netdev - Re: [PATCH net-next v5 0/7] selftests: drv-net: support testing with a remote system

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Date: Wed, 24 Apr 2024 11:57:12 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, shuah@...nel.org, petrm@...dia.com,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v5 0/7] selftests: drv-net: support testing
 with a remote system

On Wed, 24 Apr 2024 10:13:41 -0400 Willem de Bruijn wrote:
> > I haven't thought about this part much, TBH. I'm not aware of any
> > scheme used in other tests.
> > IIUC the problem is that we need root locally, and then try to SSH
> > over to remote. But normally the SSH keys belong to the non-root
> > user, so SSH'ing as root is annoying?  
> 
> Yeah. It requires "PermitRootLogin yes" in your sshd_config and
> installing root keys.
> 
> It's not a huge issue, but if we do want to fix it, doing so will be
> easier early rather than when more tests are added with implicit
> dependency on having root.

You know what, we need a diagram. We currently expect:


   ------------                                 -------------   
  |            |                               |             |   
  | Local user |                    ---------->| Remote user |                
  |            |                   /           |             |    
   ------------                   /             -------------                
                                 /                              
                                /
   ------------                /                -------------   
  |  >*exec*<  |              /                |             |   
  | Local root |-------------U---------------->| Remote root |                
  |            |             ?                 |             |    
   ------------                                 -------------                


We run locally as root. Putting sudo on all local commands would be
annoying.

On remote we don't currently explicitly say whether we need root.
The user is basically implicitly controlled by the REMOTE_ARGS
and ssh config.

REMOTE_ARGS="john@...hine"

will make us log in as john. But *from* root, so pub key of root needs
to be deployed.

We can support:

   ------------                                 -------------   
  |            |                               |             |   
  | Local user |               ?               | Remote user |                
  |       ,--------------------U-------------->|             |    
   ------/-----`               \                -------------                
        | ?su back to user?     \                               
        |                        \
   ------------                   \             -------------   
  |  >*exec*<  |                   \           |             |   
  | Local root |                    `--------->| Remote root |                
  |            |                               |             |    
   ------------                                 -------------                

but it's unclear whether that's all you're asking for, or also:

   ------------                                 -------------   
  |            |                               |             |   
  | Local user |                               | Remote user |                
  |       ,----------------------------------->->?cond sudo? |    
   ------/-----`                                -----|-------                
        | su back to user                            |          
        |                                            |
   ------------                                 -----v-------   
  |  >*exec*<  |                               |             |   
  | Local root |                               | Remote root |                
  |            |                               |             |    
   ------------                                 -------------    

which would require us to annotate privileged remote commands.