Fix apt_key tempfile race condition

The Ruby Tempfile class has a finalizer that removes the file when the
GC runs.  It's not predictible when the GC will run, so you have to
ensure that the instance of the class stays in scope for as long as you
need it.

Unfortunately the tempfile method is returning just the filename of the
temporary file, which means it goes out of scope when that method
returns.  This allows the GC to reap it at any time after return.

In both CI and production environments we've seen this race fail,
causing apt-key add to fail a small (2-3%) amount of the time.

This changes the tempfile and source_to_file methods to return the
underlying Tempfile object, pushing it up into the caller's scope.  Both
of the callers immediately use the object to get its filename and then
open the file, eliminating the race.

Tested this by adding 'GC.start; sleep(1)' immediately before the
command is run, to give the GC plenty of time to remove the tempfile if
it was going to.

diff --git a/lib/puppet/provider/apt_key/apt_key.rb b/lib/puppet/provider/apt_key/apt_key.rb
index f8c7d1976afb78b867e93148ca3e759f867bdb18..a6d68b1732dd4c0be547c0ce3bfe604aeae5ed04 100644 (file)
--- a/lib/puppet/provider/apt_key/apt_key.rb
+++ b/lib/puppet/provider/apt_key/apt_key.rb
@@ -118,7 +118,13 @@ Puppet::Type.type(:apt_key).provide(:apt_key) do
     parsedValue = URI::parse(value)
     if parsedValue.scheme.nil?
       fail("The file #{value} does not exist") unless File.exists?(value)
-      value
+      # Because the tempfile method has to return a live object to prevent GC
+      # of the underlying file from occuring too early, we also have to return
+      # a file object here.  The caller can still call the #path method on the
+      # closed file handle to get the path.
+      f = File.open(value, 'r')
+      f.close
+      f
     else
       begin
         key = parsedValue.read
@@ -132,6 +138,9 @@ Puppet::Type.type(:apt_key).provide(:apt_key) do
     end
   end
 
+  # The tempfile method needs to return the tempfile object to the caller, so
+  # that it doesn't get deleted by the GC immediately after it returns.  We
+  # want the caller to control when it goes out of scope.
   def tempfile(content)
     file = Tempfile.new('apt_key')
     file.write content
@@ -155,7 +164,7 @@ Puppet::Type.type(:apt_key).provide(:apt_key) do
         warning('/usr/bin/gpg cannot be found for verification of the id.')
       end
     end
-    file.path
+    file
   end
 
   def exists?
@@ -173,9 +182,11 @@ Puppet::Type.type(:apt_key).provide(:apt_key) do
       end
       command.push('--recv-keys', resource[:id])
     elsif resource[:content]
-      command.push('add', tempfile(resource[:content]))
+      key_file = tempfile(resource[:content])
+      command.push('add', key_file.path)
     elsif resource[:source]
-      command.push('add', source_to_file(resource[:source]))
+      key_file = source_to_file(resource[:source])
+      command.push('add', key_file.path)
     # In case we really screwed up, better safe than sorry.
     else
       fail("an unexpected condition occurred while trying to add the key: #{resource[:id]}")