1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
|
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2012 Harald Hoyer, Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <sys/stat.h>
#include <stdbool.h>
#include <errno.h>
#include <string.h>
#include <sys/mount.h>
#include <unistd.h>
#include <fcntl.h>
#include "util.h"
#include "path-util.h"
#include "switch-root.h"
#include "mkdir.h"
#include "base-filesystem.h"
#include "missing.h"
int switch_root(const char *new_root) {
/* Don't try to unmount/move the old "/", there's no way to do it. */
static const char move_mounts[] =
"/dev\0"
"/proc\0"
"/sys\0"
"/run\0";
_cleanup_close_ int old_root_fd = -1;
struct stat new_root_stat;
bool old_root_remove;
const char *i, *temporary_old_root;
int r;
if (path_equal(new_root, "/"))
return 0;
/* When using pivot_root() we assume that /mnt exists as place
* we can temporarily move the old root to. As we immediately
* unmount it from there it doesn't matter much which
* directory we choose for this, but it should be more likely
* than not that /mnt exists and is suitable as mount point
* and is on the same fs as the old root dir */
temporary_old_root = strappenda(new_root, "/mnt");
mkdir_p(temporary_old_root, 0755);
old_root_remove = in_initrd();
if (stat(new_root, &new_root_stat) < 0) {
log_error("Failed to stat directory %s: %m", new_root);
return -errno;
}
/* Work-around for a kernel bug: for some reason the kernel
* refuses switching root if any file systems are mounted
* MS_SHARED. Hence remount them MS_PRIVATE here as a
* work-around.
*
* https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
log_warning("Failed to make \"/\" private mount: %m");
NULSTR_FOREACH(i, move_mounts) {
char new_mount[PATH_MAX];
struct stat sb;
snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
char_array_0(new_mount);
mkdir_p(new_mount, 0755);
if ((stat(new_mount, &sb) < 0) ||
sb.st_dev != new_root_stat.st_dev) {
/* Mount point seems to be mounted already or
* stat failed. Unmount the old mount
* point. */
if (umount2(i, MNT_DETACH) < 0)
log_warning("Failed to unmount %s: %m", i);
continue;
}
if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) {
log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
if (umount2(i, MNT_FORCE) < 0)
log_warning("Failed to unmount %s: %m", i);
}
}
r = base_filesystem_create(new_root);
if (r < 0) {
log_error("Failed to create the base filesystem: %s", strerror(-r));
return r;
}
if (chdir(new_root) < 0) {
log_error("Failed to change directory to %s: %m", new_root);
return -errno;
}
if (old_root_remove) {
old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
if (old_root_fd < 0)
log_warning("Failed to open root directory: %m");
}
/* We first try a pivot_root() so that we can umount the old
* root dir. In many cases (i.e. where rootfs is /), that's
* not possible however, and hence we simply overmount root */
if (pivot_root(new_root, temporary_old_root) >= 0) {
/* Immediately get rid of the old root. Since we are
* running off it we need to do this lazily. */
if (umount2("/mnt", MNT_DETACH) < 0) {
log_error("Failed to umount old root dir /mnt: %m");
return -errno;
}
} else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
log_error("Failed to mount moving %s to /: %m", new_root);
return -errno;
}
if (chroot(".") < 0) {
log_error("Failed to change root: %m");
return -errno;
}
if (chdir("/") < 0) {
log_error("Failed to change directory: %m");
return -errno;
}
if (old_root_fd >= 0) {
struct stat rb;
if (fstat(old_root_fd, &rb) < 0)
log_warning("Failed to stat old root directory, leaving: %m");
else {
rm_rf_children(old_root_fd, false, false, &rb);
old_root_fd = -1;
}
}
return 0;
}
|
