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1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
2
3 /***
4 This file is part of systemd.
5
6 Copyright 2012 Harald Hoyer, Lennart Poettering
7
8 systemd is free software; you can redistribute it and/or modify it
9 under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or
11 (at your option) any later version.
12
13 systemd is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Lesser General Public License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with systemd; If not, see <http://www.gnu.org/licenses/>.
20 ***/
21
22 #include <errno.h>
23 #include <fcntl.h>
24 #include <stdbool.h>
25 #include <string.h>
26 #include <sys/mount.h>
27 #include <sys/stat.h>
28 #include <unistd.h>
29
30 #include "base-filesystem.h"
31 #include "fd-util.h"
32 #include "missing.h"
33 #include "mkdir.h"
34 #include "path-util.h"
35 #include "rm-rf.h"
36 #include "string-util.h"
37 #include "switch-root.h"
38 #include "user-util.h"
39 #include "util.h"
40
41 int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot, unsigned long mountflags) {
42
43 /* Don't try to unmount/move the old "/", there's no way to do it. */
44 static const char move_mounts[] =
45 "/dev\0"
46 "/proc\0"
47 "/sys\0"
48 "/run\0";
49
50 _cleanup_close_ int old_root_fd = -1;
51 struct stat new_root_stat;
52 bool old_root_remove;
53 const char *i, *temporary_old_root;
54
55 if (path_equal(new_root, "/"))
56 return 0;
57
58 temporary_old_root = strjoina(new_root, oldroot);
59 mkdir_p_label(temporary_old_root, 0755);
60
61 old_root_remove = in_initrd();
62
63 if (stat(new_root, &new_root_stat) < 0)
64 return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);
65
66 /* Work-around for kernel design: the kernel refuses switching
67 * root if any file systems are mounted MS_SHARED. Hence
68 * remount them MS_PRIVATE here as a work-around.
69 *
70 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
71 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
72 log_warning_errno(errno, "Failed to make \"/\" private mount: %m");
73
74 NULSTR_FOREACH(i, move_mounts) {
75 char new_mount[PATH_MAX];
76 struct stat sb;
77
78 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
79
80 mkdir_p_label(new_mount, 0755);
81
82 if ((stat(new_mount, &sb) < 0) ||
83 sb.st_dev != new_root_stat.st_dev) {
84
85 /* Mount point seems to be mounted already or
86 * stat failed. Unmount the old mount
87 * point. */
88 if (umount2(i, MNT_DETACH) < 0)
89 log_warning_errno(errno, "Failed to unmount %s: %m", i);
90 continue;
91 }
92
93 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
94 if (mountflags & MS_MOVE) {
95 log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
96
97 if (umount2(i, MNT_FORCE) < 0)
98 log_warning_errno(errno, "Failed to unmount %s: %m", i);
99 }
100 if (mountflags & MS_BIND)
101 log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);
102
103 }
104 }
105
106 /* Do not fail, if base_filesystem_create() fails. Not all
107 * switch roots are like base_filesystem_create() wants them
108 * to look like. They might even boot, if they are RO and
109 * don't have the FS layout. Just ignore the error and
110 * switch_root() nevertheless. */
111 (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
112
113 if (chdir(new_root) < 0)
114 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
115
116 if (old_root_remove) {
117 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
118 if (old_root_fd < 0)
119 log_warning_errno(errno, "Failed to open root directory: %m");
120 }
121
122 /* We first try a pivot_root() so that we can umount the old
123 * root dir. In many cases (i.e. where rootfs is /), that's
124 * not possible however, and hence we simply overmount root */
125 if (pivot_root(new_root, temporary_old_root) >= 0) {
126
127 /* Immediately get rid of the old root, if detach_oldroot is set.
128 * Since we are running off it we need to do this lazily. */
129 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
130 log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",
131 oldroot,
132 errno == ENOENT ? "ignoring" : "leaving it around");
133
134 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
135 return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root);
136
137 if (chroot(".") < 0)
138 return log_error_errno(errno, "Failed to change root: %m");
139
140 if (chdir("/") < 0)
141 return log_error_errno(errno, "Failed to change directory: %m");
142
143 if (old_root_fd >= 0) {
144 struct stat rb;
145
146 if (fstat(old_root_fd, &rb) < 0)
147 log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
148 else {
149 (void) rm_rf_children(old_root_fd, 0, &rb);
150 old_root_fd = -1;
151 }
152 }
153
154 return 0;
155 }