IB/mlx4: Check if GRH is available before using it

commit bf08e884 upstream.

Before reading GRH attributes, need to make sure AH contains GRH,
and in addition, initialize GID type.

Fixes: dbf727de ('IB/core: Use GID table in AH creation and dmac resolution')
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Daniel Jurgens <danielj@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/infiniband/hw/mlx4/qp.c

@@ -1765,14 +1765,14 @@ static int __mlx4_ib_modify_qp(struct ib_qp *ibqp,
 		u8 port_num = mlx4_is_bonded(to_mdev(ibqp->device)->dev) ? 1 :
 			attr_mask & IB_QP_PORT ? attr->port_num : qp->port;
 		union ib_gid gid;
-		struct ib_gid_attr gid_attr;
+		struct ib_gid_attr gid_attr = {.gid_type = IB_GID_TYPE_IB};
 		u16 vlan = 0xffff;
 		u8 smac[ETH_ALEN];
 		int status = 0;
 		int is_eth = rdma_cap_eth_ah(&dev->ib_dev, port_num) &&
 			attr->ah_attr.ah_flags & IB_AH_GRH;
 
-		if (is_eth) {
+		if (is_eth && attr->ah_attr.ah_flags & IB_AH_GRH) {
 			int index = attr->ah_attr.grh.sgid_index;
 
 			status = ib_get_cached_gid(ibqp->device, port_num,