diff options
Diffstat (limited to 'src/shared/switch-root.c')
| -rw-r--r-- | src/shared/switch-root.c | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/src/shared/switch-root.c b/src/shared/switch-root.c new file mode 100644 index 0000000..dbb4622 --- /dev/null +++ b/src/shared/switch-root.c @@ -0,0 +1,130 @@ +/* SPDX-License-Identifier: LGPL-2.1+ */ + +#include <errno.h> +#include <fcntl.h> +#include <limits.h> +#include <stdbool.h> +#include <stdio.h> +#include <sys/mount.h> +#include <sys/stat.h> +#include <unistd.h> + +#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 "mountpoint-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 *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; + bool old_root_remove; + const char *i; + int r; + + assert(new_root); + assert(old_root_after); + + if (path_equal(new_root, "/")) + return 0; + + /* 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"); + } + + /* 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 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) + 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(errno, "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. */ + (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); + + /* 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 (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 move %s to /: %m", new_root); + + if (chroot(".") < 0) + return log_error_errno(errno, "Failed to change root: %m"); + + if (chdir("/") < 0) + return log_error_errno(errno, "Failed to change directory: %m"); + + if (old_root_fd >= 0) { + struct stat rb; + + if (fstat(old_root_fd, &rb) < 0) + log_warning_errno(errno, "Failed to stat old root directory, leaving: %m"); + else { + (void) rm_rf_children(old_root_fd, 0, &rb); + old_root_fd = -1; + } + } + + return 0; +} |