Add ability to include subkeys when finding by fingerprint

app/models/gpg_key.rb

@@ -40,6 +40,17 @@ class GpgKey < ActiveRecord::Base
   after_commit :update_invalid_gpg_signatures, on: :create
   after_create :generate_subkeys
 
+  def self.find_with_subkeys(fingerprint)
+    keys_table = arel_table
+    subkeys_table = GpgKeySubkey.arel_table
+
+    condition = keys_table[:primary_keyid].eq(fingerprint).or(
+      subkeys_table[:keyid].eq(fingerprint)
+    )
+
+    joins(:subkeys).where(condition).first
+  end
+
   def primary_keyid
     super&.upcase
   end

lib/gitlab/gpg/commit.rb

@@ -43,7 +43,7 @@ module Gitlab
           # key belonging to the keyid.
           # This way we can add the key to the temporary keychain and extract
           # the proper signature.
-          gpg_key = GpgKey.find_by(primary_keyid: verified_signature.fingerprint)
+          gpg_key = GpgKey.find_with_subkeys(verified_signature.fingerprint)
 
           if gpg_key
             Gitlab::Gpg::CurrentKeyChain.add(gpg_key.key)