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