 act.sa_handler = tevent_common_signal_handler;
 328                 act.sa_flags = sa_flags;
 329 #ifdef SA_SIGINFO
 330                 if (sa_flags & SA_SIGINFO) {
 331                         act.sa_handler   = NULL;
 332                         act.sa_sigaction = tevent_common_signal_handler_info;
 333                         if (sig_state->sig_info[signum] == NULL) {
 334                                 sig_state->sig_info[signum] =
 335                                         talloc_zero_array(sig_state, siginfo_t,
 336                                                           TEVENT_SA_INFO_QUEUE_COUNT);
 337                                 if (sig_state->sig_info[signum] == NULL) {
 338                                         talloc_free(se);
 339                                         return NULL;
 340                                 }
 341                         }
 342                 }
 343 #endif
 344                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 345                 if (sig_state->oldact[signum] == NULL) {
 346                         talloc_free(se);
 347                         return NULL;
 348                 }
 349                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 350                         talloc_free(sig_state->oldact[signum]);
 351                         sig_state->oldact[signum] = NULL;
 352                         talloc_free(se);
 353                         return NULL;
 354                 }
 355         }
 356
 357         DLIST_ADD(se->event_ctx->signal_events, se);
 358
 359         /* Make sure the signal doesn't come in while we're mangling list. */
 360         sigemptyset(&set);
 361         sigaddset(&set, signum);
 362         sigprocmask(SIG_BLOCK, &set, &oldset);
 363         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 364         sigprocmask(SIG_SETMASK, &oldset, NULL);
 365
 366         talloc_set_destructor(se, tevent_signal_destructor);
 367         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 368
 369         return se;
 370 }
 371
 372 struct tevent_se_exists {
 373         struct tevent_se_exists **myself;
 374 };
 375
 376 static int tevent_se_exists_destructor(struct tevent_se_exists *s)
 377 {
 378         *s->myself = NULL;
 379         return 0;
 380 }
 381
 382 /*
 383   check if a signal is pending
 384   return != 0 if a signal was pending
 385 */
 386 int tevent_common_check_signal(struct tevent_context *ev)
 387 {
 388         int i;
 389
 390         if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
 391                 return 0;
 392         }
 393
 394         for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
 395                 struct tevent_common_signal_list *sl, *next;
 396                 struct tevent_sigcounter counter = sig_state->signal_count[i];
 397                 uint32_t count = tevent_sig_count(counter);
 398 #ifdef SA_SIGINFO
 399                 /* Ensure we null out any stored siginfo_t entries
 400                  * after processing for debugging purposes. */
 401                 bool clear_processed_siginfo = false;
 402 #endif
 403
 404                 if (count == 0) {
 405                         continue;
 406                 }
 407                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 408                         struct tevent_signal *se = sl->se;
 409                         struct tevent_se_exists *exists;
 410
 411                         next = sl->next;
 412
 413                         /*
 414                          * We have to be careful to not touch "se"
 415                          * after it was deleted in its handler. Thus
 416                          * we allocate a child whose destructor will
 417                          * tell by nulling out itself that its parent
 418                          * is gone.
 419                          */
 420                         exists = talloc(se, struct tevent_se_exists);
 421                         if (exists == NULL) {
 422                                 continue;
 423                         }
 424                         exists->myself = &exists;
 425                         talloc_set_destructor(
 426                                 exists, tevent_se_exists_destructor);
 427
 428 #ifdef SA_SIGINFO
 429                         if (se->sa_flags & SA_SIGINFO) {
 430                                 uint32_t j;
 431
 432                                 clear_processed_siginfo = true;
 433
 434                                 for (j=0;j<count;j++) {
 435                                         /* sig_state->signal_count[i].seen
 436                                          * % TEVENT_SA_INFO_QUEUE_COUNT is
 437                                          * the base position of the unprocessed
 438                                          * signals in the ringbuffer. */
 439                                         uint32_t ofs = (counter.seen + j)
 440                                                 % TEVENT_SA_INFO_QUEUE_COUNT;
 441                                         se->handler(ev, se, i, 1,
 442                                                     (void*)&sig_state->sig_info[i][ofs],
 443                                                     se->private_data);
 444                                         if (!exists) {
 445                                                 break;
 446                                         }
 447                                 }
 448 #ifdef SA_RESETHAND
 449                                 if (exists && (se->sa_flags & SA_RESETHAND)) {
 450                                         talloc_free(se);
 451                                 }
 452 #endif
 453                                 talloc_free(exists);
 454                                 continue;
 455                         }
 456 #endif
 457                         se->handler(ev, se, i, count, NULL, se->private_data);
 458 #ifdef SA_RESETHAND
 459                         if (exists && (se->sa_flags & SA_RESETHAND)) {
 460                                 talloc_free(se);
 461                         }
 462 #endif
 463                         talloc_free(exists);
 464                 }
 465
 466 #ifdef SA_SIGINFO
 467                 if (clear_processed_siginfo && sig_state->sig_info[i] != NULL) {
 468                         uint32_t j;
 469                         for (j=0;j<count;j++) {
 470                                 uint32_t ofs = (counter.seen + j)
 471                                         % TEVENT_SA_INFO_QUEUE_COUNT;
 472                                 memset((void*)&sig_state->sig_info[i][ofs],
 473                                         '\0',
 474                                         sizeof(siginfo_t));
 475                         }
 476                 }
 477 #endif
 478
 479                 TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
 480                 TEVENT_SIG_SEEN(sig_state->got_signal, count);
 481
 482 #ifdef SA_SIGINFO
 483                 if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
 484                         /* We'd filled the queue, unblock the
 485                            signal now the queue is empty again.
 486                            Note we MUST do this after the
 487                            TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
 488                            call to prevent a new signal running
 489                            out of room in the sig_state->sig_info[i][]
 490                            ring buffer. */
 491                         sigset_t set;
 492                         sigemptyset(&set);
 493                         sigaddset(&set, i);
 494                         TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
 495                                  tevent_sig_count(sig_state->sig_blocked[i]));
 496                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 497                 }
 498 #endif
 499         }
 500
 501         return 1;
 502 }
 503
 504 void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
 505 {
 506         struct tevent_common_signal_list *sl =
 507                 talloc_get_type_abort(se->additional_data,
 508                 struct tevent_common_signal_list);
 509
 510         tevent_common_signal_list_destructor(sl);
 511
 512         if (sig_state->sig_handlers[se->signum] == NULL) {
 513                 if (sig_state->oldact[se->signum]) {
 514                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 515                         talloc_free(sig_state->oldact[se->signum]);
 516                         sig_state->oldact[se->signum] = NULL;
 517                 }
 518         }
 519         return;
 520 }