Troubleshooting Failed Builds: Alternate Data Streams Block DLLs in Windows
In a recent situation, a unit test step in a CI/CD pipeline started failing on one build server but not on others. After investigation, it was concluded that the issue was due to security settings. This article will discuss the concept of Alternate Data Streams (ADS) in Windows and how it can block DLLs, leading to failed builds.
What are Alternate Data Streams?
Alternate Data Streams (ADS) are a feature of the NTFS file system used by Windows. They allow for the storage of metadata or additional data alongside a file, separated by a colon. For example, a file named "example.txt" could have an alternate data stream named "comments.txt". This feature is not commonly used and can often lead to unexpected behavior, especially in a CI/CD environment.
How can Alternate Data Streams Block DLLs?
In the case of a failed build, it is possible that an alternate data stream was added to a DLL file, preventing it from being loaded. This can occur due to malware or other malicious activity, as well as accidental actions. The build server may have different security settings than other servers, leading to the failure on that specific machine.
Investigating Failed Builds
When encountering a failed build due to a DLL load failure, it is often necessary to investigate the file system to determine if an alternate data stream is present. This can be done using the Windows PowerShell command "Get-ItemStream" or the Sysinternals Streams utility. These tools can display any alternate data streams associated with a file, allowing for further investigation.
Resolving the Issue
To resolve the issue, the alternate data stream must be removed from the affected DLL file. This can be done using the "Clear-ItemStream" PowerShell command or the Sysinternals Streams utility. Once the alternate data stream is removed, the DLL should be able to load properly, and the build should succeed.
Preventing Future Issues
To prevent future issues with alternate data streams and failed builds, it is recommended to implement strict security settings on build servers. This can include restricting access to sensitive areas of the file system, monitoring for suspicious activity, and regularly scanning for malware. Additionally, it is important to keep all software up to date and to follow best practices for CI/CD pipelines.
- Alternate Data Streams (ADS) are a feature of the NTFS file system used by Windows.
- ADS can allow for the storage of metadata or additional data alongside a file, separated by a colon.
- ADS can block DLLs from loading, leading to failed builds.
- Investigating failed builds due to DLL load failures may require checking for alternate data streams using PowerShell or the Sysinternals Streams utility.
- Resolving the issue involves removing the alternate data stream from the affected DLL file.
- Preventing future issues requires implementing strict security settings on build servers and following best practices for CI/CD pipelines.