wireguardnl: Go package for interacting with WireGuard via generic netlink

[Matt Layher]

Hey Jason,

Thanks very much for WireGuard and for the information.

 > Something to consider with this is the chunking.

Certainly! This was a first pass but these changes should be reasonable 
to port to Go as well.  I suppose I'll have to introduce some more 
complicated test devices to this logic.  I've filed a couple issues to 
track this and hope that I can at least implement the chunking get logic 
this week.

 > The other thing that might be sort of neat to try to implement is
falling back to the userspace API:

This is super interesting and I actually did not discover it until after 
I pushed the first few commits to my package.  I could see it making 
sense to refactor my current package layout to something like three 
packages:

- wireguardnl: netlink-based communication
- wireguardcfg: text-based userspace configuration protocol communication
- wireguard: wrapper for both that detects the module in use and 
seamlessly presents a unified interface

 > The thing you're dumping from a single device is all the peers. If 
you want a list of all interfaces, then the place to NLM_F_DUMP is 
RTM_GETLINK, where you can then inspect 
ifinfomsg->IFLA_LINKINFO->IFLA_INFO_KIND and make sure that it's 
"wireguard".

Ahhh, that makes more sense to me.  Perhaps I glossed over the 
uapi/wireguard.h documentation.  For the time being, I'm doing a call to 
Go's "net.Interfaces" which is a bit easier (though less efficient) than 
doing rtnetlink calls directly.  Perhaps this is something I can iterate 
on in the future as well.

 > If you're on IRC, come on into #wireguard on Freenode and poke me, and
we can chat about it further; I'm zx2c4.

Certainly!  I don't have any further inquiries at this time, but I'll 
join up!

Thank you again for WireGuard, and thank you very much for your time, 
feedback, and answers to my questions.

- Matt Layher


On 07/23/2018 07:59 AM, Jason A. Donenfeld wrote:
> Hey Matt,
>
> That's terrific! Thanks for making that. I look forward to seeing
> utilities develop around your library.
>
> Something to consider with this is the chunking. Since a device has
> many peers and a peer has many allowedips, it's possible that these
> might span multiple messages, larger than the maximum netlink packet
> size. For that reason, wg(8) will properly split things into several
> calls. Here's the set call:
>
> https://git.zx2c4.com/WireGuard/tree/src/tools/ipc.c#n558
>
> It accounts for toobig_allowedips and toobig_peers with some goto
> jumps that are sure to make your eyes bleed (read: you can do better
> than that :-). Similar in the get call, we coalesce peers that span
> multiple messages:
>
> https://git.zx2c4.com/WireGuard/tree/src/tools/ipc.c#n899
> https://git.zx2c4.com/WireGuard/tree/src/tools/ipc.c#n877
>
> The other thing that might be sort of neat to try to implement is
> falling back to the userspace API:
>
> https://www.wireguard.com/xplatform/
>
> This is a simple unix socket-based approach that mimics the same
> semantics as the netlink API, but is portable to different platforms.
> This is what wireguard-go and wireguard-rs and friends use for
> configuration. wg(8) implements both and provides an identical
> frontend for the two. However, I imagine you starting with netlink
> will be much more useful and is a good decision, since serious
> wireguard users are expected to continue using the serious kernel
> implementation.
>
>> While I'm here, I did have one inquiry about "WG_CMD_GET_DEVICE": after
>> working with a handful of generic netlink families, I was slightly
>> surprised to see that a request paired with "NLM_F_DUMP" doesn't return
>> a list of all WireGuard devices from the kernel.
> The thing you're dumping from a single device is all the peers. If you
> want a list of all interfaces, then the place to NLM_F_DUMP is
> RTM_GETLINK, where you can then inspect
> ifinfomsg->IFLA_LINKINFO->IFLA_INFO_KIND and make sure that it's
> "wireguard". WireGuard itself doesn't [necessarily need to] know all
> of the instances of itself, since it's instantiated by the rtnl
> subsystem. Check out kernel_get_wireguard_interfaces here:
>
> https://git.zx2c4.com/WireGuard/tree/src/tools/ipc.c#n458
>
> If you're on IRC, come on into #wireguard on Freenode and poke me, and
> we can chat about it further; I'm zx2c4.
>
> Talk soon,
> Jason