On Fri, Jan 27, 2023 at 07:38:38PM +0100, Vlad Buslov wrote: > Currently only bidirectional established connections can be offloaded > via act_ct. Such approach allows to hardcode a lot of assumptions into > act_ct, flow_table and flow_offload intermediate layer codes. In order > to enabled offloading of unidirectional UDP NEW connections start with > incrementally changing the following assumptions: > > - Drivers assume that only established connections are offloaded and > don't support updating existing connections. Extract ctinfo from meta > action cookie and refuse offloading of new connections in the drivers. > > - Fix flow_table offload fixup algorithm to calculate flow timeout > according to current connection state instead of hardcoded > "established" value. > > - Add new flow_table flow flag that designates bidirectional connections > instead of assuming it and hardcoding hardware offload of every flow > in both directions. > > - Add new flow_table flow "ext_data" field and use it in act_ct to track > the ctinfo of offloaded flows instead of assuming that it is always > "established". > > With all the necessary infrastructure in place modify act_ct to offload > UDP NEW as unidirectional connection. Pass reply direction traffic to CT > and promote connection to bidirectional when UDP connection state > changes to "assured". Rely on refresh mechanism to propagate connection > state change to supporting drivers. > > Note that early drop algorithm that is designed to free up some space in > connection tracking table when it becomes full (by randomly deleting up > to 5% of non-established connections) currently ignores connections > marked as "offloaded". Now, with UDP NEW connections becoming > "offloaded" it could allow malicious user to perform DoS attack by > filling the table with non-droppable UDP NEW connections by sending just > one packet in single direction. To prevent such scenario change early > drop algorithm to also consider "offloaded" connections for deletion. If the two changes I propose are doable, then I am OK with this. I would really like to explore my proposal to turn the workqueue into a "scanner" that iterates over the entries searching for flows that need to be offloaded (or updated to bidirectional, like in this new case). I think it is not too far from what there is in the flowtable codebase.
