Improper Handling of Exceptional Conditions

Summary

SpiceDB is a graph database purpose-built for storing and evaluating access control data. Use of a relation of the form: 'relation folder: folder | folder#parent' with an arrow such as 'folder->view' can cause LookupSubjects to only return the subjects found under subjects for either 'folder' or 'folder#parent'. This bug only manifests if the same subject type is used multiple types in a relation, relationships exist for both subject types and an arrow is used over the relation. Any user making a negative authorization decision based on the results of a LookupSubjects request is affected. As a workaround, avoid using LookupSubjects for negative authorization decisions and/or avoid using the broken schema. This issue affects the github.com/authzed/spicedb versions prior to 1.30.1.