busybox/util-linux/switch_root.c

/* vi: set sw=4 ts=4: */
/* Copyright 2005 Rob Landley <rob@landley.net>
 *
 * Switch from rootfs to another filesystem as the root of the mount tree.
 *
 * Licensed under GPL version 2, see file LICENSE in this tarball for details.
 */

#include "libbb.h"
#include <sys/vfs.h>

// Make up for header deficiencies.
#ifndef RAMFS_MAGIC
#define RAMFS_MAGIC ((unsigned)0x858458f6)
#endif

#ifndef TMPFS_MAGIC
#define TMPFS_MAGIC ((unsigned)0x01021994)
#endif

#ifndef MS_MOVE
#define MS_MOVE     8192
#endif

// Recursively delete contents of rootfs.
static void delete_contents(const char *directory, dev_t rootdev)
{
	DIR *dir;
	struct dirent *d;
	struct stat st;

	// Don't descend into other filesystems
	if (lstat(directory, &st) || st.st_dev != rootdev)
		return;

	// Recursively delete the contents of directories.
	if (S_ISDIR(st.st_mode)) {
		dir = opendir(directory);
		if (dir) {
			while ((d = readdir(dir))) {
				char *newdir = d->d_name;

				// Skip . and ..
				if (DOT_OR_DOTDOT(newdir))
					continue;

				// Recurse to delete contents
				newdir = concat_path_file(directory, newdir);
				delete_contents(newdir, rootdev);
				free(newdir);
			}
			closedir(dir);

			// Directory should now be empty.  Zap it.
			rmdir(directory);
		}

	// It wasn't a directory.  Zap it.
	} else unlink(directory);
}

int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int switch_root_main(int argc UNUSED_PARAM, char **argv)
{
	char *newroot, *console = NULL;
	struct stat st1, st2;
	struct statfs stfs;
	dev_t rootdev;

	// Parse args (-c console)
	opt_complementary = "-2"; // minimum 2 params
	getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option
	argv += optind;

	// Change to new root directory and verify it's a different fs.
	newroot = *argv++;

	xchdir(newroot);
	if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
		bb_error_msg_and_die("bad newroot %s", newroot);
	}
	rootdev = st2.st_dev;

	// Additional sanity checks: we're about to rm -rf /,  so be REALLY SURE
	// we mean it.  (I could make this a CONFIG option, but I would get email
	// from all the people who WILL eat their filesystems.)
	if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs)
	 || (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC))
	 || (getpid() != 1)
	) {
		bb_error_msg_and_die("not rootfs");
	}

	// Zap everything out of rootdev
	delete_contents("/", rootdev);

	// Overmount / with newdir and chroot into it.  The chdir is needed to
	// recalculate "." and ".." links.
	if (mount(".", "/", NULL, MS_MOVE, NULL))
		bb_error_msg_and_die("error moving root");
	xchroot(".");
	xchdir("/");

	// If a new console specified, redirect stdin/stdout/stderr to that.
	if (console) {
		close(0);
		xopen(console, O_RDWR);
		xdup2(0, 1);
		xdup2(0, 2);
	}

	// Exec real init.  (This is why we must be pid 1.)
	execv(argv[0], argv);
	bb_perror_msg_and_die("bad init %s", argv[0]);
}
1	niro	532	/* vi: set sw=4 ts=4: */
2			/* Copyright 2005 Rob Landley <rob@landley.net>
3			*
4			* Switch from rootfs to another filesystem as the root of the mount tree.
5			*
6			* Licensed under GPL version 2, see file LICENSE in this tarball for details.
7			*/
8
9	niro	816	#include "libbb.h"
10	niro	532	#include <sys/vfs.h>
11
12			// Make up for header deficiencies.
13			#ifndef RAMFS_MAGIC
14	niro	816	#define RAMFS_MAGIC ((unsigned)0x858458f6)
15	niro	532	#endif
16
17			#ifndef TMPFS_MAGIC
18	niro	816	#define TMPFS_MAGIC ((unsigned)0x01021994)
19	niro	532	#endif
20
21			#ifndef MS_MOVE
22	niro	816	#define MS_MOVE 8192
23	niro	532	#endif
24
25			// Recursively delete contents of rootfs.
26	niro	816	static void delete_contents(const char *directory, dev_t rootdev)
27	niro	532	{
28			DIR *dir;
29			struct dirent *d;
30			struct stat st;
31
32			// Don't descend into other filesystems
33	niro	816	if (lstat(directory, &st) \|\| st.st_dev != rootdev)
34			return;
35	niro	532
36			// Recursively delete the contents of directories.
37			if (S_ISDIR(st.st_mode)) {
38	niro	816	dir = opendir(directory);
39			if (dir) {
40	niro	532	while ((d = readdir(dir))) {
41	niro	816	char *newdir = d->d_name;
42	niro	532
43			// Skip . and ..
44	niro	816	if (DOT_OR_DOTDOT(newdir))
45	niro	532	continue;
46
47			// Recurse to delete contents
48	niro	816	newdir = concat_path_file(directory, newdir);
49			delete_contents(newdir, rootdev);
50			free(newdir);
51	niro	532	}
52			closedir(dir);
53
54			// Directory should now be empty. Zap it.
55			rmdir(directory);
56			}
57
58			// It wasn't a directory. Zap it.
59			} else unlink(directory);
60			}
61
62	niro	816	int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
63			int switch_root_main(int argc UNUSED_PARAM, char **argv)
64	niro	532	{
65	niro	816	char newroot, console = NULL;
66	niro	532	struct stat st1, st2;
67			struct statfs stfs;
68	niro	816	dev_t rootdev;
69	niro	532
70			// Parse args (-c console)
71	niro	816	opt_complementary = "-2"; // minimum 2 params
72			getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option
73			argv += optind;
74	niro	532
75			// Change to new root directory and verify it's a different fs.
76	niro	816	newroot = *argv++;
77	niro	532
78	niro	816	xchdir(newroot);
79			if (lstat(".", &st1) \|\| lstat("/", &st2) \|\| st1.st_dev == st2.st_dev) {
80	niro	532	bb_error_msg_and_die("bad newroot %s", newroot);
81			}
82	niro	816	rootdev = st2.st_dev;
83	niro	532
84			// Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
85			// we mean it. (I could make this a CONFIG option, but I would get email
86	niro	816	// from all the people who WILL eat their filesystems.)
87			if (lstat("/init", &st1) \|\| !S_ISREG(st1.st_mode) \|\| statfs("/", &stfs)
88			\|\| (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC))
89			\|\| (getpid() != 1)
90			) {
91	niro	532	bb_error_msg_and_die("not rootfs");
92			}
93
94			// Zap everything out of rootdev
95	niro	816	delete_contents("/", rootdev);
96	niro	532
97			// Overmount / with newdir and chroot into it. The chdir is needed to
98			// recalculate "." and ".." links.
99	niro	816	if (mount(".", "/", NULL, MS_MOVE, NULL))
100			bb_error_msg_and_die("error moving root");
101			xchroot(".");
102			xchdir("/");
103	niro	532
104			// If a new console specified, redirect stdin/stdout/stderr to that.
105			if (console) {
106			close(0);
107	niro	816	xopen(console, O_RDWR);
108			xdup2(0, 1);
109			xdup2(0, 2);
110	niro	532	}
111
112			// Exec real init. (This is why we must be pid 1.)
113	niro	816	execv(argv[0], argv);
114			bb_perror_msg_and_die("bad init %s", argv[0]);
115	niro	532	}