send monitor events back to netlink socket

Instead of of our own private monitor socket, we send the
processed event back to our netlink socket, to the multicast
group 2 -- so any number of users can listen to udev events,
just like they can listen to kernel emitted events on group 1.

4 files changed, 34 insertions, 19 deletions

diff --git a/udev/lib/libudev-monitor.c b/udev/lib/libudev-monitor.c
index c0aa99c65a..b2f76c3129 100644
--- a/udev/lib/libudev-monitor.c
+++ b/udev/lib/libudev-monitor.c
@@ -29,6 +29,7 @@ struct udev_monitor {
 	int refcount;
 	int sock;
 	struct sockaddr_nl snl;
+	struct sockaddr_nl snl_peer;
 	struct sockaddr_un sun;
 	socklen_t addrlen;
 };
@@ -90,7 +91,7 @@ struct udev_monitor *udev_monitor_new_from_socket(struct udev *udev, const char
 	return udev_monitor;
 }
 
-struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev)
+struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, unsigned int group)
 {
 	struct udev_monitor *udev_monitor;
 
@@ -110,10 +111,11 @@ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev)
 	}
 
 	udev_monitor->snl.nl_family = AF_NETLINK;
-	udev_monitor->snl.nl_pid = getpid();
-	udev_monitor->snl.nl_groups = 1;
+	udev_monitor->snl.nl_groups = group;
+	udev_monitor->snl_peer.nl_family = AF_NETLINK;
+	udev_monitor->snl_peer.nl_groups = UDEV_MONITOR_UDEV;
 
-	dbg(udev, "monitor %p created with NETLINK_KOBJECT_UEVENT\n", udev_monitor);
+	dbg(udev, "monitor %p created with NETLINK_KOBJECT_UEVENT (%u)\n", udev_monitor, group);
 	return udev_monitor;
 }
 
@@ -123,14 +125,16 @@ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
 	const int on = 1;
 
 	if (udev_monitor->snl.nl_family != 0) {
-		err = bind(udev_monitor->sock, (struct sockaddr *)&udev_monitor->snl, sizeof(struct sockaddr_nl));
+		err = bind(udev_monitor->sock,
+			   (struct sockaddr *)&udev_monitor->snl, sizeof(struct sockaddr_nl));
 		if (err < 0) {
 			err(udev_monitor->udev, "bind failed: %m\n");
 			return err;
 		}
 		dbg(udev_monitor->udev, "monitor %p listening on netlink\n", udev_monitor);
 	} else if (udev_monitor->sun.sun_family != 0) {
-		err = bind(udev_monitor->sock, (struct sockaddr *)&udev_monitor->sun, udev_monitor->addrlen);
+		err = bind(udev_monitor->sock,
+			   (struct sockaddr *)&udev_monitor->sun, udev_monitor->addrlen);
 		if (err < 0) {
 			err(udev_monitor->udev, "bind failed: %m\n");
 			return err;
@@ -381,9 +385,18 @@ int udev_monitor_send_device(struct udev_monitor *udev_monitor, struct udev_devi
 	len = udev_device_get_properties_monitor_buf(udev_device, &buf);
 	if (len < 32)
 		return -1;
-	count = sendto(udev_monitor->sock,
-		       buf, len, 0,
-		       (struct sockaddr *)&udev_monitor->sun, udev_monitor->addrlen);
+	if (udev_monitor->sun.sun_family != 0) {
+		count = sendto(udev_monitor->sock,
+			       buf, len, 0,
+			       (struct sockaddr *)&udev_monitor->sun,
+			       udev_monitor->addrlen);
+	} else {
+		/* no destination besides the muticast group, we will always get -1 ECONNREFUSED */
+		count = sendto(udev_monitor->sock,
+			       buf, len, 0,
+			       (struct sockaddr *)&udev_monitor->snl_peer,
+			       sizeof(struct sockaddr_nl));
+	}
 	info(udev_monitor->udev, "passed %zi bytes to monitor %p, \n", count, udev_monitor);
 	return count;
 }
diff --git a/udev/lib/libudev.h b/udev/lib/libudev.h
index a5d2c22e8c..be09ddb75a 100644
--- a/udev/lib/libudev.h
+++ b/udev/lib/libudev.h
@@ -76,8 +76,12 @@ extern const char *udev_device_get_sysattr_value(struct udev_device *udev_device
 
 /* udev and kernel device events */
 struct udev_monitor;
+enum udev_monitor_netlink_group {
+	UDEV_MONITOR_KERNEL	= 1,
+	UDEV_MONITOR_UDEV	= 2,
+};
 extern struct udev_monitor *udev_monitor_new_from_socket(struct udev *udev, const char *socket_path);
-extern struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev);
+extern struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, enum udev_monitor_netlink_group group);
 extern int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor);
 extern struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor);
 extern void udev_monitor_unref(struct udev_monitor *udev_monitor);
diff --git a/udev/udevadm-monitor.c b/udev/udevadm-monitor.c
index 9be02da16c..43c1cc1163 100644
--- a/udev/udevadm-monitor.c
+++ b/udev/udevadm-monitor.c
@@ -115,11 +115,6 @@ int udevadm_monitor(struct udev *udev, int argc, char *argv[])
 		print_udev =1;
 	}
 
-	if (getuid() != 0 && print_kernel) {
-		fprintf(stderr, "root privileges needed to subscribe to kernel events\n");
-		goto out;
-	}
-
 	/* set signal handlers */
 	memset(&act, 0x00, sizeof(struct sigaction));
 	act.sa_handler = (void (*)(int)) sig_handler;
@@ -130,7 +125,7 @@ int udevadm_monitor(struct udev *udev, int argc, char *argv[])
 
 	printf("monitor will print the received events for:\n");
 	if (print_udev) {
-		udev_monitor = udev_monitor_new_from_socket(udev, "@/org/kernel/udev/monitor");
+		udev_monitor = udev_monitor_new_from_netlink(udev, UDEV_MONITOR_UDEV);
 		if (udev_monitor == NULL) {
 			rc = 1;
 			goto out;
@@ -142,8 +137,9 @@ int udevadm_monitor(struct udev *udev, int argc, char *argv[])
 		printf("UDEV - the event which udev sends out after rule processing\n");
 	}
 	if (print_kernel) {
-		kernel_monitor = udev_monitor_new_from_netlink(udev);
+		kernel_monitor = udev_monitor_new_from_netlink(udev, UDEV_MONITOR_KERNEL);
 		if (kernel_monitor == NULL) {
+			fprintf(stderr, "unable to subscribe to kernel events\n");
 			rc = 3;
 			goto out;
 		}
diff --git a/udev/udevd.c b/udev/udevd.c
index 291655ef00..d9de26ea6c 100644
--- a/udev/udevd.c
+++ b/udev/udevd.c
@@ -195,7 +195,6 @@ static void event_fork(struct udev_event *event)
 	switch (pid) {
 	case 0:
 		/* child */
-		udev_monitor_unref(kernel_monitor);
 		udev_ctrl_unref(udev_ctrl);
 		logging_close();
 		logging_init("udevd-event");
@@ -235,6 +234,9 @@ static void event_fork(struct udev_event *event)
 			udev_device_update_db(event->dev);
 		}
 
+		/* send processed event back to the kernel netlink socket */
+		udev_monitor_send_device(kernel_monitor, event->dev);
+
 		info(event->udev, "seq %llu exit with %i\n", udev_device_get_seqnum(event->dev), err);
 		logging_close();
 		if (err != 0)
@@ -811,7 +813,7 @@ int main(int argc, char *argv[])
 		goto exit;
 	}
 
-	kernel_monitor = udev_monitor_new_from_netlink(udev);
+	kernel_monitor = udev_monitor_new_from_netlink(udev, UDEV_MONITOR_KERNEL);
 	if (kernel_monitor == NULL || udev_monitor_enable_receiving(kernel_monitor) < 0) {
 		fprintf(stderr, "error initializing netlink socket\n");
 		err(udev, "error initializing netlink socket\n");