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