Fix host key checking

[smortex]

The known_hosts file may contain keys associated with a hostname, an
ip-address, or both.

When validating a key, the net-ssh gem ensure that both the hostname and
the ip-address match beforce adding a key. Thus, if the known_hosts
file only contains one of these two pieces of information, the host key
verification fails.

Instead of adding keys when both the hostname and the ip-address match,
add them when any of these information match.

[smortex]

Steps to reproduce:

#!/usr/bin/env ruby

require 'net/ssh'

Net::SSH.start('example.com', 'username', :verify_host_key=>:always) do |ssh|
  puts ssh.exec!('hostname')
end

Without this patch, will only work if the known_hosts file has a line matching example.com,127.0.0.1 SSH KEY. A line example.com SSH KEY would be ignored.

[mfazekas]

@smortex thanks for the PR, can you please add a testcase for it?

[smortex]

Hi @mfazekas! My previous attempt to add tests failed because of another bug. A fresh view allowed me to spot it (b5af8a8) and add a few tests.

It also allowed me to see a difference between net-ssh and ssh(1), I detailed the issue in 855d617.

Globing is also still not handled for matching entries in the known_hosts file, but I think this can be part of another PR (only do bugfix in tis PR and add adding missing features in another one).

[smortex]

Just added a commit that fix the issue detailed in 855d617.

This is ready for review / merging 🎉

Please note that I have anther commit on top of this for matching hostnames against patterns that can be found in the known_host file. I plan to open another PR when this one is merged, but if you prefer, I can include the change in this branch. Just let me know!

[codecov-io]

Codecov Report

Merging #656 into master will decrease coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #656      +/-   ##
==========================================
- Coverage   95.82%   95.75%   -0.08%     
==========================================
  Files         144      144              
  Lines        9515     9509       -6     
==========================================
- Hits         9118     9105      -13     
- Misses        397      404       +7

Impacted Files	Coverage Δ
lib/net/ssh/transport/session.rb	95.74% <ø> (-0.18%)	⬇️
test/transport/test_session.rb	100% <100%> (ø)	⬆️
test/test_known_hosts.rb	100% <100%> (ø)	⬆️
lib/net/ssh/known_hosts.rb	98.64% <100%> (-0.04%)	⬇️
lib/net/ssh/buffered_io.rb	80.55% <0%> (-9.73%)	⬇️

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[donoghuc]

This seems like a really nice improvement. Would love to see it adopted.

[mfazekas]

@smortex thanks much for the PR, i'll probably change check_host_ip default to true in 5.1.1, and will change to false in next major version.

[donoghuc]

@mfazekas When do you expect to release 5.1.1? Would like to use this! Thanks.