Ensure users can't create environments with leading or trailing slashes (Fixes #39885)

changelogs/unreleased/issue-39885.yml

+---
+title: 'Ensure users cannot create environments with leading or trailing slashes (Fixes #39885)'
+merge_request: !15273
+author: Dylan Griffith
+type: fixed

lib/gitlab/regex.rb

@@ -40,12 +40,16 @@ module Gitlab
       'a-zA-Z0-9_/\\$\\{\\}\\. \\-'
     end
 
+    def environment_name_regex_chars_without_slash
+      'a-zA-Z0-9_\\$\\{\\}\\. -'
+    end
+
     def environment_name_regex
-      @environment_name_regex ||= /\A[#{environment_name_regex_chars}]+\z/.freeze
+      @environment_name_regex ||= /\A[#{environment_name_regex_chars_without_slash}]([#{environment_name_regex_chars}]*[#{environment_name_regex_chars_without_slash}])?\z/.freeze
     end
 
     def environment_name_regex_message
-      "can contain only letters, digits, '-', '_', '/', '$', '{', '}', '.', and spaces"
+      "can contain only letters, digits, '-', '_', '/', '$', '{', '}', '.', and spaces, but it cannot start or end with '/'"
     end
 
     def kubernetes_namespace_regex

spec/lib/gitlab/regex_spec.rb

@@ -18,6 +18,7 @@ describe Gitlab::Regex do
     subject { described_class.environment_name_regex }
 
     it { is_expected.to match('foo') }
+    it { is_expected.to match('a') }
     it { is_expected.to match('foo-1') }
     it { is_expected.to match('FOO') }
     it { is_expected.to match('foo/1') }
@@ -25,6 +26,10 @@ describe Gitlab::Regex do
     it { is_expected.not_to match('9&foo') }
     it { is_expected.not_to match('foo-^') }
     it { is_expected.not_to match('!!()()') }
+    it { is_expected.not_to match('/foo') }
+    it { is_expected.not_to match('foo/') }
+    it { is_expected.not_to match('/foo/') }
+    it { is_expected.not_to match('/') }
   end
 
   describe '.environment_slug_regex' do