/**
* mds — A micro-display server
* Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "mds.h"
#include <libmdsserver/config.h>
#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <time.h>
#include <dirent.h>
/**
* Number of elements in `argv`
*/
static int argc;
/**
* Command line arguments
*/
static char** argv;
/**
* The master server
*/
static const char* master_server = LIBEXECDIR "/mds-server";
/**
* Entry point of the program
*
* @param argc_ Number of elements in `argv_`
* @param argv_ Command line arguments
* @return Non-zero on error
*/
int main(int argc_, char** argv_)
{
int fd = -1;
int got_master_server = 0;
struct sockaddr_un address;
char pathname[PATH_MAX];
char piddata[64];
unsigned int display;
FILE* f;
int rc;
int j, r;
argc = argc_;
argv = argv_;
/* Sanity check the number of command line arguments. */
exit_if (argc > ARGC_LIMIT,
eprint("that number of arguments is ridiculous, I will not allow it."););
/* Parse command line arguments. */
for (j = 1; j < argc; j++)
{
char* arg = argv[j];
if (startswith(arg, "--master-server=")) /* Master server. */
{
exit_if (got_master_server,
eprintf("duplicate declaration of %s.", "--master-server"););
got_master_server = 1;
master_server = arg + strlen("--master-server=");
}
}
/* Stymied if the effective user is not root. */
exit_if (geteuid() != ROOT_USER_UID,
eprint("the effective user is not root, cannot continue."););
/* Set up to ignore SIGUSR1, used in mds for re-exec, but we cannot re-exec. */
if (xsigaction(SIGUSR1, SIG_IGN) < 0)
perror(*argv);
/* Set up to ignore SIGDANGER. */
if (xsigaction(SIGDANGER, SIG_IGN) < 0)
perror(*argv);
/* Create directory for socket files, PID files and such. */
if (create_directory_root(MDS_RUNTIME_ROOT_DIRECTORY))
return 1;
/* Determine display index. */
for (display = 0; display < DISPLAY_MAX; display++)
{
xsnprintf(pathname, "%s/%u.pid", MDS_RUNTIME_ROOT_DIRECTORY, display);
fd = open(pathname, O_CREAT | O_EXCL);
if (fd == -1)
{
/* Reuse display index if no longer used. */
f = fopen(pathname, "r");
if (f == NULL) /* Race, or error? */
{
perror(*argv);
continue;
}
r = is_pid_file_reusable(f);
fclose(f);
if (r == 0)
continue;
}
close(fd);
break;
}
exit_if (display == DISPLAY_MAX,
eprint("sorry, too many displays on the system."););
/* Yes, the directory could have been removed, but it probably was not. */
/* Create PID file. */
fail_if ((f = fopen(pathname, "w")) == NULL);
xsnprintf(piddata, "%u\n", getpid());
if (fwrite(piddata, 1, strlen(piddata), f) < strlen(piddata))
{
fclose(f);
if (unlink(pathname) < 0)
perror(*argv);
return 1;
}
fflush(f);
fclose(f);
if (chmod(pathname, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
perror(*argv);
/* Create data storage directory. */
xsnprintf(pathname, "%s/%u.data", MDS_STORAGE_ROOT_DIRECTORY, display);
fail_if (create_directory_root(MDS_STORAGE_ROOT_DIRECTORY));
fail_if (unlink_recursive(pathname));
fail_if (create_directory_user(pathname));
/* Save MDS_DISPLAY environment variable. */
xsnprintf(pathname, /* Excuse the reuse without renaming. */
":%u", display);
fail_if (setenv(DISPLAY_ENV, pathname, 1) < 0);
/* Create display socket. */
xsnprintf(pathname, "%s/%u.socket", MDS_RUNTIME_ROOT_DIRECTORY, display);
address.sun_family = AF_UNIX;
strcpy(address.sun_path, pathname);
unlink(pathname);
fail_if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0);
fail_if (fchmod(fd, S_IRWXU) < 0);
fail_if (bind(fd, (struct sockaddr*)(&address), sizeof(address)) < 0);
fail_if (chown(pathname, getuid(), NOBODY_GROUP_GID) < 0);
/* Start listening on socket. */
fail_if (listen(fd, SOMAXCONN) < 0);
/* Start master server and respawn it if it crashes. */
rc = spawn_and_respawn_server(fd);
done:
/* Shutdown, close and remove the socket. */
if (fd != -1)
{
shutdown(fd, SHUT_RDWR);
close(fd);
unlink(pathname);
}
/* Remove PID file. */
xsnprintf(pathname, "%s/%u.pid", MDS_RUNTIME_ROOT_DIRECTORY, display);
unlink(pathname);
/* Remove directories. */
rmdir(MDS_RUNTIME_ROOT_DIRECTORY); /* Do not care if it fails, it is probably used by another display. */
rmdir(MDS_STORAGE_ROOT_DIRECTORY); /* Do not care if it fails, it is probably used by another display. */
xsnprintf(pathname, "%s/%u.data", MDS_STORAGE_ROOT_DIRECTORY, display);
unlink_recursive(pathname); /* An error will be printed on error, do nothing more. */
return rc;
pfail:
perror(*argv);
rc = 1;
goto done;
}
/**
* Read a PID-file and determine whether it refers to an non-existing process
*
* @param f The PID-file
* @return Whether the PID-file is not longer used
*/
int is_pid_file_reusable(FILE* f)
{
char piddata[64];
size_t read_len;
read_len = fread(piddata, 1, sizeof(piddata) / sizeof(char), f);
if (ferror(f)) /* Failed to read. */
perror(*argv);
else if (feof(f) == 0) /* Did not read everything. */
eprint("the content of a PID file is larger than expected.");
else
{
pid_t pid = parse_pid_t(piddata, read_len - 1);
if (pid == (pid_t)-1)
eprint("the content of a PID file is invalid.");
else
if (kill(pid, 0) < 0) /* Check if the PID is still allocated to any process. */
return errno == ESRCH; /* PID is not used. */
}
return 0;
}
/**
* Parse an LF-terminated string as a non-negative `pid_t`
*
* @param str The string
* @param n The length of the string, excluding LF-termination
* @return The pid, `(pid_t)-1` if malformated
*/
pid_t parse_pid_t(const char* str, size_t n)
{
pid_t pid = 0;
size_t i;
for (i = 0; i < n; i++)
{
char c = str[i];
if (('0' <= c) && (c <= '9'))
pid = pid * 10 + (c & 15);
else
return (pid_t)-1;
}
if (str[n] != '\n')
return (pid_t)-1;
return pid;
}
/**
* Drop privileges and change execution image into the master server's image.
* This function will only return on error.
*
* @param child_args Command line arguments for the new image
*/
static void exec_master_server(char** child_args)
{
/* Drop privileges. They most not be propagated non-authorised components. */
/* setgid should not be set, but just to be safe we are restoring both user and group. */
if (drop_privileges())
return;
/* Start master server. */
execv(master_server, child_args);
}
/**
* Start master server and respawn it if it crashes
*
* @param fd The file descriptor of the socket
* @return Non-zero on error
*/
int spawn_and_respawn_server(int fd)
{
int time_error = 0;
int first_spawn = 1;
int rc = 0;
struct timespec time_start;
struct timespec time_end;
char* child_args[ARGC_LIMIT + LIBEXEC_ARGC_EXTRA_LIMIT + 1];
char fdstr[12 /* strlen("--socket-fd=") */ + 64];
int i;
pid_t pid;
int status;
child_args[0] = strdup(master_server);
for (i = 1; i < argc; i++)
child_args[i] = argv[i];
child_args[argc + 0] = strdup("--initial-spawn");
xsnprintf(fdstr, "--socket-fd=%i", fd);
child_args[argc + 1] = fdstr;
child_args[argc + 2] = NULL;
#if (LIBEXEC_ARGC_EXTRA_LIMIT < 2)
# error LIBEXEC_ARGC_EXTRA_LIMIT is too small, need at least 2.
#endif
respawn:
pid = fork();
if (pid == (pid_t)-1)
goto pfail;
if (pid == 0) /* Child. */
{
rc++;
exec_master_server(child_args);
goto pfail;
}
/* Parent. */
/* Get the current time. (Start of child process.) */
if ((time_error = (monotone(&time_start) < 0)))
perror(*argv);
/* Wait for master server to die. */
if (uninterruptable_waitpid(pid, &status, 0) == (pid_t)-1)
goto pfail;
/* If the server exited normally or SIGTERM, do not respawn. */
if (WIFEXITED(status) ? (WEXITSTATUS(status) == 0) :
((WTERMSIG(status) == SIGTERM) || (WTERMSIG(status) == SIGINT)))
goto done; /* Child exited normally, stop. */
/* Get the current time. (End of child process.) */
time_error |= (monotone(&time_end) < 0);
if (WIFEXITED(status))
eprintf("`%s' exited with code %i.", master_server, WEXITSTATUS(status));
else
eprintf("`%s' died by signal %i.", master_server, WTERMSIG(status));
/* Do not respawn if we could not read the time. */
if (time_error)
{
perror(*argv);
eprintf("`%s' died abnormally, not respawning because we could not read the time.", master_server);
goto fail;
}
/* Respawn if the server did not die too fast. */
if (time_end.tv_sec - time_start.tv_sec >= RESPAWN_TIME_LIMIT_SECONDS)
eprintf("`%s' died abnormally, respawning.", master_server);
else
{
eprintf("`%s' died abnormally, died too fast, not respawning.", master_server);
goto fail;
}
if (first_spawn)
{
first_spawn = 0;
free(child_args[argc + 0]);
child_args[argc + 0] = strdup("--respawn");
if (child_args[argc + 0] == NULL)
goto pfail;
}
goto respawn;
done:
rc--;
fail:
rc++;
free(child_args[0]);
free(child_args[argc + 0]);
if (rc == 2)
_exit(1);
return rc;
pfail:
perror(*argv);
goto fail;
}
/**
* Create a directory owned by the root user and root group
*
* @param pathname The pathname of the directory to create
* @return Non-zero on error
*/
int create_directory_root(const char* pathname)
{
struct stat attr;
if (stat(pathname, &attr) == 0)
{
/* Cannot create the directory, its pathname refers to an existing. */
if (S_ISDIR(attr.st_mode) == 0)
{
/* But it is not a directory so we cannot continue. */
eprintf("%s already exists but is not a directory.", pathname);
return 1;
}
}
else
/* Directory is missing, create it. */
if (mkdir(pathname, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH) < 0)
{
if (errno != EEXIST) /* Unlikely race condition. */
goto pfail;
}
else
/* Set ownership. */
if (chown(pathname, ROOT_USER_UID, ROOT_GROUP_GID) < 0)
goto pfail;
return 0;
pfail:
perror(*argv);
return 1;
}
/**
* Create a directory owned by the real user and nobody group
*
* @param pathname The pathname of the directory to create
* @return Non-zero on error
*/
int create_directory_user(const char* pathname)
{
struct stat attr;
if (stat(pathname, &attr) == 0)
{
/* Cannot create the directory, its pathname refers to an existing. */
if (S_ISDIR(attr.st_mode) == 0)
{
/* But it is not a directory so we cannot continue. */
eprintf("%s already exists but is not a directory.", pathname);
return 1;
}
}
else
{
/* Directory is missing, create it. */
if (mkdir(pathname, S_IRWXU) < 0)
{
if (errno != EEXIST) /* Unlikely race condition. */
{
perror(*argv);
return 1;
}
}
else
/* Set ownership. */
if (chown(pathname, getuid(), NOBODY_GROUP_GID) < 0)
{
perror(*argv);
return 1;
}
}
return 0;
}
/**
* Recursively remove a directory
*
* @param pathname The pathname of the directory to remove
* @return Non-zero on error, but zero if the directory does not exist
*/
int unlink_recursive(const char* pathname)
{
DIR* dir = opendir(pathname);
int rc = 0;
struct dirent* file;
/* Check that we could examine the directory. */
if (dir == NULL)
{
int errno_ = errno;
struct stat _attr;
if (stat(pathname, &_attr) < 0)
return 0; /* Directory does not exist. */
errno = errno_;
goto pfail;
}
/* Remove the content of the directory. */
while ((file = readdir(dir)) != NULL)
if (strcmp(file->d_name, ".") &&
strcmp(file->d_name, "..") &&
(unlink(file->d_name) < 0))
{
if (errno != EISDIR)
goto pfail;
unlink_recursive(file->d_name);
}
/* Remove the drectory. */
if (rmdir(pathname) < 0)
goto pfail;
done:
if (dir != NULL)
closedir(dir);
return rc;
pfail:
perror(*argv);
rc = -1;
goto done;
}
