src/spawn-agent.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2011 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU General Public License as published by
  10   the Free Software Foundation; either version 2 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <sys/types.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <string.h>
  26 #include <sys/prctl.h>
  27 #include <signal.h>
  28 #include <fcntl.h>
  29
  30 #include "log.h"
  31 #include "util.h"
  32 #include "spawn-agent.h"
  33
  34 static pid_t agent_pid = 0;
  35
  36 void agent_open(void) {
  37         pid_t parent_pid;
  38
  39         if (agent_pid > 0)
  40                 return;
  41
  42         /* We check STDIN here, not STDOUT, since this is about input,
  43          * not output */
  44         if (!isatty(STDIN_FILENO))
  45                 return;
  46
  47         parent_pid = getpid();
  48
  49         /* Spawns a temporary TTY agent, making sure it goes away when
  50          * we go away */
  51
  52         agent_pid = fork();
  53         if (agent_pid < 0) {
  54                 log_error("Failed to fork agent: %m");
  55                 return;
  56         }
  57
  58         if (agent_pid == 0) {
  59                 /* In the child */
  60
  61                 int fd;
  62                 bool stdout_is_tty, stderr_is_tty;
  63
  64                 /* Make sure the agent goes away when the parent dies */
  65                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
  66                         _exit(EXIT_FAILURE);
  67
  68                 /* Check whether our parent died before we were able
  69                  * to set the death signal */
  70                 if (getppid() != parent_pid)
  71                         _exit(EXIT_SUCCESS);
  72
  73                 /* Don't leak fds to the agent */
  74                 close_all_fds(NULL, 0);
  75
  76                 stdout_is_tty = isatty(STDOUT_FILENO);
  77                 stderr_is_tty = isatty(STDERR_FILENO);
  78
  79                 if (!stdout_is_tty || !stderr_is_tty) {
  80                         /* Detach from stdout/stderr. and reopen
  81                          * /dev/tty for them. This is important to
  82                          * ensure that when systemctl is started via
  83                          * popen() or a similar call that expects to
  84                          * read EOF we actually do generate EOF and
  85                          * not delay this indefinitely by because we
  86                          * keep an unused copy of stdin around. */
  87                         fd = open("/dev/tty", O_WRONLY);
  88                         if (fd < 0) {
  89                                 log_error("Failed to open /dev/tty: %m");
  90                                 _exit(EXIT_FAILURE);
  91                         }
  92
  93                         if (!stdout_is_tty)
  94                                 dup2(fd, STDOUT_FILENO);
  95
  96                         if (!stderr_is_tty)
  97                                 dup2(fd, STDERR_FILENO);
  98
  99                         if (fd > 2)
 100                                 close(fd);
 101                 }
 102
 103                 execl(SYSTEMD_TTY_ASK_PASSWORD_AGENT_BINARY_PATH, SYSTEMD_TTY_ASK_PASSWORD_AGENT_BINARY_PATH, "--watch", NULL);
 104
 105                 log_error("Unable to execute agent: %m");
 106                 _exit(EXIT_FAILURE);
 107         }
 108 }
 109
 110 void agent_close(void) {
 111
 112         if (agent_pid <= 0)
 113                 return;
 114
 115         /* Inform agent that we are done */
 116         kill(agent_pid, SIGTERM);
 117         kill(agent_pid, SIGCONT);
 118         wait_for_terminate(agent_pid, NULL);
 119         agent_pid = 0;
 120 }