src/src/child.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2015 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8
   9 #include "exim.h"
  10
  11 static void (*oldsignal)(int);
  12
  13
  14 /*************************************************
  15 *          Ensure an fd has a given value        *
  16 *************************************************/
  17
  18 /* This function is called when we want to ensure that a certain fd has a
  19 specific value (one of 0, 1, 2). If it hasn't got it already, close the value
  20 we want, duplicate the fd, then close the old one.
  21
  22 Arguments:
  23   oldfd        original fd
  24   newfd        the fd we want
  25
  26 Returns:       nothing
  27 */
  28
  29 static void
  30 force_fd(int oldfd, int newfd)
  31 {
  32 if (oldfd == newfd) return;
  33 (void)close(newfd);
  34 (void)dup2(oldfd, newfd);
  35 (void)close(oldfd);
  36 }
  37
  38
  39 #ifndef STAND_ALONE
  40 /*************************************************
  41 *   Build argv list and optionally re-exec Exim  *
  42 *************************************************/
  43
  44 /* This function is called when Exim wants to re-exec (overlay) itself in the
  45 current process. This is different to child_open_exim(), which runs another
  46 Exim process in parallel (but it then calls this function). The function's
  47 basic job is to build the argv list according to the values of current options
  48 settings. There is a basic list that all calls require, and an additional list
  49 that some do not require. Further additions can be given as additional
  50 arguments. An option specifies whether the exec() is actually to happen, and if
  51 so, what is to be done if it fails.
  52
  53 Arguments:
  54   exec_type      CEE_RETURN_ARGV => don't exec; return the argv list
  55                  CEE_EXEC_EXIT   => just exit() on exec failure
  56                  CEE_EXEC_PANIC  => panic-die on exec failure
  57   kill_v         if TRUE, don't pass on the D_v flag
  58   pcount         if not NULL, points to extra size of argv required, and if
  59                    CEE_RETURN_ARGV is specified, it is updated to give the
  60                    number of slots used
  61   minimal        TRUE if only minimal argv is required
  62   acount         number of additional arguments
  63   ...            further values to add to argv
  64
  65 Returns:         if CEE_RETURN_ARGV is given, returns a pointer to argv;
  66                  otherwise, does not return
  67 */
  68
  69 uschar **
  70 child_exec_exim(int exec_type, BOOL kill_v, int *pcount, BOOL minimal,
  71   int acount, ...)
  72 {
  73 int first_special = -1;
  74 int n = 0;
  75 int extra = pcount ? *pcount : 0;
  76 uschar **argv;
  77
  78 argv = store_get((extra + acount + MAX_CLMACROS + 19) * sizeof(char *), FALSE);
  79
  80 /* In all case, the list starts out with the path, any macros, and a changed
  81 config file. */
  82
  83 argv[n++] = exim_path;
  84 if (clmacro_count > 0)
  85   {
  86   memcpy(argv + n, clmacros, clmacro_count * sizeof(uschar *));
  87   n += clmacro_count;
  88   }
  89 if (f.config_changed)
  90   {
  91   argv[n++] = US"-C";
  92   argv[n++] = config_main_filename;
  93   }
  94
  95 /* These values are added only for non-minimal cases. If debug_selector is
  96 precisely D_v, we have to assume this was started by a non-admin user, and
  97 we suppress the flag when requested. (This happens when passing on an SMTP
  98 connection, and after ETRN.) If there's more debugging going on, an admin user
  99 was involved, so we do pass it on. */
 100
 101 if (!minimal)
 102   {
 103   if (debug_selector == D_v)
 104     {
 105     if (!kill_v) argv[n++] = US"-v";
 106     }
 107   else
 108     {
 109     if (debug_selector != 0)
 110       argv[n++] = string_sprintf("-d=0x%x", debug_selector);
 111     }
 112   if (!f.testsuite_delays) argv[n++] = US"-odd";
 113   if (f.dont_deliver) argv[n++] = US"-N";
 114   if (f.queue_smtp) argv[n++] = US"-odqs";
 115   if (f.synchronous_delivery) argv[n++] = US"-odi";
 116   if (connection_max_messages >= 0)
 117     argv[n++] = string_sprintf("-oB%d", connection_max_messages);
 118   if (*queue_name)
 119     {
 120     argv[n++] = US"-MCG";
 121     argv[n++] = queue_name;
 122     }
 123   }
 124
 125 /* Now add in any others that are in the call. Remember which they were,
 126 for more helpful diagnosis on failure. */
 127
 128 if (acount > 0)
 129   {
 130   va_list ap;
 131   va_start(ap, acount);
 132   first_special = n;
 133   while (acount-- > 0)
 134     argv[n++] = va_arg(ap, uschar *);
 135   va_end(ap);
 136   }
 137
 138 /* Terminate the list, and return it, if that is what is wanted. */
 139
 140 argv[n] = NULL;
 141 if (exec_type == CEE_RETURN_ARGV)
 142   {
 143   if (pcount != NULL) *pcount = n;
 144   return argv;
 145   }
 146
 147 /* Otherwise, do the exec() here, and handle the consequences of an unexpected
 148 failure. We know that there will always be at least one extra option in the
 149 call when exec() is done here, so it can be used to add to the panic data. */
 150
 151 DEBUG(D_exec) debug_print_argv(CUSS argv);
 152 exim_nullstd();                            /* Make sure std{in,out,err} exist */
 153 execv(CS argv[0], (char *const *)argv);
 154
 155 log_write(0,
 156   LOG_MAIN | ((exec_type == CEE_EXEC_EXIT)? LOG_PANIC : LOG_PANIC_DIE),
 157   "re-exec of exim (%s) with %s failed: %s", exim_path, argv[first_special],
 158   strerror(errno));
 159
 160 /* Get here if exec_type == CEE_EXEC_EXIT.
 161 Note: this must be _exit(), not exit(). */
 162
 163 _exit(EX_EXECFAILED);
 164
 165 return NULL;   /* To keep compilers happy */
 166 }
 167
 168
 169
 170
 171 /*************************************************
 172 *          Create a child Exim process           *
 173 *************************************************/
 174
 175 /* This function is called when Exim wants to run a parallel instance of itself
 176 in order to inject a message via the standard input. The function creates a
 177 child process and runs Exim in it. It sets up a pipe to the standard input of
 178 the new process, and returns that to the caller via fdptr. The function returns
 179 the pid of the new process, or -1 if things go wrong. If debug_fd is
 180 non-negative, it is passed as stderr.
 181
 182 This interface is now a just wrapper for the more complicated function
 183 child_open_exim2(), which has additional arguments. The wrapper must continue
 184 to exist, even if all calls from within Exim are changed, because it is
 185 documented for use from local_scan().
 186
 187 Argument: fdptr   pointer to int for the stdin fd
 188 Returns:          pid of the created process or -1 if anything has gone wrong
 189 */
 190
 191 pid_t
 192 child_open_exim(int *fdptr)
 193 {
 194 return child_open_exim2(fdptr, US"<>", bounce_sender_authentication);
 195 }
 196
 197
 198 /* This is a more complicated function for creating a child Exim process, with
 199 more arguments.
 200
 201 Arguments:
 202   fdptr                   pointer to int for the stdin fd
 203   sender                  for a sender address (data for -f)
 204   sender_authentication   authenticated sender address or NULL
 205
 206 Returns:          pid of the created process or -1 if anything has gone wrong
 207 */
 208
 209 pid_t
 210 child_open_exim2(int *fdptr, uschar *sender, uschar *sender_authentication)
 211 {
 212 int pfd[2];
 213 int save_errno;
 214 pid_t pid;
 215
 216 /* Create the pipe and fork the process. Ensure that SIGCHLD is set to
 217 SIG_DFL before forking, so that the child process can be waited for. We
 218 sometimes get here with it set otherwise. Save the old state for resetting
 219 on the wait. */
 220
 221 if (pipe(pfd) != 0) return (pid_t)(-1);
 222 oldsignal = signal(SIGCHLD, SIG_DFL);
 223 pid = fork();
 224
 225 /* Child process: make the reading end of the pipe into the standard input and
 226 close the writing end. If debugging, pass debug_fd as stderr. Then re-exec
 227 Exim with appropriate options. In the test harness, use -odi unless queue_only
 228 is set, so that the bounce is fully delivered before returning. Failure is
 229 signalled with EX_EXECFAILED (specified by CEE_EXEC_EXIT), but this shouldn't
 230 occur. */
 231
 232 if (pid == 0)
 233   {
 234   force_fd(pfd[pipe_read], 0);
 235   (void)close(pfd[pipe_write]);
 236   if (debug_fd > 0) force_fd(debug_fd, 2);
 237   if (f.running_in_test_harness && !queue_only)
 238     {
 239     if (sender_authentication != NULL)
 240       child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 9,
 241         US "-odi", US"-t", US"-oem", US"-oi", US"-f", sender, US"-oMas",
 242         sender_authentication, message_id_option);
 243     else
 244       child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 7,
 245         US "-odi", US"-t", US"-oem", US"-oi", US"-f", sender,
 246         message_id_option);
 247     /* Control does not return here. */
 248     }
 249   else   /* Not test harness */
 250     {
 251     if (sender_authentication != NULL)
 252       child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 8,
 253         US"-t", US"-oem", US"-oi", US"-f", sender, US"-oMas",
 254         sender_authentication, message_id_option);
 255     else
 256       child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 6,
 257         US"-t", US"-oem", US"-oi", US"-f", sender, message_id_option);
 258     /* Control does not return here. */
 259     }
 260   }
 261
 262 /* Parent process. Save fork() errno and close the reading end of the stdin
 263 pipe. */
 264
 265 save_errno = errno;
 266 (void)close(pfd[pipe_read]);
 267
 268 /* Fork succeeded */
 269
 270 if (pid > 0)
 271   {
 272   *fdptr = pfd[pipe_write];   /* return writing end of stdin pipe */
 273   return pid;                 /* and pid of new process */
 274   }
 275
 276 /* Fork failed */
 277
 278 (void)close(pfd[pipe_write]);
 279 errno = save_errno;
 280 return (pid_t)(-1);
 281 }
 282 #endif   /* STAND_ALONE */
 283
 284
 285
 286 /*************************************************
 287 *         Create a non-Exim child process        *
 288 *************************************************/
 289
 290 /* This function creates a child process and runs the given command in it. It
 291 sets up pipes to the standard input and output of the new process, and returns
 292 them to the caller. The standard error is cloned to the output. If there are
 293 any file descriptors "in the way" in the new process, they are closed. A new
 294 umask is supplied for the process, and an optional new uid and gid are also
 295 available. These are used by the queryprogram router to set an unprivileged id.
 296 SIGUSR1 is always disabled in the new process, as it is not going to be running
 297 Exim (the function child_open_exim() is provided for that). This function
 298 returns the pid of the new process, or -1 if things go wrong.
 299
 300 Arguments:
 301   argv        the argv for exec in the new process
 302   envp        the envp for exec in the new process
 303   newumask    umask to set in the new process
 304   newuid      point to uid for the new process or NULL for no change
 305   newgid      point to gid for the new process or NULL for no change
 306   infdptr     pointer to int into which the fd of the stdin of the new process
 307                 is placed
 308   outfdptr    pointer to int into which the fd of the stdout/stderr of the new
 309                 process is placed
 310   wd          if not NULL, a path to be handed to chdir() in the new process
 311   make_leader if TRUE, make the new process a process group leader
 312
 313 Returns:      the pid of the created process or -1 if anything has gone wrong
 314 */
 315
 316 pid_t
 317 child_open_uid(const uschar **argv, const uschar **envp, int newumask,
 318   uid_t *newuid, gid_t *newgid, int *infdptr, int *outfdptr, uschar *wd,
 319   BOOL make_leader)
 320 {
 321 int save_errno;
 322 int inpfd[2], outpfd[2];
 323 pid_t pid;
 324
 325 /* Create the pipes. */
 326
 327 if (pipe(inpfd) != 0) return (pid_t)(-1);
 328 if (pipe(outpfd) != 0)
 329   {
 330   (void)close(inpfd[pipe_read]);
 331   (void)close(inpfd[pipe_write]);
 332   return (pid_t)(-1);
 333   }
 334
 335 /* Fork the process. Ensure that SIGCHLD is set to SIG_DFL before forking, so
 336 that the child process can be waited for. We sometimes get here with it set
 337 otherwise. Save the old state for resetting on the wait. */
 338
 339 oldsignal = signal(SIGCHLD, SIG_DFL);
 340 pid = fork();
 341
 342 /* Handle the child process. First, set the required environment. We must do
 343 this before messing with the pipes, in order to be able to write debugging
 344 output when things go wrong. */
 345
 346 if (pid == 0)
 347   {
 348   signal(SIGUSR1, SIG_IGN);
 349   signal(SIGPIPE, SIG_DFL);
 350
 351   if (newgid != NULL && setgid(*newgid) < 0)
 352     {
 353     DEBUG(D_any) debug_printf("failed to set gid=%ld in subprocess: %s\n",
 354       (long int)(*newgid), strerror(errno));
 355     goto CHILD_FAILED;
 356     }
 357
 358   if (newuid != NULL && setuid(*newuid) < 0)
 359     {
 360     DEBUG(D_any) debug_printf("failed to set uid=%ld in subprocess: %s\n",
 361       (long int)(*newuid), strerror(errno));
 362     goto CHILD_FAILED;
 363     }
 364
 365   (void)umask(newumask);
 366
 367   if (wd != NULL && Uchdir(wd) < 0)
 368     {
 369     DEBUG(D_any) debug_printf("failed to chdir to %s: %s\n", wd,
 370       strerror(errno));
 371     goto CHILD_FAILED;
 372     }
 373
 374   /* Becomes a process group leader if requested, and then organize the pipes.
 375   Any unexpected failure is signalled with EX_EXECFAILED; these are all "should
 376   never occur" failures, except for exec failing because the command doesn't
 377   exist. */
 378
 379   if (make_leader && setpgid(0,0) < 0)
 380     {
 381     DEBUG(D_any) debug_printf("failed to set group leader in subprocess: %s\n",
 382       strerror(errno));
 383     goto CHILD_FAILED;
 384     }
 385
 386   (void)close(inpfd[pipe_write]);
 387   force_fd(inpfd[pipe_read], 0);
 388
 389   (void)close(outpfd[pipe_read]);
 390   force_fd(outpfd[pipe_write], 1);
 391
 392   (void)close(2);
 393   (void)dup2(1, 2);
 394
 395   /* Now do the exec */
 396
 397   if (envp == NULL) execv(CS argv[0], (char *const *)argv);
 398   else execve(CS argv[0], (char *const *)argv, (char *const *)envp);
 399
 400   /* Failed to execv. Signal this failure using EX_EXECFAILED. We are
 401   losing the actual errno we got back, because there is no way to return
 402   this information. */
 403
 404   CHILD_FAILED:
 405   _exit(EX_EXECFAILED);      /* Note: must be _exit(), NOT exit() */
 406   }
 407
 408 /* Parent process. Save any fork failure code, and close the reading end of the
 409 stdin pipe, and the writing end of the stdout pipe. */
 410
 411 save_errno = errno;
 412 (void)close(inpfd[pipe_read]);
 413 (void)close(outpfd[pipe_write]);
 414
 415 /* Fork succeeded; return the input/output pipes and the pid */
 416
 417 if (pid > 0)
 418   {
 419   *infdptr = inpfd[pipe_write];
 420   *outfdptr = outpfd[pipe_read];
 421   return pid;
 422   }
 423
 424 /* Fork failed; reset fork errno before returning */
 425
 426 (void)close(inpfd[pipe_write]);
 427 (void)close(outpfd[pipe_read]);
 428 errno = save_errno;
 429 return (pid_t)(-1);
 430 }
 431
 432
 433
 434
 435 /*************************************************
 436 *    Create child process without uid change     *
 437 *************************************************/
 438
 439 /* This function is a wrapper for child_open_uid() that doesn't have the uid,
 440 gid and working directory changing arguments. The function is provided so as to
 441 have a clean interface for use from local_scan(), but also saves writing NULL
 442 arguments several calls that would otherwise use child_open_uid().
 443
 444 Arguments:
 445   argv        the argv for exec in the new process
 446   envp        the envp for exec in the new process
 447   newumask    umask to set in the new process
 448   infdptr     pointer to int into which the fd of the stdin of the new process
 449                 is placed
 450   outfdptr    pointer to int into which the fd of the stdout/stderr of the new
 451                 process is placed
 452   make_leader if TRUE, make the new process a process group leader
 453
 454 Returns:      the pid of the created process or -1 if anything has gone wrong
 455 */
 456
 457 pid_t
 458 child_open(uschar **argv, uschar **envp, int newumask, int *infdptr,
 459   int *outfdptr, BOOL make_leader)
 460 {
 461 return child_open_uid(CUSS argv, CUSS envp, newumask, NULL, NULL,
 462   infdptr, outfdptr, NULL, make_leader);
 463 }
 464
 465
 466
 467
 468 /*************************************************
 469 *           Close down child process             *
 470 *************************************************/
 471
 472 /* Wait for the given process to finish, with optional timeout.
 473
 474 Arguments
 475   pid:      the pid to wait for
 476   timeout:  maximum time to wait; 0 means for as long as it takes
 477
 478 Returns:    >= 0          process terminated by exiting; value is process
 479                             ending status; if an execve() failed, the value
 480                             is typically 127 (defined as EX_EXECFAILED)
 481             < 0 & > -256  process was terminated by a signal; value is the
 482                             negation of the signal number
 483             -256          timed out
 484             -257          other error in wait(); errno still set
 485 */
 486
 487 int
 488 child_close(pid_t pid, int timeout)
 489 {
 490 int yield;
 491
 492 if (timeout > 0)
 493   {
 494   sigalrm_seen = FALSE;
 495   ALARM(timeout);
 496   }
 497
 498 for(;;)
 499   {
 500   int status;
 501   pid_t rc = waitpid(pid, &status, 0);
 502   if (rc == pid)
 503     {
 504     int lowbyte = status & 255;
 505     yield = lowbyte == 0 ? (status >> 8) & 255 : -lowbyte;
 506     break;
 507     }
 508   if (rc < 0)
 509     {
 510     /* This "shouldn't happen" test does happen on MacOS: for some reason
 511     I do not understand we seems to get an alarm signal despite not having
 512     an active alarm set. There seems to be only one, so just go round again. */
 513
 514     if (errno == EINTR && sigalrm_seen && timeout <= 0) continue;
 515
 516     yield = (errno == EINTR && sigalrm_seen) ? -256 : -257;
 517     break;
 518     }
 519   }
 520
 521 if (timeout > 0) ALARM_CLR(0);
 522
 523 signal(SIGCHLD, oldsignal);   /* restore */
 524 return yield;
 525 }
 526
 527 /* End of child.c */