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/*
* switchroot.c - switch to new root directory and start init.
*
* Copyright 2002-2009 Red Hat, Inc. All rights reserved.
*
* 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 2 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/>.
*
* Authors:
* Peter Jones <pjones@redhat.com>
* Jeremy Katz <katzj@redhat.com>
*/
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <dirent.h>
#include "c.h"
#ifndef MS_MOVE
#define MS_MOVE 8192
#endif
/* remove all files/directories below dirName -- don't cross mountpoints */
static int recursiveRemove(int fd)
{
struct stat rb;
DIR *dir;
int rc = -1;
int dfd;
if (!(dir = fdopendir(fd))) {
warn("failed to open directory");
goto done;
}
/* fdopendir() precludes us from continuing to use the input fd */
dfd = dirfd(dir);
if (fstat(dfd, &rb)) {
warn("failed to stat directory");
goto done;
}
while(1) {
struct dirent *d;
errno = 0;
if (!(d = readdir(dir))) {
if (errno) {
warn("failed to read directory");
goto done;
}
break; /* end of directory */
}
if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
continue;
if (d->d_type == DT_DIR) {
struct stat sb;
if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
warn("failed to stat %s", d->d_name);
continue;
}
/* remove subdirectories if device is same as dir */
if (sb.st_dev == rb.st_dev) {
int cfd;
cfd = openat(dfd, d->d_name, O_RDONLY);
if (cfd >= 0) {
recursiveRemove(cfd);
close(cfd);
}
} else
continue;
}
if (unlinkat(dfd, d->d_name,
d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
warn("failed to unlink %s", d->d_name);
}
rc = 0; /* success */
done:
if (dir)
closedir(dir);
return rc;
}
static int switchroot(const char *newroot)
{
/* Don't try to unmount the old "/", there's no way to do it. */
const char *umounts[] = { "/dev", "/proc", "/sys", "/run", NULL };
int i;
int cfd;
pid_t pid;
struct stat newroot_stat, sb;
if (stat(newroot, &newroot_stat) != 0) {
warn("failed to stat directory %s", newroot);
return -1;
}
for (i = 0; umounts[i] != NULL; i++) {
char newmount[PATH_MAX];
snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
if ((stat(newmount, &sb) != 0) || (sb.st_dev != newroot_stat.st_dev)) {
/* mount point seems to be mounted already or stat failed */
umount(umounts[i]);
continue;
}
if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
warn("failed to mount moving %s to %s",
umounts[i], newmount);
warnx("forcing unmount of %s", umounts[i]);
umount2(umounts[i], MNT_FORCE);
}
}
if (chdir(newroot)) {
warn("failed to change directory to %s", newroot);
return -1;
}
cfd = open("/", O_RDONLY);
if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
warn("failed to mount moving %s to /", newroot);
return -1;
}
if (chroot(".")) {
warn("failed to change root");
return -1;
}
if (cfd >= 0) {
pid = fork();
if (pid <= 0) {
recursiveRemove(cfd);
if (pid == 0)
exit(EXIT_SUCCESS);
}
close(cfd);
}
return 0;
}
static void usage(FILE *output)
{
fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
program_invocation_short_name);
exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
}
static void version(void)
{
fprintf(stdout, "%s from %s\n", program_invocation_short_name,
PACKAGE_STRING);
exit(EXIT_SUCCESS);
}
int main(int argc, char *argv[])
{
char *newroot, *init, **initargs;
if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
usage(stdout);
if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
version();
if (argc < 3)
usage(stderr);
newroot = argv[1];
init = argv[2];
initargs = &argv[2];
if (!*newroot || !*init)
usage(stderr);
if (switchroot(newroot))
errx(EXIT_FAILURE, "failed. Sorry.");
if (access(init, X_OK))
warn("cannot access %s", init);
execv(init, initargs);
err(EXIT_FAILURE, "failed to execute %s", init);
}
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