src/src/child.c

   1 /* $Cambridge: exim/src/src/child.c,v 1.9 2006/02/14 10:26:27 ph10 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2006 */
   8 /* See the file NOTICE for conditions of use and distribution. */
   9
  10
  11 #include "exim.h"
  12
  13 static void (*oldsignal)(int);
  14
  15
  16 /*************************************************
  17 *          Ensure an fd has a given value        *
  18 *************************************************/
  19
  20 /* This function is called when we want to ensure that a certain fd has a
  21 specific value (one of 0, 1, 2). If it hasn't got it already, close the value
  22 we want, duplicate the fd, then close the old one.
  23
  24 Arguments:
  25   oldfd        original fd
  26   newfd        the fd we want
  27
  28 Returns:       nothing
  29 */
  30
  31 static void
  32 force_fd(int oldfd, int newfd)
  33 {
  34 if (oldfd == newfd) return;
  35 (void)close(newfd);
  36 (void)dup2(oldfd, newfd);
  37 (void)close(oldfd);
  38 }
  39
  40
  41 #ifndef STAND_ALONE
  42 /*************************************************
  43 *   Build argv list and optionally re-exec Exim  *
  44 *************************************************/
  45
  46 /* This function is called when Exim wants to re-exec (overlay) itself in the
  47 current process. This is different to child_open_exim(), which runs another
  48 Exim process in parallel (but it then calls this function). The function's
  49 basic job is to build the argv list according to the values of current options
  50 settings. There is a basic list that all calls require, and an additional list
  51 that some do not require. Further additions can be given as additional
  52 arguments. An option specifies whether the exec() is actually to happen, and if
  53 so, what is to be done if it fails.
  54
  55 Arguments:
  56   exec_type      CEE_RETURN_ARGV => don't exec; return the argv list
  57                  CEE_EXEC_EXIT   => just exit() on exec failure
  58                  CEE_EXEC_PANIC  => panic-die on exec failure
  59   kill_v         if TRUE, don't pass on the D_v flag
  60   pcount         if not NULL, points to extra size of argv required, and if
  61                    CEE_RETURN_ARGV is specified, it is updated to give the
  62                    number of slots used
  63   minimal        TRUE if only minimal argv is required
  64   acount         number of additional arguments
  65   ...            further values to add to argv
  66
  67 Returns:         if CEE_RETURN_ARGV is given, returns a pointer to argv;
  68                  otherwise, does not return
  69 */
  70
  71 uschar **
  72 child_exec_exim(int exec_type, BOOL kill_v, int *pcount, BOOL minimal,
  73   int acount, ...)
  74 {
  75 int first_special = -1;
  76 int n = 0;
  77 int extra = (pcount != NULL)? *pcount : 0;
  78 uschar **argv =
  79   store_get((extra + acount + MAX_CLMACROS + 16) * sizeof(char *));
  80
  81 /* In all case, the list starts out with the path, any macros, and a changed
  82 config file. */
  83
  84 argv[n++] = exim_path;
  85 if (clmacro_count > 0)
  86   {
  87   memcpy(argv + n, clmacros, clmacro_count * sizeof(uschar *));
  88   n += clmacro_count;
  89   }
  90 if (config_changed)
  91   {
  92   argv[n++] = US"-C";
  93   argv[n++] = config_main_filename;
  94   }
  95
  96 /* These values are added only for non-minimal cases. If debug_selector is
  97 precisely D_v, we have to assume this was started by a non-admin user, and
  98 we suppress the flag when requested. (This happens when passing on an SMTP
  99 connection, and after ETRN.) If there's more debugging going on, an admin user
 100 was involved, so we do pass it on. */
 101
 102 if (!minimal)
 103   {
 104   if (debug_selector == D_v)
 105     {
 106     if (!kill_v) argv[n++] = US"-v";
 107     }
 108   else
 109     {
 110     if (debug_selector != 0)
 111       argv[n++] = string_sprintf("-d=0x%x", debug_selector);
 112     }
 113   if (dont_deliver) argv[n++] = US"-N";
 114   if (queue_smtp) argv[n++] = US"-odqs";
 115   if (synchronous_delivery) argv[n++] = US"-odi";
 116   if (connection_max_messages >= 0)
 117     argv[n++] = string_sprintf("-oB%d", connection_max_messages);
 118   }
 119
 120 /* Now add in any others that are in the call. Remember which they were,
 121 for more helpful diagnosis on failure. */
 122
 123 if (acount > 0)
 124   {
 125   va_list ap;
 126   va_start(ap, acount);
 127   first_special = n;
 128   while (acount-- > 0)
 129     argv[n++] = va_arg(ap, uschar *);
 130   va_end(ap);
 131   }
 132
 133 /* Terminate the list, and return it, if that is what is wanted. */
 134
 135 argv[n] = NULL;
 136 if (exec_type == CEE_RETURN_ARGV)
 137   {
 138   if (pcount != NULL) *pcount = n;
 139   return argv;
 140   }
 141
 142 /* Otherwise, do the exec() here, and handle the consequences of an unexpected
 143 failure. We know that there will always be at least one extra option in the
 144 call when exec() is done here, so it can be used to add to the panic data. */
 145
 146 DEBUG(D_exec) debug_print_argv(argv);
 147 exim_nullstd();                            /* Make sure std{in,out,err} exist */
 148 execv(CS argv[0], (char *const *)argv);
 149
 150 log_write(0,
 151   LOG_MAIN | ((exec_type == CEE_EXEC_EXIT)? LOG_PANIC : LOG_PANIC_DIE),
 152   "re-exec of exim (%s) with %s failed: %s", exim_path, argv[first_special],
 153   strerror(errno));
 154
 155 /* Get here if exec_type == CEE_EXEC_EXIT.
 156 Note: this must be _exit(), not exit(). */
 157
 158 _exit(EX_EXECFAILED);
 159
 160 return NULL;   /* To keep compilers happy */
 161 }
 162
 163
 164
 165
 166 /*************************************************
 167 *          Create a child Exim process           *
 168 *************************************************/
 169
 170 /* This function is called when Exim wants to run a parallel instance of itself
 171 in order to inject a message via the standard input. The function creates a
 172 child process and runs Exim in it. It sets up a pipe to the standard input of
 173 the new process, and returns that to the caller via fdptr. The function returns
 174 the pid of the new process, or -1 if things go wrong. If debug_fd is
 175 non-negative, it is passed as stderr.
 176
 177 This interface is now a just wrapper for the more complicated function
 178 child_open_exim2(), which has additional arguments. The wrapper must continue
 179 to exist, even if all calls from within Exim are changed, because it is
 180 documented for use from local_scan().
 181
 182 Argument: fdptr   pointer to int for the stdin fd
 183 Returns:          pid of the created process or -1 if anything has gone wrong
 184 */
 185
 186 pid_t
 187 child_open_exim(int *fdptr)
 188 {
 189 return child_open_exim2(fdptr, US"<>", bounce_sender_authentication);
 190 }
 191
 192
 193 /* This is a more complicated function for creating a child Exim process, with
 194 more arguments.
 195
 196 Arguments:
 197   fdptr                   pointer to int for the stdin fd
 198   sender                  for a sender address (data for -f)
 199   sender_authentication   authenticated sender address or NULL
 200
 201 Returns:          pid of the created process or -1 if anything has gone wrong
 202 */
 203
 204 pid_t
 205 child_open_exim2(int *fdptr, uschar *sender, uschar *sender_authentication)
 206 {
 207 int pfd[2];
 208 int save_errno;
 209 pid_t pid;
 210
 211 /* Create the pipe and fork the process. Ensure that SIGCHLD is set to
 212 SIG_DFL before forking, so that the child process can be waited for. We
 213 sometimes get here with it set otherwise. Save the old state for resetting
 214 on the wait. */
 215
 216 if (pipe(pfd) != 0) return (pid_t)(-1);
 217 oldsignal = signal(SIGCHLD, SIG_DFL);
 218 pid = fork();
 219
 220 /* Child process: make the reading end of the pipe into the standard input and
 221 close the writing end. If debugging, pass debug_fd as stderr. Then re-exec
 222 Exim. Failure is signalled with EX_EXECFAILED, but this shouldn't occur! */
 223
 224 if (pid == 0)
 225   {
 226   force_fd(pfd[pipe_read], 0);
 227   (void)close(pfd[pipe_write]);
 228   if (debug_fd > 0) force_fd(debug_fd, 2);
 229   if (sender_authentication != NULL)
 230     child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 8,
 231       US"-t", US"-oem", US"-oi", US"-f", sender, US"-oMas",
 232       sender_authentication, message_id_option);
 233   else
 234     child_exec_exim(CEE_EXEC_EXIT, FALSE, NULL, FALSE, 6,
 235       US"-t", US"-oem", US"-oi", US"-f", sender, message_id_option);
 236   /* Control does not return here. */
 237   }
 238
 239 /* Parent process. Save fork() errno and close the reading end of the stdin
 240 pipe. */
 241
 242 save_errno = errno;
 243 (void)close(pfd[pipe_read]);
 244
 245 /* Fork succeeded */
 246
 247 if (pid > 0)
 248   {
 249   *fdptr = pfd[pipe_write];   /* return writing end of stdin pipe */
 250   return pid;                 /* and pid of new process */
 251   }
 252
 253 /* Fork failed */
 254
 255 (void)close(pfd[pipe_write]);
 256 errno = save_errno;
 257 return (pid_t)(-1);
 258 }
 259 #endif
 260
 261
 262
 263 /*************************************************
 264 *         Create a non-Exim child process        *
 265 *************************************************/
 266
 267 /* This function creates a child process and runs the given command in it. It
 268 sets up pipes to the standard input and output of the new process, and returns
 269 them to the caller. The standard error is cloned to the output. If there are
 270 any file descriptors "in the way" in the new process, they are closed. A new
 271 umask is supplied for the process, and an optional new uid and gid are also
 272 available. These are used by the queryprogram router to set an unprivileged id.
 273 SIGUSR1 is always disabled in the new process, as it is not going to be running
 274 Exim (the function child_open_exim() is provided for that). This function
 275 returns the pid of the new process, or -1 if things go wrong.
 276
 277 Arguments:
 278   argv        the argv for exec in the new process
 279   envp        the envp for exec in the new process
 280   newumask    umask to set in the new process
 281   newuid      point to uid for the new process or NULL for no change
 282   newgid      point to gid for the new process or NULL for no change
 283   infdptr     pointer to int into which the fd of the stdin of the new process
 284                 is placed
 285   outfdptr    pointer to int into which the fd of the stdout/stderr of the new
 286                 process is placed
 287   wd          if not NULL, a path to be handed to chdir() in the new process
 288   make_leader if TRUE, make the new process a process group leader
 289
 290 Returns:      the pid of the created process or -1 if anything has gone wrong
 291 */
 292
 293 pid_t
 294 child_open_uid(uschar **argv, uschar **envp, int newumask, uid_t *newuid,
 295   gid_t *newgid, int *infdptr, int *outfdptr, uschar *wd, BOOL make_leader)
 296 {
 297 int save_errno;
 298 int inpfd[2], outpfd[2];
 299 pid_t pid;
 300
 301 /* Create the pipes. */
 302
 303 if (pipe(inpfd) != 0) return (pid_t)(-1);
 304 if (pipe(outpfd) != 0)
 305   {
 306   (void)close(inpfd[pipe_read]);
 307   (void)close(inpfd[pipe_write]);
 308   return (pid_t)(-1);
 309   }
 310
 311 /* Fork the process. Ensure that SIGCHLD is set to SIG_DFL before forking, so
 312 that the child process can be waited for. We sometimes get here with it set
 313 otherwise. Save the old state for resetting on the wait. */
 314
 315 oldsignal = signal(SIGCHLD, SIG_DFL);
 316 pid = fork();
 317
 318 /* Handle the child process. First, set the required environment. We must do
 319 this before messing with the pipes, in order to be able to write debugging
 320 output when things go wrong. */
 321
 322 if (pid == 0)
 323   {
 324   signal(SIGUSR1, SIG_IGN);
 325
 326   if (newgid != NULL && setgid(*newgid) < 0)
 327     {
 328     DEBUG(D_any) debug_printf("failed to set gid=%ld in subprocess: %s\n",
 329       (long int)(*newgid), strerror(errno));
 330     goto CHILD_FAILED;
 331     }
 332
 333   if (newuid != NULL && setuid(*newuid) < 0)
 334     {
 335     DEBUG(D_any) debug_printf("failed to set uid=%ld in subprocess: %s\n",
 336       (long int)(*newuid), strerror(errno));
 337     goto CHILD_FAILED;
 338     }
 339
 340   (void)umask(newumask);
 341
 342   if (wd != NULL && Uchdir(wd) < 0)
 343     {
 344     DEBUG(D_any) debug_printf("failed to chdir to %s: %s\n", wd,
 345       strerror(errno));
 346     goto CHILD_FAILED;
 347     }
 348
 349   /* Becomes a process group leader if requested, and then organize the pipes.
 350   Any unexpected failure is signalled with EX_EXECFAILED; these are all "should
 351   never occur" failures, except for exec failing because the command doesn't
 352   exist. */
 353
 354   if (make_leader && setpgid(0,0) < 0)
 355     {
 356     DEBUG(D_any) debug_printf("failed to set group leader in subprocess: %s\n",
 357       strerror(errno));
 358     goto CHILD_FAILED;
 359     }
 360
 361   (void)close(inpfd[pipe_write]);
 362   force_fd(inpfd[pipe_read], 0);
 363
 364   (void)close(outpfd[pipe_read]);
 365   force_fd(outpfd[pipe_write], 1);
 366
 367   (void)close(2);
 368   (void)dup2(1, 2);
 369
 370   /* Now do the exec */
 371
 372   if (envp == NULL) execv(CS argv[0], (char *const *)argv);
 373     else execve(CS argv[0], (char *const *)argv, (char *const *)envp);
 374
 375   /* Failed to execv. Signal this failure using EX_EXECFAILED. We are
 376   losing the actual errno we got back, because there is no way to return
 377   this information. */
 378
 379   CHILD_FAILED:
 380   _exit(EX_EXECFAILED);      /* Note: must be _exit(), NOT exit() */
 381   }
 382
 383 /* Parent process. Save any fork failure code, and close the reading end of the
 384 stdin pipe, and the writing end of the stdout pipe. */
 385
 386 save_errno = errno;
 387 (void)close(inpfd[pipe_read]);
 388 (void)close(outpfd[pipe_write]);
 389
 390 /* Fork succeeded; return the input/output pipes and the pid */
 391
 392 if (pid > 0)
 393   {
 394   *infdptr = inpfd[pipe_write];
 395   *outfdptr = outpfd[pipe_read];
 396   return pid;
 397   }
 398
 399 /* Fork failed; reset fork errno before returning */
 400
 401 (void)close(inpfd[pipe_write]);
 402 (void)close(outpfd[pipe_read]);
 403 errno = save_errno;
 404 return (pid_t)(-1);
 405 }
 406
 407
 408
 409
 410 /*************************************************
 411 *    Create child process without uid change     *
 412 *************************************************/
 413
 414 /* This function is a wrapper for child_open_uid() that doesn't have the uid,
 415 gid and working directory changing arguments. The function is provided so as to
 416 have a clean interface for use from local_scan(), but also saves writing NULL
 417 arguments several calls that would otherwise use child_open_uid().
 418
 419 Arguments:
 420   argv        the argv for exec in the new process
 421   envp        the envp for exec in the new process
 422   newumask    umask to set in the new process
 423   infdptr     pointer to int into which the fd of the stdin of the new process
 424                 is placed
 425   outfdptr    pointer to int into which the fd of the stdout/stderr of the new
 426                 process is placed
 427   make_leader if TRUE, make the new process a process group leader
 428
 429 Returns:      the pid of the created process or -1 if anything has gone wrong
 430 */
 431
 432 pid_t
 433 child_open(uschar **argv, uschar **envp, int newumask, int *infdptr,
 434   int *outfdptr, BOOL make_leader)
 435 {
 436 return child_open_uid(argv, envp, newumask, NULL, NULL, infdptr, outfdptr,
 437   NULL, make_leader);
 438 }
 439
 440
 441
 442
 443 /*************************************************
 444 *           Close down child process             *
 445 *************************************************/
 446
 447 /* Wait for the given process to finish, with optional timeout.
 448
 449 Arguments
 450   pid:      the pid to wait for
 451   timeout:  maximum time to wait; 0 means for as long as it takes
 452
 453 Returns:    >= 0          process terminated by exiting; value is process
 454                             ending status; if an execve() failed, the value
 455                             is typically 127 (defined as EX_EXECFAILED)
 456             < 0 & > -256  process was terminated by a signal; value is the
 457                             negation of the signal number
 458             -256          timed out
 459             -257          other error in wait(); errno still set
 460 */
 461
 462 int
 463 child_close(pid_t pid, int timeout)
 464 {
 465 int yield;
 466
 467 if (timeout > 0)
 468   {
 469   sigalrm_seen = FALSE;
 470   alarm(timeout);
 471   }
 472
 473 for(;;)
 474   {
 475   int status;
 476   pid_t rc = waitpid(pid, &status, 0);
 477   if (rc == pid)
 478     {
 479     int lowbyte = status & 255;
 480     if (lowbyte == 0) yield = (status >> 8) & 255;
 481       else yield = -lowbyte;
 482     break;
 483     }
 484   if (rc < 0)
 485     {
 486     yield = (errno == EINTR && sigalrm_seen)? -256 : -257;
 487     break;
 488     }
 489   }
 490
 491 if (timeout > 0) alarm(0);
 492
 493 signal(SIGCHLD, oldsignal);   /* restore */
 494 return yield;
 495 }
 496
 497 /* End of child.c */