#include <sched.h>
#include <sys/mount.h>
+#include <linux/fs.h>
#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) {
if (streq(fstype, "ext4"))
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();
+
+ /* 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");
+
+ if (ret_mount_fd)
+ *ret_mount_fd = TAKE_FD(mount_fd);
+
+ return 1;
+}
projects / thirdparty / systemd.git / commitdiff
