[ruby-core:122567] [Ruby Bug#21448] Random.urandom may fail to fall back to reading /dev/urandom on Linux < 3.17
From:
"rhenium (Kazuki Yamaguchi) via ruby-core" <ruby-core@...>
Date:
2025-06-21 08:24:14 UTC
List:
ruby-core #122567
Issue #21448 has been updated by rhenium (Kazuki Yamaguchi). FWIW `getentropy()` has recently made it into POSIX (with a slight difference in errno behavior compared to existing implementations). I think supporting it as an alternative makes sense, not just for macOS. https://pubs.opengroup.org/onlinepubs/9799919799/functions/getentropy.html My suggestion would be to use `getentropy()` as an implementation of `fill_random_bytes_syscall()` rather than replacing `fill_random_bytes_urandom()`. However, that would mean it is no longer used as a fallback after `CCRandomGenerateBytes()` or `SecRandomCopyBytes()` fails on macOS. I'm not sure it can actually happen. ---------------------------------------- Bug #21448: Random.urandom may fail to fall back to reading /dev/urandom on Linux < 3.17 https://bugs.ruby-lang.org/issues/21448#change-113797 * Author: rhenium (Kazuki Yamaguchi) * Status: Open * Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED ---------------------------------------- Origianlly reported for tmpdir: https://github.com/ruby/tmpdir/issues/50 On Linux, `Random.urandom` is expected to first attempt the `getrandom(2)` syscall (Linux >= 3.17), and fall back to reading from `/dev/urandom` if it is not supported. In Ruby 3.1, commit commit:54c91185c9273b9699693910fa95383c86f2af22 replaced the fallback routine that read from `/dev/urandom` with a call to `getentropy(3)`, if available at compile time. On Linux, glibc 2.25 and musl 1.1.20 started to provide a `getentropy(3)` implementation based on `getrandom(2)`. If Ruby is compiled with such a libc version but run on Linux 3.16 or earlier, both `getrandom()` and `getentropy(3)` fail. As a result, `Random.urandom` becomes unusable, even though `/dev/urandom` is still available. I couldn't find the orignal issue the commit was intended to address, except that it appears to related to macOS. Is there a scenario on macOS where `CCRandomGenerateBytes()` or `SecRandomCopyBytes()` might fail, while `getentropy()` will still succeed? -- https://bugs.ruby-lang.org/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/