Fix Server Side Request Forgery mitigation bypass

When we can't resolve the hostname or it is invalid, we shouldn't
even perform the request. This fix also fixes the problem the
SSRF rebinding attack.

We can't stub feature flags outside example blocks. Nevertheless,
there are some actions that calls the UrlBlocker, that are performed
outside example blocks, ie: `set` instruction.

That's why we have to use some signalign mechanism outside the scope
of the specs.

1 files changed, 13 insertions, 3 deletions

diff --git a/lib/gitlab/url_blocker.rb b/lib/gitlab/url_blocker.rb
index 9a8df719827..d9070ce5a09 100644
--- a/lib/gitlab/url_blocker.rb
+++ b/lib/gitlab/url_blocker.rb
@@ -20,6 +20,7 @@ module Gitlab
       # Returns an array with [<uri>, <original-hostname>].
       # rubocop:disable Metrics/CyclomaticComplexity
       # rubocop:disable Metrics/ParameterLists
+      # rubocop:disable Metrics/PerceivedComplexity
       def validate!(
         url,
         ports: [],
@@ -32,6 +33,7 @@ module Gitlab
         dns_rebind_protection: true)
         # rubocop:enable Metrics/CyclomaticComplexity
         # rubocop:enable Metrics/ParameterLists
+        # rubocop:enable Metrics/PerceivedComplexity
 
         return [nil, nil] if url.nil?
 
@@ -56,7 +58,15 @@ module Gitlab
             addr.ipv6_v4mapped? ? addr.ipv6_to_ipv4 : addr
           end
         rescue SocketError
-          return [uri, nil]
+          # In the test suite we use a lot of mocked urls that are either invalid or
+          # don't exist. In order to avoid modifying a ton of tests and factories
+          # we allow invalid urls unless the environment variable RSPEC_ALLOW_INVALID_URLS
+          # is not true
+          return [uri, nil] if Rails.env.test? && ENV['RSPEC_ALLOW_INVALID_URLS'] == 'true'
+
+          # If the addr can't be resolved or the url is invalid (i.e http://1.1.1.1.1)
+          # we block the url
+          raise BlockedUrlError, "Host cannot be resolved or invalid"
         end
 
         protected_uri_with_hostname = enforce_uri_hostname(addrs_info, uri, hostname, dns_rebind_protection)
@@ -92,9 +102,9 @@ module Gitlab
       # we'll be making the request to the IP address, instead of using the hostname.
       def enforce_uri_hostname(addrs_info, uri, hostname, dns_rebind_protection)
         address = addrs_info.first
-        ip_address = address&.ip_address
+        ip_address = address.ip_address
 
-        return [uri, nil] unless dns_rebind_protection && ip_address && ip_address != hostname
+        return [uri, nil] unless dns_rebind_protection && ip_address != hostname
 
         uri = uri.dup
         uri.hostname = ip_address