diff options
Diffstat (limited to 'util-linux/switch_root.c')
| -rw-r--r-- | util-linux/switch_root.c | 62 |
1 files changed, 34 insertions, 28 deletions
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c index 08aa725..f9e3444 100644 --- a/util-linux/switch_root.c +++ b/util-linux/switch_root.c @@ -5,11 +5,10 @@ * * Licensed under GPL version 2, see file LICENSE in this tarball for details. */ - #include "libbb.h" #include <sys/vfs.h> -// Make up for header deficiencies. +// Make up for header deficiencies #ifndef RAMFS_MAGIC #define RAMFS_MAGIC ((unsigned)0x858458f6) #endif @@ -22,7 +21,7 @@ #define MS_MOVE 8192 #endif -// Recursively delete contents of rootfs. +// Recursively delete contents of rootfs static void delete_contents(const char *directory, dev_t rootdev) { DIR *dir; @@ -33,7 +32,7 @@ static void delete_contents(const char *directory, dev_t rootdev) if (lstat(directory, &st) || st.st_dev != rootdev) return; - // Recursively delete the contents of directories. + // Recursively delete the contents of directories if (S_ISDIR(st.st_mode)) { dir = opendir(directory); if (dir) { @@ -51,42 +50,47 @@ static void delete_contents(const char *directory, dev_t rootdev) } closedir(dir); - // Directory should now be empty. Zap it. + // Directory should now be empty, zap it rmdir(directory); } - - // It wasn't a directory. Zap it. - } else unlink(directory); + } else { + // It wasn't a directory, zap it + unlink(directory); + } } int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int switch_root_main(int argc UNUSED_PARAM, char **argv) { char *newroot, *console = NULL; - struct stat st1, st2; + struct stat st; struct statfs stfs; dev_t rootdev; // Parse args (-c console) opt_complementary = "-2"; // minimum 2 params - getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option + getopt32(argv, "+c:", &console); // '+': stop at first non-option argv += optind; - - // Change to new root directory and verify it's a different fs. newroot = *argv++; + // Change to new root directory and verify it's a different fs xchdir(newroot); - if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) { - bb_error_msg_and_die("bad newroot %s", newroot); + xstat("/", &st); + rootdev = st.st_dev; + xstat(".", &st); + if (st.st_dev == rootdev || getpid() != 1) { + // Show usage, it says new root must be a mountpoint + // and we must be PID 1 + bb_show_usage(); } - 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 filesystems.) - if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) - || (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC)) - || (getpid() != 1) + + // 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 destroy their filesystems. + statfs("/", &stfs); // this never fails + if (lstat("/init", &st) != 0 || !S_ISREG(st.st_mode) + || ((unsigned)stfs.f_type != RAMFS_MAGIC + && (unsigned)stfs.f_type != TMPFS_MAGIC) ) { bb_error_msg_and_die("not rootfs"); } @@ -94,14 +98,16 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv) // Zap everything out of rootdev delete_contents("/", rootdev); - // Overmount / with newdir and chroot into it. The chdir is needed to - // recalculate "." and ".." links. - if (mount(".", "/", NULL, MS_MOVE, NULL)) + // Overmount / with newdir and chroot into it + if (mount(".", "/", NULL, MS_MOVE, NULL)) { + // For example, fails when newroot is not a mountpoint bb_perror_msg_and_die("error moving root"); + } + // The chdir is needed to recalculate "." and ".." links xchroot("."); xchdir("/"); - // If a new console specified, redirect stdin/stdout/stderr to that. + // If a new console specified, redirect stdin/stdout/stderr to it if (console) { close(0); xopen(console, O_RDWR); @@ -109,7 +115,7 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv) xdup2(0, 2); } - // Exec real init. (This is why we must be pid 1.) + // Exec real init execv(argv[0], argv); - bb_perror_msg_and_die("bad init %s", argv[0]); + bb_perror_msg_and_die("can't execute '%s'", argv[0]); } |