Early Detection of Configuration Errors to Reduce Failure Damage

Paper: Early Detection of Configuration Errors to Reduce Failure Damage

• Defines Latent Configuration (LC) Errors which are caused due to insufficient validations on the configuration, later until the configuration is actually used
  • There might be a large time between loading this configuration, generally in the initialization phase, to actually using it (thus latent).
• When such configurations are related to reachability, availability or serviceability, LC errors can lead to downtime.
• Two main issues with such configs
  • The values are not checked at all. eg: check if file exists
  • The values are not checked according to the usage. eg: value is used in open(config_value, WRITE)
• Paper implements a checker based on the static analysis and instrumentation
• Static analysis:
  • Taint analysis to go from the configuration to the actual usage along the data flow path. Control flow is ignored in most cases to avoid over tainting
  • Along with these instruction, the dependent values are also extracted. Eg: open(config_value, permission) <- here permission is dependent value
  • Any value that cannot be determined are skipped. Eg: a dependent value read from network
• Instrumentation:
  • Code is generated to perform same check as that in the actual usage, but in a “sandboxed” manner
  • Here any side effect on the program is avoided. Eg: a local copy of global value is used instead of the actual global value.
  • Utilities are written to check the actions performed by some library and system calls.
• This generated code is run right after the initialization phase of the program
  • Developer need to annotate two things
    • The interface of how configuration values are fetched
    • The place where program moves from initialization state to execution
• TOCTOU issues are avoided by adding support to run these checkers regularly in a thread