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