Fix use-after-free and double-free in RemoveFilament

[tritsystem]

Summary

RemoveFilament() in libpromises/dbm_test_api.c frees filament (and destroys filament->items) when StringSetSize(filament->items) == 0, but had no return after that branch — every other early-exit branch in this function does.

Without it, execution falls through unconditionally to:

bool success = OpenDB(&db, filament->db_id);

a use-after-free read of the just-freed filament. At the end of the function, StringSetDestroy(filament->items) and free(filament) run again unconditionally on that same path — a double-free of both filament and its items set.

Fix is a single return; added right after the free(filament);, matching the pattern every other early-exit branch in this same function already follows.

Test plan

• Verified with a standalone AddressSanitizer repro: RemoveFilament()'s real body extracted verbatim, with minimal stub types matching the actual DBFilament/StringSet shapes. Built with -fsanitize=address, called with a filament whose items set has size 0 (the branch that frees filament).
  • Without the fix: ASan reports a genuine heap-use-after-free at the OpenDB(&db, filament->db_id) line.
  • With the fix: clean exit, no ASan report.
• Could not build/run the full libpromises test suite in this environment (no configured build toolchain for this repo here); the fix is a minimal, one-line change matching the existing early-return convention used throughout the same function, so the risk of the change itself is low.
• codespell was run against the modified file; it flagged one pre-existing, unrelated typo elsewhere in the file (fillament at line 662), not touched by this change.

🤖 Generated with Claude Code

Together with cfengine/buildscripts#2509

[larsewi]

Thanks for the contribution @tritsystem

@cf-bottom Jenkins please :)

[cf-bottom]

Alright, I triggered a build:

Jenkins: https://ci.cfengine.com/job/pr-pipeline/14664/

Packages: http://buildcache.cfengine.com/packages/testing-pr/jenkins-pr-pipeline-14664/

[tritsystem]

Thanks for the quick response, @larsewi — appreciate you triggering the build. Let me know if there's anything else you'd like me to check or adjust.

[tritsystem]

@larsewi a status check on the Jenkins run you triggered (build 14664). On the current head, the GitHub Actions checks all pass, including asan_unit_tests, valgrind_check, unit_tests and acceptance_tests. In Jenkins, ci/FR-tests, ci/bootstrap-tests and ci/sequential-tests report failure, and many of the ci/testing_pr/PACKAGES_* contexts have been pending since the 17th.

I cannot open ci.cfengine.com (it returns 403 for me), so I don't know whether those failures come from RemoveFilament or from the build environment. If you can see the logs, could you tell me which tests failed and whether they touch this change? I will fix anything that does.

[larsewi]

@tritsystem we had to abort the previous run due to CI maintenance. @cf-bottom can you trigger another run in Jenkins please?

[cf-bottom]

Sure, I triggered a build:

Jenkins: https://ci.cfengine.com/job/pr-pipeline/14691/

Packages: http://buildcache.cfengine.com/packages/testing-pr/jenkins-pr-pipeline-14691/