Line data Source code
1 : /* SPDX-License-Identifier: LGPL-2.1+ */
2 :
3 : #include <errno.h>
4 : #include <fcntl.h>
5 : #include <limits.h>
6 : #include <stdbool.h>
7 : #include <stdio.h>
8 : #include <sys/mount.h>
9 : #include <sys/stat.h>
10 : #include <unistd.h>
11 :
12 : #include "base-filesystem.h"
13 : #include "fd-util.h"
14 : #include "fs-util.h"
15 : #include "log.h"
16 : #include "missing.h"
17 : #include "mkdir.h"
18 : #include "mount-util.h"
19 : #include "mountpoint-util.h"
20 : #include "path-util.h"
21 : #include "rm-rf.h"
22 : #include "stdio-util.h"
23 : #include "string-util.h"
24 : #include "strv.h"
25 : #include "switch-root.h"
26 : #include "user-util.h"
27 : #include "util.h"
28 :
29 0 : int switch_root(const char *new_root,
30 : const char *old_root_after, /* path below the new root, where to place the old root after the transition */
31 : bool unmount_old_root,
32 : unsigned long mount_flags) { /* MS_MOVE or MS_BIND */
33 :
34 0 : _cleanup_free_ char *resolved_old_root_after = NULL;
35 0 : _cleanup_close_ int old_root_fd = -1;
36 : bool old_root_remove;
37 : const char *i;
38 : int r;
39 :
40 0 : assert(new_root);
41 0 : assert(old_root_after);
42 :
43 0 : if (path_equal(new_root, "/"))
44 0 : return 0;
45 :
46 : /* Check if we shall remove the contents of the old root */
47 0 : old_root_remove = in_initrd();
48 0 : if (old_root_remove) {
49 0 : old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
50 0 : if (old_root_fd < 0)
51 0 : return log_error_errno(errno, "Failed to open root directory: %m");
52 : }
53 :
54 : /* Determine where we shall place the old root after the transition */
55 0 : r = chase_symlinks(old_root_after, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &resolved_old_root_after);
56 0 : if (r < 0)
57 0 : return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, old_root_after);
58 0 : if (r == 0) /* Doesn't exist yet. Let's create it */
59 0 : (void) mkdir_p_label(resolved_old_root_after, 0755);
60 :
61 : /* Work-around for kernel design: the kernel refuses MS_MOVE if any file systems are mounted MS_SHARED. Hence
62 : * remount them MS_PRIVATE here as a work-around.
63 : *
64 : * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
65 0 : if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
66 0 : return log_error_errno(errno, "Failed to set \"/\" mount propagation to private: %m");
67 :
68 0 : FOREACH_STRING(i, "/sys", "/dev", "/run", "/proc") {
69 0 : _cleanup_free_ char *chased = NULL;
70 :
71 0 : r = chase_symlinks(i, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &chased);
72 0 : if (r < 0)
73 0 : return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, i);
74 0 : if (r > 0) {
75 : /* Already exists. Let's see if it is a mount point already. */
76 0 : r = path_is_mount_point(chased, NULL, 0);
77 0 : if (r < 0)
78 0 : return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", chased);
79 0 : if (r > 0) /* If it is already mounted, then do nothing */
80 0 : continue;
81 : } else
82 : /* Doesn't exist yet? */
83 0 : (void) mkdir_p_label(chased, 0755);
84 :
85 0 : if (mount(i, chased, NULL, mount_flags, NULL) < 0)
86 0 : return log_error_errno(errno, "Failed to mount %s to %s: %m", i, chased);
87 : }
88 :
89 : /* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants
90 : * them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error
91 : * and switch_root() nevertheless. */
92 0 : (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
93 :
94 0 : if (chdir(new_root) < 0)
95 0 : return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
96 :
97 : /* We first try a pivot_root() so that we can umount the old root dir. In many cases (i.e. where rootfs is /),
98 : * that's not possible however, and hence we simply overmount root */
99 0 : if (pivot_root(new_root, resolved_old_root_after) >= 0) {
100 :
101 : /* Immediately get rid of the old root, if detach_oldroot is set.
102 : * Since we are running off it we need to do this lazily. */
103 0 : if (unmount_old_root) {
104 0 : r = umount_recursive(old_root_after, MNT_DETACH);
105 0 : if (r < 0)
106 0 : log_warning_errno(r, "Failed to unmount old root directory tree, ignoring: %m");
107 : }
108 :
109 0 : } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
110 0 : return log_error_errno(errno, "Failed to move %s to /: %m", new_root);
111 :
112 0 : if (chroot(".") < 0)
113 0 : return log_error_errno(errno, "Failed to change root: %m");
114 :
115 0 : if (chdir("/") < 0)
116 0 : return log_error_errno(errno, "Failed to change directory: %m");
117 :
118 0 : if (old_root_fd >= 0) {
119 : struct stat rb;
120 :
121 0 : if (fstat(old_root_fd, &rb) < 0)
122 0 : log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
123 : else
124 0 : (void) rm_rf_children(TAKE_FD(old_root_fd), 0, &rb); /* takes possession of the dir fd, even on failure */
125 : }
126 :
127 0 : return 0;
128 : }
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