diff options
Diffstat (limited to 'src/home/homework-mount.c')
| -rw-r--r-- | src/home/homework-mount.c | 309 |
1 files changed, 309 insertions, 0 deletions
diff --git a/src/home/homework-mount.c b/src/home/homework-mount.c new file mode 100644 index 0000000..28f09b9 --- /dev/null +++ b/src/home/homework-mount.c @@ -0,0 +1,309 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <sched.h> +#include <sys/mount.h> +#if WANT_LINUX_FS_H +#include <linux/fs.h> +#endif + +#include "alloc-util.h" +#include "fd-util.h" +#include "format-util.h" +#include "glyph-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_home_userns(uid_t stored_uid, uid_t exposed_uid) { + _cleanup_free_ char *text = NULL; + _cleanup_close_ int userns_fd = -EBADF; + 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, 1u); + 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, 1u); + if (r < 0) + return log_oom(); + + /* Leave everything else unmapped, starting from UID_NOBODY itself. Specifically, this means the + * whole space outside of 16-bit 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 = -EBADF, userns_fd = -EBADF; + 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 = -EBADF; + + return 0; + } + + return log_error_errno(errno, "Failed to open tree of home directory: %m"); + } + + userns_fd = make_home_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 = -EBADF; + + 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 " %s " UID_FMT ".", + strna(target), stored_uid, special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), exposed_uid); + + if (ret_mount_fd) + *ret_mount_fd = TAKE_FD(mount_fd); + + return 1; +} |