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disk_cache.md

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Disk Cache

Component Focus: Chromium's disk cache (net/disk_cache), specifically the backend implementation in net/disk_cache/blockfile/backend_impl.cc.

Potential Logic Flaws:

  • Cache Poisoning: Vulnerabilities that allow an attacker to inject malicious content into the disk cache. The SyncCreateEntry and SyncOnExternalCacheHit functions in backend_impl.cc are potential attack vectors.
  • Information Leakage: The disk cache could potentially leak sensitive information about cached resources. Improper error handling in the backend could contribute to information leakage.
  • Cache Invalidation Issues: Problems with cache invalidation could lead to stale or incorrect data being served.
  • Data Integrity: Corruption or tampering of cached data could have security implications. The backend_impl.cc file contains functions crucial for maintaining data integrity, such as CheckIndex, CheckAllEntries, and CheckEntry.
  • Access Control: Unauthorized access or modification of cached data could lead to vulnerabilities. The initialization and cleanup processes in backend_impl.cc should be reviewed for proper access control.
  • Denial of Service: Resource exhaustion or excessive memory usage in the backend could lead to denial-of-service vulnerabilities.
  • Race Conditions: Concurrent access to the disk cache could lead to race conditions. Thread safety should be ensured in functions like SyncOpenEntry, SyncCreateEntry, and UpdateRank.

Further Analysis and Potential Issues:

  • Review Disk Cache Implementation: Thoroughly analyze the disk cache implementation in net/disk_cache for potential vulnerabilities. Pay close attention to how cached resources are stored, retrieved, and invalidated. Focus on the backend_impl.cc file and its key functions, including Init, CleanupCache, SyncCreateEntry, SyncOpenEntry, SyncDoomEntry, and others.
  • Investigate Cache Management: Examine how the disk cache is managed, looking for potential vulnerabilities related to cache eviction policies, size limits, and handling of corrupted cache entries. The interaction between backend_impl.cc and the Rankings class is crucial for cache management.
  • Analyze Security Considerations: Review the security considerations of the disk cache, such as access controls and protection against unauthorized modification. The Init and CleanupCache functions in backend_impl.cc should be reviewed for proper access control mechanisms.
  • Error Handling and Input Validation: Robust error handling and input validation are crucial in backend_impl.cc to prevent vulnerabilities related to cache poisoning, data integrity, and denial of service.
  • Synchronization and Thread Safety: The backend_impl.cc code should be carefully reviewed for thread safety and proper synchronization to prevent race conditions during concurrent access to the disk cache.

Areas Requiring Further Investigation:

  • Interaction with Other Network Components: Investigate how the disk cache interacts with other network components, such as the HTTP cache and the network stack, looking for potential vulnerabilities.
  • Impact of Secure Contexts: Determine how secure contexts affect the disk cache and whether they mitigate any potential vulnerabilities. Consider the implications of caching resources from different origins.
  • Dirty Entry Handling: The handling of dirty entries in backend_impl.cc needs further analysis to ensure data integrity and prevent potential vulnerabilities.
  • Cache Eviction and Rankings: The interaction between the eviction mechanism and the Rankings class in backend_impl.cc requires further analysis to ensure secure and efficient cache management.
  • Resource Management and DoS: The disk space allocation and deallocation functions in backend_impl.cc should be thoroughly reviewed for potential denial-of-service vulnerabilities related to resource exhaustion.

Secure Contexts and Disk Cache:

Secure contexts are important for protecting sensitive information, and the disk cache should be designed to handle resources from secure contexts appropriately.

Privacy Implications:

The disk cache could potentially store sensitive information about browsing history, so it's important to address any potential privacy implications.

Additional Notes:

Files reviewed: net/disk_cache/blockfile/backend_impl.cc.