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/util-linux-ng/sys-utils/switch_root.c

https://review.tizen.org/git/
C | 273 lines | 193 code | 44 blank | 36 comment | 52 complexity | c704d8afa2890c82389b191bf82adee7 MD5 | raw file
  1/*
  2 * switchroot.c - switch to new root directory and start init.
  3 *
  4 * Copyright 2002-2009 Red Hat, Inc.  All rights reserved.
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License as published by
  8 * the Free Software Foundation; either version 2 of the License, or
  9 * (at your option) any later version.
 10 *
 11 * This program is distributed in the hope that it will be useful,
 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14 * GNU General Public License for more details.
 15 *
 16 * You should have received a copy of the GNU General Public License
 17 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 18 *
 19 * Authors:
 20 *	Peter Jones <pjones@redhat.com>
 21 *	Jeremy Katz <katzj@redhat.com>
 22 */
 23#include <sys/mount.h>
 24#include <sys/types.h>
 25#include <sys/stat.h>
 26#include <sys/param.h>
 27#include <fcntl.h>
 28#include <stdio.h>
 29#include <stdlib.h>
 30#include <unistd.h>
 31#include <string.h>
 32#include <errno.h>
 33#include <ctype.h>
 34#include <dirent.h>
 35#include <err.h>
 36#include <libgen.h>
 37
 38#ifndef MS_MOVE
 39#define MS_MOVE 8192
 40#endif
 41
 42/* remove all files/directories below dirName -- don't cross mountpoints */
 43static int recursiveRemove(int fd)
 44{
 45	struct stat rb;
 46	DIR *dir;
 47	int rc = -1;
 48	int dfd;
 49
 50	if (!(dir = fdopendir(fd))) {
 51		warn("failed to open directory");
 52		goto done;
 53	}
 54
 55	/* fdopendir() precludes us from continuing to use the input fd */
 56	dfd = dirfd(dir);
 57
 58	if (fstat(dfd, &rb)) {
 59		warn("failed to stat directory");
 60		goto done;
 61	}
 62
 63	while(1) {
 64		struct dirent *d;
 65
 66		errno = 0;
 67		if (!(d = readdir(dir))) {
 68			if (errno) {
 69				warn("failed to read directory");
 70				goto done;
 71			}
 72			break;	/* end of directory */
 73		}
 74
 75		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
 76			continue;
 77
 78		if (d->d_type == DT_DIR) {
 79			struct stat sb;
 80
 81			if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
 82				warn("failed to stat %s", d->d_name);
 83				continue;
 84			}
 85
 86			/* remove subdirectories if device is same as dir */
 87			if (sb.st_dev == rb.st_dev) {
 88				int cfd;
 89
 90				cfd = openat(dfd, d->d_name, O_RDONLY);
 91				if (cfd >= 0) {
 92					recursiveRemove(cfd);
 93					close(cfd);
 94				}
 95			} else
 96				continue;
 97		}
 98
 99		if (unlinkat(dfd, d->d_name,
100			     d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
101			warn("failed to unlink %s", d->d_name);
102	}
103
104	rc = 0;	/* success */
105
106done:
107	if (dir)
108		closedir(dir);
109	return rc;
110}
111
112/* find the enclosing mount point of a path, by examining the backing device
113 * of parent directories until we reach / or find a parent with a differing
114 * device. Result must be freed.
115 */
116static char *get_parent_mount(const char *path)
117{
118	struct stat sb;
119	char *dir;
120	char tmp[PATH_MAX];
121	dev_t inner_dev;
122
123	if (stat(path, &sb) != 0) {
124		warn("failed to stat %s", path);
125		return NULL;
126	}
127
128	inner_dev = sb.st_dev;
129	dir = strdup(path);
130
131	while (dir) {
132		char *parent;
133
134		strncpy(tmp, dir, PATH_MAX);
135		tmp[PATH_MAX - 1] = '\0';
136		parent = dirname(tmp);
137
138		if (stat(parent, &sb) != 0) {
139			warn("failed to stat %s", parent);
140			return NULL;
141		}
142		if (sb.st_dev != inner_dev)
143			return dir;
144
145		strncpy(dir, parent, PATH_MAX);
146		dir[PATH_MAX - 1] = '\0';
147
148		/* maybe we've reached / */
149		if (*dir == '/' && !*(dir + 1))
150			return dir;
151	}
152	return NULL;
153}
154
155static int switchroot(const char *newroot)
156{
157	/*  Don't try to unmount the old "/", there's no way to do it. */
158	const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
159	int i;
160	int cfd, rc = -1;
161	pid_t pid;
162	const char *chroot_path = NULL;
163	char *newroot_mnt;
164
165	for (i = 0; umounts[i] != NULL; i++) {
166		char newmount[PATH_MAX];
167
168		snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
169
170		if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
171			warn("failed to mount moving %s to %s",
172				umounts[i], newmount);
173			warnx("forcing unmount of %s", umounts[i]);
174			umount2(umounts[i], MNT_FORCE);
175		}
176	}
177
178	newroot_mnt = get_parent_mount(newroot);
179	if (newroot_mnt && strcmp(newroot, newroot_mnt)) {
180		/* newroot is not a mount point, so we have to MS_MOVE the
181		 * parent mount point and then chroot in to the "subroot"
182		 */
183		chroot_path = newroot + strlen(newroot_mnt);
184		newroot = newroot_mnt;
185	}
186
187	if (chdir(newroot)) {
188		warn("failed to change directory to %s", newroot);
189		goto done;
190	}
191
192	cfd = open("/", O_RDONLY);
193
194	if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
195		warn("failed to mount moving %s to /", newroot);
196		goto done;
197	}
198
199	/* move to the real root of the device */
200	if (chroot(".")) {
201		warn("failed to change root");
202		goto done;
203	}
204
205	/* move to the subdirectory on the root device (subroot) */
206	if (chroot_path) {
207		if (chdir(chroot_path)) {
208			warn("failed to chdir to subroot %s", chroot_path);
209			goto done;
210		}
211		if (chroot(".")) {
212			warn("failed to change root to subroot %s", chroot_path);
213			goto done;
214		}
215	}
216
217	if (cfd >= 0) {
218		pid = fork();
219		if (pid <= 0) {
220			recursiveRemove(cfd);
221			if (pid == 0)
222				exit(EXIT_SUCCESS);
223		}
224		close(cfd);
225	}
226	rc = 0;
227done:
228	free(newroot_mnt);
229	return rc;
230}
231
232static void usage(FILE *output)
233{
234	fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
235			program_invocation_short_name);
236	exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
237}
238
239static void version(void)
240{
241	fprintf(stdout,  "%s from %s\n", program_invocation_short_name,
242			PACKAGE_STRING);
243	exit(EXIT_SUCCESS);
244}
245
246int main(int argc, char *argv[])
247{
248	char *newroot, *init, **initargs;
249
250	if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
251		usage(stdout);
252	if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
253		version();
254	if (argc < 3)
255		usage(stderr);
256
257	newroot = argv[1];
258	init = argv[2];
259	initargs = &argv[2];
260
261	if (!*newroot || !*init)
262		usage(stderr);
263
264	if (switchroot(newroot))
265		errx(EXIT_FAILURE, "failed. Sorry.");
266
267	if (access(init, X_OK))
268		warn("cannot access %s", init);
269
270	execv(init, initargs);
271	err(EXIT_FAILURE, "failed to execute %s", init);
272}
273