xen-gntalloc: signedness bug in add_grefs()

gref->gref_id is unsigned so the error handling didn't work.
gnttab_grant_foreign_access() returns an int type, so we can add a
cast here, and it doesn't cause any problems.
gnttab_grant_foreign_access() can return a variety of errors
including -ENOSPC, -ENOSYS and -ENOMEM.

CC: stable@kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
index 23c60cf4313ed26095bb2e0e93bab5064fb22b11..e1c4c6e5b469c44449f68e9e841d264eb08dbc48 100644 (file)
--- a/drivers/xen/gntalloc.c
+++ b/drivers/xen/gntalloc.c
@@ -135,7 +135,7 @@ static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
                /* Grant foreign access to the page. */
                gref->gref_id = gnttab_grant_foreign_access(op->domid,
                        pfn_to_mfn(page_to_pfn(gref->page)), readonly);
-               if (gref->gref_id < 0) {
+               if ((int)gref->gref_id < 0) {
                        rc = gref->gref_id;
                        goto undo;
                }