RFC: AT-controlled USB-Ethernet cellular modems: extend comgt-ncm or new netifd protocol?

[Michael Wyraz]

Hello Felix,

yes, NCM and RNDIS are different USB data protocols. I did not mean to 
suggest using the NCM kernel driver for an RNDIS interface

My question was about the userspace "comgt-ncm" which combines an AT 
control port, modem-specific AT command profiles, a USB network 
interface, and a netifd-managed DHCP child interface. The netifd script 
does not appear to depend on NCM itself, it's just named so. I was 
wondering whether that AT/control and DHCP logic should be reusable for 
other USB-Ethernet modem modes, rather than duplicating it in a new 
protocol.

I understand the security concerns about RNDIS and would prefer another 
USB data mode if this modem offered one. So far, RNDIS is the only 
working data mode I have identified for this particular module. An 
integrated, fixed modem has a different threat model from arbitrary 
user-supplied USB devices, although its firmware still cannot be assumed 
trustworthy. I am not proposing to enable RNDIS by default or something.

Kind regards,

Michael.


> Hi,
>
> I'm confused. What are you suggesting:
> Aren't NCM and RNDIS mutually exclusive?
>
> RNDIS is about to be phased out. It's been deprecated for a while and a security nightmare. It ought to die. (my opinion, I'm not speaking for anyone on OpenWrt's behalf)
>
> <https://www.phoronix.com/news/RNDIS-Disable-Linux-2026-Patch>
>
> Regards
> Felix Baumann