[ssm, multicast] align source address validation across the platform - #1049
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This work adds a series of validation checks, including these new ones:
- Rejecting IPv6 sources that embed an IPv4 address: the IPv4-compatible and
IPv4-mapped forms of RFC 4291 sections 2.5.5.1 and 2.5.5.2.
- Rejecting IPv4 sources in 0.0.0.0/8 and 240.0.0.0/4:
- class E (240.0.0.0/4): the IANA special-purpose registry (RFC 6890)
marks it "Source: False".
- 0.0.0.0/8 is "Source: True", since RFC 1122 section 3.2.1.3 allows it
before a host learns its address, but an (S,G) source must be a
specific unicast address that reverse-path forwarding can resolve to
an incoming interface, which a 0.0.0.0/8 address never is.
- shared address space (100.64.0.0/10, RFC 6598) is "Source: True" and
not globally reachable, so it stays allowed here.
- We add new address predicates: `Ipv4Addr::is_this_network`,
`Ipv4Addr::is_reserved`, and `Ipv6Addr::embedded_ipv4_form`. These sit
on the address types, but source validation lives on `SourceFilter`,
so that multicast policy does not leak onto a generic address type.
- Only `Include` sets are checked btw: an `Exclude` set names traffic
to drop, and an operator may want to block an address that could
never be a real source anyway.
Note: this is not a refactor. `set_mcast_forwarding` validated no
source addresses at all before now. Every rule above is a new reject
on that path. This aligns us with the other repos and the ongoing oxnet
refactoring.
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This work adds a series of validation checks, including these new ones:
Ipv4Addr::is_this_network,Ipv4Addr::is_reserved, andIpv6Addr::embedded_ipv4_form. These sit on the address types, but source validation lives onSourceFilter, so that multicast policy does not leak onto a generic address type.Includesets are checked btw: anExcludeset names traffic to drop, and an operator may want to block an address that could never be a real source anyway.Note: this is not a refactor.
set_mcast_forwardingvalidated no source addresses at all before now. Every rule above is a new reject on that path. This aligns us with the other repos and the ongoing oxnet refactoring.