138 lines
2.7 KiB
C
138 lines
2.7 KiB
C
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/* See LICENSE file for copyright and license details. */
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#include <stdio.h>
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#include <stdlib.h>
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#include <linux/magic.h>
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#include <linux/limits.h>
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#include <unistd.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/vfs.h>
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#include <fcntl.h>
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#include <dirent.h>
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#include "util.h"
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static void
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delete_content(const char *dir, dev_t curdevice)
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{
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char path[PATH_MAX];
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DIR *d;
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struct stat st;
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struct dirent *dent;
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/* don't dive into other filesystems */
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if (lstat(dir, &st) || st.st_dev != curdevice){
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return;
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}
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/* delete contents recursively */
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if (S_ISDIR(st.st_mode)) {
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d = opendir(dir);
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if (d) {
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for(; (dent = readdir(d)) ;) {
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/* skip ".." and "." */
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if (dent->d_name[0] == '.'
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&& ((dent->d_name[1] == '.' && dent->d_name[2] == 0)
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|| (dent->d_name[1] == 0)))
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{
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continue;
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}
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/* build path and dive deeper */
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strlcat(path, dir, sizeof(path));
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strlcat(path, dent->d_name, sizeof(path));
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delete_content(path, curdevice);
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path[0] = 0;
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}
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closedir(d);
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/* remove now empty dir */
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rmdir(dir);
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}
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} else {
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/* unlink non-directory */
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unlink(dir);
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}
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}
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static void
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usage(void)
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{
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eprintf("usage: %s [-c console] [newroot] [init] (PID 1)\n", argv0);
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}
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int
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main(int argc, char **argv)
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{
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char *console = NULL;
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dev_t curdev;
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struct stat st;
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struct statfs stfs;
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ARGBEGIN {
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case 'c':
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console = EARGF(usage());
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break;
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default:
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usage();
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} ARGEND;
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/* check number of args and if we are PID 1 */
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if (argc != 2 || getpid() != 1){
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usage();
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}
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/* chdir to newroot and make sure it's a different fs */
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if (chdir(argv[0])) {
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eprintf("chdir %s:", argv[0]);
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}
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if (stat("/", &st)) {
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eprintf("stat %s:", "/");
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}
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curdev = st.st_dev;
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if (stat(".", &st)) {
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eprintf("stat %s:", ".");
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}
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if (st.st_dev == curdev) {
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usage();
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}
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/* further checks */
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if (stat("/init", &st) || !S_ISREG(st.st_mode)) {
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/* avoids trouble with real filesystems */
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eprintf("/init is not a regular file\n");
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}
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statfs("/", &stfs);
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if ((unsigned)stfs.f_type != RAMFS_MAGIC && (unsigned)stfs.f_type != TMPFS_MAGIC){
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eprintf("current filesystem is not a RAMFS or TMPFS\n");
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}
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/* wipe / */
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delete_content("/", curdev);
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/* overmount / with newroot and chroot into it */
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if (mount(".", "/", NULL, MS_MOVE, NULL)) {
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eprintf("mount %s:", ".");
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}
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if (chroot(".")) {
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eprintf("chroot failed\n");
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}
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/* if -c is set, redirect stdin/stdout/stderr to console */
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if (console) {
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close(0);
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if(open(console, O_RDWR) == -1){
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eprintf("open %s:", console);
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}
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if (dup2(0,1) == -1){
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eprintf("dup2 %s:", "0,1");
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}
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if (dup2(0,2) == -1){
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eprintf("dup2 %s:", "0,2");
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}
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}
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/* execute init */
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execv(argv[1], argv);
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eprintf("can't execute '%s'\n", argv[1]);
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}
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