Release the GVL during hashing and verification#16
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mudge
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Apr 6, 2026
mudge
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- Ensure we coerce and freeze strings ASAP
- Freeze public strings to prevent mutation
- Release the GVL lock when hashing and verifying
Freeze pwd, salt, and encoded strings with rb_str_new_frozen before any Ruby code can execute via callbacks (NUM2UINT's #to_int or StringValue's #to_str). Without this, a malicious coercion could mutate strings before they are passed to the reference C implementation. Also reduce the amount of casting of various numeric types by using Ruby's NUM2UINT to convert numbers directly to uint32_t rather than going via other types such a size_t. Avoid the truncation of a very long password and salt by ensuring it will fit in a uint32_t and raising a RangeError if not.
Argon2id::Password#encoded, #salt, and #output are exposed via public attr_readers, returning the live String objects. Without freezing, a caller holding that reference can replace them in place (e.g. encoded.replace(attacker_hash)), causing subsequent verification to check against the wrong hash.
To align with the bcrypt gem, release Ruby's Global VM Lock when performing the intentionally slow computations for hashing and verifying passwords. To do this, we effectively serialise the required arguments into a struct and invoke rb_thread_call_without_gvl. Note we don't pass an unblocking function when we do so because Argon2 provides no API to cancel a hash mid-computation so the only safe thing to do is to let it complete (this matches bcrypt). To prevent memory leaks if encoding raises (which would longjmp before the encoded string is freed), we wrap it in an ensure block. Note we defensively use ARGON2_MISSING_ARGS as a sentinel result value in case the rb_thread_call_without_gvl call ever returns without running our nogvl function. With this change, mark the extension as safe to use with Ractors.
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