diff options
| -rw-r--r-- | src/shared/switch-root.c | 139 |
1 files changed, 59 insertions, 80 deletions
diff --git a/src/shared/switch-root.c b/src/shared/switch-root.c index 4eff4f692e..afdf1ab5ad 100644 --- a/src/shared/switch-root.c +++ b/src/shared/switch-root.c @@ -28,123 +28,102 @@ #include "base-filesystem.h" #include "fd-util.h" +#include "fs-util.h" #include "log.h" #include "missing.h" #include "mkdir.h" +#include "mount-util.h" #include "path-util.h" #include "rm-rf.h" #include "stdio-util.h" #include "string-util.h" +#include "strv.h" #include "switch-root.h" #include "user-util.h" #include "util.h" -int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot, unsigned long mountflags) { - - /* 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 switch_root(const char *new_root, + const char *old_root_after, /* path below the new root, where to place the old root after the transition */ + bool unmount_old_root, + unsigned long mount_flags) { /* MS_MOVE or MS_BIND */ + _cleanup_free_ char *resolved_old_root_after = NULL; _cleanup_close_ int old_root_fd = -1; - struct stat new_root_stat; bool old_root_remove; - const char *i, *temporary_old_root; + const char *i; + int r; + + assert(new_root); + assert(old_root_after); if (path_equal(new_root, "/")) return 0; - temporary_old_root = strjoina(new_root, oldroot); - mkdir_p_label(temporary_old_root, 0755); - + /* Check if we shall remove the contents of the old root */ old_root_remove = in_initrd(); + if (old_root_remove) { + old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY); + if (old_root_fd < 0) + return log_error_errno(errno, "Failed to open root directory: %m"); + } - if (stat(new_root, &new_root_stat) < 0) - return log_error_errno(errno, "Failed to stat directory %s: %m", new_root); + /* Determine where we shall place the old root after the transition */ + r = chase_symlinks(old_root_after, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &resolved_old_root_after); + if (r < 0) + return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, old_root_after); + if (r == 0) /* Doesn't exist yet. Let's create it */ + (void) mkdir_p_label(resolved_old_root_after, 0755); - /* Work-around for kernel design: the kernel refuses switching - * root if any file systems are mounted MS_SHARED. Hence + /* Work-around for kernel design: the kernel refuses MS_MOVE 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_errno(errno, "Failed to make \"/\" private mount: %m"); - - NULSTR_FOREACH(i, move_mounts) { - char new_mount[PATH_MAX]; - struct stat sb; - size_t n; - - n = snprintf(new_mount, sizeof new_mount, "%s%s", new_root, i); - if (n >= sizeof new_mount) { - bool move = mountflags & MS_MOVE; - - log_warning("New path is too long, %s: %s%s", - move ? "forcing unmount instead" : "ignoring", - new_root, i); - - if (move) - if (umount2(i, MNT_FORCE) < 0) - log_warning_errno(errno, "Failed to unmount %s: %m", i); - continue; - } - - mkdir_p_label(new_mount, 0755); - - 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_errno(errno, "Failed to unmount %s: %m", i); - continue; - } - - if (mount(i, new_mount, NULL, mountflags, NULL) < 0) { - if (mountflags & MS_MOVE) { - log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount); - - if (umount2(i, MNT_FORCE) < 0) - log_warning_errno(errno, "Failed to unmount %s: %m", i); - - } else if (mountflags & MS_BIND) - log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount); - } + return log_error_errno(errno, "Failed to set \"/\" mount propagation to private: %m"); + + FOREACH_STRING(i, "/sys", "/dev", "/run", "/proc") { + _cleanup_free_ char *chased = NULL; + + r = chase_symlinks(i, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &chased); + if (r < 0) + return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, i); + if (r > 0) { + /* Already exists. Let's see if it is a mount point already. */ + r = path_is_mount_point(chased, NULL, 0); + if (r < 0) + return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", chased); + if (r > 0) /* If it is already mounted, then do nothing */ + continue; + } else + /* Doesn't exist yet? */ + (void) mkdir_p_label(chased, 0755); + + if (mount(i, chased, NULL, mount_flags, NULL) < 0) + return log_error_errno(r, "Failed to mount %s to %s: %m", i, chased); } - /* Do not fail, if base_filesystem_create() fails. Not all - * switch roots are like base_filesystem_create() wants them - * to look like. They might even boot, if they are RO and - * don't have the FS layout. Just ignore the error and - * switch_root() nevertheless. */ + /* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants + * them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error + * and switch_root() nevertheless. */ (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID); if (chdir(new_root) < 0) return log_error_errno(errno, "Failed to change directory to %s: %m", new_root); - 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_errno(errno, "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) { + /* 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, resolved_old_root_after) >= 0) { /* Immediately get rid of the old root, if detach_oldroot is set. * Since we are running off it we need to do this lazily. */ - if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0) - log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m", - oldroot, - errno == ENOENT ? "ignoring" : "leaving it around"); + if (unmount_old_root) { + r = umount_recursive(old_root_after, MNT_DETACH); + if (r < 0) + log_warning_errno(r, "Failed to unmount old root directory tree, ignoring: %m"); + } } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) - return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root); + return log_error_errno(errno, "Failed to move %s to /: %m", new_root); if (chroot(".") < 0) return log_error_errno(errno, "Failed to change root: %m"); |