[ruby-core:88717] [Ruby trunk Bug#15039] Random.urandom and SecureRandom arc4random use

Issue #15039 has been updated by shyouhei (Shyouhei Urabe).


Frankly, I'm not sure how less trustworthy FreeBSD libc is, compared to its kernel.  They are developed by the same people in a same repository.  Or is it not about the code quality in general?  Maybe the problem here is that having _any_ bits of instructions in a userland?

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Bug #15039: Random.urandom and SecureRandom arc4random use
https://bugs.ruby-lang.org/issues/15039#change-73773

* Author: Freaky (Thomas Hurst)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
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Random.urandom defaults to arc4random() on a lot of platforms, including FreeBSD.

On all currently released versions of FreeBSD, arc4random() is, as the name suggests, a dubious ARC4-based userspace PRNG dating from circa 1997.  Given the entire point of #9569 was that using the userspace CSPRNG in OpenSSL over /dev/urandom or equivalent is a bad idea, this seems to mean it's regressed to an *even worse* state on these platforms.  Even in cases where it's using something more modern (FreeBSD 12, OpenBSD), it's still a userspace CSPRNG.

If that's fine, we might as well *pick a known-good one* and use that everywhere.  Like, say, OpenSSL's.

Since the conclusion of #9569 seems to have been otherwise, I'd suggest dropping arc4random() as a potential source for Random.urandom due to it not matching the desired semantics.

Rust's OsRng seems a good template for alternative _syscall implementations: https://docs.rs/rand/0.5.5/rand/rngs/struct.OsRng.html#platform-sources



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