diff options
Diffstat (limited to 'src/core/switch-root.c')
| -rw-r--r-- | src/core/switch-root.c | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/src/core/switch-root.c b/src/core/switch-root.c new file mode 100644 index 0000000000..ce0e41d510 --- /dev/null +++ b/src/core/switch-root.c @@ -0,0 +1,167 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +/*** + This file is part of systemd. + + Copyright 2012 Harald Hoyer, Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <sys/stat.h> +#include <stdbool.h> +#include <errno.h> +#include <string.h> +#include <sys/mount.h> +#include <unistd.h> +#include <fcntl.h> + +#include "util.h" +#include "path-util.h" +#include "switch-root.h" +#include "missing.h" + +int switch_root(const char *new_root) { + + /* Don't try to unmount/move the old "/", there's no way to do it. */ + static const char move_mounts[] = + "/dev\0" + "/proc\0" + "/sys\0" + "/run\0"; + + int r, old_root_fd = -1; + struct stat new_root_stat; + bool old_root_remove; + const char *i; + _cleanup_free_ char *temporary_old_root = NULL; + + if (path_equal(new_root, "/")) + return 0; + + /* When using pivot_root() we assume that /mnt exists as place + * we can temporarily move the old root to. As we immediately + * unmount it from there it doesn't matter much which + * directory we choose for this, but it should be more likely + * than not that /mnt exists and is suitable as mount point + * and is on the same fs as the old root dir */ + temporary_old_root = strappend(new_root, "/mnt"); + if (!temporary_old_root) + return -ENOMEM; + + old_root_remove = in_initrd(); + + if (stat(new_root, &new_root_stat) < 0) { + r = -errno; + log_error("Failed to stat directory %s: %m", new_root); + goto fail; + } + + /* Work-around for a kernel bug: for some reason the kernel + * refuses switching root if any file systems are mounted + * MS_SHARED. Hence remount them MS_PRIVATE here as a + * work-around. + * + * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */ + if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0) + log_warning("Failed to make \"/\" private mount: %m"); + + NULSTR_FOREACH(i, move_mounts) { + char new_mount[PATH_MAX]; + struct stat sb; + + snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i); + char_array_0(new_mount); + + if ((stat(new_mount, &sb) < 0) || + sb.st_dev != new_root_stat.st_dev) { + + /* Mount point seems to be mounted already or + * stat failed. Unmount the old mount + * point. */ + if (umount2(i, MNT_DETACH) < 0) + log_warning("Failed to unmount %s: %m", i); + continue; + } + + if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) { + log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount); + + if (umount2(i, MNT_FORCE) < 0) + log_warning("Failed to unmount %s: %m", i); + } + } + + if (chdir(new_root) < 0) { + r = -errno; + log_error("Failed to change directory to %s: %m", new_root); + goto fail; + } + + if (old_root_remove) { + old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY); + if (old_root_fd < 0) + log_warning("Failed to open root directory: %m"); + } + + /* We first try a pivot_root() so that we can umount the old + * root dir. In many cases (i.e. where rootfs is /), that's + * not possible however, and hence we simply overmount root */ + if (pivot_root(new_root, temporary_old_root) >= 0) { + + /* Immediately get rid of the old root. Since we are + * running off it we need to do this lazily. */ + if (umount2(temporary_old_root, MNT_DETACH) < 0) { + r = -errno; + log_error("Failed to umount old root dir %s: %m", temporary_old_root); + goto fail; + } + + } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) { + r = -errno; + log_error("Failed to mount moving %s to /: %m", new_root); + goto fail; + } + + if (chroot(".") < 0) { + r = -errno; + log_error("Failed to change root: %m"); + goto fail; + } + + if (chdir("/") < 0) { + r = -errno; + log_error("Failed to change directory: %m"); + goto fail; + } + + if (old_root_fd >= 0) { + struct stat rb; + + if (fstat(old_root_fd, &rb) < 0) + log_warning("Failed to stat old root directory, leaving: %m"); + else { + rm_rf_children(old_root_fd, false, false, &rb); + old_root_fd = -1; + } + } + + r = 0; + +fail: + if (old_root_fd >= 0) + close_nointr_nofail(old_root_fd); + + return r; +} |