Issue #22298 has been updated by hanazuki (Kasumi Hanazuki). patch: https://github.com/ruby/ruby/pull/18666 ---------------------------------------- Bug #22298: IO::Buffer is left unfreed with an invalid pointer when fiber scheduler raises https://bugs.ruby-lang.org/issues/22298#change-118813 * Author: hanazuki (Kasumi Hanazuki) * Status: Open * ruby -v: ruby 4.1.0dev (2026-09-06T12:40:34Z master e536482403) +PRISM [x86_64-linux] * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- When an installed Fiber scheduler raises from its I/O hook, the temporary IO::Buffer passed to the hook is left unfreed. The buffer may then outlive the memory it wraps, so accessing it afterward can cause undefined behavior. This only happens when the buffer escapes from the I/O callback, which is supposed to be a bug in the scheduler, but I think it is worth fixing silent memory corruption. ```ruby class Scheduler def block(*) = Fiber.yield def unblock(*) = nil def kernel_sleep(*) = nil def io_wait(*) = 0 def fiber_interrupt(*) = nil def fiber(&block) Fiber.new(blocking: false, &block).tap(&:transfer) end def io_write(io, buffer, offset, length) $escape = buffer # This buffer wraps a borrowed temporary memory fail end end r, w = IO.pipe Fiber.set_scheduler(Scheduler.new) Fiber.schedule { w.write('hello') } rescue nil GC.start p $escape # .inspect will read freed memory ``` -- https://bugs.ruby-lang.org/