output public ssh host keys to console on boot (LP: #893400)

Currently cloud-init writes something like this to console output:
  ec2: #############################################################
  ec2: -----BEGIN SSH HOST KEY FINGERPRINTS-----
  ec2: 2048 78:ae:f3:91:04:6f:8d:ee:ef:e1:2d:72:83:6a:d0:82  root@h (RSA)
  ec2: 1024 d3:b6:32:64:22:d4:43:05:f9:25:b4:f3:65:4e:e2:51  root@h (DSA)
  ec2: -----END SSH HOST KEY FINGERPRINTS-----
  ec2: #############################################################

the key fingerprints are useful for humans to read, but not so useful
for machines, as you cannot populate a KnownHostsFile (~/.ssh/known_hosts)
from the data there.

This change adds output like:
  -----BEGIN SSH HOST KEY KEYS-----
  ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdH......STI= root@h
  ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDYRIQe6m......tWF3 root@h
  -----END SSH HOST KEY KEYS-----

Those lines can easily be grabbed and appended to a known_hosts file.

1 files changed, 16 insertions, 0 deletions

diff --git a/tools/write-ssh-key-fingerprints b/tools/write-ssh-key-fingerprints
index 7b2fc62c..5723c989 100755
--- a/tools/write-ssh-key-fingerprints
+++ b/tools/write-ssh-key-fingerprints
@@ -1,12 +1,28 @@
 #!/bin/sh
+fp_blist=",${1},"
+key_blist=",${2},"
 {
 echo
 echo "#############################################################"
 echo "-----BEGIN SSH HOST KEY FINGERPRINTS-----"
 for f in /etc/ssh/ssh_host_*key.pub; do
     [ -f "$f" ] || continue
+    read ktype line < "$f"
+    # skip the key if its type is in the blacklist
+    [ "${fp_blist#*,$ktype,}" = "${fp_blist}" ] || continue
     ssh-keygen -l -f "$f"
 done
 echo "-----END SSH HOST KEY FINGERPRINTS-----"
 echo "#############################################################"
+
 } | logger -p user.info -s -t "ec2"
+
+echo -----BEGIN SSH HOST KEY KEYS-----
+for f in /etc/ssh/ssh_host_*key.pub; do
+    [ -f "$f" ] || continue
+    read ktype line < "$f"
+    # skip the key if its type is in the blacklist
+    [ "${key_blist#*,$ktype,}" = "${key_blist}" ] || continue
+    cat $f
+done
+echo -----END SSH HOST KEY KEYS-----