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1 | /* SPDX-License-Identifier: LGPL-2.1+ */ | |
2 | /*** | |
3 | This file is part of systemd. | |
4 | ||
5 | Copyright 2012 Harald Hoyer, Lennart Poettering | |
6 | ||
7 | systemd is free software; you can redistribute it and/or modify it | |
8 | under the terms of the GNU Lesser General Public License as published by | |
9 | the Free Software Foundation; either version 2.1 of the License, or | |
10 | (at your option) any later version. | |
11 | ||
12 | systemd is distributed in the hope that it will be useful, but | |
13 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Lesser General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public License | |
18 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
19 | ***/ | |
20 | ||
21 | #include <errno.h> | |
22 | #include <fcntl.h> | |
23 | #include <limits.h> | |
24 | #include <stdbool.h> | |
25 | #include <stdio.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 "fs-util.h" | |
33 | #include "log.h" | |
34 | #include "missing.h" | |
35 | #include "mkdir.h" | |
36 | #include "mount-util.h" | |
37 | #include "path-util.h" | |
38 | #include "rm-rf.h" | |
39 | #include "stdio-util.h" | |
40 | #include "string-util.h" | |
41 | #include "strv.h" | |
42 | #include "switch-root.h" | |
43 | #include "user-util.h" | |
44 | #include "util.h" | |
45 | ||
46 | int switch_root(const char *new_root, | |
47 | const char *old_root_after, /* path below the new root, where to place the old root after the transition */ | |
48 | bool unmount_old_root, | |
49 | unsigned long mount_flags) { /* MS_MOVE or MS_BIND */ | |
50 | ||
51 | _cleanup_free_ char *resolved_old_root_after = NULL; | |
52 | _cleanup_close_ int old_root_fd = -1; | |
53 | bool old_root_remove; | |
54 | const char *i; | |
55 | int r; | |
56 | ||
57 | assert(new_root); | |
58 | assert(old_root_after); | |
59 | ||
60 | if (path_equal(new_root, "/")) | |
61 | return 0; | |
62 | ||
63 | /* Check if we shall remove the contents of the old root */ | |
64 | old_root_remove = in_initrd(); | |
65 | if (old_root_remove) { | |
66 | old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY); | |
67 | if (old_root_fd < 0) | |
68 | return log_error_errno(errno, "Failed to open root directory: %m"); | |
69 | } | |
70 | ||
71 | /* Determine where we shall place the old root after the transition */ | |
72 | r = chase_symlinks(old_root_after, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &resolved_old_root_after); | |
73 | if (r < 0) | |
74 | return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, old_root_after); | |
75 | if (r == 0) /* Doesn't exist yet. Let's create it */ | |
76 | (void) mkdir_p_label(resolved_old_root_after, 0755); | |
77 | ||
78 | /* Work-around for kernel design: the kernel refuses MS_MOVE if any file systems are mounted MS_SHARED. Hence | |
79 | * remount them MS_PRIVATE here as a work-around. | |
80 | * | |
81 | * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */ | |
82 | if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0) | |
83 | return log_error_errno(errno, "Failed to set \"/\" mount propagation to private: %m"); | |
84 | ||
85 | FOREACH_STRING(i, "/sys", "/dev", "/run", "/proc") { | |
86 | _cleanup_free_ char *chased = NULL; | |
87 | ||
88 | r = chase_symlinks(i, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &chased); | |
89 | if (r < 0) | |
90 | return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, i); | |
91 | if (r > 0) { | |
92 | /* Already exists. Let's see if it is a mount point already. */ | |
93 | r = path_is_mount_point(chased, NULL, 0); | |
94 | if (r < 0) | |
95 | return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", chased); | |
96 | if (r > 0) /* If it is already mounted, then do nothing */ | |
97 | continue; | |
98 | } else | |
99 | /* Doesn't exist yet? */ | |
100 | (void) mkdir_p_label(chased, 0755); | |
101 | ||
102 | if (mount(i, chased, NULL, mount_flags, NULL) < 0) | |
103 | return log_error_errno(r, "Failed to mount %s to %s: %m", i, chased); | |
104 | } | |
105 | ||
106 | /* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants | |
107 | * them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error | |
108 | * and switch_root() nevertheless. */ | |
109 | (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID); | |
110 | ||
111 | if (chdir(new_root) < 0) | |
112 | return log_error_errno(errno, "Failed to change directory to %s: %m", new_root); | |
113 | ||
114 | /* We first try a pivot_root() so that we can umount the old root dir. In many cases (i.e. where rootfs is /), | |
115 | * that's not possible however, and hence we simply overmount root */ | |
116 | if (pivot_root(new_root, resolved_old_root_after) >= 0) { | |
117 | ||
118 | /* Immediately get rid of the old root, if detach_oldroot is set. | |
119 | * Since we are running off it we need to do this lazily. */ | |
120 | if (unmount_old_root) { | |
121 | r = umount_recursive(old_root_after, MNT_DETACH); | |
122 | if (r < 0) | |
123 | log_warning_errno(r, "Failed to unmount old root directory tree, ignoring: %m"); | |
124 | } | |
125 | ||
126 | } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) | |
127 | return log_error_errno(errno, "Failed to move %s to /: %m", new_root); | |
128 | ||
129 | if (chroot(".") < 0) | |
130 | return log_error_errno(errno, "Failed to change root: %m"); | |
131 | ||
132 | if (chdir("/") < 0) | |
133 | return log_error_errno(errno, "Failed to change directory: %m"); | |
134 | ||
135 | if (old_root_fd >= 0) { | |
136 | struct stat rb; | |
137 | ||
138 | if (fstat(old_root_fd, &rb) < 0) | |
139 | log_warning_errno(errno, "Failed to stat old root directory, leaving: %m"); | |
140 | else { | |
141 | (void) rm_rf_children(old_root_fd, 0, &rb); | |
142 | old_root_fd = -1; | |
143 | } | |
144 | } | |
145 | ||
146 | return 0; | |
147 | } |