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122 lines
3.0 KiB
C
122 lines
3.0 KiB
C
/* vi: set sw=4 ts=4: */
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/* Copyright 2005 Rob Landley <rob@landley.net>
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*
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* Switch from rootfs to another filesystem as the root of the mount tree.
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*
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* Licensed under GPL version 2, see file LICENSE in this tarball for details.
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*/
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#include "libbb.h"
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#include <sys/vfs.h>
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// Make up for header deficiencies
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#ifndef RAMFS_MAGIC
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#define RAMFS_MAGIC ((unsigned)0x858458f6)
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#endif
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#ifndef TMPFS_MAGIC
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#define TMPFS_MAGIC ((unsigned)0x01021994)
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#endif
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#ifndef MS_MOVE
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#define MS_MOVE 8192
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#endif
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// Recursively delete contents of rootfs
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static void delete_contents(const char *directory, dev_t rootdev)
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{
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DIR *dir;
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struct dirent *d;
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struct stat st;
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// Don't descend into other filesystems
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if (lstat(directory, &st) || st.st_dev != rootdev)
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return;
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// Recursively delete the contents of directories
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if (S_ISDIR(st.st_mode)) {
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dir = opendir(directory);
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if (dir) {
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while ((d = readdir(dir))) {
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char *newdir = d->d_name;
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// Skip . and ..
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if (DOT_OR_DOTDOT(newdir))
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continue;
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// Recurse to delete contents
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newdir = concat_path_file(directory, newdir);
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delete_contents(newdir, rootdev);
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free(newdir);
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}
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closedir(dir);
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// Directory should now be empty, zap it
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rmdir(directory);
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}
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} else {
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// It wasn't a directory, zap it
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unlink(directory);
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}
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}
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int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int switch_root_main(int argc UNUSED_PARAM, char **argv)
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{
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char *newroot, *console = NULL;
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struct stat st;
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struct statfs stfs;
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dev_t rootdev;
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// Parse args (-c console)
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opt_complementary = "-2"; // minimum 2 params
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getopt32(argv, "+c:", &console); // '+': stop at first non-option
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argv += optind;
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newroot = *argv++;
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// Change to new root directory and verify it's a different fs
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xchdir(newroot);
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xstat("/", &st);
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rootdev = st.st_dev;
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xstat(".", &st);
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if (st.st_dev == rootdev || getpid() != 1) {
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// Show usage, it says new root must be a mountpoint
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// and we must be PID 1
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bb_show_usage();
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}
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// Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
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// we mean it. I could make this a CONFIG option, but I would get email
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// from all the people who WILL destroy their filesystems.
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statfs("/", &stfs); // this never fails
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if (lstat("/init", &st) != 0 || !S_ISREG(st.st_mode)
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|| ((unsigned)stfs.f_type != RAMFS_MAGIC
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&& (unsigned)stfs.f_type != TMPFS_MAGIC)
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) {
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bb_error_msg_and_die("not rootfs");
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}
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// Zap everything out of rootdev
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delete_contents("/", rootdev);
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// Overmount / with newdir and chroot into it
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if (mount(".", "/", NULL, MS_MOVE, NULL)) {
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// For example, fails when newroot is not a mountpoint
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bb_perror_msg_and_die("error moving root");
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}
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xchroot(".");
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// The chdir is needed to recalculate "." and ".." links
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xchdir("/");
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// If a new console specified, redirect stdin/stdout/stderr to it
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if (console) {
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close(0);
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xopen(console, O_RDWR);
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xdup2(0, 1);
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xdup2(0, 2);
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}
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// Exec real init
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execv(argv[0], argv);
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bb_perror_msg_and_die("can't execute '%s'", argv[0]);
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}
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