Merge branch 'git-auth-rack-attack-improvements' into 'master'

Reduce Rack Attack false positives causing 403 errors during HTTP authentication

### What does this MR do?

This MR reduces false positives causing `403 Forbidden` messages after HTTP authentication.

A Git client may attempt to access a repository without a password. If it receives a 401 error, the client often will try again, this time supplying a password. The problem is that `grack_auth.rb` considers a blank password an authentication failure and increases a Redis counter each time this happens. With enough requests, an IP can be banned temporarily even though previous attempts may have been successful. This leads users to see `403 Forbidden` errors until the ban times out (default: 1 hour).

To reduce the chance of a false positive, this MR resets the counter upon a successful authentication from an IP.

In addition, this MR logs when a user has been banned and introduces the ability to disable Rack Attack via a config variable.

### Are there points in the code the reviewer needs to double check?

rack-attack v4.2.0 doesn't support the ability to clear counters out of the box, so `rack_attack_helpers.rb` includes a number of monkey patches to make it work. It looks like this functionality may be added in v4.3.0. I've also sent pull requests to rack-attack to add the functionality necessary to delete a key.

Each time an authentication is successful, the Redis counter for that IP is cleared. I deemed it better to clear the counter than to allow for blank passwords, since the latter seems like a security risk.

### Why was this MR needed?

It was quite difficult to figure out why users were seeing `403 Forbidden`, which is why the log message was added. Users were getting a lot of false positives when accessing repositories with HTTPS. Including the username in the HTTPS URL (e.g. `https://username@mydomain.com/account/repo.git`) caused authentication failures because while the git client provided the username, it left the password blank, leading to an authentication failure.

### What are the relevant issue numbers / [Feature requests](http://feedback.gitlab.com/)?

See Issue #1171

https://github.com/kickstarter/rack-attack/issues/113

See merge request !392

2 files changed, 86 insertions, 1 deletions

diff --git a/spec/lib/gitlab/backend/grack_auth_spec.rb b/spec/lib/gitlab/backend/grack_auth_spec.rb
index 768312f0028..d0aad54f677 100644
--- a/spec/lib/gitlab/backend/grack_auth_spec.rb
+++ b/spec/lib/gitlab/backend/grack_auth_spec.rb
@@ -6,7 +6,7 @@ describe Grack::Auth do
 
   let(:app)   { lambda { |env| [200, {}, "Success!"] } }
   let!(:auth) { Grack::Auth.new(app) }
-  let(:env) { 
+  let(:env) {
     {
       "rack.input" => "",
       "REQUEST_METHOD" => "GET",
@@ -85,6 +85,17 @@ describe Grack::Auth do
             it "responds with status 401" do
               expect(status).to eq(401)
             end
+
+            context "when the user is IP banned" do
+              before do
+                expect(Rack::Attack::Allow2Ban).to receive(:filter).and_return(true)
+                allow_any_instance_of(Rack::Request).to receive(:ip).and_return('1.2.3.4')
+              end
+
+              it "responds with status 401" do
+                expect(status).to eq(401)
+              end
+            end
           end
 
           context "when authentication succeeds" do
@@ -109,10 +120,49 @@ describe Grack::Auth do
               end
 
               context "when the user isn't blocked" do
+                before do
+                 expect(Rack::Attack::Allow2Ban).to receive(:reset)
+                end
+
                 it "responds with status 200" do
                   expect(status).to eq(200)
                 end
               end
+
+              context "when blank password attempts follow a valid login" do
+                let(:options) { Gitlab.config.rack_attack.git_basic_auth }
+                let(:maxretry) { options[:maxretry] - 1 }
+                let(:ip) { '1.2.3.4' }
+
+                before do
+                  allow_any_instance_of(Rack::Request).to receive(:ip).and_return(ip)
+                  Rack::Attack::Allow2Ban.reset(ip, options)
+                end
+
+                after do
+                  Rack::Attack::Allow2Ban.reset(ip, options)
+                end
+
+                def attempt_login(include_password)
+                  password = include_password ? user.password : ""
+                  env["HTTP_AUTHORIZATION"] = ActionController::HttpAuthentication::Basic.encode_credentials(user.username, password)
+                  Grack::Auth.new(app)
+                  auth.call(env).first
+                end
+
+                it "repeated attempts followed by successful attempt" do
+                  for n in 0..maxretry do
+                    expect(attempt_login(false)).to eq(401)
+                  end
+
+                  expect(attempt_login(true)).to eq(200)
+                  expect(Rack::Attack::Allow2Ban.send(:banned?, ip)).to eq(nil)
+
+                  for n in 0..maxretry do
+                    expect(attempt_login(false)).to eq(401)
+                  end
+                end
+              end
             end
 
             context "when the user doesn't have access to the project" do
diff --git a/spec/lib/gitlab/backend/rack_attack_helpers_spec.rb b/spec/lib/gitlab/backend/rack_attack_helpers_spec.rb
new file mode 100644
index 00000000000..2ac496fd669
--- /dev/null
+++ b/spec/lib/gitlab/backend/rack_attack_helpers_spec.rb
@@ -0,0 +1,35 @@
+require "spec_helper"
+
+describe 'RackAttackHelpers' do
+  describe 'reset' do
+    let(:discriminator) { 'test-key'}
+    let(:maxretry) { 5 }
+    let(:period) { 1.minute }
+    let(:options) { { findtime: period, bantime: 60, maxretry: maxretry } }
+
+    def do_filter
+      for i in 1..maxretry - 1 do
+        status = Rack::Attack::Allow2Ban.filter(discriminator, options) { true }
+        expect(status).to eq(false)
+      end
+    end
+
+    def do_reset
+      Rack::Attack::Allow2Ban.reset(discriminator, options)
+    end
+
+    before do
+      do_reset
+    end
+
+    after do
+      do_reset
+    end
+
+    it 'user is not banned after n - 1 retries' do
+      do_filter
+      do_reset
+      do_filter
+    end
+  end
+end