listening service without MMU?

[Matt Johnston]

On 2022-06-24 11:26 am, johnea wrote:

> I've run across a number of other references since that timeframe that
> indicate that dropbear can run on no-MMU platforms using uClibc.
> 
> Searching hasn't really led to a conclusive answer. So, could you
> please confirm:
> 
> Can dropbear run as a listening service on Cortex-M3 with no-MMU?

Previously I would say no - usually it would need to run from inetd that 
executes a separate dropbear server process for each connection.
That is required because on a MMUless system the normal fork() doesn't 
create separate memory spaces for each program, so they interfere with 
each other.

But! In Dropbear 2022.82 it was changed to re-execute itself [1], so it 
is possible that it would work OK on a MMUless system. You could see if 
that works - there might be other assumptions that I have missed. Make 
sure you try a few concurrent connections.

Cheers,
Matt

[1]
- Dropbear now re-executes itself rather than just forking for each 
connection
   (only on Linux). This allows ASLR to randomise address space for each
   connection as a security mitigation. It should not have any visible 
impact
   - if there are any performance impacts in the wild please report it.