wlroots/backend/session/logind.c

#define _POSIX_C_SOURCE 200809L
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <unistd.h>
#include <wayland-server-core.h>
#include <wlr/backend/session/interface.h>
#include <wlr/config.h>
#include <wlr/util/log.h>
#include "util/signal.h"

#if WLR_HAS_SYSTEMD
	#include <systemd/sd-bus.h>
	#include <systemd/sd-login.h>
#elif WLR_HAS_ELOGIND
	#include <elogind/sd-bus.h>
	#include <elogind/sd-login.h>
#endif

enum { DRM_MAJOR = 226 };

const struct session_impl session_logind;

struct logind_session {
	struct wlr_session base;

	sd_bus *bus;
	struct wl_event_source *event;

	char *id;
	char *path;

	// specifies whether a drm device was taken
	// if so, the session will be (de)activated with the drm fd,
	// otherwise with the dbus PropertiesChanged on "active" signal
	bool has_drm;
};

static struct logind_session *logind_session_from_session(
		struct wlr_session *base) {
	assert(base->impl == &session_logind);
	return (struct logind_session *)base;
}

static int logind_take_device(struct wlr_session *base, const char *path) {
	struct logind_session *session = logind_session_from_session(base);

	int fd = -1;
	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	struct stat st;
	if (stat(path, &st) < 0) {
		wlr_log(WLR_ERROR, "Failed to stat '%s'", path);
		return -1;
	}

	if (major(st.st_rdev) == DRM_MAJOR) {
		session->has_drm = true;
	}

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		session->path, "org.freedesktop.login1.Session", "TakeDevice",
		&error, &msg, "uu", major(st.st_rdev), minor(st.st_rdev));
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to take device '%s': %s", path,
			error.message);
		goto out;
	}

	int paused = 0;
	ret = sd_bus_message_read(msg, "hb", &fd, &paused);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to parse D-Bus response for '%s': %s",
			path, strerror(-ret));
		goto out;
	}

	// The original fd seems to be closed when the message is freed
	// so we just clone it.
	fd = fcntl(fd, F_DUPFD_CLOEXEC, 0);
	if (fd < 0) {
		wlr_log(WLR_ERROR, "Failed to clone file descriptor for '%s': %s",
			path, strerror(errno));
		goto out;
	}

out:
	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
	return fd;
}

static void logind_release_device(struct wlr_session *base, int fd) {
	struct logind_session *session = logind_session_from_session(base);

	struct stat st;
	if (fstat(fd, &st) < 0) {
		wlr_log(WLR_ERROR, "Failed to stat device '%d': %s", fd,
			strerror(errno));
		return;
	}

	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;
	int ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		session->path, "org.freedesktop.login1.Session", "ReleaseDevice",
		&error, &msg, "uu", major(st.st_rdev), minor(st.st_rdev));
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to release device '%d': %s", fd,
			error.message);
	}

	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
	close(fd);
}

static bool logind_change_vt(struct wlr_session *base, unsigned vt) {
	struct logind_session *session = logind_session_from_session(base);

	// Only seat0 has VTs associated with it
	if (strcmp(session->base.seat, "seat0") != 0) {
		return true;
	}

	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		"/org/freedesktop/login1/seat/seat0", "org.freedesktop.login1.Seat", "SwitchTo",
		&error, &msg, "u", (uint32_t)vt);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to change to vt '%d'", vt);
	}

	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
	return ret >= 0;
}

static bool find_session_path(struct logind_session *session) {
	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
			"/org/freedesktop/login1", "org.freedesktop.login1.Manager",
			"GetSession", &error, &msg, "s", session->id);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to get session path: %s", error.message);
		goto out;
	}

	const char *path;
	ret = sd_bus_message_read(msg, "o", &path);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Could not parse session path: %s", error.message);
		goto out;
	}
	session->path = strdup(path);

out:
	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);

	return ret >= 0;
}

static bool session_activate(struct logind_session *session) {
	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		session->path, "org.freedesktop.login1.Session", "Activate",
		&error, &msg, "");
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to activate session: %s", error.message);
	}

	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
	return ret >= 0;
}

static bool take_control(struct logind_session *session) {
	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		session->path, "org.freedesktop.login1.Session", "TakeControl",
		&error, &msg, "b", false);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to take control of session: %s",
			error.message);
	}

	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
	return ret >= 0;
}

static void release_control(struct logind_session *session) {
	int ret;
	sd_bus_message *msg = NULL;
	sd_bus_error error = SD_BUS_ERROR_NULL;

	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
		session->path, "org.freedesktop.login1.Session", "ReleaseControl",
		&error, &msg, "");
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to release control of session: %s",
			error.message);
	}

	sd_bus_error_free(&error);
	sd_bus_message_unref(msg);
}

static void logind_session_destroy(struct wlr_session *base) {
	struct logind_session *session = logind_session_from_session(base);

	release_control(session);

	wl_event_source_remove(session->event);
	sd_bus_unref(session->bus);
	free(session->id);
	free(session->path);
	free(session);
}

static int session_removed(sd_bus_message *msg, void *userdata,
		sd_bus_error *ret_error) {
	wlr_log(WLR_INFO, "SessionRemoved signal received");
	return 0;
}

static struct wlr_device *find_device(struct wlr_session *session,
		dev_t devnum) {
	struct wlr_device *dev;

	wl_list_for_each(dev, &session->devices, link) {
		if (dev->dev == devnum) {
			return dev;
		}
	}

	wlr_log(WLR_ERROR, "Tried to use dev_t %lu not opened by session",
		(unsigned long)devnum);
	assert(0);
}

static int pause_device(sd_bus_message *msg, void *userdata,
		sd_bus_error *ret_error) {
	struct logind_session *session = userdata;
	int ret;

	uint32_t major, minor;
	const char *type;
	ret = sd_bus_message_read(msg, "uus", &major, &minor, &type);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to parse D-Bus response for PauseDevice: %s",
			strerror(-ret));
		goto error;
	}

	if (major == DRM_MAJOR && strcmp(type, "gone") != 0) {
		assert(session->has_drm);
		session->base.active = false;
		wlr_signal_emit_safe(&session->base.session_signal, session);
	}

	if (strcmp(type, "pause") == 0) {
		ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
			session->path, "org.freedesktop.login1.Session", "PauseDeviceComplete",
			ret_error, &msg, "uu", major, minor);
		if (ret < 0) {
			wlr_log(WLR_ERROR, "Failed to send PauseDeviceComplete signal: %s",
				strerror(-ret));
		}
	}

error:
	return 0;
}

static int resume_device(sd_bus_message *msg, void *userdata,
		sd_bus_error *ret_error) {
	struct logind_session *session = userdata;
	int ret;

	int fd;
	uint32_t major, minor;
	ret = sd_bus_message_read(msg, "uuh", &major, &minor, &fd);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to parse D-Bus response for ResumeDevice: %s",
			strerror(-ret));
		goto error;
	}

	if (major == DRM_MAJOR) {
		struct wlr_device *dev = find_device(&session->base, makedev(major, minor));

		close(dev->fd);
		if (fcntl(fd, F_DUPFD_CLOEXEC, dev->fd) < 0) {
			wlr_log_errno(WLR_ERROR, "Failed to duplicate file descriptor");
			goto error;
		}

		if (!session->base.active) {
			session->base.active = true;
			wlr_signal_emit_safe(&session->base.session_signal, session);
		}
	}

error:
	return 0;
}

static int properties_changed(sd_bus_message *msg, void *userdata,
		sd_bus_error *ret_error) {
	struct logind_session *session = userdata;
	int ret = 0;

	// if we have a drm fd we don't depend on this
	if (session->has_drm) {
		return 0;
	}

	// PropertiesChanged arg 1: interface
	const char *interface;
	ret = sd_bus_message_read_basic(msg, 's', &interface); // skip path
	if (ret < 0) {
		goto error;
	}

	if (strcmp(interface, "org.freedesktop.login1.Session") != 0) {
		// not interesting for us; ignore
		wlr_log(WLR_DEBUG, "ignoring PropertiesChanged from %s", interface);
		return 0;
	}

	// PropertiesChanged arg 2: changed properties with values
	ret = sd_bus_message_enter_container(msg, 'a', "{sv}");
	if (ret < 0) {
		goto error;
	}

	const char *s;
	while ((ret = sd_bus_message_enter_container(msg, 'e', "sv")) > 0) {
		ret = sd_bus_message_read_basic(msg, 's', &s);
		if (ret < 0) {
			goto error;
		}

		if (strcmp(s, "Active") == 0) {
			int ret;
			ret = sd_bus_message_enter_container(msg, 'v', "b");
			if (ret < 0) {
				goto error;
			}

			bool active;
			ret = sd_bus_message_read_basic(msg, 'b', &active);
			if (ret < 0) {
				goto error;
			}

			if (session->base.active != active) {
				session->base.active = active;
				wlr_signal_emit_safe(&session->base.session_signal, session);
			}
			return 0;
		} else {
			sd_bus_message_skip(msg, "{sv}");
		}

		ret = sd_bus_message_exit_container(msg);
		if (ret < 0) {
			goto error;
		}
	}

	if (ret < 0) {
		goto error;
	}

	ret = sd_bus_message_exit_container(msg);
	if (ret < 0) {
		goto error;
	}

	// PropertiesChanged arg 3: changed properties without values
	sd_bus_message_enter_container(msg, 'a', "s");
	while ((ret = sd_bus_message_read_basic(msg, 's', &s)) > 0) {
		if (strcmp(s, "Active") == 0) {
			sd_bus_error error = SD_BUS_ERROR_NULL;
			bool active;
			ret = sd_bus_get_property_trivial(session->bus,
				"org.freedesktop.login1", session->path,
				"org.freedesktop.login1.Session", "Active", &error,
				'b', &active);
			if (ret < 0) {
				wlr_log(WLR_ERROR, "Failed to get 'Active' property: %s",
					error.message);
				return 0;
			}

			if (session->base.active != active) {
				session->base.active = active;
				wlr_signal_emit_safe(&session->base.session_signal, session);
			}
			return 0;
		}
	}

	if (ret < 0) {
		goto error;
	}

	return 0;

error:
	wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged: %s",
		strerror(-ret));
	return 0;
}

static bool add_signal_matches(struct logind_session *session) {
	int ret;

	char str[256];
	const char fmt[] = "type='signal',"
		"sender='org.freedesktop.login1',"
		"interface='org.freedesktop.login1.%s',"
		"member='%s',"
		"path='%s'";

	snprintf(str, sizeof(str), fmt, "Manager", "SessionRemoved",
		"/org/freedesktop/login1");
	ret = sd_bus_add_match(session->bus, NULL, str, session_removed, session);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to add D-Bus match: %s", strerror(-ret));
		return false;
	}

	snprintf(str, sizeof(str), fmt, "Session", "PauseDevice", session->path);
	ret = sd_bus_add_match(session->bus, NULL, str, pause_device, session);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to add D-Bus match: %s", strerror(-ret));
		return false;
	}

	snprintf(str, sizeof(str), fmt, "Session", "ResumeDevice", session->path);
	ret = sd_bus_add_match(session->bus, NULL, str, resume_device, session);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to add D-Bus match: %s", strerror(-ret));
		return false;
	}

	ret = sd_bus_match_signal(session->bus, NULL, "org.freedesktop.login1",
		session->path, "org.freedesktop.DBus.Properties", "PropertiesChanged",
		properties_changed, session);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to add D-Bus match: %s", strerror(-ret));
		return false;
	}

	return true;
}

static int dbus_event(int fd, uint32_t mask, void *data) {
	sd_bus *bus = data;
	while (sd_bus_process(bus, NULL) > 0) {
		// Do nothing.
	}
	return 1;
}

static bool contains_str(const char *needle, const char **haystack) {
	for (int i = 0; haystack[i]; i++) {
		if (strcmp(haystack[i], needle) == 0) {
			return true;
		}
	}

	return false;
}

static bool get_greeter_session(char **session_id) {
	char *class = NULL;
	char **user_sessions = NULL;
	int user_session_count = sd_uid_get_sessions(getuid(), 1, &user_sessions);

	if (user_session_count < 0) {
		wlr_log(WLR_ERROR, "Failed to get sessions");
		goto out;
	}

	if (user_session_count == 0) {
		wlr_log(WLR_ERROR, "User has no sessions");
		goto out;
	}

	for (int i = 0; i < user_session_count; ++i) {
		int ret = sd_session_get_class(user_sessions[i], &class);
		if (ret < 0) {
			continue;
		}

		if (strcmp(class, "greeter") == 0) {
			*session_id = strdup(user_sessions[i]);
			goto out;
		}
	}

out:
	free(class);
	for (int i = 0; i < user_session_count; ++i) {
		free(user_sessions[i]);
	}
	free(user_sessions);

	return *session_id != NULL;
}

static bool get_display_session(char **session_id) {
	assert(session_id != NULL);
	int ret;

	char *type = NULL;
	char *state = NULL;
	char *xdg_session_id = getenv("XDG_SESSION_ID");

	if (xdg_session_id) {
		// This just checks whether the supplied session ID is valid
		if (sd_session_is_active(xdg_session_id) < 0) {
			wlr_log(WLR_ERROR, "Invalid XDG_SESSION_ID: '%s'", xdg_session_id);
			goto error;
		}
		*session_id = strdup(xdg_session_id);
		return true;
	}

	// If there's a session active for the current process then just use that
	ret = sd_pid_get_session(getpid(), session_id);
	if (ret == 0) {
		return true;
	}

	// Find any active sessions for the user if the process isn't part of an
	// active session itself
	ret = sd_uid_get_display(getuid(), session_id);
	if (ret < 0 && ret != -ENODATA) {
		wlr_log(WLR_ERROR, "Failed to get display: %s", strerror(-ret));
		goto error;
	}

	if (ret != 0 && !get_greeter_session(session_id)) {
		wlr_log(WLR_ERROR, "Couldn't find an active session or a greeter session");
		goto error;
	}

	assert(*session_id != NULL);

	// Check that the available session is graphical
	ret = sd_session_get_type(*session_id, &type);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Couldn't get a type for session '%s': %s",
				*session_id, strerror(-ret));
		goto error;
	}

	const char *graphical_session_types[] = {"wayland", "x11", "mir", NULL};
	if (!contains_str(type, graphical_session_types)) {
		wlr_log(WLR_ERROR, "Session '%s' isn't a graphical session (type: '%s')",
				*session_id, type);
		goto error;
	}

	// Check that the session is active
	ret = sd_session_get_state(*session_id, &state);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Couldn't get state for session '%s': %s",
				*session_id, strerror(-ret));
		goto error;
	}

	const char *active_states[] = {"active", "online", NULL};
	if (!contains_str(state, active_states)) {
		wlr_log(WLR_ERROR, "Session '%s' is not active", *session_id);
		goto error;
	}

	free(type);
	free(state);
	return true;

error:
	free(type);
	free(state);
	free(*session_id);
	*session_id = NULL;

	return false;
}

static struct wlr_session *logind_session_create(struct wl_display *disp) {
	int ret;
	struct logind_session *session = calloc(1, sizeof(*session));
	if (!session) {
		wlr_log(WLR_ERROR, "Allocation failed: %s", strerror(errno));
		return NULL;
	}

	if (!get_display_session(&session->id)) {
		goto error;
	}

	char *seat;
	ret = sd_session_get_seat(session->id, &seat);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to get seat id: %s", strerror(-ret));
		goto error;
	}
	snprintf(session->base.seat, sizeof(session->base.seat), "%s", seat);

	if (strcmp(seat, "seat0") == 0) {
		ret = sd_session_get_vt(session->id, &session->base.vtnr);
		if (ret < 0) {
			wlr_log(WLR_ERROR, "Session not running in virtual terminal");
			goto error;
		}
	}
	free(seat);

	ret = sd_bus_default_system(&session->bus);
	if (ret < 0) {
		wlr_log(WLR_ERROR, "Failed to open D-Bus connection: %s", strerror(-ret));
		goto error;
	}

	if (!find_session_path(session)) {
		sd_bus_unref(session->bus);
		goto error;
	}

	if (!add_signal_matches(session)) {
		goto error_bus;
	}

	struct wl_event_loop *event_loop = wl_display_get_event_loop(disp);
	session->event = wl_event_loop_add_fd(event_loop, sd_bus_get_fd(session->bus),
		WL_EVENT_READABLE, dbus_event, session->bus);

	if (!session_activate(session)) {
		goto error_bus;
	}

	if (!take_control(session)) {
		goto error_bus;
	}

	wlr_log(WLR_INFO, "Successfully loaded logind session");

	session->base.impl = &session_logind;
	return &session->base;

error_bus:
	sd_bus_unref(session->bus);
	free(session->path);

error:
	free(session->id);
	return NULL;
}

const struct session_impl session_logind = {
	.create = logind_session_create,
	.destroy = logind_session_destroy,
	.open = logind_take_device,
	.close = logind_release_device,
	.change_vt = logind_change_vt,
};