IB/core: Bound check alternate path port number

The alternate port number is used as an array index in the IB
security implementation, invalid values can result in a kernel panic.

Cc: <stable@vger.kernel.org> # v4.12
Fixes: d291f1a6 ("IB/core: Enforce PKey security on QPs")
Signed-off-by: NDaniel Jurgens <danielj@mellanox.com>
Reviewed-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NLeon Romanovsky <leon@kernel.org>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/core/uverbs_cmd.c

@@ -1971,6 +1971,12 @@ static int modify_qp(struct ib_uverbs_file *file,
 		goto release_qp;
 	}
 
+	if ((cmd->base.attr_mask & IB_QP_ALT_PATH) &&
+	    !rdma_is_port_valid(qp->device, cmd->base.alt_port_num)) {
+		ret = -EINVAL;
+		goto release_qp;
+	}
+
 	attr->qp_state		  = cmd->base.qp_state;
 	attr->cur_qp_state	  = cmd->base.cur_qp_state;
 	attr->path_mtu		  = cmd->base.path_mtu;