[PATCH 4.9 46/49] xen-scsiback: dont "handle" error by BUG()

[Greg Kroah-Hartman]

From: Jan Beulich <jbeulich@xxxxxxxx>

commit 7c77474b2d22176d2bfb592ec74e0f2cb71352c9 upstream.

In particular -ENOMEM may come back here, from set_foreign_p2m_mapping().
Don't make problems worse, the more that handling elsewhere (together
with map's status fields now indicating whether a mapping wasn't even
attempted, and hence has to be considered failed) doesn't require this
odd way of dealing with errors.

This is part of XSA-362.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/xen/xen-scsiback.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -423,12 +423,12 @@ static int scsiback_gnttab_data_map_batc
 		return 0;
 
 	err = gnttab_map_refs(map, NULL, pg, cnt);
-	BUG_ON(err);
 	for (i = 0; i < cnt; i++) {
 		if (unlikely(map[i].status != GNTST_okay)) {
 			pr_err("invalid buffer -- could not remap it\n");
 			map[i].handle = SCSIBACK_INVALID_HANDLE;
-			err = -ENOMEM;
+			if (!err)
+				err = -ENOMEM;
 		} else {
 			get_page(pg[i]);
 		}