Security/libsecurity_utilities/lib/daemon.cpp

   1 /*
   2  * Copyright (c) 2000-2004,2011,2014 Apple Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24
  25 //
  26 // demon - support code for writing UNIXoid demons
  27 //
  28 #include <security_utilities/daemon.h>
  29 #include <security_utilities/logging.h>
  30 #include <security_utilities/debugging.h>
  31 #include <sys/types.h>
  32 #include <errno.h>
  33 #include <unistd.h>
  34 #include <fcntl.h>
  35
  36 namespace Security {
  37 namespace Daemon {
  38
  39
  40 //
  41 // Daemonize this process, the UNIX way.
  42 //
  43 bool incarnate(bool doFork /*=true*/)
  44 {
  45         if (doFork) {
  46                 // fork with slight resilience
  47                 for (int forkTries = 1; forkTries <= 5; forkTries++) {
  48                         switch (fork()) {
  49                                 case 0:                 // child
  50                                                         // we are the daemon process (Har! Har!)
  51                                         break;
  52                                 case -1:                // parent: fork failed
  53                                         switch (errno) {
  54                                                 case EAGAIN:
  55                                                 case ENOMEM:
  56                                                         Syslog::warning("fork() short on resources (errno=%d); retrying", errno);
  57                                                         sleep(forkTries);
  58                                                         continue;
  59                                                 default:
  60                                                         Syslog::error("fork() failed (errno=%d)", errno);
  61                                                         return false;
  62                                         }
  63                                 default:                // parent
  64                                                         // @@@ we could close an assurance loop here, but we don't (yet?)
  65                                         exit(0);
  66                         }
  67                 }
  68                 // fork succeeded; we are the child; parent is terminating
  69         }
  70
  71         // create new session (the magic set-me-apart system call)
  72         setsid();
  73
  74         // redirect standard channels to /dev/null
  75         close(0);       // fail silently in case 0 is closed
  76         if (open("/dev/null", O_RDWR, 0) == 0) {        // /dev/null could be missing, I suppose...
  77                 dup2(0, 1);
  78                 dup2(0, 2);
  79         }
  80
  81         // ready to roll
  82         return true;
  83 }
  84
  85
  86 //
  87 // Re-execute myself.
  88 // This is a pretty bad hack for libraries that are pretty broken and (essentially)
  89 // don't work after a fork() unless you also exec().
  90 //
  91 // WARNING: Don't even THINK of doing this in a setuid-anything program.
  92 //
  93 bool executeSelf(char **argv)
  94 {
  95         static const char reExecEnv[] = "_RE_EXECUTE";
  96         if (getenv(reExecEnv)) {                // was re-executed
  97                 secdebug("daemon", "self-execution complete");
  98                 unsetenv(reExecEnv);
  99                 return true;
 100         } else {
 101                 setenv(reExecEnv, "go", 1);
 102                 secdebug("daemon", "self-executing (ouch!)");
 103                 execv(argv[0], argv);
 104                 perror("re-execution");
 105                 Syslog::error("Re-execution attempt failed");
 106                 return false;
 107         }
 108 }
 109
 110
 111 } // end namespace Daemon
 112 } // end namespace Security