Container scanner image 6.6.0 is failing to get relative path

Summary

One of our customers (internal) reported that container scanning is no longer working. The main error is:

[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning]  >  different prefix: "" and "/builds/SNIPPED/SNIPPED"
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning]  >  /usr/local/lib/ruby/3.1.0/pathname.rb:528:in `relative_path_from'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:112:in `diff_to_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:104:in `create_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:79:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `map'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/converter.rb:40:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/plugin/container_scan.rb:10:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/scan.rb:26:in `scan_image'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:16:in `block in scan'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `map'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `scan'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/command.rb:28:in `run'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/bundle/gems/thor-1.3.0/lib/thor.rb:527:in `dispatch'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/base.rb:584:in `start'
/usr/local/bundle/gems/gcs-6.6.0/exe/gtcs:14:in `<top (required)>'
/usr/local/bundle/bin/gtcs:25:in `load'
/usr/local/bundle/bin/gtcs:25:in `<main>'

From the stacktrace, it appears this might have been introduced here: gitlab-org/security-products/analyzers/container-scanning!2944 (merged)

When we set the image back to use 6.5.1, scan succeeds.

Steps to reproduce

See thread gitlab-org/security-products/analyzers/container-scanning!2964 (62d6a504, comment 1710640622)

Example Project

What is the current bug behavior?

Scan fails with an error.

What is the expected correct behavior?

Scan succeeds.

Relevant logs and/or screenshots

[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning]  >  different prefix: "" and "/builds/SNIPPED/SNIPPED"
[ERROR] [2023-12-21 07:43:05 +0000] [container-scanning]  >  /usr/local/lib/ruby/3.1.0/pathname.rb:528:in `relative_path_from'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:112:in `diff_to_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:104:in `create_patch'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/remediation.rb:79:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `map'
/usr/local/bundle/gems/gcs-6.6.0/ee/lib/gcs/remediations/collection.rb:19:in `to_hash'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/converter.rb:40:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/plugin/container_scan.rb:10:in `convert'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/scan.rb:26:in `scan_image'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:16:in `block in scan'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `map'
/usr/local/bundle/gems/gcs-6.6.0/lib/gcs/cli.rb:15:in `scan'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/command.rb:28:in `run'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/bundle/gems/thor-1.3.0/lib/thor.rb:527:in `dispatch'
/usr/local/bundle/gems/thor-1.3.0/lib/thor/base.rb:584:in `start'
/usr/local/bundle/gems/gcs-6.6.0/exe/gtcs:14:in `<top (required)>'
/usr/local/bundle/bin/gtcs:25:in `load'
/usr/local/bundle/bin/gtcs:25:in `<main>'

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes