guests/linux: properly quote and insert public key

plugins/communicators/ssh/communicator.rb

@@ -63,7 +63,7 @@ module VagrantPlugins
           @machine.ui.info(I18n.t("vagrant.inserting_insecure_key"))
           @machine.guest.capability(
             :insert_public_key,
-            Vagrant.source_root.join("keys", "vagrant.pub").read)
+            Vagrant.source_root.join("keys", "vagrant.pub").read.chomp)
 
           # Write out the private key in the data dir so that the
           # machine automatically picks it up.

plugins/guests/linux/cap/insert_public_key.rb

@@ -1,13 +1,17 @@
+require "vagrant/util/shell_quote"
+
 module VagrantPlugins
   module GuestLinux
     module Cap
       class InsertPublicKey
         def self.insert_public_key(machine, contents)
+          contents = Vagrant::Util::ShellQuote.escape(contents, "'")
+          contents = contents.gsub("\n", "\\n")
+
           machine.communicate.tap do |comm|
-            comm.execute("echo #{contents} > /tmp/key.pub")
             comm.execute("mkdir -p ~/.ssh")
             comm.execute("chmod 0700 ~/.ssh")
-            comm.execute("cat /tmp/key.pub >> ~/.ssh/authorized_keys")
+            comm.execute("printf '#{contents}' >> ~/.ssh/authorized_keys")
             comm.execute("chmod 0600 ~/.ssh/authorized_keys")
           end
         end