From c4c303c7c5679b4b368e12f41124aee29c325b76 Mon Sep 17 00:00:00 2001 From: Olaf Hering Date: Thu, 25 Aug 2011 18:30:11 +0200 Subject: [PATCH] xen/pv-on-hvm kexec: prevent crash in xenwatch_thread() when stale watch events arrive During repeated kexec boots xenwatch_thread() can crash because xenbus_watch->callback is cleared by xenbus_watch_path() if a node/token combo for a new watch happens to match an already registered watch from an old kernel. In this case xs_watch returns -EEXISTS, then register_xenbus_watch() does not remove the to-be-registered watch from the list of active watches but returns the -EEXISTS to the caller anyway. Because the watch is still active in xenstored it will cause an event which will arrive in the new kernel. process_msg() will find the encapsulated struct xenbus_watch in its list of registered watches and puts the "empty" watch handle in the queue for xenwatch_thread(). xenwatch_thread() then calls ->callback which was cleared earlier by xenbus_watch_path(). To prevent that crash in a guest running on an old xen toolstack remove the special -EEXIST handling. v2: - remove the EEXIST handing in register_xenbus_watch() instead of checking for ->callback in process_msg() Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Olaf Hering --- drivers/xen/xenbus/xenbus_xs.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index 5534690075af..46347a49c5b8 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -638,8 +638,7 @@ int register_xenbus_watch(struct xenbus_watch *watch) err = xs_watch(watch->node, token); - /* Ignore errors due to multiple registration. */ - if ((err != 0) && (err != -EEXIST)) { + if (err) { spin_lock(&watches_lock); list_del(&watch->list); spin_unlock(&watches_lock);