404 when requesting build trace

Summary

When trying to view the running build output of a public project (gitlab-ce) all ajax requests to get the updated trace result in a 404. The trace shouldn't 404 if I can already see part of the logs.

Steps to reproduce

• Navigate to gitlab-ce as a user who's not part of the org or as an unauthenticated guest
• Find a running build and click on it (https://gitlab.com/gitlab-org/gitlab-ce/builds?scope=running)
• Wait for the Something went wrong on our end error

Expected behavior

Should get build trace updates and autoscroll

Actual behavior

Trace requests 404 and no new build output is appended to the screen

Relevant logs and/or screenshots

Video: https://cl.ly/1t3s2C3c2R1y

Output of checks

NA - gitlab.com

Results of GitLab application Check

NA - gitlab.com

Results of GitLab environment info

NA - gitlab.com

Possible fixes

Could be related to authorize_read_build! in https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/controllers/projects/builds_controller.rb#L3