From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752610Ab1HPNRb (ORCPT ); Tue, 16 Aug 2011 09:17:31 -0400 Received: from mo-p00-ob.rzone.de ([81.169.146.160]:58044 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752580Ab1HPNRY (ORCPT ); Tue, 16 Aug 2011 09:17:24 -0400 X-RZG-AUTH: :P2EQZWCpfu+qG7CngxMFH1J+zrwiavkK6tmQaLfmztM8TOFPjjUQEnt0KA== X-RZG-CLASS-ID: mo00 From: Olaf Hering To: linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Konrad Cc: xen-devel@lists.xensource.com Subject: [PATCH 1/3] xen/pv-on-hvm kexec: prevent crash in xenwatch_thread() when stale watch events arrive Date: Tue, 16 Aug 2011 15:16:51 +0200 Message-Id: <1313500613-21394-2-git-send-email-olaf@aepfle.de> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1313500613-21394-1-git-send-email-olaf@aepfle.de> References: <1313500613-21394-1-git-send-email-olaf@aepfle.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, add a check wether xenbus_watch->callback is active. Signed-off-by: Olaf Hering --- drivers/xen/xenbus/xenbus_xs.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index 5534690..64248b2 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -828,7 +828,7 @@ static int process_msg(void) spin_lock(&watches_lock); msg->u.watch.handle = find_watch( msg->u.watch.vec[XS_WATCH_TOKEN]); - if (msg->u.watch.handle != NULL) { + if (msg->u.watch.handle && msg->u.watch.handle->callback) { spin_lock(&watch_events_lock); list_add_tail(&msg->list, &watch_events); wake_up(&watch_events_waitq); -- 1.7.3.4