RDS: null pointer dereference in rds_atomic_free_op

set rm->atomic.op_active to 0 when rds_pin_pages() fails
or the user supplied address is invalid,
this prevents a NULL pointer usage in rds_atomic_free_op()
Signed-off-by: Mohamed Ghannam <simo.ghannam@gmail.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

CVE-2018-5333
(cherry picked from commit 7d11f77f)
Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>
Acked-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>

net/rds/rdma.c

@@ -866,6 +866,7 @@ int rds_cmsg_atomic(struct rds_sock *rs, struct rds_message *rm,
 err:
 	if (page)
 		put_page(page);
+	rm->atomic.op_active = 0;
 	kfree(rm->atomic.op_notifier);
 
 	return ret;