xen-scsiback: don't "handle" error by BUG()

stable inclusion
from stable-5.10.18
commit 9bea436fc3fc9a820b8b34e83708971c1813b892
bugzilla: 50148

--------------------------------

commit 7c77474b 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: NJan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
Reviewed-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/xen/xen-scsiback.c

@@ -386,12 +386,12 @@ static int scsiback_gnttab_data_map_batch(struct gnttab_map_grant_ref *map,
 		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]);
 		}