From 979ef53a268d6f54a309fc5c6015df5d4accbbd5 Mon Sep 17 00:00:00 2001 From: Didier Roche Date: Mon, 24 Nov 2014 09:43:29 +0100 Subject: [PATCH] machine-id-setup: add a machine_id_commit call to commit on disk a transient machine-id If /etc was read only at boot time with an empty /etc/machine-id, the latter will be mounted as a tmpfs and get reset at each boot. If the system becomes rw later, this functionality enables to commit in a race-free manner the transient machine-id to disk. --- src/core/machine-id-setup.c | 79 +++++++++++++++++++++++++++++++++++++ src/core/machine-id-setup.h | 1 + src/shared/util.c | 9 +++++ src/shared/util.h | 2 + 4 files changed, 91 insertions(+) diff --git a/src/core/machine-id-setup.c b/src/core/machine-id-setup.c index d8600bde2..74582a5dc 100644 --- a/src/core/machine-id-setup.c +++ b/src/core/machine-id-setup.c @@ -188,6 +188,85 @@ static int write_machine_id(int fd, char id[34]) { return -errno; } +int machine_id_commit(const char *root) { + _cleanup_close_ int fd = -1, initial_mntns_fd = -1; + const char *etc_machine_id; + char id[34]; /* 32 + \n + \0 */ + int r; + + if (isempty(root)) + etc_machine_id = "/etc/machine-id"; + else { + char *x; + + x = strappenda(root, "/etc/machine-id"); + etc_machine_id = path_kill_slashes(x); + } + + r = path_is_mount_point(etc_machine_id, false); + if (r < 0) + return log_error_errno(r, "Failed to determine wether %s is a mount point: %m", etc_machine_id); + if (r == 0) { + log_debug("%s is is not a mount point. Nothing to do.", etc_machine_id); + return 0; + } + + /* Read existing machine-id */ + fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (fd < 0) + return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id); + + r = get_valid_machine_id(fd, id); + if (r < 0) + return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id); + + r = is_fd_on_temporary_fs(fd); + if (r < 0) + return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id); + if (r == 0) { + log_error("%s is not on a temporary file system.", etc_machine_id); + return -EROFS; + } + + fd = safe_close(fd); + + /* Store current mount namespace */ + r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL); + if (r < 0) + return log_error_errno(r, "Can't fetch current mount namespace: %m"); + + /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */ + if (unshare(CLONE_NEWNS) < 0) + return log_error_errno(errno, "Failed to enter new namespace: %m"); + + if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0) + return log_error_errno(errno, "Couldn't make-rslave / mountpoint in our private namespace: %m"); + + if (umount(etc_machine_id) < 0) + return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id); + + /* Update a persistent version of etc_machine_id */ + fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444); + if (fd < 0) + return log_error_errno(errno, "Cannot open for writing %s. This is mandatory to get a persistent machine-id: %m", etc_machine_id); + + r = write_machine_id(fd, id); + if (r < 0) + return log_error_errno(r, "Cannot write %s: %m", etc_machine_id); + + fd = safe_close(fd); + + /* Return to initial namespace and proceed a lazy tmpfs unmount */ + r = namespace_enter(-1, initial_mntns_fd, -1, -1); + if (r < 0) + return log_warning_errno(r, "Failed to switch back to initial mount namespace: %m.\nWe'll keep transient %s file until next reboot.", etc_machine_id); + + if (umount2(etc_machine_id, MNT_DETACH) < 0) + return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id); + + return 0; +} + int machine_id_setup(const char *root) { const char *etc_machine_id, *run_machine_id; _cleanup_close_ int fd = -1; diff --git a/src/core/machine-id-setup.h b/src/core/machine-id-setup.h index b0583eefc..f7707c3bf 100644 --- a/src/core/machine-id-setup.h +++ b/src/core/machine-id-setup.h @@ -21,4 +21,5 @@ along with systemd; If not, see . ***/ +int machine_id_commit(const char *root); int machine_id_setup(const char *root); diff --git a/src/shared/util.c b/src/shared/util.c index 21651708d..4fcbab97b 100644 --- a/src/shared/util.c +++ b/src/shared/util.c @@ -3052,6 +3052,15 @@ _pure_ static int is_temporary_fs(struct statfs *s) { F_TYPE_EQUAL(s->f_type, RAMFS_MAGIC); } +int is_fd_on_temporary_fs(int fd) { + struct statfs s; + + if (fstatfs(fd, &s) < 0) + return -errno; + + return is_temporary_fs(&s); +} + int rm_rf_children(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev) { struct statfs s; diff --git a/src/shared/util.h b/src/shared/util.h index b53a45da9..0b7c77b1d 100644 --- a/src/shared/util.h +++ b/src/shared/util.h @@ -454,6 +454,8 @@ int get_ctty(pid_t, dev_t *_devnr, char **r); int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid); int fchmod_and_fchown(int fd, mode_t mode, uid_t uid, gid_t gid); +int is_fd_on_temporary_fs(int fd); + int rm_rf_children(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev); int rm_rf_children_dangerous(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev); int rm_rf(const char *path, bool only_dirs, bool delete_root, bool honour_sticky); -- 2.30.2