[wicketd] Pass RSS a /56 rack subnet instead of a raw IP address (/128)

[jgallagher]

I think this should fix #5665. I checked a4x2 and it has a /56, so I think #5665 is specific to RSS when it's been run via wicket. I'll try this on madrid once a TUF repo is built.

I opened #5669 for the fact that our types allow this mistake; e.g., I think both

omicron/common/src/api/internal/shared.rs

Line 162 in 9c90e4b

pub rack_subnet: Ipv6Network,

and

omicron/nexus/db-model/src/rack.rs

Line 19 in 9c90e4b

pub rack_subnet: Option<IpNetwork>,

are incorrect in that they allow any network size, and both should probably be Ipv6Net<RACK_PREFIX> instead. Fixing that is not trivial because at least the former is serialized in the bootstore.

[sunshowers]

Thanks for catching this.

The original code makes me really uncomfortable to be honest, I don't like the fact that there's a From impl here. (Feels like the opposite of misuse-resistant.) Is that something we can fix?

[jgallagher]

The specific From impl we were hitting here is not under our control (https://docs.rs/ipnetwork/0.20.0/ipnetwork/struct.Ipv6Network.html#impl-From%3CIpv6Addr%3E). I think I'd claim that #5669 would be the right fix (i.e., stop using Ipv6Network when we know there should be a specific prefix length).

[jgallagher]

Tested on madrid; looks good:

root@oxz_switch1:~# omdb db rack list
ID                                   INITIALIZED TUF_BASE_URL RACK_SUBNET
45e3bc39-e5e9-40e3-adea-a3b9cf70aa73 true        -            fd00:1122:3344:100::/56