Fix timing bug in ensure_engine_loaded#1
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When two ensure_engine_loaded() calls were done in parallell there was a possibility that a crypto lib function was called by both instead of just one of them. This is solved by moving the implementation from erlang down into a nif function that uses a mutex to protect the sensitive part.
sverker
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Jan 13, 2022
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| /* Destroy old mutex if exists (if upgrade function called) */ | ||
| if(ensure_engine_loaded_mtx) { | ||
| enif_mutex_destroy(ensure_engine_loaded_mtx); | ||
| ensure_engine_loaded_mtx = NULL; | ||
| } |
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Det här är onödigt. Om mutexen redan finns så fortsätt använd den.
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| static void unload(ErlNifEnv* env, void* priv_data) | ||
| { | ||
| destroy_engine_mutex(env); | ||
| --library_refc; | ||
| } |
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Här borde du istället göra
if (--library_refc == 0) {
destroy_engine_mutex(env);
}
Dvs, mutexen förstörs när ingen Erlang crypto module instans längre använder crypto.so.
Om man upgraderar crypto.beam så kanske både den nya modul instansen och den gamla använda samma crypto.so och då är library_refc 2. Och unload anropas av erlang:purge_module oavsett om .so filen verkligen kommer att laddas ur eller om det finns fler användare.
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When two ensure_engine_loaded() calls were done in parallell there
was a possibility that a crypto lib function was called by both instead
of just one of them.
This is solved by moving the implementation from erlang down into a nif
function that uses a mutex to protect the sensitive part.