IB/core: Avoid unsigned int overflow in sg_alloc_table

sg_alloc_table gets unsigned int as parameter while the driver
returns it as size_t. Check npages isn't greater than maximum
unsigned int.

Fixes: eeb8461e36c9 ("IB: Refactor umem to use linear SG table")
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 224ad27..84b4eff 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -175,7 +175,7 @@
 
 	cur_base = addr & PAGE_MASK;
 
-	if (npages == 0) {
+	if (npages == 0 || npages > UINT_MAX) {
 		ret = -EINVAL;
 		goto out;
 	}