Merge tag 'for-linus-5.11-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen updates from Juergen Gross:
 "Fixes for security issues just having been disclosed:

   - a five patch series for fixing of XSA-349 (DoS via resource
     depletion in Xen dom0)

   - a patch fixing XSA-350 (access of stale pointer in a Xen dom0)"

* tag 'for-linus-5.11-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen-blkback: set ring->xenblkd to NULL after kthread_stop()
  xenbus/xenbus_backend: Disallow pending watch messages
  xen/xenbus: Count pending messages for each watch
  xen/xenbus/xen_bus_type: Support will_handle watch callback
  xen/xenbus: Add 'will_handle' callback support in xenbus_watch_path()
  xen/xenbus: Allow watches discard events before queueing

Author: torvalds

drivers/block/xen-blkback/xenbus.c

@@ -274,6 +274,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 
 		if (ring->xenblkd) {
 			kthread_stop(ring->xenblkd);
+			ring->xenblkd = NULL;
 			wake_up(&ring->shutdown_wq);
 		}
 
@@ -675,7 +676,8 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
 	/* setup back pointer */
 	be->blkif->be = be;
 
-	err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
+	err = xenbus_watch_pathfmt(dev, &be->backend_watch, NULL,
+				   backend_changed,
 				   "%s/%s", dev->nodename, "physical-device");
 	if (err)
 		goto fail;

drivers/net/xen-netback/xenbus.c

@@ -557,12 +557,14 @@ static int xen_register_credit_watch(struct xenbus_device *dev,
 		return -ENOMEM;
 	snprintf(node, maxlen, "%s/rate", dev->nodename);
 	vif->credit_watch.node = node;
+	vif->credit_watch.will_handle = NULL;
 	vif->credit_watch.callback = xen_net_rate_changed;
 	err = register_xenbus_watch(&vif->credit_watch);
 	if (err) {
 		pr_err("Failed to set watcher %s\n", vif->credit_watch.node);
 		kfree(node);
 		vif->credit_watch.node = NULL;
+		vif->credit_watch.will_handle = NULL;
 		vif->credit_watch.callback = NULL;
 	}
 	return err;
@@ -609,13 +611,15 @@ static int xen_register_mcast_ctrl_watch(struct xenbus_device *dev,
 	snprintf(node, maxlen, "%s/request-multicast-control",
 		 dev->otherend);
 	vif->mcast_ctrl_watch.node = node;
+	vif->mcast_ctrl_watch.will_handle = NULL;
 	vif->mcast_ctrl_watch.callback = xen_mcast_ctrl_changed;
 	err = register_xenbus_watch(&vif->mcast_ctrl_watch);
 	if (err) {
 		pr_err("Failed to set watcher %s\n",
 		       vif->mcast_ctrl_watch.node);
 		kfree(node);
 		vif->mcast_ctrl_watch.node = NULL;
+		vif->mcast_ctrl_watch.will_handle = NULL;
 		vif->mcast_ctrl_watch.callback = NULL;
 	}
 	return err;
@@ -820,7 +824,7 @@ static void connect(struct backend_info *be)
 	xenvif_carrier_on(be->vif);
 
 	unregister_hotplug_status_watch(be);
-	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
+	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch, NULL,
 				   hotplug_status_changed,
 				   "%s/%s", dev->nodename, "hotplug-status");
 	if (!err)

drivers/xen/xen-pciback/xenbus.c

@@ -689,7 +689,7 @@ static int xen_pcibk_xenbus_probe(struct xenbus_device *dev,
 
 	/* watch the backend node for backend configuration information */
 	err = xenbus_watch_path(dev, dev->nodename, &pdev->be_watch,
-				xen_pcibk_be_watch);
+				NULL, xen_pcibk_be_watch);
 	if (err)
 		goto out;
 

drivers/xen/xenbus/xenbus.h

@@ -44,6 +44,8 @@ struct xen_bus_type {
 	int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
 	int (*probe)(struct xen_bus_type *bus, const char *type,
 		     const char *dir);
+	bool (*otherend_will_handle)(struct xenbus_watch *watch,
+				     const char *path, const char *token);
 	void (*otherend_changed)(struct xenbus_watch *watch, const char *path,
 				 const char *token);
 	struct bus_type bus;

drivers/xen/xenbus/xenbus_client.c

@@ -127,18 +127,22 @@ EXPORT_SYMBOL_GPL(xenbus_strstate);
  */
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
+		      bool (*will_handle)(struct xenbus_watch *,
+					  const char *, const char *),
 		      void (*callback)(struct xenbus_watch *,
 				       const char *, const char *))
 {
 	int err;
 
 	watch->node = path;
+	watch->will_handle = will_handle;
 	watch->callback = callback;
 
 	err = register_xenbus_watch(watch);
 
 	if (err) {
 		watch->node = NULL;
+		watch->will_handle = NULL;
 		watch->callback = NULL;
 		xenbus_dev_fatal(dev, err, "adding watch on %s", path);
 	}
@@ -165,6 +169,8 @@ EXPORT_SYMBOL_GPL(xenbus_watch_path);
  */
 int xenbus_watch_pathfmt(struct xenbus_device *dev,
 			 struct xenbus_watch *watch,
+			 bool (*will_handle)(struct xenbus_watch *,
+					const char *, const char *),
 			 void (*callback)(struct xenbus_watch *,
 					  const char *, const char *),
 			 const char *pathfmt, ...)
@@ -181,7 +187,7 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev,
 		xenbus_dev_fatal(dev, -ENOMEM, "allocating path for watch");
 		return -ENOMEM;
 	}
-	err = xenbus_watch_path(dev, path, watch, callback);
+	err = xenbus_watch_path(dev, path, watch, will_handle, callback);
 
 	if (err)
 		kfree(path);

drivers/xen/xenbus/xenbus_probe.c

@@ -136,6 +136,7 @@ static int watch_otherend(struct xenbus_device *dev)
 		container_of(dev->dev.bus, struct xen_bus_type, bus);
 
 	return xenbus_watch_pathfmt(dev, &dev->otherend_watch,
+				    bus->otherend_will_handle,
 				    bus->otherend_changed,
 				    "%s/%s", dev->otherend, "state");
 }

drivers/xen/xenbus/xenbus_probe_backend.c

@@ -180,6 +180,12 @@ static int xenbus_probe_backend(struct xen_bus_type *bus, const char *type,
 	return err;
 }
 
+static bool frontend_will_handle(struct xenbus_watch *watch,
+				 const char *path, const char *token)
+{
+	return watch->nr_pending == 0;
+}
+
 static void frontend_changed(struct xenbus_watch *watch,
 			     const char *path, const char *token)
 {
@@ -191,6 +197,7 @@ static struct xen_bus_type xenbus_backend = {
 	.levels = 3,		/* backend/type/<frontend>/<id> */
 	.get_bus_id = backend_bus_id,
 	.probe = xenbus_probe_backend,
+	.otherend_will_handle = frontend_will_handle,
 	.otherend_changed = frontend_changed,
 	.bus = {
 		.name		= "xen-backend",

drivers/xen/xenbus/xenbus_xs.c

@@ -705,9 +705,13 @@ int xs_watch_msg(struct xs_watch_event *event)
 
 	spin_lock(&watches_lock);
 	event->handle = find_watch(event->token);
-	if (event->handle != NULL) {
+	if (event->handle != NULL &&
+			(!event->handle->will_handle ||
+			 event->handle->will_handle(event->handle,
+				 event->path, event->token))) {
 		spin_lock(&watch_events_lock);
 		list_add_tail(&event->list, &watch_events);
+		event->handle->nr_pending++;
 		wake_up(&watch_events_waitq);
 		spin_unlock(&watch_events_lock);
 	} else
@@ -765,6 +769,8 @@ int register_xenbus_watch(struct xenbus_watch *watch)
 
 	sprintf(token, "%lX", (long)watch);
 
+	watch->nr_pending = 0;
+
 	down_read(&xs_watch_rwsem);
 
 	spin_lock(&watches_lock);
@@ -814,11 +820,14 @@ void unregister_xenbus_watch(struct xenbus_watch *watch)
 
 	/* Cancel pending watch events. */
 	spin_lock(&watch_events_lock);
-	list_for_each_entry_safe(event, tmp, &watch_events, list) {
-		if (event->handle != watch)
-			continue;
-		list_del(&event->list);
-		kfree(event);
+	if (watch->nr_pending) {
+		list_for_each_entry_safe(event, tmp, &watch_events, list) {
+			if (event->handle != watch)
+				continue;
+			list_del(&event->list);
+			kfree(event);
+		}
+		watch->nr_pending = 0;
 	}
 	spin_unlock(&watch_events_lock);
 
@@ -865,7 +874,6 @@ void xs_suspend_cancel(void)
 
 static int xenwatch_thread(void *unused)
 {
-	struct list_head *ent;
 	struct xs_watch_event *event;
 
 	xenwatch_pid = current->pid;
@@ -880,13 +888,15 @@ static int xenwatch_thread(void *unused)
 		mutex_lock(&xenwatch_mutex);
 
 		spin_lock(&watch_events_lock);
-		ent = watch_events.next;
-		if (ent != &watch_events)
-			list_del(ent);
+		event = list_first_entry_or_null(&watch_events,
+				struct xs_watch_event, list);
+		if (event) {
+			list_del(&event->list);
+			event->handle->nr_pending--;
+		}
 		spin_unlock(&watch_events_lock);
 
-		if (ent != &watch_events) {
-			event = list_entry(ent, struct xs_watch_event, list);
+		if (event) {
 			event->handle->callback(event->handle, event->path,
 						event->token);
 			kfree(event);

include/xen/xenbus.h

@@ -61,6 +61,15 @@ struct xenbus_watch
 	/* Path being watched. */
 	const char *node;
 
+	unsigned int nr_pending;
+
+	/*
+	 * Called just before enqueing new event while a spinlock is held.
+	 * The event will be discarded if this callback returns false.
+	 */
+	bool (*will_handle)(struct xenbus_watch *,
+			      const char *path, const char *token);
+
 	/* Callback (executed in a process context with no locks held). */
 	void (*callback)(struct xenbus_watch *,
 			 const char *path, const char *token);
@@ -197,10 +206,14 @@ void xenbus_probe(struct work_struct *);
 
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
+		      bool (*will_handle)(struct xenbus_watch *,
+					  const char *, const char *),
 		      void (*callback)(struct xenbus_watch *,
 				       const char *, const char *));
-__printf(4, 5)
+__printf(5, 6)
 int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch,
+			 bool (*will_handle)(struct xenbus_watch *,
+					     const char *, const char *),
 			 void (*callback)(struct xenbus_watch *,
 					  const char *, const char *),
 			 const char *pathfmt, ...);