August 2026 - ruby-core - ml.ruby-lang.org

[ruby-core:124029] [Ruby Bug#21765] stop using the C runtime _read() on Windows
by YO4 (Yoshinao Muramatsu) 23 Aug '26

23 Aug '26

Issue #21765 has been reported by YO4 (Yoshinao Muramatsu). ---------------------------------------- Bug #21765: stop using the C runtime _read() on Windows https://bugs.ruby-lang.org/issues/21765 * Author: YO4 (Yoshinao Muramatsu) * Status: Open * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- When creating an IO instance in Windows, the default data mode is text mode. In reality, the IO encoding conversion mechanism is not used when encoding conversion is not performed. Instead, the CRLF conversion provided by the C runtime's `_read()` is used. This is explicitly for speed. https://bugs.ruby-lang.org/issues/6401#note-4 As a trade-off, `SET_BINARY_MODE(fptr)` and `SET_BINARY_MODE_WITH_SEEK_CUR(fptr)` are used in various places within io.c, altering the state of the file descriptor. This made the flow of operations difficult to understand and changes hard to implement, especially for developers on other platforms. Additionally, the issues I recently reported were discovered while verifying the impact of modifying the CRLF conversion to utilize the encoding conversion mechanism. #21691 On Windows some of binary read functions of IO are not functional #21687 IO＃pos goes wrong after EOF character(ctrl-z) met #21634 Combining read(1) with eof? causes dropout of results unexpectedly on Windows. These issues arise because data read into the rbuf does not match the stream due to newline conversion, or because the buffer end and file position do not align when CTRLZ is detected. As a fix for Bug #21687, I created PR #15216. However, this relies on the internal behavior of the C runtime's `_read()` function, and it seems there is no way to avoid this dependency. **I propose removing the use of C runtime _read().** Reason for Proposal - The mismatch between rbuf and stream contents complicates io_unread() and makes maintenance difficult. - Changing the O_BINARY/O_TEXT state of the file descriptor in various places hinders understanding of the behavior and makes modifications difficult. Two methods to remove C runtime _read() while maintaining current behavior 1. Interpret CRLF and CTRLZ when reading rbuf within io.c. 1. Interpret CRLF and CTRLZ within the encoding conversion framework. My initial idea was to implement the second, using encoding conversion. However, this internally changes the read operation from rbuf to cbuf, resulting in a change to the behavior of ungetc. The proposal in Bug #21682 attempted to generalize this change to minimize its impact. https://bugs.ruby-lang.org/issues/21682 **This issue proposes the first method, crlf conversion during rbuf read.** Problems caused by inconsistencies between the rbuf and stream contents are avoided, and io_unread() becomes the same as on other platforms. Compared to implementing it as an encoding conversion, the advantage is that there is no change in behavior. On the other hand, since each read method in io.c requires individual handling, using encoding conversion results in more localized changes. -- https://bugs.ruby-lang.org/

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[ruby-core:115466] [Ruby master Bug#20020] Segfault running regexp match?
by andrea.salicetti＠gmail.com (Andrea Salicetti) 23 Aug '26

23 Aug '26

Issue #20020 has been reported by andrea.salicetti(a)gmail.com (Andrea Salicetti). ---------------------------------------- Bug #20020: Segfault running regexp match? https://bugs.ruby-lang.org/issues/20020 * Author: andrea.salicetti(a)gmail.com (Andrea Salicetti) * Status: Open * Priority: Normal * ruby -v: 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-darwin23] * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- **Ruby version** : ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-darwin23] From `irb`, trying to call `match?` on this regular expression causes a segmentation falut: ```ruby irb(main):001:0> /^((a|c)|\s?){1,3}$/.match?('abc') => false irb(main):002:0> /^((a|c)|\s?){1,3}$/.match?('abc') (irb):2: [BUG] Segmentation fault at 0x000000061ba998e8 ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-darwin23] -- 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:0037 p:---- s:0207 e:000206 CFUNC :match? c:0036 p:0006 s:0202 e:000201 EVAL (irb):2 [FINISH] c:0035 p:---- s:0199 e:000198 CFUNC :eval c:0034 p:0020 s:0191 e:000190 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb/workspace.rb:119 c:0033 p:0153 s:0183 e:000181 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb/context.rb:502 c:0032 p:0119 s:0170 e:000169 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:588 c:0031 p:0024 s:0164 e:000163 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:777 c:0030 p:0007 s:0158 e:000157 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:567 c:0029 p:0126 s:0153 e:000152 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb/ruby-lex.rb:267 [FINISH] c:0028 p:---- s:0149 e:000148 CFUNC :loop c:0027 p:0005 s:0145 e:000144 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb/ruby-lex.rb:249 [FINISH] c:0026 p:---- s:0142 e:000141 CFUNC :catch c:0025 p:0010 s:0137 e:000136 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb/ruby-lex.rb:248 c:0024 p:0050 s:0132 E:000dd8 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:566 c:0023 p:0003 s:0127 e:000126 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:500 [FINISH] c:0022 p:---- s:0124 e:000123 CFUNC :catch c:0021 p:0050 s:0119 E:000d50 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:499 c:0020 p:0069 s:0113 e:000112 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/3.2.0/irb.rb:421 c:0019 p:0012 s:0107 e:000106 TOP /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.6.2/exe/irb:11 [FINISH] c:0018 p:---- s:0104 e:000103 CFUNC :load c:0017 p:0078 s:0099 e:000098 TOP /Users/andreasalicetti/.rbenv/versions/3.2.2/bin/irb:25 [FINISH] c:0016 p:---- s:0094 e:000093 CFUNC :load c:0015 p:0064 s:0089 e:000088 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/cli/exec.rb:58 c:0014 p:0050 s:0083 e:000082 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/cli/exec.rb:23 c:0013 p:0034 s:0078 e:000077 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/cli.rb:492 c:0012 p:0054 s:0073 e:000072 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/vendor/thor/lib/thor/command.rb:28 c:0011 p:0040 s:0065 e:000064 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/vendor/thor/lib/thor/invocation.rb:127 c:0010 p:0213 s:0058 e:000057 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/vendor/thor/lib/thor.rb:527 c:0009 p:0008 s:0045 e:000044 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/cli.rb:34 c:0008 p:0044 s:0040 e:000039 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/vendor/thor/lib/thor/base.rb:584 c:0007 p:0022 s:0033 e:000032 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/cli.rb:28 c:0006 p:0042 s:0028 e:000027 BLOCK /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/bundler-2.4.22/exe/bundle:37 c:0005 p:0007 s:0022 e:000021 METHOD /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/bundler/friendly_errors.rb:117 c:0004 p:0108 s:0017 E:0019b8 TOP /Users/andreasalicetti/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/bundler-2.4.22/exe/bundle:29 [FINISH] c:0003 p:---- s:0013 e:000012 CFUNC :load c:0002 p:0081 s:0008 E:000220 EVAL /Users/andreasalicetti/.rbenv/versions/3.2.2/bin/bundle:25 [FINISH] c:0001 p:0000 s:0003 E:001980 DUMMY [FINISH] ``` Sometimes this happens the very first time I try to execute the command, some other times I have to try a couple of times to see that Segmentation Fault (but usually within the first 5 attempts). ---Files-------------------------------- ruby-2023-11-23-175410.ips (20.2 KB) -- https://bugs.ruby-lang.org/

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[ruby-core:126430] [Ruby Misc#22249] DevMeeting-2026-09-10
by mame (Yusuke Endoh) 23 Aug '26

23 Aug '26

Issue #22249 has been reported by mame (Yusuke Endoh). ---------------------------------------- Misc #22249: DevMeeting-2026-09-10 https://bugs.ruby-lang.org/issues/22249 * Author: mame (Yusuke Endoh) * Status: Open ---------------------------------------- # The next dev meeting **Date: 2026/09/10 13:00-17:00** (JST) Log: *TBD* - Dev meeting *IS NOT* a decision-making place. All decisions should be done at the bug tracker. - Dev meeting is a place we can ask Matz, nobu, nurse and other developers directly. - Matz is a very busy person. Take this opportunity to ask him. If you can not attend, other attendees can ask instead of you (if attendees can understand your issue). - We will write a record of the discussion in the file or to each ticket in English. - All activities are best-effort (keep in mind that most of us are volunteer developers). - The date, time and place of the meeting are scheduled according to when/where we can reserve Matz's time. - *DO NOT* discuss then on this ticket, please. # Call for agenda items If you have a ticket that you want matz and committers to discuss, please post it into this ticket in the following format: ``` * [Ticket ref] Ticket title (your name) * Comment (A summary of the ticket, why you put this ticket here, what point should be discussed, etc.) ``` Example: ``` * [Feature #14609] `Kernel#p` without args shows the receiver (ko1) * I feel this feature is very useful and some people say :+1: so let discuss this feature. ``` - It is recommended to add a comment by 2026/09/07. We hold a preparatory meeting to create an agenda a few days before the dev-meeting. - The format is strict. We'll use [this script to automatically create an markdown-style agenda](https://gist.github.com/mame/b0390509ce1491b43610b9ebb665eb86). We may ignore a comment that does not follow the format. - Your comment is mandatory. We cannot read all discussion of the ticket in a limited time. We appreciate it if you could write a short summary and update from a previous discussion. -- https://bugs.ruby-lang.org/

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[ruby-core:124335] [Ruby Bug#21798] `bundle install` command fails if touches `$LOAD_PATH` on `Ruby::Box` enabled
by unasuke (Yusuke Nakamura) 23 Aug '26

23 Aug '26

Issue #21798 has been reported by unasuke (Yusuke Nakamura). ---------------------------------------- Bug #21798: `bundle install` command fails if touches `$LOAD_PATH` on `Ruby::Box` enabled https://bugs.ruby-lang.org/issues/21798 * Author: unasuke (Yusuke Nakamura) * Status: Open * ruby -v: 4.0.0-preview3 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- ## How to reproduce ```dockerfile FROM ruby:4.0.0-preview3-trixie WORKDIR /ruby_box_test RUN bundle gem foo --test=minitest WORKDIR /ruby_box_test/foo RUN head -n 10 foo.gemspec # PASS RUN bundle install # PASS RUN RUBY_BOX=1 bundle install RUN sed --in-place \ --expression='2i lib=File.expand_path("../lib", __FILE__)\n$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)' \ foo.gemspec RUN sed --in-place \ --expression='s/require_relative "lib\/foo\/version"/require "foo\/version"/' \ foo.gemspec RUN head -n 10 foo.gemspec # PASS RUN bundle install # FAIL RUN RUBY_BOX=1 bundle install ``` This script fails. ``` /usr/local/bin/ruby: warning: Ruby::Box is experimental, and the behavior may change in the future! See doc/language/box.md for known issues, etc. [!] There was an error while loading `foo.gemspec`: cannot load such file -- foo/version. Bundler cannot continue. # from /ruby_box_test/foo/foo.gemspec:5 # ------------------------------------------- # > require "foo/version" # # ------------------------------------------- Error: building at STEP "RUN RUBY_BOX=1 bundle install": while running runtime: exit status 14 ``` Head of the gemspec file is this. ```ruby # frozen_string_literal: true lib=File.expand_path("../lib", __FILE__) $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib) require "foo/version" Gem::Specification.new do |spec| # ..snip.. end ``` # misc I found this behavior when `RUBY_BOX=1 bundle exec rake spec` on `https://github.com/itamae-kitchen/itamae`. -- https://bugs.ruby-lang.org/

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[ruby-core:126083] [Ruby Bug#22195] `IO::Buffer` read after free silently returns empty data instead of raising
by himura467 (Akito Shitara) 22 Aug '26

22 Aug '26

Issue #22195 has been reported by himura467 (Akito Shitara). ---------------------------------------- Bug #22195: `IO::Buffer` read after free silently returns empty data instead of raising https://bugs.ruby-lang.org/issues/22195 * Author: himura467 (Akito Shitara) * Status: Open * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- Reading from an `IO::Buffer` after calling `#free` does not raise. It behaves like an empty buffer, and `#valid?` still returns `true`: ```ruby buffer = IO::Buffer.for("Hello World") buffer.free buffer.valid? # => true buffer.get_string # => "" (no error) ``` ## Why this looks like an unintended regression Originally (https://github.com/ruby/ruby/commit/e30920354f, Ruby 3.1–3.3), accessing a freed buffer raised `IO::Buffer::AllocationError` ("The buffer is not allocated!"). https://github.com/ruby/ruby/commit/c5cf4d4e12 made zero-length buffer operations succeed instead of raising, for [Bug #19542] and [Bug #18805]. Since a freed buffer also has `base == NULL, size == 0`, it was caught in the same code path and stopped raising too. Neither ticket mentions freed buffers, so this appears to be an accidental side effect rather than a decision. Note that the rdoc of `#free` still promises that access after free raises. ## Proposal How about marking a buffer as invalidated when it is explicitly freed (`#free` / `rb_io_buffer_free`), so that: * `#valid?` returns `false`. * Any byte access raises `IO::Buffer::InvalidatedError` or `IO::Buffer::AllocationError`. * `#resize` re-allocates and clears the mark, as `#free`'s rdoc promises ("You can resize a freed buffer to re-allocate it"). * The zero-length buffer semantics from https://github.com/ruby/ruby/pull/9532 are preserved: `IO::Buffer.new(0)`, `resize(0)` and zero-length slices remain valid and readable. I'm not sure which exception class is preferable: `IO::Buffer::InvalidatedError` is consistent with how invalidated slices already behave and with `#valid?` returning `false`, while `IO::Buffer::AllocationError` restores the pre-3.4 behavior. -- https://bugs.ruby-lang.org/

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[ruby-core:125416] [Ruby Feature#22056] Add zero-copy String constructor backed by an arbitrary Ruby object
by himura467 (Akito Shitara) 22 Aug '26

22 Aug '26

Issue #22056 has been reported by himura467 (Akito Shitara). ---------------------------------------- Feature #22056: Add zero-copy String constructor backed by an arbitrary Ruby object https://bugs.ruby-lang.org/issues/22056 * Author: himura467 (Akito Shitara) * Status: Open ---------------------------------------- ### Description Ruby has rich built-in functionality for working with byte sequences through `String`. Objects that manage their own byte buffers naturally want to expose their data through this interface. The straightforward approach is `rb_str_new()`, which copies the bytes: ``` c VALUE str = rb_str_new(str, len); ``` For large or frequently accessed buffers this copy is wasteful in both time and memory. One approach is to create a String that directly references the existing memory, with the GC keeping the owner alive for as long as the String is reachable. This avoids both the copy and the need for manual lifetime management. ### Existing APIs and their limitations | API | Memory behavior | | ---- | ---- | | `rb_str_new` / `rb_str_new_cstr` | Copies bytes; String owns the allocation | | `rb_str_new_shared` / `rb_str_new_frozen` | References another String's buffer; parent must be a String | | `rb_str_new_static` | References static (compile-time) storage; no lifetime management | `rb_str_new_static` avoids copying but is only safe for storage that lives forever. When memory is owned by a Ruby object, it is freed when that object is collected, and `rb_str_new_static` offers no way to express that dependency. The common workaround is to pin the owner via an instance variable: ``` c VALUE str = rb_str_new_static(str, len); rb_ivar_set(str, id_owner, owner); ``` This relies on undocumented GC behavior, incurs ivar table allocation overhead, and leaves lifetime management entirely to the caller. ### Proposal Add zero-copy String constructors that accept an explicit parent object. The proposed names are tentative and open for discussion (see below): ``` c VALUE rb_str_new_external(const char *ptr, long len, VALUE parent); VALUE rb_usascii_str_new_external(const char *ptr, long len, VALUE parent); VALUE rb_utf8_str_new_external(const char *ptr, long len, VALUE parent); VALUE rb_enc_str_new_external(const char *ptr, long len, rb_encoding *enc, VALUE parent); ``` `parent` can be any live Ruby object. The GC guarantees it is not collected before the returned String is. `ptr` must point into memory whose lifetime is tied to `parent`; no copy is made. ### Use cases *IO::Buffer#get_string* `IO::Buffer.for(string)` wraps a String's bytes in a READONLY EXTERNAL buffer. `IO::Buffer#get_string` now copies those bytes into a new String. With this API, the returned String can reference the source String directly: ``` c return rb_enc_str_new_external((const char *)base + offset, length, encoding, buffer->source); ``` The returned String holds a direct GC reference to the source String, so it remains valid even after the buffer is freed. *GLib::Bytes#to_s (ruby-gnome)* `GLib::Bytes` is an immutable, reference-counted byte buffer from GLib. The current [implementation](https://github.com/ruby-gnome/ruby-gnome/blob/1dad74d1a86f9… uses the ivar workaround: ``` c VALUE str = rb_str_new_static(data, size); rb_iv_set(str, "@bytes", self); ``` With the proposed API this becomes: ``` c return rb_str_new_external(data, size, self); ``` ### Open questions *Naming* The name `rb_str_new_external` is one option. Other candidates: * `rb_str_new_owned_by` / `rb_enc_str_new_owned_by` * `rb_str_new_pinned` / `rb_enc_str_new_pinned` * `rb_str_new_with_parent` / `rb_enc_str_new_with_parent` *Memory retention* When a String referencing a small slice of a large buffer remains reachable, the entire backing object is kept alive. This is the same concern that led Java to remove the shared-backing optimization from `String.substring()` in Java 7. The risk was also raised in the context of Ruby's own lazy substring proposal (#19315, https://bugs.ruby-lang.org/issues/19315#note-7) > I heard that Java stopped the shared substring technique 10 years ago (https://www.infoq.com/news/2013/12/Oracle-Tunes-Java-String/) because of the potential for memory leaks > > I don't disagree this proposal, but it would be nice if we could evaluate the effectiveness of this optimization. Whether the same concern applies to this proposal, and whether the API should offer a way to force an independent copy, is worth discussing. ### Proof of concept A prototype implementation is at: https://github.com/ruby/ruby/pull/16834 The implementation introduces a new flag on non-embedded strings and stores the parent reference in `RString.as.heap.aux.parent`. The GC mark phase pins embedded parent strings to prevent compaction from invalidating the raw pointer stored in the zero-copy child. -- https://bugs.ruby-lang.org/

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[ruby-core:125811] [Ruby Bug#22125] IO::Buffer triggers use-after-free when it's freed/resized during enumeration
by hanazuki (Kasumi Hanazuki) 22 Aug '26

22 Aug '26

Issue #22125 has been reported by hanazuki (Kasumi Hanazuki). ---------------------------------------- Bug #22125: IO::Buffer triggers use-after-free when it's freed/resized during enumeration https://bugs.ruby-lang.org/issues/22125 * Author: hanazuki (Kasumi Hanazuki) * Status: Open * ruby -v: ruby 4.1.0dev (2026-06-23T09:56:24Z master 55945e5c98) +PRISM [x86_64-linux] * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- The block passed to `IO::Buffer#each` can free or resize the receiver (or its parent buffer when the reciver is a slice), which invalidates the memory region being iterated. The next iteration causes use-after-free. repro: ``` ./miniruby -ve 'b=IO::Buffer.for("ruby"*10).dup; b.each {|_, v| p v; b.free }' ./miniruby -ve 'b=IO::Buffer.for("ruby"*10).dup; b.each {|_, v| p v; b.resize(20) }' ./miniruby -ve 'b=IO::Buffer.for("ruby"*10).dup; b1=b.slice; b1.each {|_, v| p v; b.free }' # No use-after-free but I think those should be errors too ./miniruby -ve 'b=IO::Buffer.for("ruby"*10).dup; b1=b.slice; b1.each {|_, v| p v; b1.free }' ./miniruby -ve 'b=IO::Buffer.for("ruby"*10).dup; b.each {|_, v| p v; b.transfer }' ``` same for `#each_byte`. -- https://bugs.ruby-lang.org/

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[ruby-core:121507] [Ruby Bug#21212] IO::Buffer can be freed while its slice is locked
by hanazuki (Kasumi Hanazuki) 22 Aug '26

22 Aug '26

Issue #21212 has been reported by hanazuki (Kasumi Hanazuki). ---------------------------------------- Bug #21212: IO::Buffer can be freed while its slice is locked https://bugs.ruby-lang.org/issues/21212 * Author: hanazuki (Kasumi Hanazuki) * Status: Open * ruby -v: ruby 3.5.0dev (2025-04-01T16:11:01Z master 30e5e7c005) +PRISM [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- ```ruby buffer = IO::Buffer.new(100) slice = buffer.slice buffer.locked do buffer.free rescue p $! #=> IO::Buffer::LockedError (expected) end slice.locked do p slice.locked? #=> true (expected) p buffer.locked? #=> false (what should this be?) slice.free rescue p $! #=> IO::Buffer::LockedError (expected) buffer.free # Should we allow this? slice.set_value(:U8, 0, 42) # raises IO::Buffer::InvalidatedError (surprising!) end ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124840] [Ruby Bug#21883] IO::Buffer can be unlocked and freed by another thread during syscall
by hanazuki (Kasumi Hanazuki) 22 Aug '26

22 Aug '26

Issue #21883 has been reported by hanazuki (Kasumi Hanazuki). ---------------------------------------- Bug #21883: IO::Buffer can be unlocked and freed by another thread during syscall https://bugs.ruby-lang.org/issues/21883 * Author: hanazuki (Kasumi Hanazuki) * Status: Open * ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [x86_64-linux] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- ```ruby # Assume this file is on a very slow device such as NFS. io = File.open('/mnt/slowfs/slow') buf = IO::Buffer.new(100) t1 = Thread.new do buf.locked do sleep 0.5 end buf.free end t2 = Thread.new do buf.read(io) # syscall takes 1 second # When the kernal writes to the memory, buf is already freed, thus use-after-free end t1.join t2.join ``` `io_buffer_blocking_region` skips taking a lock when the buffer is already locked, but this lock may be owned by another thread and can be unlocked during the syscall. -- https://bugs.ruby-lang.org/

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[ruby-core:126463] [Ruby Bug#22257] Prepending a module to an already-included module leaves stale super caches
by eightbitraptor (Matt V-H) 21 Aug '26

21 Aug '26

Issue #22257 has been updated by eightbitraptor (Matt V-H). I've created Backport patches [for 4.0](https://github.com/ruby/ruby/pull/18422) and [for 3.4](https://github.com/ruby/ruby/pull/18423) ---------------------------------------- Bug #22257: Prepending a module to an already-included module leaves stale super caches https://bugs.ruby-lang.org/issues/22257#change-118614 * Author: eightbitraptor (Matt V-H) * Status: Open * Target version: 4.1 * Backport: 3.3: WONTFIX, 3.4: REQUIRED, 4.0: REQUIRED ---------------------------------------- When a module is prepended to a module that already has includers, super call sites inside the prepended module keep calling the old method entry after the method is redefined. [**Fix implemented in this PR**](https://github.com/ruby/ruby/pull/18421) <pre> module M; def foo; :m; end; end class D; include M; end M.prepend(Module.new { def foo; super; end }) D.new.foo # prime the super call-site cache M.send(:define_method, :foo) { :hooked } p D.new.foo </pre> I found this while working on an unrelated Ractor issue. But this problem manifests itself for Ractors as follows: <pre> Ractor.new {} require 'set' Kernel.send(:define_method, :require) { |f| $hook = f } require 'set' p $hook # => nil, the hook never runs </pre> This is because creating the first Ractor prepends an internal `RactorRequire` wrapper onto Kernel. After the first require primes the cache in the wrapper, redefining Kernel#require silently does nothing. The linked PR fixes this by registering the backfilled iclass in the module's subclasses list, after the includer walk finishes. -- https://bugs.ruby-lang.org/

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