From: daniel@...
Date: 2020-08-11T08:34:22+00:00
Subject: [ruby-core:99552] [Ruby master Bug#17112] Resolv.getaddress fails with IPv6 link-local addresses

Issue #17112 has been updated by daniel-rikowski (Daniel Rikowski).


After some experiments I noticed that changing `use_ipv6?` isn't sufficient.

In `Resolv#each_address` there seems to be a check for IP addresses. In case an IP address is given no actual resolving is performed.

```ruby
if AddressRegex =~ name
  yield name
  return
end
```
with
```ruby
AddressRegex = /(?:#{IPv4::Regex})|(?:#{IPv6::Regex})/
```

Unfortunately the regex check doesn't catch link-local addresses. It looks like the IPv6 regexes cannot process the zone ID suffix. (i.e. the interface number/name after the percentage sign, e.g. 'fe80::...**%8**' or  'fe80::...**%eth0**')

As a result a regular resolving is attempted which fails (at least on my system)



----------------------------------------
Bug #17112: Resolv.getaddress fails with IPv6 link-local addresses 
https://bugs.ruby-lang.org/issues/17112#change-87014

* Author: daniel-rikowski (Daniel Rikowski)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x64-mingw32]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
I noticed that I cannot resolve any link-local IPv6 address using `Resolv.getaddress`. For example calling `Resolv.getaddress('fe80::eca4:7b00:ecc5:206c%8')` fails with `Resolv::ResolvError`
Resolving any IPv4 address succeedes, as well as resolving the loopback address `::1`. 


After some code digging I noticed that `Resolv::DNS` doesn't even attempt to resolve that IP address. It checks if there is any local IPv6 interface with an IP address which is not a loopback or a link-local address.

```ruby
def each_address(name)
  each_resource(name, Resource::IN::A) {|resource| yield resource.address}
  if use_ipv6? # <===== false on my system
	each_resource(name, Resource::IN::AAAA) {|resource| yield resource.address}
  end
end
```

`use_ipv6?` ultimately boils down to this:

```ruby
Socket.ip_address_list.any? {|a| a.ipv6? && !a.ipv6_loopback? && !a.ipv6_linklocal? }
```


In other words if the system doesn't have a "real" IPv6 address, `Resolv.getaddress` cannot resolve link-local addresses. (`::1` is resolved using `Resolv::Hosts` which doesn't perform the same check)


One could argue that IP addresses don't have to be resolved, and I could just perform a regex check and skip `Resolv.getaddress` if I already have an IP address. 
Unfortunately that is not possible when using `resolv-replace`. In that case most (all?) of Ruby's address resolving is piped through `Resolv.getaddress`. 
(That is how I noticed this bug: The RubyMine test runner uses drb which connects to a process on the same machine using a link-local IPv6 address. Since I'm using `resolv-replace` and I don't have a network interface with a non-loopback non-local-link address I encountered this bug.)

Platform:
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x64-mingw32]
Microsoft Windows [Version 10.0.18363.959]




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