bootstrap-initrd

init.c (2612B)

// bootstrap-initrd: Linux initrd to bootstrap from a small binary seed
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _POSIX_C_SOURCE 200809L
#define _XOPEN_SOURCE 700 // mknod
#include "loksh_tcc.h"
#include <errno.h>
#include <fcntl.h>  // O_RDONLY
#include <spawn.h>  // posix_spawn
#include <stdio.h>  // fprintf
#include <stdlib.h> // setenv
#include <string.h> // strerror
#include <sys/mount.h>
#include <sys/stat.h>      // mknod
#include <sys/sysmacros.h> // makedev
#include <sys/wait.h>      // waitpid
#include <unistd.h>        // chdir, environ
/* From SUS Chapter 8: Environment variable */
extern char **environ;
static int
exec_wait(char *args[])
{
	pid_t child = 0;
	// Allows to avoid a fork+exec
	int ret = posix_spawn(&child, args[0], NULL, NULL, args, environ);
	if(ret != 0)
	{
		fprintf(stderr, "Failed spawning command with argv[0] = '%s': %s\n", args[0], strerror(errno));
		return -1;
	}
	if(waitpid(child, NULL, 0) == -1)
	{
		fprintf(stderr, "Failed waiting for child of pid %d: %s\n", child, strerror(errno));
		return -1;
	}
	return 0;
}
static int
build_loksh()
{
	chdir("/loksh-7.6");
	fprintf(stderr, "Compiling loksh-7.6\n");
	if(exec_wait(loksh_tcc_cmd) < 0) return -1;
	fprintf(stderr, "Compiled loksh !\n");
	return 0;
}
int
main(int argc, char *argv[])
{
	setenv("PATH", "/bin:/usr/bin:/usr/local/bin", 1);
	setenv("HOME", "/root", 1);
	setenv("LOGNAME", "root", 1);
	if(build_loksh() < 0) return 1;
	if(mount("sysfs", "/sys", "sysfs", MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_RELATIME, NULL) < 0)
		fprintf(stderr, "Failed to mount /sys: %s\n", strerror(errno));
	if(mount("proc", "/proc", "proc", MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_RELATIME, "hidepid=2") <
	   0)
		fprintf(stderr, "Failed to mount /proc: %s\n", strerror(errno));
	if(mount("devtmpfs", "/dev", "devtmpfs", MS_NOSUID | MS_NOEXEC, NULL) < 0)
		fprintf(stderr, "Failed to mount /proc: %s\n", strerror(errno));
	errno = 0;
	if(mknod("/dev/null", S_IFCHR | 0666, makedev(0x1, 0x3)) < 0)
	{
		if(errno != 0 && errno != EEXIST)
			fprintf(stderr, "Failed to create /dev/null: %s\n", strerror(errno));
	}
	// PS1 shouldn't be exported but '\h\$ ' is an *awful* default
	// and oksh also doesn't sources ksh-specific files by default
	setenv("PS1", "$? $PWD # ", 1);
	fprintf(stderr, "Launching: /bin/loksh /init.sh\n");
	if(execl("/bin/loksh", "/bin/loksh", "/init.sh", (char *)0) < 0)
	{
		fprintf(stderr, "Failed to execute: %s\n", strerror(errno));
		return 1;
	}
	fprintf(stderr, "Unreachable\n");
}