Defer or avoid file MD5 calculation when cache is disabled #1167
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If SCAN_COLLECT_METADATA is enabled, and caching is disabled, we zero-out the hash after recording it. This results in a non-NULL and invalid-hash that may be passed to `cli_scan_fmap()` for the "raw mode" scan. It's an uncommon code path, but would result in comparing hash-sigs with a zeroed hash rather than the valid hash. This bug could result in a missed hash-based sig matches. There is no reason to invalidate or zero-out the hash if we happen to calculate it. We avoid the cache-lookup by checking the engine setting, not by checking if we have a hash.
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If the clean cache is not used (
CL_ENGINE_DISABLE_CACHE=1), it is not necessary to calculate the file's MD5 checksum in preparation for cache lookup. This change modifiescli_magic_scanto skip the MD5 calculation if the cache is disabled.