1 | /* vi:set 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 GPLv2 or later, see file LICENSE in this tarball for details.
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7 | */
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8 |
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9 | #include "busybox.h"
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10 | #include <fcntl.h>
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11 | #include <string.h>
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12 | #include <sys/vfs.h>
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13 | #include <unistd.h>
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14 |
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15 |
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16 | // Make up for header deficiencies.
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17 |
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18 | #ifndef RAMFS_MAGIC
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19 | #define RAMFS_MAGIC 0x858458f6
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20 | #endif
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21 |
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22 | #ifndef TMPFS_MAGIC
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23 | #define TMPFS_MAGIC 0x01021994
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24 | #endif
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25 |
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26 | #ifndef MS_MOVE
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27 | #define MS_MOVE 8192
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28 | #endif
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29 |
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30 | dev_t rootdev;
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31 |
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32 | // Recursively delete contents of rootfs.
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33 |
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34 | static void delete_contents(char *directory)
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35 | {
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36 | DIR *dir;
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37 | struct dirent *d;
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38 | struct stat st;
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39 |
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40 | // Don't descend into other filesystems
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41 | if (lstat(directory,&st) || st.st_dev != rootdev) return;
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42 |
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43 | // Recursively delete the contents of directories.
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44 | if (S_ISDIR(st.st_mode)) {
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45 | if((dir = opendir(directory))) {
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46 | while ((d = readdir(dir))) {
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47 | char *newdir=d->d_name;
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48 |
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49 | // Skip . and ..
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50 | if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
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51 | continue;
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52 |
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53 | // Recurse to delete contents
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54 | newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
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55 | sprintf(newdir, "%s/%s", directory, d->d_name);
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56 | delete_contents(newdir);
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57 | }
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58 | closedir(dir);
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59 |
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60 | // Directory should now be empty. Zap it.
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61 | rmdir(directory);
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62 | }
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63 |
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64 | // It wasn't a directory. Zap it.
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65 |
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66 | } else unlink(directory);
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67 | }
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68 |
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69 | int switch_root_main(int argc, char *argv[])
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70 | {
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71 | char *newroot, *console=NULL;
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72 | struct stat st1, st2;
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73 | struct statfs stfs;
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74 |
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75 | // Parse args (-c console)
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76 |
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77 | bb_opt_complementally="-2";
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78 | bb_getopt_ulflags(argc,argv,"c:",&console);
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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[optind++];
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83 |
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84 | if (chdir(newroot) || lstat(".", &st1) || lstat("/", &st2) ||
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85 | st1.st_dev == st2.st_dev)
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86 | {
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87 | bb_error_msg_and_die("bad newroot %s",newroot);
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88 | }
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89 | rootdev=st2.st_dev;
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90 |
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91 | // Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
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92 | // we mean it. (I could make this a CONFIG option, but I would get email
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93 | // from all the people who WILL eat their filesystemss.)
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94 |
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95 | if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
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96 | (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
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97 | getpid() != 1)
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98 | {
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99 | bb_error_msg_and_die("not rootfs");
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100 | }
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101 |
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102 | // Zap everything out of rootdev
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103 |
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104 | delete_contents("/");
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105 |
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106 | // Overmount / with newdir and chroot into it. The chdir is needed to
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107 | // recalculate "." and ".." links.
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108 |
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109 | if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot(".") || chdir("/"))
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110 | bb_error_msg_and_die("moving root");
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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 | if(open(console, O_RDWR) < 0)
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117 | bb_error_msg_and_die("Bad console '%s'",console);
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118 | dup2(0, 1);
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119 | dup2(0, 2);
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120 | }
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121 |
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122 | // Exec real init. (This is why we must be pid 1.)
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123 | execv(argv[optind],argv+optind);
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124 | bb_error_msg_and_die("Bad init '%s'",argv[optind]);
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125 | }
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