lxc_init.c

/* SPDX-License-Identifier: LGPL-2.1+ */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <libgen.h>
#include <limits.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include <lxc/lxccontainer.h>
#include <lxc/version.h>

#include "compiler.h"
#include "config.h"
#include "error.h"
#include "initutils.h"
#include "memory_utils.h"
#include "parse.h"
#include "process_utils.h"
#include "string_utils.h"

/* option keys for long only options */
#define OPT_USAGE 0x1000
#define OPT_VERSION (OPT_USAGE - 1)

#define QUOTE(macro) #macro
#define QUOTEVAL(macro) QUOTE(macro)

static sig_atomic_t was_interrupted;

static void interrupt_handler(int sig)
{
	if (!was_interrupted)
		was_interrupted = sig;
}

static struct option long_options[] = {
	    { "name",        required_argument, 0, 'n'         },
	    { "help",        no_argument,       0, 'h'         },
	    { "usage",       no_argument,       0, OPT_USAGE   },
	    { "version",     no_argument,       0, OPT_VERSION },
	    { "quiet",       no_argument,       0, 'q'         },
	    { "lxcpath",     required_argument, 0, 'P'         },
	    { 0,             0,                 0, 0           }
	};
static const char short_options[] = "n:hqo:l:P:";

struct arguments {
	const struct option *options;
	const char *shortopts;

	const char *name;
	bool quiet;
	const char *lxcpath;

	/* remaining arguments */
	char *const *argv;
	int argc;
};

static struct arguments my_args = {
	.options   = long_options,
	.shortopts = short_options
};

static void prevent_forking(void)
{
	__do_free char *line = NULL;
	__do_fclose FILE *f = NULL;
	char path[PATH_MAX];
	size_t len = 0;

	f = fopen("/proc/self/cgroup", "re");
	if (!f)
		return;

	while (getline(&line, &len, f) != -1) {
		__do_close int fd = -EBADF;
		int ret;
		char *p, *p2;

		p = strchr(line, ':');
		if (!p)
			continue;
		p++;
		p2 = strchr(p, ':');
		if (!p2)
			continue;
		*p2 = '\0';

		/* This is a cgroup v2 entry. Skip it. */
		if ((p2 - p) == 0)
			continue;

		if (strcmp(p, "pids") != 0)
			continue;
		p2++;

		p2 += lxc_char_left_gc(p2, strlen(p2));
		p2[lxc_char_right_gc(p2, strlen(p2))] = '\0';

		ret = snprintf(path, sizeof(path),
			       "/sys/fs/cgroup/pids/%s/pids.max", p2);
		if (ret < 0 || (size_t)ret >= sizeof(path)) {
			if (my_args.quiet)
				fprintf(stderr, "Failed to create string\n");
			return;
		}

		fd = open(path, O_WRONLY | O_CLOEXEC);
		if (fd < 0) {
			if (my_args.quiet)
				fprintf(stderr, "Failed to open \"%s\"\n", path);
			return;
		}

		ret = write(fd, "1", 1);
		if (ret != 1 && !my_args.quiet)
			fprintf(stderr, "Failed to write to \"%s\"\n", path);

		return;
	}
}

static void kill_children(pid_t pid)
{
	__do_fclose FILE *f = NULL;
	char path[PATH_MAX];
	int ret;

	ret = snprintf(path, sizeof(path), "/proc/%d/task/%d/children", pid, pid);
	if (ret < 0 || (size_t)ret >= sizeof(path)) {
		if (my_args.quiet)
			fprintf(stderr, "Failed to create string\n");
		return;
	}

	f = fopen(path, "re");
	if (!f) {
		if (my_args.quiet)
			fprintf(stderr, "Failed to open %s\n", path);
		return;
	}

	while (!feof(f)) {
		pid_t find_pid;

		if (fscanf(f, "%d ", &find_pid) != 1) {
			if (my_args.quiet)
				fprintf(stderr, "Failed to retrieve pid\n");
			return;
		}

		(void)kill_children(find_pid);
		(void)kill(find_pid, SIGKILL);
	}
}

static void remove_self(void)
{
	int ret;
	ssize_t n;
	char path[PATH_MAX] = {0};

	n = readlink("/proc/self/exe", path, sizeof(path));
	if (n < 0 || n >= PATH_MAX)
		return;
	path[n] = '\0';

	ret = umount2(path, MNT_DETACH);
	if (ret < 0)
		return;

	ret = unlink(path);
	if (ret < 0)
		return;
}

__noreturn static void print_usage_exit(const struct option longopts[])

{
	fprintf(stderr, "Usage: lxc-init [-n|--name=NAME] [-h|--help] [--usage] [--version]\n\
		[-q|--quiet] [-P|--lxcpath=LXCPATH]\n");
	exit(EXIT_SUCCESS);
}

__noreturn static void print_version_exit(void)
{
	printf("%s\n", LXC_VERSION);
	exit(EXIT_SUCCESS);
}

static void print_help(void)
{
	fprintf(stderr, "\
Usage: lxc-init --name=NAME -- COMMAND\n\
\n\
  lxc-init start a COMMAND as PID 2 inside a container\n\
\n\
Options :\n\
  -n, --name=NAME                  NAME of the container\n\
  -q, --quiet                      Don't produce any output\n\
  -P, --lxcpath=PATH               Use specified container path\n\
  -?, --help                       Give this help list\n\
      --usage                      Give a short usage message\n\
      --version                    Print the version number\n\
\n\
Mandatory or optional arguments to long options are also mandatory or optional\n\
for any corresponding short options.\n\
\n\
See the lxc-init man page for further information.\n\n");
}

static int arguments_parse(struct arguments *args, int argc,
			   char *const argv[])
{
	for (;;) {
		int c;
		int index = 0;

		c = getopt_long(argc, argv, args->shortopts, args->options, &index);
		if (c == -1)
			break;
		switch (c) {
		case 'n':
			args->name = optarg;
			break;
		case 'o':
			break;
		case 'l':
			break;
		case 'q':
			args->quiet = true;
			break;
		case 'P':
			remove_trailing_slashes(optarg);
			args->lxcpath = optarg;
			break;
		case OPT_USAGE:
			print_usage_exit(args->options);
		case OPT_VERSION:
			print_version_exit();
		case '?':
			print_help();
			exit(EXIT_FAILURE);
		case 'h':
			print_help();
			exit(EXIT_SUCCESS);
		}
	}

	/*
	 * Reclaim the remaining command arguments
	 */
	args->argv = &argv[optind];
	args->argc = argc - optind;

	/* If no lxcpath was given, use default */
	if (!args->lxcpath)
		args->lxcpath = lxc_global_config_value("lxc.lxcpath");

	/* Check the command options */
	if (!args->name) {
		if (!args->quiet)
			fprintf(stderr, "lxc-init: missing container name, use --name option\n");
		return -1;
	}

	return 0;
}

int main(int argc, char *argv[])
{
	int i, logfd, ret;
	pid_t pid;
	struct sigaction act;
	sigset_t mask, omask;
	int have_status = 0, exit_with = 1, shutdown = 0;

	if (arguments_parse(&my_args, argc, argv))
		exit(EXIT_FAILURE);

	if (!my_args.argc) {
		if (my_args.quiet)
			fprintf(stderr, "Please specify a command to execute\n");
		exit(EXIT_FAILURE);
	}

	/* Mask all the signals so we are safe to install a signal handler and
	 * to fork.
	 */
	ret = sigfillset(&mask);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&mask, SIGILL);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&mask, SIGSEGV);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&mask, SIGBUS);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = pthread_sigmask(SIG_SETMASK, &mask, &omask);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigfillset(&act.sa_mask);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&act.sa_mask, SIGILL);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&act.sa_mask, SIGSEGV);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&act.sa_mask, SIGBUS);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&act.sa_mask, SIGSTOP);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = sigdelset(&act.sa_mask, SIGKILL);
	if (ret < 0)
		exit(EXIT_FAILURE);

	act.sa_flags = 0;
	act.sa_handler = interrupt_handler;

	for (i = 1; i < NSIG; i++) {
		/* Exclude some signals: ILL, SEGV and BUS are likely to reveal
		 * a bug and we want a core. STOP and KILL cannot be handled
		 * anyway: they're here for documentation. 32 and 33 are not
		 * defined.
		 */
		if (i == SIGILL || i == SIGSEGV || i == SIGBUS ||
		    i == SIGSTOP || i == SIGKILL || i == 32 || i == 33)
			continue;

		ret = sigaction(i, &act, NULL);
		if (ret < 0) {
			if (errno == EINVAL)
				continue;

			if (my_args.quiet)
				fprintf(stderr, "Failed to change signal action\n");
			exit(EXIT_FAILURE);
		}
	}

	remove_self();

	pid = fork();
	if (pid < 0)
		exit(EXIT_FAILURE);

	if (!pid) {
		/* restore default signal handlers */
		for (i = 1; i < NSIG; i++) {
			sighandler_t sigerr;

			if (i == SIGILL || i == SIGSEGV || i == SIGBUS ||
			    i == SIGSTOP || i == SIGKILL || i == 32 || i == 33)
				continue;

			sigerr = signal(i, SIG_DFL);
			if (sigerr == SIG_ERR && !my_args.quiet)
				fprintf(stderr, "Failed to reset to default action for signal \"%d\": %d\n", i, pid);
		}

		ret = pthread_sigmask(SIG_SETMASK, &omask, NULL);
		if (ret < 0) {
			if (my_args.quiet)
				fprintf(stderr, "Failed to set signal mask\n");
			exit(EXIT_FAILURE);
		}

		(void)setsid();

		(void)ioctl(STDIN_FILENO, TIOCSCTTY, 0);

		ret = execvp(my_args.argv[0], my_args.argv);
		if (my_args.quiet)
			fprintf(stderr, "Failed to exec \"%s\"\n", my_args.argv[0]);
		exit(ret);
	}
	logfd = open("/dev/console", O_WRONLY | O_NOCTTY | O_CLOEXEC);
	if (logfd >= 0) {
		ret = dup3(logfd, STDERR_FILENO, O_CLOEXEC);
		if (ret < 0)
			exit(EXIT_FAILURE);
	}

	(void)setproctitle("init");

	/* Let's process the signals now. */
	ret = sigdelset(&omask, SIGALRM);
	if (ret < 0)
		exit(EXIT_FAILURE);

	ret = pthread_sigmask(SIG_SETMASK, &omask, NULL);
	if (ret < 0) {
		if (my_args.quiet)
			fprintf(stderr, "Failed to set signal mask\n");
		exit(EXIT_FAILURE);
	}

	/* No need of other inherited fds but stderr. */
	close(STDIN_FILENO);
	close(STDOUT_FILENO);

	for (;;) {
		int status;
		pid_t waited_pid;

		switch (was_interrupted) {
		case 0:
		/* Some applications send SIGHUP in order to get init to reload
		 * its configuration. We don't want to forward this onto the
		 * application itself, because it probably isn't expecting this
		 * signal since it was expecting init to do something with it.
		 *
		 * Instead, let's explicitly ignore it here. The actual
		 * terminal case is handled in the monitor's handler, which
		 * sends this task a SIGTERM in the case of a SIGHUP, which is
		 * what we want.
		 */
		case SIGHUP:
			break;
		case SIGPWR:
		case SIGTERM:
			if (!shutdown) {
				pid_t mypid = lxc_raw_getpid();

				shutdown = 1;
				prevent_forking();
				if (mypid != 1) {
					kill_children(mypid);
				} else {
					ret = kill(-1, SIGTERM);
					if (ret < 0 && !my_args.quiet)
						fprintf(stderr, "Failed to send SIGTERM to all children\n");
				}
				alarm(1);
			}
			break;
		case SIGALRM: {
			pid_t mypid = lxc_raw_getpid();

			prevent_forking();
			if (mypid != 1) {
				kill_children(mypid);
			} else {
				ret = kill(-1, SIGKILL);
				if (ret < 0 && !my_args.quiet)
					fprintf(stderr, "Failed to send SIGTERM to all children\n");
			}
			break;
		}
		default:
			kill(pid, was_interrupted);
			break;
		}
		ret = EXIT_SUCCESS;

		was_interrupted = 0;
		waited_pid = wait(&status);
		if (waited_pid < 0) {
			if (errno == ECHILD)
				goto out;

			if (errno == EINTR)
				continue;

			if (my_args.quiet)
				fprintf(stderr, "Failed to wait on child %d\n", pid);
			ret = -1;
			goto out;
		}

		/* Reset timer each time a process exited. */
		if (shutdown)
			alarm(1);

		/* Keep the exit code of the started application (not wrapped
		 * pid) and continue to wait for the end of the orphan group.
		 */
		if (waited_pid == pid && !have_status) {
			exit_with = lxc_error_set_and_log(waited_pid, status);
			have_status = 1;
		}
	}
out:
	if (ret < 0)
		exit(EXIT_FAILURE);
	exit(exit_with);
}