/* vi:set ts=4:*/ /* Copyright 2005 Rob Landley <rob@landley.net> * * Switch from rootfs to another filesystem as the root of the mount tree. * * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. */ #include <dirent.h> #include <fcntl.h> #include <stdio.h> #include <string.h> #include <sys/mount.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/vfs.h> #include <unistd.h> #include "busybox.h" // Make up for header deficiencies. #ifndef RAMFS_MAGIC #define RAMFS_MAGIC 0x858458f6 #endif #ifndef TMPFS_MAGIC #define TMPFS_MAGIC 0x01021994 #endif #ifndef MS_MOVE #define MS_MOVE 8192 #endif dev_t rootdev; // Recursively delete contents of rootfs. static void delete_contents(char *directory) { DIR *dir; struct dirent *d; struct stat st; // Don't descend into other filesystems if (lstat(directory,&st) || st.st_dev != rootdev) return; // Recursively delete the contents of directories. if (S_ISDIR(st.st_mode)) { if((dir = opendir(directory))) { while ((d = readdir(dir))) { char *newdir=d->d_name; // Skip . and .. if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2]))) continue; // Recurse to delete contents newdir = alloca(strlen(directory) + strlen(d->d_name) + 2); sprintf(newdir, "%s/%s", directory, d->d_name); delete_contents(newdir); } closedir(dir); // Directory should now be empty. Zap it. rmdir(directory); } // It wasn't a directory. Zap it. } else unlink(directory); } int switch_root_main(int argc, char *argv[]) { char *newroot, *console=NULL; struct stat st1, st2; struct statfs stfs; // Parse args (-c console) bb_opt_complementally="-2"; bb_getopt_ulflags(argc,argv,"c:",&console); // Change to new root directory and verify it's a different fs. newroot=argv[optind++]; if (chdir(newroot) || lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) { bb_error_msg_and_die("bad newroot %s",newroot); } rootdev=st2.st_dev; // Additional sanity checks: we're about to rm -rf /, so be REALLY SURE // we mean it. (I could make this a CONFIG option, but I would get email // from all the people who WILL eat their filesystemss.) if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) || (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) || getpid() != 1) { bb_error_msg_and_die("not rootfs"); } // Zap everything out of rootdev delete_contents("/"); // Overmount / with newdir and chroot into it. The chdir is needed to // recalculate "." and ".." links. if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot(".") || chdir("/")) bb_error_msg_and_die("moving root"); // If a new console specified, redirect stdin/stdout/stderr to that. if (console) { close(0); if(open(console, O_RDWR) < 0) bb_error_msg_and_die("Bad console '%s'",console); dup2(0, 1); dup2(0, 2); } // Exec real init. (This is why we must be pid 1.) execv(argv[optind],argv+optind); bb_error_msg_and_die("Bad init '%s'",argv[optind]); }