[java] Cdxgen Fails To Generate An Sbom While A Commercial Tool Does

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[java] cdxgen fails to generate an SBOM while a commercial tool does

Introduction

In the world of software development, generating a Software Bill of Materials (SBOM) is a crucial step in ensuring the security and integrity of a project. However, when it comes to using open-source tools like cdxgen, some users may encounter issues that prevent them from generating a complete SBOM. In this article, we will explore a case where cdxgen fails to generate an SBOM for a repository, while a commercial tool works and produces results.

The Repo in Question

The repository in question is Apache Flex BlazeDS, a popular open-source project that provides a set of tools for building rich internet applications. The project has a complex dependency tree, with multiple sub-projects and dependencies. The issue with the repository is that the developers have forgotten to update the version number correctly in all places, so pom.xml files are referring to a non-existent version (4.8.0-SNAPSHOT) instead of the correct version (4.9.0-SNAPSHOT).

Investigation

When running cdxgen with default settings (recurse=true), we encounter a number of errors like the following:

[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]
[ERROR]   The project org.apache.flex.blazeds:flex-messaging-opt-tomcat-6:4.8.0-SNAPSHOT (/Volumes/Work/sandbox/flex-blazeds-master/opt/tomcat/tomcat-6/pom.xml) has 1 error
[ERROR]     Non-resolvable parent POM for org.apache.flex.blazeds:flex-messaging-opt-tomcat-6:4.8.0-SNAPSHOT: The following artifacts could not be resolved: org.apache.flex.blazeds:flex-messagi
ng-opt-tomcat:pom:4.8.0-SNAPSHOT (absent): Could not find artifact org.apache.flex.blazeds:flex-messaging-opt-tomcat:pom:4.8.0-SNAPSHOT and 'parent.relativePath' points at wrong local POM @ lin
e 23, column 13 -> [Help 2]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildingException
[ERROR] [Help 2] http://cwiki.apache.org/confluence/display/MAVEN/UnresolvableModelException
 Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8 -Djna.library.path=/Users/prabhu/miniconda3/envs/chenpy/lib

The above build errors could be due to:

  1. Check if the pom.xml contains valid settings for parent and modules. Some projects can be built only from a specific directory.
  2. Private dependencies cannot be downloaded: Check if any additional arguments must be passed to maven and set them via MVN_ARGS environment variable.
  3. Check if all required environment variables including any maven profile arguments are passed correctly to this tool.

Fixing the Issues

After fixing the issues with the version numbers, cdxgen generates a complete SBOM with 128 components and 148 dependencies. However, this is still only half of what the commercial tool reports. So, does that mean cdxgen is bad?

Introducing Guess BOM

What the commercial tool appears to do is commonly referred to as "guessing" (or using a custom solver). When a build fails, instead of displaying Maven errors (which marketing wouldn't approve), the tool simply parses the dependencies attributes from the pom.xml files, downloads the jars, and continues parsing until it gathers several levels of information. Unfortunately, such naive algorithms are often incompatible with the package manager's dependency solver algorithms (DFS, BF, Skipper) and might even fail to account for any custom overrides, settings, or external factors (e.g., weather, time :)).

Is this wrong?

Not necessarily. Every SBOM tool, including cdxgen, makes up some information as it goes. However, users have the right to know the technique, the tool's confidence level, and the associated evidence for transparency and fair assessment. The particular commercial tool in question doesn't include evidence or confidence, making it impossible for end users to evaluate its precision. Additionally, it reinforces a misleading narrative: open-source is inferior, while commercial is superior.

What should end users do?

Learn terminologies such as lifecycles and aggregate.

  • To generate a pre-build SBOM, lock files must be available. Most package managers and repositories might not include one.
  • To generate a build SBOM, a buildable environment with the correct build tools installed is required. If the versions of these tools do not align, the SBOM may be imprecise (referred to as the reproducibility problem).
  • To generate a post-build SBOM, the artifacts must be built and generated correctly, retaining all necessary debug and library information (e.g., unshaded and debug builds).

More importantly, stop expecting magic from sbom tools. Generating xBOMs is a complex process that requires active user participation. You should understand both the project and the capabilities of the tools.

Steps to reproduce

git clone https://github.com/apache/flex-blazeds.git
cd flex-blazeds
sdk use java 8.0.442-tem
mvn compile

# sbom generated with errors
cdxgen -t java -o bom.json $(pwd)

git apply version-update.patch
# sbom generated without errors
cdxgen -t java -o bom.json $(pwd) -p

Attachments

In conclusion, generating an SBOM is a complex process that requires active user participation. While commercial tools may appear to be more effective, they often rely on naive algorithms that may not be compatible with the package manager's dependency solver algorithms. By understanding the terminologies and capabilities of the tools, end users can generate accurate SBOMs and make informed decisions about their projects.
[java] cdxgen fails to generate an SBOM while a commercial tool does - Q&A

Q: What is the main issue with cdxgen failing to generate an SBOM?

A: The main issue is that cdxgen relies on the build process to generate the SBOM, but if the build process fails, cdxgen will also fail to generate the SBOM.

Q: Why does the commercial tool appear to be more effective in generating an SBOM?

A: The commercial tool appears to be more effective because it uses a custom solver that can parse the dependencies attributes from the pom.xml files and download the jars, even if the build process fails.

Q: Is the commercial tool's approach to generating an SBOM correct?

A: Not necessarily. While the commercial tool's approach may appear to be effective, it relies on naive algorithms that may not be compatible with the package manager's dependency solver algorithms. This can lead to inaccuracies in the generated SBOM.

Q: What are the limitations of cdxgen in generating an SBOM?

A: The limitations of cdxgen include:

  • It relies on the build process to generate the SBOM, which can fail if the build process fails.
  • It may not be able to handle complex dependency trees.
  • It may not be able to account for custom overrides, settings, or external factors.

Q: What are the benefits of using cdxgen to generate an SBOM?

A: The benefits of using cdxgen include:

  • It is an open-source tool, which means it is free to use and modify.
  • It is designed to work with Maven, which is a popular build tool.
  • It can generate a SBOM in a variety of formats, including JSON and XML.

Q: How can I troubleshoot issues with cdxgen generating an SBOM?

A: To troubleshoot issues with cdxgen generating an SBOM, you can try the following:

  • Check the build process to ensure that it is successful.
  • Check the pom.xml files to ensure that they are correct and up-to-date.
  • Check the cdxgen configuration to ensure that it is correct and up-to-date.
  • Try running cdxgen with the -v flag to enable verbose mode and see if it provides any additional information.

Q: Can I use cdxgen to generate an SBOM for a project that uses a different build tool?

A: Yes, you can use cdxgen to generate an SBOM for a project that uses a different build tool, but you may need to modify the cdxgen configuration to accommodate the different build tool.

Q: How can I compare the SBOM generated by cdxgen with the SBOM generated by the commercial tool?

A: To compare the SBOM generated by cdxgen with the SBOM generated by the commercial tool, you can try the following:

  • Use a tool like diff to compare the two SBOMs.
  • Use a tool like jsonlint to validate the SBOMs and ensure that they are correct.
  • Use a tool like xmlstarlet to compare the SBOMs and ensure that they are correct.

Q: Can I use cdxgen to generate an SBOM for a project that has a complex dependency tree?

A: Yes, you can use cdxgen to generate an SBOM for a project that has a complex dependency tree, but you may need to modify the cdxgen configuration to accommodate the complex dependency tree.

Q: How can I customize the SBOM generated by cdxgen?

A: To customize the SBOM generated by cdxgen, you can try the following:

  • Use a tool like json to modify the SBOM and add or remove components.
  • Use a tool like xml to modify the SBOM and add or remove components.
  • Use a tool like xslt to transform the SBOM and add or remove components.

Q: Can I use cdxgen to generate an SBOM for a project that uses a different programming language?

A: Yes, you can use cdxgen to generate an SBOM for a project that uses a different programming language, but you may need to modify the cdxgen configuration to accommodate the different programming language.