Issue #21198 has been updated by ioquatix (Samuel Williams). Status changed from Open to Closed Assignee set to ioquatix (Samuel Williams) Fixed in <https://github.com/ruby/ruby/pull/13437>. ---------------------------------------- Bug #21198: Fiber::Scheduler#blocking_operation_wait crash due to stack-use-after-return https://bugs.ruby-lang.org/issues/21198#change-113672 * Author: peterzhu2118 (Peter Zhu) * Status: Closed * Assignee: ioquatix (Samuel Williams) * Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED, 3.4: REQUIRED ---------------------------------------- The Fiber::Scheduler#blocking_operation_wait method is passed a proc through the `rb_fiber_scheduler_blocking_operation_wait` function. This function stack allocates the arguments used for the proc ([source](https://github.com/ruby/ruby/blob/2183899fd184ab1cfee80d57c0dd6f4dcd370375/s...)). If this proc is captured anywhere, then calling it again will illegally read from and write to stack space. The following script demonstrates this issue using the [test/fiber/scheduler.rb](https://github.com/ruby/ruby/blob/master/test/fiber/scheduler.rb) scheduler: ```ruby require_relative "test/fiber/scheduler" class MyScheduler < Scheduler def blocking_operation_wait(work) super $work = work end end scheduler = MyScheduler.new Fiber.set_scheduler(scheduler) require "tempfile" Fiber.schedule do file = Tempfile.new file.write("hello world!") $work.call end scheduler.run ``` Crashes with: ``` test.rb:19: [BUG] Bus Error at 0xce0f57696add0045 ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [arm64-darwin24] -- Crash Report log information -------------------------------------------- See Crash Report log file in one of the following locations: * ~/Library/Logs/DiagnosticReports * /Library/Logs/DiagnosticReports for more details. Don't forget to include the above Crash Report log file in bug reports. -- Control frame information ----------------------------------------------- c:0003 p:---- s:0010 e:000009 IFUNC c:0002 p:0017 s:0007 e:000006 BLOCK test.rb:19 [FINISH] c:0001 p:---- s:0003 e:000002 DUMMY [FINISH] -- Ruby level backtrace information ---------------------------------------- test.rb:19:in 'block in <main>' -- Threading information --------------------------------------------------- Total ractor count: 1 Ruby thread count for this ractor: 1 Note that the Fiber scheduler is enabled -- Machine register context ------------------------------------------------ x0: 0x000000010063a5f0 x1: 0x000000014b80ce00 x2: 0x0000000000000000 x3: 0x000000014b60f060 x4: 0x0000000000000000 x5: 0x0000000000000000 x6: 0x0000000000000004 x7: 0x0000000000000000 x18: 0x0000000000000000 x19: 0x000000014b6a4840 x20: 0xce0f57696add0045 x21: 0x000000010063a5f0 x22: 0x000000014b60f060 x23: 0x0000000000000000 x24: 0x000000014b60f998 x25: 0x0000000000014273 x26: 0x000000014b60f060 x27: 0x000000014b60f060 x28: 0x000000014b80ce00 lr: 0x0000000100d881d8 fp: 0x000000011bb039f0 sp: 0x000000011bb03980 -- C level backtrace information ------------------------------------------- SEGV received in BUS handler [1] 52599 abort ruby test.rb ``` -- https://bugs.ruby-lang.org/