xen/xenbus: ensure xenbus_map_ring_valloc() returns proper grant status

xenbus_map_ring_valloc() maps a ring page and returns the status of the
used grant (0 meaning success).

There are Xen hypervisors which might return the value 1 for the status
of a failed grant mapping due to a bug. Some callers of
xenbus_map_ring_valloc() test for errors by testing the returned status
to be less than zero, resulting in no error detected and crashing later
due to a not available ring page.

Set the return value of xenbus_map_ring_valloc() to GNTST_general_error
in case the grant status reported by Xen is greater than zero.

This is part of XSA-316.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wl@xen.org>
Link: https://lore.kernel.org/r/20200326080358.1018-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index 3858432..040d2a4 100644 (file)
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -448,7 +448,14 @@ EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
 int xenbus_map_ring_valloc(struct xenbus_device *dev, grant_ref_t *gnt_refs,
                           unsigned int nr_grefs, void **vaddr)
 {
-       return ring_ops->map(dev, gnt_refs, nr_grefs, vaddr);
+       int err;
+
+       err = ring_ops->map(dev, gnt_refs, nr_grefs, vaddr);
+       /* Some hypervisors are buggy and can return 1. */
+       if (err > 0)
+               err = GNTST_general_error;
+
+       return err;
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);