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|
/**** POSIX *******************************************************************/
#include <sys/stat.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/**** RELABSD *****************************************************************/
#include <relabsd/debug.h>
/******************************************************************************/
/**** LOCAL FUNCTIONS *********************************************************/
/******************************************************************************/
/******************************************************************************/
/**** EXPORTED FUNCTIONS ******************************************************/
/******************************************************************************/
/*
* Daemon creation function made using the instructions for old-school daemons
* at https://www.freedesktop.org/software/systemd/man/daemon.html
* Only meant to be used before things really start. This won't properly create
* a daemon on an already running server instance with a virtual device and so
* on...
*/
int relabsd_server_create_daemon (void)
{
int unnamed_pipe[2];
pid_t proc_id;
errno = 0;
if (pipe(unnamed_pipe) == -1)
{
RELABSD_FATAL
(
"Unable to create an unnamed pipe for the daemon creation process: %s",
strerror(errno)
);
return -1;
}
/* 1/ Close all open file descriptors ... **********************************/
/* None were opened at this point, except the pipe, which is still needed. */
/* 2/ Reset all signal handlers ... ****************************************/
/* Those were not modified at this point. */
/* 3/ Reset the signal mask using sigprocmask() ****************************/
/* Not modified at this point. */
/* 4/ Sanitize the environment block ... ***********************************/
/* What? */
/* 5/ fork() ***************************************************************/
errno = 0;
proc_id = fork();
if (proc_id == ((pid_t) -1))
{
RELABSD_FATAL
(
"Step 5 of the daemon creation process, fork(), failed: %s.",
strerror(errno)
);
return -1;
}
if (proc_id != ((pid_t) 0))
{
char buffer;
/* Close the writing end of the pipe, as this process does not use it */
errno = 0;
if (close(unnamed_pipe[1]) == -1)
{
RELABSD_ERROR
(
"Unable to close writing end of an unnamed pipe during the daemon"
" creation process: %s.",
strerror(errno)
);
}
/* Awaiting step 14...*/
errno = 0;
if (read(unnamed_pipe[0], &buffer, (size_t) 1) == -1)
{
RELABSD_ERROR
(
"Unable to read from reading end of an unnamed pipe during the "
" daemon creation process: %s.",
strerror(errno)
);
}
if (close(unnamed_pipe[0]) == -1)
{
RELABSD_ERROR
(
"Unable to close reading end of an unnamed pipe during the daemon"
" creation process: %s.",
strerror(errno)
);
}
/* 15/ Original process exits *******************************************/
exit(0);
}
/* Close reading on the pipe, as this process does not use it */
if (close(unnamed_pipe[0]))
{
}
/* 6/ setsid() *************************************************************/
errno = 0;
proc_id = setsid();
if (proc_id == ((pid_t) -1))
{
RELABSD_FATAL
(
"Step 6 of the daemon creation process, setsid(), failed: %s.",
strerror(errno)
);
return -1;
}
/* 7/ fork() again *********************************************************/
errno = 0;
proc_id = fork();
if (proc_id == ((pid_t) -1))
{
RELABSD_FATAL
(
"Step 5 of the daemon creation process, fork(), failed: %s.",
strerror(errno)
);
return -1;
}
if (proc_id != ((pid_t) 0))
{
errno = 0;
if (close(unnamed_pipe[1]) == -1)
{
RELABSD_ERROR
(
"Unable to close writing end of an unnamed pipe during the daemon"
" creation process: %s.",
strerror(errno)
);
}
/* 8/ First child process exits *****************************************/
exit(0);
}
/* 9/ /dev/null for standard input/outputs *********************************/
/* TODO. */
/* 10/ reset umask to 0 ****************************************************/
/* Can't fail, returns previous mask. */
(void) umask(0);
/* 11/ Set current directory to / ******************************************/
errno = 0;
if (chdir("/") == -1)
{
// Can't print an error message at that point though...
RELABSD_FATAL
(
"Step 11 of the daemon creation process, fork(), failed: %s.",
strerror(errno)
);
errno = 0;
if (write(unnamed_pipe[0], (void *) "!", (size_t) 1) == -1)
{
RELABSD_ERROR
(
"Unable to write to writing end of an unnamed pipe during the"
" daemon creation process: %s.",
strerror(errno)
);
}
return -1;
}
/* 12/ lock file using PID to assert single instance ***********************/
/* Don't want to limit to a single instance. */
/* 13/ Drop privileges *****************************************************/
/* We need those. */
/* 14/ Signal completion ***************************************************/
errno = 0;
if (write(unnamed_pipe[0], (void *) "!", (size_t) 1) == -1)
{
RELABSD_ERROR
(
"Unable to write to writing end of an unnamed pipe during the daemon"
" creation process: %s.",
strerror(errno)
);
}
/* Step 15 is done on the very first process. */
errno = 0;
if (close(unnamed_pipe[1]) == -1)
{
RELABSD_ERROR
(
"Unable to close writing end of an unnamed pipe during the daemon"
" creation process: %s.",
strerror(errno)
);
}
return 0;
}
|
