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authorOlaf Hering <olaf@aepfle.de>2011-08-25 20:30:11 +0400
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2011-09-01 19:48:29 +0400
commitc4c303c7c5679b4b368e12f41124aee29c325b76 (patch)
tree53f98a9bc550edca6f3c6619ec3d363186e0521d /drivers/xen/xenbus
parent02f8c6aee8df3cdc935e9bdd4f2d020306035dbe (diff)
downloadlinux-c4c303c7c5679b4b368e12f41124aee29c325b76.tar.xz
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 <konrad.wilk@oracle.com> Signed-off-by: Olaf Hering <olaf@aepfle.de>
Diffstat (limited to 'drivers/xen/xenbus')
-rw-r--r--drivers/xen/xenbus/xenbus_xs.c3
1 files changed, 1 insertions, 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);