/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include "alloc-util.h" #include "fd-util.h" #include "format-util.h" #include "home-util.h" #include "homework-mount.h" #include "homework.h" #include "missing_mount.h" #include "missing_syscall.h" #include "mkdir.h" #include "mount-util.h" #include "namespace-util.h" #include "path-util.h" #include "string-util.h" #include "user-util.h" static const char *mount_options_for_fstype(const char *fstype) { const char *e; char *n; assert(fstype); /* Allow overriding our built-in defaults with an environment variable */ n = strjoina("SYSTEMD_HOME_MOUNT_OPTIONS_", fstype); e = getenv(ascii_strupper(n)); if (e) return e; if (streq(fstype, "ext4")) return "noquota,user_xattr"; if (streq(fstype, "xfs")) return "noquota"; if (streq(fstype, "btrfs")) return "noacl,compress=zstd:1"; return NULL; } int home_mount_node( const char *node, const char *fstype, bool discard, unsigned long flags, const char *extra_mount_options) { _cleanup_free_ char *joined = NULL; const char *default_options; int r; assert(node); assert(fstype); default_options = mount_options_for_fstype(fstype); if (default_options) { if (!strextend_with_separator(&joined, ",", default_options)) return log_oom(); } if (!strextend_with_separator(&joined, ",", discard ? "discard" : "nodiscard")) return log_oom(); if (extra_mount_options) { if (!strextend_with_separator(&joined, ",", extra_mount_options)) return log_oom(); } r = mount_nofollow_verbose(LOG_ERR, node, HOME_RUNTIME_WORK_DIR, fstype, flags|MS_RELATIME, joined); if (r < 0) return r; log_info("Mounting file system completed."); return 0; } int home_unshare_and_mkdir(void) { int r; if (unshare(CLONE_NEWNS) < 0) return log_error_errno(errno, "Couldn't unshare file system namespace: %m"); assert(path_startswith(HOME_RUNTIME_WORK_DIR, "/run")); r = mount_nofollow_verbose(LOG_ERR, "/run", "/run", NULL, MS_SLAVE|MS_REC, NULL); /* Mark /run as MS_SLAVE in our new namespace */ if (r < 0) return r; (void) mkdir_p(HOME_RUNTIME_WORK_DIR, 0700); return 0; } int home_unshare_and_mount( const char *node, const char *fstype, bool discard, unsigned long flags, const char *extra_mount_options) { int r; assert(node); assert(fstype); r = home_unshare_and_mkdir(); if (r < 0) return r; r = home_mount_node(node, fstype, discard, flags, extra_mount_options); if (r < 0) return r; r = mount_nofollow_verbose(LOG_ERR, NULL, HOME_RUNTIME_WORK_DIR, NULL, MS_PRIVATE, NULL); if (r < 0) { (void) umount_verbose(LOG_ERR, HOME_RUNTIME_WORK_DIR, UMOUNT_NOFOLLOW); return r; } return 0; } int home_move_mount(const char *mount_suffix, const char *target) { _cleanup_free_ char *subdir = NULL; const char *d; int r; assert(target); /* If 'mount_suffix' is set, then we'll mount a subdir of the source mount into the host. If it's * NULL we'll move the mount itself */ if (mount_suffix) { subdir = path_join(HOME_RUNTIME_WORK_DIR, mount_suffix); if (!subdir) return log_oom(); d = subdir; } else d = HOME_RUNTIME_WORK_DIR; (void) mkdir_p(target, 0700); r = mount_nofollow_verbose(LOG_ERR, d, target, NULL, MS_BIND, NULL); if (r < 0) return r; r = umount_recursive(HOME_RUNTIME_WORK_DIR, 0); if (r < 0) return log_error_errno(r, "Failed to unmount %s: %m", HOME_RUNTIME_WORK_DIR); log_info("Moving to final mount point %s completed.", target); return 0; } static int append_identity_range(char **text, uid_t start, uid_t next_start, uid_t exclude) { /* Creates an identity range ranging from 'start' to 'next_start-1'. Excludes the UID specified by 'exclude' if * it is in that range. */ assert(text); if (next_start <= start) /* Empty range? */ return 0; if (exclude < start || exclude >= next_start) /* UID to exclude it outside of the range? */ return strextendf(text, UID_FMT " " UID_FMT " " UID_FMT "\n", start, start, next_start - start); if (start == exclude && next_start == exclude + 1) /* The only UID in the range is the one to exclude? */ return 0; if (exclude == start) /* UID to exclude at beginning of range? */ return strextendf(text, UID_FMT " " UID_FMT " " UID_FMT "\n", start+1, start+1, next_start - start - 1); if (exclude == next_start - 1) /* UID to exclude at end of range? */ return strextendf(text, UID_FMT " " UID_FMT " " UID_FMT "\n", start, start, next_start - start - 1); return strextendf(text, UID_FMT " " UID_FMT " " UID_FMT "\n" UID_FMT " " UID_FMT " " UID_FMT "\n", start, start, exclude - start, exclude + 1, exclude + 1, next_start - exclude - 1); } static int make_userns(uid_t stored_uid, uid_t exposed_uid) { _cleanup_free_ char *text = NULL; _cleanup_close_ int userns_fd = -1; int r; assert(uid_is_valid(stored_uid)); assert(uid_is_valid(exposed_uid)); assert_cc(HOME_UID_MIN <= HOME_UID_MAX); assert_cc(HOME_UID_MAX < UID_NOBODY); /* Map everything below the homed UID range to itself (except for the UID we actually care about if * it is inside this range) */ r = append_identity_range(&text, 0, HOME_UID_MIN, stored_uid); if (r < 0) return log_oom(); /* Now map the UID we are doing this for to the target UID. */ r = strextendf(&text, UID_FMT " " UID_FMT " " UID_FMT "\n", stored_uid, exposed_uid, 1); if (r < 0) return log_oom(); /* Map everything above the homed UID range to itself (again, excluding the UID we actually care * about if it is in that range). Also we leave "nobody" itself excluded) */ r = append_identity_range(&text, HOME_UID_MAX, UID_NOBODY, stored_uid); if (r < 0) return log_oom(); /* Also map the container range. People can use that to place containers owned by high UIDs in their * home directories if they really want. We won't manage this UID range for them but pass it through * 1:1, and it will lose its meaning once migrated between hosts. */ r = append_identity_range(&text, CONTAINER_UID_BASE_MIN, CONTAINER_UID_BASE_MAX+1, stored_uid); if (r < 0) return log_oom(); /* Map nspawn's mapped root UID as identity mapping so that people can run nspawn uidmap mounted * containers off $HOME, if they want. */ r = strextendf(&text, UID_FMT " " UID_FMT " " UID_FMT "\n", UID_MAPPED_ROOT, UID_MAPPED_ROOT, 1); if (r < 0) return log_oom(); /* Leave everything else unmapped, starting from UID_NOBODY itself. Specifically, this means the * whole space outside of 16bit remains unmapped */ log_debug("Creating userns with mapping:\n%s", text); userns_fd = userns_acquire(text, text); /* same uid + gid mapping */ if (userns_fd < 0) return log_error_errno(userns_fd, "Failed to allocate user namespace: %m"); return TAKE_FD(userns_fd); } int home_shift_uid(int dir_fd, const char *target, uid_t stored_uid, uid_t exposed_uid, int *ret_mount_fd) { _cleanup_close_ int mount_fd = -1, userns_fd = -1; int r; assert(dir_fd >= 0); assert(uid_is_valid(stored_uid)); assert(uid_is_valid(exposed_uid)); /* Let's try to set up a UID mapping for this directory. This is called when first creating a home * directory or when activating it again. We do this as optimization only, to avoid having to * recursively chown() things on each activation. If the kernel or file system doesn't support this * scheme we'll handle this gracefully, and not do anything, so that the later recursive chown()ing * then fixes up things for us. Note that the chown()ing is smart enough to skip things if they look * alright already. * * Note that this always creates a new mount (i.e. we use OPEN_TREE_CLONE), since applying idmaps is * not allowed once the mount is put in place. */ mount_fd = open_tree(dir_fd, "", AT_EMPTY_PATH | OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC); if (mount_fd < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) { log_debug_errno(errno, "The open_tree() syscall is not supported, not setting up UID shift mount: %m"); if (ret_mount_fd) *ret_mount_fd = -1; return 0; } return log_error_errno(errno, "Failed to open tree of home directory: %m"); } userns_fd = make_userns(stored_uid, exposed_uid); if (userns_fd < 0) return userns_fd; /* Set the user namespace mapping attribute on the cloned mount point */ if (mount_setattr(mount_fd, "", AT_EMPTY_PATH, &(struct mount_attr) { .attr_set = MOUNT_ATTR_IDMAP, .userns_fd = userns_fd, }, MOUNT_ATTR_SIZE_VER0) < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno) || errno == EINVAL) { /* EINVAL is documented in mount_attr() as fs doesn't support idmapping */ log_debug_errno(errno, "UID/GID mapping for shifted mount not available, not setting it up: %m"); if (ret_mount_fd) *ret_mount_fd = -1; return 0; } return log_error_errno(errno, "Failed to apply UID/GID mapping: %m"); } if (target) r = move_mount(mount_fd, "", AT_FDCWD, target, MOVE_MOUNT_F_EMPTY_PATH); else r = move_mount(mount_fd, "", dir_fd, "", MOVE_MOUNT_F_EMPTY_PATH|MOVE_MOUNT_T_EMPTY_PATH); if (r < 0) return log_error_errno(errno, "Failed to apply UID/GID map: %m"); log_debug("Applied uidmap mount to %s. Mapping is " UID_FMT " → " UID_FMT ".", strna(target), stored_uid, exposed_uid); if (ret_mount_fd) *ret_mount_fd = TAKE_FD(mount_fd); return 1; }