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