From: SeongJae Park sjpark@amazon.de
commit 9996bd494794a2fe393e97e7a982388c6249aa76 upstream.
'xenbus_backend' watches 'state' of devices, which is writable by guests. Hence, if guests intensively updates it, dom0 will have lots of pending events that exhausting memory of dom0. In other words, guests can trigger dom0 memory pressure. This is known as XSA-349. However, the watch callback of it, 'frontend_changed()', reads only 'state', so doesn't need to have the pending events.
To avoid the problem, this commit disallows pending watch messages for 'xenbus_backend' using the 'will_handle()' watch callback.
This is part of XSA-349
Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park sjpark@amazon.de Reported-by: Michael Kurth mku@amazon.de Reported-by: Pawel Wieczorkiewicz wipawel@amazon.de Reviewed-by: Juergen Gross jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/xen/xenbus/xenbus_probe_backend.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/drivers/xen/xenbus/xenbus_probe_backend.c +++ b/drivers/xen/xenbus/xenbus_probe_backend.c @@ -180,6 +180,12 @@ static int xenbus_probe_backend(struct x 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_backen .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",