1 | /* vi: set sw=4 ts=4: */
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2 | /* Copyright 2005 Rob Landley <rob@landley.net>
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3 | *
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4 | * Switch from rootfs to another filesystem as the root of the mount tree.
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5 | *
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6 | * Licensed under GPL version 2, see file LICENSE in this tarball for details.
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7 | */
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8 |
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9 | #include "libbb.h"
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10 | #include <sys/vfs.h>
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11 |
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12 |
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13 | // Make up for header deficiencies.
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14 |
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15 | #ifndef RAMFS_MAGIC
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16 | #define RAMFS_MAGIC 0x858458f6
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17 | #endif
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18 |
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19 | #ifndef TMPFS_MAGIC
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20 | #define TMPFS_MAGIC 0x01021994
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21 | #endif
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22 |
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23 | #ifndef MS_MOVE
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24 | #define MS_MOVE 8192
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25 | #endif
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26 |
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27 | static dev_t rootdev;
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28 |
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29 | // Recursively delete contents of rootfs.
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30 |
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31 | static void delete_contents(const char *directory)
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32 | {
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33 | DIR *dir;
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34 | struct dirent *d;
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35 | struct stat st;
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36 |
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37 | // Don't descend into other filesystems
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38 | if (lstat(directory, &st) || st.st_dev != rootdev) return;
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39 |
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40 | // Recursively delete the contents of directories.
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41 | if (S_ISDIR(st.st_mode)) {
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42 | dir = opendir(directory);
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43 | if (dir) {
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44 | while ((d = readdir(dir))) {
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45 | char *newdir = d->d_name;
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46 |
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47 | // Skip . and ..
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48 | if (*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
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49 | continue;
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50 |
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51 | // Recurse to delete contents
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52 | newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
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53 | sprintf(newdir, "%s/%s", directory, d->d_name);
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54 | delete_contents(newdir);
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55 | }
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56 | closedir(dir);
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57 |
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58 | // Directory should now be empty. Zap it.
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59 | rmdir(directory);
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60 | }
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61 |
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62 | // It wasn't a directory. Zap it.
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63 |
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64 | } else unlink(directory);
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65 | }
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66 |
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67 | int switch_root_main(int argc, char **argv);
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68 | int switch_root_main(int argc, char **argv)
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69 | {
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70 | char *newroot, *console = NULL;
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71 | struct stat st1, st2;
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72 | struct statfs stfs;
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73 |
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74 | // Parse args (-c console)
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75 |
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76 | opt_complementary = "-2";
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77 | getopt32(argv, "c:", &console);
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78 | argv += optind;
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79 |
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80 | // Change to new root directory and verify it's a different fs.
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81 |
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82 | newroot = *argv++;
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83 |
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84 | xchdir(newroot);
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85 | if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
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86 | bb_error_msg_and_die("bad newroot %s", newroot);
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87 | }
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88 | rootdev = st2.st_dev;
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89 |
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90 | // Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
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91 | // we mean it. (I could make this a CONFIG option, but I would get email
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92 | // from all the people who WILL eat their filesystems.)
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93 |
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94 | if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
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95 | (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
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96 | getpid() != 1)
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97 | {
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98 | bb_error_msg_and_die("not rootfs");
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99 | }
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100 |
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101 | // Zap everything out of rootdev
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102 |
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103 | delete_contents("/");
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104 |
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105 | // Overmount / with newdir and chroot into it. The chdir is needed to
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106 | // recalculate "." and ".." links.
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107 |
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108 | if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot("."))
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109 | bb_error_msg_and_die("error moving root");
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110 | xchdir("/");
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111 |
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112 | // If a new console specified, redirect stdin/stdout/stderr to that.
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113 |
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114 | if (console) {
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115 | close(0);
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116 | xopen(console, O_RDWR);
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117 | dup2(0, 1);
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118 | dup2(0, 2);
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119 | }
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120 |
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121 | // Exec real init. (This is why we must be pid 1.)
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122 | execv(argv[0], argv);
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123 | bb_perror_msg_and_die("bad init %s", argv[0]);
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124 | }
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