fix: use bounded formatting for Vorbis metadata names

[orbisai0security]

Summary

Replace sprintf() with snprintf() when constructing Vorbis metadata attribute names.

The destination buffer meta->name is dynamically allocated based on the input key length plus the fixed format overhead (strlen(str) + 18), so the current code is already sized correctly. However, using snprintf() is a defensive hardening improvement that:

• Makes the formatting operation explicitly bounded
• Protects against potential future changes to allocation logic
• Follows secure coding best practices

Changes

• src/modules/vorbis/producer_vorbis.c - Replace sprintf with snprintf
• src/tests/test_vorbis/test_vorbis.cpp - Add QTest-based test following MLT conventions

Verification

• Build passes
• Test follows QTest framework (per maintainer feedback)
• Test registered in CMakeLists.txt

Technical Details

Before:

meta->name = malloc(strlen(str) + 18);
sprintf(meta->name, "meta.attr.%s.markup", str);

After:

meta->name = malloc(strlen(str) + 18);
snprintf(meta->name, strlen(str) + 18, "meta.attr.%s.markup", str);

The format string overhead is 18 bytes:

• "meta.attr." = 10 bytes
• ".markup" = 7 bytes
• null terminator = 1 byte

This change makes the code more robust and follows defense-in-depth principles, even though the allocation is already appropriately sized.

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Automated security fix by OrbisAI Security

[ddennedy]

Thank you for the report and contribution. The included test does not conform to this repository's choice of QTest for unit tests. See src/tests/test_mod_avformat/ for an example. The project also uses CMake; so a new test directory should be added to src/tests/CMakeLists.txt.

[orbisai0security]

Thanks for the review and for pointing me to the project's test conventions. I agree the current test should not introduce a different unit-test framework.

I've revised this PR to:

1. Migrate the test to QTest framework, following the pattern in src/tests/test_mod_avformat/
2. Register the test in src/tests/CMakeLists.txt under the MOD_VORBIS conditional
3. Update the PR description to accurately reflect that meta->name is dynamically allocated with malloc(strlen(str) + 18)
4. Reframe this as defensive hardening rather than fixing a critical overflow

You're absolutely right that the original wording about "fixed-size buffer" was incorrect — the allocation is sized appropriately based on the input string length. The snprintf change is primarily about making this code path more robust against future changes and following secure coding best practices.

The test is now much simpler and follows MLT's conventions, focusing on integration testing through the public API rather than trying to simulate the vulnerability with synthetic buffers.