On Thu, Jul 21, 2022 at 02:59:35PM +0300, Vladimir Oltean wrote:
On Sun, Jul 17, 2022 at 05:53:22PM +0200, netdev@kapio-technology.com wrote:
- What happens to packets with a DA matching the zero-DPV entry, are
they also discarded in hardware? If so, here we differ from the bridge driver implementation where such packets will be forwarded according to the locked entry and egress the locked port
I understand that egress will follow what is setup with regard to UC, MC and BC, though I haven't tested that. But no replies will get through of course as long as the port hasn't been opened for the iface behind the locked port.
Here, should we be rather fixing the software bridge, if the current behavior is to forward packets towards locked FDB entries?
I think the bridge needs to be fixed, but not to discard packets. If I decided to lock a port, it means I do not blindly trust whoever who is behind the port, but instead want to authorize them first. Since an unauthorized user is able to create locked FDB entries we need to carefully define what they mean. I tried looking information about MAB online, but couldn't find detailed material that answers my questions, so my answers are based on what I believe is logical, which might be wrong.
Currently, the bridge will forward packets to a locked entry which effectively means that an unauthorized host can cause the bridge to direct packets to it and sniff them. Yes, the host can't send any packets through the port (while locked) and can't overtake an existing (unlocked) FDB entry, but it still seems like an odd decision. IMO, the situation in mv88e6xxx is even worse because there an unauthorized host can cause packets to a certain DMAC to be blackholed via its zero-DPV entry.
Another (minor?) issue is that locked entries cannot roam between locked ports. Lets say that my user space MAB policy is to authorize MAC X if it appears behind one of the locked ports swp1-swp4. An unauthorized host behind locked port swp5 can generate packets with SMAC X, preventing the true owner of this MAC behind swp1 from ever being authorized.
It seems like the main purpose of these locked entries is to signal to user space the presence of a certain MAC behind a locked port, but they should not be able to affect packet forwarding in the bridge, unlike regular entries.
Regarding a separate knob for MAB, I tend to agree we need it. Otherwise we cannot control which locked ports are able to populate the FDB with locked entries. I don't particularly like the fact that we overload an existing flag ("learning") for that. Any reason not to add an explicit flag ("mab")? At least with the current implementation, locked entries cannot roam between locked ports and cannot be refreshed, which differs from regular learning.